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 )
14 import {-# SOURCE #-} TcExpr ( tcExpr )
16 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..), InPat(..),
17 collectMonoBinders, andMonoBinds
19 import RnHsSyn ( RenamedHsBinds, RenamedSig(..),
22 import TcHsSyn ( TcHsBinds, TcMonoBinds,
23 TcIdOcc(..), TcIdBndr,
28 import Inst ( Inst, LIE, emptyLIE, plusLIE, plusLIEs, InstOrigin(..),
29 newDicts, tyVarsOfInst, instToId, newMethodWithGivenTy,
32 import TcEnv ( tcExtendLocalValEnv, tcLookupLocalValueOK,
33 newLocalId, newSpecPragmaId,
34 tcGetGlobalTyVars, tcExtendGlobalTyVars
36 import TcMatches ( tcMatchesFun )
37 import TcSimplify ( tcSimplify, tcSimplifyAndCheck )
38 import TcMonoType ( tcHsType )
39 import TcPat ( tcPat )
40 import TcSimplify ( bindInstsOfLocalFuns )
41 import TcType ( TcType, TcThetaType, TcTauType,
43 newTyVarTy, newTcTyVar, tcInstSigType, tcInstSigTcType,
44 zonkTcType, zonkTcTypes, zonkTcThetaType, zonkTcTyVar
46 import Unify ( unifyTauTy, unifyTauTyLists )
48 import Kind ( isUnboxedTypeKind, mkTypeKind, isTypeKind, mkBoxedTypeKind )
49 import MkId ( mkUserId )
50 import Id ( idType, idName, idInfo, replaceIdInfo )
51 import IdInfo ( IdInfo, noIdInfo, setInlinePragInfo, InlinePragInfo(..) )
52 import Maybes ( maybeToBool, assocMaybe )
53 import Name ( getOccName, getSrcLoc, Name )
54 import Type ( mkTyVarTy, mkTyVarTys, isTyVarTy, tyVarsOfTypes,
55 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar, mkDictTy,
56 splitRhoTy, mkForAllTy, splitForAllTys
58 import TyVar ( TyVar, tyVarKind, mkTyVarSet, minusTyVarSet, emptyTyVarSet,
59 elementOfTyVarSet, unionTyVarSets, tyVarSetToList
61 import Bag ( bagToList, foldrBag, )
62 import Util ( isIn, hasNoDups, assoc )
63 import Unique ( Unique )
64 import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
65 import SrcLoc ( SrcLoc )
70 %************************************************************************
72 \subsection{Type-checking bindings}
74 %************************************************************************
76 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
77 it needs to know something about the {\em usage} of the things bound,
78 so that it can create specialisations of them. So @tcBindsAndThen@
79 takes a function which, given an extended environment, E, typechecks
80 the scope of the bindings returning a typechecked thing and (most
81 important) an LIE. It is this LIE which is then used as the basis for
82 specialising the things bound.
84 @tcBindsAndThen@ also takes a "combiner" which glues together the
85 bindings and the "thing" to make a new "thing".
87 The real work is done by @tcBindWithSigsAndThen@.
89 Recursive and non-recursive binds are handled in essentially the same
90 way: because of uniques there are no scoping issues left. The only
91 difference is that non-recursive bindings can bind primitive values.
93 Even for non-recursive binding groups we add typings for each binder
94 to the LVE for the following reason. When each individual binding is
95 checked the type of its LHS is unified with that of its RHS; and
96 type-checking the LHS of course requires that the binder is in scope.
98 At the top-level the LIE is sure to contain nothing but constant
99 dictionaries, which we resolve at the module level.
102 tcTopBindsAndThen, tcBindsAndThen
103 :: (RecFlag -> TcMonoBinds s -> this -> that) -- Combinator
105 -> TcM s (this, LIE s)
106 -> TcM s (that, LIE s)
108 tcTopBindsAndThen = tc_binds_and_then TopLevel
109 tcBindsAndThen = tc_binds_and_then NotTopLevel
111 tc_binds_and_then top_lvl combiner binds do_next
112 = tcBinds top_lvl binds `thenTc` \ (mbinds1, binds_lie, env, ids) ->
115 -- Now do whatever happens next, in the augmented envt
116 do_next `thenTc` \ (thing, thing_lie) ->
118 -- Create specialisations of functions bound here
119 -- Nota Bene: we glom the bindings all together in a single
120 -- recursive group ("recursive" passed to combiner, below)
121 -- so that we can do thsi bindInsts thing once for all the bindings
122 -- and the thing inside. This saves a quadratic-cost algorithm
123 -- when there's a long sequence of bindings.
