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


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

{-# LANGUAGE CPP #-}
{-# LANGUAGE ViewPatterns #-}

module DsGRHSs ( dsGuarded, dsGRHSs, dsGRHS, isTrueLHsExpr ) where

#include "HsVersions.h"

import GhcPrelude

import {-# SOURCE #-} DsExpr  ( dsLExpr, dsLocalBinds )
import {-# SOURCE #-} Match   ( matchSinglePatVar )

import HsSyn
import MkCore
import CoreSyn
import CoreUtils (bindNonRec)

import Check (genCaseTmCs2)
import DsMonad
import DsUtils
import Type   ( Type )
import Name
import Util
import SrcLoc
import Outputable

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

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

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

dsGRHSs :: HsMatchContext Name
        -> GRHSs GhcTc (LHsExpr GhcTc)          -- Guarded RHSs
        -> Type                                 -- Type of RHS
        -> DsM MatchResult
dsGRHSs :: HsMatchContext Name
-> GRHSs GhcTc (LHsExpr GhcTc) -> Type -> DsM MatchResult
dsGRHSs hs_ctx :: HsMatchContext Name
hs_ctx (GRHSs _ grhss :: [LGRHS GhcTc (LHsExpr GhcTc)]
grhss binds :: LHsLocalBinds GhcTc
binds) rhs_ty :: Type
rhs_ty
  = ASSERT( notNull grhss )
    do { [MatchResult]
match_results <- (LGRHS GhcTc (LHsExpr GhcTc) -> DsM MatchResult)
-> [LGRHS GhcTc (LHsExpr GhcTc)]
-> IOEnv (Env DsGblEnv DsLclEnv) [MatchResult]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM (HsMatchContext Name
-> Type -> LGRHS GhcTc (LHsExpr GhcTc) -> DsM MatchResult
dsGRHS HsMatchContext Name
hs_ctx Type
rhs_ty) [LGRHS GhcTc (LHsExpr GhcTc)]
grhss
       ; let match_result1 :: MatchResult
match_result1 = (MatchResult -> MatchResult -> MatchResult)
-> [MatchResult] -> MatchResult
forall (t :: * -> *) a. Foldable t => (a -> a -> a) -> t a -> a
foldr1 MatchResult -> MatchResult -> MatchResult
combineMatchResults [MatchResult]
match_results
             match_result2 :: MatchResult
match_result2 = (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
adjustMatchResultDs (LHsLocalBinds GhcTc -> CoreExpr -> DsM CoreExpr
dsLocalBinds LHsLocalBinds GhcTc
binds) MatchResult
match_result1
                             -- NB: nested dsLet inside matchResult
       ; MatchResult -> DsM MatchResult
forall (m :: * -> *) a. Monad m => a -> m a
return MatchResult
match_result2 }
dsGRHSs _ (XGRHSs _) _ = String -> DsM MatchResult
forall a. String -> a
panic "dsGRHSs"

dsGRHS :: HsMatchContext Name -> Type -> LGRHS GhcTc (LHsExpr GhcTc)
       -> DsM MatchResult
dsGRHS :: HsMatchContext Name
-> Type -> LGRHS GhcTc (LHsExpr GhcTc) -> DsM MatchResult
dsGRHS hs_ctx :: HsMatchContext Name
hs_ctx rhs_ty :: Type
rhs_ty (LGRHS GhcTc (LHsExpr GhcTc)
-> Located (SrcSpanLess (LGRHS GhcTc (LHsExpr GhcTc)))
forall a. HasSrcSpan a => a -> Located (SrcSpanLess a)
dL->L _ (GRHS _ guards rhs))
  = [GuardStmt GhcTc]
-> HsStmtContext Name -> LHsExpr GhcTc -> Type -> DsM MatchResult
matchGuards ((GuardLStmt GhcTc -> GuardStmt GhcTc)
-> [GuardLStmt GhcTc] -> [GuardStmt GhcTc]
forall a b. (a -> b) -> [a] -> [b]
map GuardLStmt GhcTc -> GuardStmt GhcTc
forall a. HasSrcSpan a => a -> SrcSpanLess a
unLoc [GuardLStmt GhcTc]
guards) (HsMatchContext Name -> HsStmtContext Name
forall id. HsMatchContext id -> HsStmtContext id
PatGuard HsMatchContext Name
hs_ctx) LHsExpr GhcTc
rhs Type
rhs_ty
dsGRHS _ _ (LGRHS GhcTc (LHsExpr GhcTc)
-> Located (SrcSpanLess (LGRHS GhcTc (LHsExpr GhcTc)))
forall a. HasSrcSpan a => a -> Located (SrcSpanLess a)
dL->L _ (XGRHS _)) = String -> DsM MatchResult
forall a. String -> a
panic "dsGRHS"
dsGRHS _ _ _ = String -> DsM MatchResult
forall a. String -> a
panic "dsGRHS: Impossible Match" -- due to #15884

