X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcPat.lhs;h=e8f108da88fa25e830d422deddf2a1d52b4e20e1;hb=cbcc6ec44ae3d8c17a54c0d4e5e6dac622019428;hp=0d62b6bf81b59d432382fb5ece549dc04e7cf367;hpb=d31018bce01934b8399a15dbcae35be0827b45d1;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcPat.lhs b/compiler/typecheck/TcPat.lhs
index 0d62b6b..e8f108d 100644
--- a/compiler/typecheck/TcPat.lhs
+++ b/compiler/typecheck/TcPat.lhs
@@ -130,7 +130,7 @@ tc_lam_pats ctxt pat_ty_prs (reft, res_ty) thing_inside
 	; let tys = map snd pat_ty_prs
 	; tcCheckExistentialPat pats' ex_tvs tys res_ty
 
-	; returnM (pats', res) }
+	; return (pats', res) }
 
 
 -----------------
@@ -386,6 +386,9 @@ tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
 
 	; return (LazyPat pat', [], res) }
 
+tc_pat _ p@(QuasiQuotePat _) _ _
+  = pprPanic "Should never see QuasiQuotePat in type checker" (ppr p)
+
 tc_pat pstate (WildPat _) pat_ty thing_inside
   = do	{ pat_ty' <- unBoxWildCardType pat_ty	-- Make sure it's filled in with monotypes
 	; res <- thing_inside pstate
@@ -458,7 +461,7 @@ tc_pat pstate (PArrPat pats _) pat_ty thing_inside
         ; let scoi = mkSymCoI coi
 	; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
 						pats pstate thing_inside 
-	; ifM (null pats) (zapToMonotype pat_ty)  -- c.f. ExplicitPArr in TcExpr
+	; when (null pats) (zapToMonotype pat_ty >> return ())  -- c.f. ExplicitPArr in TcExpr
 	; return (mkCoPatCoI scoi (PArrPat pats' elt_ty) pat_ty, pats_tvs, res)
         }
 
@@ -503,7 +506,7 @@ tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
 			-- pattern coercions have to
 			-- be of kind: pat_ty ~ lit_ty
 			-- hence, sym coi
-	; returnM (mkCoPatCoI (mkSymCoI coi) (LitPat simple_lit) pat_ty, 
+	; return (mkCoPatCoI (mkSymCoI coi) (LitPat simple_lit) pat_ty, 
                    [], res) }
 
 ------------------------
@@ -519,7 +522,7 @@ tc_pat pstate pat@(NPat over_lit mb_neg eq) pat_ty thing_inside
  			    do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
 			       ; return (Just neg') }
 	; res <- thing_inside pstate
-	; returnM (NPat lit' mb_neg' eq', [], res) }
+	; return (NPat lit' mb_neg' eq', [], res) }
 
 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
   = do	{ bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
@@ -537,7 +540,7 @@ tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
 	; instStupidTheta orig [mkClassPred icls [pat_ty']]	
     
 	; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
-	; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
+	; return (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
 
 tc_pat _ _other_pat _ _ = panic "tc_pat" 	-- ConPatOut, SigPatOut, VarPatOut
 \end{code}
@@ -867,11 +870,8 @@ refineAlt con pstate ex_tvs [] pat_ty
   = return pstate	-- Common case: no equational constraints
 
 refineAlt con pstate ex_tvs co_vars pat_ty
-  = do	{ opt_gadt <- doptM Opt_GADTs	-- No type-refinement unless GADTs are on
-	; if (not opt_gadt) then return pstate
-	  else do 
-
-	{ checkTc (isRigidTy pat_ty) (nonRigidMatch con)
+  = -- See Note [Flags and equational constraints]
+    do	{ checkTc (isRigidTy pat_ty) (nonRigidMatch con)
 	-- We are matching against a GADT constructor with non-trivial
 	-- constraints, but pattern type is wobbly.  For now we fail.
 	-- We can make sense of this, however:
@@ -899,9 +899,20 @@ refineAlt con pstate ex_tvs co_vars pat_ty
 				vcat [ ppr con <+> ppr ex_tvs,
 				       ppr [(v, tyVarKind v) | v <- co_vars],
 				       ppr reft]
-	} } }
+	} }
 \end{code}
 
+Note [Flags and equational constraints]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If there are equational constraints, we take account of them
+regardless of flag settings; -XGADTs etc applies only to the
+*definition* of a data type.
+
+An alternative would be also to reject a program that *used*
+constructors with equational constraints.  But want we should avoid at
+all costs is simply to *ignore* the constraints, since that gives
+incomprehensible errors (Trac #2004).
+
 
 %************************************************************************
 %*									*
@@ -1107,11 +1118,11 @@ lazyPatErr pat tvs
 
 nonRigidMatch con
   =  hang (ptext SLIT("GADT pattern match in non-rigid context for") <+> quotes (ppr con))
-	2 (ptext SLIT("Tell GHC HQ if you'd like this to unify the context"))
+	2 (ptext SLIT("Solution: add a type signature"))
 
 nonRigidResult res_ty
   =  hang (ptext SLIT("GADT pattern match with non-rigid result type") <+> quotes (ppr res_ty))
-	2 (ptext SLIT("Tell GHC HQ if you'd like this to unify the context"))
+	2 (ptext SLIT("Solution: add a type signature"))
 
 inaccessibleAlt msg
   = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg