X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcPat.lhs;h=82ac5e3596a53c1558c6800ed3f58f2b7b09a5fd;hb=3d638f1b7b665c0e67e4e20827ad98cf307ff381;hp=e21fb6883e7aa5ae8ca39231eb877e6a95cad996;hpb=a17d329568660592dad5c7668fb09f31ab77cd69;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcPat.lhs b/compiler/typecheck/TcPat.lhs
index e21fb68..82ac5e3 100644
--- a/compiler/typecheck/TcPat.lhs
+++ b/compiler/typecheck/TcPat.lhs
@@ -37,6 +37,7 @@ import TyCon
 import DataCon
 import PrelNames
 import BasicTypes hiding (SuccessFlag(..))
+import DynFlags	( DynFlag( Opt_GADTs ) )
 import SrcLoc
 import ErrUtils
 import Util
@@ -670,6 +671,12 @@ tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
 	      pstate' | no_equalities = pstate
 		      | otherwise     = pstate { pat_eqs = True }
 
+        ; gadts_on <- doptM Opt_GADTs
+	; checkTc (no_equalities || gadts_on)
+	  	  (ptext (sLit "A pattern match on a GADT requires -XGADTs"))
+		  -- Trac #2905 decided that a *pattern-match* of a GADT
+		  -- should require the GADT language flag
+
 	; unless no_equalities $ checkTc (isRigidTy pat_ty) $
                                  nonRigidMatch (pat_ctxt pstate) data_con