2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBindsAndThen,
8 tcPragmaSigs, checkSigTyVars, tcBindWithSigs,
9 sigCtxt, TcSigInfo(..) ) where
11 #include "HsVersions.h"
13 import {-# SOURCE #-} TcGRHSs ( tcGRHSsAndBinds )
15 import HsSyn ( HsBinds(..), MonoBinds(..), Sig(..), InPat(..),
18 import RnHsSyn ( RenamedHsBinds, RenamedSig(..),
21 import TcHsSyn ( TcHsBinds, TcMonoBinds,
22 TcIdOcc(..), TcIdBndr,
27 import Inst ( Inst, LIE, emptyLIE, plusLIE, plusLIEs, InstOrigin(..),
28 newDicts, tyVarsOfInst, instToId, newMethodWithGivenTy,
31 import TcEnv ( tcExtendLocalValEnv, tcLookupLocalValueOK, newLocalId,
32 tcGetGlobalTyVars, tcExtendGlobalTyVars
34 import TcMatches ( tcMatchesFun )
35 import TcSimplify ( tcSimplify, tcSimplifyAndCheck )
36 import TcMonoType ( tcHsType )
37 import TcPat ( tcPat )
38 import TcSimplify ( bindInstsOfLocalFuns )
39 import TcType ( TcType, TcThetaType, TcTauType,
41 newTyVarTy, newTcTyVar, tcInstSigType, tcInstSigTcType,
42 zonkTcType, zonkTcTypes, zonkTcThetaType, zonkTcTyVar
44 import Unify ( unifyTauTy, unifyTauTyLists )
46 import Kind ( isUnboxedTypeKind, mkTypeKind, isTypeKind, mkBoxedTypeKind )
47 import Id ( idType, mkUserId, replacePragmaInfo )
48 import IdInfo ( noIdInfo )
49 import Maybes ( maybeToBool, assocMaybe )
50 import Name ( getOccName, getSrcLoc, Name )
51 import PragmaInfo ( PragmaInfo(..) )
52 import Type ( mkTyVarTy, mkTyVarTys, isTyVarTy, tyVarsOfTypes,
53 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar, mkDictTy,
54 splitRhoTy, mkForAllTy, splitForAllTys )
55 import TyVar ( GenTyVar, TyVar, tyVarKind, mkTyVarSet, minusTyVarSet, emptyTyVarSet,
56 elementOfTyVarSet, unionTyVarSets, tyVarSetToList )
57 import Bag ( bagToList, foldrBag, )
58 import Util ( isIn, hasNoDups, assoc )
59 import Unique ( Unique )
60 import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
61 import SrcLoc ( SrcLoc )
66 %************************************************************************
68 \subsection{Type-checking bindings}
70 %************************************************************************
72 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
73 it needs to know something about the {\em usage} of the things bound,
74 so that it can create specialisations of them. So @tcBindsAndThen@
75 takes a function which, given an extended environment, E, typechecks
76 the scope of the bindings returning a typechecked thing and (most
77 important) an LIE. It is this LIE which is then used as the basis for
78 specialising the things bound.
80 @tcBindsAndThen@ also takes a "combiner" which glues together the
81 bindings and the "thing" to make a new "thing".
83 The real work is done by @tcBindWithSigsAndThen@.
85 Recursive and non-recursive binds are handled in essentially the same
86 way: because of uniques there are no scoping issues left. The only
87 difference is that non-recursive bindings can bind primitive values.
89 Even for non-recursive binding groups we add typings for each binder
90 to the LVE for the following reason. When each individual binding is
91 checked the type of its LHS is unified with that of its RHS; and
92 type-checking the LHS of course requires that the binder is in scope.
94 At the top-level the LIE is sure to contain nothing but constant
95 dictionaries, which we resolve at the module level.
98 tcTopBindsAndThen, tcBindsAndThen
99 :: (RecFlag -> TcMonoBinds s -> this -> that) -- Combinator
101 -> TcM s (this, LIE s)
102 -> TcM s (that, LIE s)
104 tcTopBindsAndThen = tc_binds_and_then TopLevel
105 tcBindsAndThen = tc_binds_and_then NotTopLevel
107 tc_binds_and_then top_lvl combiner binds do_next
108 = tcBinds top_lvl binds `thenTc` \ (mbinds1, binds_lie, env, ids) ->
111 -- Now do whatever happens next, in the augmented envt
112 do_next `thenTc` \ (thing, thing_lie) ->
114 -- Create specialisations of functions bound here
115 -- Nota Bene: we glom the bindings all together in a single
116 -- recursive group ("recursive" passed to combiner, below)
117 -- so that we can do thsi bindInsts thing once for all the bindings
118 -- and the thing inside. This saves a quadratic-cost algorithm
119 -- when there's a long sequence of bindings.
