X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcUnify.lhs;h=709b7c4aab0bae2d21562c3d5fe8f1e650ee67a9;hb=a162b85d26966ba0eecc4d2ae02d4fd71f5cb9f8;hp=7ce2fca0654167428c91a0fa01b5c95dcd672693;hpb=467f588c25e6d7825a11eff018a67727b3dea71b;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcUnify.lhs b/compiler/typecheck/TcUnify.lhs
index 7ce2fca..709b7c4 100644
--- a/compiler/typecheck/TcUnify.lhs
+++ b/compiler/typecheck/TcUnify.lhs
@@ -60,6 +60,7 @@ import BasicTypes
 import Util
 import Outputable
 import Unique
+import FastString
 
 import Control.Monad
 \end{code}
@@ -615,6 +616,12 @@ boxy_match tmpl_tvs orig_tmpl_ty boxy_tvs orig_boxy_ty subst
 			Nothing -> orig_boxy_ty
 			Just ty -> ty `boxyLub` orig_boxy_ty
 
+    go _ (TyVarTy tv) | isMetaTyVar tv
+	= subst		-- Don't fail if the template has more info than the target!
+			-- Otherwise, with tmpl_tvs = [a], matching (a -> Int) ~ (Bool -> beta)
+			-- would fail to instantiate 'a', because the meta-type-variable
+			-- beta is as yet un-filled-in
+	
     go _ _ = emptyTvSubst	-- It's important to *fail* by returning the empty substitution
 	-- Example:  Tree a ~ Maybe Int
 	-- We do not want to bind (a |-> Int) in pre-matching, because that can give very
@@ -643,6 +650,10 @@ boxyLub orig_ty1 orig_ty2
       | isTcTyVar tv1, isBoxyTyVar tv1 	-- choose ty2 if ty2 is a box
       = orig_ty2	
 
+    go ty1 (TyVarTy tv2) 		-- Symmetrical case
+      | isTcTyVar tv2, isBoxyTyVar tv2
+      = orig_ty1	
+
 	-- Look inside type synonyms, but only if the naive version fails
     go ty1 ty2 | Just ty1' <- tcView ty1 = go ty1' ty2
 	       | Just ty2' <- tcView ty1 = go ty1 ty2'
@@ -904,12 +915,13 @@ tcGen expected_ty extra_tvs thing_inside	-- We expect expected_ty to be a forall
 		   ; let skol_info = GenSkol forall_tvs (mkPhiTy theta rho_ty)
 		   ; return ((forall_tvs, theta, rho_ty), skol_info) })
 
-#ifdef DEBUG
-	; traceTc (text "tcGen" <+> vcat [text "extra_tvs" <+> ppr extra_tvs,
-				    text "expected_ty" <+> ppr expected_ty,
-				    text "inst ty" <+> ppr tvs' <+> ppr theta' <+> ppr rho',
-				    text "free_tvs" <+> ppr free_tvs])
-#endif
+        ; when debugIsOn $
+              traceTc (text "tcGen" <+> vcat [
+                           text "extra_tvs" <+> ppr extra_tvs,
+                           text "expected_ty" <+> ppr expected_ty,
+                           text "inst ty" <+> ppr tvs' <+> ppr theta'
+                               <+> ppr rho',
+                           text "free_tvs" <+> ppr free_tvs])
 
 	-- Type-check the arg and unify with poly type
 	; (result, lie) <- getLIE (thing_inside tvs' rho')
@@ -1487,17 +1499,17 @@ uMetaVar outer swapped tv1 BoxTv ref1 ps_ty2 non_var_ty2
 	-- 
 	-- It should not be the case that tv1 occurs in ty2
 	-- (i.e. no occurs check should be needed), but if perchance
-	-- it does, the unbox operation will fill it, and the DEBUG
+	-- it does, the unbox operation will fill it, and the debug code
 	-- checks for that.
-    do 	{ final_ty <- unBox ps_ty2
-#ifdef DEBUG
-	; meta_details <- readMutVar ref1
-	; case meta_details of
-	    Indirect ty -> WARN( True, ppr tv1 <+> ppr ty )
-			   return ()	-- This really should *not* happen
-	    Flexi -> return ()
-#endif
-	; checkUpdateMeta swapped tv1 ref1 final_ty
+    do { final_ty <- unBox ps_ty2
+       ; when debugIsOn $ do
+           { meta_details <- readMutVar ref1
+           ; case meta_details of
+                 Indirect ty -> WARN( True, ppr tv1 <+> ppr ty )
+                                return () -- This really should *not* happen
+                 Flexi -> return ()
+           }
+        ; checkUpdateMeta swapped tv1 ref1 final_ty
         ; return IdCo
         }