    {-
    (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

    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
        match_result <- HsMatchContextRn
    -> GRHSs GhcTc (LHsExpr GhcTc)
    -> Type
    -> NonEmpty Nablas
    -> DsM (MatchResult CoreExpr)
    dsGRHSs HsMatchContextRn
    HsMatchContext (GenLocated SrcSpanAnnN Name)
    forall fn. HsMatchContext fn
    PatBindRhs GRHSs GhcTc (LHsExpr GhcTc)
    grhss Type
    rhs_ty NonEmpty Nablas
    rhss_nablas
        error_expr <- mkErrorAppDs nON_EXHAUSTIVE_GUARDS_ERROR_ID rhs_ty
                                   (text "pattern binding")
        extractMatchResult match_result error_expr

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

    dsGRHSs :: HsMatchContextRn
            -> 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 :: HsMatchContextRn
    -> GRHSs GhcTc (LHsExpr GhcTc)
    -> Type
    -> NonEmpty Nablas
    -> DsM (MatchResult CoreExpr)
    dsGRHSs HsMatchContextRn
    hs_ctx (GRHSs XCGRHSs GhcTc (LHsExpr GhcTc)
    _ [LGRHS GhcTc (LHsExpr GhcTc)]
    grhss HsLocalBinds GhcTc
    binds) Type
    rhs_ty NonEmpty Nablas
    rhss_nablas
      = Bool -> DsM (MatchResult CoreExpr) -> DsM (MatchResult CoreExpr)
    forall a. HasCallStack => Bool -> a -> a
    assert ([GenLocated
       EpAnnCO (GRHS GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))]
    -> Bool
    forall (f :: * -> *) a. Foldable f => f a -> Bool
    notNull [LGRHS GhcTc (LHsExpr GhcTc)]
    [GenLocated
       EpAnnCO (GRHS GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))]
    grhss) (DsM (MatchResult CoreExpr) -> DsM (MatchResult CoreExpr))
    -> DsM (MatchResult CoreExpr) -> DsM (MatchResult CoreExpr)
    forall a b. (a -> b) -> a -> b
    $
        do { match_results <- Bool
    -> IOEnv (Env DsGblEnv DsLclEnv) [MatchResult CoreExpr]
    -> IOEnv (Env DsGblEnv DsLclEnv) [MatchResult CoreExpr]
    forall a. HasCallStack => Bool -> a -> a
    assert ([GenLocated
       EpAnnCO (GRHS GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))]
    -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [LGRHS GhcTc (LHsExpr GhcTc)]
    [GenLocated
       EpAnnCO (GRHS GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))]
    grhss Int -> Int -> Bool
    forall a. Eq a => a -> a -> Bool
    == NonEmpty Nablas -> Int
    forall a. NonEmpty a -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length NonEmpty Nablas
    rhss_nablas) (IOEnv (Env DsGblEnv DsLclEnv) [MatchResult CoreExpr]
     -> IOEnv (Env DsGblEnv DsLclEnv) [MatchResult CoreExpr])
    -> IOEnv (Env DsGblEnv DsLclEnv) [MatchResult CoreExpr]
    -> IOEnv (Env DsGblEnv DsLclEnv) [MatchResult CoreExpr]
    forall a b. (a -> b) -> a -> b
    $
                              (Nablas
     -> GenLocated
          EpAnnCO (GRHS GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))
     -> DsM (MatchResult CoreExpr))
    -> [Nablas]
    -> [GenLocated
          EpAnnCO (GRHS GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))]
    -> IOEnv (Env DsGblEnv DsLclEnv) [MatchResult CoreExpr]
    forall (m :: * -> *) a b c.
    Applicative m =>
    (a -> b -> m c) -> [a] -> [b] -> m [c]
    zipWithM (HsMatchContextRn
    -> Type
    -> Nablas
    -> LGRHS GhcTc (LHsExpr GhcTc)
    -> DsM (MatchResult CoreExpr)
    dsGRHS HsMatchContextRn
    hs_ctx Type
    rhs_ty) (NonEmpty Nablas -> [Nablas]
    forall a. NonEmpty a -> [a]
    toList NonEmpty Nablas
    rhss_nablas) [LGRHS GhcTc (LHsExpr GhcTc)]
    [GenLocated
       EpAnnCO (GRHS GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))]
    grhss
           ; 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      = Nablas -> DsM CoreExpr -> DsM CoreExpr
    forall a. Nablas -> DsM a -> DsM a
    updPmNablas Nablas
    nablas (DsM CoreExpr -> DsM CoreExpr)
    -> (CoreExpr -> DsM CoreExpr) -> CoreExpr -> DsM CoreExpr
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . HsLocalBinds GhcTc -> CoreExpr -> DsM CoreExpr
    dsLocalBinds HsLocalBinds GhcTc
    binds
                 match_result1 = (MatchResult CoreExpr
     -> MatchResult CoreExpr -> MatchResult CoreExpr)
    -> [MatchResult CoreExpr] -> MatchResult CoreExpr
    forall a. (a -> a -> a) -> [a] -> a
    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 = (CoreExpr -> DsM CoreExpr)
    -> MatchResult CoreExpr -> MatchResult CoreExpr
    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
           ; return match_result2 }

