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
290 tcExtendGlobalTyVars (tyVarSetToList tyvars_not_to_gen) (
291 if null tc_ty_sigs then
292 -- No signatures, so just simplify the lie
293 -- NB: no signatures => no polymorphic recursion, so no
294 -- need to use mono_lies (which will be empty anyway)
295 tcSimplify (text "tcBinds1" <+> ppr binder_names)
296 top_lvl real_tyvars_to_gen lie `thenTc` \ (lie_free, dict_binds, lie_bound) ->
297 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
300 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
301 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
302 -- It's important that sig_theta is zonked, because
303 -- dict_id is later used to form the type of the polymorphic thing,
304 -- and forall-types must be zonked so far as their bound variables
308 -- The "givens" is the stuff available. We get that from
309 -- the context of the type signature, BUT ALSO the mono_lie
310 -- so that polymorphic recursion works right (see comments at end of fn)
311 givens = dicts_sig `plusLIE` mono_lie
314 -- Check that the needed dicts can be expressed in
315 -- terms of the signature ones
316 tcAddErrCtxt (bindSigsCtxt tysig_names) $
318 (ptext SLIT("type signature for") <+>
319 hsep (punctuate comma (map (quotes . ppr) binder_names)))
320 real_tyvars_to_gen givens lie `thenTc` \ (lie_free, dict_binds) ->
322 returnTc (lie_free, dict_binds, dict_ids)
324 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
326 ASSERT( not (any (isUnboxedTypeKind . tyVarKind) real_tyvars_to_gen_list) )
327 -- The instCantBeGeneralised stuff in tcSimplify should have
328 -- already raised an error if we're trying to generalise an unboxed tyvar
329 -- (NB: unboxed tyvars are always introduced along with a class constraint)
330 -- and it's better done there because we have more precise origin information.
331 -- That's why we just use an ASSERT here.
333 -- BUILD THE POLYMORPHIC RESULT IDs
334 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
336 exports = zipWith3 mk_export binder_names mono_ids zonked_mono_id_types
337 dict_tys = map tcIdType dicts_bound
339 mk_export binder_name mono_id zonked_mono_id_ty
340 = (tyvars, TcId (replaceIdInfo poly_id (prag_info_fn binder_name)), TcId mono_id)
342 (tyvars, poly_id) = case maybeSig tc_ty_sigs binder_name of
343 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _) -> (sig_tyvars, sig_poly_id)
344 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
346 new_poly_id = mkUserId binder_name poly_ty
347 poly_ty = mkForAllTys real_tyvars_to_gen_list $ mkFunTys dict_tys $ zonked_mono_id_ty
348 -- It's important to build a fully-zonked poly_ty, because
349 -- we'll slurp out its free type variables when extending the
350 -- local environment (tcExtendLocalValEnv); if it's not zonked
351 -- it appears to have free tyvars that aren't actually free at all.
356 AbsBinds real_tyvars_to_gen_list
359 (dict_binds `AndMonoBinds` mbind'),
361 [poly_id | (_, TcId poly_id, _) <- exports]
364 no_of_binders = length binder_names
366 mk_mono_id binder_name
367 | theres_a_signature -- There's a signature; and it's overloaded,
368 && not (null sig_theta) -- so make a Method
369 = tcAddSrcLoc sig_loc $
370 newMethodWithGivenTy SignatureOrigin
371 (TcId poly_id) (mkTyVarTys sig_tyvars)
372 sig_theta sig_tau `thenNF_Tc` \ (mono_lie, TcId mono_id) ->
373 -- A bit turgid to have to strip the TcId
374 returnNF_Tc (mono_lie, mono_id)
376 | otherwise -- No signature or not overloaded;
377 = tcAddSrcLoc (getSrcLoc binder_name) $
378 (if theres_a_signature then
379 returnNF_Tc sig_tau -- Non-overloaded signature; use its type
381 newTyVarTy kind -- No signature; use a new type variable
382 ) `thenNF_Tc` \ mono_id_ty ->
384 newLocalId (getOccName binder_name) mono_id_ty `thenNF_Tc` \ mono_id ->
385 returnNF_Tc (emptyLIE, mono_id)
387 maybe_sig = maybeSig tc_ty_sigs binder_name
388 theres_a_signature = maybeToBool maybe_sig
389 Just (TySigInfo name poly_id sig_tyvars sig_theta sig_tau sig_loc) = maybe_sig
391 tysig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
392 is_unrestricted = isUnRestrictedGroup tysig_names mbind
394 kind = case is_rec of
395 Recursive -> mkBoxedTypeKind -- Recursive, so no unboxed types
396 NonRecursive -> mkTypeKind -- Non-recursive, so we permit unboxed types
399 Polymorphic recursion
400 ~~~~~~~~~~~~~~~~~~~~~
401 The game plan for polymorphic recursion in the code above is
403 * Bind any variable for which we have a type signature
404 to an Id with a polymorphic type. Then when type-checking
405 the RHSs we'll make a full polymorphic call.
