isDataTyCon should be False for all type families, even data type families

isDataTyCon advertises that it's true of "data types that are
definitely represented by heap-allocated constructors.  These are
srcutinised by Core-level @case@ expressions, and they get info tables
allocated for them."

Type-family TyCons never have this property, not even data type families.
It's the *instance* TyCons that do.

I hope that this change does not break anything that somehow relied
on the old (wrong) semantics.

diff --git a/compiler/typecheck/TcGadt.lhs b/compiler/typecheck/TcGadt.lhs
index 3761c68..4cd7e00 100644 (file)
--- a/compiler/typecheck/TcGadt.lhs
+++ b/compiler/typecheck/TcGadt.lhs
@@ -14,7 +14,6 @@ module TcGadt (
        Refinement, emptyRefinement, isEmptyRefinement, 
        gadtRefine, 
        refineType, refinePred, refineResType,
-       dataConCanMatch,
        tcUnifyTys, BindFlag(..)
   ) where
 
@@ -242,29 +241,10 @@ fixTvSubstEnv in_scope env
     fixpt = mapVarEnv (substTy (mkTvSubst in_scope fixpt)) env
 
 ----------------------------
-dataConCanMatch :: [Type] -> DataCon -> Bool
--- Returns True iff the data con can match a scrutinee of type (T tys)
---                 where T is the type constructor for the data con
---
--- Instantiate the equations and try to unify them
-dataConCanMatch tys con
-  | null eq_spec      = True   -- Common
-  | all isTyVarTy tys = True   -- Also common
-  | otherwise
-  = isJust (tcUnifyTys (\tv -> BindMe) 
-                      (map (substTyVar subst . fst) eq_spec)
-                      (map snd eq_spec))
-  where
-    dc_tvs  = dataConUnivTyVars con
-    eq_spec = dataConEqSpec con
-    subst   = zipTopTvSubst dc_tvs tys
-
-----------------------------
 tryToBind :: TyVarSet -> TyVar -> BindFlag
 tryToBind tv_set tv | tv `elemVarSet` tv_set = BindMe
                    | otherwise              = AvoidMe
 
-
 \end{code}
 
 

diff --git a/compiler/types/TyCon.lhs b/compiler/types/TyCon.lhs
index 50d76cf..90ac71c 100644 (file)
--- a/compiler/types/TyCon.lhs
+++ b/compiler/types/TyCon.lhs
@@ -616,9 +616,14 @@ isDataTyCon :: TyCon -> Bool
 --     True for all @data@ types
 --     False for newtypes
 --               unboxed tuples
+--               type families
+-- 
+-- NB: for a data type family, T, only the *instance* tycons are
+--     get an info table etc.  The family tycon does not.
+--     Hence False for OpenTyCon
 isDataTyCon tc@(AlgTyCon {algTcRhs = rhs})  
   = case rhs of
-        OpenTyCon {}  -> not (otIsNewtype rhs)
+        OpenTyCon {}  -> False
        DataTyCon {}  -> True
        NewTyCon {}   -> False
        AbstractTyCon -> False   -- We don't know, so return False