From 89e484f7a0e0c5b6a394b93631abfbeb51850c6c Mon Sep 17 00:00:00 2001
From: "simonpj@microsoft.com" <unknown>
Date: Wed, 15 Sep 2010 12:32:19 +0000
Subject: [PATCH] Improve pretty-printing of family instances

Fixed Trac #4246
---
 compiler/types/FamInstEnv.lhs |   24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/compiler/types/FamInstEnv.lhs b/compiler/types/FamInstEnv.lhs
index 4cf33fc..7f698de 100644
--- a/compiler/types/FamInstEnv.lhs
+++ b/compiler/types/FamInstEnv.lhs
@@ -88,15 +88,23 @@ pprFamInst famInst
 	2 (ptext (sLit "--") <+> pprNameLoc (getName famInst))
 
 pprFamInstHdr :: FamInst -> SDoc
-pprFamInstHdr (FamInst {fi_fam = fam, fi_tys = tys, fi_tycon = tycon})
-  = pprTyConSort <+> pprHead
+pprFamInstHdr (FamInst {fi_tycon = rep_tc})
+  = pprTyConSort <+> pp_instance <+> pprHead
   where
-    pprHead = pprTypeApp fam tys
-    pprTyConSort | isDataTyCon     tycon = ptext (sLit "data instance")
-		 | isNewTyCon      tycon = ptext (sLit "newtype instance")
-		 | isSynTyCon      tycon = ptext (sLit "type instance")
-		 | isAbstractTyCon tycon = ptext (sLit "data instance")
-		 | otherwise	         = panic "FamInstEnv.pprFamInstHdr"
+    Just (fam_tc, tys) = tyConFamInst_maybe rep_tc 
+    
+    -- For *associated* types, say "type T Int = blah" 
+    -- For *top level* type instances, say "type instance T Int = blah"
+    pp_instance 
+      | isTyConAssoc fam_tc = empty
+      | otherwise           = ptext (sLit "instance")
+
+    pprHead = pprTypeApp fam_tc tys
+    pprTyConSort | isDataTyCon     rep_tc = ptext (sLit "data")
+		 | isNewTyCon      rep_tc = ptext (sLit "newtype")
+		 | isSynTyCon      rep_tc = ptext (sLit "type")
+		 | isAbstractTyCon rep_tc = ptext (sLit "data")
+		 | otherwise	          = panic "FamInstEnv.pprFamInstHdr"
 
 pprFamInsts :: [FamInst] -> SDoc
 pprFamInsts finsts = vcat (map pprFamInst finsts)
-- 
1.7.10.4