124 bindInstsOfLocalFuns (binds_lie `plusLIE` thing_lie) ids `thenTc` \ (final_lie, mbinds2) ->
128 final_mbinds = mbinds1 `AndMonoBinds` mbinds2
130 returnTc (combiner Recursive final_mbinds thing, final_lie)
132 tcBinds :: TopLevelFlag
134 -> TcM s (TcMonoBinds s, LIE s, TcEnv s, [TcIdBndr s])
135 -- The envt is the envt with binders in scope
136 -- The binders are those bound by this group of bindings
138 tcBinds top_lvl EmptyBinds
139 = tcGetEnv `thenNF_Tc` \ env ->
140 returnTc (EmptyMonoBinds, emptyLIE, env, [])
142 -- Short-cut for the rather common case of an empty bunch of bindings
143 tcBinds top_lvl (MonoBind EmptyMonoBinds sigs is_rec)
144 = tcGetEnv `thenNF_Tc` \ env ->
145 returnTc (EmptyMonoBinds, emptyLIE, env, [])
147 tcBinds top_lvl (ThenBinds binds1 binds2)
148 = tcBinds top_lvl binds1 `thenTc` \ (mbinds1, lie1, env1, ids1) ->
150 tcBinds top_lvl binds2 `thenTc` \ (mbinds2, lie2, env2, ids2) ->
151 returnTc (mbinds1 `AndMonoBinds` mbinds2, lie1 `plusLIE` lie2, env2, ids1++ids2)
153 tcBinds top_lvl (MonoBind bind sigs is_rec)
154 = fixTc (\ ~(prag_info_fn, _) ->
155 -- This is the usual prag_info fix; the PragmaInfo field of an Id
156 -- is not inspected till ages later in the compiler, so there
157 -- should be no black-hole problems here.
159 -- TYPECHECK THE SIGNATURES
160 mapTc tcTySig ty_sigs `thenTc` \ tc_ty_sigs ->
162 tcBindWithSigs top_lvl binder_names bind
163 tc_ty_sigs is_rec prag_info_fn `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
165 -- Extend the environment to bind the new polymorphic Ids
166 tcExtendLocalValEnv binder_names poly_ids $
168 -- Build bindings and IdInfos corresponding to user pragmas
169 tcPragmaSigs sigs `thenTc` \ (prag_info_fn, prag_binds, prag_lie) ->
171 -- Catch the environment and return
172 tcGetEnv `thenNF_Tc` \ env ->
173 returnTc (prag_info_fn, (poly_binds `AndMonoBinds` prag_binds,
174 poly_lie `plusLIE` prag_lie,
176 ) ) `thenTc` \ (_, result) ->
179 binder_names = map fst (bagToList (collectMonoBinders bind))
180 ty_sigs = [sig | sig@(Sig name _ _) <- sigs]
183 An aside. The original version of @tcBindsAndThen@ which lacks a
184 combiner function, appears below. Though it is perfectly well
185 behaved, it cannot be typed by Haskell, because the recursive call is
186 at a different type to the definition itself. There aren't too many
187 examples of this, which is why I thought it worth preserving! [SLPJ]
192 -> TcM s (thing, LIE s, thing_ty))
193 -> TcM s ((TcHsBinds s, thing), LIE s, thing_ty)
195 tcBindsAndThen EmptyBinds do_next
196 = do_next `thenTc` \ (thing, lie, thing_ty) ->
197 returnTc ((EmptyBinds, thing), lie, thing_ty)
199 tcBindsAndThen (ThenBinds binds1 binds2) do_next
200 = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
201 `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
203 returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
205 tcBindsAndThen (MonoBind bind sigs is_rec) do_next
206 = tcBindAndThen bind sigs do_next
210 %************************************************************************
212 \subsection{tcBindWithSigs}
214 %************************************************************************
216 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
217 so all the clever stuff is in here.
