    {-# LANGUAGE CPP #-}
    {-# LANGUAGE DeriveFunctor #-}
    {-# LANGUAGE DerivingStrategies #-}
    {-# LANGUAGE GeneralizedNewtypeDeriving #-}
    {-# LANGUAGE MultiWayIf #-}
    {-# LANGUAGE RankNTypes #-}
    {-# LANGUAGE ScopedTypeVariables #-}
    {-# LANGUAGE TypeFamilies #-}
    {-# LANGUAGE ViewPatterns #-}

    {-# OPTIONS_GHC -Wno-orphans #-}

    -- | Monadic definitions for the constraint solver
    module GHC.Tc.Solver.Monad (

        -- The TcS monad
        TcS, runTcS, runTcSEarlyAbort, runTcSWithEvBinds, runTcSInerts,
        failTcS, warnTcS, addErrTcS, wrapTcS, ctLocWarnTcS,
        runTcSEqualities,
        nestTcS, nestImplicTcS, setEvBindsTcS,
        emitImplicationTcS, emitTvImplicationTcS,
        emitFunDepWanteds,

        selectNextWorkItem,
        getWorkList,
        updWorkListTcS,
        pushLevelNoWorkList,

        runTcPluginTcS, recordUsedGREs,
        matchGlobalInst, TcM.ClsInstResult(..),

        QCInst(..),

        -- The pipeline
        StopOrContinue(..), continueWith, stopWith,
        startAgainWith, SolverStage(Stage, runSolverStage), simpleStage,
        stopWithStage,

        -- Tracing etc
        panicTcS, traceTcS, tryEarlyAbortTcS,
        traceFireTcS, bumpStepCountTcS, csTraceTcS,
        wrapErrTcS, wrapWarnTcS,
        resetUnificationFlag, setUnificationFlag,

        -- Evidence creation and transformation
        MaybeNew(..), freshGoals, isFresh, getEvExpr,

        newTcEvBinds, newNoTcEvBinds,
        newWantedEq, emitNewWantedEq,
        newWanted,
        newWantedNC, newWantedEvVarNC,
        newBoundEvVarId,
        unifyTyVar, reportUnifications, touchabilityAndShapeTest,
        setEvBind, setWantedEq,
        setWantedEvTerm, setEvBindIfWanted,
        newEvVar, newGivenEvVar, emitNewGivens,
        checkReductionDepth,
        getSolvedDicts, setSolvedDicts,

        getInstEnvs, getFamInstEnvs,                -- Getting the environments
        getTopEnv, getGblEnv, getLclEnv, setSrcSpan,
        getTcEvBindsVar, getTcLevel,
        getTcEvTyCoVars, getTcEvBindsMap, setTcEvBindsMap,
        tcLookupClass, tcLookupId, tcLookupTyCon,

        -- Inerts
        updInertSet, updInertCans,
        getHasGivenEqs, setInertCans,
        getInertEqs, getInertCans, getInertGivens,
        getInertInsols, getInnermostGivenEqLevel,
        getInertSet, setInertSet,
        getUnsolvedInerts,
        removeInertCts, getPendingGivenScs,
        insertFunEq, addInertForAll,
        emitWorkNC, emitWork,
        lookupInertDict,

        -- The Model
        kickOutAfterUnification, kickOutRewritable,

        -- Inert Safe Haskell safe-overlap failures
        addInertSafehask, insertSafeOverlapFailureTcS, updInertSafehask,
        getSafeOverlapFailures,

        -- Inert solved dictionaries
        updSolvedDicts, lookupSolvedDict,

        -- Irreds
        foldIrreds,

        -- The family application cache
        lookupFamAppInert, lookupFamAppCache, extendFamAppCache,
        pprKicked,

        -- Instantiation
        instDFunType,

        -- Unification
        wrapUnifierTcS, unifyFunDeps, uPairsTcM, unifyForAllBody,

        -- MetaTyVars
        newFlexiTcSTy, instFlexiX,
        cloneMetaTyVar,
        tcInstSkolTyVarsX,

        TcLevel,
        isFilledMetaTyVar_maybe, isFilledMetaTyVar, isUnfilledMetaTyVar,
        zonkTyCoVarsAndFV, zonkTcType, zonkTcTypes, zonkTcTyVar, zonkCo,
        zonkTyCoVarsAndFVList,
        zonkSimples, zonkWC,
        zonkTyCoVarKind,

        -- References
        newTcRef, readTcRef, writeTcRef, updTcRef,

        -- Misc
        getDefaultInfo, getDynFlags, getGlobalRdrEnvTcS,
        matchFam, matchFamTcM,
        checkWellStagedDFun,
        pprEq,

        -- Enforcing invariants for type equalities
        checkTypeEq, checkTouchableTyVarEq
    ) where

    import GHC.Prelude

    import GHC.Driver.Env

    import qualified GHC.Tc.Utils.Instantiate as TcM
    import GHC.Core.InstEnv
    import GHC.Tc.Instance.Family as FamInst
    import GHC.Core.FamInstEnv

    import qualified GHC.Tc.Utils.Monad    as TcM
    import qualified GHC.Tc.Utils.TcMType  as TcM
    import qualified GHC.Tc.Instance.Class as TcM( matchGlobalInst, ClsInstResult(..) )
    import qualified GHC.Tc.Utils.Env      as TcM
           ( checkWellStaged, tcGetDefaultTys
           , tcLookupClass, tcLookupId, tcLookupTyCon
           , topIdLvl )
    import GHC.Tc.Zonk.Monad ( ZonkM )
    import qualified GHC.Tc.Zonk.TcType  as TcM
    import qualified GHC.Tc.Zonk.Type as TcM

    import GHC.Driver.DynFlags

    import GHC.Tc.Instance.Class( safeOverlap, instanceReturnsDictCon )
    import GHC.Tc.Instance.FunDeps( FunDepEqn(..) )
    import GHC.Tc.Utils.TcType
    import GHC.Tc.Solver.Types
    import GHC.Tc.Solver.InertSet
    import GHC.Tc.Types.Evidence
    import GHC.Tc.Errors.Types
    import GHC.Tc.Types
    import GHC.Tc.Types.Origin
    import GHC.Tc.Types.Constraint
    import GHC.Tc.Utils.Unify

    import GHC.Builtin.Names ( unsatisfiableClassNameKey )

    import GHC.Core.Type
    import GHC.Core.TyCo.Rep as Rep
    import GHC.Core.Coercion
    import GHC.Core.Coercion.Axiom( TypeEqn )
    import GHC.Core.Predicate
    import GHC.Core.Reduction
    import GHC.Core.Class
    import GHC.Core.TyCon

    import GHC.Types.Name
    import GHC.Types.TyThing
    import GHC.Types.Name.Reader
    import GHC.Types.Var
    import GHC.Types.Var.Set
    import GHC.Types.Unique.Supply
    import GHC.Types.Unique.Set( elementOfUniqSet )

    import GHC.Unit.Module ( HasModule, getModule, extractModule )
    import qualified GHC.Rename.Env as TcM

    import GHC.Utils.Outputable
    import GHC.Utils.Panic
    import GHC.Utils.Logger
    import GHC.Utils.Misc (HasDebugCallStack)

    import GHC.Data.Bag as Bag
    import GHC.Data.Pair

    import GHC.Utils.Monad

    import GHC.Exts (oneShot)
    import Control.Monad
    import Data.IORef
    import Data.List ( mapAccumL )
    import Data.Foldable
    import qualified Data.Semigroup as S
    import GHC.Types.SrcLoc
    import GHC.Rename.Env

    #if defined(DEBUG)
    import GHC.Types.Unique.Set (nonDetEltsUniqSet)
    import GHC.Data.Graph.Directed
    #endif

    {- *********************************************************************
    *                                                                      *
                   SolverStage and StopOrContinue
    *                                                                      *
    ********************************************************************* -}

    {- Note [The SolverStage monad]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The SolverStage monad allows us to write simple code like that in
    GHC.Tc.Solver.solveEquality.   At the time of writing it looked like
    this (may get out of date but the idea is clear):

    solveEquality :: ... -> SolverStage Void
    solveEquality ev eq_rel ty1 ty2
      = do { Pair ty1' ty2' <- zonkEqTypes ev eq_rel ty1 ty2
           ; mb_canon <- canonicaliseEquality ev' eq_rel ty1' ty2'
           ; case mb_canon of {
                Left irred_ct -> do { tryQCsIrredEqCt irred_ct
                                    ; solveIrred irred_ct } ;
                Right eq_ct   -> do { tryInertEqs eq_ct
                                    ; tryFunDeps  eq_ct
                                    ; tryQCsEqCt  eq_ct
                                    ; simpleStage (updInertEqs eq_ct)
                                    ; stopWithStage (eqCtEvidence eq_ct) ".." }}}

    Each sub-stage can elect to
      (a) ContinueWith: continue to the next stasge
      (b) StartAgain:   start again at the beginning of the pipeline
      (c) Stop:         stop altogether; constraint is solved

    These three possiblities are described by the `StopOrContinue` data type.
    The `SolverStage` monad does the plumbing.

    Notes:

    (SM1) Each individual stage pretty quickly drops down into
             TcS (StopOrContinue a)
        because the monadic plumbing of `SolverStage` is relatively ineffienct,
        with that three-way split.

    (SM2) We use `SolverStage Void` to express the idea that ContinueWith is
        impossible; we don't need to pattern match on it as a possible outcome:A
        see GHC.Tc.Solver.Solve.solveOne.   To that end, ContinueWith is strict.
    -}

    data StopOrContinue a
      = StartAgain Ct     -- Constraint is not solved, but some unifications
                          --   happened, so go back to the beginning of the pipeline

      | ContinueWith !a   -- The constraint was not solved, although it may have
                          --   been rewritten.  It is strict so that
                          --   ContinueWith Void can't happen; see (SM2) in
                          --   Note [The SolverStage monad]

      | Stop CtEvidence   -- The (rewritten) constraint was solved
             SDoc         -- Tells how it was solved
                          -- Any new sub-goals have been put on the work list
      deriving ((forall a b. (a -> b) -> StopOrContinue a -> StopOrContinue b)
    -> (forall a b. a -> StopOrContinue b -> StopOrContinue a)
    -> Functor StopOrContinue
    forall a b. a -> StopOrContinue b -> StopOrContinue a
    forall a b. (a -> b) -> StopOrContinue a -> StopOrContinue b
    forall (f :: * -> *).
    (forall a b. (a -> b) -> f a -> f b)
    -> (forall a b. a -> f b -> f a) -> Functor f
    $cfmap :: forall a b. (a -> b) -> StopOrContinue a -> StopOrContinue b
    fmap :: forall a b. (a -> b) -> StopOrContinue a -> StopOrContinue b
    $c<$ :: forall a b. a -> StopOrContinue b -> StopOrContinue a
    <$ :: forall a b. a -> StopOrContinue b -> StopOrContinue a
    Functor)

    instance Outputable a => Outputable (StopOrContinue a) where
      ppr :: StopOrContinue a -> SDoc
    ppr (Stop CtEvidence
    ev SDoc
    s)      = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "Stop" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    parens (SDoc
    s SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "ev:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> CtEvidence -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CtEvidence
    ev)
      ppr (ContinueWith a
    w) = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "ContinueWith" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> a -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr a
    w
      ppr (StartAgain Ct
    w)   = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "StartAgain" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Ct -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Ct
    w

    newtype SolverStage a = Stage { forall a. SolverStage a -> TcS (StopOrContinue a)
    runSolverStage :: TcS (StopOrContinue a) }
      deriving( (forall a b. (a -> b) -> SolverStage a -> SolverStage b)
    -> (forall a b. a -> SolverStage b -> SolverStage a)
    -> Functor SolverStage
    forall a b. a -> SolverStage b -> SolverStage a
    forall a b. (a -> b) -> SolverStage a -> SolverStage b
    forall (f :: * -> *).
    (forall a b. (a -> b) -> f a -> f b)
    -> (forall a b. a -> f b -> f a) -> Functor f
    $cfmap :: forall a b. (a -> b) -> SolverStage a -> SolverStage b
    fmap :: forall a b. (a -> b) -> SolverStage a -> SolverStage b
    $c<$ :: forall a b. a -> SolverStage b -> SolverStage a
    <$ :: forall a b. a -> SolverStage b -> SolverStage a
    Functor )

    instance Applicative SolverStage where
      pure :: forall a. a -> SolverStage a
    pure a
    x = TcS (StopOrContinue a) -> SolverStage a
    forall a. TcS (StopOrContinue a) -> SolverStage a
    Stage (StopOrContinue a -> TcS (StopOrContinue a)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (a -> StopOrContinue a
    forall a. a -> StopOrContinue a
    ContinueWith a
    x))
      <*> :: forall a b. SolverStage (a -> b) -> SolverStage a -> SolverStage b
    (<*>)  = SolverStage (a -> b) -> SolverStage a -> SolverStage b
    forall (m :: * -> *) a b. Monad m => m (a -> b) -> m a -> m b
    ap

    instance Monad SolverStage where
      return :: forall a. a -> SolverStage a
    return          = a -> SolverStage a
    forall a. a -> SolverStage a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure
      (Stage TcS (StopOrContinue a)
    m) >>= :: forall a b. SolverStage a -> (a -> SolverStage b) -> SolverStage b
    >>= a -> SolverStage b
    k = TcS (StopOrContinue b) -> SolverStage b
    forall a. TcS (StopOrContinue a) -> SolverStage a
    Stage (TcS (StopOrContinue b) -> SolverStage b)
    -> TcS (StopOrContinue b) -> SolverStage b
    forall a b. (a -> b) -> a -> b
    $
                        do { soc <- TcS (StopOrContinue a)
    m
                           ; case soc of
                               StartAgain Ct
    x   -> StopOrContinue b -> TcS (StopOrContinue b)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Ct -> StopOrContinue b
    forall a. Ct -> StopOrContinue a
    StartAgain Ct
    x)
                               Stop CtEvidence
    ev SDoc
    d      -> StopOrContinue b -> TcS (StopOrContinue b)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CtEvidence -> SDoc -> StopOrContinue b
    forall a. CtEvidence -> SDoc -> StopOrContinue a
    Stop CtEvidence
    ev SDoc
    d)
                               ContinueWith a
    x -> SolverStage b -> TcS (StopOrContinue b)
    forall a. SolverStage a -> TcS (StopOrContinue a)
    runSolverStage (a -> SolverStage b
    k a
    x) }

    simpleStage :: TcS a -> SolverStage a
    -- Always does a ContinueWith; no Stop or StartAgain
    simpleStage :: forall a. TcS a -> SolverStage a
    simpleStage TcS a
    thing = TcS (StopOrContinue a) -> SolverStage a
    forall a. TcS (StopOrContinue a) -> SolverStage a
    Stage (do { res <- TcS a
    thing; continueWith res })

    startAgainWith :: Ct -> TcS (StopOrContinue a)
    startAgainWith :: forall a. Ct -> TcS (StopOrContinue a)
    startAgainWith Ct
    ct = StopOrContinue a -> TcS (StopOrContinue a)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Ct -> StopOrContinue a
    forall a. Ct -> StopOrContinue a
    StartAgain Ct
    ct)

    continueWith :: a -> TcS (StopOrContinue a)
    continueWith :: forall a. a -> TcS (StopOrContinue a)
    continueWith a
    ct = StopOrContinue a -> TcS (StopOrContinue a)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (a -> StopOrContinue a
    forall a. a -> StopOrContinue a
    ContinueWith a
    ct)

    stopWith :: CtEvidence -> String -> TcS (StopOrContinue a)
    stopWith :: forall a. CtEvidence -> String -> TcS (StopOrContinue a)
    stopWith CtEvidence
    ev String
    s = StopOrContinue a -> TcS (StopOrContinue a)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CtEvidence -> SDoc -> StopOrContinue a
    forall a. CtEvidence -> SDoc -> StopOrContinue a
    Stop CtEvidence
    ev (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    s))

    stopWithStage :: CtEvidence -> String -> SolverStage a
    stopWithStage :: forall a. CtEvidence -> String -> SolverStage a
    stopWithStage CtEvidence
    ev String
    s = TcS (StopOrContinue a) -> SolverStage a
    forall a. TcS (StopOrContinue a) -> SolverStage a
    Stage (CtEvidence -> String -> TcS (StopOrContinue a)
    forall a. CtEvidence -> String -> TcS (StopOrContinue a)
    stopWith CtEvidence
    ev String
    s)

    {- *********************************************************************
    *                                                                      *
                       Inert instances: inert_insts
    *                                                                      *
    ********************************************************************* -}

    addInertForAll :: QCInst -> TcS ()
    -- Add a local Given instance, typically arising from a type signature
    addInertForAll :: QCInst -> TcS ()
    addInertForAll QCInst
    new_qci
      = do { ics  <- TcS InertCans
    getInertCans
           ; ics1 <- add_qci ics

           -- Update given equalities. C.f updateGivenEqs
           ; tclvl <- getTcLevel
           ; let pred         = QCInst -> Type
    qci_pred QCInst
    new_qci
                 not_equality = Type -> Bool
    isClassPred Type
    pred Bool -> Bool -> Bool
    && Bool -> Bool
    not (Type -> Bool
    isEqPred Type
    pred)
                      -- True <=> definitely not an equality
                      -- A qci_pred like (f a) might be an equality

                 ics2 | Bool
    not_equality = InertCans
    ics1
                      | Bool
    otherwise    = InertCans
    ics1 { inert_given_eq_lvl = tclvl
                                            , inert_given_eqs    = True }

           ; setInertCans ics2 }
      where
        add_qci :: InertCans -> TcS InertCans
        -- See Note [Do not add duplicate quantified instances]
        add_qci :: InertCans -> TcS InertCans
    add_qci ics :: InertCans
    ics@(IC { inert_insts :: InertCans -> [QCInst]
    inert_insts = [QCInst]
    qcis })
          | (QCInst -> Bool) -> [QCInst] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any QCInst -> Bool
    same_qci [QCInst]
    qcis
          = do { String -> SDoc -> TcS ()
    traceTcS String
    "skipping duplicate quantified instance" (QCInst -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr QCInst
    new_qci)
               ; InertCans -> TcS InertCans
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return InertCans
    ics }

          | Bool
    otherwise
          = do { String -> SDoc -> TcS ()
    traceTcS String
    "adding new inert quantified instance" (QCInst -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr QCInst
    new_qci)
               ; InertCans -> TcS InertCans
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (InertCans
    ics { inert_insts = new_qci : qcis }) }

        same_qci :: QCInst -> Bool
    same_qci QCInst
    old_qci = HasDebugCallStack => Type -> Type -> Bool
    Type -> Type -> Bool
    tcEqType (CtEvidence -> Type
    ctEvPred (QCInst -> CtEvidence
    qci_ev QCInst
    old_qci))
                                    (CtEvidence -> Type
    ctEvPred (QCInst -> CtEvidence
    qci_ev QCInst
    new_qci))

    {- Note [Do not add duplicate quantified instances]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    As an optimisation, we avoid adding duplicate quantified instances to the
    inert set; we use a simple duplicate check using tcEqType for simplicity,
    even though it doesn't account for superficial differences, e.g. it will count
    the following two constraints as different (#22223):

      - forall a b. C a b
      - forall b a. C a b

    The main logic that allows us to pick local instances, even in the presence of
    duplicates, is explained in Note [Use only the best matching quantified constraint]
    in GHC.Tc.Solver.Dict.
    -}

    {- *********************************************************************
    *                                                                      *
                      Kicking out
    *                                                                      *
    ************************************************************************
    -}

    -----------------------------------------
    kickOutRewritable  :: KickOutSpec -> CtFlavourRole -> TcS ()
    kickOutRewritable :: KickOutSpec -> CtFlavourRole -> TcS ()
    kickOutRewritable KickOutSpec
    ko_spec CtFlavourRole
    new_fr
      = do { ics <- TcS InertCans
    getInertCans
           ; let (kicked_out, ics') = kickOutRewritableLHS ko_spec new_fr ics
                 n_kicked = Cts -> Int
    forall a. Bag a -> Int
    lengthBag Cts
    kicked_out
           ; setInertCans ics'

           ; unless (isEmptyBag kicked_out) $
             do { emitWork kicked_out

                  -- The famapp-cache contains Given evidence from the inert set.
                  -- If we're kicking out Givens, we need to remove this evidence
                  -- from the cache, too.
                ; let kicked_given_ev_vars = (Ct -> VarSet -> VarSet) -> VarSet -> Cts -> VarSet
    forall a b. (a -> b -> b) -> b -> Bag a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr Ct -> VarSet -> VarSet
    add_one VarSet
    emptyVarSet Cts
    kicked_out
                      add_one :: Ct -> VarSet -> VarSet
                      add_one Ct
    ct VarSet
    vs | CtGiven { ctev_evar :: CtEvidence -> TcTyVar
    ctev_evar = TcTyVar
    ev_var } <- Ct -> CtEvidence
    ctEvidence Ct
    ct
                                    = VarSet
    vs VarSet -> TcTyVar -> VarSet
    `extendVarSet` TcTyVar
    ev_var
                                    | Bool
    otherwise = VarSet
    vs

                ; when (new_fr `eqCanRewriteFR` (Given, NomEq) &&
                       -- if this isn't true, no use looking through the constraints
                        not (isEmptyVarSet kicked_given_ev_vars)) $
                  do { traceTcS "Given(s) have been kicked out; drop from famapp-cache"
                                (ppr kicked_given_ev_vars)
                     ; dropFromFamAppCache kicked_given_ev_vars }

                ; csTraceTcS $
                  hang (text "Kick out")
                     2 (vcat [ text "n-kicked =" <+> int n_kicked
                             , text "kicked_out =" <+> ppr kicked_out
                             , text "Residual inerts =" <+> ppr ics' ]) } }

    kickOutAfterUnification :: [TcTyVar] -> TcS ()
    kickOutAfterUnification :: [TcTyVar] -> TcS ()
    kickOutAfterUnification [TcTyVar]
    tvs
      | [TcTyVar] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [TcTyVar]
    tvs
      = () -> TcS ()
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
      | Bool
    otherwise
      = do { let tv_set :: VarSet
    tv_set = [TcTyVar] -> VarSet
    mkVarSet [TcTyVar]
    tvs

           ; n_kicked <- KickOutSpec -> CtFlavourRole -> TcS ()
    kickOutRewritable (VarSet -> KickOutSpec
    KOAfterUnify VarSet
    tv_set) (CtFlavour
    Given, EqRel
    NomEq)
                         -- Given because the tv := xi is given; NomEq because
                         -- only nominal equalities are solved by unification

           -- Set the unification flag if we have done outer unifications
           -- that might affect an earlier implication constraint
           ; let min_tv_lvl = (TcLevel -> TcLevel -> TcLevel) -> [TcLevel] -> TcLevel
    forall a. (a -> a -> a) -> [a] -> a
    forall (t :: * -> *) a. Foldable t => (a -> a -> a) -> t a -> a
    foldr1 TcLevel -> TcLevel -> TcLevel
    minTcLevel ((TcTyVar -> TcLevel) -> [TcTyVar] -> [TcLevel]
    forall a b. (a -> b) -> [a] -> [b]
    map TcTyVar -> TcLevel
    tcTyVarLevel [TcTyVar]
    tvs)
           ; ambient_lvl <- getTcLevel
           ; when (ambient_lvl `strictlyDeeperThan` min_tv_lvl) $
             setUnificationFlag min_tv_lvl

           ; traceTcS "kickOutAfterUnification" (ppr tvs $$ text "n_kicked =" <+> ppr n_kicked)
           ; return n_kicked }

    kickOutAfterFillingCoercionHole :: CoercionHole -> TcS ()
    -- See Wrinkle (EIK2a) in Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality
    -- It's possible that this could just go ahead and unify, but could there be occurs-check
    -- problems? Seems simpler just to kick out.
    kickOutAfterFillingCoercionHole :: CoercionHole -> TcS ()
    kickOutAfterFillingCoercionHole CoercionHole
    hole
      = do { ics <- TcS InertCans
    getInertCans
           ; let (kicked_out, ics') = kick_out ics
                 n_kicked           = Bag IrredCt -> Int
    forall a. Bag a -> Int
    lengthBag Bag IrredCt
    kicked_out

           ; unless (n_kicked == 0) $
             do { updWorkListTcS (extendWorkListCts (fmap CIrredCan kicked_out))
                ; csTraceTcS $
                  hang (text "Kick out, hole =" <+> ppr hole)
                     2 (vcat [ text "n-kicked =" <+> int n_kicked
                             , text "kicked_out =" <+> ppr kicked_out
                             , text "Residual inerts =" <+> ppr ics' ]) }

