From: simonpj <unknown>
Date: Thu, 11 Mar 2004 14:29:59 +0000 (+0000)
Subject: [project @ 2004-03-11 14:29:59 by simonpj]
X-Git-Tag: Approx_11550_changesets_converted~7
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=d4b980043211a2b1e7a24a6efd9e21e9853dcde0;p=ghc-hetmet.git

[project @ 2004-03-11 14:29:59 by simonpj]
Add sanity check
---

diff --git a/ghc/compiler/types/InstEnv.lhs b/ghc/compiler/types/InstEnv.lhs
index cc75492..905cde2 100644
--- a/ghc/compiler/types/InstEnv.lhs
+++ b/ghc/compiler/types/InstEnv.lhs
@@ -299,7 +299,10 @@ lookup_inst_env env key_cls key_tys
 	  Nothing 
 		-- Does not match, so next check whether the things unify
 		-- [see notes about overlapping instances above]
-	   -> case unifyTyListsX (key_vars `unionVarSet` tpl_tyvars) key_tys tpl of
+	   -> ASSERT( not (key_vars `intersectsVarSet` tpl_tyvars) )
+		-- Unification will break badly if the variables overlap
+		-- They shouldn't because we allocate separate uniques for them
+	      case unifyTyListsX (key_vars `unionVarSet` tpl_tyvars) key_tys tpl of
 	        Just _   -> find rest ms (dfun_id:us)
 	        Nothing  -> find rest ms us