%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcMonoType]{Typechecking user-specified @MonoTypes@}
\begin{code}
module TcHsType (
tcHsSigType, tcHsSigTypeNC, tcHsDeriv, tcHsVectInst,
tcHsInstHead, tcHsQuantifiedType,
UserTypeCtxt(..),
kcHsTyVars, kcHsSigType, kcHsLiftedSigType,
kcLHsType, kcCheckLHsType, kcHsContext, kcApps,
kindGeneralizeKind, kindGeneralizeKinds,
scDsLHsKind, scDsLHsMaybeKind,
tcHsType, tcCheckHsType,
tcHsKindedContext, tcHsKindedType, tcHsBangType,
tcTyVarBndrs, tcTyVarBndrsKindGen, dsHsType,
tcDataKindSig, tcTyClTyVars,
ExpKind(..), ekConstraint, expArgKind, checkExpectedKind,
tcHsPatSigType, tcPatSig
) where
#include "HsVersions.h"
#ifdef GHCI /* Only if bootstrapped */
import TcSplice( kcSpliceType )
#endif
import HsSyn
import RnHsSyn
import TcRnMonad
import RnEnv ( dataKindsErr )
import TcHsSyn ( mkZonkTcTyVar )
import TcEvidence( HsWrapper )
import TcEnv
import TcMType
import TcUnify
import TcIface
import TcType
import Type
import Kind
import Var
import VarSet
import TyCon
import DataCon ( DataCon, dataConUserType )
import TysPrim ( liftedTypeKindTyConName, constraintKindTyConName )
import Class
import RdrName ( rdrNameSpace, nameRdrName )
import Name
import NameSet
import TysWiredIn
import BasicTypes
import SrcLoc
import DynFlags ( ExtensionFlag( Opt_DataKinds ) )
import Util
import UniqSupply
import Outputable
import BuildTyCl ( buildPromotedDataTyCon )
import FastString
import Control.Monad ( unless )
\end{code}
----------------------------
General notes
----------------------------
Generally speaking we now type-check types in three phases
1. kcHsType: kind check the HsType
*includes* performing any TH type splices;
so it returns a translated, and kind-annotated, type
2. dsHsType: convert from HsType to Type:
perform zonking
expand type synonyms [mkGenTyApps]
hoist the foralls [tcHsType]
3. checkValidType: check the validity of the resulting type
Often these steps are done one after the other (tcHsSigType).
But in mutually recursive groups of type and class decls we do
1 kind-check the whole group
2 build TyCons/Classes in a knot-tied way
3 check the validity of types in the now-unknotted TyCons/Classes
For example, when we find
(forall a m. m a -> m a)
we bind a,m to kind varibles and kind-check (m a -> m a). This makes
a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
an environment that binds a and m suitably.
The kind checker passed to tcHsTyVars needs to look at enough to
establish the kind of the tyvar:
* For a group of type and class decls, it's just the group, not
the rest of the program
* For a tyvar bound in a pattern type signature, its the types
mentioned in the other type signatures in that bunch of patterns
* For a tyvar bound in a RULE, it's the type signatures on other
universally quantified variables in the rule
Note that this may occasionally give surprising results. For example:
data T a b = MkT (a b)
Here we deduce a::*->*, b::*
But equally valid would be a::(*->*)-> *, b::*->*
Validity checking
~~~~~~~~~~~~~~~~~
Some of the validity check could in principle be done by the kind checker,
but not all:
- During desugaring, we normalise by expanding type synonyms. Only
after this step can we check things like type-synonym saturation
e.g. type T k = k Int
type S a = a
Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
and then S is saturated. This is a GHC extension.
- Similarly, also a GHC extension, we look through synonyms before complaining
about the form of a class or instance declaration
- Ambiguity checks involve functional dependencies, and it's easier to wait
until knots have been resolved before poking into them
Also, in a mutually recursive group of types, we can't look at the TyCon until we've
finished building the loop. So to keep things simple, we postpone most validity
checking until step (3).
Knot tying
~~~~~~~~~~
During step (1) we might fault in a TyCon defined in another module, and it might
(via a loop) refer back to a TyCon defined in this module. So when we tie a big
knot around type declarations with ARecThing, so that the fault-in code can get
the TyCon being defined.