           ; setInertCans ics' }
      where
        kick_out :: InertCans -> (Bag IrredCt, InertCans)
        kick_out :: InertCans -> (Bag IrredCt, InertCans)
    kick_out ics :: InertCans
    ics@(IC { inert_irreds :: InertCans -> Bag IrredCt
    inert_irreds = Bag IrredCt
    irreds })
          = -- We only care about irreds here, because any constraint blocked
            -- by a coercion hole is an irred.  See wrinkle (EIK2a) in
            -- Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Canonical
            (Bag IrredCt
    irreds_to_kick, InertCans
    ics { inert_irreds = irreds_to_keep })
          where
            (Bag IrredCt
    irreds_to_kick, Bag IrredCt
    irreds_to_keep) = (IrredCt -> Bool) -> Bag IrredCt -> (Bag IrredCt, Bag IrredCt)
    forall a. (a -> Bool) -> Bag a -> (Bag a, Bag a)
    partitionBag IrredCt -> Bool
    kick_ct Bag IrredCt
    irreds

        kick_ct :: IrredCt -> Bool
             -- True: kick out; False: keep.
        kick_ct :: IrredCt -> Bool
    kick_ct IrredCt
    ct
          | IrredCt { ir_ev :: IrredCt -> CtEvidence
    ir_ev = CtEvidence
    ev, ir_reason :: IrredCt -> CtIrredReason
    ir_reason = CtIrredReason
    reason } <- IrredCt
    ct
          , CtWanted { ctev_rewriters :: CtEvidence -> RewriterSet
    ctev_rewriters = RewriterSet UniqSet CoercionHole
    rewriters } <- CtEvidence
    ev
          , NonCanonicalReason CheckTyEqResult
    ctyeq <- CtIrredReason
    reason
          , CheckTyEqResult
    ctyeq CheckTyEqResult -> CheckTyEqProblem -> Bool
    `cterHasProblem` CheckTyEqProblem
    cteCoercionHole
          , CoercionHole
    hole CoercionHole -> UniqSet CoercionHole -> Bool
    forall a. Uniquable a => a -> UniqSet a -> Bool
    `elementOfUniqSet` UniqSet CoercionHole
    rewriters
          = Bool
    True
          | Bool
    otherwise
          = Bool
    False

    --------------
    addInertSafehask :: InertCans -> DictCt -> InertCans
    addInertSafehask :: InertCans -> DictCt -> InertCans
    addInertSafehask InertCans
    ics DictCt
    item
      = InertCans
    ics { inert_safehask = addDict item (inert_dicts ics) }

    insertSafeOverlapFailureTcS :: InstanceWhat -> DictCt -> TcS ()
    -- See Note [Safe Haskell Overlapping Instances Implementation] in GHC.Tc.Solver
    insertSafeOverlapFailureTcS :: InstanceWhat -> DictCt -> TcS ()
    insertSafeOverlapFailureTcS InstanceWhat
    what DictCt
    item
      | InstanceWhat -> Bool
    safeOverlap InstanceWhat
    what = () -> TcS ()
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
      | Bool
    otherwise        = (InertCans -> InertCans) -> TcS ()
    updInertCans (\InertCans
    ics -> InertCans -> DictCt -> InertCans
    addInertSafehask InertCans
    ics DictCt
    item)

    getSafeOverlapFailures :: TcS (Bag DictCt)
    -- See Note [Safe Haskell Overlapping Instances Implementation] in GHC.Tc.Solver
    getSafeOverlapFailures :: TcS (Bag DictCt)
    getSafeOverlapFailures
     = do { IC { inert_safehask = safehask } <- TcS InertCans
    getInertCans
          ; return $ foldDicts consBag safehask emptyBag }

    --------------
    updSolvedDicts :: InstanceWhat -> DictCt -> TcS ()
    -- Conditionally add a new item in the solved set of the monad
    -- See Note [Solved dictionaries] in GHC.Tc.Solver.InertSet
    updSolvedDicts :: InstanceWhat -> DictCt -> TcS ()
    updSolvedDicts InstanceWhat
    what dict_ct :: DictCt
    dict_ct@(DictCt { di_ev :: DictCt -> CtEvidence
    di_ev = CtEvidence
    ev })
      | CtEvidence -> Bool
    isWanted CtEvidence
    ev
      , InstanceWhat -> Bool
    instanceReturnsDictCon InstanceWhat
    what
      = do { String -> SDoc -> TcS ()
    traceTcS String
    "updSolvedDicts:" (SDoc -> TcS ()) -> SDoc -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ DictCt -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr DictCt
    dict_ct
           ; (InertSet -> InertSet) -> TcS ()
    updInertSet ((InertSet -> InertSet) -> TcS ())
    -> (InertSet -> InertSet) -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ \ InertSet
    ics ->
             InertSet
    ics { inert_solved_dicts = addSolvedDict dict_ct (inert_solved_dicts ics) } }
      | Bool
    otherwise
      = () -> TcS ()
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()

    getSolvedDicts :: TcS (DictMap DictCt)
    getSolvedDicts :: TcS (DictMap DictCt)
    getSolvedDicts = do { ics <- TcS InertSet
    getInertSet; return (inert_solved_dicts ics) }

    setSolvedDicts :: DictMap DictCt -> TcS ()
    setSolvedDicts :: DictMap DictCt -> TcS ()
    setSolvedDicts DictMap DictCt
    solved_dicts
      = (InertSet -> InertSet) -> TcS ()
    updInertSet ((InertSet -> InertSet) -> TcS ())
    -> (InertSet -> InertSet) -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ \ InertSet
    ics ->
        InertSet
    ics { inert_solved_dicts = solved_dicts }

    {- *********************************************************************
    *                                                                      *
                      Other inert-set operations
    *                                                                      *
    ********************************************************************* -}

    updInertSet :: (InertSet -> InertSet) -> TcS ()
    -- Modify the inert set with the supplied function
    updInertSet :: (InertSet -> InertSet) -> TcS ()
    updInertSet InertSet -> InertSet
    upd_fn
      = do { is_var <- TcS (IORef InertSet)
    getInertSetRef
           ; wrapTcS (do { curr_inert <- TcM.readTcRef is_var
                         ; TcM.writeTcRef is_var (upd_fn curr_inert) }) }

    getInertCans :: TcS InertCans
    getInertCans :: TcS InertCans
    getInertCans = do { inerts <- TcS InertSet
    getInertSet; return (inert_cans inerts) }

    setInertCans :: InertCans -> TcS ()
    setInertCans :: InertCans -> TcS ()
    setInertCans InertCans
    ics = (InertSet -> InertSet) -> TcS ()
    updInertSet ((InertSet -> InertSet) -> TcS ())
    -> (InertSet -> InertSet) -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ \ InertSet
    inerts -> InertSet
    inerts { inert_cans = ics }

    updRetInertCans :: (InertCans -> (a, InertCans)) -> TcS a
    -- Modify the inert set with the supplied function
    updRetInertCans :: forall a. (InertCans -> (a, InertCans)) -> TcS a
    updRetInertCans InertCans -> (a, InertCans)
    upd_fn
      = do { is_var <- TcS (IORef InertSet)
    getInertSetRef
           ; wrapTcS (do { inerts <- TcM.readTcRef is_var
                         ; let (res, cans') = upd_fn (inert_cans inerts)
                         ; TcM.writeTcRef is_var (inerts { inert_cans = cans' })
                         ; return res }) }

    updInertCans :: (InertCans -> InertCans) -> TcS ()
    -- Modify the inert set with the supplied function
    updInertCans :: (InertCans -> InertCans) -> TcS ()
    updInertCans InertCans -> InertCans
    upd_fn
      = (InertSet -> InertSet) -> TcS ()
    updInertSet ((InertSet -> InertSet) -> TcS ())
    -> (InertSet -> InertSet) -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ \ InertSet
    inerts -> InertSet
    inerts { inert_cans = upd_fn (inert_cans inerts) }

    updInertSafehask :: (DictMap DictCt -> DictMap DictCt) -> TcS ()
    -- Modify the inert set with the supplied function
    updInertSafehask :: (DictMap DictCt -> DictMap DictCt) -> TcS ()
    updInertSafehask DictMap DictCt -> DictMap DictCt
    upd_fn
      = (InertCans -> InertCans) -> TcS ()
    updInertCans ((InertCans -> InertCans) -> TcS ())
    -> (InertCans -> InertCans) -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ \ InertCans
    ics -> InertCans
    ics { inert_safehask = upd_fn (inert_safehask ics) }

    getInertEqs :: TcS InertEqs
    getInertEqs :: TcS InertEqs
    getInertEqs = do { inert <- TcS InertCans
    getInertCans; return (inert_eqs inert) }

    getInnermostGivenEqLevel :: TcS TcLevel
    getInnermostGivenEqLevel :: TcS TcLevel
    getInnermostGivenEqLevel = do { inert <- TcS InertCans
    getInertCans
                                  ; return (inert_given_eq_lvl inert) }

    -- | Retrieves all insoluble constraints from the inert set,
    -- specifically including Given constraints.
    --
    -- This consists of:
    --
    --  - insoluble equalities, such as @Int ~# Bool@;
    --  - constraints that are top-level custom type errors, of the form
    --    @TypeError msg@, but not constraints such as @Eq (TypeError msg)@
    --    in which the type error is nested;
    --  - unsatisfiable constraints, of the form @Unsatisfiable msg@.
    --
    -- The inclusion of Givens is important for pattern match warnings, as we
    -- want to consider a pattern match that introduces insoluble Givens to be
    -- redundant (see Note [Pattern match warnings with insoluble Givens] in GHC.Tc.Solver).
    getInertInsols :: TcS Cts
    getInertInsols :: TcS Cts
    getInertInsols
      = do { inert <- TcS InertCans
    getInertCans
           ; let insols = (IrredCt -> Bool) -> Bag IrredCt -> Bag IrredCt
    forall a. (a -> Bool) -> Bag a -> Bag a
    filterBag IrredCt -> Bool
    insolubleIrredCt (InertCans -> Bag IrredCt
    inert_irreds InertCans
    inert)
                 unsats = DictMap DictCt -> Unique -> Bag DictCt
    forall a. DictMap a -> Unique -> Bag a
    findDictsByTyConKey (InertCans -> DictMap DictCt
    inert_dicts InertCans
    inert) Unique
    unsatisfiableClassNameKey
           ; return $ fmap CDictCan unsats `unionBags` fmap CIrredCan insols }

    getInertGivens :: TcS [Ct]
    -- Returns the Given constraints in the inert set
    getInertGivens :: TcS [Ct]
    getInertGivens
      = do { inerts <- TcS InertCans
    getInertCans
           ; let all_cts = (IrredCt -> [Ct] -> [Ct]) -> Bag IrredCt -> [Ct] -> [Ct]
    forall b. (IrredCt -> b -> b) -> Bag IrredCt -> b -> b
    foldIrreds ((:) (Ct -> [Ct] -> [Ct]) -> (IrredCt -> Ct) -> IrredCt -> [Ct] -> [Ct]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . IrredCt -> Ct
    CIrredCan) (InertCans -> Bag IrredCt
    inert_irreds InertCans
    inerts)
                         ([Ct] -> [Ct]) -> [Ct] -> [Ct]
    forall a b. (a -> b) -> a -> b
    $ (DictCt -> [Ct] -> [Ct]) -> DictMap DictCt -> [Ct] -> [Ct]
    forall a b. (a -> b -> b) -> DictMap a -> b -> b
    foldDicts  ((:) (Ct -> [Ct] -> [Ct]) -> (DictCt -> Ct) -> DictCt -> [Ct] -> [Ct]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . DictCt -> Ct
    CDictCan) (InertCans -> DictMap DictCt
    inert_dicts InertCans
    inerts)
                         ([Ct] -> [Ct]) -> [Ct] -> [Ct]
    forall a b. (a -> b) -> a -> b
    $ (EqCt -> [Ct] -> [Ct]) -> FunEqMap EqualCtList -> [Ct] -> [Ct]
    forall b. (EqCt -> b -> b) -> FunEqMap EqualCtList -> b -> b
    foldFunEqs ((:) (Ct -> [Ct] -> [Ct]) -> (EqCt -> Ct) -> EqCt -> [Ct] -> [Ct]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . EqCt -> Ct
    CEqCan)    (InertCans -> FunEqMap EqualCtList
    inert_funeqs InertCans
    inerts)
                         ([Ct] -> [Ct]) -> [Ct] -> [Ct]
    forall a b. (a -> b) -> a -> b
    $ (EqCt -> [Ct] -> [Ct]) -> InertEqs -> [Ct] -> [Ct]
    forall b. (EqCt -> b -> b) -> InertEqs -> b -> b
    foldTyEqs  ((:) (Ct -> [Ct] -> [Ct]) -> (EqCt -> Ct) -> EqCt -> [Ct] -> [Ct]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . EqCt -> Ct
    CEqCan)    (InertCans -> InertEqs
    inert_eqs InertCans
    inerts)
                         ([Ct] -> [Ct]) -> [Ct] -> [Ct]
    forall a b. (a -> b) -> a -> b
    $ []
           ; return (filter isGivenCt all_cts) }

    getPendingGivenScs :: TcS [Ct]
    -- Find all inert Given dictionaries, or quantified constraints, such that
    --     1. cc_pend_sc flag has fuel strictly > 0
    --     2. belongs to the current level
    -- For each such dictionary:
    -- * Return it (with unmodified cc_pend_sc) in sc_pending
    -- * Modify the dict in the inert set to have cc_pend_sc = doNotExpand
    --   to record that we have expanded superclasses for this dict
    getPendingGivenScs :: TcS [Ct]
    getPendingGivenScs = do { lvl <- TcS TcLevel
    getTcLevel
                            ; updRetInertCans (get_sc_pending lvl) }

    get_sc_pending :: TcLevel -> InertCans -> ([Ct], InertCans)
    get_sc_pending :: TcLevel -> InertCans -> ([Ct], InertCans)
    get_sc_pending TcLevel
    this_lvl ic :: InertCans
    ic@(IC { inert_dicts :: InertCans -> DictMap DictCt
    inert_dicts = DictMap DictCt
    dicts, inert_insts :: InertCans -> [QCInst]
    inert_insts = [QCInst]
    insts })
      = Bool -> SDoc -> ([Ct], InertCans) -> ([Ct], InertCans)
    forall a. HasCallStack => Bool -> SDoc -> a -> a
    assertPpr ((Ct -> Bool) -> [Ct] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all Ct -> Bool
    isGivenCt [Ct]
    sc_pending) ([Ct] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [Ct]
    sc_pending)
           -- When getPendingScDics is called,
           -- there are never any Wanteds in the inert set
        ([Ct]
    sc_pending, InertCans
    ic { inert_dicts = dicts', inert_insts = insts' })
      where
        sc_pending :: [Ct]
    sc_pending = [Ct]
    sc_pend_insts [Ct] -> [Ct] -> [Ct]
    forall a. [a] -> [a] -> [a]
    ++ (DictCt -> Ct) -> [DictCt] -> [Ct]
    forall a b. (a -> b) -> [a] -> [b]
    map DictCt -> Ct
    CDictCan [DictCt]
    sc_pend_dicts

        sc_pend_dicts :: [DictCt]
        sc_pend_dicts :: [DictCt]
    sc_pend_dicts = (DictCt -> [DictCt] -> [DictCt])
    -> DictMap DictCt -> [DictCt] -> [DictCt]
    forall a b. (a -> b -> b) -> DictMap a -> b -> b
    foldDicts DictCt -> [DictCt] -> [DictCt]
    get_pending DictMap DictCt
    dicts []
        dicts' :: DictMap DictCt
    dicts' = (DictCt -> DictMap DictCt -> DictMap DictCt)
    -> DictMap DictCt -> [DictCt] -> DictMap DictCt
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr DictCt -> DictMap DictCt -> DictMap DictCt
    exhaustAndAdd DictMap DictCt
    dicts [DictCt]
    sc_pend_dicts

        ([Ct]
    sc_pend_insts, [QCInst]
    insts') = ([Ct] -> QCInst -> ([Ct], QCInst))
    -> [Ct] -> [QCInst] -> ([Ct], [QCInst])
    forall (t :: * -> *) s a b.
    Traversable t =>
    (s -> a -> (s, b)) -> s -> t a -> (s, t b)
    mapAccumL [Ct] -> QCInst -> ([Ct], QCInst)
    get_pending_inst [] [QCInst]
    insts

        exhaustAndAdd :: DictCt -> DictMap DictCt -> DictMap DictCt
        exhaustAndAdd :: DictCt -> DictMap DictCt -> DictMap DictCt
    exhaustAndAdd DictCt
    ct DictMap DictCt
    dicts = DictCt -> DictMap DictCt -> DictMap DictCt
    addDict (DictCt
    ct {di_pend_sc = doNotExpand}) DictMap DictCt
    dicts
        -- Exhaust the fuel for this constraint before adding it as
        -- we don't want to expand these constraints again

        get_pending :: DictCt -> [DictCt] -> [DictCt]  -- Get dicts with cc_pend_sc > 0
        get_pending :: DictCt -> [DictCt] -> [DictCt]
    get_pending DictCt
    dict [DictCt]
    dicts
            | DictCt -> Bool
    isPendingScDictCt DictCt
    dict
            , CtEvidence -> Bool
    belongs_to_this_level (DictCt -> CtEvidence
    dictCtEvidence DictCt
    dict)
            = DictCt
    dict DictCt -> [DictCt] -> [DictCt]
    forall a. a -> [a] -> [a]
    : [DictCt]
    dicts
            | Bool
    otherwise
            = [DictCt]
    dicts

        get_pending_inst :: [Ct] -> QCInst -> ([Ct], QCInst)
        get_pending_inst :: [Ct] -> QCInst -> ([Ct], QCInst)
    get_pending_inst [Ct]
    cts qci :: QCInst
    qci@(QCI { qci_ev :: QCInst -> CtEvidence
    qci_ev = CtEvidence
    ev })
           | Just QCInst
    qci' <- QCInst -> Maybe QCInst
    pendingScInst_maybe QCInst
    qci
           , CtEvidence -> Bool
    belongs_to_this_level CtEvidence
    ev
           = (QCInst -> Ct
    CQuantCan QCInst
    qci Ct -> [Ct] -> [Ct]
    forall a. a -> [a] -> [a]
    : [Ct]
    cts, QCInst
    qci')
           -- qci' have their fuel exhausted
           -- we don't want to expand these constraints again
           -- qci is expanded
           | Bool
    otherwise
           = ([Ct]
    cts, QCInst
    qci)

        belongs_to_this_level :: CtEvidence -> Bool
    belongs_to_this_level CtEvidence
    ev = CtLoc -> TcLevel
    ctLocLevel (CtEvidence -> CtLoc
    ctEvLoc CtEvidence
    ev) TcLevel -> TcLevel -> Bool
    forall a. Eq a => a -> a -> Bool
    == TcLevel
    this_lvl
        -- We only want Givens from this level; see (3a) in
        -- Note [The superclass story] in GHC.Tc.Solver.Dict

    getUnsolvedInerts :: TcS ( Bag Implication
                             , Cts )   -- All simple constraints
    -- Return all the unsolved [Wanted] constraints
    --
    -- Post-condition: the returned simple constraints are all fully zonked
    --                     (because they come from the inert set)
    --                 the unsolved implics may not be
    getUnsolvedInerts :: TcS (Bag Implication, Cts)
    getUnsolvedInerts
     = do { IC { inert_eqs     = tv_eqs
               , inert_funeqs  = fun_eqs
               , inert_irreds  = irreds
               , inert_dicts   = idicts
               } <- TcS InertCans
    getInertCans

          ; let unsolved_tv_eqs  = (EqCt -> Cts -> Cts) -> InertEqs -> Cts -> Cts
    forall b. (EqCt -> b -> b) -> InertEqs -> b -> b
    foldTyEqs  ((EqCt -> Ct) -> EqCt -> Cts -> Cts
    forall a. (a -> Ct) -> a -> Cts -> Cts
    add_if_unsolved EqCt -> Ct
    CEqCan)    InertEqs
    tv_eqs Cts
    emptyCts
                unsolved_fun_eqs = (EqCt -> Cts -> Cts) -> FunEqMap EqualCtList -> Cts -> Cts
    forall b. (EqCt -> b -> b) -> FunEqMap EqualCtList -> b -> b
    foldFunEqs ((EqCt -> Ct) -> EqCt -> Cts -> Cts
    forall a. (a -> Ct) -> a -> Cts -> Cts
    add_if_unsolved EqCt -> Ct
    CEqCan)    FunEqMap EqualCtList
    fun_eqs Cts
    emptyCts
                unsolved_irreds  = (IrredCt -> Cts -> Cts) -> Cts -> Bag IrredCt -> Cts
    forall a b. (a -> b -> b) -> b -> Bag a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr      ((IrredCt -> Ct) -> IrredCt -> Cts -> Cts
    forall a. (a -> Ct) -> a -> Cts -> Cts
    add_if_unsolved IrredCt -> Ct
    CIrredCan) Cts
    emptyCts Bag IrredCt
    irreds
                unsolved_dicts   = (DictCt -> Cts -> Cts) -> DictMap DictCt -> Cts -> Cts
    forall a b. (a -> b -> b) -> DictMap a -> b -> b
    foldDicts  ((DictCt -> Ct) -> DictCt -> Cts -> Cts
    forall a. (a -> Ct) -> a -> Cts -> Cts
    add_if_unsolved DictCt -> Ct
    CDictCan)  DictMap DictCt
    idicts Cts
    emptyCts

          ; implics <- getWorkListImplics

          ; traceTcS "getUnsolvedInerts" $
            vcat [ text " tv eqs =" <+> ppr unsolved_tv_eqs
                 , text "fun eqs =" <+> ppr unsolved_fun_eqs
                 , text "dicts =" <+> ppr unsolved_dicts
                 , text "irreds =" <+> ppr unsolved_irreds
                 , text "implics =" <+> ppr implics ]

          ; return ( implics, unsolved_tv_eqs `unionBags`
                              unsolved_fun_eqs `unionBags`
                              unsolved_irreds `unionBags`
                              unsolved_dicts ) }
      where
        add_if_unsolved :: (a -> Ct) -> a -> Cts -> Cts
        add_if_unsolved :: forall a. (a -> Ct) -> a -> Cts -> Cts
    add_if_unsolved a -> Ct
    mk_ct a
    thing Cts
    cts
          | Ct -> Bool
    isWantedCt Ct
    ct = Ct
    ct Ct -> Cts -> Cts
    `consCts` Cts
    cts
          | Bool
    otherwise     = Cts
    cts
          where
            ct :: Ct
    ct = a -> Ct
    mk_ct a
    thing

    getHasGivenEqs :: TcLevel             -- TcLevel of this implication
                   -> TcS ( HasGivenEqs   -- are there Given equalities?
                          , InertIrreds ) -- Insoluble equalities arising from givens
    -- See Note [Tracking Given equalities] in GHC.Tc.Solver.InertSet
    getHasGivenEqs :: TcLevel -> TcS (HasGivenEqs, Bag IrredCt)
    getHasGivenEqs TcLevel
    tclvl
      = do { inerts@(IC { inert_irreds       = irreds
                        , inert_given_eqs    = given_eqs
                        , inert_given_eq_lvl = ge_lvl })
                  <- TcS InertCans
    getInertCans
           ; let given_insols = (IrredCt -> Bool) -> Bag IrredCt -> Bag IrredCt
    forall a. (a -> Bool) -> Bag a -> Bag a
    filterBag IrredCt -> Bool
    insoluble_given_equality Bag IrredCt
    irreds
                          -- Specifically includes ones that originated in some
                          -- outer context but were refined to an insoluble by
                          -- a local equality; so no level-check needed

                 -- See Note [HasGivenEqs] in GHC.Tc.Types.Constraint, and
                 -- Note [Tracking Given equalities] in GHC.Tc.Solver.InertSet
                 has_ge | TcLevel
    ge_lvl TcLevel -> TcLevel -> Bool
    forall a. Eq a => a -> a -> Bool
    == TcLevel
    tclvl = HasGivenEqs
    MaybeGivenEqs
                        | Bool
    given_eqs       = HasGivenEqs
    LocalGivenEqs
                        | Bool
    otherwise       = HasGivenEqs
    NoGivenEqs

