\begin{code}
module TcMType (
- TcTyVar, TcKind, TcType, TcTauType, TcThetaType, TcRhoType, TcTyVarSet,
-
- --------------------------------
- -- Find the type to which a type variable is bound
- tcPutTyVar, -- :: TcTyVar -> TcType -> NF_TcM TcType
- tcGetTyVar, -- :: TcTyVar -> NF_TcM (Maybe TcType) does shorting out
+ TcTyVar, TcKind, TcType, TcTauType, TcThetaType, TcTyVarSet,
--------------------------------
-- Creating new mutable type variables
- newTyVar,
+ newTyVar,
newTyVarTy, -- Kind -> NF_TcM TcType
newTyVarTys, -- Int -> Kind -> NF_TcM [TcType]
newKindVar, newKindVars, newBoxityVar,
+ putTcTyVar, getTcTyVar,
+
+ newHoleTyVarTy, readHoleResult, zapToType,
--------------------------------
-- Instantiation
- tcInstTyVar, tcInstTyVars,
- tcInstSigVars, tcInstType,
- tcSplitRhoTyM,
+ tcInstTyVar, tcInstTyVars, tcInstType,
--------------------------------
- -- Unification
- unifyTauTy, unifyTauTyList, unifyTauTyLists,
- unifyFunTy, unifyListTy, unifyTupleTy,
- unifyKind, unifyKinds, unifyOpenTypeKind,
+ -- Checking type validity
+ Rank, UserTypeCtxt(..), checkValidType, pprUserTypeCtxt,
+ SourceTyCtxt(..), checkValidTheta,
+ checkValidInstHead, instTypeErr, checkAmbiguity,
--------------------------------
-- Zonking
- zonkTcTyVar, zonkTcTyVars, zonkTcTyVarsAndFV, zonkTcSigTyVars,
+ zonkTcTyVar, zonkTcTyVars, zonkTcTyVarsAndFV,
zonkTcType, zonkTcTypes, zonkTcClassConstraints, zonkTcThetaType,
zonkTcPredType, zonkTcTypeToType, zonkTcTyVarToTyVar, zonkKindEnv,
-- friends:
-import TypeRep ( Type(..), Kind, TyNote(..) ) -- friend
-import Type -- Lots and lots
-import TcType ( SigmaType, RhoType, tcEqType,
- tcSplitRhoTy, tcSplitPredTy_maybe, tcSplitAppTy_maybe,
- tcSplitTyConApp_maybe, tcSplitFunTy_maybe
+import TypeRep ( Type(..), SourceType(..), TyNote(..), -- Friend; can see representation
+ Kind, ThetaType
+ )
+import TcType ( TcType, TcThetaType, TcTauType, TcPredType,
+ TcTyVarSet, TcKind, TcTyVar, TyVarDetails(..),
+ tcEqType, tcCmpPred,
+ tcSplitPhiTy, tcSplitPredTy_maybe, tcSplitAppTy_maybe,
+ tcSplitTyConApp_maybe, tcSplitForAllTys,
+ tcIsTyVarTy, tcSplitSigmaTy,
+ isUnLiftedType, isIPPred, isHoleTyVar,
+
+ mkAppTy, mkTyVarTy, mkTyVarTys,
+ tyVarsOfPred, getClassPredTys_maybe,
+
+ liftedTypeKind, openTypeKind, defaultKind, superKind,
+ superBoxity, liftedBoxity, typeKind,
+ tyVarsOfType, tyVarsOfTypes,
+ eqKind, isTypeKind, isAnyTypeKind,
+
+ isFFIArgumentTy, isFFIImportResultTy
)
-import PprType ( pprType )
+import qualified Type ( splitFunTys )
import Subst ( Subst, mkTopTyVarSubst, substTy )
-import TyCon ( TyCon, mkPrimTyCon, isNewTyCon, isSynTyCon, isTupleTyCon,
- tyConArity, tupleTyConBoxity
- )
+import Class ( Class, classArity, className )
+import TyCon ( TyCon, mkPrimTyCon, isSynTyCon, isUnboxedTupleTyCon,
+ tyConArity, tyConName, tyConKind )
import PrimRep ( PrimRep(VoidRep) )
-import Var ( TyVar, varName, tyVarKind, tyVarName, isTyVar, mkTyVar,
- isMutTyVar, isSigTyVar )
+import Var ( TyVar, tyVarKind, tyVarName, isTyVar, mkTyVar, isMutTyVar )
-- others:
import TcMonad -- TcType, amongst others
-import TysWiredIn ( voidTy, listTyCon, mkListTy, mkTupleTy )
-
-import Name ( Name, NamedThing(..), setNameUnique, mkSysLocalName,
- mkLocalName, mkDerivedTyConOcc, isSystemName
+import TysWiredIn ( voidTy, listTyCon, tupleTyCon )
+import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
+import ForeignCall ( Safety(..) )
+import FunDeps ( grow )
+import PprType ( pprPred, pprSourceType, pprTheta, pprClassPred )
+import Name ( Name, NamedThing(..), setNameUnique, mkSystemName,
+ mkInternalName, mkDerivedTyConOcc
)
-import PrelNames ( floatTyConKey, doubleTyConKey, foreignPtrTyConKey,
- integerTyConKey, intTyConKey, addrTyConKey )
import VarSet
-import BasicTypes ( Boxity, Arity, isBoxed )
-import Unique ( Unique, Uniquable(..) )
+import BasicTypes ( Boxity(Boxed) )
+import CmdLineOpts ( dopt, DynFlag(..) )
+import Unique ( Uniquable(..) )
import SrcLoc ( noSrcLoc )
-import Util ( nOfThem )
+import Util ( nOfThem, isSingleton, equalLength )
+import ListSetOps ( removeDups )
import Outputable
\end{code}
newTyVar :: Kind -> NF_TcM TcTyVar
newTyVar kind
= tcGetUnique `thenNF_Tc` \ uniq ->
- tcNewMutTyVar (mkSysLocalName uniq SLIT("t")) kind
+ tcNewMutTyVar (mkSystemName uniq FSLIT("t")) kind VanillaTv
newTyVarTy :: Kind -> NF_TcM TcType
newTyVarTy kind
newKindVar :: NF_TcM TcKind
newKindVar
- = tcGetUnique `thenNF_Tc` \ uniq ->
- tcNewMutTyVar (mkSysLocalName uniq SLIT("k")) superKind `thenNF_Tc` \ kv ->
+ = tcGetUnique `thenNF_Tc` \ uniq ->
+ tcNewMutTyVar (mkSystemName uniq FSLIT("k")) superKind VanillaTv `thenNF_Tc` \ kv ->
returnNF_Tc (TyVarTy kv)
newKindVars :: Int -> NF_TcM [TcKind]
newBoxityVar :: NF_TcM TcKind
newBoxityVar
- = tcGetUnique `thenNF_Tc` \ uniq ->
- tcNewMutTyVar (mkSysLocalName uniq SLIT("bx")) superBoxity `thenNF_Tc` \ kv ->
+ = tcGetUnique `thenNF_Tc` \ uniq ->
+ tcNewMutTyVar (mkSystemName uniq FSLIT("bx")) superBoxity VanillaTv `thenNF_Tc` \ kv ->
returnNF_Tc (TyVarTy kv)
\end{code}
%************************************************************************
%* *
-\subsection{Type instantiation}
+\subsection{'hole' type variables}
%* *
%************************************************************************
-I don't understand why this is needed
-An old comments says "No need for tcSplitForAllTyM because a type
- variable can't be instantiated to a for-all type"
-But the same is true of rho types!
-
\begin{code}
-tcSplitRhoTyM :: TcType -> NF_TcM (TcThetaType, TcType)
-tcSplitRhoTyM t
- = go t t []
- where
- -- A type variable is never instantiated to a dictionary type,
- -- so we don't need to do a tcReadVar on the "arg".