120 bindInstsOfLocalFuns (binds_lie `plusLIE` thing_lie) ids `thenTc` \ (final_lie, mbinds2) ->
124 final_mbinds = mbinds1 `AndMonoBinds` mbinds2
126 returnTc (combiner Recursive final_mbinds thing, final_lie)
128 tcBinds :: TopLevelFlag
130 -> TcM s (TcMonoBinds s, LIE s, TcEnv s, [TcIdBndr s])
131 -- The envt is the envt with binders in scope
132 -- The binders are those bound by this group of bindings
134 tcBinds top_lvl EmptyBinds
135 = tcGetEnv `thenNF_Tc` \ env ->
136 returnTc (EmptyMonoBinds, emptyLIE, env, [])
138 -- Short-cut for the rather common case of an empty bunch of bindings
139 tcBinds top_lvl (MonoBind EmptyMonoBinds sigs is_rec)
140 = tcGetEnv `thenNF_Tc` \ env ->
141 returnTc (EmptyMonoBinds, emptyLIE, env, [])
143 tcBinds top_lvl (ThenBinds binds1 binds2)
144 = tcBinds top_lvl binds1 `thenTc` \ (mbinds1, lie1, env1, ids1) ->
146 tcBinds top_lvl binds2 `thenTc` \ (mbinds2, lie2, env2, ids2) ->
147 returnTc (mbinds1 `AndMonoBinds` mbinds2, lie1 `plusLIE` lie2, env2, ids1++ids2)
149 tcBinds top_lvl (MonoBind bind sigs is_rec)
150 = fixTc (\ ~(prag_info_fn, _) ->
151 -- This is the usual prag_info fix; the PragmaInfo field of an Id
152 -- is not inspected till ages later in the compiler, so there
153 -- should be no black-hole problems here.
155 -- TYPECHECK THE SIGNATURES
156 mapTc (tcTySig prag_info_fn) ty_sigs `thenTc` \ tc_ty_sigs ->
158 tcBindWithSigs top_lvl binder_names bind
159 tc_ty_sigs is_rec prag_info_fn `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
161 -- Extend the environment to bind the new polymorphic Ids
162 tcExtendLocalValEnv binder_names poly_ids $
164 -- Build bindings and IdInfos corresponding to user pragmas
165 tcPragmaSigs sigs `thenTc` \ (prag_info_fn, prag_binds, prag_lie) ->
167 -- Catch the environment and return
168 tcGetEnv `thenNF_Tc` \ env ->
169 returnTc (prag_info_fn, (poly_binds `AndMonoBinds` prag_binds,
170 poly_lie `plusLIE` prag_lie,
172 ) ) `thenTc` \ (_, result) ->
175 binder_names = map fst (bagToList (collectMonoBinders bind))
176 ty_sigs = [sig | sig@(Sig name _ _) <- sigs]
179 An aside. The original version of @tcBindsAndThen@ which lacks a
180 combiner function, appears below. Though it is perfectly well
181 behaved, it cannot be typed by Haskell, because the recursive call is
182 at a different type to the definition itself. There aren't too many
183 examples of this, which is why I thought it worth preserving! [SLPJ]
188 -> TcM s (thing, LIE s, thing_ty))
189 -> TcM s ((TcHsBinds s, thing), LIE s, thing_ty)
191 tcBindsAndThen EmptyBinds do_next
192 = do_next `thenTc` \ (thing, lie, thing_ty) ->
193 returnTc ((EmptyBinds, thing), lie, thing_ty)
195 tcBindsAndThen (ThenBinds binds1 binds2) do_next
196 = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
197 `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
199 returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
201 tcBindsAndThen (MonoBind bind sigs is_rec) do_next
202 = tcBindAndThen bind sigs do_next
206 %************************************************************************
208 \subsection{tcBindWithSigs}
210 %************************************************************************
212 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
213 so all the clever stuff is in here.
215 * binder_names and mbind must define the same set of Names
217 * The Names in tc_ty_sigs must be a subset of binder_names
219 * The Ids in tc_ty_sigs don't necessarily have to have the same name
220 as the Name in the tc_ty_sig
229 -> (Name -> PragmaInfo)
230 -> TcM s (TcMonoBinds s, LIE s, [TcIdBndr s])
232 tcBindWithSigs top_lvl binder_names mbind tc_ty_sigs is_rec prag_info_fn
234 -- If typechecking the binds fails, then return with each
235 -- signature-less binder given type (forall a.a), to minimise subsequent
237 newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ alpha_tv ->
239 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
240 poly_ids = map mk_dummy binder_names
241 mk_dummy name = case maybeSig tc_ty_sigs name of
242 Just (TySigInfo _ poly_id _ _ _ _) -> poly_id -- Signature
243 Nothing -> mkUserId name forall_a_a -- No signature
245 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
248 -- Create a new identifier for each binder, with each being given
249 -- a fresh unique, and a type-variable type.