           ; traceTcS "getHasGivenEqs" $
             vcat [ text "given_eqs:" <+> ppr given_eqs
                  , text "ge_lvl:" <+> ppr ge_lvl
                  , text "ambient level:" <+> ppr tclvl
                  , text "Inerts:" <+> ppr inerts
                  , text "Insols:" <+> ppr given_insols]
           ; return (has_ge, given_insols) }
      where
        insoluble_given_equality :: IrredCt -> Bool
        -- Check for unreachability; specifically do not include UserError/Unsatisfiable
        insoluble_given_equality :: IrredCt -> Bool
    insoluble_given_equality (IrredCt { ir_ev :: IrredCt -> CtEvidence
    ir_ev = CtEvidence
    ev, ir_reason :: IrredCt -> CtIrredReason
    ir_reason = CtIrredReason
    reason })
           = CtIrredReason -> Bool
    isInsolubleReason CtIrredReason
    reason Bool -> Bool -> Bool
    && CtEvidence -> Bool
    isGiven CtEvidence
    ev

    removeInertCts :: [Ct] -> InertCans -> InertCans
    -- ^ Remove inert constraints from the 'InertCans', for use when a
    -- typechecker plugin wishes to discard a given.
    removeInertCts :: [Ct] -> InertCans -> InertCans
    removeInertCts [Ct]
    cts InertCans
    icans = (InertCans -> Ct -> InertCans) -> InertCans -> [Ct] -> InertCans
    forall b a. (b -> a -> b) -> b -> [a] -> b
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' InertCans -> Ct -> InertCans
    removeInertCt InertCans
    icans [Ct]
    cts

    removeInertCt :: InertCans -> Ct -> InertCans
    removeInertCt :: InertCans -> Ct -> InertCans
    removeInertCt InertCans
    is Ct
    ct
      = case Ct
    ct of
          CDictCan DictCt
    dict_ct -> InertCans
    is { inert_dicts = delDict dict_ct (inert_dicts is) }
          CEqCan    EqCt
    eq_ct  -> EqCt -> InertCans -> InertCans
    delEq    EqCt
    eq_ct InertCans
    is
          CIrredCan IrredCt
    ir_ct  -> IrredCt -> InertCans -> InertCans
    delIrred IrredCt
    ir_ct InertCans
    is
          CQuantCan {}     -> String -> InertCans
    forall a. HasCallStack => String -> a
    panic String
    "removeInertCt: CQuantCan"
          CNonCanonical {} -> String -> InertCans
    forall a. HasCallStack => String -> a
    panic String
    "removeInertCt: CNonCanonical"

    -- | Looks up a family application in the inerts.
    lookupFamAppInert :: (CtFlavourRole -> Bool)  -- can it rewrite the target?
                      -> TyCon -> [Type] -> TcS (Maybe (Reduction, CtFlavourRole))
    lookupFamAppInert :: (CtFlavourRole -> Bool)
    -> TyCon -> [Type] -> TcS (Maybe (Reduction, CtFlavourRole))
    lookupFamAppInert CtFlavourRole -> Bool
    rewrite_pred TyCon
    fam_tc [Type]
    tys
      = do { IS { inert_cans = IC { inert_funeqs = inert_funeqs } } <- TcS InertSet
    getInertSet
           ; return (lookup_inerts inert_funeqs) }
      where
        lookup_inerts :: FunEqMap EqualCtList -> Maybe (Reduction, CtFlavourRole)
    lookup_inerts FunEqMap EqualCtList
    inert_funeqs
          | Just EqualCtList
    ecl <- FunEqMap EqualCtList -> TyCon -> [Type] -> Maybe EqualCtList
    forall a. FunEqMap a -> TyCon -> [Type] -> Maybe a
    findFunEq FunEqMap EqualCtList
    inert_funeqs TyCon
    fam_tc [Type]
    tys
          , Just (EqCt { eq_ev :: EqCt -> CtEvidence
    eq_ev = CtEvidence
    ctev, eq_rhs :: EqCt -> Type
    eq_rhs = Type
    rhs })
              <- (EqCt -> Bool) -> EqualCtList -> Maybe EqCt
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Maybe a
    find (CtFlavourRole -> Bool
    rewrite_pred (CtFlavourRole -> Bool) -> (EqCt -> CtFlavourRole) -> EqCt -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . EqCt -> CtFlavourRole
    eqCtFlavourRole) EqualCtList
    ecl
          = (Reduction, CtFlavourRole) -> Maybe (Reduction, CtFlavourRole)
    forall a. a -> Maybe a
    Just (Coercion -> Type -> Reduction
    mkReduction (HasDebugCallStack => CtEvidence -> Coercion
    CtEvidence -> Coercion
    ctEvCoercion CtEvidence
    ctev) Type
    rhs, CtEvidence -> CtFlavourRole
    ctEvFlavourRole CtEvidence
    ctev)
          | Bool
    otherwise = Maybe (Reduction, CtFlavourRole)
    forall a. Maybe a
    Nothing

    lookupInInerts :: CtLoc -> TcPredType -> TcS (Maybe CtEvidence)
    -- Is this exact predicate type cached in the solved or canonicals of the InertSet?
    lookupInInerts :: CtLoc -> Type -> TcS (Maybe CtEvidence)
    lookupInInerts CtLoc
    loc Type
    pty
      | ClassPred Class
    cls [Type]
    tys <- Type -> Pred
    classifyPredType Type
    pty
      = do { inerts <- TcS InertSet
    getInertSet
           ; let mb_solved = InertSet -> CtLoc -> Class -> [Type] -> Maybe CtEvidence
    lookupSolvedDict InertSet
    inerts CtLoc
    loc Class
    cls [Type]
    tys
                 mb_inert  = (DictCt -> CtEvidence) -> Maybe DictCt -> Maybe CtEvidence
    forall a b. (a -> b) -> Maybe a -> Maybe b
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap DictCt -> CtEvidence
    dictCtEvidence (InertCans -> CtLoc -> Class -> [Type] -> Maybe DictCt
    lookupInertDict (InertSet -> InertCans
    inert_cans InertSet
    inerts) CtLoc
    loc Class
    cls [Type]
    tys)
           ; return $ do -- Maybe monad
                found_ev <- mb_solved `mplus` mb_inert

                -- We're about to "solve" the wanted we're looking up, so we
                -- must make sure doing so wouldn't run afoul of
                -- Note [Solving superclass constraints] in GHC.Tc.TyCl.Instance.
                -- Forgetting this led to #20666.
                guard $ not (prohibitedSuperClassSolve (ctEvLoc found_ev) loc)

                return found_ev }
      | Bool
    otherwise -- NB: No caching for equalities, IPs, holes, or errors
      = Maybe CtEvidence -> TcS (Maybe CtEvidence)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Maybe CtEvidence
    forall a. Maybe a
    Nothing

    -- | Look up a dictionary inert.
    lookupInertDict :: InertCans -> CtLoc -> Class -> [Type] -> Maybe DictCt
    lookupInertDict :: InertCans -> CtLoc -> Class -> [Type] -> Maybe DictCt
    lookupInertDict (IC { inert_dicts :: InertCans -> DictMap DictCt
    inert_dicts = DictMap DictCt
    dicts }) CtLoc
    loc Class
    cls [Type]
    tys
      = DictMap DictCt -> CtLoc -> Class -> [Type] -> Maybe DictCt
    forall a. DictMap a -> CtLoc -> Class -> [Type] -> Maybe a
    findDict DictMap DictCt
    dicts CtLoc
    loc Class
    cls [Type]
    tys

    -- | Look up a solved inert.
    lookupSolvedDict :: InertSet -> CtLoc -> Class -> [Type] -> Maybe CtEvidence
    -- Returns just if exactly this predicate type exists in the solved.
    lookupSolvedDict :: InertSet -> CtLoc -> Class -> [Type] -> Maybe CtEvidence
    lookupSolvedDict (IS { inert_solved_dicts :: InertSet -> DictMap DictCt
    inert_solved_dicts = DictMap DictCt
    solved }) CtLoc
    loc Class
    cls [Type]
    tys
      = (DictCt -> CtEvidence) -> Maybe DictCt -> Maybe CtEvidence
    forall a b. (a -> b) -> Maybe a -> Maybe b
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap DictCt -> CtEvidence
    dictCtEvidence (DictMap DictCt -> CtLoc -> Class -> [Type] -> Maybe DictCt
    forall a. DictMap a -> CtLoc -> Class -> [Type] -> Maybe a
    findDict DictMap DictCt
    solved CtLoc
    loc Class
    cls [Type]
    tys)

    ---------------------------
    lookupFamAppCache :: TyCon -> [Type] -> TcS (Maybe Reduction)
    lookupFamAppCache :: TyCon -> [Type] -> TcS (Maybe Reduction)
    lookupFamAppCache TyCon
    fam_tc [Type]
    tys
      = do { IS { inert_famapp_cache = famapp_cache } <- TcS InertSet
    getInertSet
           ; case findFunEq famapp_cache fam_tc tys of
               result :: Maybe Reduction
    result@(Just Reduction
    redn) ->
                 do { String -> SDoc -> TcS ()
    traceTcS String
    "famapp_cache hit" ([SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ Type -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (TyCon -> [Type] -> Type
    mkTyConApp TyCon
    fam_tc [Type]
    tys)
                                                        , Reduction -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Reduction
    redn ])
                    ; Maybe Reduction -> TcS (Maybe Reduction)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Maybe Reduction
    result }
               Maybe Reduction
    Nothing -> Maybe Reduction -> TcS (Maybe Reduction)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Maybe Reduction
    forall a. Maybe a
    Nothing }

    extendFamAppCache :: TyCon -> [Type] -> Reduction -> TcS ()
    -- NB: co :: rhs ~ F tys, to match expectations of rewriter
    extendFamAppCache :: TyCon -> [Type] -> Reduction -> TcS ()
    extendFamAppCache TyCon
    tc [Type]
    xi_args stuff :: Reduction
    stuff@(Reduction Coercion
    _ Type
    ty)
      = do { dflags <- TcS DynFlags
    forall (m :: * -> *). HasDynFlags m => m DynFlags
    getDynFlags
           ; when (gopt Opt_FamAppCache dflags) $
        do { traceTcS "extendFamAppCache" (vcat [ ppr tc <+> ppr xi_args
                                                , ppr ty ])
           ; updInertSet $ \ is :: InertSet
    is@(IS { inert_famapp_cache :: InertSet -> FunEqMap Reduction
    inert_famapp_cache = FunEqMap Reduction
    fc }) ->
                InertSet
    is { inert_famapp_cache = insertFunEq fc tc xi_args stuff } } }

    -- Remove entries from the cache whose evidence mentions variables in the
    -- supplied set
    dropFromFamAppCache :: VarSet -> TcS ()
    dropFromFamAppCache :: VarSet -> TcS ()
    dropFromFamAppCache VarSet
    varset
      = (InertSet -> InertSet) -> TcS ()
    updInertSet (\inerts :: InertSet
    inerts@(IS { inert_famapp_cache :: InertSet -> FunEqMap Reduction
    inert_famapp_cache = FunEqMap Reduction
    famapp_cache }) ->
                       InertSet
    inerts { inert_famapp_cache = filterTcAppMap check famapp_cache })
      where
        check :: Reduction -> Bool
        check :: Reduction -> Bool
    check Reduction
    redn
          = Bool -> Bool
    not ((TcTyVar -> Bool) -> Coercion -> Bool
    anyFreeVarsOfCo (TcTyVar -> VarSet -> Bool
    `elemVarSet` VarSet
    varset) (Coercion -> Bool) -> Coercion -> Bool
    forall a b. (a -> b) -> a -> b
    $ Reduction -> Coercion
    reductionCoercion Reduction
    redn)

    {-
    ************************************************************************
    *                                                                      *
    *              The TcS solver monad                                    *
    *                                                                      *
    ************************************************************************

    Note [The TcS monad]
    ~~~~~~~~~~~~~~~~~~~~
    The TcS monad is a weak form of the main Tc monad

    All you can do is
        * fail
        * allocate new variables
        * fill in evidence variables

    Filling in a dictionary evidence variable means to create a binding
    for it, so TcS carries a mutable location where the binding can be
    added.  This is initialised from the innermost implication constraint.
    -}

    data TcSEnv
      = TcSEnv {
          TcSEnv -> EvBindsVar
    tcs_ev_binds    :: EvBindsVar,

          TcSEnv -> IORef Int
    tcs_unified     :: IORef Int,
             -- The number of unification variables we have filled
             -- The important thing is whether it is non-zero

          TcSEnv -> IORef (Maybe TcLevel)
    tcs_unif_lvl  :: IORef (Maybe TcLevel),
             -- The Unification Level Flag
             -- Outermost level at which we have unified a meta tyvar
             -- Starts at Nothing, then (Just i), then (Just j) where j<i
             -- See Note [The Unification Level Flag]

          TcSEnv -> IORef Int
    tcs_count     :: IORef Int, -- Global step count

          TcSEnv -> IORef InertSet
    tcs_inerts    :: IORef InertSet, -- Current inert set

          -- Whether to throw an exception if we come across an insoluble constraint.
          -- Used to fail-fast when checking for hole-fits. See Note [Speeding up
          -- valid hole-fits].
          TcSEnv -> Bool
    tcs_abort_on_insoluble :: Bool,

          -- See Note [WorkList priorities] in GHC.Tc.Solver.InertSet
          TcSEnv -> IORef WorkList
    tcs_worklist  :: IORef WorkList -- Current worklist
        }

    ---------------
    newtype TcS a = TcS { forall a. TcS a -> TcSEnv -> TcM a
    unTcS :: TcSEnv -> TcM a }
      deriving ((forall a b. (a -> b) -> TcS a -> TcS b)
    -> (forall a b. a -> TcS b -> TcS a) -> Functor TcS
    forall a b. a -> TcS b -> TcS a
    forall a b. (a -> b) -> TcS a -> TcS b
    forall (f :: * -> *).
    (forall a b. (a -> b) -> f a -> f b)
    -> (forall a b. a -> f b -> f a) -> Functor f
    $cfmap :: forall a b. (a -> b) -> TcS a -> TcS b
    fmap :: forall a b. (a -> b) -> TcS a -> TcS b
    $c<$ :: forall a b. a -> TcS b -> TcS a
    <$ :: forall a b. a -> TcS b -> TcS a
    Functor)

    instance MonadFix TcS where
      mfix :: forall a. (a -> TcS a) -> TcS a
    mfix a -> TcS a
    k = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM a) -> TcS a) -> (TcSEnv -> TcM a) -> TcS a
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    env -> (a -> TcM a) -> TcM a
    forall a.
    (a -> IOEnv (Env TcGblEnv TcLclEnv) a)
    -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. MonadFix m => (a -> m a) -> m a
    mfix (\a
    x -> TcS a -> TcSEnv -> TcM a
    forall a. TcS a -> TcSEnv -> TcM a
    unTcS (a -> TcS a
    k a
    x) TcSEnv
    env)

    -- | Smart constructor for 'TcS', as describe in Note [The one-shot state
    -- monad trick] in "GHC.Utils.Monad".
    mkTcS :: (TcSEnv -> TcM a) -> TcS a
    mkTcS :: forall a. (TcSEnv -> TcM a) -> TcS a
    mkTcS TcSEnv -> TcM a
    f = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM a) -> TcSEnv -> TcM a
    forall a b. (a -> b) -> a -> b
    oneShot TcSEnv -> TcM a
    f)

    instance Applicative TcS where
      pure :: forall a. a -> TcS a
    pure a
    x = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    mkTcS ((TcSEnv -> TcM a) -> TcS a) -> (TcSEnv -> TcM a) -> TcS a
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    _ -> a -> TcM a
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return a
    x
      <*> :: forall a b. TcS (a -> b) -> TcS a -> TcS b
    (<*>) = TcS (a -> b) -> TcS a -> TcS b
    forall (m :: * -> *) a b. Monad m => m (a -> b) -> m a -> m b
    ap

    instance Monad TcS where
      TcS a
    m >>= :: forall a b. TcS a -> (a -> TcS b) -> TcS b
    >>= a -> TcS b
    k   = (TcSEnv -> TcM b) -> TcS b
    forall a. (TcSEnv -> TcM a) -> TcS a
    mkTcS ((TcSEnv -> TcM b) -> TcS b) -> (TcSEnv -> TcM b) -> TcS b
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    ebs -> do
        TcS a -> TcSEnv -> TcM a
    forall a. TcS a -> TcSEnv -> TcM a
    unTcS TcS a
    m TcSEnv
    ebs TcM a -> (a -> TcM b) -> TcM b
    forall a b.
    IOEnv (Env TcGblEnv TcLclEnv) a
    -> (a -> IOEnv (Env TcGblEnv TcLclEnv) b)
    -> IOEnv (Env TcGblEnv TcLclEnv) b
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= (\a
    r -> TcS b -> TcSEnv -> TcM b
    forall a. TcS a -> TcSEnv -> TcM a
    unTcS (a -> TcS b
    k a
    r) TcSEnv
    ebs)

    instance MonadIO TcS where
      liftIO :: forall a. IO a -> TcS a
    liftIO IO a
    act = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM a) -> TcS a) -> (TcSEnv -> TcM a) -> TcS a
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    _env -> IO a -> TcM a
    forall a. IO a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. MonadIO m => IO a -> m a
    liftIO IO a
    act

    instance MonadFail TcS where
      fail :: forall a. String -> TcS a
    fail String
    err  = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    mkTcS ((TcSEnv -> TcM a) -> TcS a) -> (TcSEnv -> TcM a) -> TcS a
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    _ -> String -> TcM a
    forall a. String -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. MonadFail m => String -> m a
    fail String
    err

    instance MonadUnique TcS where
       getUniqueSupplyM :: TcS UniqSupply
    getUniqueSupplyM = TcM UniqSupply -> TcS UniqSupply
    forall a. TcM a -> TcS a
    wrapTcS TcM UniqSupply
    forall (m :: * -> *). MonadUnique m => m UniqSupply
    getUniqueSupplyM

    instance HasModule TcS where
       getModule :: TcS Module
    getModule = TcM Module -> TcS Module
    forall a. TcM a -> TcS a
    wrapTcS TcM Module
    forall (m :: * -> *). HasModule m => m Module
    getModule

    instance MonadThings TcS where
       lookupThing :: Name -> TcS TyThing
    lookupThing Name
    n = TcM TyThing -> TcS TyThing
    forall a. TcM a -> TcS a
    wrapTcS (Name -> TcM TyThing
    forall (m :: * -> *). MonadThings m => Name -> m TyThing
    lookupThing Name
    n)

    -- Basic functionality
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    wrapTcS :: TcM a -> TcS a
    -- Do not export wrapTcS, because it promotes an arbitrary TcM to TcS,
    -- and TcS is supposed to have limited functionality
    wrapTcS :: forall a. TcM a -> TcS a
    wrapTcS TcM a
    action = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    mkTcS ((TcSEnv -> TcM a) -> TcS a) -> (TcSEnv -> TcM a) -> TcS a
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    _env -> TcM a
    action -- a TcM action will not use the TcEvBinds

    liftZonkTcS :: ZonkM a -> TcS a
    liftZonkTcS :: forall a. ZonkM a -> TcS a
    liftZonkTcS = TcM a -> TcS a
    forall a. TcM a -> TcS a
    wrapTcS (TcM a -> TcS a) -> (ZonkM a -> TcM a) -> ZonkM a -> TcS a
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . ZonkM a -> TcM a
    forall a. ZonkM a -> TcM a
    TcM.liftZonkM

    wrap2TcS :: (TcM a -> TcM a) -> TcS a -> TcS a
    wrap2TcS :: forall a. (TcM a -> TcM a) -> TcS a -> TcS a
    wrap2TcS TcM a -> TcM a
    fn (TcS TcSEnv -> TcM a
    thing) = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    mkTcS ((TcSEnv -> TcM a) -> TcS a) -> (TcSEnv -> TcM a) -> TcS a
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    env -> TcM a -> TcM a
    fn (TcSEnv -> TcM a
    thing TcSEnv
    env)

    wrapErrTcS :: TcM a -> TcS a
    -- The thing wrapped should just fail
    -- There's no static check; it's up to the user
    -- Having a variant for each error message is too painful
    wrapErrTcS :: forall a. TcM a -> TcS a
    wrapErrTcS = TcM a -> TcS a
    forall a. TcM a -> TcS a
    wrapTcS

    wrapWarnTcS :: TcM a -> TcS a
    -- The thing wrapped should just add a warning, or no-op
    -- There's no static check; it's up to the user
    wrapWarnTcS :: forall a. TcM a -> TcS a
    wrapWarnTcS = TcM a -> TcS a
    forall a. TcM a -> TcS a
    wrapTcS

    panicTcS  :: SDoc -> TcS a
    failTcS   :: TcRnMessage -> TcS a
    warnTcS, addErrTcS :: TcRnMessage -> TcS ()
    failTcS :: forall a. TcRnMessage -> TcS a
    failTcS      = TcM a -> TcS a
    forall a. TcM a -> TcS a
    wrapTcS (TcM a -> TcS a) -> (TcRnMessage -> TcM a) -> TcRnMessage -> TcS a
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TcRnMessage -> TcM a
    forall a. TcRnMessage -> TcRn a
    TcM.failWith
    warnTcS :: TcRnMessage -> TcS ()
    warnTcS TcRnMessage
    msg  = TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcRnMessage -> TcM ()
    TcM.addDiagnostic TcRnMessage
    msg)
    addErrTcS :: TcRnMessage -> TcS ()
    addErrTcS    = TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcM () -> TcS ())
    -> (TcRnMessage -> TcM ()) -> TcRnMessage -> TcS ()
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TcRnMessage -> TcM ()
    TcM.addErr
    panicTcS :: forall a. SDoc -> TcS a
    panicTcS SDoc
    doc = String -> SDoc -> TcS a
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "GHC.Tc.Solver.Monad" SDoc
    doc

    tryEarlyAbortTcS :: TcS ()
    -- Abort (fail in the monad) if the abort_on_insoluble flag is on
    tryEarlyAbortTcS :: TcS ()
    tryEarlyAbortTcS
      = (TcSEnv -> TcM ()) -> TcS ()
    forall a. (TcSEnv -> TcM a) -> TcS a
    mkTcS (\TcSEnv
    env -> Bool -> TcM () -> TcM ()
    forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
    when (TcSEnv -> Bool
    tcs_abort_on_insoluble TcSEnv
    env) TcM ()
    forall env a. IOEnv env a
    TcM.failM)