407 This fine, but if you aren't a bit careful you end up with a horrendous
408 amount of partial application and (worse) a huge space leak. For example:
410 f :: Eq a => [a] -> [a]
413 If we don't take care, after typechecking we get
415 f = /\a -> \d::Eq a -> let f' = f a d
419 Notice the the stupid construction of (f a d), which is of course
420 identical to the function we're executing. In this case, the
421 polymorphic recursion ins't being used (but that's a very common case).
423 This can lead to a massive space leak, from the following top-level defn:
428 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
429 f' is another thunk which evaluates to the same thing... and you end
430 up with a chain of identical values all hung onto by the CAF ff.
432 Solution: when typechecking the RHSs we always have in hand the
433 *monomorphic* Ids for each binding. So we just need to make sure that
434 if (Method f a d) shows up in the constraints emerging from (...f...)
435 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
436 to the "givens" when simplifying constraints. Thats' what the "mono_lies"
440 %************************************************************************
442 \subsection{getTyVarsToGen}
444 %************************************************************************
446 @getTyVarsToGen@ decides what type variables generalise over.
448 For a "restricted group" -- see the monomorphism restriction
449 for a definition -- we bind no dictionaries, and
450 remove from tyvars_to_gen any constrained type variables
452 *Don't* simplify dicts at this point, because we aren't going
453 to generalise over these dicts. By the time we do simplify them
454 we may well know more. For example (this actually came up)
456 f x = array ... xs where xs = [1,2,3,4,5]
457 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
458 stuff. If we simplify only at the f-binding (not the xs-binding)
459 we'll know that the literals are all Ints, and we can just produce
462 Find all the type variables involved in overloading, the
463 "constrained_tyvars". These are the ones we *aren't* going to
464 generalise. We must be careful about doing this:
466 (a) If we fail to generalise a tyvar which is not actually
467 constrained, then it will never, ever get bound, and lands
468 up printed out in interface files! Notorious example:
469 instance Eq a => Eq (Foo a b) where ..
470 Here, b is not constrained, even though it looks as if it is.
471 Another, more common, example is when there's a Method inst in
472 the LIE, whose type might very well involve non-overloaded
475 (b) On the other hand, we mustn't generalise tyvars which are constrained,
476 because we are going to pass on out the unmodified LIE, with those
477 tyvars in it. They won't be in scope if we've generalised them.
479 So we are careful, and do a complete simplification just to find the
480 constrained tyvars. We don't use any of the results, except to
481 find which tyvars are constrained.
484 getTyVarsToGen is_unrestricted mono_id_tys lie
485 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
486 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
488 tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusTyVarSet` free_tyvars
492 returnTc (emptyTyVarSet, tyvars_to_gen)
494 tcSimplify (text "getTVG") NotTopLevel tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
496 -- ASSERT: dicts_sig is already zonked!
497 constrained_tyvars = foldrBag (unionTyVarSets . tyVarsOfInst) emptyTyVarSet constrained_dicts
498 reduced_tyvars_to_gen = tyvars_to_gen `minusTyVarSet` constrained_tyvars
500 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
505 isUnRestrictedGroup :: [Name] -- Signatures given for these
509 is_elem v vs = isIn "isUnResMono" v vs
511 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
512 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
513 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
514 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
515 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
516 isUnRestrictedGroup sigs mb2
517 isUnRestrictedGroup sigs EmptyMonoBinds = True
520 @defaultUncommittedTyVar@ checks for generalisation over unboxed
521 types, and defaults any TypeKind TyVars to BoxedTypeKind.
