2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
8 tcHsSigType, tcHsDeriv,
12 kcHsTyVars, kcHsSigType, kcHsLiftedSigType,
13 kcCheckHsType, kcHsContext, kcHsType,
15 -- Typechecking kinded types
16 tcHsKindedContext, tcHsKindedType, tcTyVarBndrs, dsHsType,
20 TcSigInfo(..), tcTySig, mkTcSig, maybeSig
23 #include "HsVersions.h"
25 import HsSyn ( HsType(..), LHsType, HsTyVarBndr(..), LHsTyVarBndr,
26 LHsContext, Sig(..), LSig, HsPred(..), LHsPred )
27 import RnHsSyn ( extractHsTyVars )
28 import TcHsSyn ( TcId )
31 import TcEnv ( tcExtendTyVarEnv, tcExtendKindEnv,
32 tcLookup, tcLookupClass, tcLookupTyCon,
33 TyThing(..), TcTyThing(..),
34 getInLocalScope, wrongThingErr
36 import TcMType ( newKindVar, tcInstType, newMutTyVar,
38 checkValidType, UserTypeCtxt(..), pprHsSigCtxt
40 import TcUnify ( unifyFunKind, checkExpectedKind )
41 import TcType ( Type, PredType(..), ThetaType, TyVarDetails(..),
42 TcTyVar, TcKind, TcThetaType, TcTauType,
43 mkTyVarTy, mkTyVarTys, mkFunTy,
44 mkForAllTys, mkFunTys, tcEqType, isPredTy,
45 mkSigmaTy, mkPredTy, mkGenTyConApp, mkTyConApp, mkAppTys,
46 tcSplitFunTy_maybe, tcSplitForAllTys )
47 import Kind ( liftedTypeKind, ubxTupleKind, openTypeKind, argTypeKind )
48 import Inst ( Inst, InstOrigin(..), newMethod, instToId )
50 import Id ( mkLocalId, idName, idType )
51 import Var ( TyVar, mkTyVar, tyVarKind )
52 import TyCon ( TyCon, tyConKind )
53 import Class ( Class, classTyCon )
56 import PrelNames ( genUnitTyConName )
57 import Subst ( deShadowTy )
58 import TysWiredIn ( mkListTy, mkPArrTy, mkTupleTy )
59 import BasicTypes ( Boxity(..) )
60 import SrcLoc ( SrcSpan, Located(..), unLoc, noLoc )
66 ----------------------------
68 ----------------------------
70 Generally speaking we now type-check types in three phases
72 1. kcHsType: kind check the HsType
73 *includes* performing any TH type splices;
74 so it returns a translated, and kind-annotated, type
76 2. dsHsType: convert from HsType to Type:
78 expand type synonyms [mkGenTyApps]
79 hoist the foralls [tcHsType]
81 3. checkValidType: check the validity of the resulting type
83 Often these steps are done one after the other (tcHsSigType).
84 But in mutually recursive groups of type and class decls we do
85 1 kind-check the whole group
86 2 build TyCons/Classes in a knot-tied way
87 3 check the validity of types in the now-unknotted TyCons/Classes
89 For example, when we find
90 (forall a m. m a -> m a)
91 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
92 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
93 an environment that binds a and m suitably.
95 The kind checker passed to tcHsTyVars needs to look at enough to
96 establish the kind of the tyvar:
97 * For a group of type and class decls, it's just the group, not
98 the rest of the program
99 * For a tyvar bound in a pattern type signature, its the types
100 mentioned in the other type signatures in that bunch of patterns
101 * For a tyvar bound in a RULE, it's the type signatures on other
102 universally quantified variables in the rule
104 Note that this may occasionally give surprising results. For example:
106 data T a b = MkT (a b)
108 Here we deduce a::*->*, b::*
109 But equally valid would be a::(*->*)-> *, b::*->*
114 Some of the validity check could in principle be done by the kind checker,
117 - During desugaring, we normalise by expanding type synonyms. Only
118 after this step can we check things like type-synonym saturation
119 e.g. type T k = k Int
121 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
122 and then S is saturated. This is a GHC extension.
124 - Similarly, also a GHC extension, we look through synonyms before complaining
125 about the form of a class or instance declaration
127 - Ambiguity checks involve functional dependencies, and it's easier to wait
128 until knots have been resolved before poking into them
130 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
131 finished building the loop. So to keep things simple, we postpone most validity
132 checking until step (3).
