X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcMType.lhs;h=12f3a73e01ae6f9e82d3b10ae75e21c6f2f6ce46;hb=e07e74e5a074490d25443aeff4db4f1f299040c4;hp=f206b5ee11d860c9c2060c14b3951c7aede4ed70;hpb=654a1ba16e47d3ddabeb74b809ee6097c0770d35;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcMType.lhs b/compiler/typecheck/TcMType.lhs
index f206b5e..12f3a73 100644
--- a/compiler/typecheck/TcMType.lhs
+++ b/compiler/typecheck/TcMType.lhs
@@ -81,7 +81,7 @@ import UniqSupply
 import SrcLoc
 import Outputable
 
-import Control.Monad	( when )
+import Control.Monad	( when, unless )
 import Data.List	( (\\) )
 \end{code}
 
@@ -826,12 +826,15 @@ check_tau_type rank ubx_tup ty@(TyConApp tc tys)
 		--	type Foo a = Tree [a]
 		--	f :: Foo a b -> ...
 	; case tcView ty of
-	     Just ty' -> check_tau_type rank ubx_tup ty'	-- Check expansion
-	     Nothing  -> failWithTc arity_msg
+	     Just ty' -> check_tau_type rank ubx_tup ty' -- Check expansion
+	     Nothing -> unless (isOpenTyCon tc           -- No expansion if open
+			        && tyConArity tc <= length tys) $
+		          failWithTc arity_msg
 
 	; gla_exts <- doptM Opt_GlasgowExts
-	; if gla_exts then
-	-- If -fglasgow-exts then don't check the type arguments
+	; if gla_exts && not (isOpenTyCon tc) then
+	-- If -fglasgow-exts then don't check the type arguments of 
+	-- *closed* synonyms.
 	-- This allows us to instantiate a synonym defn with a 
 	-- for-all type, or with a partially-applied type synonym.
 	-- 	e.g.   type T a b = a
@@ -1133,8 +1136,8 @@ check_inst_head dflags clas tys
   where
     (first_ty : _) = tys
 
-    head_shape_msg = parens (text "The instance type must be of form (T a b c)" $$
-			     text "where T is not a synonym, and a,b,c are distinct type variables")
+    head_shape_msg = parens (text "The instance type must be of form (T a1 ... an)" $$
+			     text "where T is not a synonym, and a1 ... an are distinct type variables")
 
 	-- For now, I only allow tau-types (not polytypes) in 
 	-- the head of an instance decl.  
@@ -1169,7 +1172,7 @@ checkValidInstance tyvars theta clas inst_tys
 	-- Check that instance inference will terminate (if we care)
 	-- For Haskell 98, checkValidTheta has already done that
 	; when (gla_exts && not undecidable_ok) $
-	  mapM_ failWithTc (checkInstTermination inst_tys theta)
+	  mapM_ addErrTc (checkInstTermination inst_tys theta)
 	
 	-- The Coverage Condition
 	; checkTc (undecidable_ok || checkInstCoverage clas inst_tys)