    dsGRHS :: HsMatchContextRn -> Type -> Nablas -> LGRHS GhcTc (LHsExpr GhcTc)
           -> DsM (MatchResult CoreExpr)
    dsGRHS :: HsMatchContextRn
    -> Type
    -> Nablas
    -> LGRHS GhcTc (LHsExpr GhcTc)
    -> DsM (MatchResult CoreExpr)
    dsGRHS HsMatchContextRn
    hs_ctx Type
    rhs_ty Nablas
    rhs_nablas (L EpAnnCO
    _ (GRHS XCGRHS GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc))
    _ [GuardLStmt GhcTc]
    guards GenLocated SrcSpanAnnA (HsExpr GhcTc)
    rhs))
      = Nablas -> DsM (MatchResult CoreExpr) -> DsM (MatchResult CoreExpr)
    forall a. Nablas -> DsM a -> DsM a
    updPmNablas Nablas
    rhs_nablas (DsM (MatchResult CoreExpr) -> DsM (MatchResult CoreExpr))
    -> DsM (MatchResult CoreExpr) -> DsM (MatchResult CoreExpr)
    forall a b. (a -> b) -> a -> b
    $
          [GuardStmt GhcTc]
    -> HsMatchContextRn
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards ((GenLocated
       SrcSpanAnnA (Stmt GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))
     -> Stmt GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))
    -> [GenLocated
          SrcSpanAnnA (Stmt GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))]
    -> [Stmt GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc))]
    forall a b. (a -> b) -> [a] -> [b]
    map GenLocated
      SrcSpanAnnA (Stmt GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))
    -> Stmt GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc))
    forall l e. GenLocated l e -> e
    unLoc [GuardLStmt GhcTc]
    [GenLocated
       SrcSpanAnnA (Stmt GhcTc (GenLocated SrcSpanAnnA (HsExpr GhcTc)))]
    guards) HsMatchContextRn
    hs_ctx LHsExpr GhcTc
    GenLocated SrcSpanAnnA (HsExpr GhcTc)
    rhs Type
    rhs_ty

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

    matchGuards :: [GuardStmt GhcTc]     -- Guard
                -> HsMatchContextRn      -- Context
                -> 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]
    -> HsMatchContextRn
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards [] HsMatchContextRn
    _ LHsExpr GhcTc
    rhs Type
    _
      = do  { core_rhs <- LHsExpr GhcTc -> DsM CoreExpr
    dsLExpr LHsExpr GhcTc
    rhs
            ; return (cantFailMatchResult 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) HsMatchContextRn
    ctx LHsExpr GhcTc
    rhs Type
    rhs_ty
      | Just CoreExpr -> DsM CoreExpr
    addTicks <- LHsExpr GhcTc -> Maybe (CoreExpr -> DsM CoreExpr)
    isTrueLHsExpr LHsExpr GhcTc
    e = do
        match_result <- [GuardStmt GhcTc]
    -> HsMatchContextRn
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards [GuardStmt GhcTc]
    stmts HsMatchContextRn
    ctx LHsExpr GhcTc
    rhs Type
    rhs_ty
        return (adjustMatchResultDs addTicks match_result)
    matchGuards (BodyStmt XBodyStmt GhcTc GhcTc (LHsExpr GhcTc)
    _ LHsExpr GhcTc
    expr SyntaxExpr GhcTc
    _ SyntaxExpr GhcTc
    _ : [GuardStmt GhcTc]
    stmts) HsMatchContextRn
    ctx LHsExpr GhcTc
    rhs Type
    rhs_ty = do
        match_result <- [GuardStmt GhcTc]
    -> HsMatchContextRn
    -> LHsExpr GhcTc
    -> Type
    -> DsM (MatchResult CoreExpr)
    matchGuards [GuardStmt GhcTc]
    stmts HsMatchContextRn
    ctx LHsExpr GhcTc
    rhs Type
    rhs_ty
        pred_expr <- dsLExpr expr
        return (mkGuardedMatchResult pred_expr match_result)

