%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcMonoType]{Typechecking user-specified @MonoTypes@}
\begin{code}
-#include "HsVersions.h"
+module TcMonoType ( tcHsType, tcHsRecType, tcIfaceType,
+ tcHsSigType, tcHsLiftedSigType,
+ tcRecTheta, checkAmbiguity,
+
+ -- Kind checking
+ kcHsTyVar, kcHsTyVars, mkTyClTyVars,
+ kcHsType, kcHsSigType, kcHsLiftedSigType, kcHsContext,
+ tcTyVars, tcHsTyVars, mkImmutTyVars,
-module TcMonoType ( tcHsType, tcHsTypeKind, tcContext, tcTyVarScope ) where
+ TcSigInfo(..), tcTySig, mkTcSig, maybeSig,
+ checkSigTyVars, sigCtxt, sigPatCtxt
+ ) where
-IMP_Ubiq(){-uitous-}
+#include "HsVersions.h"
-import HsSyn ( HsType(..), HsTyVar(..), Fake )
-import RnHsSyn ( RenamedHsType(..), RenamedContext(..) )
+import HsSyn ( HsType(..), HsTyVarBndr(..),
+ Sig(..), HsPred(..), pprParendHsType, HsTupCon(..), hsTyVarNames )
+import RnHsSyn ( RenamedHsType, RenamedHsPred, RenamedContext, RenamedSig )
+import TcHsSyn ( TcId )
import TcMonad
-import TcEnv ( tcLookupTyVar, tcLookupClass, tcLookupTyCon, tcExtendTyVarEnv )
-import TcKind ( TcKind, mkTcTypeKind, mkBoxedTypeKind,
- mkTcArrowKind, unifyKind, newKindVar,
- kindToTcKind, tcDefaultKind
+import TcEnv ( tcExtendTyVarEnv, tcLookup, tcLookupGlobal,
+ tcGetGlobalTyVars, tcEnvTcIds, tcEnvTyVars,
+ TyThing(..), TcTyThing(..), tcExtendKindEnv
+ )
+import TcType ( TcKind, TcTyVar, TcThetaType, TcTauType,
+ newKindVar, tcInstSigVar,
+ zonkKindEnv, zonkTcType, zonkTcTyVars, zonkTcTyVar
)
-import Type ( GenType, SYN_IE(Type), SYN_IE(ThetaType),
- mkTyVarTy, mkTyConTy, mkFunTy, mkAppTy, mkSynTy,
- mkSigmaTy, mkDictTy
+import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToId )
+import FunDeps ( grow )
+import TcUnify ( unifyKind, unifyOpenTypeKind )
+import Unify ( allDistinctTyVars )
+import Type ( Type, Kind, PredType(..), ThetaType, SigmaType, TauType,
+ mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy,
+ zipFunTys, hoistForAllTys,
+ mkSigmaTy, mkPredTy, mkTyConApp,
+ mkAppTys, splitForAllTys, splitRhoTy, mkRhoTy,
+ liftedTypeKind, unliftedTypeKind, mkArrowKind,
+ mkArrowKinds, getTyVar_maybe, getTyVar, splitFunTy_maybe,
+ tidyOpenType, tidyOpenTypes, tidyTyVar, tidyTyVars,
+ tyVarsOfType, tyVarsOfPred, mkForAllTys,
+ isUnboxedTupleType, isForAllTy, isIPPred
)
-import TyVar ( GenTyVar, SYN_IE(TyVar), mkTyVar )
-import PrelInfo ( cCallishClassKeys )
-import TyCon ( TyCon )
-import Name ( Name, OccName, isTvOcc )
-import TysWiredIn ( mkListTy, mkTupleTy )
-import Unique ( Unique )
-import PprStyle
-import Pretty
-import Util ( zipWithEqual, zipLazy, panic{-, pprPanic ToDo:rm-} )
+import PprType ( pprType, pprPred )
+import Subst ( mkTopTyVarSubst, substTy )
+import CoreFVs ( idFreeTyVars )
+import Id ( mkLocalId, idName, idType )
+import Var ( Id, Var, TyVar, mkTyVar, tyVarKind )
+import VarEnv
+import VarSet
+import ErrUtils ( Message )
+import TyCon ( TyCon, isSynTyCon, tyConArity, tyConKind )
+import Class ( classArity, classTyCon )
+import Name ( Name )
+import TysWiredIn ( mkListTy, mkTupleTy, genUnitTyCon )
+import BasicTypes ( Boxity(..), RecFlag(..), isRec )
+import SrcLoc ( SrcLoc )
+import Util ( mapAccumL, isSingleton )
+import Outputable
+
\end{code}
-tcHsType and tcHsTypeKind
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+%************************************************************************
+%* *
+\subsection{Kind checking}
+%* *
+%************************************************************************
-tcHsType checks that the type really is of kind Type!
+Kind checking
+~~~~~~~~~~~~~
+When we come across the binding site for some type variables, we
+proceed in two stages
-\begin{code}
-tcHsType :: RenamedHsType -> TcM s Type
+1. Figure out what kind each tyvar has
-tcHsType ty
- = tcHsTypeKind ty `thenTc` \ (kind,ty) ->
- unifyKind kind mkTcTypeKind `thenTc_`
- returnTc ty
-\end{code}
+2. Create suitably-kinded tyvars,
+ extend the envt,
+ and typecheck the body
+
+To do step 1, we proceed thus:
+
+1a. Bind each type variable to a kind variable
+1b. Apply the kind checker
+1c. Zonk the resulting kinds
+
+The kind checker is passed to tcHsTyVars as an argument.
+
+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)
-tcHsTypeKind does the real work. It returns a kind and a type.
+Here we deduce a::*->*, b::*.
+But equally valid would be
+ a::(*->*)-> *, b::*->*
\begin{code}
-tcHsTypeKind :: RenamedHsType -> TcM s (TcKind s, Type)
+tcHsTyVars :: [HsTyVarBndr Name]
+ -> TcM a -- The kind checker
+ -> ([TyVar] -> TcM b)
+ -> TcM b
+
+tcHsTyVars [] kind_check thing_inside = thing_inside []
+ -- A useful short cut for a common case!
