%
% (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,
UserTypeCtxt(..),
kcLookupKind, kcTyClTyVars, tcTyClTyVars,
tcHsConArgType, tcDataKindSig,
tcClassSigType,
KindCheckingStrategy(..), kcStrategy, kcStrategyFamDecl,
kcHsTyVarBndrs, tcHsTyVarBndrs,
tcHsLiftedType, tcHsOpenType,
tcLHsType, tcCheckLHsType,
tcHsContext, tcInferApps, tcHsArgTys,
kindGeneralize, checkKind,
tcLHsKind,
tcHsPatSigType, tcPatSig
) where
#include "HsVersions.h"
import HsSyn
import TcRnMonad
import TcEvidence( HsWrapper )
import TcEnv
import TcMType
import TcValidity
import TcUnify
import TcIface
import TcType
import Type
import TypeRep( Type(..) )
import Kind
import Var
import VarSet
import TyCon
import ConLike
import DataCon
import TysPrim ( liftedTypeKindTyConName, constraintKindTyConName )
import Class
import Name
import NameEnv
import TysWiredIn
import BasicTypes
import SrcLoc
import DynFlags ( ExtensionFlag( Opt_DataKinds ), getDynFlags )
import Unique
import UniqSupply
import Outputable
import FastString
import Util
import Control.Monad ( unless, when, zipWithM )
import PrelNames( ipClassName, funTyConKey )
\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.
%************************************************************************
%* *
Check types AND do validity checking
%* *
%************************************************************************
\begin{code}
tcHsSigType, tcHsSigTypeNC :: UserTypeCtxt -> LHsType Name -> TcM Type
tcHsSigType ctxt hs_ty
= addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
tcHsSigTypeNC ctxt hs_ty
tcHsSigTypeNC ctxt (L loc hs_ty)
= setSrcSpan loc $
do { kind <- case expectedKindInCtxt ctxt of
Nothing -> newMetaKindVar
Just k -> return k
; ty <- tcCheckHsTypeAndGen hs_ty kind
; ty <- zonkSigType ty
; checkValidType ctxt ty
; return ty }
tcHsInstHead :: UserTypeCtxt -> LHsType Name -> TcM ([TyVar], ThetaType, Class, [Type])
tcHsInstHead user_ctxt lhs_ty@(L loc hs_ty)
= setSrcSpan loc $
do { inst_ty <- tc_inst_head hs_ty
; kvs <- zonkTcTypeAndFV inst_ty
; kvs <- kindGeneralize kvs
; inst_ty <- zonkSigType (mkForAllTys kvs inst_ty)
; checkValidInstance user_ctxt lhs_ty inst_ty }
tc_inst_head :: HsType Name -> TcM TcType
tc_inst_head (HsForAllTy _ hs_tvs hs_ctxt hs_ty)
= tcHsTyVarBndrs hs_tvs $ \ tvs ->
do { ctxt <- tcHsContext hs_ctxt
; ty <- tc_lhs_type hs_ty ekConstraint
; return (mkSigmaTy tvs ctxt ty) }
tc_inst_head hs_ty
= tc_hs_type hs_ty ekConstraint
tcHsDeriv :: HsType Name -> TcM ([TyVar], Class, [Type], Kind)
tcHsDeriv hs_ty
= do { arg_kind <- newMetaKindVar
; ty <- tcCheckHsTypeAndGen hs_ty (mkArrowKind arg_kind constraintKind)
; ty <- zonkSigType ty
; arg_kind <- zonkSigType arg_kind
; let (tvs, pred) = splitForAllTys ty
; case getClassPredTys_maybe pred of
Just (cls, tys) -> return (tvs, cls, tys, arg_kind)
Nothing -> failWithTc (ptext (sLit "Illegal deriving item") <+> quotes (ppr hs_ty)) }
tcHsVectInst :: LHsType Name -> TcM (Class, [Type])
tcHsVectInst ty
| Just (L _ cls_name, tys) <- splitLHsClassTy_maybe ty
= do { (cls, cls_kind) <- tcClass cls_name
; (arg_tys, _res_kind) <- tcInferApps cls_name cls_kind tys
; 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
%************************************************************************
%* *
The main kind checker: no validity checks here
%* *
%************************************************************************
First a couple of simple wrappers for kcHsType
\begin{code}
tcClassSigType :: LHsType Name -> TcM Type
tcClassSigType lhs_ty@(L _ hs_ty)
= addTypeCtxt lhs_ty $
do { ty <- tcCheckHsTypeAndGen hs_ty liftedTypeKind
; zonkSigType ty }
tcHsConArgType :: NewOrData -> LHsType Name -> TcM Type
tcHsConArgType NewType bty = tcHsLiftedType (getBangType bty)
tcHsConArgType DataType bty = tcHsOpenType (getBangType bty)
tcHsArgTys :: SDoc -> [LHsType Name] -> [Kind] -> TcM [TcType]
tcHsArgTys what tys kinds
= sequence [ addTypeCtxt ty $
tc_lhs_type ty (expArgKind what kind n)
| (ty,kind,n) <- zip3 tys kinds [1..] ]
tc_hs_arg_tys :: SDoc -> [LHsType Name] -> [Kind] -> TcM [TcType]
tc_hs_arg_tys what tys kinds
= sequence [ tc_lhs_type ty (expArgKind what kind n)
| (ty,kind,n) <- zip3 tys kinds [1..] ]
tcHsOpenType, tcHsLiftedType :: LHsType Name -> TcM TcType
tcHsOpenType ty = addTypeCtxt ty $ tc_lhs_type ty ekOpen
tcHsLiftedType ty = addTypeCtxt ty $ tc_lhs_type ty ekLifted
tcCheckLHsType :: LHsType Name -> Kind -> TcM Type
tcCheckLHsType hs_ty exp_kind
= addTypeCtxt hs_ty $
tc_lhs_type hs_ty (EK exp_kind expectedKindMsg)
tcLHsType :: LHsType Name -> TcM (TcType, TcKind)
tcLHsType ty = addTypeCtxt ty (tc_infer_lhs_type ty)
tcCheckHsTypeAndGen :: HsType Name -> Kind -> TcM Type
tcCheckHsTypeAndGen hs_ty kind
= do { ty <- tc_hs_type hs_ty (EK kind expectedKindMsg)
; traceTc "tcCheckHsTypeAndGen" (ppr hs_ty)
; kvs <- zonkTcTypeAndFV ty
; kvs <- kindGeneralize kvs
; return (mkForAllTys kvs ty) }
\end{code}
Like tcExpr, tc_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
tc_lhs_type_fresh, to first create a new meta kind variable and use that as
the expected kind.