- go syn_t (FunTy arg res) ts = case tcSplitPredTy_maybe arg of
- Just pair -> go res res (pair:ts)
- Nothing -> returnNF_Tc (reverse ts, syn_t)
- go syn_t (NoteTy n t) ts = go syn_t t ts
- go syn_t (TyVarTy tv) ts = tcGetTyVar tv `thenNF_Tc` \ maybe_ty ->
- case maybe_ty of
- Just ty | not (isTyVarTy ty) -> go syn_t ty ts
- other -> returnNF_Tc (reverse ts, syn_t)
- go syn_t (UsageTy _ t) ts = go syn_t t ts
- go syn_t t ts = returnNF_Tc (reverse ts, syn_t)
-\end{code}
-
+newHoleTyVarTy :: NF_TcM TcType
+ = tcGetUnique `thenNF_Tc` \ uniq ->
+ tcNewMutTyVar (mkSystemName uniq FSLIT("h")) openTypeKind HoleTv `thenNF_Tc` \ tv ->
+ returnNF_Tc (TyVarTy tv)
+
+readHoleResult :: TcType -> NF_TcM TcType
+-- Read the answer out of a hole, constructed by newHoleTyVarTy
+readHoleResult (TyVarTy tv)
+ = ASSERT( isHoleTyVar tv )
+ getTcTyVar tv `thenNF_Tc` \ maybe_res ->
+ case maybe_res of
+ Just ty -> returnNF_Tc ty
+ Nothing -> pprPanic "readHoleResult: empty" (ppr tv)
+readHoleResult ty = pprPanic "readHoleResult: not hole" (ppr ty)
+
+zapToType :: TcType -> NF_TcM TcType
+zapToType (TyVarTy tv)
+ | isHoleTyVar tv
+ = getTcTyVar tv `thenNF_Tc` \ maybe_res ->
+ case maybe_res of
+ Nothing -> newTyVarTy openTypeKind `thenNF_Tc` \ ty ->
+ putTcTyVar tv ty `thenNF_Tc_`
+ returnNF_Tc ty
+ Just ty -> returnNF_Tc ty -- No need to loop; we never
+ -- have chains of holes
+
+zapToType other_ty = returnNF_Tc other_ty
+\end{code}
%************************************************************************
%* *
Instantiating a bunch of type variables
\begin{code}
-tcInstTyVars :: [TyVar]
+tcInstTyVars :: TyVarDetails -> [TyVar]
-> NF_TcM ([TcTyVar], [TcType], Subst)
-tcInstTyVars tyvars
- = mapNF_Tc tcInstTyVar tyvars `thenNF_Tc` \ tc_tyvars ->
+tcInstTyVars tv_details tyvars
+ = mapNF_Tc (tcInstTyVar tv_details) tyvars `thenNF_Tc` \ tc_tyvars ->
let
tys = mkTyVarTys tc_tyvars
in
-- they cannot possibly be captured by
-- any existing for-alls. Hence mkTopTyVarSubst
-tcInstTyVar tyvar
+tcInstTyVar tv_details tyvar
= tcGetUnique `thenNF_Tc` \ uniq ->
let
name = setNameUnique (tyVarName tyvar) uniq
-- that two different tyvars will print the same way
-- in an error message. -dppr-debug will show up the difference
-- Better watch out for this. If worst comes to worst, just
- -- use mkSysLocalName.
+ -- use mkSystemName.
in
- tcNewMutTyVar name (tyVarKind tyvar)
-
-tcInstSigVars tyvars -- Very similar to tcInstTyVar
- = tcGetUniques `thenNF_Tc` \ uniqs ->
- listTc [ ASSERT( not (kind `eqKind` openTypeKind) ) -- Shouldn't happen
- tcNewSigTyVar name kind
- | (tyvar, uniq) <- tyvars `zip` uniqs,
- let name = setNameUnique (tyVarName tyvar) uniq,
- let kind = tyVarKind tyvar
- ]
-\end{code}
-
-@tcInstType@ instantiates the outer-level for-alls of a TcType with
-fresh type variables, splits off the dictionary part, and returns the results.
-
-\begin{code}
-tcInstType :: TcType -> NF_TcM ([TcTyVar], TcThetaType, TcType)
-tcInstType ty
- = case splitForAllTys ty of
- ([], rho) -> -- There may be overloading but no type variables;
+ tcNewMutTyVar name (tyVarKind tyvar) tv_details
+
+tcInstType :: TyVarDetails -> TcType -> NF_TcM ([TcTyVar], TcThetaType, TcType)
+-- tcInstType instantiates the outer-level for-alls of a TcType with
+-- fresh (mutable) type variables, splits off the dictionary part,
+-- and returns the pieces.
+tcInstType tv_details ty
+ = case tcSplitForAllTys ty of
+ ([], rho) -> -- There may be overloading despite no type variables;
-- (?x :: Int) => Int -> Int
let
- (theta, tau) = tcSplitRhoTy rho -- Used to be tcSplitRhoTyM
+ (theta, tau) = tcSplitPhiTy rho
in
returnNF_Tc ([], theta, tau)
- (tyvars, rho) -> tcInstTyVars tyvars `thenNF_Tc` \ (tyvars', _, tenv) ->
+ (tyvars, rho) -> tcInstTyVars tv_details tyvars `thenNF_Tc` \ (tyvars', _, tenv) ->
let
- (theta, tau) = tcSplitRhoTy (substTy tenv rho) -- Used to be tcSplitRhoTyM
+ (theta, tau) = tcSplitPhiTy (substTy tenv rho)
in
returnNF_Tc (tyvars', theta, tau)
\end{code}
-
%************************************************************************
%* *
\subsection{Putting and getting mutable type variables}
%************************************************************************
\begin{code}
-tcPutTyVar :: TcTyVar -> TcType -> NF_TcM TcType
-tcGetTyVar :: TcTyVar -> NF_TcM (Maybe TcType)
+putTcTyVar :: TcTyVar -> TcType -> NF_TcM TcType
+getTcTyVar :: TcTyVar -> NF_TcM (Maybe TcType)
\end{code}
Putting is easy:
\begin{code}
-tcPutTyVar tyvar ty
+putTcTyVar tyvar ty
| not (isMutTyVar tyvar)
- = pprTrace "tcPutTyVar" (ppr tyvar) $
+ = pprTrace "putTcTyVar" (ppr tyvar) $
returnNF_Tc ty
| otherwise
= ASSERT( isMutTyVar tyvar )
- UASSERT2( not (isUTy ty), ppr tyvar <+> ppr ty )
tcWriteMutTyVar tyvar (Just ty) `thenNF_Tc_`
returnNF_Tc ty
\end{code}
Getting is more interesting. The easy thing to do is just to read, thus:
\begin{verbatim}
-tcGetTyVar tyvar = tcReadMutTyVar tyvar
+getTcTyVar tyvar = tcReadMutTyVar tyvar
\end{verbatim}
But it's more fun to short out indirections on the way: If this
We return Nothing iff the original box was unbound.