+
+tcHsTyVars tv_names kind_check thing_inside
+ = kcHsTyVars tv_names `thenNF_Tc` \ tv_names_w_kinds ->
+ tcExtendKindEnv tv_names_w_kinds kind_check `thenTc_`
+ zonkKindEnv tv_names_w_kinds `thenNF_Tc` \ tvs_w_kinds ->
+ let
+ tyvars = mkImmutTyVars tvs_w_kinds
+ in
+ tcExtendTyVarEnv tyvars (thing_inside tyvars)
+
+tcTyVars :: [Name]
+ -> TcM a -- The kind checker
+ -> TcM [TyVar]
+tcTyVars [] kind_check = returnTc []
+
+tcTyVars tv_names kind_check
+ = mapNF_Tc newNamedKindVar tv_names `thenTc` \ kind_env ->
+ tcExtendKindEnv kind_env kind_check `thenTc_`
+ zonkKindEnv kind_env `thenNF_Tc` \ tvs_w_kinds ->
+ listNF_Tc [tcNewSigTyVar name kind | (name,kind) <- tvs_w_kinds]
+\end{code}
+
+
+\begin{code}
+kcHsTyVar :: HsTyVarBndr name -> NF_TcM (name, TcKind)
+kcHsTyVars :: [HsTyVarBndr name] -> NF_TcM [(name, TcKind)]
- -- This equation isn't needed (the next one would handle it fine)
- -- but it's rather a common case, so we handle it directly
-tcHsTypeKind (MonoTyVar name)
- | isTvOcc (getOccName name)
- = tcLookupTyVar name `thenNF_Tc` \ (kind,tyvar) ->
- returnTc (kind, mkTyVarTy tyvar)
+kcHsTyVar (UserTyVar name) = newNamedKindVar name
+kcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (name, kind)
-tcHsTypeKind ty@(MonoTyVar name)
- = tcFunType ty []
+kcHsTyVars tvs = mapNF_Tc kcHsTyVar tvs
+
+newNamedKindVar name = newKindVar `thenNF_Tc` \ kind ->
+ returnNF_Tc (name, kind)
+
+---------------------------
+kcLiftedType :: RenamedHsType -> TcM ()
+ -- The type ty must be a *lifted* *type*
+kcLiftedType ty
+ = kcHsType ty `thenTc` \ kind ->
+ tcAddErrCtxt (typeKindCtxt ty) $
+ unifyKind liftedTypeKind kind
-tcHsTypeKind (MonoListTy _ ty)
- = tcHsType ty `thenTc` \ tau_ty ->
- returnTc (mkTcTypeKind, mkListTy tau_ty)
-
-tcHsTypeKind (MonoTupleTy _ tys)
- = mapTc tcHsType tys `thenTc` \ tau_tys ->
- returnTc (mkTcTypeKind, mkTupleTy (length tys) tau_tys)
-
-tcHsTypeKind (MonoFunTy ty1 ty2)
- = tcHsType ty1 `thenTc` \ tau_ty1 ->
- tcHsType ty2 `thenTc` \ tau_ty2 ->
- returnTc (mkTcTypeKind, mkFunTy tau_ty1 tau_ty2)
-
-tcHsTypeKind (MonoTyApp ty1 ty2)
- = tcTyApp ty1 [ty2]
-
-tcHsTypeKind (HsForAllTy tv_names context ty)
- = tcTyVarScope tv_names $ \ tyvars ->
- tcContext context `thenTc` \ theta ->
- tcHsType ty `thenTc` \ tau ->
- -- For-all's are of kind type!
- returnTc (mkTcTypeKind, mkSigmaTy tyvars theta tau)
-
--- for unfoldings only:
-tcHsTypeKind (MonoDictTy class_name ty)
- = tcHsTypeKind ty `thenTc` \ (arg_kind, arg_ty) ->
- tcLookupClass class_name `thenTc` \ (class_kind, clas) ->
- unifyKind class_kind arg_kind `thenTc_`
- returnTc (mkTcTypeKind, mkDictTy clas arg_ty)
+---------------------------
+kcTypeType :: RenamedHsType -> TcM ()
+ -- The type ty must be a *type*, but it can be lifted or unlifted.
