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
157 -- Used for the deriving(...) items
158 tcHsDeriv :: LHsType Name -> TcM ([TyVar], Class, [Type])
159 tcHsDeriv = addLocM (tc_hs_deriv [])
161 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
162 = kcHsTyVars tv_names $ \ tv_names' ->
163 do { cls_kind <- kcClass cls_name
164 ; (tys, res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
165 ; tcTyVarBndrs tv_names' $ \ tyvars ->
166 do { arg_tys <- dsHsTypes tys
167 ; cls <- tcLookupClass cls_name
168 ; return (tyvars, cls, arg_tys) }}
170 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
171 = -- Funny newtype deriving form
173 -- where C has arity 2. Hence can't use regular functions
174 tc_hs_deriv (tv_names1 ++ tv_names2) ty
177 = failWithTc (ptext SLIT("Illegal deriving item") <+> ppr other)
180 These functions are used during knot-tying in
181 type and class declarations, when we have to
182 separate kind-checking, desugaring, and validity checking
185 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
186 -- Used for type signatures
187 kcHsSigType ty = kcTypeType ty
188 kcHsLiftedSigType ty = kcLiftedType ty
190 tcHsKindedType :: LHsType Name -> TcM Type
191 -- Don't do kind checking, nor validity checking,
192 -- but do hoist for-alls to the top
193 -- This is used in type and class decls, where kinding is
194 -- done in advance, and validity checking is done later
195 -- [Validity checking done later because of knot-tying issues.]
197 = do { ty <- dsHsType hs_ty
198 ; return (hoistForAllTys ty) }
200 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
201 -- Used when we are expecting a ClassContext (i.e. no implicit params)
202 -- Does not do validity checking, like tcHsKindedType
203 tcHsKindedContext hs_theta = addLocM (mappM dsHsLPred) hs_theta
207 %************************************************************************
209 The main kind checker: kcHsType
211 %************************************************************************
213 First a couple of simple wrappers for kcHsType
216 ---------------------------
217 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
218 -- The type ty must be a *lifted* *type*
219 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
221 ---------------------------
222 kcTypeType :: LHsType Name -> TcM (LHsType Name)
223 -- The type ty must be a *type*, but it can be lifted or
224 -- unlifted or an unboxed tuple.
225 kcTypeType ty = kcCheckHsType ty openTypeKind
227 ---------------------------
228 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
229 -- Check that the type has the specified kind
230 -- Be sure to use checkExpectedKind, rather than simply unifying
231 -- with OpenTypeKind, because it gives better error messages
232 kcCheckHsType (L span ty) exp_kind
234 kc_hs_type ty `thenM` \ (ty', act_kind) ->
235 checkExpectedKind ty act_kind exp_kind `thenM_`
239 Here comes the main function
242 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
243 kcHsType ty = wrapLocFstM kc_hs_type ty
244 -- kcHsType *returns* the kind of the type, rather than taking an expected
245 -- kind as argument as tcExpr does.
247 -- (a) the kind of (->) is
248 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
249 -- so we'd need to generate huge numbers of bx variables.