    -- | Emit a warning within the 'TcS' monad at the location given by the 'CtLoc'.
    ctLocWarnTcS :: CtLoc -> TcRnMessage -> TcS ()
    ctLocWarnTcS :: CtLoc -> TcRnMessage -> TcS ()
    ctLocWarnTcS CtLoc
    loc TcRnMessage
    msg = TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcM () -> TcS ()) -> TcM () -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ CtLoc -> TcM () -> TcM ()
    forall a. CtLoc -> TcM a -> TcM a
    TcM.setCtLocM CtLoc
    loc (TcM () -> TcM ()) -> TcM () -> TcM ()
    forall a b. (a -> b) -> a -> b
    $ TcRnMessage -> TcM ()
    TcM.addDiagnostic TcRnMessage
    msg

    traceTcS :: String -> SDoc -> TcS ()
    traceTcS :: String -> SDoc -> TcS ()
    traceTcS String
    herald SDoc
    doc = TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (String -> SDoc -> TcM ()
    TcM.traceTc String
    herald SDoc
    doc)
    {-# INLINE traceTcS #-}  -- see Note [INLINE conditional tracing utilities]

    runTcPluginTcS :: TcPluginM a -> TcS a
    runTcPluginTcS :: forall a. TcPluginM a -> TcS a
    runTcPluginTcS = TcM a -> TcS a
    forall a. TcM a -> TcS a
    wrapTcS (TcM a -> TcS a) -> (TcPluginM a -> TcM a) -> TcPluginM a -> TcS a
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TcPluginM a -> TcM a
    forall a. TcPluginM a -> TcM a
    runTcPluginM

    instance HasDynFlags TcS where
        getDynFlags :: TcS DynFlags
    getDynFlags = TcM DynFlags -> TcS DynFlags
    forall a. TcM a -> TcS a
    wrapTcS TcM DynFlags
    forall (m :: * -> *). HasDynFlags m => m DynFlags
    getDynFlags

    getGlobalRdrEnvTcS :: TcS GlobalRdrEnv
    getGlobalRdrEnvTcS :: TcS GlobalRdrEnv
    getGlobalRdrEnvTcS = TcM GlobalRdrEnv -> TcS GlobalRdrEnv
    forall a. TcM a -> TcS a
    wrapTcS TcM GlobalRdrEnv
    TcM.getGlobalRdrEnv

    bumpStepCountTcS :: TcS ()
    bumpStepCountTcS :: TcS ()
    bumpStepCountTcS = (TcSEnv -> TcM ()) -> TcS ()
    forall a. (TcSEnv -> TcM a) -> TcS a
    mkTcS ((TcSEnv -> TcM ()) -> TcS ()) -> (TcSEnv -> TcM ()) -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    env ->
      do { let ref :: IORef Int
    ref = TcSEnv -> IORef Int
    tcs_count TcSEnv
    env
         ; n <- IORef Int -> IOEnv (Env TcGblEnv TcLclEnv) Int
    forall (m :: * -> *) a. MonadIO m => TcRef a -> m a
    TcM.readTcRef IORef Int
    ref
         ; TcM.writeTcRef ref (n+1) }

    csTraceTcS :: SDoc -> TcS ()
    csTraceTcS :: SDoc -> TcS ()
    csTraceTcS SDoc
    doc
      = TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcM () -> TcS ()) -> TcM () -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ TcM SDoc -> TcM ()
    csTraceTcM (SDoc -> TcM SDoc
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return SDoc
    doc)
    {-# INLINE csTraceTcS #-}  -- see Note [INLINE conditional tracing utilities]

    traceFireTcS :: CtEvidence -> SDoc -> TcS ()
    -- Dump a rule-firing trace
    traceFireTcS :: CtEvidence -> SDoc -> TcS ()
    traceFireTcS CtEvidence
    ev SDoc
    doc
      = (TcSEnv -> TcM ()) -> TcS ()
    forall a. (TcSEnv -> TcM a) -> TcS a
    mkTcS ((TcSEnv -> TcM ()) -> TcS ()) -> (TcSEnv -> TcM ()) -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    env -> TcM SDoc -> TcM ()
    csTraceTcM (TcM SDoc -> TcM ()) -> TcM SDoc -> TcM ()
    forall a b. (a -> b) -> a -> b
    $
        do { n <- IORef Int -> IOEnv (Env TcGblEnv TcLclEnv) Int
    forall (m :: * -> *) a. MonadIO m => TcRef a -> m a
    TcM.readTcRef (TcSEnv -> IORef Int
    tcs_count TcSEnv
    env)
           ; tclvl <- TcM.getTcLevel
           ; return (hang (text "Step" <+> int n
                           <> brackets (text "l:" <> ppr tclvl <> comma <>
                                        text "d:" <> ppr (ctLocDepth (ctEvLoc ev)))
                           <+> doc <> colon)
                         4 (ppr ev)) }
    {-# INLINE traceFireTcS #-}  -- see Note [INLINE conditional tracing utilities]

    csTraceTcM :: TcM SDoc -> TcM ()
    -- Constraint-solver tracing, -ddump-cs-trace
    csTraceTcM :: TcM SDoc -> TcM ()
    csTraceTcM TcM SDoc
    mk_doc
      = do { logger <- IOEnv (Env TcGblEnv TcLclEnv) Logger
    forall (m :: * -> *). HasLogger m => m Logger
    getLogger
           ; when (  logHasDumpFlag logger Opt_D_dump_cs_trace
                      || logHasDumpFlag logger Opt_D_dump_tc_trace)
                  ( do { msg <- mk_doc
                       ; TcM.dumpTcRn False
                           Opt_D_dump_cs_trace
                           "" FormatText
                           msg }) }
    {-# INLINE csTraceTcM #-}  -- see Note [INLINE conditional tracing utilities]

    runTcS :: TcS a                -- What to run
           -> TcM (a, EvBindMap)
    runTcS :: forall a. TcS a -> TcM (a, EvBindMap)
    runTcS TcS a
    tcs
      = do { ev_binds_var <- TcM EvBindsVar
    TcM.newTcEvBinds
           ; res <- runTcSWithEvBinds ev_binds_var tcs
           ; ev_binds <- TcM.getTcEvBindsMap ev_binds_var
           ; return (res, ev_binds) }

    -- | This variant of 'runTcS' will immediately fail upon encountering an
    -- insoluble ct. See Note [Speeding up valid hole-fits]. Its one usage
    -- site does not need the ev_binds, so we do not return them.
    runTcSEarlyAbort :: TcS a -> TcM a
    runTcSEarlyAbort :: forall a. TcS a -> TcM a
    runTcSEarlyAbort TcS a
    tcs
      = do { ev_binds_var <- TcM EvBindsVar
    TcM.newTcEvBinds
           ; runTcSWithEvBinds' True True ev_binds_var tcs }

    -- | This can deal only with equality constraints.
    runTcSEqualities :: TcS a -> TcM a
    runTcSEqualities :: forall a. TcS a -> TcM a
    runTcSEqualities TcS a
    thing_inside
      = do { ev_binds_var <- TcM EvBindsVar
    TcM.newNoTcEvBinds
           ; runTcSWithEvBinds ev_binds_var thing_inside }

    -- | A variant of 'runTcS' that takes and returns an 'InertSet' for
    -- later resumption of the 'TcS' session.
    runTcSInerts :: InertSet -> TcS a -> TcM (a, InertSet)
    runTcSInerts :: forall a. InertSet -> TcS a -> TcM (a, InertSet)
    runTcSInerts InertSet
    inerts TcS a
    tcs = do
      ev_binds_var <- TcM EvBindsVar
    TcM.newTcEvBinds
      runTcSWithEvBinds' False False ev_binds_var $ do
        setInertSet inerts
        a <- tcs
        new_inerts <- getInertSet
        return (a, new_inerts)

    runTcSWithEvBinds :: EvBindsVar
                      -> TcS a
                      -> TcM a
    runTcSWithEvBinds :: forall a. EvBindsVar -> TcS a -> TcM a
    runTcSWithEvBinds = Bool -> Bool -> EvBindsVar -> TcS a -> TcM a
    forall a. Bool -> Bool -> EvBindsVar -> TcS a -> TcM a
    runTcSWithEvBinds' Bool
    True Bool
    False

    runTcSWithEvBinds' :: Bool -- ^ Restore type variable cycles afterwards?
                               -- Don't if you want to reuse the InertSet.
                               -- See also Note [Type equality cycles]
                               -- in GHC.Tc.Solver.Equality
                       -> Bool
                       -> EvBindsVar
                       -> TcS a
                       -> TcM a
    runTcSWithEvBinds' :: forall a. Bool -> Bool -> EvBindsVar -> TcS a -> TcM a
    runTcSWithEvBinds' Bool
    restore_cycles Bool
    abort_on_insoluble EvBindsVar
    ev_binds_var TcS a
    tcs
      = do { unified_var <- Int -> IOEnv (Env TcGblEnv TcLclEnv) (IORef Int)
    forall (m :: * -> *) a. MonadIO m => a -> m (TcRef a)
    TcM.newTcRef Int
    0
           ; step_count <- TcM.newTcRef 0
           ; inert_var <- TcM.newTcRef emptyInert
           ; wl_var <- TcM.newTcRef emptyWorkList
           ; unif_lvl_var <- TcM.newTcRef Nothing
           ; let env = TcSEnv { tcs_ev_binds :: EvBindsVar
    tcs_ev_binds           = EvBindsVar
    ev_binds_var
                              , tcs_unified :: IORef Int
    tcs_unified            = IORef Int
    unified_var
                              , tcs_unif_lvl :: IORef (Maybe TcLevel)
    tcs_unif_lvl           = IORef (Maybe TcLevel)
    unif_lvl_var
                              , tcs_count :: IORef Int
    tcs_count              = IORef Int
    step_count
                              , tcs_inerts :: IORef InertSet
    tcs_inerts             = IORef InertSet
    inert_var
                              , tcs_abort_on_insoluble :: Bool
    tcs_abort_on_insoluble = Bool
    abort_on_insoluble
                              , tcs_worklist :: IORef WorkList
    tcs_worklist           = IORef WorkList
    wl_var }

                 -- Run the computation
           ; res <- unTcS tcs env

           ; count <- TcM.readTcRef step_count
           ; when (count > 0) $
             csTraceTcM $ return (text "Constraint solver steps =" <+> int count)

           ; when restore_cycles $
             do { inert_set <- TcM.readTcRef inert_var
                ; restoreTyVarCycles inert_set }

    #if defined(DEBUG)
           ; ev_binds <- TcM.getTcEvBindsMap ev_binds_var
           ; checkForCyclicBinds ev_binds
    #endif

           ; return res }

    ----------------------------
    #if defined(DEBUG)
    checkForCyclicBinds :: EvBindMap -> TcM ()
    checkForCyclicBinds ev_binds_map
      | null cycles
      = return ()
      | null coercion_cycles
      = TcM.traceTc "Cycle in evidence binds" $ ppr cycles
      | otherwise
      = pprPanic "Cycle in coercion bindings" $ ppr coercion_cycles
      where
        ev_binds = evBindMapBinds ev_binds_map

        cycles :: [[EvBind]]
        cycles = [c | CyclicSCC c <- stronglyConnCompFromEdgedVerticesUniq edges]

        coercion_cycles = [c | c <- cycles, any is_co_bind c]
        is_co_bind (EvBind { eb_lhs = b }) = isEqPrimPred (varType b)

        edges :: [ Node EvVar EvBind ]
        edges = [ DigraphNode bind bndr (nonDetEltsUniqSet (evVarsOfTerm rhs))
                | bind@(EvBind { eb_lhs = bndr, eb_rhs = rhs}) <- bagToList ev_binds ]
                -- It's OK to use nonDetEltsUFM here as
                -- stronglyConnCompFromEdgedVertices is still deterministic even
                -- if the edges are in nondeterministic order as explained in
                -- Note [Deterministic SCC] in GHC.Data.Graph.Directed.
    #endif

    ----------------------------
    setEvBindsTcS :: EvBindsVar -> TcS a -> TcS a
    setEvBindsTcS :: forall a. EvBindsVar -> TcS a -> TcS a
    setEvBindsTcS EvBindsVar
    ref (TcS TcSEnv -> TcM a
    thing_inside)
     = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM a) -> TcS a) -> (TcSEnv -> TcM a) -> TcS a
    forall a b. (a -> b) -> a -> b
    $ \ TcSEnv
    env -> TcSEnv -> TcM a
    thing_inside (TcSEnv
    env { tcs_ev_binds = ref })

    nestImplicTcS :: EvBindsVar
                  -> TcLevel -> TcS a
                  -> TcS a
    nestImplicTcS :: forall a. EvBindsVar -> TcLevel -> TcS a -> TcS a
    nestImplicTcS EvBindsVar
    ref TcLevel
    inner_tclvl (TcS TcSEnv -> TcM a
    thing_inside)
      = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM a) -> TcS a) -> (TcSEnv -> TcM a) -> TcS a
    forall a b. (a -> b) -> a -> b
    $ \ TcSEnv { tcs_unified :: TcSEnv -> IORef Int
    tcs_unified            = IORef Int
    unified_var
                       , tcs_inerts :: TcSEnv -> IORef InertSet
    tcs_inerts             = IORef InertSet
    old_inert_var
                       , tcs_count :: TcSEnv -> IORef Int
    tcs_count              = IORef Int
    count
                       , tcs_unif_lvl :: TcSEnv -> IORef (Maybe TcLevel)
    tcs_unif_lvl           = IORef (Maybe TcLevel)
    unif_lvl
                       , tcs_abort_on_insoluble :: TcSEnv -> Bool
    tcs_abort_on_insoluble = Bool
    abort_on_insoluble
                       } ->
        do { inerts <- IORef InertSet -> IOEnv (Env TcGblEnv TcLclEnv) InertSet
    forall (m :: * -> *) a. MonadIO m => TcRef a -> m a
    TcM.readTcRef IORef InertSet
    old_inert_var
           ; let nest_inert = InertSet
    inerts { inert_cycle_breakers = pushCycleBreakerVarStack
                                                                (inert_cycle_breakers inerts)
                                     , inert_cans = (inert_cans inerts)
                                                       { inert_given_eqs = False } }
                     -- All other InertSet fields are inherited
           ; new_inert_var <- TcM.newTcRef nest_inert
           ; new_wl_var    <- TcM.newTcRef emptyWorkList
           ; let nest_env = TcSEnv { tcs_count :: IORef Int
    tcs_count              = IORef Int
    count     -- Inherited
                                   , tcs_unif_lvl :: IORef (Maybe TcLevel)
    tcs_unif_lvl           = IORef (Maybe TcLevel)
    unif_lvl  -- Inherited
                                   , tcs_ev_binds :: EvBindsVar
    tcs_ev_binds           = EvBindsVar
    ref
                                   , tcs_unified :: IORef Int
    tcs_unified            = IORef Int
    unified_var
                                   , tcs_inerts :: IORef InertSet
    tcs_inerts             = IORef InertSet
    new_inert_var
                                   , tcs_abort_on_insoluble :: Bool
    tcs_abort_on_insoluble = Bool
    abort_on_insoluble
                                   , tcs_worklist :: IORef WorkList
    tcs_worklist           = IORef WorkList
    new_wl_var }
           ; res <- TcM.setTcLevel inner_tclvl $
                    thing_inside nest_env

           ; out_inert_set <- TcM.readTcRef new_inert_var
           ; restoreTyVarCycles out_inert_set

    #if defined(DEBUG)
           -- Perform a check that the thing_inside did not cause cycles
           ; ev_binds <- TcM.getTcEvBindsMap ref
           ; checkForCyclicBinds ev_binds
    #endif
           ; return res }

    nestTcS ::  TcS a -> TcS a
    -- Use the current untouchables, augmenting the current
    -- evidence bindings, and solved dictionaries
    -- But have no effect on the InertCans, or on the inert_famapp_cache
    -- (we want to inherit the latter from processing the Givens)
    nestTcS :: forall a. TcS a -> TcS a
    nestTcS (TcS TcSEnv -> TcM a
    thing_inside)
      = (TcSEnv -> TcM a) -> TcS a
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM a) -> TcS a) -> (TcSEnv -> TcM a) -> TcS a
    forall a b. (a -> b) -> a -> b
    $ \ env :: TcSEnv
    env@(TcSEnv { tcs_inerts :: TcSEnv -> IORef InertSet
    tcs_inerts = IORef InertSet
    inerts_var }) ->
        do { inerts <- IORef InertSet -> IOEnv (Env TcGblEnv TcLclEnv) InertSet
    forall (m :: * -> *) a. MonadIO m => TcRef a -> m a
    TcM.readTcRef IORef InertSet
    inerts_var
           ; new_inert_var <- TcM.newTcRef inerts
           ; new_wl_var    <- TcM.newTcRef emptyWorkList
           ; let nest_env = TcSEnv
    env { tcs_inerts   = new_inert_var
                                , tcs_worklist = new_wl_var }

           ; res <- thing_inside nest_env

           ; new_inerts <- TcM.readTcRef new_inert_var

           -- we want to propagate the safe haskell failures
           ; let old_ic = InertSet -> InertCans
    inert_cans InertSet
    inerts
                 new_ic = InertSet -> InertCans
    inert_cans InertSet
    new_inerts
                 nxt_ic = InertCans
    old_ic { inert_safehask = inert_safehask new_ic }

           ; TcM.writeTcRef inerts_var  -- See Note [Propagate the solved dictionaries]
                            (inerts { inert_solved_dicts = inert_solved_dicts new_inerts
                                    , inert_cans = nxt_ic })

           ; return res }

    emitImplicationTcS :: TcLevel -> SkolemInfoAnon
                       -> [TcTyVar]        -- Skolems
                       -> [EvVar]          -- Givens
                       -> Cts              -- Wanteds
                       -> TcS TcEvBinds
    -- Add an implication to the TcS monad work-list
    emitImplicationTcS :: TcLevel
    -> SkolemInfoAnon -> [TcTyVar] -> [TcTyVar] -> Cts -> TcS TcEvBinds
    emitImplicationTcS TcLevel
    new_tclvl SkolemInfoAnon
    skol_info [TcTyVar]
    skol_tvs [TcTyVar]
    givens Cts
    wanteds
      = do { let wc :: WantedConstraints
    wc = WantedConstraints
    emptyWC { wc_simple = wanteds }
           ; imp <- TcM Implication -> TcS Implication
    forall a. TcM a -> TcS a
    wrapTcS (TcM Implication -> TcS Implication)
    -> TcM Implication -> TcS Implication
    forall a b. (a -> b) -> a -> b
    $
                    do { ev_binds_var <- TcM EvBindsVar
    TcM.newTcEvBinds
                       ; imp <- TcM.newImplication
                       ; return (imp { ic_tclvl  = new_tclvl
                                     , ic_skols  = skol_tvs
                                     , ic_given  = givens
                                     , ic_wanted = wc
                                     , ic_binds  = ev_binds_var
                                     , ic_info   = skol_info }) }

           ; emitImplication imp
           ; return (TcEvBinds (ic_binds imp)) }

    emitTvImplicationTcS :: TcLevel -> SkolemInfoAnon
                         -> [TcTyVar]        -- Skolems
                         -> Cts              -- Wanteds
                         -> TcS ()
    -- Just like emitImplicationTcS but no givens and no bindings
    emitTvImplicationTcS :: TcLevel -> SkolemInfoAnon -> [TcTyVar] -> Cts -> TcS ()
    emitTvImplicationTcS TcLevel
    new_tclvl SkolemInfoAnon
    skol_info [TcTyVar]
    skol_tvs Cts
    wanteds
      = do { let wc :: WantedConstraints
    wc = WantedConstraints
    emptyWC { wc_simple = wanteds }
           ; imp <- TcM Implication -> TcS Implication
    forall a. TcM a -> TcS a
    wrapTcS (TcM Implication -> TcS Implication)
    -> TcM Implication -> TcS Implication
    forall a b. (a -> b) -> a -> b
    $
                    do { ev_binds_var <- TcM EvBindsVar
    TcM.newNoTcEvBinds
                       ; imp <- TcM.newImplication
                       ; return (imp { ic_tclvl  = new_tclvl
                                     , ic_skols  = skol_tvs
                                     , ic_wanted = wc
                                     , ic_binds  = ev_binds_var
                                     , ic_info   = skol_info }) }

           ; emitImplication imp }

    {- Note [Propagate the solved dictionaries]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    It's really quite important that nestTcS does not discard the solved
    dictionaries from the thing_inside.
    Consider
       Eq [a]
       forall b. empty =>  Eq [a]
    We solve the simple (Eq [a]), under nestTcS, and then turn our attention to
    the implications.  It's definitely fine to use the solved dictionaries on
    the inner implications, and it can make a significant performance difference
    if you do so.
    -}

    -- Getters and setters of GHC.Tc.Utils.Env fields
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    getUnifiedRef :: TcS (IORef Int)
    getUnifiedRef :: TcS (IORef Int)
    getUnifiedRef = (TcSEnv -> IOEnv (Env TcGblEnv TcLclEnv) (IORef Int))
    -> TcS (IORef Int)
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS (IORef Int -> IOEnv (Env TcGblEnv TcLclEnv) (IORef Int)
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (IORef Int -> IOEnv (Env TcGblEnv TcLclEnv) (IORef Int))
    -> (TcSEnv -> IORef Int)
    -> TcSEnv
    -> IOEnv (Env TcGblEnv TcLclEnv) (IORef Int)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TcSEnv -> IORef Int
    tcs_unified)

    -- Getter of inerts and worklist
    getInertSetRef :: TcS (IORef InertSet)
    getInertSetRef :: TcS (IORef InertSet)
    getInertSetRef = (TcSEnv -> IOEnv (Env TcGblEnv TcLclEnv) (IORef InertSet))
    -> TcS (IORef InertSet)
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS (IORef InertSet -> IOEnv (Env TcGblEnv TcLclEnv) (IORef InertSet)
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (IORef InertSet -> IOEnv (Env TcGblEnv TcLclEnv) (IORef InertSet))
    -> (TcSEnv -> IORef InertSet)
    -> TcSEnv
    -> IOEnv (Env TcGblEnv TcLclEnv) (IORef InertSet)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TcSEnv -> IORef InertSet
    tcs_inerts)

    getInertSet :: TcS InertSet
    getInertSet :: TcS InertSet
    getInertSet = TcS (IORef InertSet)
    getInertSetRef TcS (IORef InertSet)
    -> (IORef InertSet -> TcS InertSet) -> TcS InertSet
    forall a b. TcS a -> (a -> TcS b) -> TcS b
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= IORef InertSet -> TcS InertSet
    forall a. TcRef a -> TcS a
    readTcRef

    setInertSet :: InertSet -> TcS ()
    setInertSet :: InertSet -> TcS ()
    setInertSet InertSet
    is = do { r <- TcS (IORef InertSet)
    getInertSetRef; writeTcRef r is }

    getTcSWorkListRef :: TcS (IORef WorkList)
    getTcSWorkListRef :: TcS (IORef WorkList)
    getTcSWorkListRef = (TcSEnv -> IOEnv (Env TcGblEnv TcLclEnv) (IORef WorkList))
    -> TcS (IORef WorkList)
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS (IORef WorkList -> IOEnv (Env TcGblEnv TcLclEnv) (IORef WorkList)
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (IORef WorkList -> IOEnv (Env TcGblEnv TcLclEnv) (IORef WorkList))
    -> (TcSEnv -> IORef WorkList)
    -> TcSEnv
    -> IOEnv (Env TcGblEnv TcLclEnv) (IORef WorkList)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TcSEnv -> IORef WorkList
    tcs_worklist)

    getWorkListImplics :: TcS (Bag Implication)
    getWorkListImplics :: TcS (Bag Implication)
    getWorkListImplics
      = do { wl_var <- TcS (IORef WorkList)
    getTcSWorkListRef
           ; wl_curr <- readTcRef wl_var
           ; return (wl_implics wl_curr) }

    pushLevelNoWorkList :: SDoc -> TcS a -> TcS (TcLevel, a)
    -- Push the level and run thing_inside
    -- However, thing_inside should not generate any work items
    #if defined(DEBUG)
    pushLevelNoWorkList err_doc (TcS thing_inside)
      = TcS (\env -> TcM.pushTcLevelM $
                     thing_inside (env { tcs_worklist = wl_panic })
            )
      where
        wl_panic  = pprPanic "GHC.Tc.Solver.Monad.buildImplication" err_doc
                             -- This panic checks that the thing-inside
                             -- does not emit any work-list constraints
    #else
    pushLevelNoWorkList :: forall a. SDoc -> TcS a -> TcS (TcLevel, a)
    pushLevelNoWorkList SDoc
    _ (TcS TcSEnv -> TcM a
    thing_inside)
      = (TcSEnv -> TcM (TcLevel, a)) -> TcS (TcLevel, a)
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS (\TcSEnv
    env -> TcM a -> TcM (TcLevel, a)
    forall a. TcM a -> TcM (TcLevel, a)
    TcM.pushTcLevelM (TcSEnv -> TcM a
    thing_inside TcSEnv
    env))  -- Don't check
    #endif

    updWorkListTcS :: (WorkList -> WorkList) -> TcS ()
    updWorkListTcS :: (WorkList -> WorkList) -> TcS ()
    updWorkListTcS WorkList -> WorkList
    f
      = do { wl_var <- TcS (IORef WorkList)
    getTcSWorkListRef
           ; updTcRef wl_var f }

    emitWorkNC :: [CtEvidence] -> TcS ()
    emitWorkNC :: [CtEvidence] -> TcS ()
    emitWorkNC [CtEvidence]
    evs
      | [CtEvidence] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [CtEvidence]
    evs
      = () -> TcS ()
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
      | Bool
    otherwise
      = Cts -> TcS ()
    emitWork ([Ct] -> Cts
    forall a. [a] -> Bag a
    listToBag ((CtEvidence -> Ct) -> [CtEvidence] -> [Ct]
    forall a b. (a -> b) -> [a] -> [b]
    map CtEvidence -> Ct
    mkNonCanonical [CtEvidence]
    evs))