\begin{code}
-tcGetTyVar tyvar
+getTcTyVar tyvar
| not (isMutTyVar tyvar)
- = pprTrace "tcGetTyVar" (ppr tyvar) $
+ = pprTrace "getTcTyVar" (ppr tyvar) $
returnNF_Tc (Just (mkTyVarTy tyvar))
| otherwise
zonkTcTyVar :: TcTyVar -> NF_TcM TcType
zonkTcTyVar tyvar = zonkTyVar (\ tv -> returnNF_Tc (TyVarTy tv)) tyvar
-
-zonkTcSigTyVars :: [TcTyVar] -> NF_TcM [TcTyVar]
--- This guy is to zonk the tyvars we're about to feed into tcSimplify
--- Usually this job is done by checkSigTyVars, but in a couple of places
--- that is overkill, so we use this simpler chap
-zonkTcSigTyVars tyvars
- = zonkTcTyVars tyvars `thenNF_Tc` \ tys ->
- returnNF_Tc (map (getTyVar "zonkTcSigTyVars") tys)
\end{code}
----------------- Types
zonkTcThetaType theta = mapNF_Tc zonkTcPredType theta
zonkTcPredType :: TcPredType -> NF_TcM TcPredType
-zonkTcPredType (ClassP c ts) =
- zonkTcTypes ts `thenNF_Tc` \ new_ts ->
+zonkTcPredType (ClassP c ts)
+ = zonkTcTypes ts `thenNF_Tc` \ new_ts ->
returnNF_Tc (ClassP c new_ts)
-zonkTcPredType (IParam n t) =
- zonkTcType t `thenNF_Tc` \ new_t ->
+zonkTcPredType (IParam n t)
+ = zonkTcType t `thenNF_Tc` \ new_t ->
returnNF_Tc (IParam n new_t)
\end{code}
-- When zonking a kind, we want to
-- zonk a *kind* variable to (Type *)
-- zonk a *boxity* variable to *
- zonk_unbound_kind_var kv | tyVarKind kv `eqKind` superKind = tcPutTyVar kv liftedTypeKind
- | tyVarKind kv `eqKind` superBoxity = tcPutTyVar kv liftedBoxity
+ zonk_unbound_kind_var kv | tyVarKind kv `eqKind` superKind = putTcTyVar kv liftedTypeKind
+ | tyVarKind kv `eqKind` superBoxity = putTcTyVar kv liftedBoxity
| otherwise = pprPanic "zonkKindEnv" (ppr kv)
zonkTcTypeToType :: TcType -> NF_TcM Type
zonkTcTypeToType ty = zonkType zonk_unbound_tyvar ty
where
- -- Zonk a mutable but unbound type variable to
- -- Void if it has kind Lifted
- -- :Void otherwise
- zonk_unbound_tyvar tv
- | kind `eqKind` liftedTypeKind || kind `eqKind` openTypeKind
- = tcPutTyVar tv voidTy -- Just to avoid creating a new tycon in
- -- this vastly common case
- | otherwise
- = tcPutTyVar tv (TyConApp (mk_void_tycon tv kind) [])
- where
- kind = tyVarKind tv
-
- mk_void_tycon tv kind -- Make a new TyCon with the same kind as the
- -- type variable tv. Same name too, apart from
- -- making it start with a colon (sigh)
+ -- Zonk a mutable but unbound type variable to an arbitrary type
+ -- We know it's unbound even though we don't carry an environment,
+ -- because at the binding site for a type variable we bind the
+ -- mutable tyvar to a fresh immutable one. So the mutable store
+ -- plays the role of an environment. If we come across a mutable
+ -- type variable that isn't so bound, it must be completely free.
+ zonk_unbound_tyvar tv = putTcTyVar tv (mkArbitraryType tv)
+
+
+-- When the type checker finds a type variable with no binding,
+-- which means it can be instantiated with an arbitrary type, it
+-- usually instantiates it to Void. Eg.
+--
+-- length []
+-- ===>
+-- length Void (Nil Void)
+--
+-- But in really obscure programs, the type variable might have
+-- a kind other than *, so we need to invent a suitably-kinded type.
+--
+-- This commit uses
+-- Void for kind *
+-- List for kind *->*
+-- Tuple for kind *->...*->*
+--
+-- which deals with most cases. (Previously, it only dealt with
+-- kind *.)
+--
+-- In the other cases, it just makes up a TyCon with a suitable
+-- kind. If this gets into an interface file, anyone reading that
+-- file won't understand it. This is fixable (by making the client
+-- of the interface file make up a TyCon too) but it is tiresome and
+-- never happens, so I am leaving it
+
+mkArbitraryType :: TcTyVar -> Type
+-- Make up an arbitrary type whose kind is the same as the tyvar.
+-- We'll use this to instantiate the (unbound) tyvar.
+mkArbitraryType tv
+ | isAnyTypeKind kind = voidTy -- The vastly common case
+ | otherwise = TyConApp tycon []
+ where
+ kind = tyVarKind tv
+ (args,res) = Type.splitFunTys kind -- Kinds are simple; use Type.splitFunTys
+
+ tycon | kind `eqKind` tyConKind listTyCon -- *->*
+ = listTyCon -- No tuples this size
+
+ | all isTypeKind args && isTypeKind res
+ = tupleTyCon Boxed (length args) -- *-> ... ->*->*
+
+ | otherwise
+ = pprTrace "Urk! Inventing strangely-kinded void TyCon" (ppr tc_name) $
+ mkPrimTyCon tc_name kind 0 [] VoidRep
+ -- Same name as the tyvar, apart from making it start with a colon (sigh)
-- I dread to think what will happen if this gets out into an
-- interface file. Catastrophe likely. Major sigh.
- = pprTrace "Urk! Inventing strangely-kinded void TyCon" (ppr tc_name) $
- mkPrimTyCon tc_name kind 0 [] VoidRep
- where
- tc_name = mkLocalName (getUnique tv) (mkDerivedTyConOcc (getOccName tv)) noSrcLoc
+
+ tc_name = mkInternalName (getUnique tv) (mkDerivedTyConOcc (getOccName tv)) noSrcLoc
-- zonkTcTyVarToTyVar is applied to the *binding* occurrence
-- of a type variable, at the *end* of type checking. It changes
immut_tv = mkTyVar (tyVarName tv) (defaultKind (tyVarKind tv))
immut_tv_ty = mkTyVarTy immut_tv
- zap tv = tcPutTyVar tv immut_tv_ty
+ zap tv = putTcTyVar tv immut_tv_ty
-- Bind the mutable version to the immutable one
in
-- If the type variable is mutable, then bind it to immut_tv_ty
go (AppTy fun arg) = go fun `thenNF_Tc` \ fun' ->
go arg `thenNF_Tc` \ arg' ->
returnNF_Tc (mkAppTy fun' arg')
-
- go (UsageTy u ty) = go u `thenNF_Tc` \ u' ->
- go ty `thenNF_Tc` \ ty' ->
- returnNF_Tc (mkUTy u' ty')
+ -- NB the mkAppTy; we might have instantiated a
+ -- type variable to a type constructor, so we need
+ -- to pull the TyConApp to the top.
-- The two interesting cases!
go (TyVarTy tyvar) = zonkTyVar unbound_var_fn tyvar
returnNF_Tc (ClassP c tys')
go_pred (NType tc tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
returnNF_Tc (NType tc tys')
- go_pred (IParam n ty) = go ty `thenNF_Tc` \ ty' ->
- returnNF_Tc (IParam n ty')
+ go_pred (IParam n ty) = go ty `thenNF_Tc` \ ty' ->
+ returnNF_Tc (IParam n ty')
zonkTyVar :: (TcTyVar -> NF_TcM Type) -- What to do for an unbound mutable variable
-> TcTyVar -> NF_TcM TcType
returnNF_Tc (TyVarTy tyvar)
| otherwise
- = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
case maybe_ty of
Nothing -> unbound_var_fn tyvar -- Mutable and unbound
Just other_ty -> zonkType unbound_var_fn other_ty -- Bound
%************************************************************************
%* *
-\subsection{The Kind variants}
+\subsection{Checking a user type}
%* *
%************************************************************************
+When dealing with a user-written type, we first translate it from an HsType
+to a Type, performing kind checking, and then check various things that should
+be true about it. We don't want to perform these checks at the same time
+as the initial translation because (a) they are unnecessary for interface-file
+types and (b) when checking a mutually recursive group of type and class decls,
+we can't "look" at the tycons/classes yet. Also, the checks are are rather
+diverse, and used to really mess up the other code.
+
+One thing we check for is 'rank'.
+
+ Rank 0: monotypes (no foralls)
+ Rank 1: foralls at the front only, Rank 0 inside
+ Rank 2: foralls at the front, Rank 1 on left of fn arrow,
+
+ basic ::= tyvar | T basic ... basic
+
+ r2 ::= forall tvs. cxt => r2a
+ r2a ::= r1 -> r2a | basic
+ r1 ::= forall tvs. cxt => r0
+ r0 ::= r0 -> r0 | basic
+
+Another thing is to check that type synonyms are saturated.
+This might not necessarily show up in kind checking.
+ type A i = i
+ data T k = MkT (k Int)
+ f :: T A -- BAD!
