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 kcHsType ty `thenM` \ (ty', kind) ->
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 -- Furthermore, in newtype deriving we allow
324 -- deriving( forall a. C [a] )
325 -- where C :: *->*->*, so it's awkward to prohibit higher-kinded
326 -- bodies. In any case, if there is a higher-kinded body
327 -- and we propagate that up, the caller will find any bugs.
328 returnM (HsForAllTy exp tv_names' ctxt' ty', kind)
330 ---------------------------
331 kcApps :: TcKind -- Function kind
333 -> [LHsType Name] -- Arg types
334 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
335 kcApps fun_kind ppr_fun args
336 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
337 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
338 returnM (args', res_kind)
340 split_fk fk 0 = returnM ([], fk)
341 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
343 Nothing -> failWithTc too_many_args
344 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
347 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
349 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
350 ptext SLIT("is applied to too many type arguments")
352 ---------------------------
353 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
354 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
356 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
357 kcHsLPred = wrapLocM kcHsPred
359 kcHsPred :: HsPred Name -> TcM (HsPred Name)
360 kcHsPred pred -- Checks that the result is of kind liftedType
361 = kc_pred pred `thenM` \ (pred', kind) ->
362 checkExpectedKind pred kind liftedTypeKind `thenM_`
365 ---------------------------
366 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
367 -- Does *not* check for a saturated
368 -- application (reason: used from TcDeriv)
369 kc_pred pred@(HsIParam name ty)
370 = kcHsType ty `thenM` \ (ty', kind) ->
371 returnM (HsIParam name ty', kind)
373 kc_pred pred@(HsClassP cls tys)
374 = kcClass cls `thenM` \ kind ->
375 kcApps kind (ppr cls) tys `thenM` \ (tys', res_kind) ->
376 returnM (HsClassP cls tys', res_kind)
378 ---------------------------
379 kcTyVar :: Name -> TcM TcKind
380 kcTyVar name -- Could be a tyvar or a tycon
381 = traceTc (text "lk1" <+> ppr name) `thenM_`
382 tcLookup name `thenM` \ thing ->
383 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
385 ATyVar tv -> returnM (tyVarKind tv)
386 AThing kind -> returnM kind
387 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
388 other -> wrongThingErr "type" thing name
390 kcClass :: Name -> TcM TcKind
391 kcClass cls -- Must be a class
392 = tcLookup cls `thenM` \ thing ->
394 AThing kind -> returnM kind
395 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
396 other -> wrongThingErr "class" thing cls
400 %************************************************************************
404 %************************************************************************
408 * Transforms from HsType to Type
411 It cannot fail, and does no validity checking
414 dsHsType :: LHsType Name -> TcM Type
415 -- All HsTyVarBndrs in the intput type are kind-annotated
416 dsHsType ty = ds_type (unLoc ty)
418 ds_type ty@(HsTyVar name)
421 ds_type (HsParTy ty) -- Remove the parentheses markers
424 ds_type (HsKindSig ty k)
425 = dsHsType ty -- Kind checking done already
427 ds_type (HsListTy ty)
428 = dsHsType ty `thenM` \ tau_ty ->
429 returnM (mkListTy tau_ty)
431 ds_type (HsPArrTy ty)
432 = dsHsType ty `thenM` \ tau_ty ->
433 returnM (mkPArrTy tau_ty)
435 ds_type (HsTupleTy boxity tys)
436 = dsHsTypes tys `thenM` \ tau_tys ->
437 returnM (mkTupleTy boxity (length tys) tau_tys)
439 ds_type (HsFunTy ty1 ty2)
440 = dsHsType ty1 `thenM` \ tau_ty1 ->
441 dsHsType ty2 `thenM` \ tau_ty2 ->
442 returnM (mkFunTy tau_ty1 tau_ty2)
444 ds_type (HsOpTy ty1 (L span op) ty2)
445 = dsHsType ty1 `thenM` \ tau_ty1 ->
446 dsHsType ty2 `thenM` \ tau_ty2 ->
447 addSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
451 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
452 returnM (mkTyConApp tc [])
454 ds_type ty@(HsAppTy _ _)
457 ds_type (HsPredTy pred)
458 = dsHsPred pred `thenM` \ pred' ->
459 returnM (mkPredTy pred')
461 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
462 = tcTyVarBndrs tv_names $ \ tyvars ->
463 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
464 dsHsType ty `thenM` \ tau ->
465 returnM (mkSigmaTy tyvars theta tau)
467 dsHsTypes arg_tys = mappM dsHsType arg_tys
470 Help functions for type applications
471 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
474 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
475 ds_app (HsAppTy ty1 ty2) tys
476 = ds_app (unLoc ty1) (ty2:tys)
479 = dsHsTypes tys `thenM` \ arg_tys ->
481 HsTyVar fun -> ds_var_app fun arg_tys
482 other -> ds_type ty `thenM` \ fun_ty ->
483 returnM (mkAppTys fun_ty arg_tys)
485 ds_var_app :: Name -> [Type] -> TcM Type
486 ds_var_app name arg_tys
487 = tcLookup name `thenM` \ thing ->
489 ATyVar tv -> returnM (mkAppTys (mkTyVarTy tv) arg_tys)
490 AGlobal (ATyCon tc) -> returnM (mkGenTyConApp tc arg_tys)
491 AThing _ -> tcLookupTyCon name `thenM` \ tc ->
492 returnM (mkGenTyConApp tc arg_tys)
