+++ /dev/null
-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1998
-%
-
-\begin{code}
-module Kind (
- Kind(..), SimpleKind,
- openTypeKind, liftedTypeKind, unliftedTypeKind, unboxedTypeKind,
- argTypeKind, ubxTupleKind,
-
- isLiftedTypeKind, isUnliftedTypeKind, isUnliftedBoxedTypeKind,
- isArgTypeKind, isOpenTypeKind,
- mkArrowKind, mkArrowKinds,
-
- isSubKind, defaultKind,
- kindFunResult, splitKindFunTys,
-
- KindVar, mkKindVar, kindVarRef, kindVarUniq,
- kindVarOcc, setKindVarOcc,
-
- pprKind, pprParendKind
- ) where
-
-#include "HsVersions.h"
-
-import Unique ( Unique )
-import OccName ( OccName, mkOccName, tvName )
-import Outputable
-import DATA_IOREF
-\end{code}
-
-Kinds
-~~~~~
-There's a little subtyping at the kind level:
-
- ?
- / \
- / \
- ?? (#)
- / | \
- * ! #
-
-where * [LiftedTypeKind] means boxed type
- # [UnboxedTypeKind] means unboxed type
- (#) [UbxTupleKind] means unboxed tuple
- ?? [ArgTypeKind] is the lub of *,#
- ? [OpenTypeKind] means any type at all
-
-In particular:
-
- error :: forall a:?. String -> a
- (->) :: ?? -> ? -> *
- (\(x::t) -> ...) Here t::?? (i.e. not unboxed tuple)
-
-\begin{code}
-data Kind
- = LiftedTypeKind -- *
- | OpenTypeKind -- ?
- | UnboxedTypeKind -- #
- | UnliftedTypeKind -- !
- | UbxTupleKind -- (##)
- | ArgTypeKind -- ??
- | FunKind Kind Kind -- k1 -> k2
- | KindVar KindVar
- deriving( Eq )
-
-data KindVar = KVar Unique OccName (IORef (Maybe SimpleKind))
- -- INVARIANT: a KindVar can only be instantiated by a SimpleKind
-
-type SimpleKind = Kind
- -- A SimpleKind has no ? or # kinds in it:
- -- sk ::= * | sk1 -> sk2 | kvar
-
-instance Eq KindVar where
- (KVar u1 _ _) == (KVar u2 _ _) = u1 == u2
-
-mkKindVar :: Unique -> IORef (Maybe Kind) -> KindVar
-mkKindVar u r = KVar u kind_var_occ r
-
-kindVarRef :: KindVar -> IORef (Maybe Kind)
-kindVarRef (KVar _ _ ref) = ref
-
-kindVarUniq :: KindVar -> Unique
-kindVarUniq (KVar uniq _ _) = uniq
-
-kindVarOcc :: KindVar -> OccName
-kindVarOcc (KVar _ occ _) = occ
-
-setKindVarOcc :: KindVar -> OccName -> KindVar
-setKindVarOcc (KVar u _ r) occ = KVar u occ r
-
-kind_var_occ :: OccName -- Just one for all KindVars
- -- They may be jiggled by tidying
-kind_var_occ = mkOccName tvName "k"
-\end{code}
-
-Kind inference
-~~~~~~~~~~~~~~
-During kind inference, a kind variable unifies only with
-a "simple kind", sk
- sk ::= * | sk1 -> sk2
-For example
- data T a = MkT a (T Int#)
-fails. We give T the kind (k -> *), and the kind variable k won't unify
-with # (the kind of Int#).
-
-Type inference
-~~~~~~~~~~~~~~
-When creating a fresh internal type variable, we give it a kind to express
-constraints on it. E.g. in (\x->e) we make up a fresh type variable for x,
-with kind ??.
-
-During unification we only bind an internal type variable to a type
-whose kind is lower in the sub-kind hierarchy than the kind of the tyvar.
-
-When unifying two internal type variables, we collect their kind constraints by
-finding the GLB of the two. Since the partial order is a tree, they only
-have a glb if one is a sub-kind of the other. In that case, we bind the
-less-informative one to the more informative one. Neat, eh?
