\begin{code}
module TcSMonad (
CanonicalCts, emptyCCan, andCCan, andCCans,
singleCCan, extendCCans, isEmptyCCan, isCTyEqCan,
isCDictCan_Maybe, isCIPCan_Maybe, isCFunEqCan_Maybe,
CanonicalCt(..), Xi, tyVarsOfCanonical, tyVarsOfCanonicals, tyVarsOfCDicts,
mkWantedConstraints, deCanonicaliseWanted,
makeGivens, makeSolvedByInst,
CtFlavor (..), isWanted, isGiven, isDerived, isDerivedSC, isDerivedByInst,
isGivenCt, isWantedCt,
DerivedOrig (..),
canRewrite, canSolve,
combineCtLoc, mkGivenFlavor,
TcS, runTcS, failTcS, panicTcS, traceTcS, traceTcS0,
tryTcS, nestImplicTcS, recoverTcS, wrapErrTcS, wrapWarnTcS,
SimplContext(..), isInteractive, simplEqsOnly, performDefaulting,
newWantedCoVar, newGivOrDerCoVar, newGivOrDerEvVar,
newIPVar, newDictVar, newKindConstraint,
setWantedCoBind, setDerivedCoBind,
setIPBind, setDictBind, setEvBind,
setWantedTyBind,
newTcEvBindsTcS,
getInstEnvs, getFamInstEnvs,
getTopEnv, getGblEnv, getTcEvBinds, getUntouchables,
getTcEvBindsBag, getTcSContext, getTcSTyBinds, getTcSTyBindsMap,
newFlattenSkolemTy,
instDFunTypes,
instDFunConstraints,
isGoodRecEv,
zonkTcTypeTcS,
compatKind,
isTouchableMetaTyVar,
isTouchableMetaTyVar_InRange,
getDefaultInfo, getDynFlags,
matchClass, matchFam, MatchInstResult (..),
checkWellStagedDFun,
warnTcS,
pprEq,
mkWantedFunDepEqns
) where
#include "HsVersions.h"
import HscTypes
import BasicTypes
import Inst
import InstEnv
import FamInst
import FamInstEnv
import NameSet ( addOneToNameSet )
import qualified TcRnMonad as TcM
import qualified TcMType as TcM
import qualified TcEnv as TcM
( checkWellStaged, topIdLvl, tcLookupFamInst, tcGetDefaultTys )
import TcType
import Module
import DynFlags
import Coercion
import Class
import TyCon
import TypeRep
import Name
import Var
import VarEnv
import Outputable
import Bag
import MonadUtils
import VarSet
import FastString
import HsBinds
import Id
import FunDeps
import TcRnTypes
import Control.Monad
import Data.IORef
\end{code}
%************************************************************************
%* *
%* Canonical constraints *
%* *
%* These are the constraints the lowlevel simplifier works with *
%* *
%************************************************************************
\begin{code}
type Xi = Type
type CanonicalCts = Bag CanonicalCt
data CanonicalCt
= CDictCan {
cc_id :: EvVar,
cc_flavor :: CtFlavor,
cc_class :: Class,
cc_tyargs :: [Xi]
}
| CIPCan {
cc_id :: EvVar,
cc_flavor :: CtFlavor,
cc_ip_nm :: IPName Name,
cc_ip_ty :: TcTauType
}
| CTyEqCan {
cc_id :: EvVar,
cc_flavor :: CtFlavor,
cc_tyvar :: TcTyVar,
cc_rhs :: Xi
}
| CFunEqCan {
cc_id :: EvVar,
cc_flavor :: CtFlavor,
cc_fun :: TyCon,
cc_tyargs :: [Xi],
cc_rhs :: Xi
}
compatKind :: Kind -> Kind -> Bool
compatKind k1 k2 = k1 `isSubKind` k2 || k2 `isSubKind` k1
makeGivens :: CanonicalCts -> CanonicalCts
makeGivens = mapBag (\ct -> ct { cc_flavor = mkGivenFlavor (cc_flavor ct) UnkSkol })
makeSolvedByInst :: CanonicalCt -> CanonicalCt
makeSolvedByInst ct
