Indexed newtypes

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

diff --git a/compiler/typecheck/TcPat.lhs b/compiler/typecheck/TcPat.lhs
index f165e2e..0f923ff 100644 (file)
--- a/compiler/typecheck/TcPat.lhs
+++ b/compiler/typecheck/TcPat.lhs
@@ -47,7 +47,7 @@ import TysWiredIn     ( boolTy, parrTyCon, tupleTyCon )
 import Type            ( Type, mkTyConApp, substTys, substTheta )
 import StaticFlags     ( opt_IrrefutableTuples )
 import TyCon           ( TyCon, FieldLabel, tyConFamInst_maybe,
-                         tyConFamilyCoercion_maybe, tyConTyVars )
+                         tyConFamilyCoercion_maybe, tyConTyVars, isNewTyCon )
 import DataCon         ( DataCon, dataConTyCon, dataConFullSig, dataConName,
                          dataConFieldLabels, dataConSourceArity, 
                          dataConStupidTheta, dataConUnivTyVars )
@@ -586,6 +586,7 @@ tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
     -- representation tycon.
     --
     boxySplitTyConAppWithFamily tycon pat_ty =
+      traceTc traceMsg >>
       case tyConFamInst_maybe tycon of
         Nothing                   -> boxySplitTyConApp tycon pat_ty
        Just (fam_tycon, instTys) -> 
@@ -594,6 +595,12 @@ tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
             ; boxyUnifyList (substTys subst instTys) scrutinee_arg_tys
             ; return freshTvs
             }
+      where
+        traceMsg = sep [ text "tcConPat:boxySplitTyConAppWithFamily:" <+>
+                        ppr tycon <+> ppr pat_ty
+                      , text "  family instance:" <+> 
+                        ppr (tyConFamInst_maybe tycon)
+                       ]
 
     -- Wraps the pattern (which must be a ConPatOut pattern) in a coercion
     -- pattern if the tycon is an instance of a family.
@@ -601,6 +608,8 @@ tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
     unwrapFamInstScrutinee :: TyCon -> [Type] -> Pat Id -> Pat Id
     unwrapFamInstScrutinee tycon args pat
       | Just co_con <- tyConFamilyCoercion_maybe tycon 
+--      , not (isNewTyCon tycon)       -- newtypes are explicitly unwrapped by
+                                    -- the desugarer
           -- NB: We can use CoPat directly, rather than mkCoPat, as we know the
           --    coercion is not the identity; mkCoPat is inconvenient as it
           --    wants a located pattern.