Indexed newtypes

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

diff --git a/compiler/types/TyCon.lhs b/compiler/types/TyCon.lhs
index 15be3e2..1464fab 100644 (file)
--- a/compiler/types/TyCon.lhs
+++ b/compiler/types/TyCon.lhs
@@ -14,7 +14,8 @@ module TyCon(
        SynTyConRhs(..),
 
        isFunTyCon, isUnLiftedTyCon, isProductTyCon, 
-       isAlgTyCon, isDataTyCon, isSynTyCon, isNewTyCon, isPrimTyCon,
+       isAlgTyCon, isDataTyCon, isSynTyCon, isNewTyCon, isClosedNewTyCon,
+       isPrimTyCon, 
        isEnumerationTyCon, isGadtSyntaxTyCon, isOpenTyCon,
        assocTyConArgPoss_maybe, isTyConAssoc, setTyConArgPoss,
        isTupleTyCon, isUnboxedTupleTyCon, isBoxedTupleTyCon, tupleTyConBoxity,
@@ -550,13 +551,23 @@ isDataTyCon tc@(AlgTyCon {algTcRhs = rhs})
        OpenNewTyCon  -> False
        NewTyCon {}   -> False
        AbstractTyCon -> pprPanic "isDataTyCon" (ppr tc)
-
 isDataTyCon (TupleTyCon {tyConBoxed = boxity}) = isBoxed boxity
 isDataTyCon other = False
 
 isNewTyCon :: TyCon -> Bool
-isNewTyCon (AlgTyCon {algTcRhs = NewTyCon {}}) = True 
-isNewTyCon other                              = False
+isNewTyCon (AlgTyCon {algTcRhs = rhs}) = case rhs of
+                                          OpenNewTyCon -> True
+                                          NewTyCon {}  -> True
+                                          _            -> False
+isNewTyCon other                       = False
+
+-- This is an important refinement as typical newtype optimisations do *not*
+-- hold for newtype families.  Why?  Given a type `T a', if T is a newtype
+-- family, there is no unique right hand side by which `T a' can be replaced
+-- by a cast.
+--
+isClosedNewTyCon :: TyCon -> Bool
+isClosedNewTyCon tycon = isNewTyCon tycon && not (isOpenTyCon tycon)
 
 isProductTyCon :: TyCon -> Bool
 -- A "product" tycon
@@ -746,7 +757,10 @@ newTyConRep (AlgTyCon {tyConTyVars = tvs, algTcRhs = NewTyCon { nt_rep = rep }})
 newTyConRep tycon = pprPanic "newTyConRep" (ppr tycon)
 
 newTyConCo :: TyCon -> Maybe TyCon
-newTyConCo (AlgTyCon {tyConTyVars = tvs, algTcRhs = NewTyCon { nt_co = co }}) = co
+newTyConCo (AlgTyCon {tyConTyVars = tvs, algTcRhs = NewTyCon { nt_co = co }})
+  = co
+newTyConCo (AlgTyCon {tyConTyVars = tvs, algTcRhs = OpenNewTyCon})
+  = Nothing
 newTyConCo tycon = pprPanic "newTyConCo" (ppr tycon)
 
 tyConPrimRep :: TyCon -> PrimRep