493 other -> pprPanic "ds_app_type" (ppr name <+> ppr arg_tys)
500 dsHsLPred :: LHsPred Name -> TcM PredType
501 dsHsLPred pred = dsHsPred (unLoc pred)
503 dsHsPred pred@(HsClassP class_name tys)
504 = dsHsTypes tys `thenM` \ arg_tys ->
505 tcLookupClass class_name `thenM` \ clas ->
506 returnM (ClassP clas arg_tys)
508 dsHsPred (HsIParam name ty)
509 = dsHsType ty `thenM` \ arg_ty ->
510 returnM (IParam name arg_ty)
514 %************************************************************************
516 Type-variable binders
518 %************************************************************************
522 kcHsTyVars :: [LHsTyVarBndr Name]
523 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
524 -- They scope over the thing inside
526 kcHsTyVars tvs thing_inside
527 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
528 tcExtendKindEnv [(n,k) | L _ (KindedTyVar n k) <- bndrs]
531 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
532 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
533 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
534 returnM (KindedTyVar name kind)
535 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
538 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
539 -> ([TyVar] -> TcM r)
541 -- Used when type-checking types/classes/type-decls
542 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
543 tcTyVarBndrs bndrs thing_inside
544 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
545 tcExtendTyVarEnv tyvars (thing_inside tyvars)
547 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
548 returnM (mkTyVar name kind')
549 zonk (UserTyVar name) = pprTrace "BAD: Un-kinded tyvar" (ppr name) $
550 returnM (mkTyVar name liftedTypeKind)
554 %************************************************************************
556 Scoped type variables
558 %************************************************************************
561 tcAddScopedTyVars is used for scoped type variables added by pattern
563 e.g. \ ((x::a), (y::a)) -> x+y
564 They never have explicit kinds (because this is source-code only)
565 They are mutable (because they can get bound to a more specific type).
567 Usually we kind-infer and expand type splices, and then
568 tupecheck/desugar the type. That doesn't work well for scoped type
569 variables, because they scope left-right in patterns. (e.g. in the
570 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
572 The current not-very-good plan is to
573 * find all the types in the patterns
574 * find their free tyvars
576 * bring the kinded type vars into scope
577 * BUT throw away the kind-checked type
578 (we'll kind-check it again when we type-check the pattern)
580 This is bad because throwing away the kind checked type throws away
581 its splices. But too bad for now. [July 03]
584 We no longer specify that these type variables must be univerally
585 quantified (lots of email on the subject). If you want to put that
587 a) Do a checkSigTyVars after thing_inside
588 b) More insidiously, don't pass in expected_ty, else
589 we unify with it too early and checkSigTyVars barfs
590 Instead you have to pass in a fresh ty var, and unify
591 it with expected_ty afterwards
594 tcAddScopedTyVars :: [LHsType Name] -> TcM a -> TcM a
595 tcAddScopedTyVars [] thing_inside
596 = thing_inside -- Quick get-out for the empty case
598 tcAddScopedTyVars sig_tys thing_inside
599 = getInLocalScope `thenM` \ in_scope ->
600 getSrcSpanM `thenM` \ span ->
602 sig_tvs = [ L span (UserTyVar n)
604 n <- nameSetToList (extractHsTyVars ty),
606 -- The tyvars we want are the free type variables of
607 -- the type that are not already in scope
609 -- Behave like kcHsType on a ForAll type
610 -- i.e. make kinded tyvars with mutable kinds,
611 -- and kind-check the enclosed types
612 kcHsTyVars sig_tvs (\ kinded_tvs -> do
613 { mappM kcTypeType sig_tys
614 ; return kinded_tvs }) `thenM` \ kinded_tvs ->
616 -- Zonk the mutable kinds and bring the tyvars into scope
617 -- Rather like tcTyVarBndrs, except that it brings *mutable*
618 -- tyvars into scope, not immutable ones
620 -- Furthermore, the tyvars are PatSigTvs, which means that we get better
621 -- error messages when type variables escape:
622 -- Inferred type is less polymorphic than expected
623 -- Quantified type variable `t' escapes
624 -- It is mentioned in the environment:
625 -- t is bound by the pattern type signature at tcfail103.hs:6
626 mapM (zonk . unLoc) kinded_tvs `thenM` \ tyvars ->
627 tcExtendTyVarEnv tyvars thing_inside
630 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
631 newMutTyVar name kind' PatSigTv
632 zonk (UserTyVar name) = pprTrace "BAD: Un-kinded tyvar" (ppr name) $
633 returnM (mkTyVar name liftedTypeKind)
637 %************************************************************************
639 \subsection{Signatures}
641 %************************************************************************
643 @tcSigs@ checks the signatures for validity, and returns a list of
644 {\em freshly-instantiated} signatures. That is, the types are already
645 split up, and have fresh type variables installed. All non-type-signature
646 "RenamedSigs" are ignored.