+kcTypeType ty
+ = kcHsType ty `thenTc` \ kind ->
+ tcAddErrCtxt (typeKindCtxt ty) $
+ unifyOpenTypeKind kind
+
+---------------------------
+kcHsSigType, kcHsLiftedSigType :: RenamedHsType -> TcM ()
+ -- Used for type signatures
+kcHsSigType = kcTypeType
+kcHsLiftedSigType = kcLiftedType
+
+---------------------------
+kcHsType :: RenamedHsType -> TcM TcKind
+kcHsType (HsTyVar name) = kcTyVar name
+
+kcHsType (HsListTy ty)
+ = kcLiftedType ty `thenTc` \ tau_ty ->
+ returnTc liftedTypeKind
+
+kcHsType (HsTupleTy (HsTupCon _ boxity _) tys)
+ = mapTc kcTypeType tys `thenTc_`
+ returnTc (case boxity of
+ Boxed -> liftedTypeKind
+ Unboxed -> unliftedTypeKind)
+
+kcHsType (HsFunTy ty1 ty2)
+ = kcTypeType ty1 `thenTc_`
+ kcTypeType ty2 `thenTc_`
+ returnTc liftedTypeKind
+
+kcHsType ty@(HsOpTy ty1 op ty2)
+ = kcTyVar op `thenTc` \ op_kind ->
+ kcHsType ty1 `thenTc` \ ty1_kind ->
+ kcHsType ty2 `thenTc` \ ty2_kind ->
+ tcAddErrCtxt (appKindCtxt (ppr ty)) $
+ kcAppKind op_kind ty1_kind `thenTc` \ op_kind' ->
+ kcAppKind op_kind' ty2_kind
+
+kcHsType (HsPredTy pred)
+ = kcHsPred pred `thenTc_`
+ returnTc liftedTypeKind
+
+kcHsType ty@(HsAppTy ty1 ty2)
+ = kcHsType ty1 `thenTc` \ tc_kind ->
+ kcHsType ty2 `thenTc` \ arg_kind ->
+ tcAddErrCtxt (appKindCtxt (ppr ty)) $
+ kcAppKind tc_kind arg_kind
+
+kcHsType (HsForAllTy (Just tv_names) context ty)
+ = kcHsTyVars tv_names `thenNF_Tc` \ kind_env ->
+ tcExtendKindEnv kind_env $
+ kcHsContext context `thenTc_`
+ kcHsType ty `thenTc_`
+ returnTc liftedTypeKind
+
+---------------------------
+kcAppKind fun_kind arg_kind
+ = case splitFunTy_maybe fun_kind of
+ Just (arg_kind', res_kind)
+ -> unifyKind arg_kind arg_kind' `thenTc_`
+ returnTc res_kind
+
+ Nothing -> newKindVar `thenNF_Tc` \ res_kind ->
+ unifyKind fun_kind (mkArrowKind arg_kind res_kind) `thenTc_`
+ returnTc res_kind
+
+
+---------------------------
+kcHsContext ctxt = mapTc_ kcHsPred ctxt
+
+kcHsPred :: RenamedHsPred -> TcM ()
+kcHsPred pred@(HsIParam name ty)
+ = tcAddErrCtxt (appKindCtxt (ppr pred)) $
+ kcLiftedType ty
+
+kcHsPred pred@(HsClassP cls tys)
+ = tcAddErrCtxt (appKindCtxt (ppr pred)) $
+ kcClass cls `thenTc` \ kind ->
+ mapTc kcHsType tys `thenTc` \ arg_kinds ->
+ unifyKind kind (mkArrowKinds arg_kinds liftedTypeKind)
+
+ ---------------------------
+kcTyVar name -- Could be a tyvar or a tycon
+ = tcLookup name `thenTc` \ thing ->
+ case thing of
+ AThing kind -> returnTc kind
+ ATyVar tv -> returnTc (tyVarKind tv)
+ AGlobal (ATyCon tc) -> returnTc (tyConKind tc)
+ other -> failWithTc (wrongThingErr "type" thing name)
+
+kcClass cls -- Must be a class
+ = tcLookup cls `thenNF_Tc` \ thing ->
+ case thing of
+ AThing kind -> returnTc kind
+ AGlobal (AClass cls) -> returnTc (tyConKind (classTyCon cls))
+ other -> failWithTc (wrongThingErr "class" thing cls)
\end{code}
-Help functions for type applications
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+%************************************************************************
+%* *
+\subsection{Checking types}
+%* *
+%************************************************************************
+
+tcHsSigType and tcHsLiftedSigType
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+tcHsSigType and tcHsLiftedSigType are used for type signatures written by the programmer
+
+ * We hoist any inner for-alls to the top
+
+ * Notice that we kind-check first, because the type-check assumes
+ that the kinds are already checked.
+
+ * They are only called when there are no kind vars in the environment
+ so the kind returned is indeed a Kind not a TcKind
+
\begin{code}
-tcTyApp (MonoTyApp ty1 ty2) tys
- = tcTyApp ty1 (ty2:tys)
+tcHsSigType, tcHsLiftedSigType :: RenamedHsType -> TcM Type
+ -- Do kind checking, and hoist for-alls to the top
+tcHsSigType ty = kcTypeType ty `thenTc_` tcHsType ty
+tcHsLiftedSigType ty = kcLiftedType ty `thenTc_` tcHsType ty
+
+tcHsType :: RenamedHsType -> TcM Type
+tcHsRecType :: RecFlag -> RenamedHsType -> TcM Type
+ -- Don't do kind checking, but do hoist for-alls to the top
+ -- These are used in type and class decls, where kinding is
+ -- done in advance
+tcHsType ty = tc_type NonRecursive ty `thenTc` \ ty' -> returnTc (hoistForAllTys ty')
+tcHsRecType wimp_out ty = tc_type wimp_out ty `thenTc` \ ty' -> returnTc (hoistForAllTys ty')
+
+-- In interface files the type is already kinded,
+-- and we definitely don't want to hoist for-alls.
+-- Otherwise we'll change
+-- dmfail :: forall m:(*->*) Monad m => forall a:* => String -> m a
+-- into
+-- dmfail :: forall m:(*->*) a:* Monad m => String -> m a
+-- which definitely isn't right!
+tcIfaceType ty = tc_type NonRecursive ty
+\end{code}
-tcTyApp ty tys
- | null tys
- = tcFunType ty []
- | otherwise
- = mapAndUnzipTc tcHsTypeKind tys `thenTc` \ (arg_kinds, arg_tys) ->
- tcFunType ty arg_tys `thenTc` \ (fun_kind, result_ty) ->
-
- -- Check argument compatibility; special ca
- newKindVar `thenNF_Tc` \ result_kind ->
- unifyKind fun_kind (foldr mkTcArrowKind result_kind arg_kinds)
- `thenTc_`
- returnTc (result_kind, result_ty)
-
-tcFunType (MonoTyVar name) arg_tys
- | isTvOcc (getOccName name) -- Must be a type variable
- = tcLookupTyVar name `thenNF_Tc` \ (kind,tyvar) ->
- returnTc (kind, foldl mkAppTy (mkTyVarTy tyvar) arg_tys)
-
- | otherwise -- Must be a type constructor
- = tcLookupTyCon name `thenTc` \ (kind,maybe_arity,tycon) ->
- case maybe_arity of
- Nothing -> returnTc (kind, foldl mkAppTy (mkTyConTy tycon) arg_tys)
- Just arity -> checkTc (arity == n_args) (err arity) `thenTc_`
- returnTc (kind, mkSynTy tycon arg_tys)
+%************************************************************************
+%* *
+\subsection{tc_type}
+%* *
+%************************************************************************
+
+tc_type, the main work horse
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+ -------------------
+ *** BIG WARNING ***
+ -------------------
+
+tc_type is used to typecheck the types in the RHS of data
+constructors. In the case of recursive data types, that means that
+the type constructors themselves are (partly) black holes. e.g.