+
+
\begin{code}
-unifyKind :: TcKind -- Expected
- -> TcKind -- Actual
- -> TcM ()
-unifyKind k1 k2
- = tcAddErrCtxtM (unifyCtxt "kind" k1 k2) $
- uTys k1 k1 k2 k2
-
-unifyKinds :: [TcKind] -> [TcKind] -> TcM ()
-unifyKinds [] [] = returnTc ()
-unifyKinds (k1:ks1) (k2:ks2) = unifyKind k1 k2 `thenTc_`
- unifyKinds ks1 ks2
-unifyKinds _ _ = panic "unifyKinds: length mis-match"
+data UserTypeCtxt
+ = FunSigCtxt Name -- Function type signature
+ | ExprSigCtxt -- Expression type signature
+ | ConArgCtxt Name -- Data constructor argument
+ | TySynCtxt Name -- RHS of a type synonym decl
+ | GenPatCtxt -- Pattern in generic decl
+ -- f{| a+b |} (Inl x) = ...
+ | PatSigCtxt -- Type sig in pattern
+ -- f (x::t) = ...
+ | ResSigCtxt -- Result type sig
+ -- f x :: t = ....
+ | ForSigCtxt Name -- Foreign inport or export signature
+ | RuleSigCtxt Name -- Signature on a forall'd variable in a RULE
+
+-- Notes re TySynCtxt
+-- We allow type synonyms that aren't types; e.g. type List = []
+--
+-- If the RHS mentions tyvars that aren't in scope, we'll
+-- quantify over them:
+-- e.g. type T = a->a
+-- will become type T = forall a. a->a
+--
+-- With gla-exts that's right, but for H98 we should complain.
+
+
+pprUserTypeCtxt (FunSigCtxt n) = ptext SLIT("the type signature for") <+> quotes (ppr n)
+pprUserTypeCtxt ExprSigCtxt = ptext SLIT("an expression type signature")
+pprUserTypeCtxt (ConArgCtxt c) = ptext SLIT("the type of constructor") <+> quotes (ppr c)
+pprUserTypeCtxt (TySynCtxt c) = ptext SLIT("the RHS of a type synonym declaration") <+> quotes (ppr c)
+pprUserTypeCtxt GenPatCtxt = ptext SLIT("the type pattern of a generic definition")
+pprUserTypeCtxt PatSigCtxt = ptext SLIT("a pattern type signature")
+pprUserTypeCtxt ResSigCtxt = ptext SLIT("a result type signature")
+pprUserTypeCtxt (ForSigCtxt n) = ptext SLIT("the foreign signature for") <+> quotes (ppr n)
+pprUserTypeCtxt (RuleSigCtxt n) = ptext SLIT("the type signature on") <+> quotes (ppr n)
\end{code}
\begin{code}
-unifyOpenTypeKind :: TcKind -> TcM ()
--- Ensures that the argument kind is of the form (Type bx)
--- for some boxity bx
-
-unifyOpenTypeKind ty@(TyVarTy tyvar)
- = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty ->
- case maybe_ty of
- Just ty' -> unifyOpenTypeKind ty'
- other -> unify_open_kind_help ty
-
-unifyOpenTypeKind ty
- = case tcSplitTyConApp_maybe ty of
- Just (tycon, [_]) | tycon == typeCon -> returnTc ()
- other -> unify_open_kind_help ty
-
-unify_open_kind_help ty -- Revert to ordinary unification
- = newBoxityVar `thenNF_Tc` \ boxity ->
- unifyKind ty (mkTyConApp typeCon [boxity])
-\end{code}
+checkValidType :: UserTypeCtxt -> Type -> TcM ()
+-- Checks that the type is valid for the given context
+checkValidType ctxt ty
+ = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts ->
+ let
+ rank | gla_exts = Arbitrary
+ | otherwise
+ = case ctxt of -- Haskell 98
+ GenPatCtxt -> Rank 0
+ PatSigCtxt -> Rank 0
+ ResSigCtxt -> Rank 0
+ TySynCtxt _ -> Rank 0
+ ExprSigCtxt -> Rank 1
+ FunSigCtxt _ -> Rank 1
+ ConArgCtxt _ -> Rank 1 -- We are given the type of the entire
+ -- constructor, hence rank 1
+ ForSigCtxt _ -> Rank 1
+ RuleSigCtxt _ -> Rank 1
+
+ actual_kind = typeKind ty
+
+ actual_kind_is_lifted = actual_kind `eqKind` liftedTypeKind
+
+ kind_ok = case ctxt of
+ TySynCtxt _ -> True -- Any kind will do
+ GenPatCtxt -> actual_kind_is_lifted
+ ForSigCtxt _ -> actual_kind_is_lifted
+ other -> isTypeKind actual_kind
+
+ ubx_tup | not gla_exts = UT_NotOk
+ | otherwise = case ctxt of
+ TySynCtxt _ -> UT_Ok
+ other -> UT_NotOk
+ -- Unboxed tuples ok in function results,
+ -- but for type synonyms we allow them even at
+ -- top level
+ in
+ tcAddErrCtxt (checkTypeCtxt ctxt ty) $
+ -- Check that the thing has kind Type, and is lifted if necessary
+ checkTc kind_ok (kindErr actual_kind) `thenTc_`
-%************************************************************************
-%* *
-\subsection[Unify-exported]{Exported unification functions}
-%* *
-%************************************************************************
+ -- Check the internal validity of the type itself
+ check_poly_type rank ubx_tup ty
-The exported functions are all defined as versions of some
-non-exported generic functions.
-Unify two @TauType@s. Dead straightforward.
+checkTypeCtxt ctxt ty
+ = vcat [ptext SLIT("In the type:") <+> ppr_ty ty,
+ ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ]
-\begin{code}
-unifyTauTy :: TcTauType -> TcTauType -> TcM ()
-unifyTauTy ty1 ty2 -- ty1 expected, ty2 inferred
- = tcAddErrCtxtM (unifyCtxt "type" ty1 ty2) $
- uTys ty1 ty1 ty2 ty2
+ -- Hack alert. If there are no tyvars, (ppr sigma_ty) will print
+ -- something strange like {Eq k} -> k -> k, because there is no
+ -- ForAll at the top of the type. Since this is going to the user
+ -- we want it to look like a proper Haskell type even then; hence the hack
+ --
+ -- This shows up in the complaint about
+ -- case C a where
+ -- op :: Eq a => a -> a
+ppr_ty ty | null forall_tvs && not (null theta) = pprTheta theta <+> ptext SLIT("=>") <+> ppr tau
+ | otherwise = ppr ty
+ where
+ (forall_tvs, theta, tau) = tcSplitSigmaTy ty
\end{code}
-@unifyTauTyList@ unifies corresponding elements of two lists of
-@TauType@s. It uses @uTys@ to do the real work. The lists should be
-of equal length. We charge down the list explicitly so that we can
-complain if their lengths differ.
\begin{code}
-unifyTauTyLists :: [TcTauType] -> [TcTauType] -> TcM ()
-unifyTauTyLists [] [] = returnTc ()
-unifyTauTyLists (ty1:tys1) (ty2:tys2) = uTys ty1 ty1 ty2 ty2 `thenTc_`
- unifyTauTyLists tys1 tys2
-unifyTauTyLists ty1s ty2s = panic "Unify.unifyTauTyLists: mismatched type lists!"
-\end{code}
+data Rank = Rank Int | Arbitrary
-@unifyTauTyList@ takes a single list of @TauType@s and unifies them
-all together. It is used, for example, when typechecking explicit
-lists, when all the elts should be of the same type.