| Wanted loc <- cc_flavor ct = ct { cc_flavor = Derived loc DerInst }
| otherwise = ct
mkWantedConstraints :: CanonicalCts -> Bag Implication -> WantedConstraints
mkWantedConstraints flats implics
= mapBag (WcEvVar . deCanonicaliseWanted) flats `unionBags` mapBag WcImplic implics
deCanonicaliseWanted :: CanonicalCt -> WantedEvVar
deCanonicaliseWanted ct
= WARN( not (isWanted $ cc_flavor ct), ppr ct )
let Wanted loc = cc_flavor ct
in WantedEvVar (cc_id ct) loc
tyVarsOfCanonical :: CanonicalCt -> TcTyVarSet
tyVarsOfCanonical (CTyEqCan { cc_tyvar = tv, cc_rhs = xi }) = extendVarSet (tyVarsOfType xi) tv
tyVarsOfCanonical (CFunEqCan { cc_tyargs = tys, cc_rhs = xi }) = tyVarsOfTypes (xi:tys)
tyVarsOfCanonical (CDictCan { cc_tyargs = tys }) = tyVarsOfTypes tys
tyVarsOfCanonical (CIPCan { cc_ip_ty = ty }) = tyVarsOfType ty
tyVarsOfCDict :: CanonicalCt -> TcTyVarSet
tyVarsOfCDict (CDictCan { cc_tyargs = tys }) = tyVarsOfTypes tys
tyVarsOfCDict _ct = emptyVarSet
tyVarsOfCDicts :: CanonicalCts -> TcTyVarSet
tyVarsOfCDicts = foldrBag (unionVarSet . tyVarsOfCDict) emptyVarSet
tyVarsOfCanonicals :: CanonicalCts -> TcTyVarSet
tyVarsOfCanonicals = foldrBag (unionVarSet . tyVarsOfCanonical) emptyVarSet
instance Outputable CanonicalCt where
ppr (CDictCan d fl cls tys)
= ppr fl <+> ppr d <+> dcolon <+> pprClassPred cls tys
ppr (CIPCan ip fl ip_nm ty)
= ppr fl <+> ppr ip <+> dcolon <+> parens (ppr ip_nm <> dcolon <> ppr ty)
ppr (CTyEqCan co fl tv ty)
= ppr fl <+> ppr co <+> dcolon <+> pprEqPred (mkTyVarTy tv, ty)
ppr (CFunEqCan co fl tc tys ty)
= ppr fl <+> ppr co <+> dcolon <+> pprEqPred (mkTyConApp tc tys, ty)
\end{code}
Note [No touchables as FunEq RHS]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Notice that (F xis ~ beta), where beta is an touchable unification
variable, is not canonical. Why?
* If (F xis ~ beta) was the only wanted constraint, we'd
definitely want to spontaneouslyunify it
* But suppose we had an earlier wanted (beta ~ Int), and
have already spontaneously unified it. Then we have an
identity given (id : beta ~ Int) in the inert set.
* But (F xis ~ beta) does not react with that given (because we
don't subsitute on the RHS of a function equality). So there's a
serious danger that we'd spontaneously unify it a second time.
Hence the invariant.
The invariant is
Note [Canonical implicit parameter constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The type in a canonical implicit parameter constraint doesn't need to
be a xi (typefunctionfree type) since we can defer the flattening
until checking this type for equality with another type. If we
encounter two IP constraints with the same name, they MUST have the
same type, and at that point we can generate a flattened equality
constraint between the types. (On the other hand, the types in two
class constraints for the same class MAY be equal, so they need to be
flattened in the first place to facilitate comparing them.)