    emitWork :: Cts -> TcS ()
    emitWork :: Cts -> TcS ()
    emitWork Cts
    cts
      | Cts -> Bool
    forall a. Bag a -> Bool
    isEmptyBag Cts
    cts    -- Avoid printing, among other work
      = () -> TcS ()
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
      | Bool
    otherwise
      = do { String -> SDoc -> TcS ()
    traceTcS String
    "Emitting fresh work" (Cts -> SDoc
    forall a. Outputable a => Bag a -> SDoc
    pprBag Cts
    cts)
             -- Zonk the rewriter set of Wanteds, because that affects
             -- the prioritisation of the work-list. Suppose a constraint
             -- c1 is rewritten by another, c2.  When c2 gets solved,
             -- c1 has no rewriters, and can be prioritised; see
             -- Note [Prioritise Wanteds with empty RewriterSet]
             -- in GHC.Tc.Types.Constraint wrinkle (WRW1)
           ; cts <- TcM Cts -> TcS Cts
    forall a. TcM a -> TcS a
    wrapTcS (TcM Cts -> TcS Cts) -> TcM Cts -> TcS Cts
    forall a b. (a -> b) -> a -> b
    $ (Ct -> IOEnv (Env TcGblEnv TcLclEnv) Ct) -> Cts -> TcM Cts
    forall (m :: * -> *) a b.
    Monad m =>
    (a -> m b) -> Bag a -> m (Bag b)
    mapBagM Ct -> IOEnv (Env TcGblEnv TcLclEnv) Ct
    TcM.zonkCtRewriterSet Cts
    cts
           ; updWorkListTcS (extendWorkListCts cts) }

    emitImplication :: Implication -> TcS ()
    emitImplication :: Implication -> TcS ()
    emitImplication Implication
    implic
      = (WorkList -> WorkList) -> TcS ()
    updWorkListTcS (Implication -> WorkList -> WorkList
    extendWorkListImplic Implication
    implic)

    newTcRef :: a -> TcS (TcRef a)
    newTcRef :: forall a. a -> TcS (TcRef a)
    newTcRef a
    x = TcM (TcRef a) -> TcS (TcRef a)
    forall a. TcM a -> TcS a
    wrapTcS (a -> TcM (TcRef a)
    forall (m :: * -> *) a. MonadIO m => a -> m (TcRef a)
    TcM.newTcRef a
    x)

    readTcRef :: TcRef a -> TcS a
    readTcRef :: forall a. TcRef a -> TcS a
    readTcRef TcRef a
    ref = TcM a -> TcS a
    forall a. TcM a -> TcS a
    wrapTcS (TcRef a -> TcM a
    forall (m :: * -> *) a. MonadIO m => TcRef a -> m a
    TcM.readTcRef TcRef a
    ref)

    writeTcRef :: TcRef a -> a -> TcS ()
    writeTcRef :: forall a. TcRef a -> a -> TcS ()
    writeTcRef TcRef a
    ref a
    val = TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcRef a -> a -> TcM ()
    forall (m :: * -> *) a. MonadIO m => TcRef a -> a -> m ()
    TcM.writeTcRef TcRef a
    ref a
    val)

    updTcRef :: TcRef a -> (a->a) -> TcS ()
    updTcRef :: forall a. TcRef a -> (a -> a) -> TcS ()
    updTcRef TcRef a
    ref a -> a
    upd_fn = TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcRef a -> (a -> a) -> TcM ()
    forall (m :: * -> *) a. MonadIO m => TcRef a -> (a -> a) -> m ()
    TcM.updTcRef TcRef a
    ref a -> a
    upd_fn)

    getTcEvBindsVar :: TcS EvBindsVar
    getTcEvBindsVar :: TcS EvBindsVar
    getTcEvBindsVar = (TcSEnv -> TcM EvBindsVar) -> TcS EvBindsVar
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS (EvBindsVar -> TcM EvBindsVar
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (EvBindsVar -> TcM EvBindsVar)
    -> (TcSEnv -> EvBindsVar) -> TcSEnv -> TcM EvBindsVar
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TcSEnv -> EvBindsVar
    tcs_ev_binds)

    getTcLevel :: TcS TcLevel
    getTcLevel :: TcS TcLevel
    getTcLevel = TcM TcLevel -> TcS TcLevel
    forall a. TcM a -> TcS a
    wrapTcS TcM TcLevel
    TcM.getTcLevel

    getTcEvTyCoVars :: EvBindsVar -> TcS TyCoVarSet
    getTcEvTyCoVars :: EvBindsVar -> TcS VarSet
    getTcEvTyCoVars EvBindsVar
    ev_binds_var
      = TcM VarSet -> TcS VarSet
    forall a. TcM a -> TcS a
    wrapTcS (TcM VarSet -> TcS VarSet) -> TcM VarSet -> TcS VarSet
    forall a b. (a -> b) -> a -> b
    $ EvBindsVar -> TcM VarSet
    TcM.getTcEvTyCoVars EvBindsVar
    ev_binds_var

    getTcEvBindsMap :: EvBindsVar -> TcS EvBindMap
    getTcEvBindsMap :: EvBindsVar -> TcS EvBindMap
    getTcEvBindsMap EvBindsVar
    ev_binds_var
      = TcM EvBindMap -> TcS EvBindMap
    forall a. TcM a -> TcS a
    wrapTcS (TcM EvBindMap -> TcS EvBindMap) -> TcM EvBindMap -> TcS EvBindMap
    forall a b. (a -> b) -> a -> b
    $ EvBindsVar -> TcM EvBindMap
    TcM.getTcEvBindsMap EvBindsVar
    ev_binds_var

    setTcEvBindsMap :: EvBindsVar -> EvBindMap -> TcS ()
    setTcEvBindsMap :: EvBindsVar -> EvBindMap -> TcS ()
    setTcEvBindsMap EvBindsVar
    ev_binds_var EvBindMap
    binds
      = TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcM () -> TcS ()) -> TcM () -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ EvBindsVar -> EvBindMap -> TcM ()
    TcM.setTcEvBindsMap EvBindsVar
    ev_binds_var EvBindMap
    binds

    unifyTyVar :: TcTyVar -> TcType -> TcS ()
    -- Unify a meta-tyvar with a type
    -- We keep track of how many unifications have happened in tcs_unified,
    --
    -- We should never unify the same variable twice!
    unifyTyVar :: TcTyVar -> Type -> TcS ()
    unifyTyVar TcTyVar
    tv Type
    ty
      = Bool -> SDoc -> TcS () -> TcS ()
    forall a. HasCallStack => Bool -> SDoc -> a -> a
    assertPpr (TcTyVar -> Bool
    isMetaTyVar TcTyVar
    tv) (TcTyVar -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TcTyVar
    tv) (TcS () -> TcS ()) -> TcS () -> TcS ()
    forall a b. (a -> b) -> a -> b
    $
        (TcSEnv -> TcM ()) -> TcS ()
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM ()) -> TcS ()) -> (TcSEnv -> TcM ()) -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ \ TcSEnv
    env ->
        do { String -> SDoc -> TcM ()
    TcM.traceTc String
    "unifyTyVar" (TcTyVar -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TcTyVar
    tv SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    ":=" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Type -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Type
    ty)
           ; ZonkM () -> TcM ()
    forall a. ZonkM a -> TcM a
    TcM.liftZonkM (ZonkM () -> TcM ()) -> ZonkM () -> TcM ()
    forall a b. (a -> b) -> a -> b
    $ HasDebugCallStack => TcTyVar -> Type -> ZonkM ()
    TcTyVar -> Type -> ZonkM ()
    TcM.writeMetaTyVar TcTyVar
    tv Type
    ty
           ; IORef Int -> (Int -> Int) -> TcM ()
    forall (m :: * -> *) a. MonadIO m => TcRef a -> (a -> a) -> m ()
    TcM.updTcRef (TcSEnv -> IORef Int
    tcs_unified TcSEnv
    env) (Int -> Int -> Int
    forall a. Num a => a -> a -> a
    +Int
    1) }

    reportUnifications :: TcS a -> TcS (Int, a)
    reportUnifications :: forall a. TcS a -> TcS (Int, a)
    reportUnifications (TcS TcSEnv -> TcM a
    thing_inside)
      = (TcSEnv -> TcM (Int, a)) -> TcS (Int, a)
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM (Int, a)) -> TcS (Int, a))
    -> (TcSEnv -> TcM (Int, a)) -> TcS (Int, a)
    forall a b. (a -> b) -> a -> b
    $ \ TcSEnv
    env ->
        do { inner_unified <- Int -> IOEnv (Env TcGblEnv TcLclEnv) (IORef Int)
    forall (m :: * -> *) a. MonadIO m => a -> m (TcRef a)
    TcM.newTcRef Int
    0
           ; res <- thing_inside (env { tcs_unified = inner_unified })
           ; n_unifs <- TcM.readTcRef inner_unified
           ; TcM.updTcRef (tcs_unified env) (+ n_unifs)
           ; return (n_unifs, res) }

    getDefaultInfo ::  TcS ([Type], (Bool, Bool))
    getDefaultInfo :: TcS ([Type], (Bool, Bool))
    getDefaultInfo = TcM ([Type], (Bool, Bool)) -> TcS ([Type], (Bool, Bool))
    forall a. TcM a -> TcS a
    wrapTcS TcM ([Type], (Bool, Bool))
    TcM.tcGetDefaultTys

    getWorkList :: TcS WorkList
    getWorkList :: TcS WorkList
    getWorkList = do { wl_var <- TcS (IORef WorkList)
    getTcSWorkListRef
                     ; wrapTcS (TcM.readTcRef wl_var) }

    selectNextWorkItem :: TcS (Maybe Ct)
    -- Pick which work item to do next
    -- See Note [Prioritise equalities]
    selectNextWorkItem :: TcS (Maybe Ct)
    selectNextWorkItem
      = do { wl_var <- TcS (IORef WorkList)
    getTcSWorkListRef
           ; wl <- readTcRef wl_var
           ; case selectWorkItem wl of {
               Maybe (Ct, WorkList)
    Nothing -> Maybe Ct -> TcS (Maybe Ct)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Maybe Ct
    forall a. Maybe a
    Nothing ;
               Just (Ct
    ct, WorkList
    new_wl) ->
        do { -- checkReductionDepth (ctLoc ct) (ctPred ct)
             -- This is done by GHC.Tc.Solver.Dict.chooseInstance
           ; IORef WorkList -> WorkList -> TcS ()
    forall a. TcRef a -> a -> TcS ()
    writeTcRef IORef WorkList
    wl_var WorkList
    new_wl
           ; Maybe Ct -> TcS (Maybe Ct)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Ct -> Maybe Ct
    forall a. a -> Maybe a
    Just Ct
    ct) } } }

    -- Just get some environments needed for instance looking up and matching
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    getInstEnvs :: TcS InstEnvs
    getInstEnvs :: TcS InstEnvs
    getInstEnvs = TcM InstEnvs -> TcS InstEnvs
    forall a. TcM a -> TcS a
    wrapTcS (TcM InstEnvs -> TcS InstEnvs) -> TcM InstEnvs -> TcS InstEnvs
    forall a b. (a -> b) -> a -> b
    $ TcM InstEnvs
    TcM.tcGetInstEnvs

    getFamInstEnvs :: TcS (FamInstEnv, FamInstEnv)
    getFamInstEnvs :: TcS (FamInstEnv, FamInstEnv)
    getFamInstEnvs = TcM (FamInstEnv, FamInstEnv) -> TcS (FamInstEnv, FamInstEnv)
    forall a. TcM a -> TcS a
    wrapTcS (TcM (FamInstEnv, FamInstEnv) -> TcS (FamInstEnv, FamInstEnv))
    -> TcM (FamInstEnv, FamInstEnv) -> TcS (FamInstEnv, FamInstEnv)
    forall a b. (a -> b) -> a -> b
    $ TcM (FamInstEnv, FamInstEnv)
    FamInst.tcGetFamInstEnvs

    getTopEnv :: TcS HscEnv
    getTopEnv :: TcS HscEnv
    getTopEnv = TcM HscEnv -> TcS HscEnv
    forall a. TcM a -> TcS a
    wrapTcS (TcM HscEnv -> TcS HscEnv) -> TcM HscEnv -> TcS HscEnv
    forall a b. (a -> b) -> a -> b
    $ TcM HscEnv
    forall gbl lcl. TcRnIf gbl lcl HscEnv
    TcM.getTopEnv

    getGblEnv :: TcS TcGblEnv
    getGblEnv :: TcS TcGblEnv
    getGblEnv = TcM TcGblEnv -> TcS TcGblEnv
    forall a. TcM a -> TcS a
    wrapTcS (TcM TcGblEnv -> TcS TcGblEnv) -> TcM TcGblEnv -> TcS TcGblEnv
    forall a b. (a -> b) -> a -> b
    $ TcM TcGblEnv
    forall gbl lcl. TcRnIf gbl lcl gbl
    TcM.getGblEnv

    getLclEnv :: TcS TcLclEnv
    getLclEnv :: TcS TcLclEnv
    getLclEnv = TcM TcLclEnv -> TcS TcLclEnv
    forall a. TcM a -> TcS a
    wrapTcS (TcM TcLclEnv -> TcS TcLclEnv) -> TcM TcLclEnv -> TcS TcLclEnv
    forall a b. (a -> b) -> a -> b
    $ TcM TcLclEnv
    forall gbl lcl. TcRnIf gbl lcl lcl
    TcM.getLclEnv

    setSrcSpan :: RealSrcSpan -> TcS a -> TcS a
    setSrcSpan :: forall a. RealSrcSpan -> TcS a -> TcS a
    setSrcSpan RealSrcSpan
    ss = (TcM a -> TcM a) -> TcS a -> TcS a
    forall a. (TcM a -> TcM a) -> TcS a -> TcS a
    wrap2TcS (SrcSpan -> TcM a -> TcM a
    forall a. SrcSpan -> TcRn a -> TcRn a
    TcM.setSrcSpan (RealSrcSpan -> Maybe BufSpan -> SrcSpan
    RealSrcSpan RealSrcSpan
    ss Maybe BufSpan
    forall a. Monoid a => a
    mempty))

    tcLookupClass :: Name -> TcS Class
    tcLookupClass :: Name -> TcS Class
    tcLookupClass Name
    c = TcM Class -> TcS Class
    forall a. TcM a -> TcS a
    wrapTcS (TcM Class -> TcS Class) -> TcM Class -> TcS Class
    forall a b. (a -> b) -> a -> b
    $ Name -> TcM Class
    TcM.tcLookupClass Name
    c

    tcLookupId :: Name -> TcS Id
    tcLookupId :: Name -> TcS TcTyVar
    tcLookupId Name
    n = TcM TcTyVar -> TcS TcTyVar
    forall a. TcM a -> TcS a
    wrapTcS (TcM TcTyVar -> TcS TcTyVar) -> TcM TcTyVar -> TcS TcTyVar
    forall a b. (a -> b) -> a -> b
    $ Name -> TcM TcTyVar
    TcM.tcLookupId Name
    n

    tcLookupTyCon :: Name -> TcS TyCon
    tcLookupTyCon :: Name -> TcS TyCon
    tcLookupTyCon Name
    n = TcM TyCon -> TcS TyCon
    forall a. TcM a -> TcS a
    wrapTcS (TcM TyCon -> TcS TyCon) -> TcM TyCon -> TcS TyCon
    forall a b. (a -> b) -> a -> b
    $ Name -> TcM TyCon
    TcM.tcLookupTyCon Name
    n

    -- Any use of this function is a bit suspect, because it violates the
    -- pure veneer of TcS. But it's just about warnings around unused imports
    -- and local constructors (GHC will issue fewer warnings than it otherwise
    -- might), so it's not worth losing sleep over.
    recordUsedGREs :: Bag GlobalRdrElt -> TcS ()
    recordUsedGREs :: Bag GlobalRdrElt -> TcS ()
    recordUsedGREs Bag GlobalRdrElt
    gres
      = do { TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcM () -> TcS ()) -> TcM () -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ DeprecationWarnings -> [GlobalRdrElt] -> TcM ()
    TcM.addUsedGREs DeprecationWarnings
    NoDeprecationWarnings [GlobalRdrElt]
    gre_list
             -- If a newtype constructor was imported, don't warn about not
             -- importing it...
           ; TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcM () -> TcS ()) -> TcM () -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ (GlobalRdrElt -> TcM ()) -> [GlobalRdrElt] -> TcM ()
    forall (t :: * -> *) (f :: * -> *) a b.
    (Foldable t, Applicative f) =>
    (a -> f b) -> t a -> f ()
    traverse_ (Name -> TcM ()
    TcM.keepAlive (Name -> TcM ())
    -> (GlobalRdrElt -> Name) -> GlobalRdrElt -> TcM ()
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . GlobalRdrElt -> Name
    forall info. GlobalRdrEltX info -> Name
    greName) [GlobalRdrElt]
    gre_list }
             -- ...and similarly, if a newtype constructor was defined in the same
             -- module, don't warn about it being unused.
             -- See Note [Tracking unused binding and imports] in GHC.Tc.Utils.

      where
        gre_list :: [GlobalRdrElt]
    gre_list = Bag GlobalRdrElt -> [GlobalRdrElt]
    forall a. Bag a -> [a]
    bagToList Bag GlobalRdrElt
    gres

    -- Various smaller utilities [TODO, maybe will be absorbed in the instance matcher]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    checkWellStagedDFun :: CtLoc -> InstanceWhat -> PredType -> TcS ()
    -- Check that we do not try to use an instance before it is available.  E.g.
    --    instance Eq T where ...
    --    f x = $( ... (\(p::T) -> p == p)... )
    -- Here we can't use the equality function from the instance in the splice

    checkWellStagedDFun :: CtLoc -> InstanceWhat -> Type -> TcS ()
    checkWellStagedDFun CtLoc
    loc InstanceWhat
    what Type
    pred
      = do
          mbind_lvl <- InstanceWhat -> TcS (Maybe Int)
    checkWellStagedInstanceWhat InstanceWhat
    what
          case mbind_lvl of
            Just Int
    bind_lvl | Int
    bind_lvl Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    > Int
    impLevel ->
              TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcM () -> TcS ()) -> TcM () -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ CtLoc -> TcM () -> TcM ()
    forall a. CtLoc -> TcM a -> TcM a
    TcM.setCtLocM CtLoc
    loc (TcM () -> TcM ()) -> TcM () -> TcM ()
    forall a b. (a -> b) -> a -> b
    $ do
                  { use_stage <- TcM ThStage
    TcM.getStage
                  ; TcM.checkWellStaged (StageCheckInstance what pred) bind_lvl (thLevel use_stage) }
            Maybe Int
    _ ->
              () -> TcS ()
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()

    -- | Returns the ThLevel of evidence for the solved constraint (if it has evidence)
    -- See Note [Well-staged instance evidence]
    checkWellStagedInstanceWhat :: InstanceWhat -> TcS (Maybe ThLevel)
    checkWellStagedInstanceWhat :: InstanceWhat -> TcS (Maybe Int)
    checkWellStagedInstanceWhat InstanceWhat
    what
      | TopLevInstance { iw_dfun_id :: InstanceWhat -> TcTyVar
    iw_dfun_id = TcTyVar
    dfun_id } <- InstanceWhat
    what
        = Maybe Int -> TcS (Maybe Int)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Maybe Int -> TcS (Maybe Int)) -> Maybe Int -> TcS (Maybe Int)
    forall a b. (a -> b) -> a -> b
    $ Int -> Maybe Int
    forall a. a -> Maybe a
    Just (TcTyVar -> Int
    TcM.topIdLvl TcTyVar
    dfun_id)
      | BuiltinTypeableInstance TyCon
    tc <- InstanceWhat
    what
        = do
            cur_mod <- TcGblEnv -> Module
    forall t. ContainsModule t => t -> Module
    extractModule (TcGblEnv -> Module) -> TcS TcGblEnv -> TcS Module
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> TcS TcGblEnv
    getGblEnv
            return $ Just (if nameIsLocalOrFrom cur_mod (tyConName tc)
                            then outerLevel
                            else impLevel)
      | Bool
    otherwise = Maybe Int -> TcS (Maybe Int)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Maybe Int
    forall a. Maybe a
    Nothing

    {-
    Note [Well-staged instance evidence]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    Evidence for instances must obey the same level restrictions as normal bindings.
    In particular, it is forbidden to use an instance in a top-level splice in the
    module which the instance is defined. This is because the evidence is bound at
    the top-level and top-level definitions are forbidden from being using in top-level splices in
    the same module.

    For example, suppose you have a function..  foo :: Show a => Code Q a -> Code Q ()
    then the following program is disallowed,

    ```
    data T a = T a deriving (Show)

    main :: IO ()
    main =
      let x = $$(foo [|| T () ||])
      in return ()
    ```

    because the `foo` function (used in a top-level splice) requires `Show T` evidence,
    which is defined at the top-level and therefore fails with an error that we have violated
    the stage restriction.

    ```
    Main.hs:12:14: error:
        • GHC stage restriction:
            instance for ‘Show
                            (T ())’ is used in a top-level splice, quasi-quote, or annotation,
            and must be imported, not defined locally
        • In the expression: foo [|| T () ||]
          In the Template Haskell splice $$(foo [|| T () ||])
          In the expression: $$(foo [|| T () ||])
       |
    12 |   let x = $$(foo [|| T () ||])
       |
    ```

    Solving a `Typeable (T t1 ...tn)` constraint generates code that relies on
    `$tcT`, the `TypeRep` for `T`; and we must check that this reference to `$tcT`
    is well staged.  It's easy to know the stage of `$tcT`: for imported TyCons it
    will be `impLevel`, and for local TyCons it will be `toplevel`.

    Therefore the `InstanceWhat` type had to be extended with
    a special case for `Typeable`, which recorded the TyCon the evidence was for and
    could them be used to check that we were not attempting to evidence in a stage incorrect
    manner.