250 -- (b) kinds are so simple that the error messages are fine
252 -- The translated type has explicitly-kinded type-variable binders
254 kc_hs_type (HsParTy ty)
255 = kcHsType ty `thenM` \ (ty', kind) ->
256 returnM (HsParTy ty', kind)
258 -- kcHsType (HsSpliceTy s)
261 kc_hs_type (HsTyVar name)
262 = kcTyVar name `thenM` \ kind ->
263 returnM (HsTyVar name, kind)
265 kc_hs_type (HsListTy ty)
266 = kcLiftedType ty `thenM` \ ty' ->
267 returnM (HsListTy ty', liftedTypeKind)
269 kc_hs_type (HsPArrTy ty)
270 = kcLiftedType ty `thenM` \ ty' ->
271 returnM (HsPArrTy ty', liftedTypeKind)
273 kc_hs_type (HsNumTy n)
274 = returnM (HsNumTy n, liftedTypeKind)
276 kc_hs_type (HsKindSig ty k)
277 = kcCheckHsType ty k `thenM` \ ty' ->
278 returnM (HsKindSig ty' k, k)
280 kc_hs_type (HsTupleTy Boxed tys)
281 = mappM kcLiftedType tys `thenM` \ tys' ->
282 returnM (HsTupleTy Boxed tys', liftedTypeKind)
284 kc_hs_type (HsTupleTy Unboxed tys)
285 = mappM kcTypeType tys `thenM` \ tys' ->
286 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
288 kc_hs_type (HsFunTy ty1 ty2)
289 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
290 kcTypeType ty2 `thenM` \ ty2' ->
291 returnM (HsFunTy ty1' ty2', liftedTypeKind)
293 kc_hs_type ty@(HsOpTy ty1 op ty2)
294 = addLocM kcTyVar op `thenM` \ op_kind ->
295 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
296 returnM (HsOpTy ty1' op ty2', res_kind)
298 kc_hs_type ty@(HsAppTy ty1 ty2)
299 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
300 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
301 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
303 (fun_ty, arg_tys) = split ty1 [ty2]
304 split (L _ (HsAppTy f a)) as = split f (a:as)
306 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
307 -- the application; they are never used
309 kc_hs_type (HsPredTy pred)
310 = kcHsPred pred `thenM` \ pred' ->
311 returnM (HsPredTy pred', liftedTypeKind)
313 kc_hs_type (HsForAllTy exp tv_names context ty)
314 = kcHsTyVars tv_names $ \ tv_names' ->
315 kcHsContext context `thenM` \ ctxt' ->
316 kcLiftedType ty `thenM` \ ty' ->
317 -- The body of a forall is usually a type, but in principle
318 -- there's no reason to prohibit *unlifted* types.
319 -- In fact, GHC can itself construct a function with an
320 -- unboxed tuple inside a for-all (via CPR analyis; see
321 -- typecheck/should_compile/tc170)
323 -- Still, that's only for internal interfaces, which aren't
324 -- kind-checked, so we only allow liftedTypeKind here
325 returnM (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind)
327 ---------------------------
328 kcApps :: TcKind -- Function kind
330 -> [LHsType Name] -- Arg types
331 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
332 kcApps fun_kind ppr_fun args
333 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
334 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
335 returnM (args', res_kind)
337 split_fk fk 0 = returnM ([], fk)
338 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
340 Nothing -> failWithTc too_many_args
341 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
344 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
346 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
347 ptext SLIT("is applied to too many type arguments")
349 ---------------------------
350 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
351 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
353 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
354 kcHsLPred = wrapLocM kcHsPred
356 kcHsPred :: HsPred Name -> TcM (HsPred Name)
357 kcHsPred pred -- Checks that the result is of kind liftedType
358 = kc_pred pred `thenM` \ (pred', kind) ->
359 checkExpectedKind pred kind liftedTypeKind `thenM_`
362 ---------------------------
363 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
364 -- Does *not* check for a saturated
365 -- application (reason: used from TcDeriv)
366 kc_pred pred@(HsIParam name ty)
367 = kcHsType ty `thenM` \ (ty', kind) ->
368 returnM (HsIParam name ty', kind)
370 kc_pred pred@(HsClassP cls tys)
371 = kcClass cls `thenM` \ kind ->
372 kcApps kind (ppr cls) tys `thenM` \ (tys', res_kind) ->
373 returnM (HsClassP cls tys', res_kind)
375 ---------------------------
376 kcTyVar :: Name -> TcM TcKind
377 kcTyVar name -- Could be a tyvar or a tycon
378 = traceTc (text "lk1" <+> ppr name) `thenM_`
379 tcLookup name `thenM` \ thing ->
380 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
382 ATyVar tv -> returnM (tyVarKind tv)
