    {-# LANGUAGE CPP #-}

    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    Matching guarded right-hand-sides (GRHSs)
    -}

    module GHC.HsToCore.GuardedRHSs ( dsGuarded, dsGRHSs, isTrueLHsExpr ) where

    #include "HsVersions.h"

    import GHC.Prelude

    import {-# SOURCE #-} GHC.HsToCore.Expr  ( dsLExpr, dsLocalBinds )
    import {-# SOURCE #-} GHC.HsToCore.Match ( matchSinglePatVar )

    import GHC.Hs
    import GHC.Core.Make
    import GHC.Core
    import GHC.Core.Utils (bindNonRec)

    import GHC.HsToCore.Monad
    import GHC.HsToCore.Utils
    import GHC.HsToCore.Pmc.Types ( Nablas )
    import GHC.Core.Type ( Type )
    import GHC.Utils.Misc
    import GHC.Types.SrcLoc
    import GHC.Utils.Outputable
    import GHC.Utils.Panic
    import GHC.Core.Multiplicity
    import Control.Monad ( zipWithM )
    import Data.List.NonEmpty ( NonEmpty, toList )

    {-
    @dsGuarded@ is used for GRHSs.
    It desugars:
    \begin{verbatim}
            | g1 -> e1
            ...
            | gn -> en
            where binds
    \end{verbatim}
    producing an expression with a runtime error in the corner case if
    necessary.  The type argument gives the type of the @ei@.
    -}

    dsGuarded :: GRHSs GhcTc (LHsExpr GhcTc) -> Type -> NonEmpty Nablas -> DsM CoreExpr
    dsGuarded :: GRHSs GhcTc (LHsExpr GhcTc)
    -> Type -> NonEmpty Nablas -> DsM CoreExpr
    dsGuarded GRHSs GhcTc (LHsExpr GhcTc)
    grhss Type
    rhs_ty NonEmpty Nablas
    rhss_nablas = do
        MatchResult CoreExpr
    match_result <- HsMatchContext GhcRn
    -> GRHSs GhcTc (LHsExpr GhcTc)
    -> Type
    -> NonEmpty Nablas
    -> DsM (MatchResult CoreExpr)
    dsGRHSs forall p. HsMatchContext p
    PatBindRhs GRHSs GhcTc (LHsExpr GhcTc)
    grhss Type
    rhs_ty NonEmpty Nablas
    rhss_nablas
        CoreExpr
    error_expr <- Id -> Type -> SDoc -> DsM CoreExpr
    mkErrorAppDs Id
    nON_EXHAUSTIVE_GUARDS_ERROR_ID Type
    rhs_ty SDoc
    empty
        MatchResult CoreExpr -> CoreExpr -> DsM CoreExpr
    extractMatchResult MatchResult CoreExpr
    match_result CoreExpr
    error_expr

    -- In contrast, @dsGRHSs@ produces a @MatchResult CoreExpr@.