136 During step (1) we might fault in a TyCon defined in another module, and it might
137 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
138 knot around type declarations with ARecThing, so that the fault-in code can get
139 the TyCon being defined.
142 %************************************************************************
144 \subsection{Checking types}
146 %************************************************************************
149 tcHsSigType :: UserTypeCtxt -> LHsType Name -> TcM Type
150 -- Do kind checking, and hoist for-alls to the top
151 tcHsSigType ctxt hs_ty
152 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
153 do { kinded_ty <- kcTypeType hs_ty
154 ; ty <- tcHsKindedType kinded_ty
155 ; checkValidType ctxt ty
158 -- Used for the deriving(...) items
159 tcHsDeriv :: LHsType Name -> TcM ([TyVar], Class, [Type])
160 tcHsDeriv = addLocM (tc_hs_deriv [])
162 tc_hs_deriv tv_names (HsPredTy (L _ (HsClassP cls_name hs_tys)))
163 = kcHsTyVars tv_names $ \ tv_names' ->
164 do { cls_kind <- kcClass cls_name
165 ; (tys, res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
166 ; tcTyVarBndrs tv_names' $ \ tyvars ->
167 do { arg_tys <- dsHsTypes tys
168 ; cls <- tcLookupClass cls_name
169 ; return (tyvars, cls, arg_tys) }}
171 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
172 = -- Funny newtype deriving form
174 -- where C has arity 2. Hence can't use regular functions
175 tc_hs_deriv (tv_names1 ++ tv_names2) ty
178 = failWithTc (ptext SLIT("Illegal deriving item") <+> ppr other)
181 These functions are used during knot-tying in
182 type and class declarations, when we have to
183 separate kind-checking, desugaring, and validity checking
186 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
187 -- Used for type signatures
188 kcHsSigType ty = kcTypeType ty
189 kcHsLiftedSigType ty = kcLiftedType ty
191 tcHsKindedType :: LHsType Name -> TcM Type
192 -- Don't do kind checking, nor validity checking,
193 -- but do hoist for-alls to the top
194 -- This is used in type and class decls, where kinding is
195 -- done in advance, and validity checking is done later
196 -- [Validity checking done later because of knot-tying issues.]
198 = do { ty <- dsHsType hs_ty
199 ; return (hoistForAllTys ty) }
201 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
202 -- Used when we are expecting a ClassContext (i.e. no implicit params)
203 -- Does not do validity checking, like tcHsKindedType
204 tcHsKindedContext hs_theta = addLocM (mappM dsHsPred) hs_theta
208 %************************************************************************
210 The main kind checker: kcHsType
212 %************************************************************************
214 First a couple of simple wrappers for kcHsType
217 ---------------------------
218 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
219 -- The type ty must be a *lifted* *type*
220 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
222 ---------------------------
223 kcTypeType :: LHsType Name -> TcM (LHsType Name)
224 -- The type ty must be a *type*, but it can be lifted or
225 -- unlifted or an unboxed tuple.
226 kcTypeType ty = kcCheckHsType ty openTypeKind
228 ---------------------------
229 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
230 -- Check that the type has the specified kind
231 -- Be sure to use checkExpectedKind, rather than simply unifying
232 -- with OpenTypeKind, because it gives better error messages
233 kcCheckHsType (L span ty) exp_kind
235 kc_hs_type ty `thenM` \ (ty', act_kind) ->
236 checkExpectedKind ty act_kind exp_kind `thenM_`
240 Here comes the main function
243 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
244 kcHsType ty = wrapLocFstM kc_hs_type ty
245 -- kcHsType *returns* the kind of the type, rather than taking an expected
246 -- kind as argument as tcExpr does.
248 -- (a) the kind of (->) is
249 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
250 -- so we'd need to generate huge numbers of bx variables.