383 AThing kind -> returnM kind
384 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
385 other -> wrongThingErr "type" thing name
387 kcClass :: Name -> TcM TcKind
388 kcClass cls -- Must be a class
389 = tcLookup cls `thenM` \ thing ->
391 AThing kind -> returnM kind
392 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
393 other -> wrongThingErr "class" thing cls
397 %************************************************************************
401 %************************************************************************
405 * Transforms from HsType to Type
408 It cannot fail, and does no validity checking
411 dsHsType :: LHsType Name -> TcM Type
412 -- All HsTyVarBndrs in the intput type are kind-annotated
413 dsHsType ty = ds_type (unLoc ty)
415 ds_type ty@(HsTyVar name)
418 ds_type (HsParTy ty) -- Remove the parentheses markers
421 ds_type (HsKindSig ty k)
422 = dsHsType ty -- Kind checking done already
424 ds_type (HsListTy ty)
425 = dsHsType ty `thenM` \ tau_ty ->
426 returnM (mkListTy tau_ty)
428 ds_type (HsPArrTy ty)
429 = dsHsType ty `thenM` \ tau_ty ->
430 returnM (mkPArrTy tau_ty)
432 ds_type (HsTupleTy boxity tys)
433 = dsHsTypes tys `thenM` \ tau_tys ->
434 returnM (mkTupleTy boxity (length tys) tau_tys)
436 ds_type (HsFunTy ty1 ty2)
437 = dsHsType ty1 `thenM` \ tau_ty1 ->
438 dsHsType ty2 `thenM` \ tau_ty2 ->
439 returnM (mkFunTy tau_ty1 tau_ty2)
441 ds_type (HsOpTy ty1 (L span op) ty2)
442 = dsHsType ty1 `thenM` \ tau_ty1 ->
443 dsHsType ty2 `thenM` \ tau_ty2 ->
444 addSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
448 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
449 returnM (mkTyConApp tc [])
451 ds_type ty@(HsAppTy _ _)
454 ds_type (HsPredTy pred)
455 = dsHsPred pred `thenM` \ pred' ->
456 returnM (mkPredTy pred')
458 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
459 = tcTyVarBndrs tv_names $ \ tyvars ->
460 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
461 dsHsType ty `thenM` \ tau ->
462 returnM (mkSigmaTy tyvars theta tau)
464 dsHsTypes arg_tys = mappM dsHsType arg_tys
467 Help functions for type applications
468 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
471 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
472 ds_app (HsAppTy ty1 ty2) tys
473 = ds_app (unLoc ty1) (ty2:tys)
476 = dsHsTypes tys `thenM` \ arg_tys ->
478 HsTyVar fun -> ds_var_app fun arg_tys
479 other -> ds_type ty `thenM` \ fun_ty ->
480 returnM (mkAppTys fun_ty arg_tys)
482 ds_var_app :: Name -> [Type] -> TcM Type
483 ds_var_app name arg_tys
484 = tcLookup name `thenM` \ thing ->
486 ATyVar tv -> returnM (mkAppTys (mkTyVarTy tv) arg_tys)
487 AGlobal (ATyCon tc) -> returnM (mkGenTyConApp tc arg_tys)
488 AThing _ -> tcLookupTyCon name `thenM` \ tc ->
489 returnM (mkGenTyConApp tc arg_tys)
490 other -> pprPanic "ds_app_type" (ppr name <+> ppr arg_tys)
497 dsHsLPred :: LHsPred Name -> TcM PredType
498 dsHsLPred pred = dsHsPred (unLoc pred)
500 dsHsPred pred@(HsClassP class_name tys)
501 = dsHsTypes tys `thenM` \ arg_tys ->
502 tcLookupClass class_name `thenM` \ clas ->
503 returnM (ClassP clas arg_tys)
505 dsHsPred (HsIParam name ty)
506 = dsHsType ty `thenM` \ arg_ty ->
507 returnM (IParam name arg_ty)
511 %************************************************************************
513 Type-variable binders
515 %************************************************************************
519 kcHsTyVars :: [LHsTyVarBndr Name]
520 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
521 -- They scope over the thing inside
523 kcHsTyVars tvs thing_inside
524 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
525 tcExtendKindEnv [(n,k) | L _ (KindedTyVar n k) <- bndrs]
528 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
529 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
530 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
531 returnM (KindedTyVar name kind)
532 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
535 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
536 -> ([TyVar] -> TcM r)
538 -- Used when type-checking types/classes/type-decls
539 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
540 tcTyVarBndrs bndrs thing_inside
541 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
542 tcExtendTyVarEnv tyvars (thing_inside tyvars)
544 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
545 returnM (mkTyVar name kind')
546 zonk (UserTyVar name) = pprTrace "BAD: Un-kinded tyvar" (ppr name) $
547 returnM (mkTyVar name liftedTypeKind)