    dsGRHSs :: HsMatchContext GhcRn
            -> GRHSs GhcTc (LHsExpr GhcTc) -- ^ Guarded RHSs
            -> Type                        -- ^ Type of RHS
            -> NonEmpty Nablas             -- ^ Refined pattern match checking
                                           --   models, one for the pattern part and
                                           --   one for each GRHS.
            -> DsM (MatchResult CoreExpr)
    dsGRHSs :: HsMatchContext GhcRn
    -> GRHSs GhcTc (LHsExpr GhcTc)
    -> Type
    -> NonEmpty Nablas
    -> DsM (MatchResult CoreExpr)
    dsGRHSs HsMatchContext GhcRn
    hs_ctx (GRHSs XCGRHSs GhcTc (LHsExpr GhcTc)
    _ [LGRHS GhcTc (LHsExpr GhcTc)]
    grhss HsLocalBinds GhcTc
    binds) Type
    rhs_ty NonEmpty Nablas
    rhss_nablas
      = ASSERT( notNull grhss )
        do { [MatchResult CoreExpr]
    match_results <- ASSERT( length grhss == length rhss_nablas )
                              forall (m :: * -> *) a b c.
    Applicative m =>
    (a -> b -> m c) -> [a] -> [b] -> m [c]
    zipWithM (HsMatchContext GhcRn
    -> Type
    -> Nablas
    -> LGRHS GhcTc (LHsExpr GhcTc)
    -> DsM (MatchResult CoreExpr)
    dsGRHS HsMatchContext GhcRn
    hs_ctx Type
    rhs_ty) (forall a. NonEmpty a -> [a]
    toList NonEmpty Nablas
    rhss_nablas) [LGRHS GhcTc (LHsExpr GhcTc)]
    grhss
           ; Nablas
    nablas <- DsM Nablas
    getPmNablas
           -- We need to remember the Nablas from the particular match context we
           -- are in, which might be different to when dsLocalBinds is actually
           -- called.
           ; let ds_binds :: CoreExpr -> DsM CoreExpr
    ds_binds      = forall a. Nablas -> DsM a -> DsM a
    updPmNablas Nablas
    nablas forall b c a. (b -> c) -> (a -> b) -> a -> c
    . HsLocalBinds GhcTc -> CoreExpr -> DsM CoreExpr
    dsLocalBinds HsLocalBinds GhcTc
    binds
                 match_result1 :: MatchResult CoreExpr
    match_result1 = forall (t :: * -> *) a. Foldable t => (a -> a -> a) -> t a -> a
    foldr1 MatchResult CoreExpr
    -> MatchResult CoreExpr -> MatchResult CoreExpr
    combineMatchResults [MatchResult CoreExpr]
    match_results
                 match_result2 :: MatchResult CoreExpr
    match_result2 = forall a b. (a -> DsM b) -> MatchResult a -> MatchResult b
    adjustMatchResultDs CoreExpr -> DsM CoreExpr
    ds_binds MatchResult CoreExpr
    match_result1
                                 -- NB: nested dsLet inside matchResult
           ; forall (m :: * -> *) a. Monad m => a -> m a
    return MatchResult CoreExpr
    match_result2 }

    dsGRHS :: HsMatchContext GhcRn -> Type -> Nablas -> LGRHS GhcTc (LHsExpr GhcTc)
           -> DsM (MatchResult CoreExpr)
    dsGRHS :: HsMatchContext GhcRn
    -> Type
    -> Nablas
    -> LGRHS GhcTc (LHsExpr GhcTc)
    -> DsM (MatchResult CoreExpr)
    dsGRHS HsMatchContext GhcRn
    hs_ctx Type
    rhs_ty Nablas
    rhs_nablas (L SrcSpan
    _ (GRHS XCGRHS GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc))
    _ [GuardLStmt GhcTc]
    guards GenLocated SrcSpanAnnA (HsExpr GhcTc)
    rhs))
      = [GuardStmt GhcTc]
    -> HsStmtContext GhcRn
    -> Nablas
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards (forall a b. (a -> b) -> [a] -> [b]
    map forall l e. GenLocated l e -> e
    unLoc [GuardLStmt GhcTc]
    guards) (forall p. HsMatchContext p -> HsStmtContext p
    PatGuard HsMatchContext GhcRn
    hs_ctx) Nablas
    rhs_nablas GenLocated SrcSpanAnnA (HsExpr GhcTc)
    rhs Type
    rhs_ty

    {-
    ************************************************************************
    *                                                                      *
    *  matchGuard : make a MatchResult CoreExpr CoreExpr from a guarded RHS                  *
    *                                                                      *
    ************************************************************************
    -}

    matchGuards :: [GuardStmt GhcTc]     -- Guard
                -> HsStmtContext GhcRn   -- Context
                -> Nablas                -- The RHS's covered set for PmCheck
                -> LHsExpr GhcTc         -- RHS
                -> Type                  -- Type of RHS of guard
                -> DsM (MatchResult CoreExpr)