+decRank :: Rank -> Rank
+decRank Arbitrary = Arbitrary
+decRank (Rank n) = Rank (n-1)
-\begin{code}
-unifyTauTyList :: [TcTauType] -> TcM ()
-unifyTauTyList [] = returnTc ()
-unifyTauTyList [ty] = returnTc ()
-unifyTauTyList (ty1:tys@(ty2:_)) = unifyTauTy ty1 ty2 `thenTc_`
- unifyTauTyList tys
-\end{code}
+----------------------------------------
+data UbxTupFlag = UT_Ok | UT_NotOk
+ -- The "Ok" version means "ok if -fglasgow-exts is on"
-%************************************************************************
-%* *
-\subsection[Unify-uTys]{@uTys@: getting down to business}
-%* *
-%************************************************************************
+----------------------------------------
+check_poly_type :: Rank -> UbxTupFlag -> Type -> TcM ()
+check_poly_type (Rank 0) ubx_tup ty
+ = check_tau_type (Rank 0) ubx_tup ty
-@uTys@ is the heart of the unifier. Each arg happens twice, because
-we want to report errors in terms of synomyms if poss. The first of
-the pair is used in error messages only; it is always the same as the
-second, except that if the first is a synonym then the second may be a
-de-synonym'd version. This way we get better error messages.
+check_poly_type rank ubx_tup ty
+ = let
+ (tvs, theta, tau) = tcSplitSigmaTy ty
+ in
+ check_valid_theta SigmaCtxt theta `thenTc_`
+ check_tau_type (decRank rank) ubx_tup tau `thenTc_`
+ checkFreeness tvs theta `thenTc_`
+ checkAmbiguity tvs theta (tyVarsOfType tau)
+
+----------------------------------------
+check_arg_type :: Type -> TcM ()
+-- The sort of type that can instantiate a type variable,
+-- or be the argument of a type constructor.
+-- Not an unboxed tuple, not a forall.
+-- Other unboxed types are very occasionally allowed as type
+-- arguments depending on the kind of the type constructor
+--
+-- For example, we want to reject things like:
+--
+-- instance Ord a => Ord (forall s. T s a)
+-- and
+-- g :: T s (forall b.b)
+--
+-- NB: unboxed tuples can have polymorphic or unboxed args.
+-- This happens in the workers for functions returning
+-- product types with polymorphic components.
+-- But not in user code.
+-- Anyway, they are dealt with by a special case in check_tau_type
+
+check_arg_type ty
+ = check_tau_type (Rank 0) UT_NotOk ty `thenTc_`
+ checkTc (not (isUnLiftedType ty)) (unliftedArgErr ty)
+
+----------------------------------------
+check_tau_type :: Rank -> UbxTupFlag -> Type -> TcM ()
+-- Rank is allowed rank for function args
+-- No foralls otherwise
+
+check_tau_type rank ubx_tup ty@(ForAllTy _ _) = failWithTc (forAllTyErr ty)
+check_tau_type rank ubx_tup (SourceTy sty) = getDOptsTc `thenNF_Tc` \ dflags ->
+ check_source_ty dflags TypeCtxt sty
+check_tau_type rank ubx_tup (TyVarTy _) = returnTc ()
+check_tau_type rank ubx_tup ty@(FunTy arg_ty res_ty)
+ = check_poly_type rank UT_NotOk arg_ty `thenTc_`
+ check_tau_type rank UT_Ok res_ty
+
+check_tau_type rank ubx_tup (AppTy ty1 ty2)
+ = check_arg_type ty1 `thenTc_` check_arg_type ty2
+
+check_tau_type rank ubx_tup (NoteTy note ty)
+ = check_tau_type rank ubx_tup ty
+ -- Synonym notes are built only when the synonym is
+ -- saturated (see Type.mkSynTy)
+ -- Not checking the 'note' part allows us to instantiate a synonym
+ -- defn with a for-all type, or with a partially-applied type synonym,
+ -- but that seems OK too
+
+check_tau_type rank ubx_tup ty@(TyConApp tc tys)
+ | isSynTyCon tc
+ = -- NB: Type.mkSynTy builds a TyConApp (not a NoteTy) for an unsaturated
+ -- synonym application, leaving it to checkValidType (i.e. right here
+ -- to find the error
+ checkTc syn_arity_ok arity_msg `thenTc_`
+ mapTc_ check_arg_type tys
+
+ | isUnboxedTupleTyCon tc
+ = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts ->
+ checkTc (ubx_tup_ok gla_exts) ubx_tup_msg `thenTc_`
+ mapTc_ (check_tau_type (Rank 0) UT_Ok) tys
+ -- Args are allowed to be unlifted, or
+ -- more unboxed tuples, so can't use check_arg_ty
-We call the first one \tr{ps_ty1}, \tr{ps_ty2} for ``possible synomym''.
+ | otherwise
+ = mapTc_ check_arg_type tys
-\begin{code}
-uTys :: TcTauType -> TcTauType -- Error reporting ty1 and real ty1
- -- ty1 is the *expected* type
-
- -> TcTauType -> TcTauType -- Error reporting ty2 and real ty2
- -- ty2 is the *actual* type
- -> TcM ()
-
- -- Always expand synonyms (see notes at end)
- -- (this also throws away FTVs)
-uTys ps_ty1 (NoteTy n1 ty1) ps_ty2 ty2 = uTys ps_ty1 ty1 ps_ty2 ty2
-uTys ps_ty1 ty1 ps_ty2 (NoteTy n2 ty2) = uTys ps_ty1 ty1 ps_ty2 ty2
-
- -- Ignore usage annotations inside typechecker
-uTys ps_ty1 (UsageTy _ ty1) ps_ty2 ty2 = uTys ps_ty1 ty1 ps_ty2 ty2
-uTys ps_ty1 ty1 ps_ty2 (UsageTy _ ty2) = uTys ps_ty1 ty1 ps_ty2 ty2
-
- -- Variables; go for uVar
-uTys ps_ty1 (TyVarTy tyvar1) ps_ty2 ty2 = uVar False tyvar1 ps_ty2 ty2
-uTys ps_ty1 ty1 ps_ty2 (TyVarTy tyvar2) = uVar True tyvar2 ps_ty1 ty1
- -- "True" means args swapped
-
- -- Predicates
-uTys _ (SourceTy (IParam n1 t1)) _ (SourceTy (IParam n2 t2))
- | n1 == n2 = uTys t1 t1 t2 t2
-uTys _ (SourceTy (ClassP c1 tys1)) _ (SourceTy (ClassP c2 tys2))
- | c1 == c2 = unifyTauTyLists tys1 tys2
-uTys _ (SourceTy (NType tc1 tys1)) _ (SourceTy (NType tc2 tys2))
- | tc1 == tc2 = unifyTauTyLists tys1 tys2
-
- -- Functions; just check the two parts
-uTys _ (FunTy fun1 arg1) _ (FunTy fun2 arg2)
- = uTys fun1 fun1 fun2 fun2 `thenTc_` uTys arg1 arg1 arg2 arg2
-
- -- Type constructors must match
-uTys ps_ty1 (TyConApp con1 tys1) ps_ty2 (TyConApp con2 tys2)
- | con1 == con2 && length tys1 == length tys2
- = unifyTauTyLists tys1 tys2
-
- | con1 == openKindCon
- -- When we are doing kind checking, we might match a kind '?'
- -- against a kind '*' or '#'. Notably, CCallable :: ? -> *, and
- -- (CCallable Int) and (CCallable Int#) are both OK
- = unifyOpenTypeKind ps_ty2
-
- -- Applications need a bit of care!
- -- They can match FunTy and TyConApp, so use splitAppTy_maybe
- -- NB: we've already dealt with type variables and Notes,
- -- so if one type is an App the other one jolly well better be too
-uTys ps_ty1 (AppTy s1 t1) ps_ty2 ty2
- = case tcSplitAppTy_maybe ty2 of
- Just (s2,t2) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2
- Nothing -> unifyMisMatch ps_ty1 ps_ty2
-
- -- Now the same, but the other way round
- -- Don't swap the types, because the error messages get worse
-uTys ps_ty1 ty1 ps_ty2 (AppTy s2 t2)
- = case tcSplitAppTy_maybe ty1 of
- Just (s1,t1) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2
- Nothing -> unifyMisMatch ps_ty1 ps_ty2
-
- -- Not expecting for-alls in unification
- -- ... but the error message from the unifyMisMatch more informative
- -- than a panic message!
