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 e5ccbd0..9746e0c 100644 (file)
--- a/compiler/typecheck/TcMType.lhs
+++ b/compiler/typecheck/TcMType.lhs
@@ -1179,15 +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