X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FdeSugar%2FDsExpr.lhs;h=a58e9b4b892b8fcb5def528fa338874413f6fbb3;hb=4573fe62a3672b8668ddd4705d770540b10e6e81;hp=d8bd7cdeeae27ed309bb45f15fc446877c9d7163;hpb=eeef817a869bdbfa8820608be081f133dad71071;p=ghc-hetmet.git

diff --git a/compiler/deSugar/DsExpr.lhs b/compiler/deSugar/DsExpr.lhs
index d8bd7cd..a58e9b4 100644
--- a/compiler/deSugar/DsExpr.lhs
+++ b/compiler/deSugar/DsExpr.lhs
@@ -643,6 +643,9 @@ 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!
 
+We fix this by disabling rules in rule LHSs, and testing that
+flag here; see Note [Desugaring RULE left hand sides] in Desugar
+
 To test this I've added a (static) flag -fsimple-list-literals, which
 makes all list literals be generated via the simple route.  
 
@@ -657,6 +660,7 @@ dsExplicitList elt_ty xs
        ; if opt_SimpleListLiterals 	       		-- -fsimple-list-literals
          || not (dopt Opt_EnableRewriteRules dflags)	-- Rewrite rules off
 	    	-- Don't generate a build if there are no rules to eliminate it!
+		-- See Note [Desugaring RULE left hand sides] in Desugar
          || null dynamic_prefix   -- Avoid build (\c n. foldr c n xs)!
          then return $ mkListExpr elt_ty xs'
          else mkBuildExpr elt_ty (mkSplitExplicitList dynamic_prefix static_suffix) }