+
+ data T a = MkT a [T a]
+
+While typechecking the [T a] on the RHS, T itself is not yet fully
+defined. That in turn places restrictions on what you can check in
+tcHsType; if you poke on too much you get a black hole. I keep
+forgetting this, hence this warning!
+
+The wimp_out argument tells when we are in a mutually-recursive
+group of type declarations, so omit various checks else we
+get a black hole. They'll be done again later, in TcTyClDecls.tcGroup.
+
+ --------------------------
+ *** END OF BIG WARNING ***
+ --------------------------
+
+
+\begin{code}
+tc_type :: RecFlag -> RenamedHsType -> TcM Type
+
+tc_type wimp_out ty@(HsTyVar name)
+ = tc_app wimp_out ty []
+
+tc_type wimp_out (HsListTy ty)
+ = tc_arg_type wimp_out ty `thenTc` \ tau_ty ->
+ returnTc (mkListTy tau_ty)
+
+tc_type wimp_out (HsTupleTy (HsTupCon _ boxity arity) tys)
+ = ASSERT( arity == length tys )
+ mapTc tc_tup_arg tys `thenTc` \ tau_tys ->
+ returnTc (mkTupleTy boxity arity tau_tys)
where
- err arity = arityErr "Type synonym constructor" name arity n_args
- n_args = length arg_tys
+ tc_tup_arg = case boxity of
+ Boxed -> tc_arg_type wimp_out
+ Unboxed -> tc_type wimp_out
+ -- Unboxed tuples can have polymorphic or unboxed args.
+ -- This happens in the workers for functions returning
+ -- product types with polymorphic components
+
+tc_type wimp_out (HsFunTy ty1 ty2)
+ = tc_type wimp_out ty1 `thenTc` \ tau_ty1 ->
+ -- Function argument can be polymorphic, but
+ -- must not be an unboxed tuple
+ checkTc (not (isUnboxedTupleType tau_ty1))
+ (ubxArgTyErr ty1) `thenTc_`
+ tc_type wimp_out ty2 `thenTc` \ tau_ty2 ->
+ returnTc (mkFunTy tau_ty1 tau_ty2)
+
+tc_type wimp_out (HsNumTy n)
+ = ASSERT(n== 1)
+ returnTc (mkTyConApp genUnitTyCon [])
+
+tc_type wimp_out (HsOpTy ty1 op ty2) =
+ tc_arg_type wimp_out ty1 `thenTc` \ tau_ty1 ->
+ tc_arg_type wimp_out ty2 `thenTc` \ tau_ty2 ->
+ tc_fun_type op [tau_ty1,tau_ty2]
+
+tc_type wimp_out (HsAppTy ty1 ty2)
+ = tc_app wimp_out ty1 [ty2]
+
+tc_type wimp_out (HsPredTy pred)
+ = tc_pred wimp_out pred `thenTc` \ pred' ->
+ returnTc (mkPredTy pred')
+
+tc_type wimp_out full_ty@(HsForAllTy (Just tv_names) ctxt ty)
+ = let
+ kind_check = kcHsContext ctxt `thenTc_` kcHsType ty
+ in
+ tcHsTyVars tv_names kind_check $ \ tyvars ->
+ tcRecTheta wimp_out ctxt `thenTc` \ theta ->
+
+ -- Context behaves like a function type
+ -- This matters. Return-unboxed-tuple analysis can
+ -- give overloaded functions like
+ -- f :: forall a. Num a => (# a->a, a->a #)
+ -- And we want these to get through the type checker
+ (if null theta then
+ tc_arg_type wimp_out ty
+ else
+ tc_type wimp_out ty
+ ) `thenTc` \ tau ->
+
+ checkAmbiguity wimp_out is_source tyvars theta tau
+ where
+ is_source = case tv_names of
+ (UserTyVar _ : _) -> True
+ other -> False
+
+
+ -- tc_arg_type checks that the argument of a
+ -- type appplication isn't a for-all type or an unboxed tuple type
+ -- For example, we want to reject things like:
+ --
+ -- instance Ord a => Ord (forall s. T s a)
+ -- and
+ -- g :: T s (forall b.b)
+ --
+ -- Other unboxed types are very occasionally allowed as type
+ -- arguments depending on the kind of the type constructor
+
+tc_arg_type wimp_out arg_ty
+ | isRec wimp_out
+ = tc_type wimp_out arg_ty
+
+ | otherwise
+ = tc_type wimp_out arg_ty `thenTc` \ arg_ty' ->
+ checkTc (not (isForAllTy arg_ty')) (polyArgTyErr arg_ty) `thenTc_`
+ checkTc (not (isUnboxedTupleType arg_ty')) (ubxArgTyErr arg_ty) `thenTc_`
+ returnTc arg_ty'
+
+tc_arg_types wimp_out arg_tys = mapTc (tc_arg_type wimp_out) arg_tys
+\end{code}
-tcFunType ty arg_tys
- = tcHsTypeKind ty `thenTc` \ (fun_kind, fun_ty) ->
- returnTc (fun_kind, foldl mkAppTy fun_ty arg_tys)
+Help functions for type applications
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+\begin{code}
+tc_app :: RecFlag -> RenamedHsType -> [RenamedHsType] -> TcM Type
+tc_app wimp_out (HsAppTy ty1 ty2) tys
+ = tc_app wimp_out ty1 (ty2:tys)
+
+tc_app wimp_out ty tys
+ = tcAddErrCtxt (appKindCtxt pp_app) $
+ tc_arg_types wimp_out tys `thenTc` \ arg_tys ->
+ case ty of
+ HsTyVar fun -> tc_fun_type fun arg_tys
+ other -> tc_type wimp_out ty `thenTc` \ fun_ty ->
+ returnNF_Tc (mkAppTys fun_ty arg_tys)
+ where
+ pp_app = ppr ty <+> sep (map pprParendHsType tys)
+
+-- (tc_fun_type ty arg_tys) returns (mkAppTys ty arg_tys)
+-- But not quite; for synonyms it checks the correct arity, and builds a SynTy
+-- hence the rather strange functionality.