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

matchGuards :: [GuardStmt GhcTc]     -- Guard
            -> HsStmtContext Name    -- Context
            -> LHsExpr GhcTc         -- RHS
            -> Type                  -- Type of RHS of guard
            -> DsM MatchResult

-- 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 Name -> LHsExpr GhcTc -> Type -> DsM MatchResult
matchGuards [] _ rhs :: LHsExpr GhcTc
rhs _
  = do  { CoreExpr
core_rhs <- LHsExpr GhcTc -> DsM CoreExpr
dsLExpr LHsExpr GhcTc
rhs
        ; MatchResult -> DsM MatchResult
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreExpr -> MatchResult
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 _ e :: LHsExpr GhcTc
e _ _ : stmts :: [GuardStmt GhcTc]
stmts) ctx :: HsStmtContext Name
ctx rhs :: LHsExpr GhcTc
rhs rhs_ty :: Type
rhs_ty
  | Just addTicks :: CoreExpr -> DsM CoreExpr
addTicks <- LHsExpr GhcTc -> Maybe (CoreExpr -> DsM CoreExpr)
isTrueLHsExpr LHsExpr GhcTc
e = do
    MatchResult
match_result <- [GuardStmt GhcTc]
-> HsStmtContext Name -> LHsExpr GhcTc -> Type -> DsM MatchResult
matchGuards [GuardStmt GhcTc]
stmts HsStmtContext Name
ctx LHsExpr GhcTc
rhs Type
rhs_ty
    MatchResult -> DsM MatchResult
forall (m :: * -> *) a. Monad m => a -> m a
return ((CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
adjustMatchResultDs CoreExpr -> DsM CoreExpr
addTicks MatchResult
match_result)
matchGuards (BodyStmt _ expr :: LHsExpr GhcTc
expr _ _ : stmts :: [GuardStmt GhcTc]
stmts) ctx :: HsStmtContext Name
ctx rhs :: LHsExpr GhcTc
rhs rhs_ty :: Type
rhs_ty = do
    MatchResult
match_result <- [GuardStmt GhcTc]
-> HsStmtContext Name -> LHsExpr GhcTc -> Type -> DsM MatchResult
matchGuards [GuardStmt GhcTc]
stmts HsStmtContext Name
ctx LHsExpr GhcTc
rhs Type
rhs_ty
    CoreExpr
pred_expr <- LHsExpr GhcTc -> DsM CoreExpr
dsLExpr LHsExpr GhcTc
expr
    MatchResult -> DsM MatchResult
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreExpr -> MatchResult -> MatchResult
mkGuardedMatchResult CoreExpr
pred_expr MatchResult
match_result)