%************************************************************************
%* *
\subsection{Checking types}
%* *
%************************************************************************
\begin{code}
tcHsSigType, tcHsSigTypeNC :: UserTypeCtxt -> LHsType Name -> TcM Type
tcHsSigType ctxt hs_ty
= addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
tcHsSigTypeNC ctxt hs_ty
tcHsSigTypeNC ctxt hs_ty
= do { kinded_ty <- case expectedKindInCtxt ctxt of
Nothing -> fmap fst (kc_lhs_type_fresh hs_ty)
Just k -> kc_lhs_type hs_ty (EK k (ptext (sLit "Expected")))
; ty <- tcHsKindedType kinded_ty
; checkValidType ctxt ty
; return ty }
tcCheckHsType :: LHsType Name -> Kind -> TcM Type
tcCheckHsType hs_ty exp_kind
= do { kinded_ty <- kcCheckLHsType hs_ty (EK exp_kind (ptext (sLit "Expected")))
; ty <- tcHsKindedType kinded_ty
; return ty }
tcHsType :: LHsType Name -> TcM Type
tcHsType hs_ty
= do { (kinded_ty, _) <- kc_lhs_type_fresh hs_ty
; ty <- tcHsKindedType kinded_ty
; return ty }
tcHsInstHead :: UserTypeCtxt -> LHsType Name -> TcM ([TyVar], ThetaType, Class, [Type])
tcHsInstHead ctxt lhs_ty@(L loc hs_ty)
= setSrcSpan loc $
do { kinded_ty <- kc_hs_type hs_ty ekConstraint
; ty <- ds_type kinded_ty
; let (tvs, theta, tau) = tcSplitSigmaTy ty
; case getClassPredTys_maybe tau of
Nothing -> failWithTc (ptext (sLit "Malformed instance type"))
Just (clas,tys) -> do { checkValidInstance ctxt lhs_ty tvs theta clas tys
; return (tvs, theta, clas, tys) } }
tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
tcHsQuantifiedType tv_names hs_ty
= kcHsTyVars tv_names $ \ tv_names' ->
do { kc_ty <- kcHsSigType hs_ty
; tcTyVarBndrs tv_names' $ \ tvs ->
do { ty <- dsHsType kc_ty
; return (tvs, ty) } }
tcHsDeriv :: HsType Name -> TcM ([TyVar], Class, [Type])
tcHsDeriv = tc_hs_deriv []
tc_hs_deriv :: [LHsTyVarBndr Name] -> HsType Name
-> TcM ([TyVar], Class, [Type])
tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
=
tc_hs_deriv (tv_names1 ++ tv_names2) ty
tc_hs_deriv tv_names ty
| Just (cls_name, hs_tys) <- splitHsClassTy_maybe ty
= kcHsTyVars tv_names $ \ tv_names' ->
do { cls_kind <- kcClass cls_name
; (tys, _res_kind) <- kcApps cls_name cls_kind hs_tys
; tcTyVarBndrsKindGen tv_names' $ \ tyvars ->
do { arg_tys <- dsHsTypes tys
; cls <- tcLookupClass cls_name
; return (tyvars, cls, arg_tys) }}
| otherwise
= failWithTc (ptext (sLit "Illegal deriving item") <+> ppr ty)
tcHsVectInst :: LHsType Name -> TcM (Class, [Type])
tcHsVectInst ty
| Just (L _ cls_name, tys) <- splitLHsClassTy_maybe ty
= do { cls_kind <- kcClass cls_name
; (tys, _res_kind) <- kcApps cls_name cls_kind tys
; arg_tys <- dsHsTypes tys
; cls <- tcLookupClass cls_name
; return (cls, arg_tys)
}
| otherwise
= failWithTc $ ptext (sLit "Malformed instance type")
\end{code}
These functions are used during knot-tying in
type and class declarations, when we have to
separate kind-checking, desugaring, and validity checking
\begin{code}
kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
kcHsSigType ty = addKcTypeCtxt ty $ kcArgType ty
kcHsLiftedSigType ty = addKcTypeCtxt ty $ kcLiftedType ty
tcHsKindedType :: LHsType Name -> TcM Type
tcHsKindedType hs_ty = dsHsType hs_ty
tcHsBangType :: LHsType Name -> TcM Type
tcHsBangType (L _ (HsBangTy _ ty)) = tcHsKindedType ty
tcHsBangType ty = tcHsKindedType ty
tcHsKindedContext :: LHsContext Name -> TcM ThetaType
tcHsKindedContext hs_theta = addLocM (mapM dsHsType) hs_theta
\end{code}
%************************************************************************
%* *
The main kind checker: kcHsType
%* *
%************************************************************************
First a couple of simple wrappers for kcHsType
\begin{code}
kcLiftedType :: LHsType Name -> TcM (LHsType Name)
kcLiftedType ty = kc_lhs_type ty ekLifted
kcArgs :: SDoc -> [LHsType Name] -> Kind -> TcM [LHsType Name]
kcArgs what tys kind
= sequence [ kc_lhs_type ty (expArgKind what kind n)
| (ty,n) <- tys `zip` [1..] ]
kcArgType :: LHsType Name -> TcM (LHsType Name)
kcArgType ty = kc_lhs_type ty ekArg
kcCheckLHsType :: LHsType Name -> ExpKind -> TcM (LHsType Name)
kcCheckLHsType ty kind = addKcTypeCtxt ty $ kc_lhs_type ty kind
\end{code}
Like tcExpr, kc_hs_type takes an expected kind which it unifies with
the kind it figures out. When we don't know what kind to expect, we use
kc_lhs_type_fresh, to first create a new meta kind variable and use that as
the expected kind.
\begin{code}
kcLHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
kcLHsType ty = addKcTypeCtxt ty (kc_lhs_type_fresh ty)
kc_lhs_type_fresh :: LHsType Name -> TcM (LHsType Name, TcKind)
kc_lhs_type_fresh ty = do
kv <- newMetaKindVar