+
+tc_fun_type name arg_tys
+ = tcLookup name `thenTc` \ thing ->
+ case thing of
+ ATyVar tv -> returnTc (mkAppTys (mkTyVarTy tv) arg_tys)
+
+ AGlobal (ATyCon tc)
+ | isSynTyCon tc -> checkTc arity_ok err_msg `thenTc_`
+ returnTc (mkAppTys (mkSynTy tc (take arity arg_tys))
+ (drop arity arg_tys))
+
+ | otherwise -> returnTc (mkTyConApp tc arg_tys)
+ where
+
+ arity_ok = arity <= n_args
+ arity = tyConArity tc
+ -- It's OK to have an *over-applied* type synonym
+ -- data Tree a b = ...
+ -- type Foo a = Tree [a]
+ -- f :: Foo a b -> ...
+ err_msg = arityErr "Type synonym" name arity n_args
+ n_args = length arg_tys
+
+ other -> failWithTc (wrongThingErr "type constructor" thing name)
\end{code}
Contexts
~~~~~~~~
\begin{code}
+tcRecTheta :: RecFlag -> RenamedContext -> TcM ThetaType
+ -- Used when we are expecting a ClassContext (i.e. no implicit params)
+tcRecTheta wimp_out context = mapTc (tc_pred wimp_out) context
+
+tc_pred wimp_out assn@(HsClassP class_name tys)
+ = tcAddErrCtxt (appKindCtxt (ppr assn)) $
+ tc_arg_types wimp_out tys `thenTc` \ arg_tys ->
+ tcLookupGlobal class_name `thenTc` \ thing ->
+ case thing of
+ AClass clas -> checkTc (arity == n_tys) err `thenTc_`
+ returnTc (ClassP clas arg_tys)
+ where
+ arity = classArity clas
+ n_tys = length tys
+ err = arityErr "Class" class_name arity n_tys
+
+ other -> failWithTc (wrongThingErr "class" (AGlobal thing) class_name)
+
+tc_pred wimp_out assn@(HsIParam name ty)
+ = tcAddErrCtxt (appKindCtxt (ppr assn)) $
+ tc_arg_type wimp_out ty `thenTc` \ arg_ty ->
+ returnTc (IParam name arg_ty)
+\end{code}
+
-tcContext :: RenamedContext -> TcM s ThetaType
-tcContext context = mapTc tcClassAssertion context
+Check for ambiguity
+~~~~~~~~~~~~~~~~~~~
+ forall V. P => tau
+is ambiguous if P contains generic variables
+(i.e. one of the Vs) that are not mentioned in tau
+
+However, we need to take account of functional dependencies
+when we speak of 'mentioned in tau'. Example:
+ class C a b | a -> b where ...
+Then the type
+ forall x y. (C x y) => x
+is not ambiguous because x is mentioned and x determines y
+
+NOTE: In addition, GHC insists that at least one type variable
+in each constraint is in V. So we disallow a type like
+ forall a. Eq b => b -> b
+even in a scope where b is in scope.
+This is the is_free test below.
+
+Notes on the 'is_source_polytype' test above
+Check ambiguity only for source-program types, not
+for types coming from inteface files. The latter can
+legitimately have ambiguous types. Example
+ class S a where s :: a -> (Int,Int)
+ instance S Char where s _ = (1,1)
+ f:: S a => [a] -> Int -> (Int,Int)
+ f (_::[a]) x = (a*x,b)
+ where (a,b) = s (undefined::a)
+Here the worker for f gets the type
+ fw :: forall a. S a => Int -> (# Int, Int #)
+
+If the list of tv_names is empty, we have a monotype,
+and then we don't need to check for ambiguity either,
+because the test can't fail (see is_ambig).
-tcClassAssertion (class_name, ty)
- = checkTc (canBeUsedInContext class_name)
- (naughtyCCallContextErr class_name) `thenTc_`
+\begin{code}
+checkAmbiguity :: RecFlag -> Bool
+ -> [TyVar] -> ThetaType -> TauType
+ -> TcM SigmaType
+checkAmbiguity wimp_out is_source_polytype forall_tyvars theta tau
+ | isRec wimp_out = returnTc sigma_ty
+ | otherwise = mapTc_ check_pred theta `thenTc_`
+ returnTc sigma_ty
+ where
+ sigma_ty = mkSigmaTy forall_tyvars theta tau
+ tau_vars = tyVarsOfType tau
+ extended_tau_vars = grow theta tau_vars
- tcLookupClass class_name `thenTc` \ (class_kind, clas) ->
- tcHsTypeKind ty `thenTc` \ (ty_kind, ty) ->
+ is_ambig ct_var = (ct_var `elem` forall_tyvars) &&
+ not (ct_var `elemVarSet` extended_tau_vars)
+ is_free ct_var = not (ct_var `elem` forall_tyvars)
+
+ check_pred pred = checkTc (not any_ambig) (ambigErr pred sigma_ty) `thenTc_`
+ checkTc (isIPPred pred || not all_free) (freeErr pred sigma_ty)
+ where
+ ct_vars = varSetElems (tyVarsOfPred pred)
+ all_free = all is_free ct_vars
+ any_ambig = is_source_polytype && any is_ambig ct_vars
+\end{code}
- unifyKind class_kind ty_kind `thenTc_`
+%************************************************************************
+%* *
+\subsection{Type variables, with knot tying!}
+%* *
+%************************************************************************
- returnTc (clas, ty)
+\begin{code}
+mkImmutTyVars :: [(Name,Kind)] -> [TyVar]
+mkImmutTyVars pairs = [mkTyVar name kind | (name, kind) <- pairs]
+
+mkTyClTyVars :: Kind -- Kind of the tycon or class
+ -> [HsTyVarBndr Name]
+ -> [TyVar]
+mkTyClTyVars kind tyvar_names
+ = mkImmutTyVars tyvars_w_kinds
+ where
+ (tyvars_w_kinds, _) = zipFunTys (hsTyVarNames tyvar_names) kind
\end{code}
-HACK warning: Someone discovered that @CCallable@ and @CReturnable@
-could be used in contexts such as:
-\begin{verbatim}
-foo :: CCallable a => a -> PrimIO Int
-\end{verbatim}
-Doing this utterly wrecks the whole point of introducing these
-classes so we specifically check that this isn't being done.
