X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;ds=sidebyside;f=ghc%2Fcompiler%2Fiface%2FTcIface.lhs;h=39eadfb681b61453db59be4dc4970b66f2d2b797;hb=9d458d01d2a75b1e452ba00c4e76f3c3d0bc5ba6;hp=071948bde4e8fb61f7696dceea9627d856b2176f;hpb=c7c96efc57e5a08e704f13dd05c1baf2c568eb40;p=ghc-hetmet.git

diff --git a/ghc/compiler/iface/TcIface.lhs b/ghc/compiler/iface/TcIface.lhs
index 071948b..39eadfb 100644
--- a/ghc/compiler/iface/TcIface.lhs
+++ b/ghc/compiler/iface/TcIface.lhs
@@ -29,7 +29,7 @@ import HscTypes		( ExternalPackageState(..), PackageInstEnv, PackageRuleBase,
 			  HscEnv, TyThing(..), implicitTyThings, typeEnvIds,
 			  ModIface(..), ModDetails(..), InstPool, ModGuts,
 			  TypeEnv, mkTypeEnv, extendTypeEnvList, lookupTypeEnv,
-			  DeclPool, RulePool, Pool(..), Gated, addRuleToPool )
+			  RulePool, Pool(..) )
 import InstEnv		( extendInstEnv )
 import CoreSyn
 import PprCore		( pprIdRules )
@@ -529,8 +529,9 @@ selectInsts pool@(Pool insts n_in n_out) cls tycons
 
 	-- Reverses the gated decls, but that doesn't matter
     choose2 (gis, decls) (gates, decl)
-	| any (`elem` tycons) gates = (gis, 	           decl:decls)
-	| otherwise		    = ((gates,decl) : gis, decls)
+	|  null gates 	-- Happens when we have 'instance T a where ...'
+        || any (`elem` tycons) gates = (gis, 	           decl:decls)
+	| otherwise		     = ((gates,decl) : gis, decls)
 \end{code}
 
 %************************************************************************
@@ -586,7 +587,7 @@ selectRules (Pool rules n_in n_out) type_env
 	| null gates' = (pool, rule:if_rules)
 	| otherwise   = ((gates',rule) : pool, if_rules)
 	where
-	  gates' = filter (`elemNameEnv` type_env) gates
+	  gates' = filter (not . (`elemNameEnv` type_env)) gates
 
 
 tcIfaceRule :: IfaceRule -> IfL IdCoreRule