250 -- For "mono_lies" see comments about polymorphic recursion at the
251 -- end of the function.
252 mapAndUnzipNF_Tc mk_mono_id binder_names `thenNF_Tc` \ (mono_lies, mono_ids) ->
254 mono_lie = plusLIEs mono_lies
255 mono_id_tys = map idType mono_ids
258 -- TYPECHECK THE BINDINGS
259 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs `thenTc` \ (mbind', lie) ->
261 -- CHECK THAT THE SIGNATURES MATCH
262 -- (must do this before getTyVarsToGen)
263 checkSigMatch tc_ty_sigs `thenTc` \ sig_theta ->
265 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
266 -- The tyvars_not_to_gen are free in the environment, and hence
267 -- candidates for generalisation, but sometimes the monomorphism
268 -- restriction means we can't generalise them nevertheless
269 getTyVarsToGen is_unrestricted mono_id_tys lie `thenTc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
271 -- DEAL WITH TYPE VARIABLE KINDS
272 -- **** This step can do unification => keep other zonking after this ****
273 mapTc defaultUncommittedTyVar (tyVarSetToList tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
275 real_tyvars_to_gen = mkTyVarSet real_tyvars_to_gen_list
276 -- It's important that the final list
277 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
278 -- zonked, *including boxity*, because they'll be included in the forall types of
279 -- the polymorphic Ids, and instances of these Ids will be generated from them.
281 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
282 -- real_tyvars_to_gen
287 tcExtendGlobalTyVars (tyVarSetToList tyvars_not_to_gen) (
288 if null tc_ty_sigs then
289 -- No signatures, so just simplify the lie
290 -- NB: no signatures => no polymorphic recursion, so no
291 -- need to use mono_lies (which will be empty anyway)
292 tcSimplify (text "tcBinds1" <+> ppr binder_names)
293 top_lvl real_tyvars_to_gen lie `thenTc` \ (lie_free, dict_binds, lie_bound) ->
294 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
297 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
298 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
299 -- It's important that sig_theta is zonked, because
300 -- dict_id is later used to form the type of the polymorphic thing,
301 -- and forall-types must be zonked so far as their bound variables
305 -- The "givens" is the stuff available. We get that from
306 -- the context of the type signature, BUT ALSO the mono_lie
307 -- so that polymorphic recursion works right (see comments at end of fn)
308 givens = dicts_sig `plusLIE` mono_lie
311 -- Check that the needed dicts can be expressed in
312 -- terms of the signature ones
313 tcAddErrCtxt (bindSigsCtxt tysig_names) $
315 (ptext SLIT("type signature for") <+>
316 hsep (punctuate comma (map (quotes . ppr) binder_names)))
317 real_tyvars_to_gen givens lie `thenTc` \ (lie_free, dict_binds) ->
319 returnTc (lie_free, dict_binds, dict_ids)
321 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
323 ASSERT( not (any (isUnboxedTypeKind . tyVarKind) real_tyvars_to_gen_list) )
324 -- The instCantBeGeneralised stuff in tcSimplify should have
325 -- already raised an error if we're trying to generalise an unboxed tyvar
326 -- (NB: unboxed tyvars are always introduced along with a class constraint)
327 -- and it's better done there because we have more precise origin information.
328 -- That's why we just use an ASSERT here.
330 -- BUILD THE POLYMORPHIC RESULT IDs
331 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
333 exports = zipWith3 mk_export binder_names mono_ids zonked_mono_id_types
334 dict_tys = map tcIdType dicts_bound
336 mk_export binder_name mono_id zonked_mono_id_ty
337 | maybeToBool maybe_sig = (sig_tyvars, TcId sig_poly_id, TcId mono_id)
338 | otherwise = (real_tyvars_to_gen_list, TcId poly_id, TcId mono_id)
340 maybe_sig = maybeSig tc_ty_sigs binder_name
341 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _) = maybe_sig
342 poly_id = replacePragmaInfo (mkUserId binder_name poly_ty) (prag_info_fn binder_name)
343 poly_ty = mkForAllTys real_tyvars_to_gen_list $ mkFunTys dict_tys $ zonked_mono_id_ty
344 -- It's important to build a fully-zonked poly_ty, because
345 -- we'll slurp out its free type variables when extending the
346 -- local environment (tcExtendLocalValEnv); if it's not zonked
347 -- it appears to have free tyvars that aren't actually free at all.