+%************************************************************************
+%* *
+\subsection{Signatures}
+%* *
+%************************************************************************
+
+@tcSigs@ checks the signatures for validity, and returns a list of
+{\em freshly-instantiated} signatures. That is, the types are already
+split up, and have fresh type variables installed. All non-type-signature
+"RenamedSigs" are ignored.
+
+The @TcSigInfo@ contains @TcTypes@ because they are unified with
+the variable's type, and after that checked to see whether they've
+been instantiated.
\begin{code}
-canBeUsedInContext :: Name -> Bool
-canBeUsedInContext n = not (uniqueOf n `elem` cCallishClassKeys)
+data TcSigInfo
+ = TySigInfo
+ Name -- N, the Name in corresponding binding
+
+ TcId -- *Polymorphic* binder for this value...
+ -- Has name = N
+
+ [TcTyVar] -- tyvars
+ TcThetaType -- theta
+ TcTauType -- tau
+
+ TcId -- *Monomorphic* binder for this value
+ -- Does *not* have name = N
+ -- Has type tau
+
+ [Inst] -- Empty if theta is null, or
+ -- (method mono_id) otherwise
+
+ SrcLoc -- Of the signature
+
+instance Outputable TcSigInfo where
+ ppr (TySigInfo nm id tyvars theta tau _ inst loc) =
+ ppr nm <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
+
+maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo)
+ -- Search for a particular signature
+maybeSig [] name = Nothing
+maybeSig (sig@(TySigInfo sig_name _ _ _ _ _ _ _) : sigs) name
+ | name == sig_name = Just sig
+ | otherwise = maybeSig sigs name
\end{code}
-Type variables, with knot tying!
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
\begin{code}
-tcTyVarScope
- :: [HsTyVar Name] -- Names of some type variables
- -> ([TyVar] -> TcM s a) -- Thing to type check in their scope
- -> TcM s a -- Result
+tcTySig :: RenamedSig -> TcM TcSigInfo
+
+tcTySig (Sig v ty src_loc)
+ = tcAddSrcLoc src_loc $
+ tcAddErrCtxt (tcsigCtxt v) $
+ tcHsSigType ty `thenTc` \ sigma_tc_ty ->
+ mkTcSig (mkLocalId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig ->
+ returnTc sig
+
+mkTcSig :: TcId -> SrcLoc -> NF_TcM TcSigInfo
+mkTcSig poly_id src_loc
+ = -- Instantiate this type
+ -- It's important to do this even though in the error-free case
+ -- we could just split the sigma_tc_ty (since the tyvars don't
+ -- unified with anything). But in the case of an error, when
+ -- the tyvars *do* get unified with something, we want to carry on
+ -- typechecking the rest of the program with the function bound
+ -- to a pristine type, namely sigma_tc_ty
+ let
+ (tyvars, rho) = splitForAllTys (idType poly_id)
+ in
+ mapNF_Tc tcInstSigVar tyvars `thenNF_Tc` \ tyvars' ->
+ -- Make *signature* type variables
+
+ let
+ tyvar_tys' = mkTyVarTys tyvars'
+ rho' = substTy (mkTopTyVarSubst tyvars tyvar_tys') rho
+ -- mkTopTyVarSubst because the tyvars' are fresh
+ (theta', tau') = splitRhoTy rho'
+ -- This splitRhoTy tries hard to make sure that tau' is a type synonym
+ -- wherever possible, which can improve interface files.
+ in
+ newMethodWithGivenTy SignatureOrigin
+ poly_id
+ tyvar_tys'
+ theta' tau' `thenNF_Tc` \ inst ->
+ -- We make a Method even if it's not overloaded; no harm
+
+ returnNF_Tc (TySigInfo name poly_id tyvars' theta' tau' (instToId inst) [inst] src_loc)
+ where
+ name = idName poly_id
+\end{code}
+
+
+
+%************************************************************************
+%* *
+\subsection{Checking signature type variables}
+%* *
+%************************************************************************
+
+@checkSigTyVars@ is used after the type in a type signature has been unified with
+the actual type found. It then checks that the type variables of the type signature
+are
+ (a) Still all type variables
+ eg matching signature [a] against inferred type [(p,q)]
+ [then a will be unified to a non-type variable]
+
+ (b) Still all distinct
+ eg matching signature [(a,b)] against inferred type [(p,p)]
+ [then a and b will be unified together]
+
+ (c) Not mentioned in the environment
+ eg the signature for f in this:
+
+ g x = ... where
+ f :: a->[a]
+ f y = [x,y]
+
+ Here, f is forced to be monorphic by the free occurence of x.
+
+ (d) Not (unified with another type variable that is) in scope.
+ eg f x :: (r->r) = (\y->y) :: forall a. a->r
+ when checking the expression type signature, we find that
+ even though there is nothing in scope whose type mentions r,
+ nevertheless the type signature for the expression isn't right.
+
+ Another example is in a class or instance declaration:
+ class C a where
+ op :: forall b. a -> b
+ op x = x
+ Here, b gets unified with a
-tcTyVarScope tyvar_names thing_inside
- = mapAndUnzipNF_Tc tcHsTyVar tyvar_names `thenNF_Tc` \ (names, kinds) ->
+Before doing this, the substitution is applied to the signature type variable.
- fixTc (\ ~(rec_tyvars, _) ->
- -- Ok to look at names, kinds, but not tyvars!
+We used to have the notion of a "DontBind" type variable, which would
+only be bound to itself or nothing. Then points (a) and (b) were
+self-checking. But it gave rise to bogus consequential error messages.