\begin{code}
singleCCan :: CanonicalCt -> CanonicalCts
singleCCan = unitBag
andCCan :: CanonicalCts -> CanonicalCts -> CanonicalCts
andCCan = unionBags
extendCCans :: CanonicalCts -> CanonicalCt -> CanonicalCts
extendCCans = snocBag
andCCans :: [CanonicalCts] -> CanonicalCts
andCCans = unionManyBags
emptyCCan :: CanonicalCts
emptyCCan = emptyBag
isEmptyCCan :: CanonicalCts -> Bool
isEmptyCCan = isEmptyBag
isCTyEqCan :: CanonicalCt -> Bool
isCTyEqCan (CTyEqCan {}) = True
isCTyEqCan (CFunEqCan {}) = False
isCTyEqCan _ = False
isCDictCan_Maybe :: CanonicalCt -> Maybe Class
isCDictCan_Maybe (CDictCan {cc_class = cls }) = Just cls
isCDictCan_Maybe _ = Nothing
isCIPCan_Maybe :: CanonicalCt -> Maybe (IPName Name)
isCIPCan_Maybe (CIPCan {cc_ip_nm = nm }) = Just nm
isCIPCan_Maybe _ = Nothing
isCFunEqCan_Maybe :: CanonicalCt -> Maybe TyCon
isCFunEqCan_Maybe (CFunEqCan { cc_fun = tc }) = Just tc
isCFunEqCan_Maybe _ = Nothing
\end{code}
%************************************************************************
%* *
CtFlavor
The "flavor" of a canonical constraint
%* *
%************************************************************************
\begin{code}
data CtFlavor
= Given GivenLoc
| Derived WantedLoc DerivedOrig
| Wanted WantedLoc
data DerivedOrig = DerSC | DerInst
instance Outputable CtFlavor where
ppr (Given _) = ptext (sLit "[Given]")
ppr (Wanted _) = ptext (sLit "[Wanted]")
ppr (Derived {}) = ptext (sLit "[Derived]")
isWanted :: CtFlavor -> Bool
isWanted (Wanted {}) = True
isWanted _ = False
isGiven :: CtFlavor -> Bool
isGiven (Given {}) = True
isGiven _ = False
isDerived :: CtFlavor -> Bool
isDerived (Derived {}) = True
isDerived _ = False
isDerivedSC :: CtFlavor -> Bool
isDerivedSC (Derived _ DerSC) = True
isDerivedSC _ = False
isDerivedByInst :: CtFlavor -> Bool
isDerivedByInst (Derived _ DerInst) = True
isDerivedByInst _ = False
isWantedCt :: CanonicalCt -> Bool
isWantedCt ct = isWanted (cc_flavor ct)
isGivenCt :: CanonicalCt -> Bool
isGivenCt ct = isGiven (cc_flavor ct)
canSolve :: CtFlavor -> CtFlavor -> Bool
canSolve (Given {}) _ = True
canSolve (Derived {}) (Wanted {}) = True
canSolve (Derived {}) (Derived {}) = True
canSolve (Wanted {}) (Wanted {}) = True
canSolve _ _ = False
canRewrite :: CtFlavor -> CtFlavor -> Bool
canRewrite = canSolve
combineCtLoc :: CtFlavor -> CtFlavor -> WantedLoc
combineCtLoc (Wanted loc) _ = loc
combineCtLoc _ (Wanted loc) = loc
combineCtLoc (Derived loc _) _ = loc
combineCtLoc _ (Derived loc _) = loc
combineCtLoc _ _ = panic "combineCtLoc: both given"
mkGivenFlavor :: CtFlavor -> SkolemInfo -> CtFlavor
mkGivenFlavor (Wanted loc) sk = Given (setCtLocOrigin loc sk)
mkGivenFlavor (Derived loc _) sk = Given (setCtLocOrigin loc sk)
mkGivenFlavor (Given loc) sk = Given (setCtLocOrigin loc sk)
\end{code}
%************************************************************************
%* *
%* 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.