-
- -- Anything else fails
-uTys ps_ty1 ty1 ps_ty2 ty2 = unifyMisMatch ps_ty1 ps_ty2
+ where
+ ubx_tup_ok gla_exts = case ubx_tup of { UT_Ok -> gla_exts; other -> False }
+
+ syn_arity_ok = tc_arity <= n_args
+ -- It's OK to have an *over-applied* type synonym
+ -- data Tree a b = ...
+ -- type Foo a = Tree [a]
+ -- f :: Foo a b -> ...
+ n_args = length tys
+ tc_arity = tyConArity tc
+
+ arity_msg = arityErr "Type synonym" (tyConName tc) tc_arity n_args
+ ubx_tup_msg = ubxArgTyErr ty
+
+----------------------------------------
+forAllTyErr ty = ptext SLIT("Illegal polymorphic type:") <+> ppr_ty ty
+unliftedArgErr ty = ptext SLIT("Illegal unlifted type argument:") <+> ppr_ty ty
+ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as function argument:") <+> ppr_ty ty
+kindErr kind = ptext SLIT("Expecting an ordinary type, but found a type of kind") <+> ppr kind
\end{code}
+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
-Notes on synonyms
-~~~~~~~~~~~~~~~~~
-If you are tempted to make a short cut on synonyms, as in this
-pseudocode...
+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
-\begin{verbatim}
--- NO uTys (SynTy con1 args1 ty1) (SynTy con2 args2 ty2)
--- NO = if (con1 == con2) then
--- NO -- Good news! Same synonym constructors, so we can shortcut
--- NO -- by unifying their arguments and ignoring their expansions.
--- NO unifyTauTypeLists args1 args2
--- NO else
--- NO -- Never mind. Just expand them and try again
--- NO uTys ty1 ty2
-\end{verbatim}
+NB; the ambiguity check is only used for *user* types, not for types
+coming from inteface files. The latter can legitimately have
+ambiguous types. Example
-then THINK AGAIN. Here is the whole story, as detected and reported
-by Chris Okasaki \tr{<Chris_Okasaki@loch.mess.cs.cmu.edu>}:
-\begin{quotation}
-Here's a test program that should detect the problem:
+ 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)
-\begin{verbatim}
- type Bogus a = Int
- x = (1 :: Bogus Char) :: Bogus Bool
-\end{verbatim}
+Here the worker for f gets the type
+ fw :: forall a. S a => Int -> (# Int, Int #)
-The problem with [the attempted shortcut code] is that
-\begin{verbatim}
- con1 == con2
-\end{verbatim}
-is not a sufficient condition to be able to use the shortcut!
-You also need to know that the type synonym actually USES all
-its arguments. For example, consider the following type synonym
-which does not use all its arguments.
-\begin{verbatim}
- type Bogus a = Int
-\end{verbatim}
+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).
+
+\begin{code}
+checkAmbiguity :: [TyVar] -> ThetaType -> TyVarSet -> TcM ()
+checkAmbiguity forall_tyvars theta tau_tyvars
+ = mapTc_ complain (filter is_ambig theta)
+ where
+ complain pred = addErrTc (ambigErr pred)
+ extended_tau_vars = grow theta tau_tyvars
+ is_ambig pred = any ambig_var (varSetElems (tyVarsOfPred pred))
-If you ever tried unifying, say, \tr{Bogus Char} with \tr{Bogus Bool},
-the unifier would blithely try to unify \tr{Char} with \tr{Bool} and
-would fail, even though the expanded forms (both \tr{Int}) should
-match.
+ ambig_var ct_var = (ct_var `elem` forall_tyvars) &&
+ not (ct_var `elemVarSet` extended_tau_vars)
-Similarly, unifying \tr{Bogus Char} with \tr{Bogus t} would
-unnecessarily bind \tr{t} to \tr{Char}.
+ is_free ct_var = not (ct_var `elem` forall_tyvars)
-... You could explicitly test for the problem synonyms and mark them
-somehow as needing expansion, perhaps also issuing a warning to the
-user.
-\end{quotation}
+ambigErr pred
+ = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred),
+ 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 '=>'"))]
+\end{code}
+
+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.
+
+\begin{code}
+checkFreeness forall_tyvars theta
+ = mapTc_ complain (filter is_free theta)
+ where
+ is_free pred = not (isIPPred pred)
+ && not (any bound_var (varSetElems (tyVarsOfPred pred)))
+ bound_var ct_var = ct_var `elem` forall_tyvars
+ complain pred = addErrTc (freeErr pred)
+
+freeErr pred
+ = sep [ptext SLIT("All of the type variables in the constraint") <+> quotes (pprPred pred) <+>
+ ptext SLIT("are already in scope"),
+ nest 4 (ptext SLIT("At least one must be universally quantified here"))
+ ]
+\end{code}
%************************************************************************
%* *
-\subsection[Unify-uVar]{@uVar@: unifying with a type variable}
+\subsection{Checking a theta or source type}
%* *
%************************************************************************
-@uVar@ is called when at least one of the types being unified is a
-variable. It does {\em not} assume that the variable is a fixed point
-of the substitution; rather, notice that @uVar@ (defined below) nips
-back into @uTys@ if it turns out that the variable is already bound.
-
\begin{code}
-uVar :: Bool -- False => tyvar is the "expected"
- -- True => ty is the "expected" thing
- -> TcTyVar
- -> TcTauType -> TcTauType -- printing and real versions
- -> TcM ()
-
-uVar swapped tv1 ps_ty2 ty2
- = tcGetTyVar tv1 `thenNF_Tc` \ maybe_ty1 ->
- case maybe_ty1 of
- Just ty1 | swapped -> uTys ps_ty2 ty2 ty1 ty1 -- Swap back
- | otherwise -> uTys ty1 ty1 ps_ty2 ty2 -- Same order
- other -> uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2
-
- -- Expand synonyms; ignore FTVs
-uUnboundVar swapped tv1 maybe_ty1 ps_ty2 (NoteTy n2 ty2)
- = uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2
-
+data SourceTyCtxt
+ = ClassSCCtxt Name -- Superclasses of clas
+ | SigmaCtxt -- Context of a normal for-all type
+ | DataTyCtxt Name -- Context of a data decl
+ | TypeCtxt -- Source type in an ordinary type
+ | InstThetaCtxt -- Context of an instance decl
+ | InstHeadCtxt -- Head of an instance decl
+
+pprSourceTyCtxt (ClassSCCtxt c) = ptext SLIT("the super-classes of class") <+> quotes (ppr c)
+pprSourceTyCtxt SigmaCtxt = ptext SLIT("the context of a polymorphic type")
+pprSourceTyCtxt (DataTyCtxt tc) = ptext SLIT("the context of the data type declaration for") <+> quotes (ppr tc)
+pprSourceTyCtxt InstThetaCtxt = ptext SLIT("the context of an instance declaration")
+pprSourceTyCtxt InstHeadCtxt = ptext SLIT("the head of an instance declaration")
+pprSourceTyCtxt TypeCtxt = ptext SLIT("the context of a type")
+\end{code}
- -- The both-type-variable case
-uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2@(TyVarTy tv2)
+\begin{code}
+checkValidTheta :: SourceTyCtxt -> ThetaType -> TcM ()
+checkValidTheta ctxt theta
+ = tcAddErrCtxt (checkThetaCtxt ctxt theta) (check_valid_theta ctxt theta)
- -- Same type variable => no-op
- | tv1 == tv2
+-------------------------
+check_valid_theta ctxt []
= returnTc ()
+check_valid_theta ctxt theta
+ = getDOptsTc `thenNF_Tc` \ dflags ->
+ warnTc (not (null dups)) (dupPredWarn dups) `thenNF_Tc_`
+ mapTc_ (check_source_ty dflags ctxt) theta
+ where
+ (_,dups) = removeDups tcCmpPred theta
- -- Distinct type variables
- -- ASSERT maybe_ty1 /= Just
- | otherwise
- = tcGetTyVar tv2 `thenNF_Tc` \ maybe_ty2 ->
- case maybe_ty2 of
- Just ty2' -> uUnboundVar swapped tv1 maybe_ty1 ty2' ty2'
+-------------------------
+check_source_ty dflags ctxt pred@(ClassP cls tys)
+ = -- Class predicates are valid in all contexts
+ mapTc_ check_arg_type tys `thenTc_`
+ checkTc (arity == n_tys) arity_err `thenTc_`
+ checkTc (all tyvar_head tys || arby_preds_ok)
+ (predTyVarErr pred $$ how_to_allow)
- Nothing | update_tv2
+ where
+ class_name = className cls
+ arity = classArity cls
+ n_tys = length tys
+ arity_err = arityErr "Class" class_name arity n_tys
+
+ arby_preds_ok = case ctxt of
+ InstHeadCtxt -> True -- We check for instance-head formation
+ -- in checkValidInstHead
+ InstThetaCtxt -> dopt Opt_AllowUndecidableInstances dflags
+ other -> dopt Opt_GlasgowExts dflags
+
+ how_to_allow = case ctxt of
+ InstHeadCtxt -> empty -- Should not happen
+ InstThetaCtxt -> parens undecidableMsg
+ other -> parens (ptext SLIT("Use -fglasgow-exts to permit this"))
+
+check_source_ty dflags SigmaCtxt (IParam _ ty) = check_arg_type ty
+ -- Implicit parameters only allows in type
+ -- signatures; not in instance decls, superclasses etc
+ -- The reason for not allowing implicit params in instances is a bit subtle
+ -- If we allowed instance (?x::Int, Eq a) => Foo [a] where ...