r <- kc_lhs_type ty (EK kv (ptext (sLit "Expected")))
return (r, kv)
kc_lhs_types :: [(LHsType Name, ExpKind)] -> TcM [LHsType Name]
kc_lhs_types tys_w_kinds = mapM (uncurry kc_lhs_type) tys_w_kinds
kc_lhs_type :: LHsType Name -> ExpKind -> TcM (LHsType Name)
kc_lhs_type (L span ty) exp_kind
= setSrcSpan span $
do { traceTc "kc_lhs_type" (ppr ty <+> ppr exp_kind)
; ty' <- kc_hs_type ty exp_kind
; return (L span ty') }
kc_hs_type :: HsType Name -> ExpKind -> TcM (HsType Name)
kc_hs_type (HsParTy ty) exp_kind = do
ty' <- kc_lhs_type ty exp_kind
return (HsParTy ty')
kc_hs_type (HsTyVar name) exp_kind
| name == tyConName unitTyCon
= kc_hs_type (HsTupleTy HsBoxedOrConstraintTuple []) exp_kind
| otherwise = do
(ty, k) <- kcTyVar name
checkExpectedKind ty k exp_kind
return ty
kc_hs_type (HsListTy ty) exp_kind = do
ty' <- kcLiftedType ty
checkExpectedKind ty liftedTypeKind exp_kind
return (HsListTy ty')
kc_hs_type (HsPArrTy ty) exp_kind = do
ty' <- kcLiftedType ty
checkExpectedKind ty liftedTypeKind exp_kind
return (HsPArrTy ty')
kc_hs_type (HsKindSig ty sig_k) exp_kind = do
sig_k' <- scDsLHsKind sig_k
ty' <- kc_lhs_type ty
(EK sig_k' (ptext (sLit "An enclosing kind signature specified")))
checkExpectedKind ty sig_k' exp_kind
return (HsKindSig ty' sig_k)
kc_hs_type ty@(HsTupleTy HsBoxedOrConstraintTuple tys) exp_kind@(EK exp_k _ctxt)
| isConstraintOrLiftedKind exp_k
= do { tys' <- kcArgs (ptext (sLit "a tuple")) tys exp_k
; return $ if isConstraintKind exp_k
then HsTupleTy HsConstraintTuple tys'
else HsTupleTy HsBoxedTuple tys' }
| otherwise
= do { k <- newMetaKindVar
; tys' <- kcArgs (ptext (sLit "a tuple")) tys k
; k' <- zonkTcKind k
; if isConstraintKind k'
then do { checkExpectedKind ty k' exp_kind
; return (HsTupleTy HsConstraintTuple tys') }
else do { tys'' <- kcArgs (ptext (sLit "a tuple")) tys liftedTypeKind
; checkExpectedKind ty liftedTypeKind exp_kind
; return (HsTupleTy HsBoxedTuple tys'') } }
kc_hs_type ty@(HsTupleTy tup_sort tys) exp_kind
= do { tys' <- kcArgs cxt_doc tys arg_kind
; checkExpectedKind ty out_kind exp_kind
; return (HsTupleTy tup_sort tys') }
where
arg_kind = case tup_sort of
HsBoxedTuple -> liftedTypeKind
HsUnboxedTuple -> argTypeKind
HsConstraintTuple -> constraintKind
_ -> panic "kc_hs_type arg_kind"
out_kind = case tup_sort of
HsUnboxedTuple -> ubxTupleKind
_ -> arg_kind
cxt_doc = case tup_sort of
HsBoxedTuple -> ptext (sLit "a tuple")
HsUnboxedTuple -> ptext (sLit "an unboxed tuple")
HsConstraintTuple -> ptext (sLit "a constraint tuple")
_ -> panic "kc_hs_type tup_sort"
kc_hs_type ty@(HsFunTy ty1 ty2) exp_kind@(EK _ ctxt) = do
ty1' <- kc_lhs_type ty1 (EK argTypeKind ctxt)
ty2' <- kc_lhs_type ty2 (EK openTypeKind ctxt)
checkExpectedKind ty liftedTypeKind exp_kind
return (HsFunTy ty1' ty2')
kc_hs_type ty@(HsOpTy ty1 (_, l_op@(L loc op)) ty2) exp_kind = do
(wop, op_kind) <- kcTyVar op
[ty1',ty2'] <- kcCheckApps l_op op_kind [ty1,ty2] ty exp_kind
let op' = case wop of
HsTyVar name -> (WpKiApps [], L loc name)
HsWrapTy wrap (HsTyVar name) -> (wrap, L loc name)
_ -> panic "kc_hs_type HsOpTy"
return (HsOpTy ty1' op' ty2')
kc_hs_type ty@(HsAppTy ty1 ty2) exp_kind = do
let (fun_ty, arg_tys) = splitHsAppTys ty1 [ty2]
(fun_ty', fun_kind) <- kc_lhs_type_fresh fun_ty
arg_tys' <- kcCheckApps fun_ty fun_kind arg_tys ty exp_kind
return (mkHsAppTys fun_ty' arg_tys')
kc_hs_type ipTy@(HsIParamTy n ty) exp_kind = do
ty' <- kc_lhs_type ty
(EK liftedTypeKind
(ptext (sLit "The type argument of the implicit parameter had")))
checkExpectedKind ipTy constraintKind exp_kind
return (HsIParamTy n ty')
kc_hs_type ty@(HsEqTy ty1 ty2) exp_kind = do
(ty1', kind1) <- kc_lhs_type_fresh ty1
(ty2', kind2) <- kc_lhs_type_fresh ty2
checkExpectedKind ty2 kind2
(EK kind1 (ptext (sLit "The left argument of the equality predicate had")))
checkExpectedKind ty constraintKind exp_kind
return (HsEqTy ty1' ty2')
kc_hs_type (HsCoreTy ty) exp_kind = do
checkExpectedKind ty (typeKind ty) exp_kind
return (HsCoreTy ty)
kc_hs_type (HsForAllTy exp tv_names context ty) exp_kind
= kcHsTyVars tv_names $ \ tv_names' ->
do { ctxt' <- kcHsContext context
; ty' <- kc_lhs_type ty exp_kind
; return (HsForAllTy exp tv_names' ctxt' ty') }
kc_hs_type (HsBangTy b ty) exp_kind
= do { ty' <- kc_lhs_type ty exp_kind
; return (HsBangTy b ty') }
kc_hs_type ty@(HsRecTy _) _exp_kind
= failWithTc (ptext (sLit "Unexpected record type") <+> ppr ty)
#ifdef GHCI /* Only if bootstrapped */
kc_hs_type (HsSpliceTy sp fvs _) exp_kind = do
(ty, k) <- kcSpliceType sp fvs
checkExpectedKind ty k exp_kind
return ty
#else
kc_hs_type ty@(HsSpliceTy {}) _exp_kind =
failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
#endif
kc_hs_type (HsQuasiQuoteTy {}) _exp_kind =