\begin{code}
data TcSEnv
= TcSEnv {
tcs_ev_binds :: EvBindsVar,
tcs_ty_binds :: IORef (TyVarEnv (TcTyVar, TcType)),
tcs_context :: SimplContext,
tcs_untch :: Untouchables
}
data SimplContext
= SimplInfer
| SimplRuleLhs
| SimplInteractive
| SimplCheck
instance Outputable SimplContext where
ppr SimplInfer = ptext (sLit "SimplInfer")
ppr SimplRuleLhs = ptext (sLit "SimplRuleLhs")
ppr SimplInteractive = ptext (sLit "SimplInteractive")
ppr SimplCheck = ptext (sLit "SimplCheck")
isInteractive :: SimplContext -> Bool
isInteractive SimplInteractive = True
isInteractive _ = False
simplEqsOnly :: SimplContext -> Bool
simplEqsOnly SimplRuleLhs = True
simplEqsOnly _ = False
performDefaulting :: SimplContext -> Bool
performDefaulting SimplInfer = False
performDefaulting SimplRuleLhs = False
performDefaulting SimplInteractive = True
performDefaulting SimplCheck = True
newtype TcS a = TcS { unTcS :: TcSEnv -> TcM a }
instance Functor TcS where
fmap f m = TcS $ fmap f . unTcS m
instance Monad TcS where
return x = TcS (\_ -> return x)
fail err = TcS (\_ -> fail err)
m >>= k = TcS (\ebs -> unTcS m ebs >>= \r -> unTcS (k r) ebs)
wrapTcS :: TcM a -> TcS a
wrapTcS = TcS . const
wrapErrTcS :: TcM a -> TcS a
wrapErrTcS = wrapTcS
wrapWarnTcS :: TcM a -> TcS a
wrapWarnTcS = wrapTcS
failTcS, panicTcS :: SDoc -> TcS a
failTcS = wrapTcS . TcM.failWith
panicTcS doc = pprPanic "TcCanonical" doc
traceTcS :: String -> SDoc -> TcS ()
traceTcS herald doc = TcS $ \_env -> TcM.traceTc herald doc
traceTcS0 :: String -> SDoc -> TcS ()
traceTcS0 herald doc = TcS $ \_env -> TcM.traceTcN 0 herald doc
runTcS :: SimplContext
-> Untouchables
-> TcS a
-> TcM (a, Bag EvBind)
runTcS context untouch tcs
= do { ty_binds_var <- TcM.newTcRef emptyVarEnv
; ev_binds_var@(EvBindsVar evb_ref _) <- TcM.newTcEvBinds
; let env = TcSEnv { tcs_ev_binds = ev_binds_var
, tcs_ty_binds = ty_binds_var
, tcs_context = context
, tcs_untch = untouch }
; res <- unTcS tcs env
; ty_binds <- TcM.readTcRef ty_binds_var
; mapM_ do_unification (varEnvElts ty_binds)
; ev_binds <- TcM.readTcRef evb_ref
; return (res, evBindMapBinds ev_binds) }
where
do_unification (tv,ty) = TcM.writeMetaTyVar tv ty
nestImplicTcS :: EvBindsVar -> Untouchables -> TcS a -> TcS a
nestImplicTcS ref untch (TcS thing_inside)
= TcS $ \ TcSEnv { tcs_ty_binds = ty_binds, tcs_context = ctxt } ->
let
nest_env = TcSEnv { tcs_ev_binds = ref
, tcs_ty_binds = ty_binds
, tcs_untch = untch
, tcs_context = ctxtUnderImplic ctxt }
in
thing_inside nest_env
recoverTcS :: TcS a -> TcS a -> TcS a
recoverTcS (TcS recovery_code) (TcS thing_inside)
= TcS $ \ env ->
TcM.recoverM (recovery_code env) (thing_inside env)
ctxtUnderImplic :: SimplContext -> SimplContext
ctxtUnderImplic SimplRuleLhs = SimplCheck
ctxtUnderImplic ctxt = ctxt
tryTcS :: TcS a -> TcS a
tryTcS tcs
= TcS (\env -> do { ty_binds_var <- TcM.newTcRef emptyVarEnv
; ev_binds_var <- TcM.newTcEvBinds
; let env1 = env { tcs_ev_binds = ev_binds_var
, tcs_ty_binds = ty_binds_var }
; unTcS tcs env1 })
getDynFlags :: TcS DynFlags
getDynFlags = wrapTcS TcM.getDOpts
getTcSContext :: TcS SimplContext
getTcSContext = TcS (return . tcs_context)
getTcEvBinds :: TcS EvBindsVar