    -- See comments with HsExpr.Stmt re what a BodyStmt means
    -- Here we must be in a guard context (not do-expression, nor list-comp)

    matchGuards :: [GuardStmt GhcTc]
    -> HsStmtContext GhcRn
    -> Nablas
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards [] HsStmtContext GhcRn
    _ Nablas
    nablas LHsExpr GhcTc
    rhs Type
    _
      = do  { CoreExpr
    core_rhs <- forall a. Nablas -> DsM a -> DsM a
    updPmNablas Nablas
    nablas (LHsExpr GhcTc -> DsM CoreExpr
    dsLExpr LHsExpr GhcTc
    rhs)
            ; forall (m :: * -> *) a. Monad m => a -> m a
    return (CoreExpr -> MatchResult CoreExpr
    cantFailMatchResult CoreExpr
    core_rhs) }

            -- BodyStmts must be guards
            -- Turn an "otherwise" guard is a no-op.  This ensures that
            -- you don't get a "non-exhaustive eqns" message when the guards
            -- finish in "otherwise".
            -- NB:  The success of this clause depends on the typechecker not
            --      wrapping the 'otherwise' in empty HsTyApp or HsWrap constructors
            --      If it does, you'll get bogus overlap warnings
    matchGuards (BodyStmt XBodyStmt GhcTc GhcTc (LHsExpr GhcTc)
    _ LHsExpr GhcTc
    e SyntaxExpr GhcTc
    _ SyntaxExpr GhcTc
    _ : [GuardStmt GhcTc]
    stmts) HsStmtContext GhcRn
    ctx Nablas
    nablas LHsExpr GhcTc
    rhs Type
    rhs_ty
      | Just CoreExpr -> DsM CoreExpr
    addTicks <- LHsExpr GhcTc -> Maybe (CoreExpr -> DsM CoreExpr)
    isTrueLHsExpr LHsExpr GhcTc
    e = do
        MatchResult CoreExpr
    match_result <- [GuardStmt GhcTc]
    -> HsStmtContext GhcRn
    -> Nablas
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards [GuardStmt GhcTc]
    stmts HsStmtContext GhcRn
    ctx Nablas
    nablas LHsExpr GhcTc
    rhs Type
    rhs_ty
        forall (m :: * -> *) a. Monad m => a -> m a
    return (forall a b. (a -> DsM b) -> MatchResult a -> MatchResult b
    adjustMatchResultDs CoreExpr -> DsM CoreExpr
    addTicks MatchResult CoreExpr
    match_result)
    matchGuards (BodyStmt XBodyStmt GhcTc GhcTc (LHsExpr GhcTc)
    _ LHsExpr GhcTc
    expr SyntaxExpr GhcTc
    _ SyntaxExpr GhcTc
    _ : [GuardStmt GhcTc]
    stmts) HsStmtContext GhcRn
    ctx Nablas
    nablas LHsExpr GhcTc
    rhs Type
    rhs_ty = do
        MatchResult CoreExpr
    match_result <- [GuardStmt GhcTc]
    -> HsStmtContext GhcRn
    -> Nablas
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards [GuardStmt GhcTc]
    stmts HsStmtContext GhcRn
    ctx Nablas
    nablas LHsExpr GhcTc
    rhs Type
    rhs_ty
        CoreExpr
    pred_expr <- LHsExpr GhcTc -> DsM CoreExpr
    dsLExpr LHsExpr GhcTc
    expr
        forall (m :: * -> *) a. Monad m => a -> m a
    return (CoreExpr -> MatchResult CoreExpr -> MatchResult CoreExpr
    mkGuardedMatchResult CoreExpr
    pred_expr MatchResult CoreExpr
    match_result)

    matchGuards (LetStmt XLetStmt GhcTc GhcTc (LHsExpr GhcTc)
    _ HsLocalBinds GhcTc
    binds : [GuardStmt GhcTc]
    stmts) HsStmtContext GhcRn
    ctx Nablas
    nablas LHsExpr GhcTc
    rhs Type
    rhs_ty = do
        MatchResult CoreExpr
    match_result <- [GuardStmt GhcTc]
    -> HsStmtContext GhcRn
    -> Nablas
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards [GuardStmt GhcTc]
    stmts HsStmtContext GhcRn
    ctx Nablas
    nablas LHsExpr GhcTc
    rhs Type
    rhs_ty
        forall (m :: * -> *) a. Monad m => a -> m a
    return (forall a b. (a -> DsM b) -> MatchResult a -> MatchResult b
    adjustMatchResultDs (HsLocalBinds GhcTc -> CoreExpr -> DsM CoreExpr
    dsLocalBinds HsLocalBinds GhcTc
    binds) MatchResult CoreExpr
    match_result)
            -- NB the dsLet occurs inside the match_result
            -- Reason: dsLet takes the body expression as its argument
            --         so we can't desugar the bindings without the
            --         body expression in hand