    matchGuards (LetStmt XLetStmt GhcTc GhcTc (LHsExpr GhcTc)
    _ HsLocalBinds GhcTc
    binds : [GuardStmt GhcTc]
    stmts) HsMatchContextRn
    ctx LHsExpr GhcTc
    rhs Type
    rhs_ty = do
        ldi_nablas <- DsM Nablas
    getPmNablas
        match_result <- matchGuards stmts ctx rhs rhs_ty
          -- Propagate long-distance information when desugaring let bindings, e.g.
          --
          --  f r@(K1 {})
          --    | let g = fld r
          --    = g
          --
          -- Failing to do so resulted in #25749.
        return (adjustMatchResultDs (updPmNablas ldi_nablas . dsLocalBinds binds) 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) HsMatchContextRn
    ctx LHsExpr GhcTc
    rhs Type
    rhs_ty = do
        let upat :: Pat GhcTc
    upat = GenLocated SrcSpanAnnA (Pat GhcTc) -> Pat GhcTc
    forall l e. GenLocated l e -> e
    unLoc LPat GhcTc
    GenLocated SrcSpanAnnA (Pat GhcTc)
    pat
        match_var <- Type -> Pat GhcTc -> DsM Id
    selectMatchVar Type
    ManyTy Pat GhcTc
    upat
           -- We only allow unrestricted patterns in guards, hence the `Many`
           -- above. It isn't clear what linear patterns would mean, maybe we will
           -- figure it out in the future.

        match_result <- matchGuards stmts ctx rhs rhs_ty
        core_rhs <- dsLExpr bind_rhs
        match_result' <-
          matchSinglePatVar match_var (Just core_rhs) (StmtCtxt $ PatGuard ctx)
          pat rhs_ty match_result
        return $ bindNonRec match_var core_rhs <$> match_result'

    matchGuards (LastStmt  {} : [GuardStmt GhcTc]
    _) HsMatchContextRn
    _ LHsExpr GhcTc
    _ Type
    _ = String -> DsM (MatchResult CoreExpr)
    forall a. HasCallStack => String -> a
    panic String
    "matchGuards LastStmt"
    matchGuards (ParStmt   {} : [GuardStmt GhcTc]
    _) HsMatchContextRn
    _ LHsExpr GhcTc
    _ Type
    _ = String -> DsM (MatchResult CoreExpr)
    forall a. HasCallStack => String -> a
    panic String
    "matchGuards ParStmt"
    matchGuards (TransStmt {} : [GuardStmt GhcTc]
    _) HsMatchContextRn
    _ LHsExpr GhcTc
    _ Type
    _ = String -> DsM (MatchResult CoreExpr)
    forall a. HasCallStack => String -> a
    panic String
    "matchGuards TransStmt"
    matchGuards (RecStmt   {} : [GuardStmt GhcTc]
    _) HsMatchContextRn
    _ LHsExpr GhcTc
    _ Type
    _ = String -> DsM (MatchResult CoreExpr)
    forall a. HasCallStack => String -> a
    panic String
    "matchGuards RecStmt"
    matchGuards (ApplicativeStmt {} : [GuardStmt GhcTc]
    _) HsMatchContextRn
    _ LHsExpr GhcTc
    _ Type
    _ =
      String -> DsM (MatchResult CoreExpr)
    forall a. HasCallStack => 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}
    -}