524 defaultUncommittedTyVar tyvar
525 | isTypeKind (tyVarKind tyvar)
526 = newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ boxed_tyvar ->
527 unifyTauTy (mkTyVarTy boxed_tyvar) (mkTyVarTy tyvar) `thenTc_`
535 %************************************************************************
537 \subsection{tcMonoBind}
539 %************************************************************************
541 @tcMonoBinds@ deals with a single @MonoBind@.
542 The signatures have been dealt with already.
545 tcMonoBinds :: RenamedMonoBinds
546 -> [Name] -> [TcIdBndr s]
548 -> TcM s (TcMonoBinds s, LIE s)
550 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs
551 = tcExtendLocalValEnv binder_names mono_ids (
555 sig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
556 sig_ids = [id | (TySigInfo _ id _ _ _ _) <- tc_ty_sigs]
558 tc_mono_binds EmptyMonoBinds = returnTc (EmptyMonoBinds, emptyLIE)
560 tc_mono_binds (AndMonoBinds mb1 mb2)
561 = tc_mono_binds mb1 `thenTc` \ (mb1a, lie1) ->
562 tc_mono_binds mb2 `thenTc` \ (mb2a, lie2) ->
563 returnTc (AndMonoBinds mb1a mb2a, lie1 `plusLIE` lie2)
565 tc_mono_binds (FunMonoBind name inf matches locn)
567 tcLookupLocalValueOK "tc_mono_binds" name `thenNF_Tc` \ id ->
569 -- Before checking the RHS, extend the envt with
570 -- bindings for the *polymorphic* Ids from any type signatures
571 tcExtendLocalValEnv sig_names sig_ids $
572 tcMatchesFun name (idType id) matches `thenTc` \ (matches', lie) ->
574 returnTc (FunMonoBind (TcId id) inf matches' locn, lie)
576 tc_mono_binds bind@(PatMonoBind pat grhss_and_binds locn)
578 tcAddErrCtxt (patMonoBindsCtxt bind) $
579 tcPat pat `thenTc` \ (pat2, lie_pat, pat_ty) ->
581 -- Before checking the RHS, but after the pattern, extend the envt with
582 -- bindings for the *polymorphic* Ids from any type signatures
583 tcExtendLocalValEnv sig_names sig_ids $
584 tcGRHSsAndBinds pat_ty grhss_and_binds `thenTc` \ (grhss_and_binds2, lie) ->
585 returnTc (PatMonoBind pat2 grhss_and_binds2 locn,
589 %************************************************************************
591 \subsection{Signatures}
593 %************************************************************************
595 @tcSigs@ checks the signatures for validity, and returns a list of
596 {\em freshly-instantiated} signatures. That is, the types are already
597 split up, and have fresh type variables installed. All non-type-signature
598 "RenamedSigs" are ignored.
600 The @TcSigInfo@ contains @TcTypes@ because they are unified with
601 the variable's type, and after that checked to see whether they've
607 Name -- N, the Name in corresponding binding
608 (TcIdBndr s) -- *Polymorphic* binder for this value...
609 -- Usually has name = N, but doesn't have to.
616 maybeSig :: [TcSigInfo s] -> Name -> Maybe (TcSigInfo s)
617 -- Search for a particular signature
618 maybeSig [] name = Nothing
619 maybeSig (sig@(TySigInfo sig_name _ _ _ _ _) : sigs) name
620 | name == sig_name = Just sig
621 | otherwise = maybeSig sigs name
626 tcTySig :: RenamedSig
627 -> TcM s (TcSigInfo s)
629 tcTySig (Sig v ty src_loc)
630 = tcAddSrcLoc src_loc $
631 tcHsType ty `thenTc` \ sigma_ty ->
633 -- Convert from Type to TcType
634 tcInstSigType sigma_ty `thenNF_Tc` \ sigma_tc_ty ->
636 poly_id = mkUserId v sigma_tc_ty
638 -- Instantiate this type
639 -- It's important to do this even though in the error-free case
640 -- we could just split the sigma_tc_ty (since the tyvars don't
641 -- unified with anything). But in the case of an error, when
642 -- the tyvars *do* get unified with something, we want to carry on
643 -- typechecking the rest of the program with the function bound
644 -- to a pristine type, namely sigma_tc_ty
645 tcInstSigTcType sigma_tc_ty `thenNF_Tc` \ (tyvars, rho) ->
647 (theta, tau) = splitRhoTy rho
648 -- This splitSigmaTy tries hard to make sure that tau' is a type synonym
649 -- wherever possible, which can improve interface files.
