Fix Trac #3092

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

diff --git a/compiler/typecheck/TcPat.lhs b/compiler/typecheck/TcPat.lhs
index c6caa54..82ac5e3 100644 (file)
--- 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
@@ -427,7 +428,7 @@ tc_pat pstate (orig@(ViewPat expr pat _)) overall_pat_ty thing_inside
 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
   = do { (inner_ty, tv_binds, coi) <- tcPatSig (patSigCtxt pstate) sig_ty 
                                                                     pat_ty
-        ; unless (isIdentityCoercion coi) $ 
+        ; unless (isIdentityCoI coi) $ 
             failWithTc (badSigPat pat_ty)
        ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
                              tc_lpat pat inner_ty pstate thing_inside
@@ -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
 
@@ -702,7 +709,7 @@ tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
             ; (_, freshTvs, subst) <- tcInstTyVars (tyConTyVars tycon)
              ; let instTys' = substTys subst instTys
             ; cois <- boxyUnifyList instTys' scrutinee_arg_tys
-             ; let coi = if isIdentityCoercion coi1
+             ; let coi = if isIdentityCoI coi1
                          then  -- pat_ty was splittable
                                -- => boxyUnifyList had real work to do
                            mkTyConAppCoI fam_tycon instTys' cois