panic "kc_hs_type"
kc_hs_type (HsDocTy ty _) exp_kind
= kc_hs_type (unLoc ty) exp_kind
kc_hs_type ty@(HsExplicitListTy _k tys) exp_kind
= do { ty_k_s <- mapM kc_lhs_type_fresh tys
; kind <- unifyKinds (ptext (sLit "In a promoted list")) ty_k_s
; checkExpectedKind ty (mkListTy kind) exp_kind
; return (HsExplicitListTy kind (map fst ty_k_s)) }
kc_hs_type ty@(HsExplicitTupleTy _ tys) exp_kind = do
ty_k_s <- mapM kc_lhs_type_fresh tys
let tupleKi = mkTyConApp (tupleTyCon BoxedTuple (length tys)) (map snd ty_k_s)
checkExpectedKind ty tupleKi exp_kind
return (HsExplicitTupleTy (map snd ty_k_s) (map fst ty_k_s))
kc_hs_type (HsWrapTy {}) _exp_kind =
panic "kc_hs_type HsWrapTy"
kcApps :: Outputable a
=> a
-> TcKind
-> [LHsType Name]
-> TcM ([LHsType Name], TcKind)
kcApps the_fun fun_kind args
= do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
; args' <- kc_lhs_types args_w_kinds
; return (args', res_kind) }
kcCheckApps :: Outputable a => a -> TcKind -> [LHsType Name]
-> HsType Name
-> ExpKind
-> TcM ([LHsType Name])
kcCheckApps the_fun fun_kind args ty exp_kind
= do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
; args_w_kinds' <- kc_lhs_types args_w_kinds
; checkExpectedKind ty res_kind exp_kind
; return args_w_kinds' }
splitFunKind :: SDoc -> Int -> TcKind -> [b] -> TcM ([(b,ExpKind)], TcKind)
splitFunKind _ _ fk [] = return ([], fk)
splitFunKind the_fun arg_no fk (arg:args)
= do { mb_fk <- matchExpectedFunKind fk
; case mb_fk of
Nothing -> failWithTc too_many_args
Just (ak,fk') -> do { (aks, rk) <- splitFunKind the_fun (arg_no+1) fk' args
; return ((arg
,expArgKind (quotes the_fun) ak arg_no)
:aks ,rk) } }
where
too_many_args = quotes the_fun <+>
ptext (sLit "is applied to too many type arguments")
kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
kcHsContext ctxt = wrapLocM (mapM kcHsLPredType) ctxt
kcHsLPredType :: LHsType Name -> TcM (LHsType Name)
kcHsLPredType pred = kc_lhs_type pred ekConstraint
kcTyVar :: Name -> TcM (HsType Name, TcKind)
kcTyVar name
= do { traceTc "lk1" (ppr name)
; thing <- tcLookup name
; traceTc "lk2" (ppr name <+> ppr thing)
; case thing of
ATyVar _ ty -> wrap_mono (typeKind ty)
AThing kind -> wrap_poly kind
AGlobal (ATyCon tc) -> wrap_poly (tyConKind tc)
AGlobal (ADataCon dc) -> kcDataCon dc >>= wrap_poly
_ -> wrongThingErr "type" thing name }
where
wrap_mono kind = do { traceTc "lk3" (ppr name <+> dcolon <+> ppr kind)
; return (HsTyVar name, kind) }
wrap_poly kind
| null kvs = wrap_mono kind
| otherwise
= do { traceTc "lk4" (ppr name <+> dcolon <+> ppr kind)
; kvs' <- mapM (const newMetaKindVar) kvs
; let ki = substKiWith kvs kvs' ki_body
; return (HsWrapTy (WpKiApps kvs') (HsTyVar name), ki) }
where (kvs, ki_body) = splitForAllTys kind
kcDataCon :: DataCon -> TcM TcKind
kcDataCon dc = do
let ty = dataConUserType dc
unless (isPromotableType ty) $ promoteErr dc ty
let ki = promoteType ty
traceTc "prm" (ppr ty <+> ptext (sLit "~~>") <+> ppr ki)
return ki
where
promoteErr dc ty = failWithTc (quotes (ppr dc) <+> ptext (sLit "of type")
<+> quotes (ppr ty) <+> ptext (sLit "is not promotable"))
kcClass :: Name -> TcM TcKind
kcClass cls = do
thing <- tcLookup cls
case thing of
AThing kind -> return kind
AGlobal (ATyCon tc)
| Just cls <- tyConClass_maybe tc -> return (tyConKind (classTyCon cls))
_ -> wrongThingErr "class" thing cls
\end{code}
%************************************************************************
%* *
Desugaring
%* *
%************************************************************************
Note [Desugaring types]
~~~~~~~~~~~~~~~~~~~~~~~
The type desugarer is phase 2 of dealing with HsTypes. Specifically:
* It transforms from HsType to Type
* It zonks any kinds. The returned type should have no mutable kind
or type variables (hence returning Type not TcType):
- any unconstrained kind variables are defaulted to AnyK just
as in TcHsSyn.
- there are no mutable type variables because we are
kind-checking a type
Reason: the returned type may be put in a TyCon or DataCon where
it will never subsequently be zonked.
You might worry about nested scopes:
..a:kappa in scope..
let f :: forall b. T '[a,b] -> Int
In this case, f's type could have a mutable kind variable kappa in it;
and we might then default it to AnyK when dealing with f's type
signature. But we don't expect this to happen because we can't get a
lexically scoped type variable with a mutable kind variable in it. A
delicate point, this. If it becomes an issue we might need to
distinguish top-level from nested uses.
Moreover
* it cannot fail,
* it does no unifications
* it does no validity checking, except for structural matters, such as
(a) spurious ! annotations.
