[project @ 2001-07-23 16:27:41 by simonpj]

Wibble

diff --git a/ghc/compiler/types/FunDeps.lhs b/ghc/compiler/types/FunDeps.lhs
index f06c506..e971a20 100644 (file)
--- 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