getTcEvBinds = TcS (return . tcs_ev_binds)
getUntouchables :: TcS Untouchables
getUntouchables = TcS (return . tcs_untch)
getTcSTyBinds :: TcS (IORef (TyVarEnv (TcTyVar, TcType)))
getTcSTyBinds = TcS (return . tcs_ty_binds)
getTcSTyBindsMap :: TcS (TyVarEnv (TcTyVar, TcType))
getTcSTyBindsMap = getTcSTyBinds >>= wrapTcS . (TcM.readTcRef)
getTcEvBindsBag :: TcS EvBindMap
getTcEvBindsBag
= do { EvBindsVar ev_ref _ <- getTcEvBinds
; wrapTcS $ TcM.readTcRef ev_ref }
setWantedCoBind :: CoVar -> Coercion -> TcS ()
setWantedCoBind cv co
= setEvBind cv (EvCoercion co)
setDerivedCoBind :: CoVar -> Coercion -> TcS ()
setDerivedCoBind cv co
= setEvBind cv (EvCoercion co)
setWantedTyBind :: TcTyVar -> TcType -> TcS ()
setWantedTyBind tv ty
= do { ref <- getTcSTyBinds
; wrapTcS $
do { ty_binds <- TcM.readTcRef ref
; TcM.writeTcRef ref (extendVarEnv ty_binds tv (tv,ty)) } }
setIPBind :: EvVar -> EvTerm -> TcS ()
setIPBind = setEvBind
setDictBind :: EvVar -> EvTerm -> TcS ()
setDictBind = setEvBind
setEvBind :: EvVar -> EvTerm -> TcS ()
setEvBind ev rhs
= do { tc_evbinds <- getTcEvBinds
; wrapTcS (TcM.addTcEvBind tc_evbinds ev rhs) }
newTcEvBindsTcS :: TcS EvBindsVar
newTcEvBindsTcS = wrapTcS (TcM.newTcEvBinds)
warnTcS :: CtLoc orig -> Bool -> SDoc -> TcS ()
warnTcS loc warn_if doc
| warn_if = wrapTcS $ TcM.setCtLoc loc $ TcM.addWarnTc doc
| otherwise = return ()
getDefaultInfo :: TcS (SimplContext, [Type], (Bool, Bool))
getDefaultInfo
= do { ctxt <- getTcSContext
; (tys, flags) <- wrapTcS (TcM.tcGetDefaultTys (isInteractive ctxt))
; return (ctxt, tys, flags) }
getInstEnvs :: TcS (InstEnv, InstEnv)
getInstEnvs = wrapTcS $ Inst.tcGetInstEnvs
getFamInstEnvs :: TcS (FamInstEnv, FamInstEnv)
getFamInstEnvs = wrapTcS $ FamInst.tcGetFamInstEnvs
getTopEnv :: TcS HscEnv
getTopEnv = wrapTcS $ TcM.getTopEnv
getGblEnv :: TcS TcGblEnv
getGblEnv = wrapTcS $ TcM.getGblEnv
checkWellStagedDFun :: PredType -> DFunId -> WantedLoc -> TcS ()
checkWellStagedDFun pred dfun_id loc
= wrapTcS $ TcM.setCtLoc loc $
do { use_stage <- TcM.getStage
; TcM.checkWellStaged pp_thing bind_lvl (thLevel use_stage) }
where
pp_thing = ptext (sLit "instance for") <+> quotes (ppr pred)
bind_lvl = TcM.topIdLvl dfun_id
pprEq :: TcType -> TcType -> SDoc
pprEq ty1 ty2 = pprPred $ mkEqPred (ty1,ty2)
isTouchableMetaTyVar :: TcTyVar -> TcS Bool
isTouchableMetaTyVar tv
= do { untch <- getUntouchables
; return $ isTouchableMetaTyVar_InRange untch tv }
isTouchableMetaTyVar_InRange :: Untouchables -> TcTyVar -> Bool
isTouchableMetaTyVar_InRange untch tv
= case tcTyVarDetails tv of
MetaTv TcsTv _ -> True
MetaTv {} -> inTouchableRange untch tv
_ -> False
\end{code}
Note [Touchable meta type variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Meta type variables allocated *by the constraint solver itself* are always
touchable. Example:
instance C a b => D [a] where...
if we use this instance declaration we "make up" a fresh meta type
variable for 'b', which we must later guess. (Perhaps C has a
functional dependency.) But since we aren't in the constraint *generator*
we can't allocate a Unique in the touchable range for this implication
constraint. Instead, we mark it as a "TcsTv", which makes it alwaystouchable.