(b) a class used as a type
\begin{code}
zonkTcKindToKind :: TcKind -> TcM Kind
zonkTcKindToKind = zonkType (mkZonkTcTyVar (\ _ -> return anyKind) mkTyVarTy)
dsHsType :: LHsType Name -> TcM Type
dsHsType ty = ds_type (unLoc ty)
ds_type :: HsType Name -> TcM Type
ds_type ty@(HsTyVar _)
= ds_app ty []
ds_type (HsParTy ty)
= dsHsType ty
ds_type ty@(HsBangTy {})
= failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
ds_type ty@(HsRecTy {})
= failWithTc (ptext (sLit "Unexpected record type:") <+> ppr ty)
ds_type (HsKindSig ty _)
= dsHsType ty
ds_type (HsListTy ty) = do
tau_ty <- dsHsType ty
checkWiredInTyCon listTyCon
return (mkListTy tau_ty)
ds_type (HsPArrTy ty) = do
tau_ty <- dsHsType ty
checkWiredInTyCon parrTyCon
return (mkPArrTy tau_ty)
ds_type (HsTupleTy hs_con tys) = do
con <- case hs_con of
HsUnboxedTuple -> return UnboxedTuple
HsBoxedTuple -> return BoxedTuple
HsConstraintTuple -> return ConstraintTuple
_ -> panic "ds_type HsTupleTy"
let tycon = tupleTyCon con (length tys)
tau_tys <- dsHsTypes tys
checkWiredInTyCon tycon
return (mkTyConApp tycon tau_tys)
ds_type (HsFunTy ty1 ty2) = do
tau_ty1 <- dsHsType ty1
tau_ty2 <- dsHsType ty2
return (mkFunTy tau_ty1 tau_ty2)
ds_type (HsOpTy ty1 (wrap, (L span op)) ty2) =
setSrcSpan span (ds_app (HsWrapTy wrap (HsTyVar op)) [ty1,ty2])
ds_type ty@(HsAppTy _ _)
= ds_app ty []
ds_type (HsIParamTy n ty) = do
tau_ty <- dsHsType ty
return (mkIPPred n tau_ty)
ds_type (HsEqTy ty1 ty2) = do
tau_ty1 <- dsHsType ty1
tau_ty2 <- dsHsType ty2
return (mkEqPred (tau_ty1, tau_ty2))
ds_type (HsForAllTy _ tv_names ctxt ty)
= tcTyVarBndrsKindGen tv_names $ \ tyvars -> do
theta <- mapM dsHsType (unLoc ctxt)
tau <- dsHsType ty
return (mkSigmaTy tyvars theta tau)
ds_type (HsDocTy ty _)
= dsHsType ty
ds_type (HsSpliceTy _ _ kind)
= do { kind' <- zonkType (mkZonkTcTyVar (\ _ -> return liftedTypeKind) mkTyVarTy)
kind
; newFlexiTyVarTy kind' }
ds_type (HsQuasiQuoteTy {}) = panic "ds_type"
ds_type (HsCoreTy ty) = return ty
ds_type (HsExplicitListTy kind tys) = do
kind' <- zonkTcKindToKind kind
ds_tys <- mapM dsHsType tys
return $
foldr (\a b -> mkTyConApp (buildPromotedDataTyCon consDataCon) [kind', a, b])
(mkTyConApp (buildPromotedDataTyCon nilDataCon) [kind']) ds_tys
ds_type (HsExplicitTupleTy kis tys) = do
MASSERT( length kis == length tys )
kis' <- mapM zonkTcKindToKind kis
tys' <- mapM dsHsType tys
return $ mkTyConApp (buildPromotedDataTyCon (tupleCon BoxedTuple (length kis'))) (kis' ++ tys')
ds_type (HsWrapTy (WpKiApps kappas) ty) = do
tau <- ds_type ty
kappas' <- mapM zonkTcKindToKind kappas
return (mkAppTys tau kappas')
dsHsTypes :: [LHsType Name] -> TcM [Type]
dsHsTypes arg_tys = mapM dsHsType arg_tys
\end{code}
Note [Kind of a type splice]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider these terms, each with TH type splice inside:
[| e1 :: Maybe $(..blah..) |]
[| e2 :: $(..blah..) |]
When kind-checking the type signature, we'll kind-check the splice
$(..blah..); we want to give it a kind that can fit in any context,
as if $(..blah..) :: forall k. k.
In the e1 example, the context of the splice fixes kappa to *. But
in the e2 example, we'll desugar the type, zonking the kind unification
variables as we go. When we encournter the unconstrained kappa, we
want to default it to '*', not to AnyK.
Help functions for type applications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
\begin{code}
ds_app :: HsType Name -> [LHsType Name] -> TcM Type
ds_app (HsAppTy ty1 ty2) tys
= ds_app (unLoc ty1) (ty2:tys)
ds_app ty tys = do
arg_tys <- dsHsTypes tys
case ty of
HsTyVar fun -> ds_var_app fun arg_tys
_ -> do fun_ty <- ds_type ty
return (mkAppTys fun_ty arg_tys)
ds_var_app :: Name -> [Type] -> TcM Type
ds_var_app name arg_tys
| isTvNameSpace (rdrNameSpace (nameRdrName name))
= do { thing <- tcLookup name
; case thing of
ATyVar _ ty -> return (mkAppTys ty arg_tys)
_ -> wrongThingErr "type" thing name }
| otherwise
= do { thing <- tcLookupGlobal name
; case thing of
ATyCon tc -> return (mkTyConApp tc arg_tys)
ADataCon dc -> return (mkTyConApp (buildPromotedDataTyCon dc) arg_tys)
_ -> wrongThingErr "type" (AGlobal thing) name }
addKcTypeCtxt :: LHsType Name -> TcM a -> TcM a
addKcTypeCtxt (L _ other_ty) thing = addErrCtxt (typeCtxt other_ty) thing
typeCtxt :: HsType Name -> SDoc
typeCtxt ty = ptext (sLit "In the type") <+> quotes (ppr ty)
\end{code}
%************************************************************************
%* *
Type-variable binders
%* *
%************************************************************************
Note [Kind-checking kind-polymorphic types]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider:
f :: forall (f::k -> *) a. f a -> Int
Here, the [LHsTyVarBndr Name] of the forall type will be [f,a], where
a is a UserTyVar -> type variable without kind annotation
f is a KindedTyVar -> type variable with kind annotation
If were were to allow binding sites for kind variables, thus
f :: forall @k (f :: k -> *) a. f a -> Int
then we'd also need
k is a UserKiVar -> kind variable (they don't need annotation,
since we only have BOX for a super kind)
\begin{code}
kcHsTyVars :: [LHsTyVarBndr Name]
