New syntax for GADT-style record declarations, and associated refactoring

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

diff --git a/compiler/typecheck/TcPat.lhs b/compiler/typecheck/TcPat.lhs
index b8bbed7..bef5ec7 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
@@ -364,8 +365,11 @@ tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
        -- getLIE/extendLIEs: see Note [Hopping the LIE in lazy patterns]
 
        -- Check no existentials
-       ; if (null pat_tvs) then return ()
-         else lazyPatErr lpat pat_tvs
+       ; unless (null pat_tvs) $ lazyPatErr lpat pat_tvs
+
+       -- Check there are no unlifted types under the lazy pattern
+       ; when (any (isUnLiftedType . idType) $ collectPatBinders pat') $
+               lazyUnliftedPatErr lpat
 
        -- Check that the pattern has a lifted type
        ; pat_tv <- newBoxyTyVar liftedTypeKind
@@ -427,7 +431,7 @@ 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 +674,12 @@ 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 +712,7 @@ 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
@@ -978,7 +988,7 @@ patCtxt pat             = Just (hang (ptext (sLit "In the pattern:"))
 existentialExplode :: LPat Name -> SDoc
 existentialExplode pat
   = hang (vcat [text "My brain just exploded.",
-               text "I can't handle pattern bindings for existentially-quantified constructors.",
+               text "I can't handle pattern bindings for existential or GADT data constructors.",
                text "Instead, use a case-expression, or do-notation, to unpack the constructor.",
                text "In the binding group for"])
        4 (ppr pat)
@@ -1030,9 +1040,15 @@ existentialProcPat con
 lazyPatErr :: Pat name -> [TcTyVar] -> TcM ()
 lazyPatErr _ tvs
   = failWithTc $
-    hang (ptext (sLit "A lazy (~) pattern cannot bind existential type variables"))
+    hang (ptext (sLit "A lazy (~) pattern cannot match existential or GADT data constructors"))
        2 (vcat (map pprSkolTvBinding tvs))
 
+lazyUnliftedPatErr :: OutputableBndr name => Pat name -> TcM ()
+lazyUnliftedPatErr pat
+  = failWithTc $
+    hang (ptext (sLit "A lazy (~) pattern cannot contain unlifted types"))
+       2 (ppr pat)
+
 nonRigidMatch :: PatCtxt -> DataCon -> SDoc
 nonRigidMatch ctxt con
   =  hang (ptext (sLit "GADT pattern match in non-rigid context for") <+> quotes (ppr con))