251 -- (b) kinds are so simple that the error messages are fine
253 -- The translated type has explicitly-kinded type-variable binders
255 kc_hs_type (HsParTy ty)
256 = kcHsType ty `thenM` \ (ty', kind) ->
257 returnM (HsParTy ty', kind)
259 -- kcHsType (HsSpliceTy s)
262 kc_hs_type (HsTyVar name)
263 = kcTyVar name `thenM` \ kind ->
264 returnM (HsTyVar name, kind)
266 kc_hs_type (HsListTy ty)
267 = kcLiftedType ty `thenM` \ ty' ->
268 returnM (HsListTy ty', liftedTypeKind)
270 kc_hs_type (HsPArrTy ty)
271 = kcLiftedType ty `thenM` \ ty' ->
272 returnM (HsPArrTy ty', liftedTypeKind)
274 kc_hs_type (HsNumTy n)
275 = returnM (HsNumTy n, liftedTypeKind)
277 kc_hs_type (HsKindSig ty k)
278 = kcCheckHsType ty k `thenM` \ ty' ->
279 returnM (HsKindSig ty' k, k)
281 kc_hs_type (HsTupleTy Boxed tys)
282 = mappM kcLiftedType tys `thenM` \ tys' ->
283 returnM (HsTupleTy Boxed tys', liftedTypeKind)
285 kc_hs_type (HsTupleTy Unboxed tys)
286 = mappM kcTypeType tys `thenM` \ tys' ->
287 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
289 kc_hs_type (HsFunTy ty1 ty2)
290 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
291 kcTypeType ty2 `thenM` \ ty2' ->
292 returnM (HsFunTy ty1' ty2', liftedTypeKind)
294 kc_hs_type ty@(HsOpTy ty1 op ty2)
295 = addLocM kcTyVar op `thenM` \ op_kind ->
296 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
297 returnM (HsOpTy ty1' op ty2', res_kind)
299 kc_hs_type ty@(HsAppTy ty1 ty2)
300 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
301 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
302 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
304 (fun_ty, arg_tys) = split ty1 [ty2]
305 split (L _ (HsAppTy f a)) as = split f (a:as)
307 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
308 -- the application; they are never used
310 kc_hs_type (HsPredTy pred)
311 = kcHsPred pred `thenM` \ pred' ->
312 returnM (HsPredTy pred', liftedTypeKind)
314 kc_hs_type (HsForAllTy exp tv_names context ty)
315 = kcHsTyVars tv_names $ \ tv_names' ->
316 kcHsContext context `thenM` \ ctxt' ->
317 kcHsType ty `thenM` \ (ty', kind) ->
318 -- The body of a forall is usually a type, but in principle
319 -- there's no reason to prohibit *unlifted* types.
320 -- In fact, GHC can itself construct a function with an
321 -- unboxed tuple inside a for-all (via CPR analyis; see
322 -- typecheck/should_compile/tc170)
324 -- Furthermore, in newtype deriving we allow
325 -- deriving( forall a. C [a] )
326 -- where C :: *->*->*, so it's awkward to prohibit higher-kinded
327 -- bodies. In any case, if there is a higher-kinded body
328 -- and we propagate that up, the caller will find any bugs.
329 returnM (HsForAllTy exp tv_names' ctxt' ty', kind)
331 ---------------------------
332 kcApps :: TcKind -- Function kind
334 -> [LHsType Name] -- Arg types
335 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
336 kcApps fun_kind ppr_fun args
337 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
338 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
339 returnM (args', res_kind)
341 split_fk fk 0 = returnM ([], fk)
342 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
344 Nothing -> failWithTc too_many_args
345 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
348 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
350 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
351 ptext SLIT("is applied to too many type arguments")
353 ---------------------------
354 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
355 kcHsContext ctxt = wrapLocM (mappM kcHsPred) ctxt
357 kcHsPred (L span pred) -- Checks that the result is of kind liftedType
359 kc_pred pred `thenM` \ (pred', kind) ->
360 checkExpectedKind pred kind liftedTypeKind `thenM_`
361 returnM (L span pred')
363 ---------------------------
364 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
365 -- Does *not* check for a saturated
366 -- application (reason: used from TcDeriv)
367 kc_pred pred@(HsIParam name ty)
368 = kcHsType ty `thenM` \ (ty', kind) ->
369 returnM (HsIParam name ty', kind)
371 kc_pred pred@(HsClassP cls tys)
372 = kcClass cls `thenM` \ kind ->
373 kcApps kind (ppr cls) tys `thenM` \ (tys', res_kind) ->
374 returnM (HsClassP cls tys', res_kind)
376 ---------------------------
377 kcTyVar :: Name -> TcM TcKind
378 kcTyVar name -- Could be a tyvar or a tycon
379 = traceTc (text "lk1" <+> ppr name) `thenM_`
380 tcLookup name `thenM` \ thing ->
381 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