\begin{code}
tc_infer_lhs_type :: LHsType Name -> TcM (TcType, TcKind)
tc_infer_lhs_type ty =
do { kv <- newMetaKindVar
; r <- tc_lhs_type ty (EK kv expectedKindMsg)
; return (r, kv) }
tc_lhs_type :: LHsType Name -> ExpKind -> TcM TcType
tc_lhs_type (L span ty) exp_kind
= setSrcSpan span $
do { traceTc "tc_lhs_type:" (ppr ty $$ ppr exp_kind)
; tc_hs_type ty exp_kind }
tc_lhs_types :: [(LHsType Name, ExpKind)] -> TcM [TcType]
tc_lhs_types tys_w_kinds = mapM (uncurry tc_lhs_type) tys_w_kinds
tc_fun_type :: HsType Name -> LHsType Name -> LHsType Name -> ExpKind -> TcM TcType
tc_fun_type ty ty1 ty2 exp_kind@(EK _ ctxt)
= do { ty1' <- tc_lhs_type ty1 (EK openTypeKind ctxt)
; ty2' <- tc_lhs_type ty2 (EK openTypeKind ctxt)
; checkExpectedKind ty liftedTypeKind exp_kind
; return (mkFunTy ty1' ty2') }
tc_hs_type :: HsType Name -> ExpKind -> TcM TcType
tc_hs_type (HsParTy ty) exp_kind = tc_lhs_type ty exp_kind
tc_hs_type (HsDocTy ty _) exp_kind = tc_lhs_type ty exp_kind
tc_hs_type (HsQuasiQuoteTy {}) _ = panic "tc_hs_type: qq"
tc_hs_type ty@(HsBangTy {}) _
= failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
tc_hs_type (HsRecTy _) _ = panic "tc_hs_type: record"
tc_hs_type hs_ty@(HsTyVar name) exp_kind
= do { (ty, k) <- tcTyVar name
; checkExpectedKind hs_ty k exp_kind
; return ty }
tc_hs_type ty@(HsFunTy ty1 ty2) exp_kind
= tc_fun_type ty ty1 ty2 exp_kind
tc_hs_type hs_ty@(HsOpTy ty1 (_, l_op@(L _ op)) ty2) exp_kind
| op `hasKey` funTyConKey
= tc_fun_type hs_ty ty1 ty2 exp_kind
| otherwise
= do { (op', op_kind) <- tcTyVar op
; tys' <- tcCheckApps hs_ty l_op op_kind [ty1,ty2] exp_kind
; return (mkNakedAppTys op' tys') }
tc_hs_type hs_ty@(HsAppTy ty1 ty2) exp_kind
= do { (fun_ty', fun_kind) <- tc_infer_lhs_type fun_ty
; arg_tys' <- tcCheckApps hs_ty fun_ty fun_kind arg_tys exp_kind
; return (mkNakedAppTys fun_ty' arg_tys') }
where
(fun_ty, arg_tys) = splitHsAppTys ty1 [ty2]
tc_hs_type hs_ty@(HsForAllTy _ hs_tvs context ty) exp_kind
= tcHsTyVarBndrs hs_tvs $ \ tvs' ->
do { ctxt' <- tcHsContext context
; ty' <- if null (unLoc context) then
tc_lhs_type ty exp_kind
else
do { checkExpectedKind hs_ty liftedTypeKind exp_kind
; tc_lhs_type ty ekOpen }
; return (mkSigmaTy tvs' ctxt' ty') }
tc_hs_type hs_ty@(HsListTy elt_ty) exp_kind
= do { tau_ty <- tc_lhs_type elt_ty ekLifted
; checkExpectedKind hs_ty liftedTypeKind exp_kind
; checkWiredInTyCon listTyCon
; return (mkListTy tau_ty) }
tc_hs_type hs_ty@(HsPArrTy elt_ty) exp_kind
= do { tau_ty <- tc_lhs_type elt_ty ekLifted
; checkExpectedKind hs_ty liftedTypeKind exp_kind
; checkWiredInTyCon parrTyCon
; return (mkPArrTy tau_ty) }
tc_hs_type hs_ty@(HsTupleTy HsBoxedOrConstraintTuple hs_tys) exp_kind@(EK exp_k _ctxt)
| Just tup_sort <- tupKindSort_maybe exp_k
= tc_tuple hs_ty tup_sort hs_tys exp_kind
| otherwise
= do { (tys, kinds) <- mapAndUnzipM tc_infer_lhs_type hs_tys
; kinds <- mapM zonkTcKind kinds
; let (arg_kind, tup_sort)
= case [ (k,s) | k <- kinds
, Just s <- [tupKindSort_maybe k] ] of
((k,s) : _) -> (k,s)
[] -> (liftedTypeKind, BoxedTuple)
; sequence_ [ setSrcSpan loc $
checkExpectedKind ty kind
(expArgKind (ptext (sLit "a tuple")) arg_kind n)
| (ty@(L loc _),kind,n) <- zip3 hs_tys kinds [1..] ]
; finish_tuple hs_ty tup_sort tys exp_kind }
tc_hs_type hs_ty@(HsTupleTy hs_tup_sort tys) exp_kind
= tc_tuple hs_ty tup_sort tys exp_kind
where
tup_sort = case hs_tup_sort of
HsUnboxedTuple -> UnboxedTuple
HsBoxedTuple -> BoxedTuple
HsConstraintTuple -> ConstraintTuple
_ -> panic "tc_hs_type HsTupleTy"
tc_hs_type hs_ty@(HsExplicitListTy _k tys) exp_kind
= do { tks <- mapM tc_infer_lhs_type tys
; let taus = map fst tks
; kind <- unifyKinds (ptext (sLit "In a promoted list")) tks
; checkExpectedKind hs_ty (mkPromotedListTy kind) exp_kind
; return (foldr (mk_cons kind) (mk_nil kind) taus) }
where
mk_cons k a b = mkTyConApp (promoteDataCon consDataCon) [k, a, b]
mk_nil k = mkTyConApp (promoteDataCon nilDataCon) [k]
tc_hs_type hs_ty@(HsExplicitTupleTy _ tys) exp_kind
= do { tks <- mapM tc_infer_lhs_type tys
; let n = length tys
kind_con = promotedTupleTyCon BoxedTuple n
ty_con = promotedTupleDataCon BoxedTuple n
(taus, ks) = unzip tks
tup_k = mkTyConApp kind_con ks
; checkExpectedKind hs_ty tup_k exp_kind
; return (mkTyConApp ty_con (ks ++ taus)) }
tc_hs_type ipTy@(HsIParamTy n ty) exp_kind
= do { ty' <- tc_lhs_type ty ekLifted
; checkExpectedKind ipTy constraintKind exp_kind
; ipClass <- tcLookupClass ipClassName
; let n' = mkStrLitTy $ hsIPNameFS n
; return (mkClassPred ipClass [n',ty'])
}
tc_hs_type ty@(HsEqTy ty1 ty2) exp_kind
= do { (ty1', kind1) <- tc_infer_lhs_type ty1
; (ty2', kind2) <- tc_infer_lhs_type ty2
; checkExpectedKind ty2 kind2
(EK kind1 msg_fn)
; checkExpectedKind ty constraintKind exp_kind
; return (mkNakedTyConApp eqTyCon [kind1, ty1', ty2']) }
where
msg_fn pkind = ptext (sLit "The left argument of the equality had kind")
<+> quotes (pprKind pkind)
tc_hs_type (HsKindSig ty sig_k) exp_kind
= do { sig_k' <- tcLHsKind sig_k
; checkExpectedKind ty sig_k' exp_kind
; tc_lhs_type ty (EK sig_k' msg_fn) }