352 AbsBinds real_tyvars_to_gen_list
355 (dict_binds `AndMonoBinds` mbind'),
357 [poly_id | (_, TcId poly_id, _) <- exports]
360 no_of_binders = length binder_names
362 mk_mono_id binder_name
363 | theres_a_signature -- There's a signature; and it's overloaded,
364 && not (null sig_theta) -- so make a Method
365 = tcAddSrcLoc sig_loc $
366 newMethodWithGivenTy SignatureOrigin
367 (TcId poly_id) (mkTyVarTys sig_tyvars)
368 sig_theta sig_tau `thenNF_Tc` \ (mono_lie, TcId mono_id) ->
369 -- A bit turgid to have to strip the TcId
370 returnNF_Tc (mono_lie, mono_id)
372 | otherwise -- No signature or not overloaded;
373 = tcAddSrcLoc (getSrcLoc binder_name) $
374 (if theres_a_signature then
375 returnNF_Tc sig_tau -- Non-overloaded signature; use its type
377 newTyVarTy kind -- No signature; use a new type variable
378 ) `thenNF_Tc` \ mono_id_ty ->
380 newLocalId (getOccName binder_name) mono_id_ty `thenNF_Tc` \ mono_id ->
381 returnNF_Tc (emptyLIE, mono_id)
383 maybe_sig = maybeSig tc_ty_sigs binder_name
384 theres_a_signature = maybeToBool maybe_sig
385 Just (TySigInfo name poly_id sig_tyvars sig_theta sig_tau sig_loc) = maybe_sig
387 tysig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
388 is_unrestricted = isUnRestrictedGroup tysig_names mbind
390 kind = case is_rec of
391 Recursive -> mkBoxedTypeKind -- Recursive, so no unboxed types
392 NonRecursive -> mkTypeKind -- Non-recursive, so we permit unboxed types
395 Polymorphic recursion
396 ~~~~~~~~~~~~~~~~~~~~~
397 The game plan for polymorphic recursion in the code above is
399 * Bind any variable for which we have a type signature
400 to an Id with a polymorphic type. Then when type-checking
401 the RHSs we'll make a full polymorphic call.
403 This fine, but if you aren't a bit careful you end up with a horrendous
404 amount of partial application and (worse) a huge space leak. For example:
406 f :: Eq a => [a] -> [a]
409 If we don't take care, after typechecking we get
411 f = /\a -> \d::Eq a -> let f' = f a d
415 Notice the the stupid construction of (f a d), which is of course
416 identical to the function we're executing. In this case, the
417 polymorphic recursion ins't being used (but that's a very common case).
419 This can lead to a massive space leak, from the following top-level defn:
424 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
425 f' is another thunk which evaluates to the same thing... and you end
426 up with a chain of identical values all hung onto by the CAF ff.
428 Solution: when typechecking the RHSs we always have in hand the
429 *monomorphic* Ids for each binding. So we just need to make sure that
430 if (Method f a d) shows up in the constraints emerging from (...f...)
431 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
432 to the "givens" when simplifying constraints. Thats' what the "mono_lies"
436 %************************************************************************
438 \subsection{getTyVarsToGen}
440 %************************************************************************
442 @getTyVarsToGen@ decides what type variables generalise over.
444 For a "restricted group" -- see the monomorphism restriction
445 for a definition -- we bind no dictionaries, and
446 remove from tyvars_to_gen any constrained type variables
448 *Don't* simplify dicts at this point, because we aren't going
449 to generalise over these dicts. By the time we do simplify them
450 we may well know more. For example (this actually came up)
452 f x = array ... xs where xs = [1,2,3,4,5]
453 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
454 stuff. If we simplify only at the f-binding (not the xs-binding)
455 we'll know that the literals are all Ints, and we can just produce
458 Find all the type variables involved in overloading, the
459 "constrained_tyvars". These are the ones we *aren't* going to
460 generalise. We must be careful about doing this:
462 (a) If we fail to generalise a tyvar which is not actually
463 constrained, then it will never, ever get bound, and lands
464 up printed out in interface files! Notorious example:
465 instance Eq a => Eq (Foo a b) where ..
466 Here, b is not constrained, even though it looks as if it is.
467 Another, more common, example is when there's a Method inst in
468 the LIE, whose type might very well involve non-overloaded
471 (b) On the other hand, we mustn't generalise tyvars which are constrained,
472 because we are going to pass on out the unmodified LIE, with those
473 tyvars in it. They won't be in scope if we've generalised them.
475 So we are careful, and do a complete simplification just to find the
476 constrained tyvars. We don't use any of the results, except to
477 find which tyvars are constrained.
480 getTyVarsToGen is_unrestricted mono_id_tys lie
481 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
482 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
484 tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusTyVarSet` free_tyvars
488 returnTc (emptyTyVarSet, tyvars_to_gen)
490 tcSimplify (text "getTVG") NotTopLevel tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
492 -- ASSERT: dicts_sig is already zonked!
