X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FcoreSyn%2FCoreArity.lhs;h=f39b6b92352ebe07a18c5851a536dc73423e9b1b;hb=21eea25f1212ec306aac806233a2ec048212d529;hp=0d1b394db212c613b62c050d197f78e5fca9f465;hpb=62eeda5aed31173b234b2965ccf4bd6979ffd9a4;p=ghc-hetmet.git

diff --git a/compiler/coreSyn/CoreArity.lhs b/compiler/coreSyn/CoreArity.lhs
index 0d1b394..f39b6b9 100644
--- a/compiler/coreSyn/CoreArity.lhs
+++ b/compiler/coreSyn/CoreArity.lhs
@@ -22,11 +22,9 @@ import CoreSubst ( Subst, substBndr, substBndrs, substExpr
        		 , mkEmptySubst, isEmptySubst )
 import Var
 import VarEnv
-#if mingw32_TARGET_OS
-import Packages
-#endif
 import Id
 import Type
+import TcType	( isDictLikeTy )
 import Coercion
 import BasicTypes
 import Unique
@@ -296,7 +294,7 @@ arityType dflags (Let b e)
   where
     cheap_bind (NonRec b e) = is_cheap (b,e)
     cheap_bind (Rec prs)    = all is_cheap prs
-    is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
+    is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictLikeTy (idType b))
 		   || exprIsCheap e
 	-- If the experimental -fdicts-cheap flag is on, we eta-expand through
 	-- dictionary bindings.  This improves arities. Thereby, it also
@@ -314,6 +312,9 @@ arityType dflags (Let b e)
 	--
 	-- One could go further and make exprIsCheap reply True to any
 	-- dictionary-typed expression, but that's more work.
+	-- 
+	-- See Note [Dictionary-like types] in TcType.lhs for why we use
+	-- isDictLikeTy here rather than isDictTy
 
 arityType _ _ = ATop
 \end{code}