where
msg_fn pkind = ptext (sLit "The signature specified kind")
<+> quotes (pprKind pkind)
tc_hs_type (HsCoreTy ty) exp_kind
= do { checkExpectedKind ty (typeKind ty) exp_kind
; return ty }
tc_hs_type ty@(HsSpliceTy {}) _exp_kind
= failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
tc_hs_type (HsWrapTy {}) _exp_kind
= panic "tc_hs_type HsWrapTy"
tc_hs_type hs_ty@(HsTyLit (HsNumTy n)) exp_kind
= do { checkExpectedKind hs_ty typeNatKind exp_kind
; checkWiredInTyCon typeNatKindCon
; return (mkNumLitTy n) }
tc_hs_type hs_ty@(HsTyLit (HsStrTy s)) exp_kind
= do { checkExpectedKind hs_ty typeSymbolKind exp_kind
; checkWiredInTyCon typeSymbolKindCon
; return (mkStrLitTy s) }
tupKindSort_maybe :: TcKind -> Maybe TupleSort
tupKindSort_maybe k
| isConstraintKind k = Just ConstraintTuple
| isLiftedTypeKind k = Just BoxedTuple
| otherwise = Nothing
tc_tuple :: HsType Name -> TupleSort -> [LHsType Name] -> ExpKind -> TcM TcType
tc_tuple hs_ty tup_sort tys exp_kind
= do { tau_tys <- tc_hs_arg_tys cxt_doc tys (repeat arg_kind)
; finish_tuple hs_ty tup_sort tau_tys exp_kind }
where
arg_kind = case tup_sort of
BoxedTuple -> liftedTypeKind
UnboxedTuple -> openTypeKind
ConstraintTuple -> constraintKind
cxt_doc = case tup_sort of
BoxedTuple -> ptext (sLit "a tuple")
UnboxedTuple -> ptext (sLit "an unboxed tuple")
ConstraintTuple -> ptext (sLit "a constraint tuple")
finish_tuple :: HsType Name -> TupleSort -> [TcType] -> ExpKind -> TcM TcType
finish_tuple hs_ty tup_sort tau_tys exp_kind
= do { checkExpectedKind hs_ty res_kind exp_kind
; checkWiredInTyCon tycon
; return (mkTyConApp tycon tau_tys) }
where
tycon = tupleTyCon tup_sort (length tau_tys)
res_kind = case tup_sort of
UnboxedTuple -> unliftedTypeKind
BoxedTuple -> liftedTypeKind
ConstraintTuple -> constraintKind
tcInferApps :: Outputable a
=> a
-> TcKind
-> [LHsType Name]
-> TcM ([TcType], TcKind)
tcInferApps the_fun fun_kind args
= do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) fun_kind args
; args' <- tc_lhs_types args_w_kinds
; return (args', res_kind) }
tcCheckApps :: Outputable a
=> HsType Name
-> a
-> TcKind -> [LHsType Name]
-> ExpKind
-> TcM [TcType]
tcCheckApps hs_ty the_fun fun_kind args exp_kind
= do { (arg_tys, res_kind) <- tcInferApps the_fun fun_kind args
; checkExpectedKind hs_ty res_kind exp_kind
; return arg_tys }
splitFunKind :: SDoc -> TcKind -> [b] -> TcM ([(b,ExpKind)], TcKind)
splitFunKind the_fun fun_kind args
= go 1 fun_kind args
where
go _ fk [] = return ([], fk)
go 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) <- go (arg_no+1) fk' args
; let exp_kind = expArgKind (quotes the_fun) ak arg_no
; return ((arg, exp_kind) : aks, rk) } }
too_many_args = quotes the_fun <+>
ptext (sLit "is applied to too many type arguments")
tcHsContext :: LHsContext Name -> TcM [PredType]
tcHsContext ctxt = mapM tcHsLPredType (unLoc ctxt)
tcHsLPredType :: LHsType Name -> TcM PredType
tcHsLPredType pred = tc_lhs_type pred ekConstraint
tcTyVar :: Name -> TcM (TcType, TcKind)
tcTyVar name
= do { traceTc "lk1" (ppr name)
; thing <- tcLookup name
; case thing of
ATyVar _ tv
| isKindVar tv
-> failWithTc (ptext (sLit "Kind variable") <+> quotes (ppr tv)
<+> ptext (sLit "used as a type"))
| otherwise
-> return (mkTyVarTy tv, tyVarKind tv)
AThing kind -> do { tc <- get_loopy_tc name
; inst_tycon (mkNakedTyConApp tc) kind }
AGlobal (ATyCon tc) -> inst_tycon (mkTyConApp tc) (tyConKind tc)
AGlobal (AConLike (RealDataCon dc))
| Just tc <- promoteDataCon_maybe dc
-> do { data_kinds <- xoptM Opt_DataKinds
; unless data_kinds $ promotionErr name NoDataKinds
; inst_tycon (mkTyConApp tc) (tyConKind tc) }
| otherwise -> failWithTc (ptext (sLit "Data constructor") <+> quotes (ppr dc)
<+> ptext (sLit "comes from an un-promotable type")
<+> quotes (ppr (dataConTyCon dc)))
APromotionErr err -> promotionErr name err
_ -> wrongThingErr "type" thing name }
where
get_loopy_tc name
= do { env <- getGblEnv
; case lookupNameEnv (tcg_type_env env) name of
Just (ATyCon tc) -> return tc
_ -> return (aThingErr "tcTyVar" name) }
inst_tycon :: ([Type] -> Type) -> Kind -> TcM (Type, Kind)
inst_tycon mk_tc_app kind
| null kvs
= return (mk_tc_app [], ki_body)
| otherwise
= do { traceTc "lk4" (ppr name <+> dcolon <+> ppr kind)
; ks <- mapM (const newMetaKindVar) kvs
; return (mk_tc_app ks, substKiWith kvs ks ki_body) }
where
(kvs, ki_body) = splitForAllTys kind
tcClass :: Name -> TcM (Class, TcKind)
tcClass cls
= do { thing <- tcLookup cls
; case thing of
AThing kind -> return (aThingErr "tcClass" cls, kind)
AGlobal (ATyCon tc)
| Just cls <- tyConClass_maybe tc
-> return (cls, tyConKind tc)
_ -> wrongThingErr "class" thing cls }
aThingErr :: String -> Name -> b
aThingErr str x = pprPanic "AThing evaluated unexpectedly" (text str <+> ppr x)
\end{code}
Note [Zonking inside the knot]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we are checking the argument types of a data constructor. We
must zonk the types before making the DataCon, because once built we
can't change it. So we must traverse the type.