-
-
-\begin{code}
-liftedTypeKind = LiftedTypeKind
-unboxedTypeKind = UnboxedTypeKind
-unliftedTypeKind = UnliftedTypeKind
-openTypeKind = OpenTypeKind
-argTypeKind = ArgTypeKind
-ubxTupleKind = UbxTupleKind
-
-mkArrowKind :: Kind -> Kind -> Kind
-mkArrowKind k1 k2 = k1 `FunKind` k2
-
-mkArrowKinds :: [Kind] -> Kind -> Kind
-mkArrowKinds arg_kinds result_kind = foldr mkArrowKind result_kind arg_kinds
-\end{code}
-
-%************************************************************************
-%* *
- Functions over Kinds
-%* *
-%************************************************************************
-
-\begin{code}
-kindFunResult :: Kind -> Kind
-kindFunResult (FunKind _ k) = k
-kindFunResult k = pprPanic "kindFunResult" (ppr k)
-
-splitKindFunTys :: Kind -> ([Kind],Kind)
-splitKindFunTys (FunKind k1 k2) = case splitKindFunTys k2 of
- (as, r) -> (k1:as, r)
-splitKindFunTys k = ([], k)
-
-isLiftedTypeKind, isUnliftedTypeKind :: Kind -> Bool
-isLiftedTypeKind LiftedTypeKind = True
-isLiftedTypeKind other = False
-
-isUnliftedBoxedTypeKind UnliftedTypeKind = True
-isUnliftedBoxedTypeKind other = False
-
-isUnliftedTypeKind UnliftedTypeKind = True
-isUnliftedTypeKind UnboxedTypeKind = True
-isUnliftedTypeKind other = False
-
-isArgTypeKind :: Kind -> Bool
--- True of any sub-kind of ArgTypeKind
-isArgTypeKind LiftedTypeKind = True
-isArgTypeKind UnliftedTypeKind = True
-isArgTypeKind UnboxedTypeKind = True
-isArgTypeKind ArgTypeKind = True
-isArgTypeKind other = False
-
-isOpenTypeKind :: Kind -> Bool
--- True of any sub-kind of OpenTypeKind (i.e. anything except arrow)
-isOpenTypeKind (FunKind _ _) = False
-isOpenTypeKind (KindVar _) = False -- This is a conservative answer
- -- It matters in the call to isSubKind in
- -- checkExpectedKind.
-isOpenTypeKind other = True
-
-isSubKind :: Kind -> Kind -> Bool
--- (k1 `isSubKind` k2) checks that k1 <: k2
-isSubKind LiftedTypeKind LiftedTypeKind = True
-isSubKind UnliftedTypeKind UnliftedTypeKind = True
-isSubKind UnboxedTypeKind UnboxedTypeKind = True
-isSubKind UbxTupleKind UbxTupleKind = True
-isSubKind k1 OpenTypeKind = isOpenTypeKind k1
-isSubKind k1 ArgTypeKind = isArgTypeKind k1
-isSubKind (FunKind a1 r1) (FunKind a2 r2) = (a2 `isSubKind` a1) && (r1 `isSubKind` r2)
-isSubKind k1 k2 = False
-
-defaultKind :: Kind -> Kind
--- Used when generalising: default kind '?' and '??' to '*'
---
--- When we generalise, we make generic type variables whose kind is
--- simple (* or *->* etc). So generic type variables (other than
--- built-in constants like 'error') always have simple kinds. This is important;
--- consider
--- f x = True
--- We want f to get type
--- f :: forall (a::*). a -> Bool
--- Not
--- f :: forall (a::??). a -> Bool
--- because that would allow a call like (f 3#) as well as (f True),
---and the calling conventions differ. This defaulting is done in TcMType.zonkTcTyVarBndr.
-defaultKind OpenTypeKind = LiftedTypeKind
-defaultKind ArgTypeKind = LiftedTypeKind
-defaultKind kind = kind
-\end{code}
-
-
-%************************************************************************
-%* *
- Pretty printing
-%* *
-%************************************************************************
-
-\begin{code}
-instance Outputable KindVar where
- ppr (KVar uniq occ _) = ppr occ <> ifPprDebug (ppr uniq)
-
-instance Outputable Kind where
- ppr k = pprKind k
-
-pprParendKind :: Kind -> SDoc
-pprParendKind k@(FunKind _ _) = parens (pprKind k)
-pprParendKind k = pprKind k
-
-pprKind (KindVar v) = ppr v
-pprKind LiftedTypeKind = ptext SLIT("*")
-pprKind UnliftedTypeKind = ptext SLIT("!")
-pprKind UnboxedTypeKind = ptext SLIT("#")
-pprKind OpenTypeKind = ptext SLIT("?")
-pprKind ArgTypeKind = ptext SLIT("??")
-pprKind UbxTupleKind = ptext SLIT("(#)")
-pprKind (FunKind k1 k2) = sep [ pprParendKind k1, arrow <+> pprKind k2]
-
-\end{code}
projects / ghc-hetmet.git / blobdiff