383 ATyVar tv -> returnM (tyVarKind tv)
384 AThing kind -> returnM kind
385 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
386 other -> wrongThingErr "type" thing name
388 kcClass :: Name -> TcM TcKind
389 kcClass cls -- Must be a class
390 = tcLookup cls `thenM` \ thing ->
392 AThing kind -> returnM kind
393 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
394 other -> wrongThingErr "class" thing cls
398 %************************************************************************
402 %************************************************************************
406 * Transforms from HsType to Type
409 It cannot fail, and does no validity checking
412 dsHsType :: LHsType Name -> TcM Type
413 -- All HsTyVarBndrs in the intput type are kind-annotated
414 dsHsType ty = ds_type (unLoc ty)
416 ds_type ty@(HsTyVar name)
419 ds_type (HsParTy ty) -- Remove the parentheses markers
422 ds_type (HsKindSig ty k)
423 = dsHsType ty -- Kind checking done already
425 ds_type (HsListTy ty)
426 = dsHsType ty `thenM` \ tau_ty ->
427 returnM (mkListTy tau_ty)
429 ds_type (HsPArrTy ty)
430 = dsHsType ty `thenM` \ tau_ty ->
431 returnM (mkPArrTy tau_ty)
433 ds_type (HsTupleTy boxity tys)
434 = dsHsTypes tys `thenM` \ tau_tys ->
435 returnM (mkTupleTy boxity (length tys) tau_tys)
437 ds_type (HsFunTy ty1 ty2)
438 = dsHsType ty1 `thenM` \ tau_ty1 ->
439 dsHsType ty2 `thenM` \ tau_ty2 ->
440 returnM (mkFunTy tau_ty1 tau_ty2)
442 ds_type (HsOpTy ty1 (L span op) ty2)
443 = dsHsType ty1 `thenM` \ tau_ty1 ->
444 dsHsType ty2 `thenM` \ tau_ty2 ->
445 addSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
449 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
450 returnM (mkTyConApp tc [])
452 ds_type ty@(HsAppTy _ _)
455 ds_type (HsPredTy pred)
456 = dsHsPred pred `thenM` \ pred' ->
457 returnM (mkPredTy pred')
459 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
460 = tcTyVarBndrs tv_names $ \ tyvars ->
461 mappM dsHsPred (unLoc ctxt) `thenM` \ theta ->
462 dsHsType ty `thenM` \ tau ->
463 returnM (mkSigmaTy tyvars theta tau)
465 dsHsTypes arg_tys = mappM dsHsType arg_tys
468 Help functions for type applications
469 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
472 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
473 ds_app (HsAppTy ty1 ty2) tys
474 = ds_app (unLoc ty1) (ty2:tys)
477 = dsHsTypes tys `thenM` \ arg_tys ->
479 HsTyVar fun -> ds_var_app fun arg_tys
480 other -> ds_type ty `thenM` \ fun_ty ->
481 returnM (mkAppTys fun_ty arg_tys)
483 ds_var_app :: Name -> [Type] -> TcM Type
484 ds_var_app name arg_tys
485 = tcLookup name `thenM` \ thing ->
487 ATyVar tv -> returnM (mkAppTys (mkTyVarTy tv) arg_tys)
488 AGlobal (ATyCon tc) -> returnM (mkGenTyConApp tc arg_tys)
489 AThing _ -> tcLookupTyCon name `thenM` \ tc ->
490 returnM (mkGenTyConApp tc arg_tys)
491 other -> pprPanic "ds_app_type" (ppr name <+> ppr arg_tys)
498 dsHsPred :: LHsPred Name -> TcM PredType
499 dsHsPred pred = ds_pred (unLoc pred)
501 ds_pred pred@(HsClassP class_name tys)
502 = dsHsTypes tys `thenM` \ arg_tys ->
503 tcLookupClass class_name `thenM` \ clas ->
504 returnM (ClassP clas arg_tys)
506 ds_pred (HsIParam name ty)
507 = dsHsType ty `thenM` \ arg_ty ->
508 returnM (IParam name arg_ty)
512 %************************************************************************
514 Type-variable binders
516 %************************************************************************
520 kcHsTyVars :: [LHsTyVarBndr Name]
521 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
522 -- They scope over the thing inside
524 kcHsTyVars tvs thing_inside
525 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
526 tcExtendKindEnv [(n,k) | L _ (KindedTyVar n k) <- bndrs]
529 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
530 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
531 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
532 returnM (KindedTyVar name kind)
533 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
536 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
537 -> ([TyVar] -> TcM r)
539 -- Used when type-checking types/classes/type-decls
540 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
541 tcTyVarBndrs bndrs thing_inside
542 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
543 tcExtendTyVarEnv tyvars (thing_inside tyvars)
545 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
546 returnM (mkTyVar name kind')
547 zonk (UserTyVar name) = pprTrace "BAD: Un-kinded tyvar" (ppr name) $
548 returnM (mkTyVar name liftedTypeKind)