BUT the parent TyCon is knot-tied, so we can't look at it yet.
So we must be careful not to use "smart constructors" for types that
look at the TyCon or Class involved.
* Hence the use of mkNakedXXX functions. These do *not* enforce
the invariants (for example that we use (FunTy s t) rather
than (TyConApp (->) [s,t])).
* Ditto in zonkTcType (which may be applied more than once, eg to
squeeze out kind meta-variables), we are careful not to look at
the TyCon.
* We arrange to call zonkSigType *once* right at the end, and it
does establish the invariants. But in exchange we can't look
at the result (not even its structure) until we have emerged
from the "knot".
* TcHsSyn.zonkTcTypeToType also can safely check/establish
invariants.
This is horribly delicate. I hate it. A good example of how
delicate it is can be seen in Trac #7903.
\begin{code}
mkNakedTyConApp :: TyCon -> [Type] -> Type
mkNakedTyConApp tc tys = TyConApp tc tys
mkNakedAppTys :: Type -> [Type] -> Type
mkNakedAppTys ty1 [] = ty1
mkNakedAppTys (TyConApp tc tys1) tys2 = mkNakedTyConApp tc (tys1 ++ tys2)
mkNakedAppTys ty1 tys2 = foldl AppTy ty1 tys2
zonkSigType :: TcType -> TcM TcType
zonkSigType ty
= go ty
where
go (TyConApp tc tys) = do tys' <- mapM go tys
return (mkTyConApp tc tys')
go (LitTy n) = return (LitTy n)
go (FunTy arg res) = do arg' <- go arg
res' <- go res
return (FunTy arg' res')
go (AppTy fun arg) = do fun' <- go fun
arg' <- go arg
return (mkAppTy fun' arg')
go (TyVarTy tyvar) | isTcTyVar tyvar = zonkTcTyVar tyvar
| otherwise = TyVarTy <$> updateTyVarKindM go tyvar
go (ForAllTy tv ty) = do { tv' <- zonkTcTyVarBndr tv
; ty' <- go ty
; return (ForAllTy tv' ty') }
\end{code}
Note [Body kind of a forall]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The body of a forall is usually a type, but in principle
there's no reason to prohibit *unlifted* types.
In fact, GHC can itself construct a function with an
unboxed tuple inside a for-all (via CPR analyis; see
typecheck/should_compile/tc170).
Moreover in instance heads we get forall-types with
kind Constraint.
Moreover if we have a signature
f :: Int#
then we represent it as (HsForAll Implicit [] [] Int#). And this must
be legal! We can't drop the empty forall until *after* typechecking
the body because of kind polymorphism:
Typeable :: forall k. k -> Constraint
data Apply f t = Apply (f t)
-- Apply :: forall k. (k -> *) -> k -> *
instance Typeable Apply where ...
Then the dfun has type
df :: forall k. Typeable ((k->*) -> k -> *) (Apply k)
f :: Typeable Apply
f :: forall (t:k->*) (a:k). t a -> t a
class C a b where
op :: a b -> Typeable Apply
data T a = MkT (Typeable Apply)
| T2 a
T :: * -> *
MkT :: forall k. (Typeable ((k->*) -> k -> *) (Apply k)) -> T a
f :: (forall (k:BOX). forall (t:: k->*) (a:k). t a -> t a) -> Int
f :: (forall a. a -> Typeable Apply) -> Int
So we *must* keep the HsForAll on the instance type
HsForAll Implicit [] [] (Typeable Apply)
so that we do kind generalisation on it.
Really we should check that it's a type of value kind
{*, Constraint, #}, but I'm not doing that yet
Example that should be rejected:
f :: (forall (a:*->*). a) Int
Note [Inferring tuple kinds]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Give a tuple type (a,b,c), which the parser labels as HsBoxedOrConstraintTuple,
we try to figure out whether it's a tuple of kind * or Constraint.
Step 1: look at the expected kind
Step 2: infer argument kinds
If after Step 2 it's not clear from the arguments that it's
Constraint, then it must be *. Once having decided that we re-check
the Check the arguments again to give good error messages
in eg. `(Maybe, Maybe)`
Note that we will still fail to infer the correct kind in this case:
type T a = ((a,a), D a)
type family D :: Constraint -> Constraint
While kind checking T, we do not yet know the kind of D, so we will default the
kind of T to * -> *. It works if we annotate `a` with kind `Constraint`.
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
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 encounter the unconstrained kappa, we
want to default it to '*', not to AnyK.
Help functions for type applications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
\begin{code}
addTypeCtxt :: LHsType Name -> TcM a -> TcM a
addTypeCtxt (L _ ty) thing
= addErrCtxt doc thing
where
doc = ptext (sLit "In the type") <+> quotes (ppr ty)
\end{code}
%************************************************************************
%* *
Type-variable binders
%* *
%************************************************************************
Note [Kind-checking strategies]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There are three main declarations that we have to kind check carefully in the
presence of -XPolyKinds: classes, datatypes, and data/type families. They each
have a different kind-checking strategy (labeled in the parentheses above each
section). This should potentially be cleaned up in the future, but this is how
it stands now (June 2013).
