%
-% (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, tcHsSigType, tcHsBoxedSigType,
+ tcContext, tcClassContext,
-module TcMonoType ( tcPolyType, tcMonoType, tcMonoTypeKind, tcContext ) where
+ -- Kind checking
+ kcHsTyVar, kcHsTyVars, mkTyClTyVars,
+ kcHsType, kcHsSigType, kcHsBoxedSigType, kcHsContext,
+ tcTyVars, tcHsTyVars, mkImmutTyVars,
-import Ubiq{-uitous-}
+ TcSigInfo(..), tcTySig, mkTcSig, maybeSig,
+ checkSigTyVars, sigCtxt, sigPatCtxt
+ ) where
-import HsSyn ( PolyType(..), MonoType(..), Fake )
-import RnHsSyn ( RenamedPolyType(..), RenamedMonoType(..),
- RenamedContext(..)
- )
+#include "HsVersions.h"
+import HsSyn ( HsType(..), HsTyVarBndr(..), HsUsageAnn(..),
+ Sig(..), HsPred(..), pprParendHsType, HsTupCon(..), hsTyVarNames )
+import RnHsSyn ( RenamedHsType, RenamedHsPred, RenamedContext, RenamedSig )
+import TcHsSyn ( TcId )
import TcMonad
-import TcEnv ( tcLookupTyVar, tcLookupClass, tcLookupTyCon,
- tcTyVarScope, tcTyVarScopeGivenKinds
+import TcEnv ( tcExtendTyVarEnv, tcExtendKindEnv,
+ tcLookupGlobal, tcLookup,
+ tcEnvTcIds, tcEnvTyVars,
+ tcGetGlobalTyVars,
+ TyThing(..), TcTyThing(..)
)
-import TcKind ( TcKind, mkTcTypeKind, mkBoxedTypeKind,
- mkTcArrowKind, unifyKind, newKindVar,
- kindToTcKind
+import TcType ( TcType, TcKind, TcTyVar, TcThetaType, TcTauType,
+ newKindVar, tcInstSigVar,
+ zonkKindEnv, zonkTcType, zonkTcTyVars, zonkTcTyVar
)
-import Type ( GenType, Type(..), ThetaType(..),
- mkTyVarTy, mkTyConTy, mkFunTy, mkAppTy, mkSynTy,
- mkSigmaTy
+import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToIdBndr,
+ instFunDeps, instFunDepsOfTheta )
+import FunDeps ( tyVarFunDep, oclose )
+import TcUnify ( unifyKind, unifyOpenTypeKind )
+import Type ( Type, Kind, PredType(..), ThetaType, UsageAnn(..),
+ mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy, mkUsgTy,
+ mkUsForAllTy, zipFunTys, hoistForAllTys,
+ mkSigmaTy, mkPredTy, mkTyConApp,
+ mkAppTys, splitForAllTys, splitRhoTy, mkRhoTy,
+ boxedTypeKind, unboxedTypeKind, mkArrowKind,
+ mkArrowKinds, getTyVar_maybe, getTyVar, splitFunTy_maybe,
+ tidyOpenType, tidyOpenTypes, tidyTyVar, tidyTyVars,
+ tyVarsOfType, tyVarsOfPred, mkForAllTys,
+ classesOfPreds, isUnboxedTupleType
)
-import TyVar ( GenTyVar, TyVar(..), mkTyVar )
-import PrelInfo ( mkListTy, mkTupleTy )
-import Type ( mkDictTy )
-import Class ( cCallishClassKeys )
-import TyCon ( TyCon, Arity(..) )
-import Unique ( Unique )
-import Name ( Name(..), getNameShortName, isTyConName, getSynNameArity )
-import PprStyle
-import Pretty
-import Util ( zipWithEqual, panic )
+import PprType ( pprType, pprPred )
+import Subst ( mkTopTyVarSubst, substTy )
+import Id ( Id, mkVanillaId, idName, idType, idFreeTyVars )
+import Var ( Var, TyVar, mkTyVar, tyVarKind )
+import VarEnv
+import VarSet
+import ErrUtils ( Message )
+import TyCon ( TyCon, isSynTyCon, tyConArity, tyConKind, tyConName )
+import Class ( ClassContext, classArity, classTyCon )
+import Name ( Name, isLocallyDefined )
+import TysWiredIn ( mkListTy, mkTupleTy, genUnitTyCon )
+import UniqFM ( elemUFM )
+import BasicTypes ( Boxity(..) )
+import SrcLoc ( SrcLoc )
+import Util ( mapAccumL, isSingleton )
+import Outputable
+import HscTypes ( TyThing(..) )
\end{code}
-tcMonoType and tcMonoTypeKind
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+%************************************************************************
+%* *
+\subsection{Kind checking}
+%* *
+%************************************************************************
+
+Kind checking
+~~~~~~~~~~~~~
+When we come across the binding site for some type variables, we
+proceed in two stages
+
+1. Figure out what kind each tyvar has
+
+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
-tcMonoType checks that the type really is of kind Type!