-> ([LHsTyVarBndr Name] -> TcM r)
-> TcM r
kcHsTyVars tvs thing_inside
= do { kinded_tvs <- mapM (wrapLocM kcHsTyVar) tvs
; tcExtendKindEnvTvs kinded_tvs thing_inside }
kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
kcHsTyVar tyvar = do in_scope <- getInLocalScope
if in_scope (hsTyVarName tyvar)
then do inscope_tyvar <- tcLookupTyVar (hsTyVarName tyvar)
return (UserTyVar (tyVarName inscope_tyvar)
(tyVarKind inscope_tyvar))
else kcHsTyVar' tyvar
where
kcHsTyVar' (UserTyVar name _) = UserTyVar name <$> newMetaKindVar
kcHsTyVar' (KindedTyVar name kind _) = do
kind' <- scDsLHsKind kind
return (KindedTyVar name kind kind')
tcTyVarBndrs :: [LHsTyVarBndr Name]
-> ([TyVar] -> TcM r)
-> TcM r
tcTyVarBndrs bndrs thing_inside = do
tyvars <- mapM (zonk . hsTyVarNameKind . unLoc) bndrs
tcExtendTyVarEnv tyvars (thing_inside tyvars)
where
zonk (name, kind)
= do { kind' <- zonkTcKind kind
; checkTc (noHashInKind kind') (ptext (sLit "Kind signature contains # or (#)"))
; return (mkTyVar name kind') }
tcTyVarBndrsKindGen :: [LHsTyVarBndr Name] -> ([TyVar] -> TcM r) -> TcM r
tcTyVarBndrsKindGen bndrs thing_inside
= do { let kinds = map (hsTyVarKind . unLoc) bndrs
; (kvs, zonked_kinds) <- kindGeneralizeKinds kinds
; let tyvars = zipWith mkTyVar (map hsLTyVarName bndrs) zonked_kinds
ktvs = kvs ++ tyvars
; traceTc "tcTyVarBndrsKindGen" (ppr (bndrs, kvs, tyvars))
; tcExtendTyVarEnv ktvs (thing_inside ktvs) }
\end{code}
Note [Kinds of quantified type variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tcTyVarBndrsKindGen quantifies over a specified list of type variables,
*and* over the kind variables mentioned in the kinds of those tyvars.
Note that we must zonk those kinds (obviously) but less obviously, we
must return type variables whose kinds are zonked too. Example
(a :: k7) where k7 := k9 -> k9
We must return
[k9, a:k9->k9]
and NOT
[k9, a:k7]
Reason: we're going to turn this into a for-all type,
forall k9. forall (a:k7). blah
which the type checker will then instantiate, and instantiate does not
look through unification variables!
Hence using zonked_kinds when forming 'tyvars'.
\begin{code}
tcTyClTyVars :: Name -> [LHsTyVarBndr Name]
-> ([TyVar] -> Kind -> TcM a) -> TcM a
tcTyClTyVars tycon tyvars thing_inside
= do { thing <- tcLookup tycon
; let { kind =
case thing of
AThing kind -> kind
_ -> panic "tcTyClTyVars"
; (kvs, body) = splitForAllTys kind
; (kinds, res) = splitKindFunTysN (length names) body
; names = hsLTyVarNames tyvars
; tvs = zipWith mkTyVar names kinds
; all_vs = kvs ++ tvs }
; tcExtendTyVarEnv all_vs (thing_inside all_vs res) }
kindGeneralizeKinds :: [TcKind] -> TcM ([KindVar], [Kind])
kindGeneralizeKinds kinds
= do {
; zonked_kinds <- mapM zonkTcKind kinds
; gbl_tvs <- tcGetGlobalTyVars
; let kvs_to_quantify = tyVarsOfTypes zonked_kinds
`minusVarSet` gbl_tvs
; kvs <- ASSERT2 (all isKiVar (varSetElems kvs_to_quantify), ppr kvs_to_quantify)
zonkQuantifiedTyVars kvs_to_quantify
; final_kinds <- mapM zonkTcKind zonked_kinds
; traceTc "generalizeKind" ( ppr kinds <+> ppr kvs_to_quantify
<+> ppr kvs <+> ppr final_kinds)
; return (kvs, final_kinds) }
kindGeneralizeKind :: TcKind -> TcM ( [KindVar]
, Kind )
kindGeneralizeKind kind = do
(kvs, [kind']) <- kindGeneralizeKinds [kind]
return (kvs, kind')
tcDataKindSig :: Kind -> TcM [TyVar]
tcDataKindSig kind
= do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
; span <- getSrcSpanM
; us <- newUniqueSupply
; let uniqs = uniqsFromSupply us
; return [ mk_tv span uniq str kind
| ((kind, str), uniq) <- arg_kinds `zip` dnames `zip` uniqs ] }
where
(arg_kinds, res_kind) = splitKindFunTys kind
mk_tv loc uniq str kind = mkTyVar name kind
where
name = mkInternalName uniq occ loc
occ = mkOccName tvName str
dnames = map ('$' :) names
names :: [String]
names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
badKindSig :: Kind -> SDoc
badKindSig kind
= hang (ptext (sLit "Kind signature on data type declaration has non-* return kind"))
2 (ppr kind)
\end{code}
Note [Avoid name clashes for associated data types]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider class C a b where
data D b :: * -> *
When typechecking the decl for D, we'll invent an extra type variable for D,
to fill out its kind. We *don't* want this type variable to be 'a', because
in an .hi file we'd get
class C a b where
data D b a
which makes it look as if there are *two* type indices. But there aren't!
So we use $a instead, which cannot clash with a user-written type variable.
Remember that type variable binders in interface files are just FastStrings,
not proper Names.
(The tidying phase can't help here because we don't tidy TyCons. Another
alternative would be to record the number of indexing parameters in the
interface file.)
%************************************************************************
%* *
Scoped type variables
%* *
%************************************************************************
tcAddScopedTyVars is used for scoped type variables added by pattern
type signatures
e.g. \ ((x::a), (y::a)) -> x+y
They never have explicit kinds (because this is source-code only)
They are mutable (because they can get bound to a more specific type).