219 * binder_names and mbind must define the same set of Names
221 * The Names in tc_ty_sigs must be a subset of binder_names
223 * The Ids in tc_ty_sigs don't necessarily have to have the same name
224 as the Name in the tc_ty_sig
234 -> TcM s (TcMonoBinds s, LIE s, [TcIdBndr s])
236 tcBindWithSigs top_lvl binder_names mbind tc_ty_sigs is_rec prag_info_fn
238 -- If typechecking the binds fails, then return with each
239 -- signature-less binder given type (forall a.a), to minimise subsequent
241 newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ alpha_tv ->
243 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
244 poly_ids = map mk_dummy binder_names
245 mk_dummy name = case maybeSig tc_ty_sigs name of
246 Just (TySigInfo _ poly_id _ _ _ _) -> poly_id -- Signature
247 Nothing -> mkUserId name forall_a_a -- No signature
249 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
252 -- Create a new identifier for each binder, with each being given
253 -- a fresh unique, and a type-variable type.
254 -- For "mono_lies" see comments about polymorphic recursion at the
255 -- end of the function.
256 mapAndUnzipNF_Tc mk_mono_id binder_names `thenNF_Tc` \ (mono_lies, mono_ids) ->
258 mono_lie = plusLIEs mono_lies
259 mono_id_tys = map idType mono_ids
262 -- TYPECHECK THE BINDINGS
263 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs `thenTc` \ (mbind', lie) ->
265 -- CHECK THAT THE SIGNATURES MATCH
266 -- (must do this before getTyVarsToGen)
267 checkSigMatch tc_ty_sigs `thenTc` \ sig_theta ->
269 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
270 -- The tyvars_not_to_gen are free in the environment, and hence
271 -- candidates for generalisation, but sometimes the monomorphism
272 -- restriction means we can't generalise them nevertheless
273 getTyVarsToGen is_unrestricted mono_id_tys lie `thenTc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
275 -- DEAL WITH TYPE VARIABLE KINDS
276 -- **** This step can do unification => keep other zonking after this ****
277 mapTc defaultUncommittedTyVar (tyVarSetToList tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
279 real_tyvars_to_gen = mkTyVarSet real_tyvars_to_gen_list
280 -- It's important that the final list
281 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
282 -- zonked, *including boxity*, because they'll be included in the forall types of
283 -- the polymorphic Ids, and instances of these Ids will be generated from them.
285 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
286 -- real_tyvars_to_gen
291 tcExtendGlobalTyVars (tyVarSetToList tyvars_not_to_gen) (
292 if null tc_ty_sigs then
293 -- No signatures, so just simplify the lie
294 -- NB: no signatures => no polymorphic recursion, so no
295 -- need to use mono_lies (which will be empty anyway)
296 tcSimplify (text "tcBinds1" <+> ppr binder_names)
297 top_lvl real_tyvars_to_gen lie `thenTc` \ (lie_free, dict_binds, lie_bound) ->
298 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
301 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
302 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
303 -- It's important that sig_theta is zonked, because
304 -- dict_id is later used to form the type of the polymorphic thing,
305 -- and forall-types must be zonked so far as their bound variables
309 -- The "givens" is the stuff available. We get that from
310 -- the context of the type signature, BUT ALSO the mono_lie
311 -- so that polymorphic recursion works right (see comments at end of fn)
312 givens = dicts_sig `plusLIE` mono_lie
315 -- Check that the needed dicts can be expressed in
316 -- terms of the signature ones
317 tcAddErrCtxt (bindSigsCtxt tysig_names) $
319 (ptext SLIT("type signature for") <+>
320 hsep (punctuate comma (map (quotes . ppr) binder_names)))
321 real_tyvars_to_gen givens lie `thenTc` \ (lie_free, dict_binds) ->
323 returnTc (lie_free, dict_binds, dict_ids)
325 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
327 ASSERT( not (any (isUnboxedTypeKind . tyVarKind) real_tyvars_to_gen_list) )
328 -- The instCantBeGeneralised stuff in tcSimplify should have
329 -- already raised an error if we're trying to generalise an unboxed tyvar
330 -- (NB: unboxed tyvars are always introduced along with a class constraint)
331 -- and it's better done there because we have more precise origin information.
332 -- That's why we just use an ASSERT here.
334 -- BUILD THE POLYMORPHIC RESULT IDs
335 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
337 exports = zipWith3 mk_export binder_names mono_ids zonked_mono_id_types
338 dict_tys = map tcIdType dicts_bound
340 mk_export binder_name mono_id zonked_mono_id_ty
341 = (tyvars, TcId (replaceIdInfo poly_id (prag_info_fn binder_name)), TcId mono_id)
343 (tyvars, poly_id) = case maybeSig tc_ty_sigs binder_name of
344 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _) -> (sig_tyvars, sig_poly_id)
345 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
347 new_poly_id = mkUserId binder_name poly_ty
348 poly_ty = mkForAllTys real_tyvars_to_gen_list $ mkFunTys dict_tys $ zonked_mono_id_ty
349 -- It's important to build a fully-zonked poly_ty, because
350 -- we'll slurp out its free type variables when extending the
351 -- local environment (tcExtendLocalValEnv); if it's not zonked
352 -- it appears to have free tyvars that aren't actually free at all.