493 constrained_tyvars = foldrBag (unionTyVarSets . tyVarsOfInst) emptyTyVarSet constrained_dicts
494 reduced_tyvars_to_gen = tyvars_to_gen `minusTyVarSet` constrained_tyvars
496 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
501 isUnRestrictedGroup :: [Name] -- Signatures given for these
505 is_elem v vs = isIn "isUnResMono" v vs
507 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
508 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
509 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
510 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
511 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
512 isUnRestrictedGroup sigs mb2
513 isUnRestrictedGroup sigs EmptyMonoBinds = True
516 @defaultUncommittedTyVar@ checks for generalisation over unboxed
517 types, and defaults any TypeKind TyVars to BoxedTypeKind.
520 defaultUncommittedTyVar tyvar
521 | isTypeKind (tyVarKind tyvar)
522 = newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ boxed_tyvar ->
523 unifyTauTy (mkTyVarTy boxed_tyvar) (mkTyVarTy tyvar) `thenTc_`
531 %************************************************************************
533 \subsection{tcMonoBind}
535 %************************************************************************
537 @tcMonoBinds@ deals with a single @MonoBind@.
538 The signatures have been dealt with already.
541 tcMonoBinds :: RenamedMonoBinds
542 -> [Name] -> [TcIdBndr s]
544 -> TcM s (TcMonoBinds s, LIE s)
546 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs
547 = tcExtendLocalValEnv binder_names mono_ids (
551 sig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
552 sig_ids = [id | (TySigInfo _ id _ _ _ _) <- tc_ty_sigs]
554 tc_mono_binds EmptyMonoBinds = returnTc (EmptyMonoBinds, emptyLIE)
556 tc_mono_binds (AndMonoBinds mb1 mb2)
557 = tc_mono_binds mb1 `thenTc` \ (mb1a, lie1) ->
558 tc_mono_binds mb2 `thenTc` \ (mb2a, lie2) ->
559 returnTc (AndMonoBinds mb1a mb2a, lie1 `plusLIE` lie2)
561 tc_mono_binds (FunMonoBind name inf matches locn)
563 tcLookupLocalValueOK "tc_mono_binds" name `thenNF_Tc` \ id ->
565 -- Before checking the RHS, extend the envt with
566 -- bindings for the *polymorphic* Ids from any type signatures
567 tcExtendLocalValEnv sig_names sig_ids $
568 tcMatchesFun name (idType id) matches `thenTc` \ (matches', lie) ->
570 returnTc (FunMonoBind (TcId id) inf matches' locn, lie)
572 tc_mono_binds bind@(PatMonoBind pat grhss_and_binds locn)
574 tcAddErrCtxt (patMonoBindsCtxt bind) $
575 tcPat pat `thenTc` \ (pat2, lie_pat, pat_ty) ->
577 -- Before checking the RHS, but after the pattern, extend the envt with
578 -- bindings for the *polymorphic* Ids from any type signatures
579 tcExtendLocalValEnv sig_names sig_ids $
580 tcGRHSsAndBinds pat_ty grhss_and_binds `thenTc` \ (grhss_and_binds2, lie) ->
581 returnTc (PatMonoBind pat2 grhss_and_binds2 locn,
585 %************************************************************************
587 \subsection{Signatures}
589 %************************************************************************
591 @tcSigs@ checks the signatures for validity, and returns a list of
592 {\em freshly-instantiated} signatures. That is, the types are already
593 split up, and have fresh type variables installed. All non-type-signature
594 "RenamedSigs" are ignored.
596 The @TcSigInfo@ contains @TcTypes@ because they are unified with
597 the variable's type, and after that checked to see whether they've
603 Name -- N, the Name in corresponding binding
604 (TcIdBndr s) -- *Polymorphic* binder for this value...
605 -- Usually has name = N, but doesn't have to.
612 maybeSig :: [TcSigInfo s] -> Name -> Maybe (TcSigInfo s)
613 -- Search for a particular signature
614 maybeSig [] name = Nothing
615 maybeSig (sig@(TySigInfo sig_name _ _ _ _ _) : sigs) name
616 | name == sig_name = Just sig
617 | otherwise = maybeSig sigs name
622 tcTySig :: (Name -> PragmaInfo)
624 -> TcM s (TcSigInfo s)
626 tcTySig prag_info_fn (Sig v ty src_loc)
627 = tcAddSrcLoc src_loc $
628 tcHsType ty `thenTc` \ sigma_ty ->
630 -- Convert from Type to TcType
631 tcInstSigType sigma_ty `thenNF_Tc` \ sigma_tc_ty ->
633 poly_id = replacePragmaInfo (mkUserId v sigma_tc_ty) (prag_info_fn v)
635 -- Instantiate this type
636 -- It's important to do this even though in the error-free case
637 -- we could just split the sigma_tc_ty (since the tyvars don't
638 -- unified with anything). But in the case of an error, when
639 -- the tyvars *do* get unified with something, we want to carry on
640 -- typechecking the rest of the program with the function bound
641 -- to a pristine type, namely sigma_tc_ty
642 tcInstSigTcType sigma_tc_ty `thenNF_Tc` \ (tyvars, rho) ->
644 (theta, tau) = splitRhoTy rho
645 -- This splitSigmaTy tries hard to make sure that tau' is a type synonym
646 -- wherever possible, which can improve interface files.