+For example:
- tcExtendTyVarEnv names (kinds `zipLazy` rec_tyvars)
- (thing_inside rec_tyvars) `thenTc` \ result ->
-
- -- Get the tyvar's Kinds from their TcKinds
- mapNF_Tc tcDefaultKind kinds `thenNF_Tc` \ kinds' ->
+ f = (*) -- Monomorphic
- -- Construct the real TyVars
+ g :: Num a => a -> a
+ g x = f x x
+
+Here, we get a complaint when checking the type signature for g,
+that g isn't polymorphic enough; but then we get another one when
+dealing with the (Num x) context arising from f's definition;
+we try to unify x with Int (to default it), but find that x has already
+been unified with the DontBind variable "a" from g's signature.
+This is really a problem with side-effecting unification; we'd like to
+undo g's effects when its type signature fails, but unification is done
+by side effect, so we can't (easily).
+
+So we revert to ordinary type variables for signatures, and try to
+give a helpful message in checkSigTyVars.
+
+\begin{code}
+checkSigTyVars :: [TcTyVar] -- Universally-quantified type variables in the signature
+ -> TcTyVarSet -- Tyvars that are free in the type signature
+ -- Not necessarily zonked
+ -- These should *already* be in the free-in-env set,
+ -- and are used here only to improve the error message
+ -> TcM [TcTyVar] -- Zonked signature type variables
+
+checkSigTyVars [] free = returnTc []
+checkSigTyVars sig_tyvars free_tyvars
+ = zonkTcTyVars sig_tyvars `thenNF_Tc` \ sig_tys ->
+ tcGetGlobalTyVars `thenNF_Tc` \ globals ->
+
+ checkTcM (allDistinctTyVars sig_tys globals)
+ (complain sig_tys globals) `thenTc_`
+
+ returnTc (map (getTyVar "checkSigTyVars") sig_tys)
+
+ where
+ complain sig_tys globals
+ = -- For the in-scope ones, zonk them and construct a map
+ -- from the zonked tyvar to the in-scope one
+ -- If any of the in-scope tyvars zonk to a type, then ignore them;
+ -- that'll be caught later when we back up to their type sig
+ tcGetEnv `thenNF_Tc` \ env ->
+ let
+ in_scope_tvs = tcEnvTyVars env
+ in
+ zonkTcTyVars in_scope_tvs `thenNF_Tc` \ in_scope_tys ->
+ let
+ in_scope_assoc = [ (zonked_tv, in_scope_tv)
+ | (z_ty, in_scope_tv) <- in_scope_tys `zip` in_scope_tvs,
+ Just zonked_tv <- [getTyVar_maybe z_ty]
+ ]
+ in_scope_env = mkVarEnv in_scope_assoc
+ in
+
+ -- "check" checks each sig tyvar in turn
+ foldlNF_Tc check
+ (env2, in_scope_env, [])
+ (tidy_tvs `zip` tidy_tys) `thenNF_Tc` \ (env3, _, msgs) ->
+
+ failWithTcM (env3, main_msg $$ nest 4 (vcat msgs))
+ where
+ (env1, tidy_tvs) = mapAccumL tidyTyVar emptyTidyEnv sig_tyvars
+ (env2, tidy_tys) = tidyOpenTypes env1 sig_tys
+
+ main_msg = ptext SLIT("Inferred type is less polymorphic than expected")
+
+ check (tidy_env, acc, msgs) (sig_tyvar,ty)
+ -- sig_tyvar is from the signature;
+ -- ty is what you get if you zonk sig_tyvar and then tidy it
+ --
+ -- acc maps a zonked type variable back to a signature type variable
+ = case getTyVar_maybe ty of {
+ Nothing -> -- Error (a)!
+ returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (ppr ty) : msgs) ;
+
+ Just tv ->
+
+ case lookupVarEnv acc tv of {
+ Just sig_tyvar' -> -- Error (b) or (d)!
+ returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (ppr sig_tyvar') : msgs) ;
+
+ Nothing ->
+
+ if tv `elemVarSet` globals -- Error (c)! Type variable escapes
+ -- The least comprehensible, so put it last
+ -- Game plan:
+ -- a) get the local TcIds from the environment,
+ -- and pass them to find_globals (they might have tv free)
+ -- b) similarly, find any free_tyvars that mention tv
+ then tcGetEnv `thenNF_Tc` \ ve ->
+ find_globals tv tidy_env [] (tcEnvTcIds ve) `thenNF_Tc` \ (tidy_env1, globs) ->
+ find_frees tv tidy_env1 [] (varSetElems free_tyvars) `thenNF_Tc` \ (tidy_env2, frees) ->
+ returnNF_Tc (tidy_env2, acc, escape_msg sig_tyvar tv globs frees : msgs)
+
+ else -- All OK
+ returnNF_Tc (tidy_env, extendVarEnv acc tv sig_tyvar, msgs)
+ }}
+
+-- find_globals looks at the value environment and finds values
+-- whose types mention the offending type variable. It has to be
+-- careful to zonk the Id's type first, so it has to be in the monad.
+-- We must be careful to pass it a zonked type variable, too.