Classes (ParametricKinds):
- kind-polymorphic by default
- each un-annotated type variable is given a fresh meta kind variable
- every explicit kind variable becomes a SigTv during inference
- no generalisation is done while kind-checking the recursive group
Taken together, this means that classes cannot participate in polymorphic
recursion. Thus, the following is not definable:
class Fugly (a :: k) where
foo :: forall (b :: k -> *). Fugly b => b a
But, because explicit kind variables are SigTvs, it is OK for the kind to
be forced to be the same kind that is used in a separate declaration. See
test case polykinds/T7020.hs.
Datatypes:
Here we have two cases, whether or not a Full Kind Signature is provided.
A Full Kind Signature means that there is a top-level :: in the definition
of the datatype. For example:
data T1 :: k -> Bool -> * where ... -- YES
data T2 (a :: k) :: Bool -> * where ... -- YES
data T3 (a :: k) (b :: Bool) :: * where ... -- YES
data T4 (a :: k) (b :: Bool) where ... -- NO
Kind signatures are not allowed on datatypes declared in the H98 style,
so those always have no Full Kind Signature.
Full Kind Signature (FullKindSignature):
- each un-annotated type variable defaults to *
- every explicit kind variable becomes a skolem during type inference
- these kind variables are generalised *before* kind-checking the group
With these rules, polymorphic recursion is possible. This is essentially
because of the generalisation step before kind-checking the group -- it
gives the kind-checker enough flexibility to supply the right kind arguments
to support polymorphic recursion.
no Full Kind Signature (ParametricKinds):
- kind-polymorphic by default
- each un-annotated type variable is given a fresh meta kind variable
- every explicit kind variable becomes a SigTv during inference
- no generalisation is done while kind-checking the recursive group
Thus, no polymorphic recursion in this case. See also Trac #6093 & #6049.
Type families:
Here we have three cases: open top-level families, closed top-level families,
and open associated types. (There are no closed associated types, for good
reason.)
Open top-level families (FullKindSignature):
- All open top-level families are considered to have a Full Kind Signature
- All arguments and the result default to *
- All kind variables are skolems
- All kind variables are generalised before kind-checking the group
This behaviour supports kind-indexed type and data families, because we
need to have generalised before kind-checking for this to work. For example:
type family F (a :: k)
type instance F Int = Bool
type instance F Maybe = Char
type instance F (x :: * -> * -> *) = Double
Closed top-level families (NonParametricKinds):
- kind-monomorphic by default
- each un-annotated type variable is given a fresh meta kind variable
- every explicit kind variable becomes a skolem during inference
- all such skolems are generalised before kind-checking; other kind
variables are not generalised
- all unconstrained meta kind variables are defaulted to * at the
end of kind checking
This behaviour is to allow kind inference to occur in closed families, but
without becoming too polymorphic. For example:
type family F a where
F Int = Bool
F Bool = Char
We would want F to have kind * -> * from this definition, although something
like k1 -> k2 would be perfectly sound. The reason we want this restriction is
that it is better to have (F Maybe) be a kind error than simply stuck.
The kind inference gives us also
type family Not b where
Not False = True
Not True = False
With an open family, the above would need kind annotations in its header.
The tricky case is
type family G a (b :: k) where
G Int Int = False
G Bool Maybe = True
We want this to work. But, we also want (G Maybe Maybe) to be a kind error
(in the first argument). So, we need to generalise the skolem "k" but not
the meta kind variable associated with "a".
Associated families (FullKindSignature):
- Kind-monomorphic by default
- Result kind defaults to *
- Each type variable is either in the class header or not:
- Type variables in the class header are given the kind inherited from
the class header (and checked against an annotation, if any)
- Un-annotated type variables default to *
- Each kind variable mentioned in the class header becomes a SigTv during
kind inference.
- Each kind variable not mentioned in the class header becomes a skolem during
kind inference.
- Only the skolem kind variables are generalised before kind checking.
Here are some examples:
class Foo1 a b where
type Bar1 (a :: k) (b :: k)
The kind of Foo1 will be k -> k -> Constraint. Kind annotations on associated
type declarations propagate to the header because the type variables in Bar1's
declaration inherit the (meta) kinds of the class header.
class Foo2 a where
type Bar2 a
The kind of Bar2 will be k -> *.
class Foo3 a where
type Bar3 a (b :: k)
meth :: Bar3 a Maybe -> ()
The kind of Bar3 will be k1 -> k2 -> *. This only kind-checks because the kind
of b is generalised before kind-checking.
class Foo4 a where
type Bar4 a b
Here, the kind of Bar4 will be k -> * -> *, because b is not mentioned in the
class header, so it defaults to *.
