X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FdeSugar%2FDsGRHSs.lhs;h=60c67bc440eef4efcb619951fdc91aa51460a419;hb=550421384b8364cdaf3135f7859c9f7d7ee1fff1;hp=938d8657ed0fe4f99a035b1ebc797e9851a79964;hpb=7b0181919416d8f04324575b7e17031ca692f5b0;p=ghc-hetmet.git

diff --git a/ghc/compiler/deSugar/DsGRHSs.lhs b/ghc/compiler/deSugar/DsGRHSs.lhs
index 938d865..60c67bc 100644
--- a/ghc/compiler/deSugar/DsGRHSs.lhs
+++ b/ghc/compiler/deSugar/DsGRHSs.lhs
@@ -1,32 +1,30 @@
 %
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1994
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
 %
 \section[DsGRHSs]{Matching guarded right-hand-sides (GRHSs)}
 
 \begin{code}
-#include "HsVersions.h"
-
 module DsGRHSs ( dsGuarded, dsGRHSs ) where
 
-import Ubiq
-import DsLoop		-- break dsExpr/dsBinds-ish loop
+#include "HsVersions.h"
+
+import {-# SOURCE #-} DsExpr  ( dsLExpr, dsLet )
+import {-# SOURCE #-} Match   ( matchSinglePat )
 
-import HsSyn		( GRHSsAndBinds(..), GRHS(..),
-			  HsExpr, HsBinds )
-import TcHsSyn		( TypecheckedGRHSsAndBinds(..), TypecheckedGRHS(..),
-			  TypecheckedPat(..), TypecheckedHsBinds(..),
-			  TypecheckedHsExpr(..)	)
-import CoreSyn		( CoreBinding(..), CoreExpr(..), mkCoLetsAny )
+import HsSyn		( Stmt(..), HsExpr(..), GRHSs(..), GRHS(..), 
+			  HsMatchContext(..), Pat(..), LStmt )
+import CoreSyn		( CoreExpr )
+import Type		( Type )
+import Var		( Id )
 
 import DsMonad
 import DsUtils
-
-import CoreUtils	( mkCoreIfThenElse )
-import PrelInfo		( stringTy, nON_EXHAUSTIVE_GUARDS_ERROR_ID )
-import PprStyle		( PprStyle(..) )
-import Pretty		( ppShow )
-import SrcLoc		( SrcLoc{-instance-} )
-import Util		( panic )
+import Unique		( Uniquable(..) )
+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.
@@ -38,63 +36,83 @@ It desugars:
 	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.
+necessary.  The type argument gives the type of the @ei@.
 
 \begin{code}
-dsGuarded :: TypecheckedGRHSsAndBinds
-	  -> DsM CoreExpr
-
-dsGuarded (GRHSsAndBindsOut grhss binds err_ty)
-  = dsBinds binds				`thenDs` \ core_binds ->
-    dsGRHSs err_ty PatBindMatch [] grhss 	`thenDs` \ (MatchResult can_it_fail _ core_grhss_fn _) ->
-    case can_it_fail of
-	CantFail -> returnDs (mkCoLetsAny core_binds (core_grhss_fn (panic "It can't fail")))
-	CanFail  -> mkErrorAppDs nON_EXHAUSTIVE_GUARDS_ERROR_ID err_ty "" `thenDs` \ error_expr ->
-		    returnDs (mkCoLetsAny core_binds (core_grhss_fn error_expr))
+dsGuarded :: GRHSs Id -> DsM CoreExpr
+
+dsGuarded grhss
+  = dsGRHSs PatBindRhs [] grhss 				`thenDs` \ (err_ty, match_result) ->
+    mkErrorAppDs nON_EXHAUSTIVE_GUARDS_ERROR_ID err_ty ""	`thenDs` \ error_expr ->
+    extractMatchResult match_result error_expr
 \end{code}
 