+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::*->*
+
+\begin{code}
+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}
-tcMonoType :: RenamedMonoType -> TcM s Type
+kcHsTyVar :: HsTyVarBndr name -> NF_TcM (name, TcKind)
+kcHsTyVars :: [HsTyVarBndr name] -> NF_TcM [(name, TcKind)]
-tcMonoType ty
- = tcMonoTypeKind ty `thenTc` \ (kind,ty) ->
- unifyKind kind mkTcTypeKind `thenTc_`
- returnTc ty
+kcHsTyVar (UserTyVar name) = newNamedKindVar name
+kcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (name, kind)
+
+kcHsTyVars tvs = mapNF_Tc kcHsTyVar tvs
+
+newNamedKindVar name = newKindVar `thenNF_Tc` \ kind ->
+ returnNF_Tc (name, kind)
+
+---------------------------
+kcBoxedType :: RenamedHsType -> TcM ()
+ -- The type ty must be a *boxed* *type*
+kcBoxedType ty
+ = kcHsType ty `thenTc` \ kind ->
+ tcAddErrCtxt (typeKindCtxt ty) $
+ unifyKind boxedTypeKind kind
+
+---------------------------
+kcTypeType :: RenamedHsType -> TcM ()
+ -- The type ty must be a *type*, but it can be boxed or unboxed.
+kcTypeType ty
+ = kcHsType ty `thenTc` \ kind ->
+ tcAddErrCtxt (typeKindCtxt ty) $
+ unifyOpenTypeKind kind
+
+---------------------------
+kcHsSigType, kcHsBoxedSigType :: RenamedHsType -> TcM ()
+ -- Used for type signatures
+kcHsSigType = kcTypeType
+kcHsBoxedSigType = kcBoxedType
+
+---------------------------
+kcHsType :: RenamedHsType -> TcM TcKind
+kcHsType (HsTyVar name) = kcTyVar name
+kcHsType (HsUsgTy _ ty) = kcHsType ty
+kcHsType (HsUsgForAllTy _ ty) = kcHsType ty
+
+kcHsType (HsListTy ty)
+ = kcBoxedType ty `thenTc` \ tau_ty ->
+ returnTc boxedTypeKind
+
+kcHsType (HsTupleTy (HsTupCon _ Boxed) tys)
+ = mapTc kcBoxedType tys `thenTc_`
+ returnTc boxedTypeKind
+
+kcHsType ty@(HsTupleTy (HsTupCon _ Unboxed) tys)
+ = failWithTc (unboxedTupleErr ty)
+ -- Unboxed tuples are illegal everywhere except
+ -- just after a function arrow (see kcFunResType)
+
+kcHsType (HsFunTy ty1 ty2)
+ = kcTypeType ty1 `thenTc_`
+ kcFunResType ty2 `thenTc_`
+ returnTc boxedTypeKind
+
+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 boxedTypeKind
+
+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_`
+
+ -- 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 context then
+ kcHsType ty
+ else
+ kcFunResType ty `thenTc_`
+ returnTc boxedTypeKind
+
+---------------------------
+kcFunResType :: RenamedHsType -> TcM TcKind
+-- The only place an unboxed tuple type is allowed
+-- is at the right hand end of an arrow
+kcFunResType (HsTupleTy (HsTupCon _ Unboxed) tys)
+ = mapTc kcTypeType tys `thenTc_`
+ returnTc unboxedTypeKind
+
+kcFunResType ty = kcHsType ty
+
+---------------------------
+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@(HsPIParam name ty)
+ = tcAddErrCtxt (appKindCtxt (ppr pred)) $
+ kcBoxedType ty
+
+kcHsPred pred@(HsPClass cls tys)
+ = tcAddErrCtxt (appKindCtxt (ppr pred)) $
+ kcClass cls `thenTc` \ kind ->
+ mapTc kcHsType tys `thenTc` \ arg_kinds ->
+ unifyKind kind (mkArrowKinds arg_kinds boxedTypeKind)
+
+---------------------------
+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}
-tcMonoTypeKind does the real work. It returns a kind and a type.