    matchGuards (BindStmt XBindStmt GhcTc GhcTc (LHsExpr GhcTc)
    _ LPat GhcTc
    pat LHsExpr GhcTc
    bind_rhs : [GuardStmt GhcTc]
    stmts) HsStmtContext GhcRn
    ctx Nablas
    nablas LHsExpr GhcTc
    rhs Type
    rhs_ty = do
        let upat :: Pat GhcTc
    upat = forall l e. GenLocated l e -> e
    unLoc LPat GhcTc
    pat
        Id
    match_var <- Type -> Pat GhcTc -> DsM Id
    selectMatchVar Type
    Many Pat GhcTc
    upat
           -- We only allow unrestricted patterns in guard, hence the `Many`
           -- above. It isn't clear what linear patterns would mean, maybe we will
           -- figure it out in the future.

        MatchResult CoreExpr
    match_result <- [GuardStmt GhcTc]
    -> HsStmtContext GhcRn
    -> Nablas
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards [GuardStmt GhcTc]
    stmts HsStmtContext GhcRn
    ctx Nablas
    nablas LHsExpr GhcTc
    rhs Type
    rhs_ty
        CoreExpr
    core_rhs <- LHsExpr GhcTc -> DsM CoreExpr
    dsLExpr LHsExpr GhcTc
    bind_rhs
        MatchResult CoreExpr
    match_result' <- Id
    -> Maybe CoreExpr
    -> HsMatchContext GhcRn
    -> LPat GhcTc
    -> Type
    -> MatchResult CoreExpr
    -> DsM (MatchResult CoreExpr)
    matchSinglePatVar Id
    match_var (forall a. a -> Maybe a
    Just CoreExpr
    core_rhs) (forall p. HsStmtContext p -> HsMatchContext p
    StmtCtxt HsStmtContext GhcRn
    ctx)
                                           LPat GhcTc
    pat Type
    rhs_ty MatchResult CoreExpr
    match_result
        forall (f :: * -> *) a. Applicative f => a -> f a
    pure forall a b. (a -> b) -> a -> b
    $ Id -> CoreExpr -> CoreExpr -> CoreExpr
    bindNonRec Id
    match_var CoreExpr
    core_rhs forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> MatchResult CoreExpr
    match_result'

    matchGuards (LastStmt  {} : [GuardStmt GhcTc]
    _) HsStmtContext GhcRn
    _ Nablas
    _ LHsExpr GhcTc
    _ Type
    _ = forall a. String -> a
    panic String
    "matchGuards LastStmt"
    matchGuards (ParStmt   {} : [GuardStmt GhcTc]
    _) HsStmtContext GhcRn
    _ Nablas
    _ LHsExpr GhcTc
    _ Type
    _ = forall a. String -> a
    panic String
    "matchGuards ParStmt"
    matchGuards (TransStmt {} : [GuardStmt GhcTc]
    _) HsStmtContext GhcRn
    _ Nablas
    _ LHsExpr GhcTc
    _ Type
    _ = forall a. String -> a
    panic String
    "matchGuards TransStmt"
    matchGuards (RecStmt   {} : [GuardStmt GhcTc]
    _) HsStmtContext GhcRn
    _ Nablas
    _ LHsExpr GhcTc
    _ Type
    _ = forall a. String -> a
    panic String
    "matchGuards RecStmt"
    matchGuards (ApplicativeStmt {} : [GuardStmt GhcTc]
    _) HsStmtContext GhcRn
    _ Nablas
    _ LHsExpr GhcTc
    _ Type
    _ =
      forall a. String -> a
    panic String
    "matchGuards ApplicativeLastStmt"

    {-
    Should {\em fail} if @e@ returns @D@
    \begin{verbatim}
    f x | p <- e', let C y# = e, f y# = r1
        | otherwise          = r2
    \end{verbatim}
    -}