\begin{code}
newFlattenSkolemTy :: TcType -> TcS TcType
newFlattenSkolemTy ty = mkTyVarTy <$> newFlattenSkolemTyVar ty
newFlattenSkolemTyVar :: TcType -> TcS TcTyVar
newFlattenSkolemTyVar ty
= wrapTcS $ do { uniq <- TcM.newUnique
; let name = mkSysTvName uniq (fsLit "f")
; return $ mkTcTyVar name (typeKind ty) (FlatSkol ty) }
instDFunTypes :: [Either TyVar TcType] -> TcS [TcType]
instDFunTypes mb_inst_tys
= mapM inst_tv mb_inst_tys
where
inst_tv :: Either TyVar TcType -> TcS Type
inst_tv (Left tv) = mkTyVarTy <$> newFlexiTcS tv
inst_tv (Right ty) = return ty
instDFunConstraints :: TcThetaType -> TcS [EvVar]
instDFunConstraints preds = wrapTcS $ TcM.newWantedEvVars preds
newFlexiTcS :: TyVar -> TcS TcTyVar
newFlexiTcS tv = newFlexiTcSHelper (tyVarName tv) (tyVarKind tv)
newKindConstraint :: TcTyVar -> Kind -> TcS (CoVar, Type)
newKindConstraint tv knd
= do { tv_k <- newFlexiTcSHelper (tyVarName tv) knd
; let ty_k = mkTyVarTy tv_k
; co_var <- newWantedCoVar (mkTyVarTy tv) ty_k
; return (co_var, ty_k) }
newFlexiTcSHelper :: Name -> Kind -> TcS TcTyVar
newFlexiTcSHelper tvname tvkind
= wrapTcS $
do { uniq <- TcM.newUnique
; ref <- TcM.newMutVar Flexi
; let name = setNameUnique tvname uniq
kind = tvkind
; return (mkTcTyVar name kind (MetaTv TcsTv ref)) }
newGivOrDerEvVar :: TcPredType -> EvTerm -> TcS EvVar
newGivOrDerEvVar pty evtrm
= do { ev <- wrapTcS $ TcM.newEvVar pty
; setEvBind ev evtrm
; return ev }
newGivOrDerCoVar :: TcType -> TcType -> Coercion -> TcS EvVar
newGivOrDerCoVar ty1 ty2 co
= do { cv <- newCoVar ty1 ty2
; setEvBind cv (EvCoercion co)
; return cv }
newWantedCoVar :: TcType -> TcType -> TcS EvVar
newWantedCoVar ty1 ty2 = wrapTcS $ TcM.newWantedCoVar ty1 ty2
newCoVar :: TcType -> TcType -> TcS EvVar
newCoVar ty1 ty2 = wrapTcS $ TcM.newCoVar ty1 ty2
newIPVar :: IPName Name -> TcType -> TcS EvVar
newIPVar nm ty = wrapTcS $ TcM.newIP nm ty
newDictVar :: Class -> [TcType] -> TcS EvVar
newDictVar cl tys = wrapTcS $ TcM.newDict cl tys
\end{code}
\begin{code}
isGoodRecEv :: EvVar -> WantedEvVar -> TcS Bool
isGoodRecEv ev_var (WantedEvVar wv _)
= do { tc_evbinds <- getTcEvBindsBag
; mb <- chase_ev_var tc_evbinds wv 0 [] ev_var
; return $ case mb of
Nothing -> True
Just min_guardedness -> min_guardedness > 0
}
where chase_ev_var :: EvBindMap
-> EvVar
-> Int
-> [EvVar]
-> EvVar
-> TcS (Maybe Int)
chase_ev_var assocs trg curr_grav visited orig
| trg == orig = return $ Just curr_grav
| orig `elem` visited = return $ Nothing
| Just (EvBind _ ev_trm) <- lookupEvBind assocs orig
= chase_ev assocs trg curr_grav (orig:visited) ev_trm
| otherwise = return Nothing
chase_ev assocs trg curr_grav visited (EvId v)
= chase_ev_var assocs trg curr_grav visited v
chase_ev assocs trg curr_grav visited (EvSuperClass d_id _)
= chase_ev_var assocs trg (curr_grav1) visited d_id
chase_ev assocs trg curr_grav visited (EvCast v co)
= do { m1 <- chase_ev_var assocs trg curr_grav visited v
; m2 <- chase_co assocs trg curr_grav visited co
; return (comb_chase_res Nothing [m1,m2]) }
chase_ev assocs trg curr_grav visited (EvCoercion co)
= chase_co assocs trg curr_grav visited co
chase_ev assocs trg curr_grav visited (EvDFunApp _ _ ev_vars)
= do { chase_results <- mapM (chase_ev_var assocs trg (curr_grav+1) visited) ev_vars
; return (comb_chase_res Nothing chase_results) }