651 returnTc (TySigInfo v poly_id tyvars theta tau src_loc)
654 @checkSigMatch@ does the next step in checking signature matching.
655 The tau-type part has already been unified. What we do here is to
656 check that this unification has not over-constrained the (polymorphic)
657 type variables of the original signature type.
659 The error message here is somewhat unsatisfactory, but it'll do for
664 = returnTc (error "checkSigMatch")
666 checkSigMatch tc_ty_sigs@( sig1@(TySigInfo _ id1 _ theta1 _ _) : all_sigs_but_first )
667 = -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
668 -- Doesn't affect substitution
669 mapTc check_one_sig tc_ty_sigs `thenTc_`
671 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
672 -- The type signatures on a mutually-recursive group of definitions
673 -- must all have the same context (or none).
675 -- We unify them because, with polymorphic recursion, their types
676 -- might not otherwise be related. This is a rather subtle issue.
678 mapTc check_one_cxt all_sigs_but_first `thenTc_`
682 sig1_dict_tys = mk_dict_tys theta1
683 n_sig1_dict_tys = length sig1_dict_tys
685 check_one_cxt sig@(TySigInfo _ id _ theta _ src_loc)
686 = tcAddSrcLoc src_loc $
687 tcAddErrCtxt (sigContextsCtxt id1 id) $
688 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
689 sigContextsErr `thenTc_`
690 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
692 this_sig_dict_tys = mk_dict_tys theta
694 check_one_sig (TySigInfo name id sig_tyvars _ sig_tau src_loc)
695 = tcAddSrcLoc src_loc $
696 tcAddErrCtxt (sigCtxt id) $
697 checkSigTyVars sig_tyvars sig_tau
699 mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
703 @checkSigTyVars@ is used after the type in a type signature has been unified with
704 the actual type found. It then checks that the type variables of the type signature
706 (a) still all type variables
707 eg matching signature [a] against inferred type [(p,q)]
708 [then a will be unified to a non-type variable]
710 (b) still all distinct
711 eg matching signature [(a,b)] against inferred type [(p,p)]
712 [then a and b will be unified together]
714 (c) not mentioned in the environment
715 eg the signature for f in this:
721 Here, f is forced to be monorphic by the free occurence of x.
723 Before doing this, the substitution is applied to the signature type variable.
725 We used to have the notion of a "DontBind" type variable, which would
726 only be bound to itself or nothing. Then points (a) and (b) were
727 self-checking. But it gave rise to bogus consequential error messages.
730 f = (*) -- Monomorphic
735 Here, we get a complaint when checking the type signature for g,
736 that g isn't polymorphic enough; but then we get another one when
737 dealing with the (Num x) context arising from f's definition;
738 we try to unify x with Int (to default it), but find that x has already
739 been unified with the DontBind variable "a" from g's signature.
740 This is really a problem with side-effecting unification; we'd like to
741 undo g's effects when its type signature fails, but unification is done
742 by side effect, so we can't (easily).
744 So we revert to ordinary type variables for signatures, and try to
745 give a helpful message in checkSigTyVars.
