Make records work properly with type families

[ghc-hetmet.git] / compiler / types / Type.lhs

diff --git a/compiler/types/Type.lhs b/compiler/types/Type.lhs
index 25c5968..37f915b 100644 (file)
--- a/compiler/types/Type.lhs
+++ b/compiler/types/Type.lhs
@@ -54,7 +54,7 @@ module Type (
        applyTy, applyTys, isForAllTy, dropForAlls,
 
        -- Source types
-       predTypeRep, mkPredTy, mkPredTys, pprSourceTyCon,
+       predTypeRep, mkPredTy, mkPredTys, pprSourceTyCon, mkFamilyTyConApp,
 
        -- Newtypes
        splitRecNewType_maybe, newTyConInstRhs,
@@ -603,13 +603,27 @@ predTypeRep (ClassP clas tys) = mkTyConApp (classTyCon clas) tys
        -- look through that too if necessary
 predTypeRep (EqPred ty1 ty2) = pprPanic "predTypeRep" (ppr (EqPred ty1 ty2))
 
+mkFamilyTyConApp :: TyCon -> [Type] -> Type
+-- Given a family instance TyCon and its arg types, return the
+-- corresponding family type.  E.g.
+--     data family T a
+--     data instance T (Maybe b) = MkT b       -- Instance tycon :RTL
+-- Then 
+--     mkFamilyTyConApp :RTL Int  =  T (Maybe Int)
+mkFamilyTyConApp tc tys
+  | Just (fam_tc, fam_tys) <- tyConFamInst_maybe tc
+  , let fam_subst = zipTopTvSubst (tyConTyVars tc) tys
+  = mkTyConApp fam_tc (substTys fam_subst fam_tys)
+  | otherwise
+  = mkTyConApp tc tys
+
 -- Pretty prints a tycon, using the family instance in case of a
 -- representation tycon.  For example
 --     e.g.  data T [a] = ...
 -- In that case we want to print `T [a]', where T is the family TyCon
 pprSourceTyCon tycon 
-  | Just (repTyCon, tys) <- tyConFamInst_maybe tycon
-  = ppr $ repTyCon `TyConApp` tys             -- can't be FunTyCon
+  | Just (fam_tc, tys) <- tyConFamInst_maybe tycon
+  = ppr $ fam_tc `TyConApp` tys               -- can't be FunTyCon
   | otherwise
   = ppr tycon
 \end{code}
@@ -637,9 +651,6 @@ splitRecNewType_maybe (TyConApp tc tys)
                         Just (substTyWith tvs tys rep_ty)
        
 splitRecNewType_maybe other = Nothing
-
-
-
 \end{code}