648 returnTc (TySigInfo v poly_id tyvars theta tau src_loc)
651 @checkSigMatch@ does the next step in checking signature matching.
652 The tau-type part has already been unified. What we do here is to
653 check that this unification has not over-constrained the (polymorphic)
654 type variables of the original signature type.
656 The error message here is somewhat unsatisfactory, but it'll do for
661 = returnTc (error "checkSigMatch")
663 checkSigMatch tc_ty_sigs@( sig1@(TySigInfo _ id1 _ theta1 _ _) : all_sigs_but_first )
664 = -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
665 -- Doesn't affect substitution
666 mapTc check_one_sig tc_ty_sigs `thenTc_`
668 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
669 -- The type signatures on a mutually-recursive group of definitions
670 -- must all have the same context (or none).
672 -- We unify them because, with polymorphic recursion, their types
673 -- might not otherwise be related. This is a rather subtle issue.
675 mapTc check_one_cxt all_sigs_but_first `thenTc_`
679 sig1_dict_tys = mk_dict_tys theta1
680 n_sig1_dict_tys = length sig1_dict_tys
682 check_one_cxt sig@(TySigInfo _ id _ theta _ src_loc)
683 = tcAddSrcLoc src_loc $
684 tcAddErrCtxt (sigContextsCtxt id1 id) $
685 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
686 sigContextsErr `thenTc_`
687 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
689 this_sig_dict_tys = mk_dict_tys theta
691 check_one_sig (TySigInfo name id sig_tyvars _ sig_tau src_loc)
692 = tcAddSrcLoc src_loc $
693 tcAddErrCtxt (sigCtxt id) $
694 checkSigTyVars sig_tyvars sig_tau
696 mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
700 @checkSigTyVars@ is used after the type in a type signature has been unified with
701 the actual type found. It then checks that the type variables of the type signature
703 (a) still all type variables
704 eg matching signature [a] against inferred type [(p,q)]
705 [then a will be unified to a non-type variable]
707 (b) still all distinct
708 eg matching signature [(a,b)] against inferred type [(p,p)]
709 [then a and b will be unified together]
711 (c) not mentioned in the environment
712 eg the signature for f in this:
718 Here, f is forced to be monorphic by the free occurence of x.
720 Before doing this, the substitution is applied to the signature type variable.
722 We used to have the notion of a "DontBind" type variable, which would
723 only be bound to itself or nothing. Then points (a) and (b) were
724 self-checking. But it gave rise to bogus consequential error messages.
727 f = (*) -- Monomorphic
732 Here, we get a complaint when checking the type signature for g,
733 that g isn't polymorphic enough; but then we get another one when
734 dealing with the (Num x) context arising from f's definition;
735 we try to unify x with Int (to default it), but find that x has already
736 been unified with the DontBind variable "a" from g's signature.
737 This is really a problem with side-effecting unification; we'd like to
738 undo g's effects when its type signature fails, but unification is done
739 by side effect, so we can't (easily).
741 So we revert to ordinary type variables for signatures, and try to
742 give a helpful message in checkSigTyVars.
745 checkSigTyVars :: [TcTyVar s] -- The original signature type variables
746 -> TcType s -- signature type (for err msg)
747 -> TcM s [TcTyVar s] -- Zonked signature type variables
749 checkSigTyVars sig_tyvars sig_tau
750 = mapNF_Tc zonkTcTyVar sig_tyvars `thenNF_Tc` \ sig_tys ->
752 sig_tyvars' = map (getTyVar "checkSigTyVars") sig_tys
755 -- Check points (a) and (b)
756 checkTcM (all isTyVarTy sig_tys && hasNoDups sig_tyvars')
757 (zonkTcType sig_tau `thenNF_Tc` \ sig_tau' ->
758 failWithTc (badMatchErr sig_tau sig_tau')
762 -- We want to report errors in terms of the original signature tyvars,
763 -- ie sig_tyvars, NOT sig_tyvars'. sig_tyvars' correspond
764 -- 1-1 with sig_tyvars, so we can just map back.
