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,
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...