Tweak the undecidable-instance-checking logic

[ghc-hetmet.git] / compiler / typecheck / TcMType.lhs

diff --git a/compiler/typecheck/TcMType.lhs b/compiler/typecheck/TcMType.lhs
index 3ae9cef..9746e0c 100644 (file)
--- a/compiler/typecheck/TcMType.lhs
+++ b/compiler/typecheck/TcMType.lhs
@@ -838,10 +838,9 @@ check_tau_type rank ubx_tup ty@(TyConApp tc tys)
                                && tyConArity tc <= length tys) $
                          failWithTc arity_msg
 
-       ; gla_exts <- doptM Opt_GlasgowExts
-       ; if gla_exts && not (isOpenTyCon tc) then
-       -- If -fglasgow-exts then don't check the type arguments of 
-       -- *closed* synonyms.
+       ; ok <- doptM Opt_PartiallyAppliedClosedTypeSynonyms
+       ; if ok && not (isOpenTyCon tc) 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
@@ -1180,15 +1179,15 @@ instTypeErr pp_ty msg
 \begin{code}
 checkValidInstance :: [TyVar] -> ThetaType -> Class -> [TcType] -> TcM ()
 checkValidInstance tyvars theta clas inst_tys
-  = do { gla_exts <- doptM Opt_GlasgowExts
-       ; undecidable_ok <- doptM Opt_AllowUndecidableInstances
+  = do { undecidable_ok <- doptM Opt_AllowUndecidableInstances
 
        ; checkValidTheta InstThetaCtxt theta
        ; checkAmbiguity tyvars theta (tyVarsOfTypes 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) $
+       -- For Haskell 98 this will already have been done by checkValidTheta,
+    -- but as we may be using other extensions we need to check.
+       ; unless undecidable_ok $
          mapM_ addErrTc (checkInstTermination inst_tys theta)
        
        -- The Coverage Condition