551 %************************************************************************
553 Scoped type variables
555 %************************************************************************
558 tcAddScopedTyVars is used for scoped type variables added by pattern
560 e.g. \ ((x::a), (y::a)) -> x+y
561 They never have explicit kinds (because this is source-code only)
562 They are mutable (because they can get bound to a more specific type).
564 Usually we kind-infer and expand type splices, and then
565 tupecheck/desugar the type. That doesn't work well for scoped type
566 variables, because they scope left-right in patterns. (e.g. in the
567 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
569 The current not-very-good plan is to
570 * find all the types in the patterns
571 * find their free tyvars
573 * bring the kinded type vars into scope
574 * BUT throw away the kind-checked type
575 (we'll kind-check it again when we type-check the pattern)
577 This is bad because throwing away the kind checked type throws away
578 its splices. But too bad for now. [July 03]
581 We no longer specify that these type variables must be univerally
582 quantified (lots of email on the subject). If you want to put that
584 a) Do a checkSigTyVars after thing_inside
585 b) More insidiously, don't pass in expected_ty, else
586 we unify with it too early and checkSigTyVars barfs
587 Instead you have to pass in a fresh ty var, and unify
588 it with expected_ty afterwards
591 tcAddScopedTyVars :: [LHsType Name] -> TcM a -> TcM a
592 tcAddScopedTyVars [] thing_inside
593 = thing_inside -- Quick get-out for the empty case
595 tcAddScopedTyVars sig_tys thing_inside
596 = getInLocalScope `thenM` \ in_scope ->
597 getSrcSpanM `thenM` \ span ->
599 sig_tvs = [ L span (UserTyVar n)
601 n <- nameSetToList (extractHsTyVars ty),
603 -- The tyvars we want are the free type variables of
604 -- the type that are not already in scope
606 -- Behave like kcHsType on a ForAll type
607 -- i.e. make kinded tyvars with mutable kinds,
608 -- and kind-check the enclosed types
609 kcHsTyVars sig_tvs (\ kinded_tvs -> do
610 { mappM kcTypeType sig_tys
611 ; return kinded_tvs }) `thenM` \ kinded_tvs ->
613 -- Zonk the mutable kinds and bring the tyvars into scope
614 -- Rather like tcTyVarBndrs, except that it brings *mutable*
615 -- tyvars into scope, not immutable ones
617 -- Furthermore, the tyvars are PatSigTvs, which means that we get better
618 -- error messages when type variables escape:
619 -- Inferred type is less polymorphic than expected
620 -- Quantified type variable `t' escapes
621 -- It is mentioned in the environment:
622 -- t is bound by the pattern type signature at tcfail103.hs:6
623 mapM (zonk . unLoc) kinded_tvs `thenM` \ tyvars ->
624 tcExtendTyVarEnv tyvars thing_inside
627 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
628 newMutTyVar name kind' PatSigTv
629 zonk (UserTyVar name) = pprTrace "BAD: Un-kinded tyvar" (ppr name) $
630 returnM (mkTyVar name liftedTypeKind)
634 %************************************************************************
636 \subsection{Signatures}
638 %************************************************************************
640 @tcSigs@ checks the signatures for validity, and returns a list of
641 {\em freshly-instantiated} signatures. That is, the types are already
642 split up, and have fresh type variables installed. All non-type-signature
643 "RenamedSigs" are ignored.
645 The @TcSigInfo@ contains @TcTypes@ because they are unified with
646 the variable's type, and after that checked to see whether they've
652 sig_poly_id :: TcId, -- *Polymorphic* binder for this value...