552 %************************************************************************
554 Scoped type variables
556 %************************************************************************
559 tcAddScopedTyVars is used for scoped type variables added by pattern
561 e.g. \ ((x::a), (y::a)) -> x+y
562 They never have explicit kinds (because this is source-code only)
563 They are mutable (because they can get bound to a more specific type).
565 Usually we kind-infer and expand type splices, and then
566 tupecheck/desugar the type. That doesn't work well for scoped type
567 variables, because they scope left-right in patterns. (e.g. in the
568 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
570 The current not-very-good plan is to
571 * find all the types in the patterns
572 * find their free tyvars
574 * bring the kinded type vars into scope
575 * BUT throw away the kind-checked type
576 (we'll kind-check it again when we type-check the pattern)
578 This is bad because throwing away the kind checked type throws away
579 its splices. But too bad for now. [July 03]
582 We no longer specify that these type variables must be univerally
583 quantified (lots of email on the subject). If you want to put that
585 a) Do a checkSigTyVars after thing_inside
586 b) More insidiously, don't pass in expected_ty, else
587 we unify with it too early and checkSigTyVars barfs
588 Instead you have to pass in a fresh ty var, and unify
589 it with expected_ty afterwards
592 tcAddScopedTyVars :: [LHsType Name] -> TcM a -> TcM a
593 tcAddScopedTyVars [] thing_inside
594 = thing_inside -- Quick get-out for the empty case
596 tcAddScopedTyVars sig_tys thing_inside
597 = getInLocalScope `thenM` \ in_scope ->
598 getSrcSpanM `thenM` \ span ->
600 sig_tvs = [ L span (UserTyVar n)
602 n <- nameSetToList (extractHsTyVars ty),
604 -- The tyvars we want are the free type variables of
605 -- the type that are not already in scope
607 -- Behave like kcHsType on a ForAll type
608 -- i.e. make kinded tyvars with mutable kinds,
609 -- and kind-check the enclosed types
610 kcHsTyVars sig_tvs (\ kinded_tvs -> do
611 { mappM kcTypeType sig_tys
612 ; return kinded_tvs }) `thenM` \ kinded_tvs ->
614 -- Zonk the mutable kinds and bring the tyvars into scope
615 -- Rather like tcTyVarBndrs, except that it brings *mutable*
616 -- tyvars into scope, not immutable ones
618 -- Furthermore, the tyvars are PatSigTvs, which means that we get better
619 -- error messages when type variables escape:
620 -- Inferred type is less polymorphic than expected
621 -- Quantified type variable `t' escapes
622 -- It is mentioned in the environment:
623 -- t is bound by the pattern type signature at tcfail103.hs:6
624 mapM (zonk . unLoc) kinded_tvs `thenM` \ tyvars ->
625 tcExtendTyVarEnv tyvars thing_inside
628 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
629 newMutTyVar name kind' PatSigTv
630 zonk (UserTyVar name) = pprTrace "BAD: Un-kinded tyvar" (ppr name) $
631 returnM (mkTyVar name liftedTypeKind)
635 %************************************************************************
637 \subsection{Signatures}
639 %************************************************************************
641 @tcSigs@ checks the signatures for validity, and returns a list of
642 {\em freshly-instantiated} signatures. That is, the types are already
643 split up, and have fresh type variables installed. All non-type-signature
644 "RenamedSigs" are ignored.
646 The @TcSigInfo@ contains @TcTypes@ because they are unified with
647 the variable's type, and after that checked to see whether they've
653 sig_poly_id :: TcId, -- *Polymorphic* binder for this value...