matchGuards (LetStmt _ binds :: LHsLocalBinds GhcTc
binds : stmts :: [GuardStmt GhcTc]
stmts) ctx :: HsStmtContext Name
ctx rhs :: LHsExpr GhcTc
rhs rhs_ty :: Type
rhs_ty = do
    MatchResult
match_result <- [GuardStmt GhcTc]
-> HsStmtContext Name -> LHsExpr GhcTc -> Type -> DsM MatchResult
matchGuards [GuardStmt GhcTc]
stmts HsStmtContext Name
ctx LHsExpr GhcTc
rhs Type
rhs_ty
    MatchResult -> DsM MatchResult
forall (m :: * -> *) a. Monad m => a -> m a
return ((CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
adjustMatchResultDs (LHsLocalBinds GhcTc -> CoreExpr -> DsM CoreExpr
dsLocalBinds LHsLocalBinds GhcTc
binds) MatchResult
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 _ pat :: LPat GhcTc
pat bind_rhs :: LHsExpr GhcTc
bind_rhs _ _ : stmts :: [GuardStmt GhcTc]
stmts) ctx :: HsStmtContext Name
ctx rhs :: LHsExpr GhcTc
rhs rhs_ty :: Type
rhs_ty = do
    let upat :: SrcSpanLess (LPat GhcTc)
upat = LPat GhcTc -> SrcSpanLess (LPat GhcTc)
forall a. HasSrcSpan a => a -> SrcSpanLess a
unLoc LPat GhcTc
pat
        dicts :: Bag Id
dicts = LPat GhcTc -> Bag Id
collectEvVarsPat LPat GhcTc
upat
    Id
match_var <- LPat GhcTc -> DsM Id
selectMatchVar LPat GhcTc
upat
    Bag SimpleEq
tm_cs <- Maybe (LHsExpr GhcTc) -> [LPat GhcTc] -> [Id] -> DsM (Bag SimpleEq)
genCaseTmCs2 (LHsExpr GhcTc -> Maybe (LHsExpr GhcTc)
forall a. a -> Maybe a
Just LHsExpr GhcTc
bind_rhs) [LPat GhcTc
upat] [Id
match_var]
    MatchResult
match_result <- Bag Id -> DsM MatchResult -> DsM MatchResult
forall a. Bag Id -> DsM a -> DsM a
addDictsDs Bag Id
dicts (DsM MatchResult -> DsM MatchResult)
-> DsM MatchResult -> DsM MatchResult
forall a b. (a -> b) -> a -> b
$
                    Bag SimpleEq -> DsM MatchResult -> DsM MatchResult
forall a. Bag SimpleEq -> DsM a -> DsM a
addTmCsDs Bag SimpleEq
tm_cs  (DsM MatchResult -> DsM MatchResult)
-> DsM MatchResult -> DsM MatchResult
forall a b. (a -> b) -> a -> b
$
                      -- See Note [Type and Term Equality Propagation] in Check
                    [GuardStmt GhcTc]
-> HsStmtContext Name -> LHsExpr GhcTc -> Type -> DsM MatchResult
matchGuards [GuardStmt GhcTc]
stmts HsStmtContext Name
ctx LHsExpr GhcTc
rhs Type
rhs_ty
    CoreExpr
core_rhs <- LHsExpr GhcTc -> DsM CoreExpr
dsLExpr LHsExpr GhcTc
bind_rhs
    MatchResult
match_result' <- Id
-> HsMatchContext Name
-> LPat GhcTc
-> Type
-> MatchResult
-> DsM MatchResult
matchSinglePatVar Id
match_var (HsStmtContext Name -> HsMatchContext Name
forall id. HsStmtContext id -> HsMatchContext id
StmtCtxt HsStmtContext Name
ctx) LPat GhcTc
pat Type
rhs_ty
                                       MatchResult
match_result
    MatchResult -> DsM MatchResult
forall (f :: * -> *) a. Applicative f => a -> f a
pure (MatchResult -> DsM MatchResult) -> MatchResult -> DsM MatchResult
forall a b. (a -> b) -> a -> b
$ DsWrapper -> MatchResult -> MatchResult
adjustMatchResult (Id -> CoreExpr -> DsWrapper
bindNonRec Id
match_var CoreExpr
core_rhs) MatchResult
match_result'

matchGuards (LastStmt  {} : _) _ _ _ = String -> DsM MatchResult
forall a. String -> a
panic "matchGuards LastStmt"
matchGuards (ParStmt   {} : _) _ _ _ = String -> DsM MatchResult
forall a. String -> a
panic "matchGuards ParStmt"
matchGuards (TransStmt {} : _) _ _ _ = String -> DsM MatchResult
forall a. String -> a
panic "matchGuards TransStmt"
matchGuards (RecStmt   {} : _) _ _ _ = String -> DsM MatchResult
forall a. String -> a
panic "matchGuards RecStmt"
matchGuards (ApplicativeStmt {} : _) _ _ _ =
  String -> DsM MatchResult
forall a. String -> a
panic "matchGuards ApplicativeLastStmt"
matchGuards (XStmtLR {} : _) _ _ _ =
  String -> DsM MatchResult
forall a. String -> a
panic "matchGuards XStmtLR"

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