+ -- then when we saw (e :: (?x::Int) => t) it would be unclear how to
+ -- discharge all the potential usas of the ?x in e. For example, a
+ -- constraint Foo [Int] might come out of e,and applying the
+ -- instance decl would show up two uses of ?x.
+
+check_source_ty dflags TypeCtxt (NType tc tys) = mapTc_ check_arg_type tys
+
+-- Catch-all
+check_source_ty dflags ctxt sty = failWithTc (badSourceTyErr sty)
+
+-------------------------
+tyvar_head ty -- Haskell 98 allows predicates of form
+ | tcIsTyVarTy ty = True -- C (a ty1 .. tyn)
+ | otherwise -- where a is a type variable
+ = case tcSplitAppTy_maybe ty of
+ Just (ty, _) -> tyvar_head ty
+ Nothing -> False
+\end{code}
- -> WARN( not (k1 `hasMoreBoxityInfo` k2), (ppr tv1 <+> ppr k1) $$ (ppr tv2 <+> ppr k2) )
- tcPutTyVar tv2 (TyVarTy tv1) `thenNF_Tc_`
- returnTc ()
- | otherwise
+\begin{code}
+badSourceTyErr sty = ptext SLIT("Illegal constraint") <+> pprSourceType sty
+predTyVarErr pred = ptext SLIT("Non-type variables in constraint:") <+> pprPred pred
+dupPredWarn dups = ptext SLIT("Duplicate constraint(s):") <+> pprWithCommas pprPred (map head dups)
- -> WARN( not (k2 `hasMoreBoxityInfo` k1), (ppr tv2 <+> ppr k2) $$ (ppr tv1 <+> ppr k1) )
- (tcPutTyVar tv1 ps_ty2 `thenNF_Tc_`
- returnTc ())
- where
- k1 = tyVarKind tv1
- k2 = tyVarKind tv2
- update_tv2 = (k2 `eqKind` openTypeKind) || (not (k1 `eqKind` openTypeKind) && nicer_to_update_tv2)
- -- Try to get rid of open type variables as soon as poss
-
- nicer_to_update_tv2 = isSigTyVar tv1
- -- Don't unify a signature type variable if poss
- || isSystemName (varName tv2)
- -- Try to update sys-y type variables in preference to sig-y ones
-
- -- Second one isn't a type variable
-uUnboundVar swapped tv1 maybe_ty1 ps_ty2 non_var_ty2
- = -- Check that the kinds match
- checkKinds swapped tv1 non_var_ty2 `thenTc_`
-
- -- Check that tv1 isn't a type-signature type variable
- checkTcM (not (isSigTyVar tv1))
- (failWithTcM (unifyWithSigErr tv1 ps_ty2)) `thenTc_`
-
- -- Check that we aren't losing boxity info (shouldn't happen)
- warnTc (not (typeKind non_var_ty2 `hasMoreBoxityInfo` tyVarKind tv1))
- ((ppr tv1 <+> ppr (tyVarKind tv1)) $$
- (ppr non_var_ty2 <+> ppr (typeKind non_var_ty2))) `thenNF_Tc_`
-
- -- Occurs check
- -- Basically we want to update tv1 := ps_ty2
- -- because ps_ty2 has type-synonym info, which improves later error messages
- --
- -- But consider
- -- type A a = ()
- --
- -- f :: (A a -> a -> ()) -> ()
- -- f = \ _ -> ()
- --
- -- x :: ()
- -- x = f (\ x p -> p x)
- --
- -- In the application (p x), we try to match "t" with "A t". If we go
- -- ahead and bind t to A t (= ps_ty2), we'll lead the type checker into
- -- an infinite loop later.
- -- But we should not reject the program, because A t = ().
- -- Rather, we should bind t to () (= non_var_ty2).
- --
- -- That's why we have this two-state occurs-check
- zonkTcType ps_ty2 `thenNF_Tc` \ ps_ty2' ->
- if not (tv1 `elemVarSet` tyVarsOfType ps_ty2') then
- tcPutTyVar tv1 ps_ty2' `thenNF_Tc_`
- returnTc ()
- else
- zonkTcType non_var_ty2 `thenNF_Tc` \ non_var_ty2' ->
- if not (tv1 `elemVarSet` tyVarsOfType non_var_ty2') then
- -- This branch rarely succeeds, except in strange cases
- -- like that in the example above
- tcPutTyVar tv1 non_var_ty2' `thenNF_Tc_`
- returnTc ()
- else
- failWithTcM (unifyOccurCheck tv1 ps_ty2')
-
-
-checkKinds swapped tv1 ty2
--- We're about to unify a type variable tv1 with a non-tyvar-type ty2.
--- We need to check that we don't unify a lifted type variable with an
--- unlifted type: e.g. (id 3#) is illegal
- | tk1 `eqKind` liftedTypeKind && tk2 `eqKind` unliftedTypeKind
- = tcAddErrCtxtM (unifyKindCtxt swapped tv1 ty2) $
- unifyMisMatch k1 k2
- | otherwise
- = returnTc ()
- where
- (k1,k2) | swapped = (tk2,tk1)
- | otherwise = (tk1,tk2)
- tk1 = tyVarKind tv1
- tk2 = typeKind ty2
+checkThetaCtxt ctxt theta
+ = vcat [ptext SLIT("In the context:") <+> pprTheta theta,
+ ptext SLIT("While checking") <+> pprSourceTyCtxt ctxt ]
\end{code}
%************************************************************************
%* *
-\subsection[Unify-fun]{@unifyFunTy@}
+\subsection{Checking for a decent instance head type}
%* *
%************************************************************************
-@unifyFunTy@ is used to avoid the fruitless creation of type variables.
+@checkValidInstHead@ checks the type {\em and} its syntactic constraints:
+it must normally look like: @instance Foo (Tycon a b c ...) ...@
-\begin{code}
-unifyFunTy :: TcType -- Fail if ty isn't a function type
- -> TcM (TcType, TcType) -- otherwise return arg and result types
+The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
+flag is on, or (2)~the instance is imported (they must have been
+compiled elsewhere). In these cases, we let them go through anyway.
