fix bug in unification

diff --git a/src/HM.hs b/src/HM.hs
index e643938..9591706 100644 (file)
--- a/src/HM.hs
+++ b/src/HM.hs
@@ -86,7 +86,7 @@ unify (TypeVar a) t = varBind a t
 unify t (TypeVar a) = varBind a t
 unify (TypeFunction a b) (TypeFunction a' b') = do
   s1 <- unify a a'
-  s2 <- unify b b'
+  s2 <- unify (substituteT s1 b) (substituteT s1 b')
   return $ s1 `composeSub` s2
 unify (Primitive a) (Primitive b) | a == b = return idSub
 unify a b = fail $ "cannot unify " ++ show a ++ " with " ++ show b
@@ -127,7 +127,6 @@ ti e (NTTerm (Let x a b)) = do
       e' = Map.insert x t' e
   (s2, t2) <- ti (Map.map (substituteS s1) e') b
   return (s1 `composeSub` s2, t2)
-  
  
 algW :: TypedTerm -> Either String Type
 algW t = fst . runTI $ do