357 AbsBinds real_tyvars_to_gen_list
360 (dict_binds `AndMonoBinds` mbind'),
362 [poly_id | (_, TcId poly_id, _) <- exports]
365 no_of_binders = length binder_names
367 mk_mono_id binder_name
368 | theres_a_signature -- There's a signature; and it's overloaded,
369 && not (null sig_theta) -- so make a Method
370 = tcAddSrcLoc sig_loc $
371 newMethodWithGivenTy SignatureOrigin
372 (TcId poly_id) (mkTyVarTys sig_tyvars)
373 sig_theta sig_tau `thenNF_Tc` \ (mono_lie, TcId mono_id) ->
374 -- A bit turgid to have to strip the TcId
375 returnNF_Tc (mono_lie, mono_id)
377 | otherwise -- No signature or not overloaded;
378 = tcAddSrcLoc (getSrcLoc binder_name) $
379 (if theres_a_signature then
380 returnNF_Tc sig_tau -- Non-overloaded signature; use its type
382 newTyVarTy kind -- No signature; use a new type variable
383 ) `thenNF_Tc` \ mono_id_ty ->
385 newLocalId (getOccName binder_name) mono_id_ty `thenNF_Tc` \ mono_id ->
386 returnNF_Tc (emptyLIE, mono_id)
388 maybe_sig = maybeSig tc_ty_sigs binder_name
389 theres_a_signature = maybeToBool maybe_sig
390 Just (TySigInfo name poly_id sig_tyvars sig_theta sig_tau sig_loc) = maybe_sig
392 tysig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
393 is_unrestricted = isUnRestrictedGroup tysig_names mbind
395 kind = case is_rec of
396 Recursive -> mkBoxedTypeKind -- Recursive, so no unboxed types
397 NonRecursive -> mkTypeKind -- Non-recursive, so we permit unboxed types
400 Polymorphic recursion
401 ~~~~~~~~~~~~~~~~~~~~~
402 The game plan for polymorphic recursion in the code above is
404 * Bind any variable for which we have a type signature
405 to an Id with a polymorphic type. Then when type-checking
406 the RHSs we'll make a full polymorphic call.
408 This fine, but if you aren't a bit careful you end up with a horrendous
409 amount of partial application and (worse) a huge space leak. For example:
411 f :: Eq a => [a] -> [a]
414 If we don't take care, after typechecking we get
416 f = /\a -> \d::Eq a -> let f' = f a d
420 Notice the the stupid construction of (f a d), which is of course
421 identical to the function we're executing. In this case, the
422 polymorphic recursion ins't being used (but that's a very common case).
424 This can lead to a massive space leak, from the following top-level defn:
429 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
430 f' is another thunk which evaluates to the same thing... and you end
431 up with a chain of identical values all hung onto by the CAF ff.
433 Solution: when typechecking the RHSs we always have in hand the
434 *monomorphic* Ids for each binding. So we just need to make sure that
435 if (Method f a d) shows up in the constraints emerging from (...f...)
436 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
437 to the "givens" when simplifying constraints. Thats' what the "mono_lies"
441 %************************************************************************
443 \subsection{getTyVarsToGen}
445 %************************************************************************
447 @getTyVarsToGen@ decides what type variables generalise over.
449 For a "restricted group" -- see the monomorphism restriction
450 for a definition -- we bind no dictionaries, and
451 remove from tyvars_to_gen any constrained type variables
453 *Don't* simplify dicts at this point, because we aren't going
454 to generalise over these dicts. By the time we do simplify them
455 we may well know more. For example (this actually came up)
457 f x = array ... xs where xs = [1,2,3,4,5]
458 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
459 stuff. If we simplify only at the f-binding (not the xs-binding)
460 we'll know that the literals are all Ints, and we can just produce
463 Find all the type variables involved in overloading, the
464 "constrained_tyvars". These are the ones we *aren't* going to
465 generalise. We must be careful about doing this:
467 (a) If we fail to generalise a tyvar which is not actually
468 constrained, then it will never, ever get bound, and lands
469 up printed out in interface files! Notorious example:
470 instance Eq a => Eq (Foo a b) where ..
