X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FdeSugar%2FDsExpr.lhs;h=ef69b479893e843f34244b57fb8a6ea0b3538827;hp=11fddf57af96ab769a95d37faad8e6243e42f94b;hb=85f969a6585c06168645114d9524e7169dbc6e32;hpb=fb6d198f498d4e325a540f28aaa6e1d1530839c3

diff --git a/compiler/deSugar/DsExpr.lhs b/compiler/deSugar/DsExpr.lhs
index 11fddf5..ef69b47 100644
--- a/compiler/deSugar/DsExpr.lhs
+++ b/compiler/deSugar/DsExpr.lhs
@@ -323,6 +323,9 @@ dsExpr (HsDo ListComp stmts body result_ty)
 dsExpr (HsDo DoExpr stmts body result_ty)
   = dsDo stmts body result_ty
 
+dsExpr (HsDo GhciStmt stmts body result_ty)
+  = dsDo stmts body result_ty
+
 dsExpr (HsDo (MDoExpr tbl) stmts body result_ty)
   = dsMDo tbl stmts body result_ty
 
@@ -643,6 +646,9 @@ 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.  
 
@@ -656,6 +662,8 @@ dsExplicitList elt_ty xs
        ; let (dynamic_prefix, static_suffix) = spanTail is_static 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) }