chase_co assocs trg curr_grav visited co
=
let co_vars = foldVarSet (\v vrs -> if isCoVar v then (v:vrs) else vrs) []
(tyVarsOfType co)
in do { chase_results <- mapM (chase_ev_var assocs trg curr_grav visited) co_vars
; return (comb_chase_res Nothing chase_results) }
comb_chase_res f [] = f
comb_chase_res f (Nothing:rest) = comb_chase_res f rest
comb_chase_res Nothing (Just n:rest) = comb_chase_res (Just n) rest
comb_chase_res (Just m) (Just n:rest) = comb_chase_res (Just (min n m)) rest
data MatchInstResult mi
= MatchInstNo
| MatchInstSingle mi
| MatchInstMany
matchClass :: Class -> [Type] -> TcS (MatchInstResult (DFunId, [Either TyVar TcType]))
matchClass clas tys
= do { let pred = mkClassPred clas tys
; instEnvs <- getInstEnvs
; case lookupInstEnv instEnvs clas tys of {
([], unifs)
-> do { traceTcS "matchClass not matching"
(vcat [ text "dict" <+> ppr pred,
text "unifs" <+> ppr unifs ])
; return MatchInstNo
} ;
([(ispec, inst_tys)], [])
-> do { let dfun_id = is_dfun ispec
; traceTcS "matchClass success"
(vcat [text "dict" <+> ppr pred,
text "witness" <+> ppr dfun_id
<+> ppr (idType dfun_id) ])
; record_dfun_usage dfun_id
; return $ MatchInstSingle (dfun_id, inst_tys)
} ;
(matches, unifs)
-> do { traceTcS "matchClass multiple matches, deferring choice"
(vcat [text "dict" <+> ppr pred,
text "matches" <+> ppr matches,
text "unifs" <+> ppr unifs])
; return MatchInstMany
}
}
}
where record_dfun_usage :: Id -> TcS ()
record_dfun_usage dfun_id
= do { hsc_env <- getTopEnv
; let dfun_name = idName dfun_id
dfun_mod = ASSERT( isExternalName dfun_name )
nameModule dfun_name
; if isInternalName dfun_name ||
modulePackageId dfun_mod /= thisPackage (hsc_dflags hsc_env)
then return ()
else do updInstUses dfun_id
}
updInstUses :: Id -> TcS ()
updInstUses dfun_id
= do { tcg_env <- getGblEnv
; wrapTcS $ TcM.updMutVar (tcg_inst_uses tcg_env)
(`addOneToNameSet` idName dfun_id)
}
matchFam :: TyCon
-> [Type]
-> TcS (MatchInstResult (TyCon, [Type]))
matchFam tycon args
= do { mb <- wrapTcS $ TcM.tcLookupFamInst tycon args
; case mb of
Nothing -> return MatchInstNo
Just res -> return $ MatchInstSingle res
}
zonkTcTypeTcS :: TcType -> TcS TcType
zonkTcTypeTcS ty
= do { subst <- getTcSTyBindsMap >>= return . varEnvElts
; let (dom,rng) = unzip subst
apply_once = substTyWith dom rng
; let rng_idemp = [ substTyWith dom rng_idemp (apply_once t) | t <- rng ]
; return (substTyWith dom rng_idemp ty) }
mkWantedFunDepEqns :: WantedLoc -> [(Equation, (PredType, SDoc), (PredType, SDoc))]
-> TcS [WantedEvVar]
mkWantedFunDepEqns _ [] = return []
mkWantedFunDepEqns loc eqns
= do { traceTcS "Improve:" (vcat (map pprEquationDoc eqns))
; wevvars <- mapM to_work_item eqns
; return $ concat wevvars }
where
to_work_item :: (Equation, (PredType,SDoc), (PredType,SDoc)) -> TcS [WantedEvVar]
to_work_item ((qtvs, pairs), _, _)
= do { let tvs = varSetElems qtvs
; tvs' <- mapM newFlexiTcS tvs
; let subst = zipTopTvSubst tvs (mkTyVarTys tvs')
; mapM (do_one subst) pairs }
do_one subst (ty1, ty2) = do { let sty1 = substTy subst ty1
sty2 = substTy subst ty2
; ev <- newWantedCoVar sty1 sty2
; return (WantedEvVar ev loc) }
pprEquationDoc :: (Equation, (PredType, SDoc), (PredType, SDoc)) -> SDoc
pprEquationDoc (eqn, (p1, _), (p2, _))
= vcat [pprEquation eqn, nest 2 (ppr p1), nest 2 (ppr p2)]
\end{code}