Make records work properly with type families

[ghc-hetmet.git] / compiler / basicTypes / DataCon.lhs

diff --git a/compiler/basicTypes/DataCon.lhs b/compiler/basicTypes/DataCon.lhs
index ee2c685..a83d5f8 100644 (file)
--- a/compiler/basicTypes/DataCon.lhs
+++ b/compiler/basicTypes/DataCon.lhs
@@ -246,6 +246,8 @@ data DataCon
                --       The declaration format is held in the TyCon (algTcGadtSyntax)
 
        dcUnivTyVars :: [TyVar],        -- Universally-quantified type vars 
+                                       -- INVARIANT: length matches arity of the dcRepTyCon
+
        dcExTyVars   :: [TyVar],        -- Existentially-quantified type vars 
                -- In general, the dcUnivTyVars are NOT NECESSARILY THE SAME AS THE TYVARS
                -- FOR THE PARENT TyCon. With GADTs the data con might not even have 
@@ -484,20 +486,13 @@ mkDataCon name declared_infix
     real_stricts = map mk_dict_strict_mark theta ++ arg_stricts
 
        -- Example
-       --   data instance T [a] where 
-       --      TI :: forall b. b -> T [Maybe b]
+       --   data instance T (b,c) where 
+       --      TI :: forall e. e -> T (e,e)
+       --
        -- The representation tycon looks like this:
-       --   data :R7T a where 
-       --      TI :: forall b c. (c :=: Maybe b) b -> :R7T c
-    orig_res_ty 
-       | Just (fam_tc, fam_tys) <- tyConFamInst_maybe tycon
-       , let fam_subst = zipTopTvSubst (tyConTyVars fam_tc) res_tys
-       = mkTyConApp fam_tc (substTys fam_subst fam_tys)
-       | otherwise
-       = mkTyConApp tycon res_tys
-       where
-         res_tys = substTyVars (mkTopTvSubst eq_spec) univ_tvs
-               -- In the example above, res_tys is a singleton, (Maybe b)
+       --   data :R7T b c where 
+       --      TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
+    orig_res_ty = mkFamilyTyConApp tycon (substTyVars (mkTopTvSubst eq_spec) univ_tvs)
 
        -- Representation arguments and demands
        -- To do: eliminate duplication with MkId
@@ -639,9 +634,9 @@ dataConStupidTheta dc = dcStupidTheta dc
 dataConUserType :: DataCon -> Type
 -- The user-declared type of the data constructor
 -- in the nice-to-read form 
---     T :: forall a. a -> T [a]
+--     T :: forall a b. a -> b -> T [a]
 -- rather than
---     T :: forall b. forall a. (a=[b]) => a -> T b
+--     T :: forall a c. forall b. (c=[a]) => a -> b -> T c
 -- NB: If the constructor is part of a data instance, the result type
 -- mentions the family tycon, not the internal one.
 dataConUserType  (MkData { dcUnivTyVars = univ_tvs, 
@@ -750,7 +745,8 @@ splitProductType_maybe ty
                                        -- and for constructors visible
           -> Just (tycon, ty_args, data_con, dataConInstArgTys data_con ty_args)
           where
-             data_con = head (tyConDataCons tycon)
+             data_con = ASSERT( not (null (tyConDataCons tycon)) ) 
+                        head (tyConDataCons tycon)
        other -> Nothing
 
 splitProductType str ty