748 checkSigTyVars :: [TcTyVar s] -- The original signature type variables
749 -> TcType s -- signature type (for err msg)
750 -> TcM s [TcTyVar s] -- Zonked signature type variables
752 checkSigTyVars sig_tyvars sig_tau
753 = mapNF_Tc zonkTcTyVar sig_tyvars `thenNF_Tc` \ sig_tys ->
755 sig_tyvars' = map (getTyVar "checkSigTyVars") sig_tys
758 -- Check points (a) and (b)
759 checkTcM (all isTyVarTy sig_tys && hasNoDups sig_tyvars')
760 (zonkTcType sig_tau `thenNF_Tc` \ sig_tau' ->
761 failWithTc (badMatchErr sig_tau sig_tau')
765 -- We want to report errors in terms of the original signature tyvars,
766 -- ie sig_tyvars, NOT sig_tyvars'. sig_tyvars' correspond
767 -- 1-1 with sig_tyvars, so we can just map back.
768 tcGetGlobalTyVars `thenNF_Tc` \ globals ->
770 mono_tyvars' = [sig_tv' | sig_tv' <- sig_tyvars',
771 sig_tv' `elementOfTyVarSet` globals]
773 mono_tyvars = map (assoc "checkSigTyVars" (sig_tyvars' `zip` sig_tyvars)) mono_tyvars'
775 checkTcM (null mono_tyvars')
776 (failWithTc (notAsPolyAsSigErr sig_tau mono_tyvars)) `thenTc_`
782 %************************************************************************
784 \subsection{SPECIALIZE pragmas}
786 %************************************************************************
789 @tcPragmaSigs@ munches up the "signatures" that arise through *user*
790 pragmas. It is convenient for them to appear in the @[RenamedSig]@
791 part of a binding because then the same machinery can be used for
792 moving them into place as is done for type signatures.
795 tcPragmaSigs :: [RenamedSig] -- The pragma signatures
796 -> TcM s (Name -> IdInfo, -- Maps name to the appropriate IdInfo
801 = mapAndUnzip3Tc tcPragmaSig sigs `thenTc` \ (maybe_info_modifiers, binds, lies) ->
803 prag_fn name = foldr ($) noIdInfo [f | Just (n,f) <- maybe_info_modifiers, n==name]
805 returnTc (prag_fn, andMonoBinds binds, plusLIEs lies)
808 The interesting case is for SPECIALISE pragmas. There are two forms.
809 Here's the first form:
811 f :: Ord a => [a] -> b -> b
812 {-# SPECIALIZE f :: [Int] -> b -> b #-}
815 For this we generate:
817 f* = /\ b -> let d1 = ...
821 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
822 retain a right-hand-side that the simplifier will otherwise discard as
823 dead code... the simplifier has a flag that tells it not to discard
824 SpecPragmaId bindings.
826 In this case the f* retains a call-instance of the overloaded
827 function, f, (including appropriate dictionaries) so that the
828 specialiser will subsequently discover that there's a call of @f@ at
829 Int, and will create a specialisation for @f@. After that, the
830 binding for @f*@ can be discarded.
832 The second form is this:
834 f :: Ord a => [a] -> b -> b
835 {-# SPECIALIZE f :: [Int] -> b -> b = g #-}
838 Here @g@ is specified as a function that implements the specialised
839 version of @f@. Suppose that g has type (a->b->b); that is, g's type
840 is more general than that required. For this we generate
842 f@Int = /\b -> g Int b
846 Here @f@@Int@ is a SpecId, the specialised version of @f@. It inherits
847 f's export status etc. @f*@ is a SpecPragmaId, as before, which just serves
848 to prevent @f@@Int@ from being discarded prematurely. After specialisation,
849 if @f@@Int@ is going to be used at all it will be used explicitly, so the simplifier can
850 discard the f* binding.
852 Actually, there is really only point in giving a SPECIALISE pragma on exported things,
853 and the simplifer won't discard SpecIds for exporte things anyway, so maybe this is
857 tcPragmaSig :: RenamedSig -> TcM s (Maybe (Name, IdInfo -> IdInfo), TcMonoBinds s, LIE s)
858 tcPragmaSig (Sig _ _ _) = returnTc (Nothing, EmptyMonoBinds, emptyLIE)
859 tcPragmaSig (SpecInstSig _ _) = returnTc (Nothing, EmptyMonoBinds, emptyLIE)
861 tcPragmaSig (InlineSig name loc)
862 = returnTc (Just (name, setInlinePragInfo IWantToBeINLINEd), EmptyMonoBinds, emptyLIE)
864 tcPragmaSig (SpecSig name poly_ty maybe_spec_name src_loc)
865 = -- SPECIALISE f :: forall b. theta => tau = g
866 tcAddSrcLoc src_loc $
867 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
869 -- Get and instantiate its alleged specialised type
870 tcHsType poly_ty `thenTc` \ sig_sigma ->
871 tcInstSigType sig_sigma `thenNF_Tc` \ sig_ty ->
873 -- Check that f has a more general type, and build a RHS for
874 -- the spec-pragma-id at the same time
875 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
877 case maybe_spec_name of
878 Nothing -> -- Just specialise "f" by building a pecPragmaId binding
879 -- It is the thing that makes sure we don't prematurely
880 -- dead-code-eliminate the binding we are really interested in.