655 sig_tvs :: [TcTyVar], -- tyvars
656 sig_theta :: TcThetaType, -- theta
657 sig_tau :: TcTauType, -- tau
659 sig_mono_id :: TcId, -- *Monomorphic* binder for this value
660 -- Does *not* have name = N
663 sig_insts :: [Inst], -- Empty if theta is null, or
664 -- (method mono_id) otherwise
666 sig_loc :: SrcSpan -- The location of the signature
670 instance Outputable TcSigInfo where
671 ppr (TySigInfo id tyvars theta tau _ inst _) =
672 ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
674 maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo)
675 -- Search for a particular signature
676 maybeSig [] name = Nothing
677 maybeSig (sig@(TySigInfo sig_id _ _ _ _ _ _) : sigs) name
678 | name == idName sig_id = Just sig
679 | otherwise = maybeSig sigs name
684 tcTySig :: LSig Name -> TcM TcSigInfo
686 tcTySig (L span (Sig (L _ v) ty))
688 tcHsSigType (FunSigCtxt v) ty `thenM` \ sigma_tc_ty ->
689 mkTcSig (mkLocalId v sigma_tc_ty) `thenM` \ sig ->
692 mkTcSig :: TcId -> TcM TcSigInfo
694 = -- Instantiate this type
695 -- It's important to do this even though in the error-free case
696 -- we could just split the sigma_tc_ty (since the tyvars don't
697 -- unified with anything). But in the case of an error, when
698 -- the tyvars *do* get unified with something, we want to carry on
699 -- typechecking the rest of the program with the function bound
700 -- to a pristine type, namely sigma_tc_ty
701 tcInstType SigTv (idType poly_id) `thenM` \ (tyvars', theta', tau') ->
703 getInstLoc SignatureOrigin `thenM` \ inst_loc ->
704 newMethod inst_loc poly_id
706 theta' tau' `thenM` \ inst ->
707 -- We make a Method even if it's not overloaded; no harm
708 -- But do not extend the LIE! We're just making an Id.
710 getSrcSpanM `thenM` \ src_loc ->
711 returnM (TySigInfo { sig_poly_id = poly_id, sig_tvs = tyvars',
712 sig_theta = theta', sig_tau = tau',
713 sig_mono_id = instToId inst,
714 sig_insts = [inst], sig_loc = src_loc })
718 %************************************************************************
720 \subsection{Errors and contexts}
722 %************************************************************************
726 hoistForAllTys :: Type -> Type
727 -- Used for user-written type signatures only
728 -- Move all the foralls and constraints to the top
729 -- e.g. T -> forall a. a ==> forall a. T -> a
730 -- T -> (?x::Int) -> Int ==> (?x::Int) -> T -> Int
732 -- Also: eliminate duplicate constraints. These can show up
733 -- when hoisting constraints, notably implicit parameters.
735 -- We want to 'look through' type synonyms when doing this
736 -- so it's better done on the Type than the HsType
740 no_shadow_ty = deShadowTy ty
741 -- Running over ty with an empty substitution gives it the
742 -- no-shadowing property. This is important. For example:
743 -- type Foo r = forall a. a -> r
744 -- foo :: Foo (Foo ())
745 -- Here the hoisting should give
746 -- foo :: forall a a1. a -> a1 -> ()
748 -- What about type vars that are lexically in scope in the envt?
749 -- We simply rely on them having a different unique to any
750 -- binder in 'ty'. Otherwise we'd have to slurp the in-scope-tyvars
751 -- out of the envt, which is boring and (I think) not necessary.
753 case hoist no_shadow_ty of
754 (tvs, theta, body) -> mkForAllTys tvs (mkFunTys (nubBy tcEqType theta) body)
755 -- The 'nubBy' eliminates duplicate constraints,
756 -- notably implicit parameters
759 | (tvs1, body_ty) <- tcSplitForAllTys ty,
761 = case hoist body_ty of
762 (tvs2,theta,tau) -> (tvs1 ++ tvs2, theta, tau)
764 | Just (arg, res) <- tcSplitFunTy_maybe ty
766 arg' = hoistForAllTys arg -- Don't forget to apply hoist recursively
767 in -- to the argument type
768 if (isPredTy arg') then
770 (tvs,theta,tau) -> (tvs, arg':theta, tau)
773 (tvs,theta,tau) -> (tvs, theta, mkFunTy arg' tau)
775 | otherwise = ([], [], ty)