X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FdeSugar%2FDsGRHSs.lhs;h=eea61bafb2cfae76a00e7215de4fc79de759a9c0;hb=eb57096f08bbccf59e6551b135fbde5ed22a0fa8;hp=63c41d70a46f5e1996f8588c07ebc18dd1fbe1c5;hpb=44f98be5b3bc7aaf2c5961667b16ee8eca3e67c1;p=ghc-hetmet.git

diff --git a/ghc/compiler/deSugar/DsGRHSs.lhs b/ghc/compiler/deSugar/DsGRHSs.lhs
index 63c41d7..eea61ba 100644
--- a/ghc/compiler/deSugar/DsGRHSs.lhs
+++ b/ghc/compiler/deSugar/DsGRHSs.lhs
@@ -1,46 +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}
+module DsGRHSs ( dsGuarded, dsGRHSs ) where
+
 #include "HsVersions.h"
 
-module DsGRHSs ( dsGuarded, dsGRHSs ) where
+import {-# SOURCE #-} DsExpr  ( dsLExpr, dsLocalBinds )
+import {-# SOURCE #-} Match   ( matchSinglePat )
 
-IMP_Ubiq()
-#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ <= 201
-IMPORT_DELOOPER(DsLoop)		-- break dsExpr/dsBinds-ish loop
-#else
-import {-# SOURCE #-} DsExpr  ( dsExpr )
-import {-# SOURCE #-} DsBinds ( dsBinds )
-import {-# SOURCE #-} Match   ( match )
-#endif
-
-import HsSyn		( GRHSsAndBinds(..), GRHS(..),
-			  HsExpr(..), HsBinds, Stmt(..), 
-			  HsLit, Match, Fixity, DoOrListComp, HsType, ArithSeqInfo
-			 )
-import TcHsSyn		( SYN_IE(TypecheckedGRHSsAndBinds), SYN_IE(TypecheckedGRHS),
-			  SYN_IE(TypecheckedPat), SYN_IE(TypecheckedHsBinds),
-			  SYN_IE(TypecheckedHsExpr), SYN_IE(TypecheckedStmt)
-			)
-import CoreSyn		( SYN_IE(CoreBinding), GenCoreBinding(..), SYN_IE(CoreExpr), mkCoLetsAny )
+import HsSyn		( Stmt(..), HsExpr(..), GRHSs(..), GRHS(..), 
+			  LHsExpr, HsMatchContext(..), Pat(..) )
+import CoreSyn		( CoreExpr )
+import Var		( Id )
+import Type		( Type )
 
 import DsMonad
 import DsUtils
-
-#if __GLASGOW_HASKELL__ < 200
-import Id		( GenId )
-#endif
-import CoreUtils	( coreExprType, mkCoreIfThenElse )
-import PrelVals		( nON_EXHAUSTIVE_GUARDS_ERROR_ID )
-import Outputable	( PprStyle(..) )
-import SrcLoc		( SrcLoc{-instance-} )
-import Type             ( SYN_IE(Type) )
-import Unique		( Unique, otherwiseIdKey )
-import UniqFM           ( Uniquable(..) )
-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.
@@ -52,65 +36,39 @@ 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 False{-don't auto scc-} 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 -> Type -> DsM CoreExpr
+
+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}
 
-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
+dsGRHSs :: HsMatchContext Name -> [Pat Id]	-- These are to build a MatchContext from
+	-> GRHSs Id				-- Guarded RHSs
+	-> Type					-- Type of RHS
 	-> 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 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 (dsLocalBinds binds) match_result1
+		-- NB: nested dsLet inside matchResult
     in
-    returnDs (MatchResult CantFail ty expr_fn (DsMatchContext kind pats locn))
+    returnDs match_result2
 
-dsGRHS ty kind pats (GRHS guard expr locn)
-  = putSrcLocDs locn $
-    dsExpr expr 	`thenDs` \ core_expr ->
-    let
-	expr_fn = \ ignore -> core_expr
-    in
-    matchGuard guard (MatchResult CantFail ty expr_fn (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}
 
 
-
-
 %************************************************************************
 %*									*
 %*  matchGuard : make a MatchResult from a guarded RHS			*
@@ -118,34 +76,53 @@ dsGRHS ty kind pats (GRHS guard expr locn)
 %************************************************************************
 
 \begin{code}
-matchGuard :: [TypecheckedStmt] 	-- Guard
-	   -> MatchResult		-- What to do if the guard succeeds
-	   -> DsM MatchResult
-
-matchGuard [] body_result = returnDs body_result
-
-	-- Turn an "otherwise" guard is a no-op
-matchGuard (GuardStmt (HsVar v) _ : stmts) body_result
-  | uniqueOf v == otherwiseIdKey
-  = matchGuard stmts body_result
-
-matchGuard (GuardStmt expr _ : stmts) body_result
-  = matchGuard stmts body_result	`thenDs` \ (MatchResult _ ty body_fn cxt) ->
-    dsExpr expr				`thenDs` \ core_expr ->
-    let
-	expr_fn = \ fail -> mkCoreIfThenElse core_expr (body_fn fail) fail
-    in
-    returnDs (MatchResult CanFail ty expr_fn cxt)
-
-matchGuard (LetStmt binds : stmts) body_result
-  = matchGuard stmts body_result	  `thenDs` \ match_result ->
-    dsBinds False{-don't auto scc-} binds `thenDs` \ core_binds ->
-    returnDs (mkCoLetsMatchResult core_binds match_result)
-
-matchGuard (BindStmt pat rhs _ : stmts) body_result
-  = matchGuard stmts body_result			`thenDs` \ match_result ->
-    dsExpr rhs						`thenDs` \ core_rhs ->
-    newSysLocalDs (coreExprType core_rhs)		`thenDs` \ scrut_var ->
-    match [scrut_var] [EqnInfo [pat] match_result] []	`thenDs` \ match_result' ->
-    returnDs (mkCoLetsMatchResult [NonRec scrut_var core_rhs] match_result')
+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)	
+
+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.  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
+  = matchGuards stmts ctx rhs rhs_ty
+
+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)
+
+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
+	-- 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@
+\begin{verbatim}
+f x | p <- e', let C y# = e, f y# = r1
+    | otherwise 	 = r2 
+\end{verbatim}