765 tcGetGlobalTyVars `thenNF_Tc` \ globals ->
767 mono_tyvars' = [sig_tv' | sig_tv' <- sig_tyvars',
768 sig_tv' `elementOfTyVarSet` globals]
770 mono_tyvars = map (assoc "checkSigTyVars" (sig_tyvars' `zip` sig_tyvars)) mono_tyvars'
772 checkTcM (null mono_tyvars')
773 (failWithTc (notAsPolyAsSigErr sig_tau mono_tyvars)) `thenTc_`
779 %************************************************************************
781 \subsection{SPECIALIZE pragmas}
783 %************************************************************************
786 @tcPragmaSigs@ munches up the "signatures" that arise through *user*
787 pragmas. It is convenient for them to appear in the @[RenamedSig]@
788 part of a binding because then the same machinery can be used for
789 moving them into place as is done for type signatures.
792 tcPragmaSigs :: [RenamedSig] -- The pragma signatures
793 -> TcM s (Name -> PragmaInfo, -- Maps name to the appropriate PragmaInfo
797 -- For now we just deal with INLINE pragmas
798 tcPragmaSigs sigs = returnTc (prag_fn, EmptyMonoBinds, emptyLIE )
800 prag_fn name | any has_inline sigs = IWantToBeINLINEd
801 | otherwise = NoPragmaInfo
803 has_inline (InlineSig n _) = (n == name)
804 has_inline other = False
809 = mapAndUnzip3Tc tcPragmaSig sigs `thenTc` \ (names_w_id_infos, binds, lies) ->
811 name_to_info name = foldr ($) noIdInfo
812 [info_fn | (n,info_fn) <- names_w_id_infos, n==name]
814 returnTc (name_to_info,
815 foldr ThenBinds EmptyBinds binds,
816 foldr plusLIE emptyLIE lies)
819 Here are the easy cases for tcPragmaSigs
822 tcPragmaSig (InlineSig name loc)
823 = returnTc ((name, addUnfoldInfo (iWantToBeINLINEd UnfoldAlways)), EmptyBinds, emptyLIE)
824 tcPragmaSig (MagicUnfoldingSig name string loc)
825 = returnTc ((name, addUnfoldInfo (mkMagicUnfolding string)), EmptyBinds, emptyLIE)
828 The interesting case is for SPECIALISE pragmas. There are two forms.
829 Here's the first form:
831 f :: Ord a => [a] -> b -> b
832 {-# SPECIALIZE f :: [Int] -> b -> b #-}
835 For this we generate:
837 f* = /\ b -> let d1 = ...
841 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
842 retain a right-hand-side that the simplifier will otherwise discard as
843 dead code... the simplifier has a flag that tells it not to discard
844 SpecPragmaId bindings.
846 In this case the f* retains a call-instance of the overloaded
847 function, f, (including appropriate dictionaries) so that the
848 specialiser will subsequently discover that there's a call of @f@ at
849 Int, and will create a specialisation for @f@. After that, the
850 binding for @f*@ can be discarded.
852 The second form is this:
854 f :: Ord a => [a] -> b -> b
855 {-# SPECIALIZE f :: [Int] -> b -> b = g #-}
858 Here @g@ is specified as a function that implements the specialised
859 version of @f@. Suppose that g has type (a->b->b); that is, g's type
860 is more general than that required. For this we generate
862 f@Int = /\b -> g Int b
866 Here @f@@Int@ is a SpecId, the specialised version of @f@. It inherits
867 f's export status etc. @f*@ is a SpecPragmaId, as before, which just serves
868 to prevent @f@@Int@ from being discarded prematurely. After specialisation,
869 if @f@@Int@ is going to be used at all it will be used explicitly, so the simplifier can
870 discard the f* binding.
872 Actually, there is really only point in giving a SPECIALISE pragma on exported things,
873 and the simplifer won't discard SpecIds for exporte things anyway, so maybe this is
877 tcPragmaSig (SpecSig name poly_ty maybe_spec_name src_loc)
878 = tcAddSrcLoc src_loc $
879 tcAddErrCtxt (valSpecSigCtxt name spec_ty) $
881 -- Get and instantiate its alleged specialised type
882 tcHsType poly_ty `thenTc` \ sig_sigma ->
883 tcInstSigType sig_sigma `thenNF_Tc` \ sig_ty ->
885 (sig_tyvars, sig_theta, sig_tau) = splitSigmaTy sig_ty
886 origin = ValSpecOrigin name
889 -- Check that the SPECIALIZE pragma had an empty context
890 checkTc (null sig_theta)
891 (panic "SPECIALIZE non-empty context (ToDo: msg)") `thenTc_`
893 -- Get and instantiate the type of the id mentioned
894 tcLookupLocalValueOK "tcPragmaSig" name `thenNF_Tc` \ main_id ->
895 tcInstSigType [] (idType main_id) `thenNF_Tc` \ main_ty ->
897 (main_tyvars, main_rho) = splitForAllTys main_ty
898 (main_theta,main_tau) = splitRhoTy main_rho
899 main_arg_tys = mkTyVarTys main_tyvars
902 -- Check that the specialised type is indeed an instance of
903 -- the type of the main function.