Usually we kind-infer and expand type splices, and then
tupecheck/desugar the type. That doesn't work well for scoped type
variables, because they scope left-right in patterns. (e.g. in the
example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
The current not-very-good plan is to
* find all the types in the patterns
* find their free tyvars
* do kind inference
* bring the kinded type vars into scope
* BUT throw away the kind-checked type
(we'll kind-check it again when we type-check the pattern)
This is bad because throwing away the kind checked type throws away
its splices. But too bad for now. [July 03]
Historical note:
We no longer specify that these type variables must be univerally
quantified (lots of email on the subject). If you want to put that
back in, you need to
a) Do a checkSigTyVars after thing_inside
b) More insidiously, don't pass in expected_ty, else
we unify with it too early and checkSigTyVars barfs
Instead you have to pass in a fresh ty var, and unify
it with expected_ty afterwards
\begin{code}
tcHsPatSigType :: UserTypeCtxt
-> LHsType Name
-> TcM ([TyVar],
Type)
tcHsPatSigType ctxt hs_ty
= addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
do {
in_scope <- getInLocalScope
; let span = getLoc hs_ty
sig_tvs = userHsTyVarBndrs $ map (L span) $
filterOut in_scope $
nameSetToList (extractHsTyVars hs_ty)
; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
; checkValidType ctxt sig_ty
; return (tyvars, sig_ty)
}
tcPatSig :: UserTypeCtxt
-> LHsType Name
-> TcSigmaType
-> TcM (TcType,
[(Name, TcType)],
HsWrapper)
tcPatSig ctxt sig res_ty
= do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
; if null sig_tvs then do {
wrap <- tcSubType PatSigOrigin ctxt res_ty sig_ty
; return (sig_ty, [], wrap)
} else do {
; let in_pat_bind = case ctxt of
BindPatSigCtxt -> True
_ -> False
; ASSERT( not in_pat_bind || null sig_tvs ) return ()
; let bad_tvs = filterOut (`elemVarSet` exactTyVarsOfType sig_ty) sig_tvs
; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
; sig_tvs' <- tcInstSigTyVars sig_tvs
; let sig_ty' = substTyWith sig_tvs sig_tv_tys' sig_ty
sig_tv_tys' = mkTyVarTys sig_tvs'
; wrap <- tcSubType PatSigOrigin ctxt res_ty sig_ty'
; binds_in_scope <- getScopedTyVarBinds
; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys'
; check binds_in_scope tv_binds
; return (sig_ty', tv_binds, wrap)
} }
where
check _ [] = return ()
check in_scope ((n,ty):rest) = do { check_one in_scope n ty
; check ((n,ty):in_scope) rest }
check_one in_scope n ty
= checkTc (null dups) (dupInScope n (head dups) ty)
where
dups = [n' | (n',ty') <- in_scope, eqType ty' ty]
\end{code}
%************************************************************************
%* *
Checking kinds
%* *
%************************************************************************
We would like to get a decent error message from
(a) Under-applied type constructors
f :: (Maybe, Maybe)
(b) Over-applied type constructors
f :: Int x -> Int x
\begin{code}
data ExpKind = EK TcKind SDoc
instance Outputable ExpKind where
ppr (EK k _) = ptext (sLit "Expected kind:") <+> ppr k
ekLifted, ekArg, ekConstraint :: ExpKind
ekLifted = EK liftedTypeKind (ptext (sLit "Expected"))
ekArg = EK argTypeKind (ptext (sLit "Expected"))
ekConstraint = EK constraintKind (ptext (sLit "Expected"))
expArgKind :: SDoc -> TcKind -> Int -> ExpKind
expArgKind exp kind arg_no = EK kind (ptext (sLit "The") <+> speakNth arg_no
<+> ptext (sLit "argument of") <+> exp
<+> ptext (sLit "should have"))
unifyKinds :: SDoc -> [(LHsType Name, TcKind)] -> TcM TcKind
unifyKinds fun act_kinds = do
kind <- newMetaKindVar
let checkArgs (arg_no, (ty, act_kind)) =
checkExpectedKind ty act_kind (expArgKind (quotes fun) kind arg_no)
mapM_ checkArgs (zip [1..] act_kinds)
return kind
checkExpectedKind :: Outputable a => a -> TcKind -> ExpKind -> TcM ()
checkExpectedKind ty act_kind ek@(EK exp_kind ek_ctxt) = do
traceTc "checkExpectedKind" (ppr ty $$ ppr act_kind $$ ppr ek)
(_errs, mb_r) <- tryTc (unifyKind act_kind exp_kind)
case mb_r of
Just _ -> return ()
Nothing -> do
exp_kind <- zonkTcKind exp_kind
act_kind <- zonkTcKind act_kind
env0 <- tcInitTidyEnv
let (exp_as, _) = splitKindFunTys exp_kind
(act_as, _) = splitKindFunTys act_kind
n_exp_as = length exp_as
n_act_as = length act_as
n_diff_as = n_act_as n_exp_as
(env1, tidy_exp_kind) = tidyOpenKind env0 exp_kind
(env2, tidy_act_kind) = tidyOpenKind env1 act_kind
err | n_exp_as < n_act_as
= ptext (sLit "Expecting") <+>
speakN n_diff_as <+> ptext (sLit "more argument") <>
(if n_diff_as > 1 then char 's' else empty) <+>
ptext (sLit "to") <+> quotes (ppr ty)
| isConstraintKind tidy_act_kind
= text "Predicate" <+> quotes (ppr ty) <+> text "used as a type"
| isConstraintKind tidy_exp_kind
= text "Type of kind" <+> ppr tidy_act_kind <+> text "used as a constraint"
| isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind
= ptext (sLit "Expecting a lifted type, but") <+> quotes (ppr ty)
<+> ptext (sLit "is unlifted")
| isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind
= ptext (sLit "Expecting an unlifted type, but") <+> quotes (ppr ty)
<+> ptext (sLit "is lifted")
| otherwise
= ptext (sLit "Kind mis-match") $$ more_info
more_info = sep [ ek_ctxt <+> ptext (sLit "kind")
<+> quotes (pprKind tidy_exp_kind) <> comma,
ptext (sLit "but") <+> quotes (ppr ty) <+>
ptext (sLit "has kind") <+> quotes (pprKind tidy_act_kind)]
failWithTcM (env2, err)
\end{code}
%************************************************************************
%* *
Sort checking kinds
%* *
%************************************************************************
scDsLHsKind converts a user-written kind to an internal, sort-checked kind.