656 sig_tvs :: [TcTyVar], -- tyvars
657 sig_theta :: TcThetaType, -- theta
658 sig_tau :: TcTauType, -- tau
660 sig_mono_id :: TcId, -- *Monomorphic* binder for this value
661 -- Does *not* have name = N
664 sig_insts :: [Inst], -- Empty if theta is null, or
665 -- (method mono_id) otherwise
667 sig_loc :: SrcSpan -- The location of the signature
671 instance Outputable TcSigInfo where
672 ppr (TySigInfo id tyvars theta tau _ inst _) =
673 ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
675 maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo)
676 -- Search for a particular signature
677 maybeSig [] name = Nothing
678 maybeSig (sig@(TySigInfo sig_id _ _ _ _ _ _) : sigs) name
679 | name == idName sig_id = Just sig
680 | otherwise = maybeSig sigs name
685 tcTySig :: LSig Name -> TcM TcSigInfo
687 tcTySig (L span (Sig (L _ v) ty))
689 tcHsSigType (FunSigCtxt v) ty `thenM` \ sigma_tc_ty ->
690 mkTcSig (mkLocalId v sigma_tc_ty) `thenM` \ sig ->
693 mkTcSig :: TcId -> TcM TcSigInfo
695 = -- Instantiate this type
696 -- It's important to do this even though in the error-free case
697 -- we could just split the sigma_tc_ty (since the tyvars don't
698 -- unified with anything). But in the case of an error, when
699 -- the tyvars *do* get unified with something, we want to carry on
700 -- typechecking the rest of the program with the function bound
701 -- to a pristine type, namely sigma_tc_ty
702 tcInstType SigTv (idType poly_id) `thenM` \ (tyvars', theta', tau') ->
704 getInstLoc SignatureOrigin `thenM` \ inst_loc ->
705 newMethod inst_loc poly_id
707 theta' tau' `thenM` \ inst ->
708 -- We make a Method even if it's not overloaded; no harm
709 -- But do not extend the LIE! We're just making an Id.
711 getSrcSpanM `thenM` \ src_loc ->
712 returnM (TySigInfo { sig_poly_id = poly_id, sig_tvs = tyvars',
713 sig_theta = theta', sig_tau = tau',
714 sig_mono_id = instToId inst,
715 sig_insts = [inst], sig_loc = src_loc })
719 %************************************************************************
721 \subsection{Errors and contexts}
723 %************************************************************************
727 hoistForAllTys :: Type -> Type
728 -- Used for user-written type signatures only
729 -- Move all the foralls and constraints to the top
730 -- e.g. T -> forall a. a ==> forall a. T -> a
731 -- T -> (?x::Int) -> Int ==> (?x::Int) -> T -> Int
733 -- Also: eliminate duplicate constraints. These can show up
734 -- when hoisting constraints, notably implicit parameters.
736 -- We want to 'look through' type synonyms when doing this
737 -- so it's better done on the Type than the HsType
741 no_shadow_ty = deShadowTy ty
742 -- Running over ty with an empty substitution gives it the
743 -- no-shadowing property. This is important. For example:
744 -- type Foo r = forall a. a -> r
745 -- foo :: Foo (Foo ())
746 -- Here the hoisting should give
747 -- foo :: forall a a1. a -> a1 -> ()
749 -- What about type vars that are lexically in scope in the envt?
750 -- We simply rely on them having a different unique to any
751 -- binder in 'ty'. Otherwise we'd have to slurp the in-scope-tyvars
752 -- out of the envt, which is boring and (I think) not necessary.
754 case hoist no_shadow_ty of
755 (tvs, theta, body) -> mkForAllTys tvs (mkFunTys (nubBy tcEqType theta) body)
756 -- The 'nubBy' eliminates duplicate constraints,
757 -- notably implicit parameters
760 | (tvs1, body_ty) <- tcSplitForAllTys ty,
762 = case hoist body_ty of
763 (tvs2,theta,tau) -> (tvs1 ++ tvs2, theta, tau)
765 | Just (arg, res) <- tcSplitFunTy_maybe ty
767 arg' = hoistForAllTys arg -- Don't forget to apply hoist recursively
768 in -- to the argument type
769 if (isPredTy arg') then
771 (tvs,theta,tau) -> (tvs, arg':theta, tau)
774 (tvs,theta,tau) -> (tvs, theta, mkFunTy arg' tau)
776 | otherwise = ([], [], ty)