+
+find_globals :: Var
+ -> TidyEnv
+ -> [(Name,Type)]
+ -> [Id]
+ -> NF_TcM (TidyEnv,[(Name,Type)])
+
+find_globals tv tidy_env acc []
+ = returnNF_Tc (tidy_env, acc)
+
+find_globals tv tidy_env acc (id:ids)
+ | isEmptyVarSet (idFreeTyVars id)
+ = find_globals tv tidy_env acc ids
+
+ | otherwise
+ = zonkTcType (idType id) `thenNF_Tc` \ id_ty ->
+ if tv `elemVarSet` tyVarsOfType id_ty then
+ let
+ (tidy_env', id_ty') = tidyOpenType tidy_env id_ty
+ acc' = (idName id, id_ty') : acc
+ in
+ find_globals tv tidy_env' acc' ids
+ else
+ find_globals tv tidy_env acc ids
+
+find_frees tv tidy_env acc []
+ = returnNF_Tc (tidy_env, acc)
+find_frees tv tidy_env acc (ftv:ftvs)
+ = zonkTcTyVar ftv `thenNF_Tc` \ ty ->
+ if tv `elemVarSet` tyVarsOfType ty then
let
- tyvars = zipWithEqual "tcTyVarScope" mkTyVar names kinds'
+ (tidy_env', ftv') = tidyTyVar tidy_env ftv
in
- returnTc (tyvars, result)
- ) `thenTc` \ (_,result) ->
- returnTc result
-
-tcHsTyVar (UserTyVar name)
- = newKindVar `thenNF_Tc` \ tc_kind ->
- returnNF_Tc (name, tc_kind)
-tcHsTyVar (IfaceTyVar name kind)
- = returnNF_Tc (name, kindToTcKind kind)
+ find_frees tv tidy_env' (ftv':acc) ftvs
+ else
+ find_frees tv tidy_env acc ftvs
+
+
+escape_msg sig_tv tv globs frees
+ = mk_msg sig_tv <+> ptext SLIT("escapes") $$
+ if not (null globs) then
+ vcat [pp_it <+> ptext SLIT("is mentioned in the environment"),
+ ptext SLIT("The following variables in the environment mention") <+> quotes (ppr tv),
+ nest 2 (vcat_first 10 [ppr name <+> dcolon <+> ppr ty | (name,ty) <- globs])
+ ]
+ else if not (null frees) then
+ vcat [ptext SLIT("It is reachable from the type variable(s)") <+> pprQuotedList frees,
+ nest 2 (ptext SLIT("which") <+> is_are <+> ptext SLIT("free in the signature"))
+ ]
+ else
+ empty -- Sigh. It's really hard to give a good error message
+ -- all the time. One bad case is an existential pattern match
+ where
+ is_are | isSingleton frees = ptext SLIT("is")
+ | otherwise = ptext SLIT("are")
+ pp_it | sig_tv /= tv = ptext SLIT("It unifies with") <+> quotes (ppr tv) <> comma <+> ptext SLIT("which")
+ | otherwise = ptext SLIT("It")
+
+ vcat_first :: Int -> [SDoc] -> SDoc
+ vcat_first n [] = empty
+ vcat_first 0 (x:xs) = text "...others omitted..."
+ vcat_first n (x:xs) = x $$ vcat_first (n-1) xs
+
+unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> quotes thing
+mk_msg tv = ptext SLIT("Quantified type variable") <+> quotes (ppr tv)
\end{code}
-Errors and contexts
-~~~~~~~~~~~~~~~~~~~
+These two context are used with checkSigTyVars
+
+\begin{code}
+sigCtxt :: Message -> [TcTyVar] -> TcThetaType -> TcTauType
+ -> TidyEnv -> NF_TcM (TidyEnv, Message)
+sigCtxt when sig_tyvars sig_theta sig_tau tidy_env
+ = zonkTcType sig_tau `thenNF_Tc` \ actual_tau ->
+ let
+ (env1, tidy_sig_tyvars) = tidyTyVars tidy_env sig_tyvars
+ (env2, tidy_sig_rho) = tidyOpenType env1 (mkRhoTy sig_theta sig_tau)
+ (env3, tidy_actual_tau) = tidyOpenType env2 actual_tau
+ msg = vcat [ptext SLIT("Signature type: ") <+> pprType (mkForAllTys tidy_sig_tyvars tidy_sig_rho),
+ ptext SLIT("Type to generalise:") <+> pprType tidy_actual_tau,
+ when
+ ]
+ in
+ returnNF_Tc (env3, msg)
+
+sigPatCtxt bound_tvs bound_ids tidy_env
+ = returnNF_Tc (env1,
+ sep [ptext SLIT("When checking a pattern that binds"),
+ nest 4 (vcat (zipWith ppr_id show_ids tidy_tys))])
+ where
+ show_ids = filter is_interesting bound_ids
+ is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
+
+ (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
+ ppr_id id ty = ppr id <+> dcolon <+> ppr ty
+ -- Don't zonk the types so we get the separate, un-unified versions
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Errors and contexts}
+%* *
+%************************************************************************
+
\begin{code}
-naughtyCCallContextErr clas_name sty
- = ppSep [ppPStr SLIT("Can't use class"), ppr sty clas_name, ppPStr SLIT("in a context")]
+tcsigCtxt v = ptext SLIT("In a type signature for") <+> quotes (ppr v)
+
+typeKindCtxt :: RenamedHsType -> Message
+typeKindCtxt ty = sep [ptext SLIT("When checking that"),
+ nest 2 (quotes (ppr ty)),
+ ptext SLIT("is a type")]
+
+appKindCtxt :: SDoc -> Message
+appKindCtxt pp = ptext SLIT("When checking kinds in") <+> quotes pp
+
+wrongThingErr expected thing name
+ = pp_thing thing <+> quotes (ppr name) <+> ptext SLIT("used as a") <+> text expected
+ where
+ pp_thing (AGlobal (ATyCon _)) = ptext SLIT("Type constructor")
+ pp_thing (AGlobal (AClass _)) = ptext SLIT("Class")
+ pp_thing (AGlobal (AnId _)) = ptext SLIT("Identifier")
+ pp_thing (ATyVar _) = ptext SLIT("Type variable")
+ pp_thing (ATcId _) = ptext SLIT("Local identifier")
+ pp_thing (AThing _) = ptext SLIT("Utterly bogus")
+
+ambigErr pred ty
+ = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred),
+ nest 4 (ptext SLIT("for the type:") <+> ppr ty),
+ nest 4 (ptext SLIT("At least one of the forall'd type variables mentioned by the constraint") $$
+ ptext SLIT("must be reachable from the type after the =>"))]
+
+freeErr pred ty
+ = sep [ptext SLIT("The constraint") <+> quotes (pprPred pred) <+>
+ ptext SLIT("does not mention any of the universally quantified type variables"),
+ nest 4 (ptext SLIT("in the type") <+> quotes (ppr ty))
+ ]
+
+polyArgTyErr ty = ptext SLIT("Illegal polymorphic type as argument:") <+> ppr ty
+ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as argument:") <+> ppr ty
\end{code}
projects / ghc-hetmet.git / blobdiff