#include "HsVersions.h"
-import {-# SOURCE #-} DsExpr ( dsExpr, dsLet )
+import {-# SOURCE #-} DsExpr ( dsLExpr, dsLocalBinds )
import {-# SOURCE #-} Match ( matchSinglePat )
-import HsSyn ( Stmt(..), HsExpr(..), GRHSs(..), GRHS(..), HsMatchContext(..) )
-import TcHsSyn ( TypecheckedGRHSs, TypecheckedPat, TypecheckedStmt, TypecheckedMatchContext )
+import HsSyn ( Stmt(..), HsExpr(..), GRHSs(..), GRHS(..),
+ LHsExpr, HsMatchContext(..), Pat(..) )
import CoreSyn ( CoreExpr )
+import Var ( Id )
import Type ( Type )
import DsMonad
import PrelInfo ( nON_EXHAUSTIVE_GUARDS_ERROR_ID )
import TysWiredIn ( trueDataConId )
import PrelNames ( otherwiseIdKey, hasKey )
+import Name ( Name )
+import SrcLoc ( unLoc, Located(..) )
\end{code}
@dsGuarded@ is used for both @case@ expressions and pattern bindings.
necessary. The type argument gives the type of the @ei@.
\begin{code}
-dsGuarded :: TypecheckedGRHSs -> DsM CoreExpr
+dsGuarded :: GRHSs Id -> Type -> DsM CoreExpr
-dsGuarded grhss
- = dsGRHSs PatBindRhs [] grhss `thenDs` \ (err_ty, match_result) ->
- mkErrorAppDs nON_EXHAUSTIVE_GUARDS_ERROR_ID err_ty "" `thenDs` \ error_expr ->
+dsGuarded grhss rhs_ty
+ = dsGRHSs PatBindRhs [] grhss rhs_ty `thenDs` \ match_result ->
+ mkErrorAppDs nON_EXHAUSTIVE_GUARDS_ERROR_ID rhs_ty "" `thenDs` \ error_expr ->
extractMatchResult match_result error_expr
\end{code}
In contrast, @dsGRHSs@ produces a @MatchResult@.
\begin{code}
-dsGRHSs :: TypecheckedMatchContext -> [TypecheckedPat] -- These are to build a MatchContext from
- -> TypecheckedGRHSs -- Guarded RHSs
- -> DsM (Type, MatchResult)
+dsGRHSs :: HsMatchContext Name -> [Pat Id] -- These are to build a MatchContext from
+ -> GRHSs Id -- Guarded RHSs
+ -> Type -- Type of RHS
+ -> DsM MatchResult
-dsGRHSs kind pats (GRHSs grhss binds ty)
- = mapDs (dsGRHS kind pats) grhss `thenDs` \ match_results ->
+dsGRHSs hs_ctx pats (GRHSs grhss binds) rhs_ty
+ = mappM (dsGRHS hs_ctx pats rhs_ty) grhss `thenDs` \ match_results ->
let
match_result1 = foldr1 combineMatchResults match_results
- match_result2 = adjustMatchResultDs (dsLet binds) match_result1
+ match_result2 = adjustMatchResultDs (dsLocalBinds binds) match_result1
-- NB: nested dsLet inside matchResult
in
- returnDs (ty, match_result2)
+ returnDs match_result2
-dsGRHS kind pats (GRHS guard locn)
- = matchGuard guard (DsMatchContext kind pats locn)
+dsGRHS hs_ctx pats rhs_ty (L loc (GRHS guards rhs))
+ = matchGuards (map unLoc guards) hs_ctx rhs rhs_ty
\end{code}
%************************************************************************
\begin{code}
-matchGuard :: [TypecheckedStmt] -- Guard
- -> DsMatchContext -- Context
- -> DsM MatchResult
+matchGuards :: [Stmt Id] -- Guard
+ -> HsMatchContext Name -- Context
+ -> LHsExpr Id -- RHS
+ -> Type -- Type of RHS of guard
+ -> DsM MatchResult
-- See comments with HsExpr.Stmt re what an ExprStmt means
-- Here we must be in a guard context (not do-expression, nor list-comp)
-matchGuard [ResultStmt expr locn] ctx
- = putSrcLocDs locn (dsExpr expr) `thenDs` \ core_expr ->
- returnDs (cantFailMatchResult core_expr)
+matchGuards [] ctx rhs rhs_ty
+ = do { core_rhs <- dsLExpr rhs
+ ; return (cantFailMatchResult core_rhs) }
-- ExprStmts must be guards
- -- Turn an "otherwise" guard is a no-op
-matchGuard (ExprStmt (HsVar v) _ _ : stmts) ctx
+ -- 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 HsCoerce constructors
+ -- If it does, you'll get bogus overlap warnings
+matchGuards (ExprStmt (L _ (HsVar v)) _ _ : stmts) ctx rhs rhs_ty
| v `hasKey` otherwiseIdKey
|| v `hasKey` getUnique trueDataConId
- -- trueDataConId doesn't have the same
- -- unique as trueDataCon
- = matchGuard stmts ctx
+ -- trueDataConId doesn't have the same unique as trueDataCon
+ = matchGuards stmts ctx rhs rhs_ty
-matchGuard (ExprStmt expr _ locn : stmts) ctx
- = matchGuard stmts ctx `thenDs` \ match_result ->
- putSrcLocDs locn (dsExpr expr) `thenDs` \ pred_expr ->
+matchGuards (ExprStmt expr _ _ : stmts) ctx rhs rhs_ty
+ = matchGuards stmts ctx rhs rhs_ty `thenDs` \ match_result ->
+ dsLExpr expr `thenDs` \ pred_expr ->
returnDs (mkGuardedMatchResult pred_expr match_result)
-matchGuard (LetStmt binds : stmts) ctx
- = matchGuard stmts ctx `thenDs` \ match_result ->
- returnDs (adjustMatchResultDs (dsLet binds) match_result)
+matchGuards (LetStmt binds : stmts) ctx rhs rhs_ty
+ = matchGuards stmts ctx rhs rhs_ty `thenDs` \ match_result ->
+ returnDs (adjustMatchResultDs (dsLocalBinds binds) match_result)
-- NB the dsLet occurs inside the match_result
-
-matchGuard (BindStmt pat rhs locn : stmts) ctx
- = matchGuard stmts ctx `thenDs` \ match_result ->
- putSrcLocDs locn (dsExpr rhs) `thenDs` \ core_rhs ->
- matchSinglePat core_rhs ctx pat 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 bind_rhs _ _ : stmts) ctx rhs rhs_ty
+ = matchGuards stmts ctx rhs rhs_ty `thenDs` \ match_result ->
+ dsLExpr bind_rhs `thenDs` \ core_rhs ->
+ matchSinglePat core_rhs ctx pat rhs_ty match_result
\end{code}
Should {\em fail} if @e@ returns @D@
projects / ghc-hetmet.git / blobdiff