904 unifyTauTy sig_tau main_tau `thenTc_`
905 checkSigTyVars sig_tyvars sig_tau `thenTc_`
907 -- Check that the type variables of the polymorphic function are
908 -- either left polymorphic, or instantiate to ground type.
909 -- Also check that the overloaded type variables are instantiated to
910 -- ground type; or equivalently that all dictionaries have ground type
911 zonkTcTypes main_arg_tys `thenNF_Tc` \ main_arg_tys' ->
912 zonkTcThetaType main_theta `thenNF_Tc` \ main_theta' ->
913 tcAddErrCtxt (specGroundnessCtxt main_arg_tys')
914 (checkTc (all isGroundOrTyVarTy main_arg_tys')) `thenTc_`
915 tcAddErrCtxt (specContextGroundnessCtxt main_theta')
916 (checkTc (and [isGroundTy ty | (_,ty) <- theta'])) `thenTc_`
918 -- Build the SpecPragmaId; it is the thing that makes sure we
919 -- don't prematurely dead-code-eliminate the binding we are really interested in.
920 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_pragma_id ->
922 -- Build a suitable binding; depending on whether we were given
923 -- a value (Maybe Name) to be used as the specialisation.
925 Nothing -> -- No implementation function specified
927 -- Make a Method inst for the occurrence of the overloaded function
928 newMethodWithGivenTy (OccurrenceOf name)
929 (TcId main_id) main_arg_tys main_rho `thenNF_Tc` \ (lie, meth_id) ->
932 pseudo_bind = VarMonoBind spec_pragma_id pseudo_rhs
933 pseudo_rhs = mkHsTyLam sig_tyvars (HsVar (TcId meth_id))
935 returnTc (pseudo_bind, lie, \ info -> info)
937 Just spec_name -> -- Use spec_name as the specialisation value ...
939 -- Type check a simple occurrence of the specialised Id
940 tcId spec_name `thenTc` \ (spec_body, spec_lie, spec_tau) ->
942 -- Check that it has the correct type, and doesn't constrain the
943 -- signature variables at all
944 unifyTauTy sig_tau spec_tau `thenTc_`
945 checkSigTyVars sig_tyvars sig_tau `thenTc_`
947 -- Make a local SpecId to bind to applied spec_id
948 newSpecId main_id main_arg_tys sig_ty `thenNF_Tc` \ local_spec_id ->
951 spec_rhs = mkHsTyLam sig_tyvars spec_body
952 spec_binds = VarMonoBind local_spec_id spec_rhs
954 VarMonoBind spec_pragma_id (HsVar (TcId local_spec_id))
955 spec_info = SpecInfo spec_tys (length main_theta) local_spec_id
957 returnTc ((name, addSpecInfo spec_info), spec_binds, spec_lie)
962 %************************************************************************
964 \subsection[TcBinds-errors]{Error contexts and messages}
966 %************************************************************************
970 patMonoBindsCtxt bind
971 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
973 -----------------------------------------------
975 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
976 nest 4 (ppr v <+> ptext SLIT(" ::") <+> ppr ty)]
978 -----------------------------------------------
979 notAsPolyAsSigErr sig_tau mono_tyvars
980 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
981 4 (vcat [text "Can't for-all the type variable(s)" <+>
982 pprQuotedList mono_tyvars,
983 text "in the type" <+> quotes (ppr sig_tau)
986 -----------------------------------------------
987 badMatchErr sig_ty inferred_ty
988 = hang (ptext SLIT("Type signature doesn't match inferred type"))
989 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
990 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
993 -----------------------------------------------
995 = sep [ptext SLIT("When checking the type signature for"), quotes (ppr id)]
998 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
1000 -----------------------------------------------
1002 = ptext SLIT("Mismatched contexts")
1003 sigContextsCtxt s1 s2
1004 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
1005 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
1006 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
1008 -----------------------------------------------
1010 = panic "specGroundnessCtxt"
1012 --------------------------------------------
1013 specContextGroundnessCtxt -- err_ctxt dicts
1014 = panic "specContextGroundnessCtxt"
1017 sep [hsep [ptext SLIT("In the SPECIALIZE pragma for"), ppr name],
1018 hcat [ptext SLIT(" specialised to the type"), ppr spec_ty],
1020 ptext SLIT("... not all overloaded type variables were instantiated"),
1021 ptext SLIT("to ground types:")])
1022 4 (vcat [hsep [ppr c, ppr t]
1023 | (c,t) <- map getDictClassAndType dicts])
1025 (name, spec_ty, locn, pp_spec_id)
1027 ValSpecSigCtxt n ty loc -> (n, ty, loc, \ x -> empty)
1028 ValSpecSpecIdCtxt n ty spec loc ->
1030 hsep [ptext SLIT("... type of explicit id"), ppr spec])