881 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
882 returnTc (Nothing, VarMonoBind (TcId spec_id) spec_expr, spec_lie)
884 Just g_name -> -- Don't create a SpecPragmaId. Instead add some suitable IdIfo
886 panic "Can't handle SPECIALISE with a '= g' part"
888 {- Not yet. Because we're still in the TcType world we
889 can't really add to the SpecEnv of the Id. Instead we have to
890 record the information in a different sort of Sig, and add it to
891 the IdInfo after zonking.
893 For now we just leave out this case
895 -- Get the type of f, and find out what types
896 -- f has to be instantiated at to give the signature type
897 tcLookupLocalValueOK "tcPragmaSig" name `thenNF_Tc` \ f_id ->
898 tcInstSigTcType (idType f_id) `thenNF_Tc` \ (f_tyvars, f_rho) ->
901 (sig_tyvars, sig_theta, sig_tau) = splitSigmaTy sig_ty
902 (f_theta, f_tau) = splitRhoTy f_rho
903 sig_tyvar_set = mkTyVarSet sig_tyvars
905 unifyTauTy sig_tau f_tau `thenTc_`
907 tcPolyExpr str (HsVar g_name) (mkSigmaTy sig_tyvars f_theta sig_tau) `thenTc` \ (_, _,
910 tcPragmaSig other = pprTrace "tcPragmaSig: ignoring" (ppr other) $
911 returnTc (Nothing, EmptyMonoBinds, emptyLIE)
915 %************************************************************************
917 \subsection[TcBinds-errors]{Error contexts and messages}
919 %************************************************************************
923 patMonoBindsCtxt bind
924 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
926 -----------------------------------------------
928 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
929 nest 4 (ppr v <+> ptext SLIT(" ::") <+> ppr ty)]
931 -----------------------------------------------
932 notAsPolyAsSigErr sig_tau mono_tyvars
933 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
934 4 (vcat [text "Can't for-all the type variable(s)" <+>
935 pprQuotedList mono_tyvars,
936 text "in the type" <+> quotes (ppr sig_tau)
939 -----------------------------------------------
940 badMatchErr sig_ty inferred_ty
941 = hang (ptext SLIT("Type signature doesn't match inferred type"))
942 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
943 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
946 -----------------------------------------------
948 = sep [ptext SLIT("When checking the type signature for"), quotes (ppr id)]
951 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
953 -----------------------------------------------
955 = ptext SLIT("Mismatched contexts")
956 sigContextsCtxt s1 s2
957 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
958 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
959 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
961 -----------------------------------------------
963 = panic "specGroundnessCtxt"
965 --------------------------------------------
966 specContextGroundnessCtxt -- err_ctxt dicts
967 = panic "specContextGroundnessCtxt"
970 sep [hsep [ptext SLIT("In the SPECIALIZE pragma for"), ppr name],
971 hcat [ptext SLIT(" specialised to the type"), ppr spec_ty],
973 ptext SLIT("... not all overloaded type variables were instantiated"),
974 ptext SLIT("to ground types:")])
975 4 (vcat [hsep [ppr c, ppr t]
976 | (c,t) <- map getDictClassAndType dicts])
978 (name, spec_ty, locn, pp_spec_id)
980 ValSpecSigCtxt n ty loc -> (n, ty, loc, \ x -> empty)
981 ValSpecSpecIdCtxt n ty spec loc ->
983 hsep [ptext SLIT("... type of explicit id"), ppr spec])