471 Here, b is not constrained, even though it looks as if it is.
472 Another, more common, example is when there's a Method inst in
473 the LIE, whose type might very well involve non-overloaded
476 (b) On the other hand, we mustn't generalise tyvars which are constrained,
477 because we are going to pass on out the unmodified LIE, with those
478 tyvars in it. They won't be in scope if we've generalised them.
480 So we are careful, and do a complete simplification just to find the
481 constrained tyvars. We don't use any of the results, except to
482 find which tyvars are constrained.
485 getTyVarsToGen is_unrestricted mono_id_tys lie
486 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
487 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
489 tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusTyVarSet` free_tyvars
493 returnTc (emptyTyVarSet, tyvars_to_gen)
495 tcSimplify (text "getTVG") NotTopLevel tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
497 -- ASSERT: dicts_sig is already zonked!
498 constrained_tyvars = foldrBag (unionTyVarSets . tyVarsOfInst) emptyTyVarSet constrained_dicts
499 reduced_tyvars_to_gen = tyvars_to_gen `minusTyVarSet` constrained_tyvars
501 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
506 isUnRestrictedGroup :: [Name] -- Signatures given for these
510 is_elem v vs = isIn "isUnResMono" v vs
512 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
513 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
514 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
515 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
516 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
517 isUnRestrictedGroup sigs mb2
518 isUnRestrictedGroup sigs EmptyMonoBinds = True
521 @defaultUncommittedTyVar@ checks for generalisation over unboxed
522 types, and defaults any TypeKind TyVars to BoxedTypeKind.
525 defaultUncommittedTyVar tyvar
526 | isTypeKind (tyVarKind tyvar)
527 = newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ boxed_tyvar ->
528 unifyTauTy (mkTyVarTy boxed_tyvar) (mkTyVarTy tyvar) `thenTc_`
536 %************************************************************************
538 \subsection{tcMonoBind}
540 %************************************************************************
542 @tcMonoBinds@ deals with a single @MonoBind@.
543 The signatures have been dealt with already.
546 tcMonoBinds :: RenamedMonoBinds
547 -> [Name] -> [TcIdBndr s]
549 -> TcM s (TcMonoBinds s, LIE s)
551 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs
552 = tcExtendLocalValEnv binder_names mono_ids (
556 sig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
557 sig_ids = [id | (TySigInfo _ id _ _ _ _) <- tc_ty_sigs]
559 tc_mono_binds EmptyMonoBinds = returnTc (EmptyMonoBinds, emptyLIE)
561 tc_mono_binds (AndMonoBinds mb1 mb2)
562 = tc_mono_binds mb1 `thenTc` \ (mb1a, lie1) ->
563 tc_mono_binds mb2 `thenTc` \ (mb2a, lie2) ->
564 returnTc (AndMonoBinds mb1a mb2a, lie1 `plusLIE` lie2)
566 tc_mono_binds (FunMonoBind name inf matches locn)
568 tcLookupLocalValueOK "tc_mono_binds" name `thenNF_Tc` \ id ->
570 -- Before checking the RHS, extend the envt with
571 -- bindings for the *polymorphic* Ids from any type signatures
572 tcExtendLocalValEnv sig_names sig_ids $
573 tcMatchesFun name (idType id) matches `thenTc` \ (matches', lie) ->
575 returnTc (FunMonoBind (TcId id) inf matches' locn, lie)
577 tc_mono_binds bind@(PatMonoBind pat grhss_and_binds locn)
579 tcAddErrCtxt (patMonoBindsCtxt bind) $
580 tcPat pat `thenTc` \ (pat2, lie_pat, pat_ty) ->
582 -- Before checking the RHS, but after the pattern, extend the envt with
583 -- bindings for the *polymorphic* Ids from any type signatures
584 tcExtendLocalValEnv sig_names sig_ids $
585 tcGRHSsAndBinds pat_ty grhss_and_binds `thenTc` \ (grhss_and_binds2, lie) ->
586 returnTc (PatMonoBind pat2 grhss_and_binds2 locn,
590 %************************************************************************
592 \subsection{Signatures}
594 %************************************************************************
596 @tcSigs@ checks the signatures for validity, and returns a list of
597 {\em freshly-instantiated} signatures. That is, the types are already
598 split up, and have fresh type variables installed. All non-type-signature
599 "RenamedSigs" are ignored.
601 The @TcSigInfo@ contains @TcTypes@ because they are unified with
602 the variable's type, and after that checked to see whether they've
608 Name -- N, the Name in corresponding binding
609 (TcIdBndr s) -- *Polymorphic* binder for this value...