    -}

    pprEq :: TcType -> TcType -> SDoc
    pprEq :: Type -> Type -> SDoc
    pprEq Type
    ty1 Type
    ty2 = Type -> SDoc
    pprParendType Type
    ty1 SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Char -> SDoc
    forall doc. IsLine doc => Char -> doc
    char Char
    '~' SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Type -> SDoc
    pprParendType Type
    ty2

    isFilledMetaTyVar_maybe :: TcTyVar -> TcS (Maybe Type)
    isFilledMetaTyVar_maybe :: TcTyVar -> TcS (Maybe Type)
    isFilledMetaTyVar_maybe TcTyVar
    tv = TcM (Maybe Type) -> TcS (Maybe Type)
    forall a. TcM a -> TcS a
    wrapTcS (TcTyVar -> TcM (Maybe Type)
    TcM.isFilledMetaTyVar_maybe TcTyVar
    tv)

    isFilledMetaTyVar :: TcTyVar -> TcS Bool
    isFilledMetaTyVar :: TcTyVar -> TcS Bool
    isFilledMetaTyVar TcTyVar
    tv = TcM Bool -> TcS Bool
    forall a. TcM a -> TcS a
    wrapTcS (TcTyVar -> TcM Bool
    TcM.isFilledMetaTyVar TcTyVar
    tv)

    isUnfilledMetaTyVar :: TcTyVar -> TcS Bool
    isUnfilledMetaTyVar :: TcTyVar -> TcS Bool
    isUnfilledMetaTyVar TcTyVar
    tv = TcM Bool -> TcS Bool
    forall a. TcM a -> TcS a
    wrapTcS (TcM Bool -> TcS Bool) -> TcM Bool -> TcS Bool
    forall a b. (a -> b) -> a -> b
    $ TcTyVar -> TcM Bool
    TcM.isUnfilledMetaTyVar TcTyVar
    tv

    zonkTyCoVarsAndFV :: TcTyCoVarSet -> TcS TcTyCoVarSet
    zonkTyCoVarsAndFV :: VarSet -> TcS VarSet
    zonkTyCoVarsAndFV VarSet
    tvs = ZonkM VarSet -> TcS VarSet
    forall a. ZonkM a -> TcS a
    liftZonkTcS (VarSet -> ZonkM VarSet
    TcM.zonkTyCoVarsAndFV VarSet
    tvs)

    zonkTyCoVarsAndFVList :: [TcTyCoVar] -> TcS [TcTyCoVar]
    zonkTyCoVarsAndFVList :: [TcTyVar] -> TcS [TcTyVar]
    zonkTyCoVarsAndFVList [TcTyVar]
    tvs = ZonkM [TcTyVar] -> TcS [TcTyVar]
    forall a. ZonkM a -> TcS a
    liftZonkTcS ([TcTyVar] -> ZonkM [TcTyVar]
    TcM.zonkTyCoVarsAndFVList [TcTyVar]
    tvs)

    zonkCo :: Coercion -> TcS Coercion
    zonkCo :: Coercion -> TcS Coercion
    zonkCo = TcM Coercion -> TcS Coercion
    forall a. TcM a -> TcS a
    wrapTcS (TcM Coercion -> TcS Coercion)
    -> (Coercion -> TcM Coercion) -> Coercion -> TcS Coercion
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (ZonkM Coercion -> TcM Coercion)
    -> (Coercion -> ZonkM Coercion) -> Coercion -> TcM Coercion
    forall a b. (a -> b) -> (Coercion -> a) -> Coercion -> b
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap ZonkM Coercion -> TcM Coercion
    forall a. ZonkM a -> TcM a
    TcM.liftZonkM Coercion -> ZonkM Coercion
    TcM.zonkCo

    zonkTcType :: TcType -> TcS TcType
    zonkTcType :: Type -> TcS Type
    zonkTcType Type
    ty = ZonkM Type -> TcS Type
    forall a. ZonkM a -> TcS a
    liftZonkTcS (Type -> ZonkM Type
    TcM.zonkTcType Type
    ty)

    zonkTcTypes :: [TcType] -> TcS [TcType]
    zonkTcTypes :: [Type] -> TcS [Type]
    zonkTcTypes [Type]
    tys = ZonkM [Type] -> TcS [Type]
    forall a. ZonkM a -> TcS a
    liftZonkTcS ([Type] -> ZonkM [Type]
    TcM.zonkTcTypes [Type]
    tys)

    zonkTcTyVar :: TcTyVar -> TcS TcType
    zonkTcTyVar :: TcTyVar -> TcS Type
    zonkTcTyVar TcTyVar
    tv = ZonkM Type -> TcS Type
    forall a. ZonkM a -> TcS a
    liftZonkTcS (TcTyVar -> ZonkM Type
    TcM.zonkTcTyVar TcTyVar
    tv)

    zonkSimples :: Cts -> TcS Cts
    zonkSimples :: Cts -> TcS Cts
    zonkSimples Cts
    cts = ZonkM Cts -> TcS Cts
    forall a. ZonkM a -> TcS a
    liftZonkTcS (Cts -> ZonkM Cts
    TcM.zonkSimples Cts
    cts)

    zonkWC :: WantedConstraints -> TcS WantedConstraints
    zonkWC :: WantedConstraints -> TcS WantedConstraints
    zonkWC WantedConstraints
    wc = ZonkM WantedConstraints -> TcS WantedConstraints
    forall a. ZonkM a -> TcS a
    liftZonkTcS (WantedConstraints -> ZonkM WantedConstraints
    TcM.zonkWC WantedConstraints
    wc)

    zonkTyCoVarKind :: TcTyCoVar -> TcS TcTyCoVar
    zonkTyCoVarKind :: TcTyVar -> TcS TcTyVar
    zonkTyCoVarKind TcTyVar
    tv = ZonkM TcTyVar -> TcS TcTyVar
    forall a. ZonkM a -> TcS a
    liftZonkTcS (TcTyVar -> ZonkM TcTyVar
    TcM.zonkTyCoVarKind TcTyVar
    tv)

    ----------------------------
    pprKicked :: Int -> SDoc
    pprKicked :: Int -> SDoc
    pprKicked Int
    0 = SDoc
    forall doc. IsOutput doc => doc
    empty
    pprKicked Int
    n = SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    parens (Int -> SDoc
    forall doc. IsLine doc => Int -> doc
    int Int
    n SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "kicked out")

    {- *********************************************************************
    *                                                                      *
    *              The Unification Level Flag                              *
    *                                                                      *
    ********************************************************************* -}

    {- Note [The Unification Level Flag]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider a deep tree of implication constraints
       forall[1] a.                              -- Outer-implic
          C alpha[1]                               -- Simple
          forall[2] c. ....(C alpha[1])....        -- Implic-1
          forall[2] b. ....(alpha[1] ~ Int)....    -- Implic-2

    The (C alpha) is insoluble until we know alpha.  We solve alpha
    by unifying alpha:=Int somewhere deep inside Implic-2. But then we
    must try to solve the Outer-implic all over again. This time we can
    solve (C alpha) both in Outer-implic, and nested inside Implic-1.

    When should we iterate solving a level-n implication?
    Answer: if any unification of a tyvar at level n takes place
            in the ic_implics of that implication.

    * What if a unification takes place at level n-1? Then don't iterate
      level n, because we'll iterate level n-1, and that will in turn iterate
      level n.

    * What if a unification takes place at level n, in the ic_simples of
      level n?  No need to track this, because the kick-out mechanism deals
      with it.  (We can't drop kick-out in favour of iteration, because kick-out
      works for skolem-equalities, not just unifications.)

    So the monad-global Unification Level Flag, kept in tcs_unif_lvl keeps
    track of
      - Whether any unifications at all have taken place (Nothing => no unifications)
      - If so, what is the outermost level that has seen a unification (Just lvl)

    The iteration is done in the simplify_loop/maybe_simplify_again loop in GHC.Tc.Solver.

    It helpful not to iterate unless there is a chance of progress.  #8474 is
    an example:

      * There's a deeply-nested chain of implication constraints.
           ?x:alpha => ?y1:beta1 => ... ?yn:betan => [W] ?x:Int

      * From the innermost one we get a [W] alpha[1] ~ Int,
        so we can unify.

      * It's better not to iterate the inner implications, but go all the
        way out to level 1 before iterating -- because iterating level 1
        will iterate the inner levels anyway.

    (In the olden days when we "floated" thse Derived constraints, this was
    much, much more important -- we got exponential behaviour, as each iteration
    produced the same Derived constraint.)
    -}

    resetUnificationFlag :: TcS Bool
    -- We are at ambient level i
    -- If the unification flag = Just i, reset it to Nothing and return True
    -- Otherwise leave it unchanged and return False
    resetUnificationFlag :: TcS Bool
    resetUnificationFlag
      = (TcSEnv -> TcM Bool) -> TcS Bool
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM Bool) -> TcS Bool)
    -> (TcSEnv -> TcM Bool) -> TcS Bool
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    env ->
        do { let ref :: IORef (Maybe TcLevel)
    ref = TcSEnv -> IORef (Maybe TcLevel)
    tcs_unif_lvl TcSEnv
    env
           ; ambient_lvl <- TcM TcLevel
    TcM.getTcLevel
           ; mb_lvl <- TcM.readTcRef ref
           ; TcM.traceTc "resetUnificationFlag" $
             vcat [ text "ambient:" <+> ppr ambient_lvl
                  , text "unif_lvl:" <+> ppr mb_lvl ]
           ; case mb_lvl of
               Maybe TcLevel
    Nothing       -> Bool -> TcM Bool
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Bool
    False
               Just TcLevel
    unif_lvl | TcLevel
    ambient_lvl TcLevel -> TcLevel -> Bool
    `strictlyDeeperThan` TcLevel
    unif_lvl
                             -> Bool -> TcM Bool
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Bool
    False
                             | Bool
    otherwise
                             -> do { IORef (Maybe TcLevel) -> Maybe TcLevel -> TcM ()
    forall (m :: * -> *) a. MonadIO m => TcRef a -> a -> m ()
    TcM.writeTcRef IORef (Maybe TcLevel)
    ref Maybe TcLevel
    forall a. Maybe a
    Nothing
                                   ; Bool -> TcM Bool
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Bool
    True } }

    setUnificationFlag :: TcLevel -> TcS ()
    -- (setUnificationFlag i) sets the unification level to (Just i)
    -- unless it already is (Just j) where j <= i
    setUnificationFlag :: TcLevel -> TcS ()
    setUnificationFlag TcLevel
    lvl
      = (TcSEnv -> TcM ()) -> TcS ()
    forall a. (TcSEnv -> TcM a) -> TcS a
    TcS ((TcSEnv -> TcM ()) -> TcS ()) -> (TcSEnv -> TcM ()) -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ \TcSEnv
    env ->
        do { let ref :: IORef (Maybe TcLevel)
    ref = TcSEnv -> IORef (Maybe TcLevel)
    tcs_unif_lvl TcSEnv
    env
           ; mb_lvl <- IORef (Maybe TcLevel)
    -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe TcLevel)
    forall (m :: * -> *) a. MonadIO m => TcRef a -> m a
    TcM.readTcRef IORef (Maybe TcLevel)
    ref
           ; case mb_lvl of
               Just TcLevel
    unif_lvl | TcLevel
    lvl TcLevel -> TcLevel -> Bool
    `deeperThanOrSame` TcLevel
    unif_lvl
                             -> () -> TcM ()
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
               Maybe TcLevel
    _ -> IORef (Maybe TcLevel) -> Maybe TcLevel -> TcM ()
    forall (m :: * -> *) a. MonadIO m => TcRef a -> a -> m ()
    TcM.writeTcRef IORef (Maybe TcLevel)
    ref (TcLevel -> Maybe TcLevel
    forall a. a -> Maybe a
    Just TcLevel
    lvl) }

    {- *********************************************************************
    *                                                                      *
    *                Instantiation etc.
    *                                                                      *
    ********************************************************************* -}

    -- Instantiations
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    instDFunType :: DFunId -> [DFunInstType] -> TcS ([TcType], TcThetaType)
    instDFunType :: TcTyVar -> [Maybe Type] -> TcS ([Type], [Type])
    instDFunType TcTyVar
    dfun_id [Maybe Type]
    inst_tys
      = TcM ([Type], [Type]) -> TcS ([Type], [Type])
    forall a. TcM a -> TcS a
    wrapTcS (TcM ([Type], [Type]) -> TcS ([Type], [Type]))
    -> TcM ([Type], [Type]) -> TcS ([Type], [Type])
    forall a b. (a -> b) -> a -> b
    $ TcTyVar -> [Maybe Type] -> TcM ([Type], [Type])
    TcM.instDFunType TcTyVar
    dfun_id [Maybe Type]
    inst_tys

    newFlexiTcSTy :: Kind -> TcS TcType
    newFlexiTcSTy :: Type -> TcS Type
    newFlexiTcSTy Type
    knd = TcM Type -> TcS Type
    forall a. TcM a -> TcS a
    wrapTcS (Type -> TcM Type
    TcM.newFlexiTyVarTy Type
    knd)

    cloneMetaTyVar :: TcTyVar -> TcS TcTyVar
    cloneMetaTyVar :: TcTyVar -> TcS TcTyVar
    cloneMetaTyVar TcTyVar
    tv = TcM TcTyVar -> TcS TcTyVar
    forall a. TcM a -> TcS a
    wrapTcS (TcTyVar -> TcM TcTyVar
    TcM.cloneMetaTyVar TcTyVar
    tv)

    instFlexiX :: Subst -> [TKVar] -> TcS Subst
    instFlexiX :: Subst -> [TcTyVar] -> TcS Subst
    instFlexiX Subst
    subst [TcTyVar]
    tvs = TcM Subst -> TcS Subst
    forall a. TcM a -> TcS a
    wrapTcS (Subst -> [TcTyVar] -> TcM Subst
    instFlexiXTcM Subst
    subst [TcTyVar]
    tvs)

    instFlexiXTcM :: Subst -> [TKVar] -> TcM Subst
    -- Makes fresh tyvar, extends the substitution, and the in-scope set
    -- Takes account of the case [k::Type, a::k, ...],
    -- where we must substitute for k in a's kind
    instFlexiXTcM :: Subst -> [TcTyVar] -> TcM Subst
    instFlexiXTcM Subst
    subst []
      = Subst -> TcM Subst
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Subst
    subst
    instFlexiXTcM Subst
    subst (TcTyVar
    tv:[TcTyVar]
    tvs)
      = do { uniq <- TcRnIf TcGblEnv TcLclEnv Unique
    forall gbl lcl. TcRnIf gbl lcl Unique
    TcM.newUnique
           ; details <- TcM.newMetaDetails TauTv
           ; let name   = Name -> Unique -> Name
    setNameUnique (TcTyVar -> Name
    tyVarName TcTyVar
    tv) Unique
    uniq
                 kind   = Subst -> Type -> Type
    substTyUnchecked Subst
    subst (TcTyVar -> Type
    tyVarKind TcTyVar
    tv)
                 tv'    = Name -> Type -> TcTyVarDetails -> TcTyVar
    mkTcTyVar Name
    name Type
    kind TcTyVarDetails
    details
                 subst' = Subst -> TcTyVar -> TcTyVar -> Subst
    extendTvSubstWithClone Subst
    subst TcTyVar
    tv TcTyVar
    tv'
           ; instFlexiXTcM subst' tvs  }

    matchGlobalInst :: DynFlags
                    -> Bool      -- True <=> caller is the short-cut solver
                                 -- See Note [Shortcut solving: overlap]
                    -> Class -> [Type] -> CtLoc -> TcS TcM.ClsInstResult
    matchGlobalInst :: DynFlags -> Bool -> Class -> [Type] -> CtLoc -> TcS ClsInstResult
    matchGlobalInst DynFlags
    dflags Bool
    short_cut Class
    cls [Type]
    tys CtLoc
    loc
      = TcM ClsInstResult -> TcS ClsInstResult
    forall a. TcM a -> TcS a
    wrapTcS (TcM ClsInstResult -> TcS ClsInstResult)
    -> TcM ClsInstResult -> TcS ClsInstResult
    forall a b. (a -> b) -> a -> b
    $ CtLoc -> TcM ClsInstResult -> TcM ClsInstResult
    forall a. CtLoc -> TcM a -> TcM a
    TcM.setCtLocM CtLoc
    loc (TcM ClsInstResult -> TcM ClsInstResult)
    -> TcM ClsInstResult -> TcM ClsInstResult
    forall a b. (a -> b) -> a -> b
    $ DynFlags -> Bool -> Class -> [Type] -> TcM ClsInstResult
    TcM.matchGlobalInst DynFlags
    dflags Bool
    short_cut Class
    cls [Type]
    tys

    tcInstSkolTyVarsX :: SkolemInfo -> Subst -> [TyVar] -> TcS (Subst, [TcTyVar])
    tcInstSkolTyVarsX :: SkolemInfo -> Subst -> [TcTyVar] -> TcS (Subst, [TcTyVar])
    tcInstSkolTyVarsX SkolemInfo
    skol_info Subst
    subst [TcTyVar]
    tvs = TcM (Subst, [TcTyVar]) -> TcS (Subst, [TcTyVar])
    forall a. TcM a -> TcS a
    wrapTcS (TcM (Subst, [TcTyVar]) -> TcS (Subst, [TcTyVar]))
    -> TcM (Subst, [TcTyVar]) -> TcS (Subst, [TcTyVar])
    forall a b. (a -> b) -> a -> b
    $ SkolemInfo -> Subst -> [TcTyVar] -> TcM (Subst, [TcTyVar])
    TcM.tcInstSkolTyVarsX SkolemInfo
    skol_info Subst
    subst [TcTyVar]
    tvs

    -- Creating and setting evidence variables and CtFlavors
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    data MaybeNew = Fresh CtEvidence | Cached EvExpr

    isFresh :: MaybeNew -> Bool
    isFresh :: MaybeNew -> Bool
    isFresh (Fresh {})  = Bool
    True
    isFresh (Cached {}) = Bool
    False

    freshGoals :: [MaybeNew] -> [CtEvidence]
    freshGoals :: [MaybeNew] -> [CtEvidence]
    freshGoals [MaybeNew]
    mns = [ CtEvidence
    ctev | Fresh CtEvidence
    ctev <- [MaybeNew]
    mns ]

    getEvExpr :: MaybeNew -> EvExpr
    getEvExpr :: MaybeNew -> EvExpr
    getEvExpr (Fresh CtEvidence
    ctev) = HasDebugCallStack => CtEvidence -> EvExpr
    CtEvidence -> EvExpr
    ctEvExpr CtEvidence
    ctev
    getEvExpr (Cached EvExpr
    evt) = EvExpr
    evt

    setEvBind :: EvBind -> TcS ()
    setEvBind :: EvBind -> TcS ()
    setEvBind EvBind
    ev_bind
      = do { evb <- TcS EvBindsVar
    getTcEvBindsVar
           ; wrapTcS $ TcM.addTcEvBind evb ev_bind }

    -- | Mark variables as used filling a coercion hole
    useVars :: CoVarSet -> TcS ()
    useVars :: VarSet -> TcS ()
    useVars VarSet
    co_vars
      = do { ev_binds_var <- TcS EvBindsVar
    getTcEvBindsVar
           ; let ref = EvBindsVar -> IORef VarSet
    ebv_tcvs EvBindsVar
    ev_binds_var
           ; wrapTcS $
             do { tcvs <- TcM.readTcRef ref
                ; let tcvs' = VarSet
    tcvs VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    co_vars
                ; TcM.writeTcRef ref tcvs' } }

    -- | Equalities only
    setWantedEq :: HasDebugCallStack => TcEvDest -> Coercion -> TcS ()
    setWantedEq :: HasDebugCallStack => TcEvDest -> Coercion -> TcS ()
    setWantedEq (HoleDest CoercionHole
    hole) Coercion
    co
      = do { VarSet -> TcS ()
    useVars (Coercion -> VarSet
    coVarsOfCo Coercion
    co)
           ; CoercionHole -> Coercion -> TcS ()
    fillCoercionHole CoercionHole
    hole Coercion
    co }
    setWantedEq (EvVarDest TcTyVar
    ev) Coercion
    _ = String -> SDoc -> TcS ()
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "setWantedEq: EvVarDest" (TcTyVar -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TcTyVar
    ev)

    -- | Good for both equalities and non-equalities
    setWantedEvTerm :: TcEvDest -> Canonical -> EvTerm -> TcS ()
    setWantedEvTerm :: TcEvDest -> Bool -> EvTerm -> TcS ()
    setWantedEvTerm (HoleDest CoercionHole
    hole) Bool
    _canonical EvTerm
    tm
      | Just Coercion
    co <- EvTerm -> Maybe Coercion
    evTermCoercion_maybe EvTerm
    tm
      = do { VarSet -> TcS ()
    useVars (Coercion -> VarSet
    coVarsOfCo Coercion
    co)
           ; CoercionHole -> Coercion -> TcS ()
    fillCoercionHole CoercionHole
    hole Coercion
    co }
      | Bool
    otherwise
      = -- See Note [Yukky eq_sel for a HoleDest]
        do { let co_var :: TcTyVar
    co_var = CoercionHole -> TcTyVar
    coHoleCoVar CoercionHole
    hole
           ; EvBind -> TcS ()
    setEvBind (TcTyVar -> Bool -> EvTerm -> EvBind
    mkWantedEvBind TcTyVar
    co_var Bool
    True EvTerm
    tm)
           ; CoercionHole -> Coercion -> TcS ()
    fillCoercionHole CoercionHole
    hole (TcTyVar -> Coercion
    mkCoVarCo TcTyVar
    co_var) }

    setWantedEvTerm (EvVarDest TcTyVar
    ev_id) Bool
    canonical EvTerm
    tm
      = EvBind -> TcS ()
    setEvBind (TcTyVar -> Bool -> EvTerm -> EvBind
    mkWantedEvBind TcTyVar
    ev_id Bool
    canonical EvTerm
    tm)

    {- Note [Yukky eq_sel for a HoleDest]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    How can it be that a Wanted with HoleDest gets evidence that isn't
    just a coercion? i.e. evTermCoercion_maybe returns Nothing.

    Consider [G] forall a. blah => a ~ T
             [W] S ~# T

    Then doTopReactEqPred carefully looks up the (boxed) constraint (S ~ T)
    in the quantified constraints, and wraps the (boxed) evidence it
    gets back in an eq_sel to extract the unboxed (S ~# T).  We can't put
    that term into a coercion, so we add a value binding
        h = eq_sel (...)
    and the coercion variable h to fill the coercion hole.
    We even re-use the CoHole's Id for this binding!

    Yuk!
    -}

    fillCoercionHole :: CoercionHole -> Coercion -> TcS ()
    fillCoercionHole :: CoercionHole -> Coercion -> TcS ()
    fillCoercionHole CoercionHole
    hole Coercion
    co
      = do { TcM () -> TcS ()
    forall a. TcM a -> TcS a
    wrapTcS (TcM () -> TcS ()) -> TcM () -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ CoercionHole -> Coercion -> TcM ()
    TcM.fillCoercionHole CoercionHole
    hole Coercion
    co
           ; CoercionHole -> TcS ()
    kickOutAfterFillingCoercionHole CoercionHole
    hole }

    setEvBindIfWanted :: CtEvidence -> Canonical -> EvTerm -> TcS ()
    setEvBindIfWanted :: CtEvidence -> Bool -> EvTerm -> TcS ()
    setEvBindIfWanted CtEvidence
    ev Bool
    canonical EvTerm
    tm
      = case CtEvidence
    ev of
          CtWanted { ctev_dest :: CtEvidence -> TcEvDest
    ctev_dest = TcEvDest
    dest } -> TcEvDest -> Bool -> EvTerm -> TcS ()
    setWantedEvTerm TcEvDest
    dest Bool
    canonical EvTerm
    tm
          CtEvidence
    _                             -> () -> TcS ()
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()

    newTcEvBinds :: TcS EvBindsVar
    newTcEvBinds :: TcS EvBindsVar
    newTcEvBinds = TcM EvBindsVar -> TcS EvBindsVar
    forall a. TcM a -> TcS a
    wrapTcS TcM EvBindsVar
    TcM.newTcEvBinds

    newNoTcEvBinds :: TcS EvBindsVar
    newNoTcEvBinds :: TcS EvBindsVar
    newNoTcEvBinds = TcM EvBindsVar -> TcS EvBindsVar
    forall a. TcM a -> TcS a
    wrapTcS TcM EvBindsVar
    TcM.newNoTcEvBinds

    newEvVar :: TcPredType -> TcS EvVar
    newEvVar :: Type -> TcS TcTyVar
    newEvVar Type
    pred = TcM TcTyVar -> TcS TcTyVar
    forall a. TcM a -> TcS a
    wrapTcS (Type -> TcM TcTyVar
    forall gbl lcl. Type -> TcRnIf gbl lcl TcTyVar
    TcM.newEvVar Type
    pred)

    newGivenEvVar :: CtLoc -> (TcPredType, EvTerm) -> TcS CtEvidence
    -- Make a new variable of the given PredType,
    -- immediately bind it to the given term
    -- and return its CtEvidence
    -- See Note [Bind new Givens immediately] in GHC.Tc.Types.Constraint
    newGivenEvVar :: CtLoc -> (Type, EvTerm) -> TcS CtEvidence
    newGivenEvVar CtLoc
    loc (Type
    pred, EvTerm
    rhs)
      = do { new_ev <- Type -> EvTerm -> TcS TcTyVar
    newBoundEvVarId Type
    pred EvTerm
    rhs
           ; return (CtGiven { ctev_pred = pred, ctev_evar = new_ev, ctev_loc = loc }) }

    -- | Make a new 'Id' of the given type, bound (in the monad's EvBinds) to the
    -- given term
    newBoundEvVarId :: TcPredType -> EvTerm -> TcS EvVar
    newBoundEvVarId :: Type -> EvTerm -> TcS TcTyVar
    newBoundEvVarId Type
    pred EvTerm
    rhs
      = do { new_ev <- Type -> TcS TcTyVar
    newEvVar Type
    pred
           ; setEvBind (mkGivenEvBind new_ev rhs)
           ; return new_ev }

    emitNewGivens :: CtLoc -> [(Role,TcType,TcType,TcCoercion)] -> TcS ()
    emitNewGivens :: CtLoc -> [(Role, Type, Type, Coercion)] -> TcS ()
    emitNewGivens CtLoc
    loc [(Role, Type, Type, Coercion)]
    pts
      = do { evs <- ((Type, EvTerm) -> TcS CtEvidence)
    -> [(Type, EvTerm)] -> TcS [CtEvidence]
    forall (t :: * -> *) (m :: * -> *) a b.
    (Traversable t, Monad m) =>
    (a -> m b) -> t a -> m (t b)
    forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
    mapM (CtLoc -> (Type, EvTerm) -> TcS CtEvidence
    newGivenEvVar CtLoc
    loc) ([(Type, EvTerm)] -> TcS [CtEvidence])
    -> [(Type, EvTerm)] -> TcS [CtEvidence]
    forall a b. (a -> b) -> a -> b
    $
                    [ (Role -> Type -> Type -> Type
    mkPrimEqPredRole Role
    role Type
    ty1 Type
    ty2, Coercion -> EvTerm
    evCoercion Coercion
    co)
                    | (Role
    role, Type
    ty1, Type
    ty2, Coercion
    co) <- [(Role, Type, Type, Coercion)]
    pts
                    , Bool -> Bool
    not (Type
    ty1 HasDebugCallStack => Type -> Type -> Bool
    Type -> Type -> Bool
    `tcEqType` Type
    ty2) ] -- Kill reflexive Givens at birth
           ; emitWorkNC evs }

    emitNewWantedEq :: CtLoc -> RewriterSet -> Role -> TcType -> TcType -> TcS Coercion
    -- | Emit a new Wanted equality into the work-list
    emitNewWantedEq :: CtLoc -> RewriterSet -> Role -> Type -> Type -> TcS Coercion
    emitNewWantedEq CtLoc
    loc RewriterSet
    rewriters Role
    role Type
    ty1 Type
    ty2
      = do { (ev, co) <- CtLoc
    -> RewriterSet
    -> Role
    -> Type
    -> Type
    -> TcS (CtEvidence, Coercion)
    newWantedEq CtLoc
    loc RewriterSet
    rewriters Role
    role Type
    ty1 Type
    ty2
           ; updWorkListTcS (extendWorkListEq rewriters (mkNonCanonical ev))
           ; return co }

