; let tys = map snd pat_ty_prs
; tcCheckExistentialPat pats' ex_tvs tys res_ty
- ; returnM (pats', res) }
+ ; return (pats', res) }
-----------------
; 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
; 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)
}
-- 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) }
------------------------
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)
; 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}
= 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:
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).
+
%************************************************************************
%* *