610 -- Usually has name = N, but doesn't have to.
617 maybeSig :: [TcSigInfo s] -> Name -> Maybe (TcSigInfo s)
618 -- Search for a particular signature
619 maybeSig [] name = Nothing
620 maybeSig (sig@(TySigInfo sig_name _ _ _ _ _) : sigs) name
621 | name == sig_name = Just sig
622 | otherwise = maybeSig sigs name
627 tcTySig :: RenamedSig
628 -> TcM s (TcSigInfo s)
630 tcTySig (Sig v ty src_loc)
631 = tcAddSrcLoc src_loc $
632 tcHsType ty `thenTc` \ sigma_ty ->
634 -- Convert from Type to TcType
635 tcInstSigType sigma_ty `thenNF_Tc` \ sigma_tc_ty ->
637 poly_id = mkUserId v sigma_tc_ty
639 -- Instantiate this type
640 -- It's important to do this even though in the error-free case
641 -- we could just split the sigma_tc_ty (since the tyvars don't
642 -- unified with anything). But in the case of an error, when
643 -- the tyvars *do* get unified with something, we want to carry on
644 -- typechecking the rest of the program with the function bound
645 -- to a pristine type, namely sigma_tc_ty
646 tcInstSigTcType sigma_tc_ty `thenNF_Tc` \ (tyvars, rho) ->
648 (theta, tau) = splitRhoTy rho
649 -- This splitSigmaTy tries hard to make sure that tau' is a type synonym
650 -- wherever possible, which can improve interface files.
652 returnTc (TySigInfo v poly_id tyvars theta tau src_loc)
655 @checkSigMatch@ does the next step in checking signature matching.
656 The tau-type part has already been unified. What we do here is to
657 check that this unification has not over-constrained the (polymorphic)
658 type variables of the original signature type.
660 The error message here is somewhat unsatisfactory, but it'll do for
665 = returnTc (error "checkSigMatch")
667 checkSigMatch tc_ty_sigs@( sig1@(TySigInfo _ id1 _ theta1 _ _) : all_sigs_but_first )
668 = -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
669 -- Doesn't affect substitution
670 mapTc check_one_sig tc_ty_sigs `thenTc_`
672 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
673 -- The type signatures on a mutually-recursive group of definitions
674 -- must all have the same context (or none).
676 -- We unify them because, with polymorphic recursion, their types
677 -- might not otherwise be related. This is a rather subtle issue.
679 mapTc check_one_cxt all_sigs_but_first `thenTc_`
683 sig1_dict_tys = mk_dict_tys theta1
684 n_sig1_dict_tys = length sig1_dict_tys
686 check_one_cxt sig@(TySigInfo _ id _ theta _ src_loc)
687 = tcAddSrcLoc src_loc $
688 tcAddErrCtxt (sigContextsCtxt id1 id) $
689 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
690 sigContextsErr `thenTc_`
691 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
693 this_sig_dict_tys = mk_dict_tys theta
695 check_one_sig (TySigInfo name id sig_tyvars _ sig_tau src_loc)
696 = tcAddSrcLoc src_loc $
697 tcAddErrCtxt (sigCtxt id) $
698 checkSigTyVars sig_tyvars sig_tau
700 mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
704 @checkSigTyVars@ is used after the type in a type signature has been unified with
705 the actual type found. It then checks that the type variables of the type signature
707 (a) still all type variables
708 eg matching signature [a] against inferred type [(p,q)]
709 [then a will be unified to a non-type variable]
711 (b) still all distinct
712 eg matching signature [(a,b)] against inferred type [(p,p)]
713 [then a and b will be unified together]
715 (c) not mentioned in the environment
716 eg the signature for f in this:
722 Here, f is forced to be monorphic by the free occurence of x.
724 Before doing this, the substitution is applied to the signature type variable.
726 We used to have the notion of a "DontBind" type variable, which would
727 only be bound to itself or nothing. Then points (a) and (b) were
728 self-checking. But it gave rise to bogus consequential error messages.
731 f = (*) -- Monomorphic
736 Here, we get a complaint when checking the type signature for g,
737 that g isn't polymorphic enough; but then we get another one when
738 dealing with the (Num x) context arising from f's definition;
739 we try to unify x with Int (to default it), but find that x has already
740 been unified with the DontBind variable "a" from g's signature.
741 This is really a problem with side-effecting unification; we'd like to
742 undo g's effects when its type signature fails, but unification is done
743 by side effect, so we can't (easily).