+%************************************************************************
+%* *
+\subsection{Checking types}
+%* *
+%************************************************************************
+
+tcHsSigType and tcHsBoxedSigType
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+tcHsSigType and tcHsBoxedSigType 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}
-tcMonoTypeKind :: RenamedMonoType -> TcM s (TcKind s, Type)
+tcHsSigType :: RenamedHsType -> TcM TcType
+tcHsSigType ty
+ = kcTypeType ty `thenTc_`
+ tcHsType ty `thenTc` \ ty' ->
+ returnTc (hoistForAllTys ty')
+
+tcHsBoxedSigType :: RenamedHsType -> TcM Type
+tcHsBoxedSigType ty
+ = kcBoxedType ty `thenTc_`
+ tcHsType ty `thenTc` \ ty' ->
+ returnTc (hoistForAllTys ty')
+\end{code}
-tcMonoTypeKind (MonoTyVar name)
- = tcLookupTyVar name `thenNF_Tc` \ (kind,tyvar) ->
- returnTc (kind, mkTyVarTy tyvar)
-
-tcMonoTypeKind (MonoListTy ty)
- = tcMonoType ty `thenTc` \ tau_ty ->
- returnTc (mkTcTypeKind, mkListTy tau_ty)
-
-tcMonoTypeKind (MonoTupleTy tys)
- = mapTc tcMonoType tys `thenTc` \ tau_tys ->
- returnTc (mkTcTypeKind, mkTupleTy (length tys) tau_tys)
-
-tcMonoTypeKind (MonoFunTy ty1 ty2)
- = tcMonoType ty1 `thenTc` \ tau_ty1 ->
- tcMonoType ty2 `thenTc` \ tau_ty2 ->
- returnTc (mkTcTypeKind, mkFunTy tau_ty1 tau_ty2)
-
-tcMonoTypeKind (MonoTyApp name@(Short _ _) tys)
- = -- Must be a type variable
- tcLookupTyVar name `thenNF_Tc` \ (kind,tyvar) ->
- tcMonoTyApp kind (mkTyVarTy tyvar) tys
-
-tcMonoTypeKind (MonoTyApp name tys)
- | isTyConName name -- Must be a type constructor
- = tcLookupTyCon name `thenNF_Tc` \ (kind,maybe_arity,tycon) ->
- case maybe_arity of
- Just arity -> tcSynApp name kind arity tycon tys -- synonum
- Nothing -> tcMonoTyApp kind (mkTyConTy tycon) tys -- newtype or data
-
--- for unfoldings only:
-tcMonoTypeKind (MonoForAllTy tyvars_w_kinds ty)
- = tcTyVarScopeGivenKinds names tc_kinds (\ tyvars ->
- tcMonoTypeKind ty `thenTc` \ (kind, ty') ->
- unifyKind kind mkTcTypeKind `thenTc_`
- returnTc (mkTcTypeKind, ty')
- )
+tcHsType, the main work horse
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+\begin{code}
+tcHsType :: RenamedHsType -> TcM Type
+tcHsType ty@(HsTyVar name)
+ = tc_app ty []
+
+tcHsType (HsListTy ty)
+ = tcHsType ty `thenTc` \ tau_ty ->
+ returnTc (mkListTy tau_ty)
+
+tcHsType (HsTupleTy (HsTupCon _ boxity) tys)
+ = mapTc tcHsType tys `thenTc` \ tau_tys ->
+ returnTc (mkTupleTy boxity (length tys) tau_tys)
+
+tcHsType (HsFunTy ty1 ty2)
+ = tcHsType ty1 `thenTc` \ tau_ty1 ->
+ tcHsType ty2 `thenTc` \ tau_ty2 ->
+ returnTc (mkFunTy tau_ty1 tau_ty2)
+
+tcHsType (HsNumTy n)
+ = ASSERT(n== 1)
+ returnTc (mkTyConApp genUnitTyCon [])
+
+tcHsType (HsOpTy ty1 op ty2) =
+ tcHsType ty1 `thenTc` \ tau_ty1 ->
+ tcHsType ty2 `thenTc` \ tau_ty2 ->
+ tc_fun_type op [tau_ty1,tau_ty2]
+
+tcHsType (HsAppTy ty1 ty2)
+ = tc_app ty1 [ty2]
+
+tcHsType (HsPredTy pred)
+ = tcClassAssertion True pred `thenTc` \ pred' ->
+ returnTc (mkPredTy pred')
+
+tcHsType full_ty@(HsForAllTy (Just tv_names) ctxt ty)
+ = let
+ kind_check = kcHsContext ctxt `thenTc_` kcFunResType ty
+ in
+ tcHsTyVars tv_names kind_check $ \ tyvars ->
+ tcContext ctxt `thenTc` \ theta ->
+ tcHsType ty `thenTc` \ tau ->
+ checkAmbiguity full_ty tyvars theta tau `thenTc_`
+ returnTc (mkSigmaTy tyvars theta tau)
+
+ -- 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.