-Desugar a list of (grhs, expr) pairs [grhs = guarded
-right-hand-side], as in:
-\begin{verbatim}
-p | g1 = e1
-  | g2 = e2
-  ...
-  | gm = em
-\end{verbatim}
-We supply a @CoreExpr@ for the case in which all of
-the guards fail.
+In contrast, @dsGRHSs@ produces a @MatchResult@.
 
 \begin{code}
-dsGRHSs :: Type				-- Type of RHSs
-	-> DsMatchKind -> [TypecheckedPat]	-- These are to build a MatchContext from
-	-> [TypecheckedGRHS]			-- Guarded RHSs
-	-> DsM MatchResult
-
-dsGRHSs ty kind pats [grhs] = dsGRHS ty kind pats grhs
-
-dsGRHSs ty kind pats (grhs:grhss)
-  = dsGRHS ty kind pats grhs	`thenDs` \ match_result1 ->
-    dsGRHSs ty kind pats grhss	`thenDs` \ match_result2 ->
-    combineGRHSMatchResults match_result1 match_result2
-
-dsGRHS ty kind pats (OtherwiseGRHS expr locn)
-  = putSrcLocDs locn		 (
-    dsExpr expr 	`thenDs` \ core_expr ->
-    let
-	expr_fn = \ ignore -> core_expr
+dsGRHSs :: HsMatchContext Name -> [Pat Id]	-- These are to build a MatchContext from
+	-> GRHSs Id				-- Guarded RHSs
+	-> DsM (Type, MatchResult)
+
+dsGRHSs kind pats (GRHSs grhss binds ty)
+  = mappM (dsGRHS kind pats) grhss		`thenDs` \ match_results ->
+    let 
+	match_result1 = foldr1 combineMatchResults match_results
+	match_result2 = adjustMatchResultDs (dsLet binds) match_result1
+		-- NB: nested dsLet inside matchResult
     in
-    returnDs (MatchResult CantFail ty expr_fn (DsMatchContext kind pats locn))
-    )
-
-dsGRHS ty kind pats (GRHS guard expr locn)
-  = putSrcLocDs locn		 (
-    dsExpr guard 	`thenDs` \ core_guard ->
-    dsExpr expr  	`thenDs` \ core_expr  ->
-    let
-	expr_fn = \ fail -> mkCoreIfThenElse core_guard core_expr fail
-    in
-    returnDs (MatchResult CanFail ty expr_fn (DsMatchContext kind pats locn))
-    )
+    returnDs (ty, match_result2)
+
+dsGRHS kind pats (L loc (GRHS guard))
+  = matchGuard (map unLoc guard) (DsMatchContext kind pats loc)
 \end{code}
 
 
+%************************************************************************
+%*									*
+%*  matchGuard : make a MatchResult from a guarded RHS			*
+%*									*
+%************************************************************************
+
+\begin{code}
+matchGuard :: [Stmt Id] 	-- Guard
+           -> DsMatchContext            -- Context
+	   -> 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] ctx 
+  = dsLExpr expr 	`thenDs` \ core_expr ->
+    returnDs (cantFailMatchResult core_expr)
+
+	-- ExprStmts must be guards
+	-- Turn an "otherwise" guard is a no-op
+matchGuard (ExprStmt (L _ (HsVar v)) _ : stmts) ctx
+  |  v `hasKey` otherwiseIdKey
+  || v `hasKey` getUnique trueDataConId	
+	-- trueDataConId doesn't have the same 
+	-- unique as trueDataCon
+  = matchGuard stmts ctx
+
+matchGuard (ExprStmt expr _ : stmts) ctx
+  = matchGuard stmts ctx 	`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)
+	-- NB the dsLet occurs inside the match_result
+
+matchGuard (BindStmt pat rhs : stmts) ctx
+  = matchGuard stmts ctx 		`thenDs` \ match_result ->
+    dsLExpr rhs				`thenDs` \ core_rhs ->
+    matchSinglePat core_rhs ctx pat match_result
+\end{code}
+
+Should {\em fail} if @e@ returns @D@
+\begin{verbatim}
+f x | p <- e', let C y# = e, f y# = r1
+    | otherwise 	 = r2 
+\end{verbatim}