From 9528fa3e6229f36e424c5e327255694066017e10 Mon Sep 17 00:00:00 2001
From: simonpj <unknown>
Date: Mon, 23 Jul 2001 16:27:41 +0000
Subject: [PATCH] [project @ 2001-07-23 16:27:41 by simonpj] Wibble

---
 ghc/compiler/types/FunDeps.lhs |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/ghc/compiler/types/FunDeps.lhs b/ghc/compiler/types/FunDeps.lhs
index f06c506..e971a20 100644
--- a/ghc/compiler/types/FunDeps.lhs
+++ b/ghc/compiler/types/FunDeps.lhs
@@ -289,10 +289,12 @@ checkClsFD qtvs fd clas_tvs tys1 tys2
 	Nothing   -> []
 	Just unif -> [ (qtvs', substTy full_unif r1, substTy full_unif r2)
 		     | (r1,r2) <- rs1 `zip` rs2,
-		       not (maybeToBool (unifyExtendTysX qtvs' unif r1 r2))]
+		       not (maybeToBool (unifyExtendTysX qtvs unif r1 r2))]
 			-- Don't include any equations that already hold
 			-- taking account of the fact that any qtvs that aren't 
 			-- already instantiated can be instantiated to anything at all
+			-- NB: qtvs, not qtvs' because unifyExtendTysX only tries to
+			--     look template tyvars up in the substitution
 		  where
 		    full_unif = mkSubst emptyInScopeSet unif
 			-- No for-alls in sight; hmm
-- 
1.7.10.4