    -- | Create a new Wanted constraint holding a coercion hole
    -- for an equality between the two types at the given 'Role'.
    newWantedEq :: CtLoc -> RewriterSet -> Role -> TcType -> TcType
                -> TcS (CtEvidence, Coercion)
    newWantedEq :: CtLoc
    -> RewriterSet
    -> Role
    -> Type
    -> Type
    -> TcS (CtEvidence, Coercion)
    newWantedEq CtLoc
    loc RewriterSet
    rewriters Role
    role Type
    ty1 Type
    ty2
      = do { hole <- TcM CoercionHole -> TcS CoercionHole
    forall a. TcM a -> TcS a
    wrapTcS (TcM CoercionHole -> TcS CoercionHole)
    -> TcM CoercionHole -> TcS CoercionHole
    forall a b. (a -> b) -> a -> b
    $ CtLoc -> Type -> TcM CoercionHole
    TcM.newCoercionHole CtLoc
    loc Type
    pty
           ; return ( CtWanted { ctev_pred      = pty
                               , ctev_dest      = HoleDest hole
                               , ctev_loc       = loc
                               , ctev_rewriters = rewriters }
                    , mkHoleCo hole ) }
      where
        pty :: Type
    pty = Role -> Type -> Type -> Type
    mkPrimEqPredRole Role
    role Type
    ty1 Type
    ty2

    -- | Create a new Wanted constraint holding an evidence variable.
    --
    -- Don't use this for equality constraints: use 'newWantedEq' instead.
    newWantedEvVarNC :: CtLoc -> RewriterSet
                     -> TcPredType -> TcS CtEvidence
    -- Don't look up in the solved/inerts; we know it's not there
    newWantedEvVarNC :: CtLoc -> RewriterSet -> Type -> TcS CtEvidence
    newWantedEvVarNC CtLoc
    loc RewriterSet
    rewriters Type
    pty
      = do { new_ev <- Type -> TcS TcTyVar
    newEvVar Type
    pty
           ; traceTcS "Emitting new wanted" (ppr new_ev <+> dcolon <+> ppr pty $$
                                             pprCtLoc loc)
           ; return (CtWanted { ctev_pred      = pty
                              , ctev_dest      = EvVarDest new_ev
                              , ctev_loc       = loc
                              , ctev_rewriters = rewriters })}

    -- | Like 'newWantedEvVarNC', except it might look up in the inert set
    -- to see if an inert already exists, and uses that instead of creating
    -- a new Wanted constraint.
    --
    -- Don't use this for equality constraints: this function is only for
    -- constraints with 'EvVarDest'.
    newWantedEvVar :: CtLoc -> RewriterSet
                   -> TcPredType -> TcS MaybeNew
    -- For anything except ClassPred, this is the same as newWantedEvVarNC
    newWantedEvVar :: CtLoc -> RewriterSet -> Type -> TcS MaybeNew
    newWantedEvVar CtLoc
    loc RewriterSet
    rewriters Type
    pty
      = Bool -> SDoc -> TcS MaybeNew -> TcS MaybeNew
    forall a. HasCallStack => Bool -> SDoc -> a -> a
    assertPpr (Bool -> Bool
    not (Type -> Bool
    isEqPrimPred Type
    pty))
          ([SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "newWantedEvVar: HoleDestPred"
                , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "pty:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Type -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Type
    pty ]) (TcS MaybeNew -> TcS MaybeNew) -> TcS MaybeNew -> TcS MaybeNew
    forall a b. (a -> b) -> a -> b
    $
        do { mb_ct <- CtLoc -> Type -> TcS (Maybe CtEvidence)
    lookupInInerts CtLoc
    loc Type
    pty
           ; case mb_ct of
                Just CtEvidence
    ctev
                  -> do { String -> SDoc -> TcS ()
    traceTcS String
    "newWantedEvVar/cache hit" (SDoc -> TcS ()) -> SDoc -> TcS ()
    forall a b. (a -> b) -> a -> b
    $ CtEvidence -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CtEvidence
    ctev
                        ; MaybeNew -> TcS MaybeNew
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (MaybeNew -> TcS MaybeNew) -> MaybeNew -> TcS MaybeNew
    forall a b. (a -> b) -> a -> b
    $ EvExpr -> MaybeNew
    Cached (HasDebugCallStack => CtEvidence -> EvExpr
    CtEvidence -> EvExpr
    ctEvExpr CtEvidence
    ctev) }
                Maybe CtEvidence
    _ -> do { ctev <- CtLoc -> RewriterSet -> Type -> TcS CtEvidence
    newWantedEvVarNC CtLoc
    loc RewriterSet
    rewriters Type
    pty
                        ; return (Fresh ctev) } }

    -- | Create a new Wanted constraint, potentially looking up
    -- non-equality constraints in the cache instead of creating
    -- a new one from scratch.
    --
    -- Deals with both equality and non-equality constraints.
    newWanted :: CtLoc -> RewriterSet -> PredType -> TcS MaybeNew
    newWanted :: CtLoc -> RewriterSet -> Type -> TcS MaybeNew
    newWanted CtLoc
    loc RewriterSet
    rewriters Type
    pty
      | Just (Role
    role, Type
    ty1, Type
    ty2) <- Type -> Maybe (Role, Type, Type)
    getEqPredTys_maybe Type
    pty
      = CtEvidence -> MaybeNew
    Fresh (CtEvidence -> MaybeNew)
    -> ((CtEvidence, Coercion) -> CtEvidence)
    -> (CtEvidence, Coercion)
    -> MaybeNew
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (CtEvidence, Coercion) -> CtEvidence
    forall a b. (a, b) -> a
    fst ((CtEvidence, Coercion) -> MaybeNew)
    -> TcS (CtEvidence, Coercion) -> TcS MaybeNew
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> CtLoc
    -> RewriterSet
    -> Role
    -> Type
    -> Type
    -> TcS (CtEvidence, Coercion)
    newWantedEq CtLoc
    loc RewriterSet
    rewriters Role
    role Type
    ty1 Type
    ty2
      | Bool
    otherwise
      = CtLoc -> RewriterSet -> Type -> TcS MaybeNew
    newWantedEvVar CtLoc
    loc RewriterSet
    rewriters Type
    pty

    -- | Create a new Wanted constraint.
    --
    -- Deals with both equality and non-equality constraints.
    --
    -- Does not attempt to re-use non-equality constraints that already
    -- exist in the inert set.
    newWantedNC :: CtLoc -> RewriterSet -> PredType -> TcS CtEvidence
    newWantedNC :: CtLoc -> RewriterSet -> Type -> TcS CtEvidence
    newWantedNC CtLoc
    loc RewriterSet
    rewriters Type
    pty
      | Just (Role
    role, Type
    ty1, Type
    ty2) <- Type -> Maybe (Role, Type, Type)
    getEqPredTys_maybe Type
    pty
      = (CtEvidence, Coercion) -> CtEvidence
    forall a b. (a, b) -> a
    fst ((CtEvidence, Coercion) -> CtEvidence)
    -> TcS (CtEvidence, Coercion) -> TcS CtEvidence
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> CtLoc
    -> RewriterSet
    -> Role
    -> Type
    -> Type
    -> TcS (CtEvidence, Coercion)
    newWantedEq CtLoc
    loc RewriterSet
    rewriters Role
    role Type
    ty1 Type
    ty2
      | Bool
    otherwise
      = CtLoc -> RewriterSet -> Type -> TcS CtEvidence
    newWantedEvVarNC CtLoc
    loc RewriterSet
    rewriters Type
    pty

    -- | Checks if the depth of the given location is too much. Fails if
    -- it's too big, with an appropriate error message.
    checkReductionDepth :: CtLoc -> TcType   -- ^ type being reduced
                        -> TcS ()
    checkReductionDepth :: CtLoc -> Type -> TcS ()
    checkReductionDepth CtLoc
    loc Type
    ty
      = do { dflags <- TcS DynFlags
    forall (m :: * -> *). HasDynFlags m => m DynFlags
    getDynFlags
           ; when (subGoalDepthExceeded (reductionDepth dflags) (ctLocDepth loc)) $
             wrapErrTcS $ solverDepthError loc ty }

    matchFam :: TyCon -> [Type] -> TcS (Maybe ReductionN)
    matchFam :: TyCon -> [Type] -> TcS (Maybe Reduction)
    matchFam TyCon
    tycon [Type]
    args = TcM (Maybe Reduction) -> TcS (Maybe Reduction)
    forall a. TcM a -> TcS a
    wrapTcS (TcM (Maybe Reduction) -> TcS (Maybe Reduction))
    -> TcM (Maybe Reduction) -> TcS (Maybe Reduction)
    forall a b. (a -> b) -> a -> b
    $ TyCon -> [Type] -> TcM (Maybe Reduction)
    matchFamTcM TyCon
    tycon [Type]
    args

    matchFamTcM :: TyCon -> [Type] -> TcM (Maybe ReductionN)
    -- Given (F tys) return (ty, co), where co :: F tys ~N ty
    matchFamTcM :: TyCon -> [Type] -> TcM (Maybe Reduction)
    matchFamTcM TyCon
    tycon [Type]
    args
      = do { fam_envs <- TcM (FamInstEnv, FamInstEnv)
    FamInst.tcGetFamInstEnvs
           ; let match_fam_result
                  = (FamInstEnv, FamInstEnv)
    -> Role -> TyCon -> [Type] -> Maybe Reduction
    reduceTyFamApp_maybe (FamInstEnv, FamInstEnv)
    fam_envs Role
    Nominal TyCon
    tycon [Type]
    args
           ; TcM.traceTc "matchFamTcM" $
             vcat [ text "Matching:" <+> ppr (mkTyConApp tycon args)
                  , ppr_res match_fam_result ]
           ; return match_fam_result }
      where
        ppr_res :: Maybe Reduction -> SDoc
    ppr_res Maybe Reduction
    Nothing = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "Match failed"
        ppr_res (Just (Reduction Coercion
    co Type
    ty))
          = SDoc -> Int -> SDoc -> SDoc
    hang (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "Match succeeded:")
              Int
    2 ([SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "Rewrites to:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Type -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Type
    ty
                      , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "Coercion:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Coercion -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Coercion
    co ])

    solverDepthError :: CtLoc -> TcType -> TcM a
    solverDepthError :: forall a. CtLoc -> Type -> TcM a
    solverDepthError CtLoc
    loc Type
    ty
      = CtLoc -> TcM a -> TcM a
    forall a. CtLoc -> TcM a -> TcM a
    TcM.setCtLocM CtLoc
    loc (TcM a -> TcM a) -> TcM a -> TcM a
    forall a b. (a -> b) -> a -> b
    $
        do { (ty, env0) <- ZonkM (Type, TidyEnv) -> TcM (Type, TidyEnv)
    forall a. ZonkM a -> TcM a
    TcM.liftZonkM (ZonkM (Type, TidyEnv) -> TcM (Type, TidyEnv))
    -> ZonkM (Type, TidyEnv) -> TcM (Type, TidyEnv)
    forall a b. (a -> b) -> a -> b
    $
               do { ty   <- Type -> ZonkM Type
    TcM.zonkTcType Type
    ty
                  ; env0 <- TcM.tcInitTidyEnv
                  ; return (ty, env0) }
           ; let tidy_env     = TidyEnv -> [TcTyVar] -> TidyEnv
    tidyFreeTyCoVars TidyEnv
    env0 (Type -> [TcTyVar]
    tyCoVarsOfTypeList Type
    ty)
                 tidy_ty      = TidyEnv -> Type -> Type
    tidyType TidyEnv
    tidy_env Type
    ty
                 msg = Type -> SubGoalDepth -> TcRnMessage
    TcRnSolverDepthError Type
    tidy_ty SubGoalDepth
    depth
           ; TcM.failWithTcM (tidy_env, msg) }
      where
        depth :: SubGoalDepth
    depth = CtLoc -> SubGoalDepth
    ctLocDepth CtLoc
    loc

    {-
    ************************************************************************
    *                                                                      *
                  Emitting equalities arising from fundeps
    *                                                                      *
    ************************************************************************
    -}

    emitFunDepWanteds :: CtEvidence  -- The work item
                      -> [FunDepEqn (CtLoc, RewriterSet)]
                      -> TcS Bool  -- True <=> some unification happened

    emitFunDepWanteds :: CtEvidence -> [FunDepEqn (CtLoc, RewriterSet)] -> TcS Bool
    emitFunDepWanteds CtEvidence
    _ [] = Bool -> TcS Bool
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return Bool
    False -- common case noop
    -- See Note [FunDep and implicit parameter reactions]

    emitFunDepWanteds CtEvidence
    ev [FunDepEqn (CtLoc, RewriterSet)]
    fd_eqns
      = CtEvidence -> Role -> (UnifyEnv -> TcM ()) -> TcS Bool
    unifyFunDeps CtEvidence
    ev Role
    Nominal UnifyEnv -> TcM ()
    do_fundeps
      where
        do_fundeps :: UnifyEnv -> TcM ()
        do_fundeps :: UnifyEnv -> TcM ()
    do_fundeps UnifyEnv
    env = (FunDepEqn (CtLoc, RewriterSet) -> TcM ())
    -> [FunDepEqn (CtLoc, RewriterSet)] -> TcM ()
    forall (t :: * -> *) (m :: * -> *) a b.
    (Foldable t, Monad m) =>
    (a -> m b) -> t a -> m ()
    mapM_ (UnifyEnv -> FunDepEqn (CtLoc, RewriterSet) -> TcM ()
    do_one UnifyEnv
    env) [FunDepEqn (CtLoc, RewriterSet)]
    fd_eqns

        do_one :: UnifyEnv -> FunDepEqn (CtLoc, RewriterSet) -> TcM ()
        do_one :: UnifyEnv -> FunDepEqn (CtLoc, RewriterSet) -> TcM ()
    do_one UnifyEnv
    uenv (FDEqn { fd_qtvs :: forall loc. FunDepEqn loc -> [TcTyVar]
    fd_qtvs = [TcTyVar]
    tvs, fd_eqs :: forall loc. FunDepEqn loc -> [TypeEqn]
    fd_eqs = [TypeEqn]
    eqs, fd_loc :: forall loc. FunDepEqn loc -> loc
    fd_loc = (CtLoc
    loc, RewriterSet
    rewriters) })
          = do { eqs' <- [TcTyVar] -> [TypeEqn] -> TcM [TypeEqn]
    instantiate_eqs [TcTyVar]
    tvs ([TypeEqn] -> [TypeEqn]
    forall a. [a] -> [a]
    reverse [TypeEqn]
    eqs)
                         -- (reverse eqs): See Note [Reverse order of fundep equations]
               ; uPairsTcM env_one eqs' }
          where
            env_one :: UnifyEnv
    env_one = UnifyEnv
    uenv { u_rewriters = u_rewriters uenv S.<> rewriters
                           , u_loc       = loc }

        instantiate_eqs :: [TyVar] -> [TypeEqn] -> TcM [TypeEqn]
        instantiate_eqs :: [TcTyVar] -> [TypeEqn] -> TcM [TypeEqn]
    instantiate_eqs [TcTyVar]
    tvs [TypeEqn]
    eqs
          | [TcTyVar] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [TcTyVar]
    tvs
          = [TypeEqn] -> TcM [TypeEqn]
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return [TypeEqn]
    eqs
          | Bool
    otherwise
          = do { String -> SDoc -> TcM ()
    TcM.traceTc String
    "emitFunDepWanteds 2" ([TcTyVar] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [TcTyVar]
    tvs SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ [TypeEqn] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [TypeEqn]
    eqs)
               ; subst <- Subst -> [TcTyVar] -> TcM Subst
    instFlexiXTcM Subst
    emptySubst [TcTyVar]
    tvs  -- Takes account of kind substitution
               ; return [ Pair (substTyUnchecked subst' ty1) ty2
                               -- ty2 does not mention fd_qtvs, so no need to subst it.
                               -- See GHC.Tc.Instance.Fundeps Note [Improving against instances]
                               --     Wrinkle (1)
                        | Pair ty1 ty2 <- eqs
                        , let subst' = Subst -> VarSet -> Subst
    extendSubstInScopeSet Subst
    subst (Type -> VarSet
    tyCoVarsOfType Type
    ty1) ]
                              -- The free vars of ty1 aren't just fd_qtvs: ty1 is the result
                              -- of matching with the [W] constraint. So we add its free
                              -- vars to InScopeSet, to satisfy substTy's invariants, even
                              -- though ty1 will never (currently) be a poytype, so this
                              -- InScopeSet will never be looked at.
               }

    {-
    ************************************************************************
    *                                                                      *
                  Unification
    *                                                                      *
    ************************************************************************

    Note [wrapUnifierTcS]
    ~~~~~~~~~~~~~~~~~~~
    When decomposing equalities we often create new wanted constraints for
    (s ~ t).  But what if s=t?  Then it'd be faster to return Refl right away.

    Rather than making an equality test (which traverses the structure of the type,
    perhaps fruitlessly), we call uType (via wrapUnifierTcS) to traverse the common
    structure, and bales out when it finds a difference by creating a new deferred
    Wanted constraint.  But where it succeeds in finding common structure, it just
    builds a coercion to reflect it.

    This is all much faster than creating a new constraint, putting it in the
    work list, picking it out, canonicalising it, etc etc.

    Note [unifyFunDeps]
    ~~~~~~~~~~~~~~~~~~~
    The Bool returned by `unifyFunDeps` is True if we have unified a variable
    that occurs in the constraint we are trying to solve; it is not in the
    inert set so `wrapUnifierTcS` won't kick it out.  Instead we want to send it
    back to the start of the pipeline.  Hence the Bool.

    It's vital that we don't return (not (null unified)) because the fundeps
    may create fresh variables; unifying them (alone) should not make us send
    the constraint back to the start, or we'll get an infinite loop.  See
    Note [Fundeps with instances, and equality orientation] in GHC.Tc.Solver.Dict
    and Note [Improvement orientation] in GHC.Tc.Solver.Equality.
    -}

    uPairsTcM :: UnifyEnv -> [TypeEqn] -> TcM ()
    uPairsTcM :: UnifyEnv -> [TypeEqn] -> TcM ()
    uPairsTcM UnifyEnv
    uenv [TypeEqn]
    eqns = (TypeEqn -> TcM Coercion) -> [TypeEqn] -> TcM ()
    forall (t :: * -> *) (m :: * -> *) a b.
    (Foldable t, Monad m) =>
    (a -> m b) -> t a -> m ()
    mapM_ (\(Pair Type
    ty1 Type
    ty2) -> UnifyEnv -> Type -> Type -> TcM Coercion
    uType UnifyEnv
    uenv Type
    ty1 Type
    ty2) [TypeEqn]
    eqns

    unifyFunDeps :: CtEvidence -> Role
                 -> (UnifyEnv -> TcM ())
                 -> TcS Bool
    unifyFunDeps :: CtEvidence -> Role -> (UnifyEnv -> TcM ()) -> TcS Bool
    unifyFunDeps CtEvidence
    ev Role
    role UnifyEnv -> TcM ()
    do_unifications
      = do { (_, _, unified) <- CtEvidence
    -> Role -> (UnifyEnv -> TcM ()) -> TcS ((), Cts, [TcTyVar])
    forall a.
    CtEvidence
    -> Role -> (UnifyEnv -> TcM a) -> TcS (a, Cts, [TcTyVar])
    wrapUnifierTcS CtEvidence
    ev Role
    role UnifyEnv -> TcM ()
    do_unifications
           ; return (any (`elemVarSet` fvs) unified) }
             -- See Note [unifyFunDeps]
      where
        fvs :: VarSet
    fvs = Type -> VarSet
    tyCoVarsOfType (CtEvidence -> Type
    ctEvPred CtEvidence
    ev)

    unifyForAllBody :: CtEvidence -> Role -> (UnifyEnv -> TcM a)
                    -> TcS (a, Cts)
    -- We /return/ the equality constraints we generate,
    -- rather than emitting them into the monad.
    -- See See (SF5) in Note [Solving forall equalities] in GHC.Tc.Solver.Equality
    unifyForAllBody :: forall a. CtEvidence -> Role -> (UnifyEnv -> TcM a) -> TcS (a, Cts)
    unifyForAllBody CtEvidence
    ev Role
    role UnifyEnv -> TcM a
    unify_body
      = do { (res, cts, unified, _rewriters) <- CtEvidence
    -> Role
    -> (UnifyEnv -> TcM a)
    -> TcS (a, Cts, [TcTyVar], RewriterSet)
    forall a.
    CtEvidence
    -> Role
    -> (UnifyEnv -> TcM a)
    -> TcS (a, Cts, [TcTyVar], RewriterSet)
    wrapUnifierX CtEvidence
    ev Role
    role UnifyEnv -> TcM a
    unify_body
             -- Ignore the rewriters. They are used in wrapUnifierTcS only
             -- as an optimistion to prioritise the work list; but they are
             -- /also/ stored in each individual constraint we return.