\begin{code}
data KindCheckingStrategy
= ParametricKinds
| NonParametricKinds
| FullKindSignature
deriving (Eq)
kcStrategy :: TyClDecl Name -> KindCheckingStrategy
kcStrategy d@(ForeignType {}) = pprPanic "kcStrategy" (ppr d)
kcStrategy (FamDecl fam_decl)
= kcStrategyFamDecl fam_decl
kcStrategy (SynDecl {}) = ParametricKinds
kcStrategy (DataDecl { tcdDataDefn = HsDataDefn { dd_kindSig = m_ksig }})
| Just _ <- m_ksig = FullKindSignature
| otherwise = ParametricKinds
kcStrategy (ClassDecl {}) = ParametricKinds
kcStrategyFamDecl :: FamilyDecl Name -> KindCheckingStrategy
kcStrategyFamDecl (FamilyDecl { fdInfo = ClosedTypeFamily (_:_) }) = NonParametricKinds
kcStrategyFamDecl _ = FullKindSignature
mkKindSigVar :: Name -> TcM KindVar
mkKindSigVar n
= do { mb_thing <- tcLookupLcl_maybe n
; case mb_thing of
Just (AThing k)
| Just kvar <- getTyVar_maybe k
-> return kvar
_ -> return $ mkTcTyVar n superKind (SkolemTv False) }
kcScopedKindVars :: [Name] -> TcM a -> TcM a
kcScopedKindVars kv_ns thing_inside
= do { kvs <- mapM (\n -> newSigTyVar n superKind) kv_ns
; tcExtendTyVarEnv2 (kv_ns `zip` kvs) thing_inside }
kcHsTyVarBndrs :: KindCheckingStrategy
-> LHsTyVarBndrs Name
-> TcM (Kind, r)
-> TcM (Kind, r)
kcHsTyVarBndrs strat (HsQTvs { hsq_kvs = kv_ns, hsq_tvs = hs_tvs }) thing_inside
= do { kvs <- if skolem_kvs
then mapM mkKindSigVar kv_ns
else mapM (\n -> newSigTyVar n superKind) kv_ns
; tcExtendTyVarEnv2 (kv_ns `zip` kvs) $
do { nks <- mapM (kc_hs_tv . unLoc) hs_tvs
; (res_kind, stuff) <- tcExtendKindEnv nks thing_inside
; let full_kind = mkArrowKinds (map snd nks) res_kind
kvs = filter (not . isMetaTyVar) $
varSetElems $ tyVarsOfType full_kind
gen_kind = if generalise
then mkForAllTys kvs full_kind
else full_kind
; return (gen_kind, stuff) } }
where
(skolem_kvs, default_to_star, generalise) = case strat of
ParametricKinds -> (False, False, False)
NonParametricKinds -> (True, False, True)
FullKindSignature -> (True, True, True)
kc_hs_tv :: HsTyVarBndr Name -> TcM (Name, TcKind)
kc_hs_tv (UserTyVar n)
= do { mb_thing <- tcLookupLcl_maybe n
; kind <- case mb_thing of
Just (AThing k) -> return k
_ | default_to_star -> return liftedTypeKind
| otherwise -> newMetaKindVar
; return (n, kind) }
kc_hs_tv (KindedTyVar n k)
= do { kind <- tcLHsKind k
; mb_thing <- tcLookupLcl_maybe n
; case mb_thing of
Nothing -> return ()
Just (AThing ks) -> checkKind kind ks
Just thing -> pprPanic "check_in_scope" (ppr thing)
; return (n, kind) }
tcHsTyVarBndrs :: LHsTyVarBndrs Name
-> ([TcTyVar] -> TcM r)
-> TcM r
tcHsTyVarBndrs (HsQTvs { hsq_kvs = kv_ns, hsq_tvs = hs_tvs }) thing_inside
= do { kvs <- mapM mkKindSigVar kv_ns
; tcExtendTyVarEnv kvs $ do
{ tvs <- mapM tcHsTyVarBndr hs_tvs
; traceTc "tcHsTyVarBndrs {" (vcat [ text "Hs kind vars:" <+> ppr kv_ns
, text "Hs type vars:" <+> ppr hs_tvs
, text "Kind vars:" <+> ppr kvs
, text "Type vars:" <+> ppr tvs ])
; res <- tcExtendTyVarEnv tvs (thing_inside (kvs ++ tvs))
; traceTc "tcHsTyVarBndrs }" (vcat [ text "Hs kind vars:" <+> ppr kv_ns
, text "Hs type vars:" <+> ppr hs_tvs
, text "Kind vars:" <+> ppr kvs
, text "Type vars:" <+> ppr tvs ])
; return res } }
tcHsTyVarBndr :: LHsTyVarBndr Name -> TcM TcTyVar
tcHsTyVarBndr (L _ hs_tv)
= do { let name = hsTyVarName hs_tv
; mb_tv <- tcLookupLcl_maybe name
; case mb_tv of {
Just (ATyVar _ tv) -> return tv ;
_ -> do
{ kind <- case hs_tv of
UserTyVar {} -> newMetaKindVar
KindedTyVar _ kind -> tcLHsKind kind
; return ( mkTcTyVar name kind (SkolemTv False)) } } }
kindGeneralize :: TyVarSet -> TcM [KindVar]
kindGeneralize tkvs
= do { gbl_tvs <- tcGetGlobalTyVars
; quantifyTyVars gbl_tvs (filterVarSet isKindVar tkvs) }
\end{code}
Note [Kind generalisation]
~~~~~~~~~~~~~~~~~~~~~~~~~~
We do kind generalisation only at the outer level of a type signature.
For example, consider
T :: forall k. k -> *
f :: (forall a. T a -> Int) -> Int
When kind-checking f's type signature we generalise the kind at
the outermost level, thus:
f1 :: forall k. (forall (a:k). T k a -> Int) -> Int -- YES!
and *not* at the inner forall:
f2 :: (forall k. forall (a:k). T k a -> Int) -> Int -- NO!
Reason: same as for HM inference on value level declarations,
we want to infer the most general type. The f2 type signature
would be *less applicable* than f1, because it requires a more
polymorphic argument.
Note [Kinds of quantified type variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tcTyVarBndrsGen 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 tvs'.
\begin{code}
kcLookupKind :: Name -> TcM Kind
kcLookupKind nm
= do { tc_ty_thing <- tcLookup nm
; case tc_ty_thing of
AThing k -> return k
AGlobal (ATyCon tc) -> return (tyConKind tc)
_ -> pprPanic "kcLookupKind" (ppr tc_ty_thing) }
kcTyClTyVars :: Name -> LHsTyVarBndrs Name -> TcM a -> TcM a
kcTyClTyVars name (HsQTvs { hsq_kvs = kvs, hsq_tvs = hs_tvs }) thing_inside
= kcScopedKindVars kvs $
do { tc_kind <- kcLookupKind name
; let (arg_ks, _res_k) = splitKindFunTysN (length hs_tvs) tc_kind
; name_ks <- zipWithM kc_tv hs_tvs arg_ks
; tcExtendKindEnv name_ks thing_inside }
where
kc_tv :: LHsTyVarBndr Name -> Kind -> TcM (Name, Kind)
kc_tv (L _ (UserTyVar n)) exp_k
= return (n, exp_k)
kc_tv (L _ (KindedTyVar n hs_k)) exp_k
= do { k <- tcLHsKind hs_k
; checkKind k exp_k
; return (n, exp_k) }
tcTyClTyVars :: Name -> LHsTyVarBndrs Name
-> ([TyVar] -> Kind -> TcM a) -> TcM a