648 The @TcSigInfo@ contains @TcTypes@ because they are unified with
649 the variable's type, and after that checked to see whether they've
655 sig_poly_id :: TcId, -- *Polymorphic* binder for this value...
658 sig_tvs :: [TcTyVar], -- tyvars
659 sig_theta :: TcThetaType, -- theta
660 sig_tau :: TcTauType, -- tau
662 sig_mono_id :: TcId, -- *Monomorphic* binder for this value
663 -- Does *not* have name = N
666 sig_insts :: [Inst], -- Empty if theta is null, or
667 -- (method mono_id) otherwise
669 sig_loc :: SrcSpan -- The location of the signature
673 instance Outputable TcSigInfo where
674 ppr (TySigInfo id tyvars theta tau _ inst _) =
675 ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
677 maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo)
678 -- Search for a particular signature
679 maybeSig [] name = Nothing
680 maybeSig (sig@(TySigInfo sig_id _ _ _ _ _ _) : sigs) name
681 | name == idName sig_id = Just sig
682 | otherwise = maybeSig sigs name
687 tcTySig :: LSig Name -> TcM TcSigInfo
689 tcTySig (L span (Sig (L _ v) ty))
691 tcHsSigType (FunSigCtxt v) ty `thenM` \ sigma_tc_ty ->
692 mkTcSig (mkLocalId v sigma_tc_ty) `thenM` \ sig ->
695 mkTcSig :: TcId -> TcM TcSigInfo
697 = -- Instantiate this type
698 -- It's important to do this even though in the error-free case
699 -- we could just split the sigma_tc_ty (since the tyvars don't
700 -- unified with anything). But in the case of an error, when
701 -- the tyvars *do* get unified with something, we want to carry on
702 -- typechecking the rest of the program with the function bound
703 -- to a pristine type, namely sigma_tc_ty
704 tcInstType SigTv (idType poly_id) `thenM` \ (tyvars', theta', tau') ->
706 getInstLoc SignatureOrigin `thenM` \ inst_loc ->
707 newMethod inst_loc poly_id
709 theta' tau' `thenM` \ inst ->
710 -- We make a Method even if it's not overloaded; no harm
711 -- But do not extend the LIE! We're just making an Id.
713 getSrcSpanM `thenM` \ src_loc ->
714 returnM (TySigInfo { sig_poly_id = poly_id, sig_tvs = tyvars',
715 sig_theta = theta', sig_tau = tau',
716 sig_mono_id = instToId inst,
717 sig_insts = [inst], sig_loc = src_loc })
721 %************************************************************************
723 \subsection{Errors and contexts}
725 %************************************************************************
729 hoistForAllTys :: Type -> Type
730 -- Used for user-written type signatures only
731 -- Move all the foralls and constraints to the top
732 -- e.g. T -> forall a. a ==> forall a. T -> a
733 -- T -> (?x::Int) -> Int ==> (?x::Int) -> T -> Int
735 -- Also: eliminate duplicate constraints. These can show up
736 -- when hoisting constraints, notably implicit parameters.
738 -- We want to 'look through' type synonyms when doing this
739 -- so it's better done on the Type than the HsType
743 no_shadow_ty = deShadowTy ty
744 -- Running over ty with an empty substitution gives it the
745 -- no-shadowing property. This is important. For example:
746 -- type Foo r = forall a. a -> r
747 -- foo :: Foo (Foo ())
748 -- Here the hoisting should give
749 -- foo :: forall a a1. a -> a1 -> ()
751 -- What about type vars that are lexically in scope in the envt?
752 -- We simply rely on them having a different unique to any
753 -- binder in 'ty'. Otherwise we'd have to slurp the in-scope-tyvars
754 -- out of the envt, which is boring and (I think) not necessary.
756 case hoist no_shadow_ty of
757 (tvs, theta, body) -> mkForAllTys tvs (mkFunTys (nubBy tcEqType theta) body)
758 -- The 'nubBy' eliminates duplicate constraints,
759 -- notably implicit parameters
762 | (tvs1, body_ty) <- tcSplitForAllTys ty,
764 = case hoist body_ty of
765 (tvs2,theta,tau) -> (tvs1 ++ tvs2, theta, tau)
767 | Just (arg, res) <- tcSplitFunTy_maybe ty
769 arg' = hoistForAllTys arg -- Don't forget to apply hoist recursively
770 in -- to the argument type
771 if (isPredTy arg') then
773 (tvs,theta,tau) -> (tvs, arg':theta, tau)
776 (tvs,theta,tau) -> (tvs, theta, mkFunTy arg' tau)
778 | otherwise = ([], [], ty)