+
+checkAmbiguity full_ty forall_tyvars theta tau
+ = mapTc check_pred theta
where
- (names, kinds) = unzip tyvars_w_kinds
- tc_kinds = map kindToTcKind kinds
-
--- for unfoldings only:
-tcMonoTypeKind (MonoDictTy class_name ty)
- = tcMonoTypeKind ty `thenTc` \ (arg_kind, arg_ty) ->
- tcLookupClass class_name `thenNF_Tc` \ (class_kind, clas) ->
- unifyKind class_kind arg_kind `thenTc_`
- returnTc (mkTcTypeKind, mkDictTy clas arg_ty)
+ tau_vars = tyVarsOfType tau
+ fds = instFunDepsOfTheta theta
+ tvFundep = tyVarFunDep fds
+ extended_tau_vars = oclose tvFundep tau_vars
+
+ is_ambig ct_var = (ct_var `elem` forall_tyvars) &&
+ not (ct_var `elemUFM` extended_tau_vars)
+ is_free ct_var = not (ct_var `elem` forall_tyvars)
+
+ check_pred pred = checkTc (not any_ambig) (ambigErr pred full_ty) `thenTc_`
+ checkTc (not all_free) (freeErr pred full_ty)
+ where
+ ct_vars = varSetElems (tyVarsOfPred pred)
+ all_free = all is_free ct_vars
+ any_ambig = is_source_polytype && any is_ambig ct_vars
+
+ -- 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).
+ is_source_polytype
+ = case full_ty of
+ HsForAllTy (Just (UserTyVar _ : _)) _ _ -> True
+ other -> False
\end{code}
Help functions for type applications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
\begin{code}
-tcMonoTyApp fun_kind fun_ty tys
- = mapAndUnzipTc tcMonoTypeKind tys `thenTc` \ (arg_kinds, arg_tys) ->
- newKindVar `thenNF_Tc` \ result_kind ->
- unifyKind fun_kind (foldr mkTcArrowKind result_kind arg_kinds) `thenTc_`
- returnTc (result_kind, foldl mkAppTy fun_ty arg_tys)
-
-tcSynApp name syn_kind arity tycon tys
- = mapAndUnzipTc tcMonoTypeKind tys `thenTc` \ (arg_kinds, arg_tys) ->
- newKindVar `thenNF_Tc` \ result_kind ->
- unifyKind syn_kind (foldr mkTcArrowKind result_kind arg_kinds) `thenTc_`
-
- -- Check that it's applied to the right number of arguments
- checkTc (arity == n_args) (err arity) `thenTc_`
- returnTc (result_kind, mkSynTy tycon arg_tys)
+tc_app :: RenamedHsType -> [RenamedHsType] -> TcM Type
+tc_app (HsAppTy ty1 ty2) tys
+ = tc_app ty1 (ty2:tys)
+
+tc_app ty tys
+ = tcAddErrCtxt (appKindCtxt pp_app) $
+ mapTc tcHsType tys `thenTc` \ arg_tys ->
+ case ty of
+ HsTyVar fun -> tc_fun_type fun arg_tys
+ other -> tcHsType ty `thenTc` \ fun_ty ->
+ returnNF_Tc (mkAppTys fun_ty arg_tys)
where
- err arity = arityErr "Type synonym constructor" name arity n_args
- n_args = length tys
+ 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}
+tcClassContext :: RenamedContext -> TcM ClassContext
+ -- Used when we are expecting a ClassContext (i.e. no implicit params)
+tcClassContext context
+ = tcContext context `thenTc` \ theta ->
+ returnTc (classesOfPreds theta)
+
+tcContext :: RenamedContext -> TcM ThetaType
+tcContext context = mapTc (tcClassAssertion False) context
+
+tcClassAssertion ccall_ok assn@(HsPClass class_name tys)
+ = tcAddErrCtxt (appKindCtxt (ppr assn)) $
+ mapTc tcHsType tys `thenTc` \ arg_tys ->
+ tcLookupGlobal class_name `thenTc` \ thing ->
+ case thing of
+ AClass clas -> checkTc (arity == n_tys) err `thenTc_`
+ returnTc (Class 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)
+
+tcClassAssertion ccall_ok assn@(HsPIParam name ty)
+ = tcAddErrCtxt (appKindCtxt (ppr assn)) $
+ tcHsType ty `thenTc` \ arg_ty ->
+ returnTc (IParam name arg_ty)
+\end{code}
-tcContext :: RenamedContext -> TcM s ThetaType
-tcContext context = mapTc tcClassAssertion context
-tcClassAssertion (class_name, tyvar_name)
- = checkTc (canBeUsedInContext class_name)
- (naughtyCCallContextErr class_name) `thenTc_`
+%************************************************************************
+%* *