-unifyFunTy ty@(TyVarTy tyvar)
- = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty ->
- case maybe_ty of
- Just ty' -> unifyFunTy ty'
- other -> unify_fun_ty_help ty
-
-unifyFunTy ty
- = case tcSplitFunTy_maybe ty of
- Just arg_and_res -> returnTc arg_and_res
- Nothing -> unify_fun_ty_help ty
-
-unify_fun_ty_help ty -- Special cases failed, so revert to ordinary unification
- = newTyVarTy openTypeKind `thenNF_Tc` \ arg ->
- newTyVarTy openTypeKind `thenNF_Tc` \ res ->
- unifyTauTy ty (mkFunTy arg res) `thenTc_`
- returnTc (arg,res)
-\end{code}
+We can also have instances for functions: @instance Foo (a -> b) ...@.
\begin{code}
-unifyListTy :: TcType -- expected list type
- -> TcM TcType -- list element type
+checkValidInstHead :: Type -> TcM (Class, [TcType])
+
+checkValidInstHead ty -- Should be a source type
+ = case tcSplitPredTy_maybe ty of {
+ Nothing -> failWithTc (instTypeErr (ppr ty) empty) ;
+ Just pred ->
+
+ case getClassPredTys_maybe pred of {
+ Nothing -> failWithTc (instTypeErr (pprPred pred) empty) ;
+ Just (clas,tys) ->
+
+ getDOptsTc `thenNF_Tc` \ dflags ->
+ mapTc_ check_arg_type tys `thenTc_`
+ check_inst_head dflags clas tys `thenTc_`
+ returnTc (clas, tys)
+ }}
+
+check_inst_head dflags clas tys
+ | -- CCALL CHECK
+ -- A user declaration of a CCallable/CReturnable instance
+ -- must be for a "boxed primitive" type.
+ (clas `hasKey` cCallableClassKey
+ && not (ccallable_type first_ty))
+ || (clas `hasKey` cReturnableClassKey
+ && not (creturnable_type first_ty))
+ = failWithTc (nonBoxedPrimCCallErr clas first_ty)
+
+ -- If GlasgowExts then check at least one isn't a type variable
+ | dopt Opt_GlasgowExts dflags
+ = check_tyvars dflags clas tys
+
+ -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
+ | isSingleton tys,
+ Just (tycon, arg_tys) <- tcSplitTyConApp_maybe first_ty,
+ not (isSynTyCon tycon), -- ...but not a synonym
+ all tcIsTyVarTy arg_tys, -- Applied to type variables
+ equalLength (varSetElems (tyVarsOfTypes arg_tys)) arg_tys
+ -- This last condition checks that all the type variables are distinct
+ = returnTc ()
-unifyListTy ty@(TyVarTy tyvar)
- = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty ->
- case maybe_ty of
- Just ty' -> unifyListTy ty'
- other -> unify_list_ty_help ty
-
-unifyListTy ty
- = case tcSplitTyConApp_maybe ty of
- Just (tycon, [arg_ty]) | tycon == listTyCon -> returnTc arg_ty
- other -> unify_list_ty_help ty
-
-unify_list_ty_help ty -- Revert to ordinary unification
- = newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
- unifyTauTy ty (mkListTy elt_ty) `thenTc_`
- returnTc elt_ty
-\end{code}
+ | otherwise
+ = failWithTc (instTypeErr (pprClassPred clas tys) head_shape_msg)
-\begin{code}
-unifyTupleTy :: Boxity -> Arity -> TcType -> TcM [TcType]
-unifyTupleTy boxity arity ty@(TyVarTy tyvar)
- = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty ->
- case maybe_ty of
- Just ty' -> unifyTupleTy boxity arity ty'
- other -> unify_tuple_ty_help boxity arity ty
-
-unifyTupleTy boxity arity ty
- = case tcSplitTyConApp_maybe ty of
- Just (tycon, arg_tys)
- | isTupleTyCon tycon
- && tyConArity tycon == arity
- && tupleTyConBoxity tycon == boxity
- -> returnTc arg_tys
- other -> unify_tuple_ty_help boxity arity ty
-
-unify_tuple_ty_help boxity arity ty
- = newTyVarTys arity kind `thenNF_Tc` \ arg_tys ->
- unifyTauTy ty (mkTupleTy boxity arity arg_tys) `thenTc_`
- returnTc arg_tys
where
- kind | isBoxed boxity = liftedTypeKind
- | otherwise = openTypeKind
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection[Unify-context]{Errors and contexts}
-%* *
-%************************************************************************
+ (first_ty : _) = tys
+
+ ccallable_type ty = isFFIArgumentTy dflags PlayRisky ty
+ creturnable_type ty = isFFIImportResultTy dflags ty
+
+ head_shape_msg = parens (text "The instance type must be of form (T a b c)" $$
+ text "where T is not a synonym, and a,b,c are distinct type variables")
+
+check_tyvars dflags clas tys
+ -- Check that at least one isn't a type variable
+ -- unless -fallow-undecideable-instances
+ | dopt Opt_AllowUndecidableInstances dflags = returnTc ()
+ | not (all tcIsTyVarTy tys) = returnTc ()
+ | otherwise = failWithTc (instTypeErr (pprClassPred clas tys) msg)
+ where
+ msg = parens (ptext SLIT("There must be at least one non-type-variable in the instance head")
+ $$ undecidableMsg)
-Errors
-~~~~~~
+undecidableMsg = ptext SLIT("Use -fallow-undecidable-instances to permit this")
+\end{code}
\begin{code}
-unifyCtxt s ty1 ty2 tidy_env -- ty1 expected, ty2 inferred
- = zonkTcType ty1 `thenNF_Tc` \ ty1' ->
- zonkTcType ty2 `thenNF_Tc` \ ty2' ->
- returnNF_Tc (err ty1' ty2')
- where
- err ty1 ty2 = (env1,
- nest 4
- (vcat [
- text "Expected" <+> text s <> colon <+> ppr tidy_ty1,
- text "Inferred" <+> text s <> colon <+> ppr tidy_ty2
- ]))
- where
- (env1, [tidy_ty1,tidy_ty2]) = tidyOpenTypes tidy_env [ty1,ty2]
-
-unifyKindCtxt swapped tv1 ty2 tidy_env -- not swapped => tv1 expected, ty2 inferred
- -- tv1 is zonked already
- = zonkTcType ty2 `thenNF_Tc` \ ty2' ->
- returnNF_Tc (err ty2')
- where
- err ty2 = (env2, ptext SLIT("When matching types") <+>
- sep [quotes pp_expected, ptext SLIT("and"), quotes pp_actual])
- where
- (pp_expected, pp_actual) | swapped = (pp2, pp1)
- | otherwise = (pp1, pp2)
- (env1, tv1') = tidyTyVar tidy_env tv1
- (env2, ty2') = tidyOpenType env1 ty2
- pp1 = ppr tv1'
- pp2 = ppr ty2'
-
-unifyMisMatch ty1 ty2
- = zonkTcType ty1 `thenNF_Tc` \ ty1' ->
- zonkTcType ty2 `thenNF_Tc` \ ty2' ->
- let
- (env, [tidy_ty1, tidy_ty2]) = tidyOpenTypes emptyTidyEnv [ty1',ty2']
- msg = hang (ptext SLIT("Couldn't match"))
- 4 (sep [quotes (ppr tidy_ty1),
- ptext SLIT("against"),
- quotes (ppr tidy_ty2)])
- in
- failWithTcM (env, msg)
+instTypeErr pp_ty msg
+ = sep [ptext SLIT("Illegal instance declaration for") <+> quotes pp_ty,
+ nest 4 msg]
-unifyWithSigErr tyvar ty
- = (env2, hang (ptext SLIT("Cannot unify the type-signature variable") <+> quotes (ppr tidy_tyvar))
- 4 (ptext SLIT("with the type") <+> quotes (ppr tidy_ty)))
- where
- (env1, tidy_tyvar) = tidyTyVar emptyTidyEnv tyvar
- (env2, tidy_ty) = tidyOpenType env1 ty
-
-unifyOccurCheck tyvar ty
- = (env2, hang (ptext SLIT("Occurs check: cannot construct the infinite type:"))
- 4 (sep [ppr tidy_tyvar, char '=', ppr tidy_ty]))
- where
- (env1, tidy_tyvar) = tidyTyVar emptyTidyEnv tyvar
- (env2, tidy_ty) = tidyOpenType env1 ty
+nonBoxedPrimCCallErr clas inst_ty
+ = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
+ 4 (pprClassPred clas [inst_ty])
\end{code}
projects / ghc-hetmet.git / blobdiff