It does sort checking and desugaring at the same time, in one single pass.
It fails when the kinds are not well-formed (eg. data A :: * Int), or if there
are non-promotable or non-fully applied kinds.
\begin{code}
scDsLHsKind :: LHsKind Name -> TcM Kind
scDsLHsKind k = addErrCtxt (ptext (sLit "In the kind") <+> quotes (ppr k)) $
sc_ds_lhs_kind k
scDsLHsMaybeKind :: Maybe (LHsKind Name) -> TcM (Maybe Kind)
scDsLHsMaybeKind Nothing = return Nothing
scDsLHsMaybeKind (Just k) = do k' <- scDsLHsKind k
return (Just k')
sc_ds_lhs_kind :: LHsKind Name -> TcM Kind
sc_ds_lhs_kind (L span ki) = setSrcSpan span (sc_ds_hs_kind ki)
sc_ds_hs_kind :: HsKind Name -> TcM Kind
sc_ds_hs_kind k@(HsTyVar _) = sc_ds_app k []
sc_ds_hs_kind k@(HsAppTy _ _) = sc_ds_app k []
sc_ds_hs_kind (HsParTy ki) = sc_ds_lhs_kind ki
sc_ds_hs_kind (HsFunTy ki1 ki2) =
do kappa_ki1 <- sc_ds_lhs_kind ki1
kappa_ki2 <- sc_ds_lhs_kind ki2
return (mkArrowKind kappa_ki1 kappa_ki2)
sc_ds_hs_kind (HsListTy ki) =
do kappa <- sc_ds_lhs_kind ki
checkWiredInTyCon listTyCon
return $ mkListTy kappa
sc_ds_hs_kind (HsTupleTy _ kis) =
do kappas <- mapM sc_ds_lhs_kind kis
checkWiredInTyCon tycon
return $ mkTyConApp tycon kappas
where tycon = tupleTyCon BoxedTuple (length kis)
sc_ds_hs_kind k = panic ("sc_ds_hs_kind: " ++ showPpr k)
sc_ds_app :: HsKind Name -> [LHsKind Name] -> TcM Kind
sc_ds_app (HsAppTy ki1 ki2) kis = sc_ds_app (unLoc ki1) (ki2:kis)
sc_ds_app (HsTyVar tc) kis =
do arg_kis <- mapM sc_ds_lhs_kind kis
sc_ds_var_app tc arg_kis
sc_ds_app ki _ = failWithTc (quotes (ppr ki) <+>
ptext (sLit "is not a kind constructor"))
sc_ds_var_app :: Name -> [Kind] -> TcM Kind
sc_ds_var_app name arg_kis
| name == liftedTypeKindTyConName
|| name == constraintKindTyConName = do
unless (null arg_kis)
(failWithTc (text "Kind" <+> ppr name <+> text "cannot be applied"))
thing <- tcLookup name
case thing of
AGlobal (ATyCon tc) -> return (mkTyConApp tc [])
_ -> panic "sc_ds_var_app 1"
sc_ds_var_app name arg_kis = do
(_errs, mb_thing) <- tryTc (tcLookup name)
case mb_thing of
Just (AGlobal (ATyCon tc))
| isAlgTyCon tc || isTupleTyCon tc -> do
data_kinds <- xoptM Opt_DataKinds
unless data_kinds $ addErr (dataKindsErr name)
let tc_kind = tyConKind tc
case isPromotableKind tc_kind of
Just n | n == length arg_kis ->
return (mkTyConApp (mkPromotedTypeTyCon tc) arg_kis)
Just _ -> err tc_kind "is not fully applied"
Nothing -> err tc_kind "is not promotable"
Just thing -> wrongThingErr "promoted type" thing name
Nothing -> ASSERT2 ( isTyConName name, ppr name )
failWithTc (ptext (sLit "Promoted kind") <+>
quotes (ppr name) <+>
ptext (sLit "used in a mutually recursive group"))
where err k m = failWithTc ( quotes (ppr name) <+> ptext (sLit "of kind")
<+> quotes (ppr k) <+> ptext (sLit m))
\end{code}
%************************************************************************
%* *
Scoped type variables
%* *
%************************************************************************
\begin{code}
pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
pprHsSigCtxt ctxt hs_ty = sep [ ptext (sLit "In") <+> pprUserTypeCtxt ctxt <> colon,
nest 2 (pp_sig ctxt) ]
where
pp_sig (FunSigCtxt n) = pp_n_colon n
pp_sig (ConArgCtxt n) = pp_n_colon n
pp_sig (ForSigCtxt n) = pp_n_colon n
pp_sig _ = ppr (unLoc hs_ty)
pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
badPatSigTvs :: TcType -> [TyVar] -> SDoc
badPatSigTvs sig_ty bad_tvs
= vcat [ fsep [ptext (sLit "The type variable") <> plural bad_tvs,
quotes (pprWithCommas ppr bad_tvs),
ptext (sLit "should be bound by the pattern signature") <+> quotes (ppr sig_ty),
ptext (sLit "but are actually discarded by a type synonym") ]
, ptext (sLit "To fix this, expand the type synonym")
, ptext (sLit "[Note: I hope to lift this restriction in due course]") ]
dupInScope :: Name -> Name -> Type -> SDoc
dupInScope n n' _
= hang (ptext (sLit "The scoped type variables") <+> quotes (ppr n) <+> ptext (sLit "and") <+> quotes (ppr n'))
2 (vcat [ptext (sLit "are bound to the same type (variable)"),
ptext (sLit "Distinct scoped type variables must be distinct")])
\end{code}