           -- Kick out any inert constraint that we have unified
           ; _ <- kickOutAfterUnification unified

           ; return (res, cts) }

    wrapUnifierTcS :: CtEvidence -> Role
                   -> (UnifyEnv -> TcM a)  -- Some calls to uType
                   -> TcS (a, Bag Ct, [TcTyVar])
    -- Invokes the do_unifications argument, with a suitable UnifyEnv.
    -- Emit deferred equalities and kick-out from the inert set as a
    -- result of any unifications.
    -- Very good short-cut when the two types are equal, or nearly so
    -- See Note [wrapUnifierTcS]
    --
    -- The [TcTyVar] is the list of unification variables that were
    -- unified the process; the (Bag Ct) are the deferred constraints.

    wrapUnifierTcS :: forall a.
    CtEvidence
    -> Role -> (UnifyEnv -> TcM a) -> TcS (a, Cts, [TcTyVar])
    wrapUnifierTcS CtEvidence
    ev Role
    role UnifyEnv -> TcM a
    do_unifications
      = do { (res, cts, unified, rewriters) <- CtEvidence
    -> Role
    -> (UnifyEnv -> TcM a)
    -> TcS (a, Cts, [TcTyVar], RewriterSet)
    forall a.
    CtEvidence
    -> Role
    -> (UnifyEnv -> TcM a)
    -> TcS (a, Cts, [TcTyVar], RewriterSet)
    wrapUnifierX CtEvidence
    ev Role
    role UnifyEnv -> TcM a
    do_unifications

           -- Emit the deferred constraints
           -- See Note [Work-list ordering] in GHC.Tc.Solved.Equality
           --
           -- All the constraints in `cts` share the same rewriter set so,
           -- rather than looking at it one by one, we pass it to
           -- extendWorkListEqs; just a small optimisation.
           ; unless (isEmptyBag cts) $
             updWorkListTcS (extendWorkListEqs rewriters cts)

           -- And kick out any inert constraint that we have unified
           ; _ <- kickOutAfterUnification unified

           ; return (res, cts, unified) }

    wrapUnifierX :: CtEvidence -> Role
                 -> (UnifyEnv -> TcM a)  -- Some calls to uType
                 -> TcS (a, Bag Ct, [TcTyVar], RewriterSet)
    wrapUnifierX :: forall a.
    CtEvidence
    -> Role
    -> (UnifyEnv -> TcM a)
    -> TcS (a, Cts, [TcTyVar], RewriterSet)
    wrapUnifierX CtEvidence
    ev Role
    role UnifyEnv -> TcM a
    do_unifications
      = do { unif_count_ref <- TcS (IORef Int)
    getUnifiedRef
           ; wrapTcS $
             do { defer_ref   <- TcM.newTcRef emptyBag
                ; unified_ref <- TcM.newTcRef []
                ; rewriters   <- TcM.zonkRewriterSet (ctEvRewriters ev)
                ; let env = UE { u_role :: Role
    u_role      = Role
    role
                               , u_rewriters :: RewriterSet
    u_rewriters = RewriterSet
    rewriters
                               , u_loc :: CtLoc
    u_loc       = CtEvidence -> CtLoc
    ctEvLoc CtEvidence
    ev
                               , u_defer :: TcRef Cts
    u_defer     = TcRef Cts
    defer_ref
                               , u_unified :: Maybe (TcRef [TcTyVar])
    u_unified   = TcRef [TcTyVar] -> Maybe (TcRef [TcTyVar])
    forall a. a -> Maybe a
    Just TcRef [TcTyVar]
    unified_ref}

                ; res <- do_unifications env

                ; cts     <- TcM.readTcRef defer_ref
                ; unified <- TcM.readTcRef unified_ref

                -- Don't forget to update the count of variables
                -- unified, lest we forget to iterate (#24146)
                ; unless (null unified) $
                  TcM.updTcRef unif_count_ref (+ (length unified))

                ; return (res, cts, unified, rewriters) } }

    {-
    ************************************************************************
    *                                                                      *
                  Breaking type variable cycles
    *                                                                      *
    ************************************************************************
    -}

    checkTouchableTyVarEq
       :: CtEvidence
       -> TcTyVar    -- A touchable meta-tyvar
       -> TcType     -- The RHS
       -> TcS (PuResult () Reduction)
    -- Used for Nominal, Wanted equalities, with a touchable meta-tyvar on LHS
    -- If checkTouchableTyVarEq tv ty = PuOK cts redn
    --   then we can unify
    --       tv := ty |> redn
    --   with extra wanteds 'cts'
    -- If it returns (PuFail reason) we can't unify, and the reason explains why.
    checkTouchableTyVarEq :: CtEvidence -> TcTyVar -> Type -> TcS (PuResult () Reduction)
    checkTouchableTyVarEq CtEvidence
    ev TcTyVar
    lhs_tv Type
    rhs
      | Bool -> TcTyVar -> Type -> Bool
    simpleUnifyCheck Bool
    True TcTyVar
    lhs_tv Type
    rhs
        -- True <=> type families are ok on the RHS
      = do { String -> SDoc -> TcS ()
    traceTcS String
    "checkTouchableTyVarEq: simple-check wins" (TcTyVar -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TcTyVar
    lhs_tv SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ Type -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Type
    rhs)
           ; PuResult () Reduction -> TcS (PuResult () Reduction)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Reduction -> PuResult () Reduction
    forall a. a -> PuResult () a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure (Role -> Type -> Reduction
    mkReflRedn Role
    Nominal Type
    rhs)) }

      | Bool
    otherwise
      = do { String -> SDoc -> TcS ()
    traceTcS String
    "checkTouchableTyVarEq {" (TcTyVar -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TcTyVar
    lhs_tv SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ Type -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Type
    rhs)
           ; check_result <- TcM (PuResult Ct Reduction) -> TcS (PuResult Ct Reduction)
    forall a. TcM a -> TcS a
    wrapTcS (Type -> TcM (PuResult Ct Reduction)
    check_rhs Type
    rhs)
           ; traceTcS "checkTouchableTyVarEq }" (ppr lhs_tv $$ ppr check_result)
           ; case check_result of
                PuFail CheckTyEqResult
    reason -> PuResult () Reduction -> TcS (PuResult () Reduction)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CheckTyEqResult -> PuResult () Reduction
    forall a b. CheckTyEqResult -> PuResult a b
    PuFail CheckTyEqResult
    reason)
                PuOK Cts
    cts Reduction
    redn -> do { Cts -> TcS ()
    emitWork Cts
    cts
                                    ; PuResult () Reduction -> TcS (PuResult () Reduction)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Reduction -> PuResult () Reduction
    forall a. a -> PuResult () a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure Reduction
    redn) } }

      where
        (MetaInfo
    lhs_tv_info, TcLevel
    lhs_tv_lvl) = case TcTyVar -> TcTyVarDetails
    tcTyVarDetails TcTyVar
    lhs_tv of
           MetaTv { mtv_info :: TcTyVarDetails -> MetaInfo
    mtv_info = MetaInfo
    info, mtv_tclvl :: TcTyVarDetails -> TcLevel
    mtv_tclvl = TcLevel
    lvl } -> (MetaInfo
    info,TcLevel
    lvl)
           TcTyVarDetails
    _ -> String -> SDoc -> (MetaInfo, TcLevel)
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "checkTouchableTyVarEq" (TcTyVar -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TcTyVar
    lhs_tv)
                -- lhs_tv should be a meta-tyvar

        is_concrete_lhs_tv :: Bool
    is_concrete_lhs_tv = MetaInfo -> Bool
    isConcreteInfo MetaInfo
    lhs_tv_info

        check_rhs :: Type -> TcM (PuResult Ct Reduction)
    check_rhs Type
    rhs
           -- Crucial special case for  alpha ~ F tys
           -- We don't want to flatten that (F tys)!
           | Just (TyFamLHS TyCon
    tc [Type]
    tys) <- Type -> Maybe CanEqLHS
    canTyFamEqLHS_maybe Type
    rhs
           = if Bool
    is_concrete_lhs_tv
             then CheckTyEqResult -> TcM (PuResult Ct Reduction)
    forall a b. CheckTyEqResult -> TcM (PuResult a b)
    failCheckWith (CheckTyEqProblem -> CheckTyEqResult
    cteProblem CheckTyEqProblem
    cteConcrete)
             else TyEqFlags Ct -> TyCon -> [Type] -> TcM (PuResult Ct Reduction)
    forall a.
    TyEqFlags a -> TyCon -> [Type] -> TcM (PuResult a Reduction)
    recurseIntoTyConApp TyEqFlags Ct
    arg_flags TyCon
    tc [Type]
    tys
           | Bool
    otherwise
           = TyEqFlags Ct -> Type -> TcM (PuResult Ct Reduction)
    forall a. TyEqFlags a -> Type -> TcM (PuResult a Reduction)
    checkTyEqRhs TyEqFlags Ct
    flags Type
    rhs

        flags :: TyEqFlags Ct
    flags = TEF { tef_foralls :: Bool
    tef_foralls  = Bool
    False -- isRuntimeUnkSkol lhs_tv
                    , tef_fam_app :: TyEqFamApp Ct
    tef_fam_app  = CtEvidence
    -> EqRel -> (Type -> TcM (PuResult Ct Reduction)) -> TyEqFamApp Ct
    forall a. CtEvidence -> EqRel -> FamAppBreaker a -> TyEqFamApp a
    mkTEFA_Break CtEvidence
    ev EqRel
    NomEq Type -> TcM (PuResult Ct Reduction)
    break_wanted
                    , tef_unifying :: AreUnifying
    tef_unifying = MetaInfo -> TcLevel -> LevelCheck -> AreUnifying
    Unifying MetaInfo
    lhs_tv_info TcLevel
    lhs_tv_lvl LevelCheck
    LC_Promote
                    , tef_lhs :: CanEqLHS
    tef_lhs      = TcTyVar -> CanEqLHS
    TyVarLHS TcTyVar
    lhs_tv
                    , tef_occurs :: CheckTyEqProblem
    tef_occurs   = CheckTyEqProblem
    cteInsolubleOccurs }

        arg_flags :: TyEqFlags Ct
    arg_flags = TyEqFlags Ct -> TyEqFlags Ct
    forall a. TyEqFlags a -> TyEqFlags a
    famAppArgFlags TyEqFlags Ct
    flags

        break_wanted :: Type -> TcM (PuResult Ct Reduction)
    break_wanted Type
    fam_app
          -- Occurs check or skolem escape; so flatten
          = do { let fam_app_kind :: Type
    fam_app_kind = HasDebugCallStack => Type -> Type
    Type -> Type
    typeKind Type
    fam_app
               ; reason <- CheckTyEqProblem
    -> TcTyVar -> TcLevel -> VarSet -> TcM CheckTyEqResult
    checkPromoteFreeVars CheckTyEqProblem
    cteInsolubleOccurs
                                TcTyVar
    lhs_tv TcLevel
    lhs_tv_lvl (Type -> VarSet
    tyCoVarsOfType Type
    fam_app_kind)
               ; if not (cterHasNoProblem reason)  -- Failed to promote free vars
                 then failCheckWith reason
                 else
            do { new_tv_ty <-
                  case lhs_tv_info of
                    ConcreteTv ConcreteTvOrigin
    conc_info ->
                      -- Make a concrete tyvar if lhs_tv is concrete
                      -- e.g.  alpha[2,conc] ~ Maybe (F beta[4])
                      --       We want to flatten to
                      --       alpha[2,conc] ~ Maybe gamma[2,conc]
                      --       gamma[2,conc] ~ F beta[4]
                      ConcreteTvOrigin -> TcLevel -> Type -> TcM Type
    TcM.newConcreteTyVarTyAtLevel ConcreteTvOrigin
    conc_info TcLevel
    lhs_tv_lvl Type
    fam_app_kind
                    MetaInfo
    _ -> TcLevel -> Type -> TcM Type
    TcM.newMetaTyVarTyAtLevel TcLevel
    lhs_tv_lvl Type
    fam_app_kind

               ; let pty = Role -> Type -> Type -> Type
    mkPrimEqPredRole Role
    Nominal Type
    fam_app Type
    new_tv_ty
               ; hole <- TcM.newVanillaCoercionHole pty
               ; let new_ev = CtWanted { ctev_pred :: Type
    ctev_pred      = Type
    pty
                                       , ctev_dest :: TcEvDest
    ctev_dest      = CoercionHole -> TcEvDest
    HoleDest CoercionHole
    hole
                                       , ctev_loc :: CtLoc
    ctev_loc       = CtLoc
    cb_loc
                                       , ctev_rewriters :: RewriterSet
    ctev_rewriters = CtEvidence -> RewriterSet
    ctEvRewriters CtEvidence
    ev }
               ; return (PuOK (singleCt (mkNonCanonical new_ev))
                              (mkReduction (HoleCo hole) new_tv_ty)) } }

        -- See Detail (7) of the Note
        cb_loc :: CtLoc
    cb_loc = CtLoc -> (CtOrigin -> CtOrigin) -> CtLoc
    updateCtLocOrigin (CtEvidence -> CtLoc
    ctEvLoc CtEvidence
    ev) CtOrigin -> CtOrigin
    CycleBreakerOrigin

    ------------------------
    checkTypeEq :: CtEvidence -> EqRel -> CanEqLHS -> TcType
                -> TcS (PuResult () Reduction)
    -- Used for general CanEqLHSs, ones that do
    -- not have a touchable type variable on the LHS (i.e. not unifying)
    checkTypeEq :: CtEvidence
    -> EqRel -> CanEqLHS -> Type -> TcS (PuResult () Reduction)
    checkTypeEq CtEvidence
    ev EqRel
    eq_rel CanEqLHS
    lhs Type
    rhs
      | CtEvidence -> Bool
    isGiven CtEvidence
    ev
      = do { String -> SDoc -> TcS ()
    traceTcS String
    "checkTypeEq {" ([SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "lhs:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> CanEqLHS -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CanEqLHS
    lhs
                                            , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "rhs:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Type -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Type
    rhs ])
           ; check_result <- TcM (PuResult (TcTyVar, Type) Reduction)
    -> TcS (PuResult (TcTyVar, Type) Reduction)
    forall a. TcM a -> TcS a
    wrapTcS (Type -> TcM (PuResult (TcTyVar, Type) Reduction)
    check_given_rhs Type
    rhs)
           ; traceTcS "checkTypeEq }" (ppr check_result)
           ; case check_result of
                PuFail CheckTyEqResult
    reason -> PuResult () Reduction -> TcS (PuResult () Reduction)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CheckTyEqResult -> PuResult () Reduction
    forall a b. CheckTyEqResult -> PuResult a b
    PuFail CheckTyEqResult
    reason)
                PuOK Bag (TcTyVar, Type)
    prs Reduction
    redn -> do { new_givens <- ((TcTyVar, Type) -> TcS Ct) -> Bag (TcTyVar, Type) -> TcS Cts
    forall (m :: * -> *) a b.
    Monad m =>
    (a -> m b) -> Bag a -> m (Bag b)
    mapBagM (TcTyVar, Type) -> TcS Ct
    mk_new_given Bag (TcTyVar, Type)
    prs
                                    ; emitWork new_givens
                                    ; updInertSet (addCycleBreakerBindings prs)
                                    ; return (pure redn) } }

      | Bool
    otherwise  -- Wanted
      = do { check_result <- TcM (PuResult Ct Reduction) -> TcS (PuResult Ct Reduction)
    forall a. TcM a -> TcS a
    wrapTcS (TyEqFlags Ct -> Type -> TcM (PuResult Ct Reduction)
    forall a. TyEqFlags a -> Type -> TcM (PuResult a Reduction)
    checkTyEqRhs TyEqFlags Ct
    wanted_flags Type
    rhs)
           ; case check_result of
                PuFail CheckTyEqResult
    reason -> PuResult () Reduction -> TcS (PuResult () Reduction)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CheckTyEqResult -> PuResult () Reduction
    forall a b. CheckTyEqResult -> PuResult a b
    PuFail CheckTyEqResult
    reason)
                PuOK Cts
    cts Reduction
    redn -> do { Cts -> TcS ()
    emitWork Cts
    cts
                                    ; PuResult () Reduction -> TcS (PuResult () Reduction)
    forall a. a -> TcS a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Reduction -> PuResult () Reduction
    forall a. a -> PuResult () a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure Reduction
    redn) } }
      where
        check_given_rhs :: TcType -> TcM (PuResult (TcTyVar,TcType) Reduction)
        check_given_rhs :: Type -> TcM (PuResult (TcTyVar, Type) Reduction)
    check_given_rhs Type
    rhs
           -- See Note [Special case for top-level of Given equality]
           | Just (TyFamLHS TyCon
    tc [Type]
    tys) <- Type -> Maybe CanEqLHS
    canTyFamEqLHS_maybe Type
    rhs
           = TyEqFlags (TcTyVar, Type)
    -> TyCon -> [Type] -> TcM (PuResult (TcTyVar, Type) Reduction)
    forall a.
    TyEqFlags a -> TyCon -> [Type] -> TcM (PuResult a Reduction)
    recurseIntoTyConApp TyEqFlags (TcTyVar, Type)
    arg_flags TyCon
    tc [Type]
    tys
           | Bool
    otherwise
           = TyEqFlags (TcTyVar, Type)
    -> Type -> TcM (PuResult (TcTyVar, Type) Reduction)
    forall a. TyEqFlags a -> Type -> TcM (PuResult a Reduction)
    checkTyEqRhs TyEqFlags (TcTyVar, Type)
    given_flags Type
    rhs

        arg_flags :: TyEqFlags (TcTyVar, Type)
    arg_flags = TyEqFlags (TcTyVar, Type) -> TyEqFlags (TcTyVar, Type)
    forall a. TyEqFlags a -> TyEqFlags a
    famAppArgFlags TyEqFlags (TcTyVar, Type)
    given_flags

        given_flags :: TyEqFlags (TcTyVar,TcType)
        given_flags :: TyEqFlags (TcTyVar, Type)
    given_flags = TEF { tef_lhs :: CanEqLHS
    tef_lhs      = CanEqLHS
    lhs
                          , tef_foralls :: Bool
    tef_foralls  = Bool
    False
                          , tef_unifying :: AreUnifying
    tef_unifying = AreUnifying
    NotUnifying
                          , tef_fam_app :: TyEqFamApp (TcTyVar, Type)
    tef_fam_app  = CtEvidence
    -> EqRel
    -> (Type -> TcM (PuResult (TcTyVar, Type) Reduction))
    -> TyEqFamApp (TcTyVar, Type)
    forall a. CtEvidence -> EqRel -> FamAppBreaker a -> TyEqFamApp a
    mkTEFA_Break CtEvidence
    ev EqRel
    eq_rel Type -> TcM (PuResult (TcTyVar, Type) Reduction)
    break_given
                          , tef_occurs :: CheckTyEqProblem
    tef_occurs   = CheckTyEqProblem
    occ_prob }
            -- TEFA_Break used for: [G] a ~ Maybe (F a)
            --                   or [W] F a ~ Maybe (F a)

        wanted_flags :: TyEqFlags Ct
    wanted_flags = TEF { tef_lhs :: CanEqLHS
    tef_lhs      = CanEqLHS
    lhs
                           , tef_foralls :: Bool
    tef_foralls  = Bool
    False
                           , tef_unifying :: AreUnifying
    tef_unifying = AreUnifying
    NotUnifying
                           , tef_fam_app :: TyEqFamApp Ct
    tef_fam_app  = TyEqFamApp Ct
    forall a. TyEqFamApp a
    TEFA_Recurse
                           , tef_occurs :: CheckTyEqProblem
    tef_occurs   = CheckTyEqProblem
    occ_prob }
            -- TEFA_Recurse: see Note [Don't cycle-break Wanteds when not unifying]

        -- occ_prob: see Note [Occurs check and representational equality]
        occ_prob :: CheckTyEqProblem
    occ_prob = case EqRel
    eq_rel of
                     EqRel
    NomEq  -> CheckTyEqProblem
    cteInsolubleOccurs
                     EqRel
    ReprEq -> CheckTyEqProblem
    cteSolubleOccurs

        break_given :: TcType -> TcM (PuResult (TcTyVar,TcType) Reduction)
        break_given :: Type -> TcM (PuResult (TcTyVar, Type) Reduction)
    break_given Type
    fam_app
          = do { new_tv <- Type -> TcM TcTyVar
    TcM.newCycleBreakerTyVar (HasDebugCallStack => Type -> Type
    Type -> Type
    typeKind Type
    fam_app)
               ; return (PuOK (unitBag (new_tv, fam_app))
                              (mkReflRedn Nominal (mkTyVarTy new_tv))) }
                        -- Why reflexive? See Detail (4) of the Note

        ---------------------------
        mk_new_given :: (TcTyVar, TcType) -> TcS Ct
        mk_new_given :: (TcTyVar, Type) -> TcS Ct
    mk_new_given (TcTyVar
    new_tv, Type
    fam_app)
          = CtEvidence -> Ct
    mkNonCanonical (CtEvidence -> Ct) -> TcS CtEvidence -> TcS Ct
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> CtLoc -> (Type, EvTerm) -> TcS CtEvidence
    newGivenEvVar CtLoc
    cb_loc (Type
    given_pred, EvTerm
    given_term)
          where
            new_ty :: Type
    new_ty     = TcTyVar -> Type
    mkTyVarTy TcTyVar
    new_tv
            given_pred :: Type
    given_pred = Type -> Type -> Type
    mkPrimEqPred Type
    fam_app Type
    new_ty
            given_term :: EvTerm
    given_term = Coercion -> EvTerm
    evCoercion (Coercion -> EvTerm) -> Coercion -> EvTerm
    forall a b. (a -> b) -> a -> b
    $ Type -> Coercion
    mkNomReflCo Type
    new_ty  -- See Detail (4) of Note

        -- See Detail (7) of the Note
        cb_loc :: CtLoc
    cb_loc = CtLoc -> (CtOrigin -> CtOrigin) -> CtLoc
    updateCtLocOrigin (CtEvidence -> CtLoc
    ctEvLoc CtEvidence
    ev) CtOrigin -> CtOrigin
    CycleBreakerOrigin

    mkTEFA_Break :: CtEvidence -> EqRel -> FamAppBreaker a -> TyEqFamApp a
    mkTEFA_Break :: forall a. CtEvidence -> EqRel -> FamAppBreaker a -> TyEqFamApp a
    mkTEFA_Break CtEvidence
    ev EqRel
    eq_rel FamAppBreaker a
    breaker
      | EqRel
    NomEq <- EqRel
    eq_rel
      , Bool -> Bool
    not Bool
    cycle_breaker_origin
      = FamAppBreaker a -> TyEqFamApp a
    forall a. FamAppBreaker a -> TyEqFamApp a
    TEFA_Break FamAppBreaker a
    breaker
      | Bool
    otherwise
      = TyEqFamApp a
    forall a. TyEqFamApp a
    TEFA_Recurse
      where
        -- cycle_breaker_origin: see Detail (7) of Note [Type equality cycles]
        -- in GHC.Tc.Solver.Equality
        cycle_breaker_origin :: Bool
    cycle_breaker_origin = case CtLoc -> CtOrigin
    ctLocOrigin (CtEvidence -> CtLoc
    ctEvLoc CtEvidence
    ev) of
                                  CycleBreakerOrigin {} -> Bool
    True
                                  CtOrigin
    _                     -> Bool
    False

    -------------------------
    -- | Fill in CycleBreakerTvs with the variables they stand for.
    -- See Note [Type equality cycles] in GHC.Tc.Solver.Equality
    restoreTyVarCycles :: InertSet -> TcM ()
    restoreTyVarCycles :: InertSet -> TcM ()
    restoreTyVarCycles InertSet
    is
      = ZonkM () -> TcM ()
    forall a. ZonkM a -> TcM a
    TcM.liftZonkM
      (ZonkM () -> TcM ()) -> ZonkM () -> TcM ()
    forall a b. (a -> b) -> a -> b
    $ CycleBreakerVarStack -> (TcTyVar -> Type -> ZonkM ()) -> ZonkM ()
    forall (m :: * -> *).
    Monad m =>
    CycleBreakerVarStack -> (TcTyVar -> Type -> m ()) -> m ()
    forAllCycleBreakerBindings_ (InertSet -> CycleBreakerVarStack
    inert_cycle_breakers InertSet
    is) HasDebugCallStack => TcTyVar -> Type -> ZonkM ()
    TcTyVar -> Type -> ZonkM ()
    TcM.writeMetaTyVar
    {-# SPECIALISE forAllCycleBreakerBindings_ ::
          CycleBreakerVarStack -> (TcTyVar -> TcType -> ZonkM ()) -> ZonkM () #-}

    {- Note [Occurs check and representational equality]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    (a ~R# b a) is soluble if b later turns out to be Identity
    So we treat this as a "soluble occurs check".

    Note [Special case for top-level of Given equality]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We take care when examining
        [G] F ty ~ G (...(F ty)...)
    where both sides are TyFamLHSs.  We don't want to flatten that RHS to
        [G] F ty ~ cbv
        [G] G (...(F ty)...) ~ cbv
    Instead we'd like to say "occurs-check" and swap LHS and RHS, which yields a
    canonical constraint
        [G] G (...(F ty)...) ~ F ty
    That tents to rewrite a big type to smaller one. This happens in T15703,
    where we had:
        [G] Pure g ~ From1 (To1 (Pure g))
    Making a loop breaker and rewriting left to right just makes much bigger
    types than swapping it over.

    (We might hope to have swapped it over before getting to checkTypeEq,
    but better safe than sorry.)

    NB: We never see a TyVarLHS here, such as
        [G] a ~ F tys here
    because we'd have swapped it to
       [G] F tys ~ a
    in canEqCanLHS2, before getting to checkTypeEq.

    Note [Don't cycle-break Wanteds when not unifying]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consdier
      [W] a[2] ~ Maybe (F a[2])

    Should we cycle-break this Wanted, thus?

      [W] a[2] ~ Maybe delta[2]
      [W] delta[2] ~ F a[2]

    For a start, this is dodgy because we might just unify delta, thus undoing
    what we have done, and getting an infinite loop in the solver.  Even if we
    somehow prevented ourselves from doing so, is there any merit in the split?
    Maybe: perhaps we can use that equality on `a` to unlock other constraints?
    Consider
      type instance F (Maybe _) = Bool

      [G] g1: a ~ Maybe Bool
      [W] w1: a ~ Maybe (F a)

    If we loop-break w1 to get
      [W] w1': a ~ Maybe gamma
      [W] w3:  gamma ~ F a
    Now rewrite w3 with w1'
      [W] w3':  gamma ~ F (Maybe gamma)
    Now use the type instance to get
      gamma := Bool
    Now we are left with
      [W] w1': a ~ Maybe Bool
    which we can solve from the Given.

    BUT in this situation we could have rewritten the
    /original/ Wanted from the Given, like this:
      [W] w1': Maybe Bool ~ Maybe (F (Maybe Bool))
    and that is readily soluble.

    In short: loop-breaking Wanteds, when we aren't unifying,
    seems of no merit.  Hence TEFA_Recurse, rather than TEFA_Break,
    in `wanted_flags` in `checkTypeEq`.
    -}