tcTyClTyVars tycon (HsQTvs { hsq_kvs = hs_kvs, hsq_tvs = hs_tvs }) thing_inside
= kcScopedKindVars hs_kvs $
do { thing <- tcLookup tycon
; let { kind = case thing of
AThing kind -> kind
_ -> panic "tcTyClTyVars"
; (kvs, body) = splitForAllTys kind
; (kinds, res) = splitKindFunTysN (length hs_tvs) body }
; tvs <- zipWithM tc_hs_tv hs_tvs kinds
; tcExtendTyVarEnv tvs (thing_inside (kvs ++ tvs) res) }
where
tc_hs_tv (L _ (UserTyVar n)) kind = return (mkTyVar n kind)
tc_hs_tv (L _ (KindedTyVar n hs_k)) kind = do { tc_kind <- tcLHsKind hs_k
; checkKind kind tc_kind
; return (mkTyVar n 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
-> HsWithBndrs (LHsType Name)
-> TcM ( Type
, [(Name, TcTyVar)] )
tcHsPatSigType ctxt (HsWB { hswb_cts = hs_ty, hswb_kvs = sig_kvs, hswb_tvs = sig_tvs })
= addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
do { kvs <- mapM new_kv sig_kvs
; tvs <- mapM new_tv sig_tvs
; let ktv_binds = (sig_kvs `zip` kvs) ++ (sig_tvs `zip` tvs)
; sig_ty <- tcExtendTyVarEnv2 ktv_binds $
tcHsLiftedType hs_ty
; sig_ty <- zonkSigType sig_ty
; checkValidType ctxt sig_ty
; return (sig_ty, ktv_binds) }
where
new_kv name = new_tkv name superKind
new_tv name = do { kind <- newMetaKindVar
; new_tkv name kind }
new_tkv name kind
= case ctxt of
RuleSigCtxt {} -> return (mkTcTyVar name kind (SkolemTv False))
_ -> newSigTyVar name kind
tcPatSig :: UserTypeCtxt
-> HsWithBndrs (LHsType Name)
-> TcSigmaType
-> TcM (TcType,
[(Name, TcTyVar)],
HsWrapper)
tcPatSig ctxt sig res_ty
= do { (sig_ty, sig_tvs) <- 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
; when in_pat_bind (addErr (patBindSigErr sig_tvs))
; let bad_tvs = [ tv | (_, tv) <- sig_tvs
, not (tv `elemVarSet` exactTyVarsOfType sig_ty) ]
; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
; wrap <- tcSubType PatSigOrigin ctxt res_ty sig_ty
; return (sig_ty, sig_tvs, wrap)
} }
patBindSigErr :: [(Name, TcTyVar)] -> SDoc
patBindSigErr sig_tvs
= hang (ptext (sLit "You cannot bind scoped type variable") <> plural sig_tvs
<+> pprQuotedList (map fst sig_tvs))
2 (ptext (sLit "in a pattern binding signature"))
\end{code}
Note [Pattern signature binders]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data T = forall a. T a (a->Int)
f (T x (f :: a->Int) = blah)
Here
* The pattern (T p1 p2) creates a *skolem* type variable 'a_sk',
It must be a skolem so that that it retains its identity, and
TcErrors.getSkolemInfo can thereby find the binding site for the skolem.
* The type signature pattern (f :: a->Int) binds "a" -> a_sig in the envt
* Then unificaiton makes a_sig := a_sk
That's why we must make a_sig a MetaTv (albeit a SigTv),
not a SkolemTv, so that it can unify to a_sk.
For RULE binders, though, things are a bit different (yuk).
RULE "foo" forall (x::a) (y::[a]). f x y = ...
Here this really is the binding site of the type variable so we'd like
to use a skolem, so that we get a complaint if we unify two of them
together.
Note [Unifying SigTvs]
~~~~~~~~~~~~~~~~~~~~~~
ALAS we have no decent way of avoiding two SigTvs getting unified.
Consider
f (x::(a,b)) (y::c)) = [fst x, y]
Here we'd really like to complain that 'a' and 'c' are unified. But
for the reasons above we can't make a,b,c into skolems, so they
are just SigTvs that can unify. And indeed, this would be ok,
f x (y::c) = case x of
(x1 :: a1, True) -> [x,y]
(x1 :: a2, False) -> [x,y,y]
Here the type of x's first component is called 'a1' in one branch and
'a2' in the other. We could try insisting on the same OccName, but
they definitely won't have the sane lexical Name.
I think we could solve this by recording in a SigTv a list of all the
in-scope varaibles that it should not unify with, but it's fiddly.
%************************************************************************
%* *
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 (TcKind -> SDoc)
instance Outputable ExpKind where
ppr (EK k f) = f k
ekLifted, ekOpen, ekConstraint :: ExpKind
ekLifted = EK liftedTypeKind expectedKindMsg
ekOpen = EK openTypeKind expectedKindMsg
ekConstraint = EK constraintKind expectedKindMsg
expectedKindMsg :: TcKind -> SDoc
expectedKindMsg pkind
| isConstraintKind pkind = ptext (sLit "Expected a constraint")
| isOpenTypeKind pkind = ptext (sLit "Expected a type")
| otherwise = ptext (sLit "Expected kind") <+> quotes (pprKind pkind)
expArgKind :: SDoc -> TcKind -> Int -> ExpKind
expArgKind exp kind arg_no = EK kind msg_fn
where
msg_fn pkind
= sep [ ptext (sLit "The") <+> speakNth arg_no
<+> ptext (sLit "argument of") <+> exp
, nest 2 $ ptext (sLit "should have kind")
<+> quotes (pprKind pkind) ]
unifyKinds :: SDoc -> [(TcType, TcKind)] -> TcM TcKind
unifyKinds fun act_kinds
= do { kind <- newMetaKindVar
; let check (arg_no, (ty, act_kind))
= checkExpectedKind ty act_kind (expArgKind (quotes fun) kind arg_no)
; mapM_ check (zip [1..] act_kinds)
; return kind }
checkKind :: TcKind -> TcKind -> TcM ()
checkKind act_kind exp_kind
= do { mb_subk <- unifyKindX act_kind exp_kind
; case mb_subk of
Just EQ -> return ()
_ -> unifyKindMisMatch act_kind exp_kind }
checkExpectedKind :: Outputable a => a -> TcKind -> ExpKind -> TcM ()
checkExpectedKind ty act_kind (EK exp_kind ek_ctxt)
= do { mb_subk <- unifyKindX act_kind exp_kind
; case mb_subk of {
Just LT -> return () ;
Just EQ -> return () ;
_other -> do
{
exp_kind <- zonkTcKind exp_kind
