X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FdeSugar%2FDsExpr.lhs;h=509cce23b6e710c4a25a7f0bbf401394d3cf7da1;hb=cd7593af81c290085eb857d5b2d05aeaf9cb2cf0;hp=b91380dcbc043a4748ea56f81d028efad4f86031;hpb=05dce654a3c65e1c7a68ca55f990eed8bd3ec700;p=ghc-hetmet.git

diff --git a/compiler/deSugar/DsExpr.lhs b/compiler/deSugar/DsExpr.lhs
index b91380d..509cce2 100644
--- a/compiler/deSugar/DsExpr.lhs
+++ b/compiler/deSugar/DsExpr.lhs
@@ -47,6 +47,7 @@ import CoreUtils
 import MkCore
 
 import DynFlags
+import StaticFlags
 import CostCentre
 import Id
 import PrelInfo
@@ -272,7 +273,7 @@ dsExpr (HsCoreAnn fs expr)
 dsExpr (HsCase discrim matches@(MatchGroup _ rhs_ty)) 
   | isEmptyMatchGroup matches	-- A Core 'case' is always non-empty
   = 		      		-- So desugar empty HsCase to error call
-    mkErrorAppDs pAT_ERROR_ID (funResultTy rhs_ty) "case"
+    mkErrorAppDs pAT_ERROR_ID (funResultTy rhs_ty) (ptext (sLit "case"))
 
   | otherwise
   = do { core_discrim <- dsLExpr discrim
@@ -395,8 +396,8 @@ dsExpr (RecordCon (L _ data_con_id) con_expr rbinds) = do
           = case findField (rec_flds rbinds) lbl of
               (rhs:rhss) -> ASSERT( null rhss )
                             dsLExpr rhs
-              []         -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
-        unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
+              []         -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (ppr lbl)
+        unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty empty
 
         labels = dataConFieldLabels (idDataCon data_con_id)
         -- The data_con_id is guaranteed to be the wrapper id of the constructor
@@ -609,6 +610,23 @@ allocation in some nofib programs. Specifically
 
 Of course, if rules aren't turned on then there is pretty much no
 point doing this fancy stuff, and it may even be harmful.
+
+=======>  Note by SLPJ Dec 08.
+
+I'm unconvinced that we should *ever* generate a build for an explicit
+list.  See the comments in GHC.Base about the foldr/cons rule, which 
+points out that (foldr k z [a,b,c]) may generate *much* less code than
+(a `k` b `k` c `k` z).
+
+Furthermore generating builds messes up the LHS of RULES. 
+Example: the foldr/single rule in GHC.Base
+   foldr k z [x] = ...
+We do not want to generate a build invocation on the LHS of this RULE!
+
+To test this I've added a (static) flag -fsimple-list-literals, which
+makes all list literals be generated via the simple route.  
+
+
 \begin{code}
 
 dsExplicitList :: PostTcType -> [LHsExpr Id] -> DsM CoreExpr
@@ -616,7 +634,7 @@ dsExplicitList :: PostTcType -> [LHsExpr Id] -> DsM CoreExpr
 dsExplicitList elt_ty xs = do
     dflags <- getDOptsDs
     xs' <- mapM dsLExpr xs
-    if not (dopt Opt_EnableRewriteRules dflags)
+    if  opt_SimpleListLiterals || not (dopt Opt_EnableRewriteRules dflags)
         then return $ mkListExpr elt_ty xs'
         else mkBuildExpr elt_ty (mkSplitExplicitList (thisPackage dflags) xs')
   where