X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FCoercion.lhs;h=25d04ecd249eab0ed571018ceffb19e4ca5c0904;hb=bb106f283663e9c16a4c72ec9ca57109ae57a0ed;hp=cb85028ce8add7c56b21664ff880f91476b7fc15;hpb=a7bda9e63ce091e4f33b6058a96686d7cde3d40d;p=ghc-hetmet.git

diff --git a/compiler/types/Coercion.lhs b/compiler/types/Coercion.lhs
index cb85028..25d04ec 100644
--- a/compiler/types/Coercion.lhs
+++ b/compiler/types/Coercion.lhs
@@ -37,12 +37,14 @@ import TypeRep
 import Type	  ( Type, Kind, PredType, substTyWith, mkAppTy, mkForAllTy,
                     mkFunTy, splitAppTy_maybe, splitForAllTy_maybe, coreView,
                     kindView, mkTyConApp, isCoercionKind, isEqPred, mkAppTys,
-                    coreEqType, splitAppTys, isTyVarTy, splitTyConApp_maybe
+                    coreEqType, splitAppTys, isTyVarTy, splitTyConApp_maybe,
+                    tyVarsOfType
                   )
 import TyCon      ( TyCon, tyConArity, mkCoercionTyCon, isNewTyCon,
                     newTyConRhs, newTyConCo, 
                     isCoercionTyCon, isCoercionTyCon_maybe )
 import Var	  ( Var, TyVar, isTyVar, tyVarKind )
+import VarSet     ( elemVarSet )
 import Name       ( BuiltInSyntax(..), Name, mkWiredInName, tcName )
 import OccName    ( mkOccNameFS )
 import PrelNames  ( symCoercionTyConKey, 
@@ -277,28 +279,51 @@ splitRightCoercion_maybe (TyConApp tc [co])
 splitRightCoercion_maybe other = Nothing
 
 -- Unsafe coercion is not safe, it is used when we know we are dealing with
--- bottom, which is the one case in which it is safe.  It is also used to 
+-- bottom, which is one case in which it is safe.  It is also used to 
 -- implement the unsafeCoerce# primitive.
 mkUnsafeCoercion :: Type -> Type -> Coercion
 mkUnsafeCoercion ty1 ty2 
   = mkCoercion unsafeCoercionTyCon [ty1, ty2]
 
 
--- Make the coercion associated with a newtype.  If we have
---
---   newtype T a b = MkT (Int, a, b)
---
--- Then (mkNewTypeCoercion CoT T [a,b] (Int, a, b)) creates the coercion
--- CoT, such kinding rule such that
---
---   CoT S U :: (Int, S, U) :=: T S U
+-- See note [Newtype coercions] in TyCon
 mkNewTypeCoercion :: Name -> TyCon -> [TyVar] -> Type -> TyCon
 mkNewTypeCoercion name tycon tvs rhs_ty 
   = ASSERT (length tvs == tyConArity tycon)
-    mkCoercionTyCon name (tyConArity tycon) rule
+    mkCoercionTyCon name co_con_arity (mkKindingFun rule)
   where
-    rule args = mkCoKind (substTyWith tvs args rhs_ty) (TyConApp tycon args)
+    rule args = (TyConApp tycon tys, substTyWith tvs_eta tys rhs_eta, rest)
+        where
+          tys  = take co_con_arity args
+          rest = drop co_con_arity args
+
+      -- if the rhs_ty is a type application and it has a tail equal to a tail
+      -- of the tvs, then we eta-contract the type of the coercion
+    rhs_args = let (ty, ty_args) = splitAppTys rhs_ty in ty_args
+
+    n_eta_tys = count_eta (reverse rhs_args) (reverse tvs)
 
+    count_eta ((TyVarTy tv):rest_ty) (tv':rest_tv)
+      | tv == tv' && (not $ any (elemVarSet tv . tyVarsOfType) rest_ty)
+                  -- if the last types are the same, and not free anywhere else
+                  -- then eta contract
+      = 1 + (count_eta rest_ty rest_tv)
+      | otherwise -- don't 
+      = 0
+    count_eta _ _ = 0
+     
+
+    eqVar (TyVarTy tv) tv' = tv == tv'
+    eqVar _            _   = False
+
+    co_con_arity = (tyConArity tycon) - n_eta_tys
+
+    tvs_eta = (reverse (drop n_eta_tys (reverse tvs)))
+
+    rhs_eta
+      | (ty, ty_args) <- splitAppTys rhs_ty
+      = mkAppTys ty (reverse (drop n_eta_tys (reverse ty_args)))
+ 
 --------------------------------------
 -- Coercion Type Constructors...