; act_kind <- zonkTcKind act_kind
; traceTc "checkExpectedKind" (ppr ty $$ ppr act_kind $$ ppr exp_kind)
; env0 <- tcInitTidyEnv
; dflags <- getDynFlags
; let (exp_as, _) = splitKindFunTys exp_kind
(act_as, _) = splitKindFunTys act_kind
n_exp_as = length exp_as
n_act_as = length act_as
n_diff_as = n_act_as n_exp_as
(env1, tidy_exp_kind) = tidyOpenKind env0 exp_kind
(env2, tidy_act_kind) = tidyOpenKind env1 act_kind
occurs_check
| Just act_tv <- tcGetTyVar_maybe act_kind
= check_occ act_tv exp_kind
| Just exp_tv <- tcGetTyVar_maybe exp_kind
= check_occ exp_tv act_kind
| otherwise
= False
check_occ tv k = case occurCheckExpand dflags tv k of
OC_Occurs -> True
_bad -> False
err | isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind
= ptext (sLit "Expecting a lifted type, but") <+> quotes (ppr ty)
<+> ptext (sLit "is unlifted")
| isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind
= ptext (sLit "Expecting an unlifted type, but") <+> quotes (ppr ty)
<+> ptext (sLit "is lifted")
| occurs_check
= ptext (sLit "Kind occurs check") $$ more_info
| n_exp_as < n_act_as
= vcat [ 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)
, more_info ]
| otherwise
= more_info
more_info = sep [ ek_ctxt tidy_exp_kind <> comma
, nest 2 $ ptext (sLit "but") <+> quotes (ppr ty)
<+> ptext (sLit "has kind") <+> quotes (pprKind tidy_act_kind)]
; traceTc "checkExpectedKind 1" (ppr ty $$ ppr tidy_act_kind $$ ppr tidy_exp_kind $$ ppr env1 $$ ppr env2)
; failWithTcM (env2, err) } } }
\end{code}
%************************************************************************
%* *
Sort checking kinds
%* *
%************************************************************************
tcLHsKind 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}
tcLHsKind :: LHsKind Name -> TcM Kind
tcLHsKind k = addErrCtxt (ptext (sLit "In the kind") <+> quotes (ppr k)) $
tc_lhs_kind k
tc_lhs_kind :: LHsKind Name -> TcM Kind
tc_lhs_kind (L span ki) = setSrcSpan span (tc_hs_kind ki)
tc_hs_kind :: HsKind Name -> TcM Kind
tc_hs_kind (HsTyVar tc) = tc_kind_var_app tc []
tc_hs_kind k@(HsAppTy _ _) = tc_kind_app k []
tc_hs_kind (HsParTy ki) = tc_lhs_kind ki
tc_hs_kind (HsFunTy ki1 ki2) =
do kappa_ki1 <- tc_lhs_kind ki1
kappa_ki2 <- tc_lhs_kind ki2
return (mkArrowKind kappa_ki1 kappa_ki2)
tc_hs_kind (HsListTy ki) =
do kappa <- tc_lhs_kind ki
checkWiredInTyCon listTyCon
return $ mkPromotedListTy kappa
tc_hs_kind (HsTupleTy _ kis) =
do kappas <- mapM tc_lhs_kind kis
checkWiredInTyCon tycon
return $ mkTyConApp tycon kappas
where
tycon = promotedTupleTyCon BoxedTuple (length kis)
tc_hs_kind k = pprPanic "tc_hs_kind" (ppr k)
tc_kind_app :: HsKind Name -> [LHsKind Name] -> TcM Kind
tc_kind_app (HsAppTy ki1 ki2) kis = tc_kind_app (unLoc ki1) (ki2:kis)
tc_kind_app (HsTyVar tc) kis = do { arg_kis <- mapM tc_lhs_kind kis
; tc_kind_var_app tc arg_kis }
tc_kind_app ki _ = failWithTc (quotes (ppr ki) <+>
ptext (sLit "is not a kind constructor"))
tc_kind_var_app :: Name -> [Kind] -> TcM Kind
tc_kind_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 "tc_kind_var_app 1" }
tc_kind_var_app name arg_kis
= do { thing <- tcLookup name
; case thing of
AGlobal (ATyCon tc)
-> do { data_kinds <- xoptM Opt_DataKinds
; unless data_kinds $ addErr (dataKindsErr name)
; case promotableTyCon_maybe tc of
Just prom_tc | arg_kis `lengthIs` tyConArity prom_tc
-> return (mkTyConApp prom_tc arg_kis)
Just _ -> tycon_err tc "is not fully applied"
Nothing -> tycon_err tc "is not promotable" }
ATyVar _ kind_var
| not (isKindVar kind_var)
-> failWithTc (ptext (sLit "Type variable") <+> quotes (ppr kind_var)
<+> ptext (sLit "used as a kind"))
| not (null arg_kis)
-> failWithTc (ptext (sLit "Kind variable") <+> quotes (ppr name)
<+> ptext (sLit "cannot appear in a function position"))
| otherwise
-> return (mkAppTys (mkTyVarTy kind_var) arg_kis)
AThing _
| isTyVarName name
-> failWithTc (ptext (sLit "Type variable") <+> quotes (ppr name)
<+> ptext (sLit "used in a kind"))
| otherwise
-> failWithTc (hang (ptext (sLit "Type constructor") <+> quotes (ppr name)
<+> ptext (sLit "used in a kind"))
2 (ptext (sLit "inside its own recursive group")))
APromotionErr err -> promotionErr name err
_ -> wrongThingErr "promoted type" thing name
}
where
tycon_err tc msg = failWithTc (quotes (ppr tc) <+> ptext (sLit "of kind")
<+> quotes (ppr (tyConKind tc)) <+> ptext (sLit msg))
dataKindsErr :: Name -> SDoc
dataKindsErr name
= hang (ptext (sLit "Illegal kind:") <+> quotes (ppr name))
2 (ptext (sLit "Perhaps you intended to use DataKinds"))
promotionErr :: Name -> PromotionErr -> TcM a
promotionErr name err
= failWithTc (hang (pprPECategory err <+> quotes (ppr name) <+> ptext (sLit "cannot be used here"))
2 (parens reason))
where
reason = case err of
FamDataConPE -> ptext (sLit "it comes from a data family instance")
NoDataKinds -> ptext (sLit "Perhaps you intended to use DataKinds")
_ -> ptext (sLit "it is defined and used in the same recursive group")
\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 = pprPrefixOcc 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]") ]
unifyKindMisMatch :: TcKind -> TcKind -> TcM a
unifyKindMisMatch ki1 ki2 = do
ki1' <- zonkTcKind ki1
ki2' <- zonkTcKind ki2
let msg = hang (ptext (sLit "Couldn't match kind"))
2 (sep [quotes (ppr ki1'),
ptext (sLit "against"),
quotes (ppr ki2')])
failWithTc msg
\end{code}