745 So we revert to ordinary type variables for signatures, and try to
746 give a helpful message in checkSigTyVars.
749 checkSigTyVars :: [TcTyVar s] -- The original signature type variables
750 -> TcType s -- signature type (for err msg)
751 -> TcM s [TcTyVar s] -- Zonked signature type variables
753 checkSigTyVars sig_tyvars sig_tau
754 = mapNF_Tc zonkTcTyVar sig_tyvars `thenNF_Tc` \ sig_tys ->
756 sig_tyvars' = map (getTyVar "checkSigTyVars") sig_tys
759 -- Check points (a) and (b)
760 checkTcM (all isTyVarTy sig_tys && hasNoDups sig_tyvars')
761 (zonkTcType sig_tau `thenNF_Tc` \ sig_tau' ->
762 failWithTc (badMatchErr sig_tau sig_tau')
766 -- We want to report errors in terms of the original signature tyvars,
767 -- ie sig_tyvars, NOT sig_tyvars'. sig_tyvars' correspond
768 -- 1-1 with sig_tyvars, so we can just map back.
769 tcGetGlobalTyVars `thenNF_Tc` \ globals ->
771 mono_tyvars' = [sig_tv' | sig_tv' <- sig_tyvars',
772 sig_tv' `elementOfTyVarSet` globals]
774 mono_tyvars = map (assoc "checkSigTyVars" (sig_tyvars' `zip` sig_tyvars)) mono_tyvars'
776 checkTcM (null mono_tyvars')
777 (failWithTc (notAsPolyAsSigErr sig_tau mono_tyvars)) `thenTc_`
783 %************************************************************************
785 \subsection{SPECIALIZE pragmas}
787 %************************************************************************
790 @tcPragmaSigs@ munches up the "signatures" that arise through *user*
791 pragmas. It is convenient for them to appear in the @[RenamedSig]@
792 part of a binding because then the same machinery can be used for
793 moving them into place as is done for type signatures.
796 tcPragmaSigs :: [RenamedSig] -- The pragma signatures
797 -> TcM s (Name -> IdInfo, -- Maps name to the appropriate IdInfo
802 = mapAndUnzip3Tc tcPragmaSig sigs `thenTc` \ (maybe_info_modifiers, binds, lies) ->
804 prag_fn name = foldr ($) noIdInfo [f | Just (n,f) <- maybe_info_modifiers, n==name]
806 returnTc (prag_fn, andMonoBinds binds, plusLIEs lies)
809 The interesting case is for SPECIALISE pragmas. There are two forms.
810 Here's the first form:
812 f :: Ord a => [a] -> b -> b
813 {-# SPECIALIZE f :: [Int] -> b -> b #-}
816 For this we generate:
818 f* = /\ b -> let d1 = ...
822 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
823 retain a right-hand-side that the simplifier will otherwise discard as
824 dead code... the simplifier has a flag that tells it not to discard
825 SpecPragmaId bindings.
827 In this case the f* retains a call-instance of the overloaded
828 function, f, (including appropriate dictionaries) so that the
829 specialiser will subsequently discover that there's a call of @f@ at
830 Int, and will create a specialisation for @f@. After that, the
831 binding for @f*@ can be discarded.
833 The second form is this:
835 f :: Ord a => [a] -> b -> b
836 {-# SPECIALIZE f :: [Int] -> b -> b = g #-}
839 Here @g@ is specified as a function that implements the specialised
840 version of @f@. Suppose that g has type (a->b->b); that is, g's type
841 is more general than that required. For this we generate
843 f@Int = /\b -> g Int b
847 Here @f@@Int@ is a SpecId, the specialised version of @f@. It inherits
848 f's export status etc. @f*@ is a SpecPragmaId, as before, which just serves
849 to prevent @f@@Int@ from being discarded prematurely. After specialisation,
850 if @f@@Int@ is going to be used at all it will be used explicitly, so the simplifier can
851 discard the f* binding.