+\subsection{Type variables, with knot tying!}
+%* *
+%************************************************************************
- tcLookupClass class_name `thenNF_Tc` \ (class_kind, clas) ->
- tcLookupTyVar tyvar_name `thenNF_Tc` \ (tyvar_kind, tyvar) ->
+\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}
- unifyKind class_kind tyvar_kind `thenTc_`
- returnTc (clas, mkTyVarTy tyvar)
-\end{code}
+%************************************************************************
+%* *
+\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}
+data TcSigInfo
+ = TySigInfo
+ Name -- N, the Name in corresponding binding
-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}
+ 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}
-Doing this utterly wrecks the whole point of introducing these
-classes so we specifically check that this isn't being done.
\begin{code}
-canBeUsedInContext :: Name -> Bool
-canBeUsedInContext (ClassName uniq _ _) = not (uniq `elem` cCallishClassKeys)
-canBeUsedInContext other = True
+tcTySig :: RenamedSig -> TcM TcSigInfo
+
+tcTySig (Sig v ty src_loc)
+ = tcAddSrcLoc src_loc $
+ tcAddErrCtxt (tcsigCtxt v) $
+ tcHsSigType ty `thenTc` \ sigma_tc_ty ->
+ mkTcSig (mkVanillaId 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
+ instFunDeps SignatureOrigin theta' `thenNF_Tc` \ fds ->
+
+ returnNF_Tc (TySigInfo name poly_id tyvars' theta' tau' (instToIdBndr inst) (inst : fds) src_loc)
+ where
+ name = idName poly_id
\end{code}
-Polytypes
-~~~~~~~~~
+
+%************************************************************************
+%* *
+\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
+
+Before doing this, the substitution is applied to the signature type variable.
+
+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:
+
+ f = (*) -- Monomorphic
+
+ 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
+ -- These should *already* be in the global-var 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 (all_ok sig_tys globals)
+ (complain sig_tys globals) `thenTc_`
+
+ returnTc (map (getTyVar "checkSigTyVars") sig_tys)
+
+ where
+ all_ok [] acc = True
+ all_ok (ty:tys) acc = case getTyVar_maybe ty of
+ Nothing -> False -- Point (a)
+ Just tv | tv `elemVarSet` acc -> False -- Point (b) or (c)
+ | otherwise -> all_ok tys (acc `extendVarSet` tv)
+
+
+ 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` \ tc_env ->
+ find_globals tv tidy_env [] (tcEnvTcIds tc_env) `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
+ (tidy_env', ftv') = tidyTyVar tidy_env ftv
+ in
+ 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}
+
+These two context are used with checkSigTyVars
+
\begin{code}
-tcPolyType :: RenamedPolyType -> TcM s Type
-tcPolyType (HsForAllTy tyvar_names context ty)
- = tcTyVarScope tyvar_names (\ tyvars ->
- tcContext context `thenTc` \ theta ->
- tcMonoType ty `thenTc` \ tau ->
- returnTc (mkSigmaTy tyvars theta tau)
- )
+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}
-Errors and contexts
-~~~~~~~~~~~~~~~~~~~
+
+%************************************************************************
+%* *
+\subsection{Errors and contexts}
+%* *
+%************************************************************************
+
\begin{code}
-naughtyCCallContextErr clas_name sty
- = ppSep [ppStr "Can't use class", ppr sty clas_name, ppStr "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("Each forall'd type variable mentioned by the constraint must appear 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))
+ ]
+
+unboxedTupleErr ty
+ = sep [ptext (SLIT("Illegal unboxed tuple as a function or contructor argument:")), nest 4 (ppr ty)]
\end{code}