853 Actually, there is really only point in giving a SPECIALISE pragma on exported things,
854 and the simplifer won't discard SpecIds for exporte things anyway, so maybe this is
858 tcPragmaSig :: RenamedSig -> TcM s (Maybe (Name, IdInfo -> IdInfo), TcMonoBinds s, LIE s)
859 tcPragmaSig (Sig _ _ _) = returnTc (Nothing, EmptyMonoBinds, emptyLIE)
860 tcPragmaSig (SpecInstSig _ _) = returnTc (Nothing, EmptyMonoBinds, emptyLIE)
862 tcPragmaSig (InlineSig name loc)
863 = returnTc (Just (name, setInlinePragInfo IWantToBeINLINEd), EmptyMonoBinds, emptyLIE)
865 tcPragmaSig (SpecSig name poly_ty maybe_spec_name src_loc)
866 = -- SPECIALISE f :: forall b. theta => tau = g
867 tcAddSrcLoc src_loc $
868 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
870 -- Get and instantiate its alleged specialised type
871 tcHsType poly_ty `thenTc` \ sig_sigma ->
872 tcInstSigType sig_sigma `thenNF_Tc` \ sig_ty ->
874 -- Check that f has a more general type, and build a RHS for
875 -- the spec-pragma-id at the same time
876 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
878 case maybe_spec_name of
879 Nothing -> -- Just specialise "f" by building a pecPragmaId binding
880 -- It is the thing that makes sure we don't prematurely
881 -- dead-code-eliminate the binding we are really interested in.
882 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
883 returnTc (Nothing, VarMonoBind (TcId spec_id) spec_expr, spec_lie)
885 Just g_name -> -- Don't create a SpecPragmaId. Instead add some suitable IdIfo
887 panic "Can't handle SPECIALISE with a '= g' part"
889 {- Not yet. Because we're still in the TcType world we
890 can't really add to the SpecEnv of the Id. Instead we have to
891 record the information in a different sort of Sig, and add it to
892 the IdInfo after zonking.
894 For now we just leave out this case
896 -- Get the type of f, and find out what types
897 -- f has to be instantiated at to give the signature type
898 tcLookupLocalValueOK "tcPragmaSig" name `thenNF_Tc` \ f_id ->
899 tcInstSigTcType (idType f_id) `thenNF_Tc` \ (f_tyvars, f_rho) ->
902 (sig_tyvars, sig_theta, sig_tau) = splitSigmaTy sig_ty
903 (f_theta, f_tau) = splitRhoTy f_rho
904 sig_tyvar_set = mkTyVarSet sig_tyvars
906 unifyTauTy sig_tau f_tau `thenTc_`
908 tcPolyExpr str (HsVar g_name) (mkSigmaTy sig_tyvars f_theta sig_tau) `thenTc` \ (_, _,
911 tcPragmaSig other = pprTrace "tcPragmaSig: ignoring" (ppr other) $
912 returnTc (Nothing, EmptyMonoBinds, emptyLIE)
916 %************************************************************************
918 \subsection[TcBinds-errors]{Error contexts and messages}
920 %************************************************************************
924 patMonoBindsCtxt bind
925 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
927 -----------------------------------------------
929 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
930 nest 4 (ppr v <+> ptext SLIT(" ::") <+> ppr ty)]
932 -----------------------------------------------
933 notAsPolyAsSigErr sig_tau mono_tyvars
934 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
935 4 (vcat [text "Can't for-all the type variable(s)" <+>
936 pprQuotedList mono_tyvars,
937 text "in the type" <+> quotes (ppr sig_tau)
940 -----------------------------------------------
941 badMatchErr sig_ty inferred_ty
942 = hang (ptext SLIT("Type signature doesn't match inferred type"))
943 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
944 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
947 -----------------------------------------------
949 = sep [ptext SLIT("When checking the type signature for"), quotes (ppr id)]
952 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
954 -----------------------------------------------
956 = ptext SLIT("Mismatched contexts")
957 sigContextsCtxt s1 s2
958 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
959 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
960 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
962 -----------------------------------------------
964 = panic "specGroundnessCtxt"
966 --------------------------------------------
967 specContextGroundnessCtxt -- err_ctxt dicts
968 = panic "specContextGroundnessCtxt"
971 sep [hsep [ptext SLIT("In the SPECIALIZE pragma for"), ppr name],
972 hcat [ptext SLIT(" specialised to the type"), ppr spec_ty],
974 ptext SLIT("... not all overloaded type variables were instantiated"),
975 ptext SLIT("to ground types:")])
976 4 (vcat [hsep [ppr c, ppr t]
977 | (c,t) <- map getDictClassAndType dicts])
979 (name, spec_ty, locn, pp_spec_id)
981 ValSpecSigCtxt n ty loc -> (n, ty, loc, \ x -> empty)
982 ValSpecSpecIdCtxt n ty spec loc ->
984 hsep [ptext SLIT("... type of explicit id"), ppr spec])