2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBindsAndThen, bindInstsOfLocalFuns,
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, RenamedMonoBinds )
20 import TcHsSyn ( TcHsBinds, TcMonoBinds,
21 TcIdOcc(..), TcIdBndr,
26 import Inst ( Inst, LIE, emptyLIE, plusLIE, plusLIEs, InstOrigin(..),
27 newDicts, tyVarsOfInst, instToId, newMethodWithGivenTy,
30 import TcEnv ( tcExtendLocalValEnv, tcLookupLocalValueOK,
31 newLocalId, newSpecPragmaId,
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 MkId ( mkUserId )
48 import Id ( idType, idName, idInfo, replaceIdInfo )
49 import IdInfo ( IdInfo, noIdInfo, setInlinePragInfo, InlinePragInfo(..) )
50 import Maybes ( maybeToBool, assocMaybe )
51 import Name ( getOccName, getSrcLoc, Name )
52 import Type ( mkTyVarTy, mkTyVarTys, isTyVarTy, tyVarsOfTypes,
53 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar, mkDictTy,
54 splitRhoTy, mkForAllTy, splitForAllTys
56 import TyVar ( TyVar, tyVarKind, mkTyVarSet, minusTyVarSet, emptyTyVarSet,
57 elementOfTyVarSet, unionTyVarSets, tyVarSetToList
59 import Bag ( bagToList, foldrBag, )
60 import Util ( isIn, hasNoDups, assoc )
61 import Unique ( Unique )
62 import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
63 import SrcLoc ( SrcLoc )
68 %************************************************************************
70 \subsection{Type-checking bindings}
72 %************************************************************************
74 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
75 it needs to know something about the {\em usage} of the things bound,
76 so that it can create specialisations of them. So @tcBindsAndThen@
77 takes a function which, given an extended environment, E, typechecks
78 the scope of the bindings returning a typechecked thing and (most
79 important) an LIE. It is this LIE which is then used as the basis for
80 specialising the things bound.
82 @tcBindsAndThen@ also takes a "combiner" which glues together the
83 bindings and the "thing" to make a new "thing".
85 The real work is done by @tcBindWithSigsAndThen@.
87 Recursive and non-recursive binds are handled in essentially the same
88 way: because of uniques there are no scoping issues left. The only
89 difference is that non-recursive bindings can bind primitive values.
91 Even for non-recursive binding groups we add typings for each binder
92 to the LVE for the following reason. When each individual binding is
93 checked the type of its LHS is unified with that of its RHS; and
94 type-checking the LHS of course requires that the binder is in scope.
96 At the top-level the LIE is sure to contain nothing but constant
97 dictionaries, which we resolve at the module level.
100 tcTopBindsAndThen, tcBindsAndThen
101 :: (RecFlag -> TcMonoBinds s -> this -> that) -- Combinator
103 -> TcM s (this, LIE s)
104 -> TcM s (that, LIE s)
106 tcTopBindsAndThen = tc_binds_and_then TopLevel
107 tcBindsAndThen = tc_binds_and_then NotTopLevel
109 tc_binds_and_then top_lvl combiner binds do_next
110 = tcBinds top_lvl binds `thenTc` \ (mbinds1, binds_lie, env, ids) ->
113 -- Now do whatever happens next, in the augmented envt
114 do_next `thenTc` \ (thing, thing_lie) ->
116 -- Create specialisations of functions bound here
117 -- Nota Bene: we glom the bindings all together in a single
118 -- recursive group ("recursive" passed to combiner, below)
119 -- so that we can do thsi bindInsts thing once for all the bindings
120 -- and the thing inside. This saves a quadratic-cost algorithm
121 -- when there's a long sequence of bindings.
122 bindInstsOfLocalFuns (binds_lie `plusLIE` thing_lie) ids `thenTc` \ (final_lie, mbinds2) ->
126 final_mbinds = mbinds1 `AndMonoBinds` mbinds2
128 returnTc (combiner Recursive final_mbinds thing, final_lie)
130 tcBinds :: TopLevelFlag
132 -> TcM s (TcMonoBinds s, LIE s, TcEnv s, [TcIdBndr s])
133 -- The envt is the envt with binders in scope
134 -- The binders are those bound by this group of bindings
136 tcBinds top_lvl EmptyBinds
137 = tcGetEnv `thenNF_Tc` \ env ->
138 returnTc (EmptyMonoBinds, emptyLIE, env, [])
140 -- Short-cut for the rather common case of an empty bunch of bindings
141 tcBinds top_lvl (MonoBind EmptyMonoBinds sigs is_rec)
142 = tcGetEnv `thenNF_Tc` \ env ->
143 returnTc (EmptyMonoBinds, emptyLIE, env, [])
145 tcBinds top_lvl (ThenBinds binds1 binds2)
146 = tcBinds top_lvl binds1 `thenTc` \ (mbinds1, lie1, env1, ids1) ->
148 tcBinds top_lvl binds2 `thenTc` \ (mbinds2, lie2, env2, ids2) ->
149 returnTc (mbinds1 `AndMonoBinds` mbinds2, lie1 `plusLIE` lie2, env2, ids1++ids2)
151 tcBinds top_lvl (MonoBind bind sigs is_rec)
152 = fixTc (\ ~(prag_info_fn, _) ->
153 -- This is the usual prag_info fix; the PragmaInfo field of an Id
154 -- is not inspected till ages later in the compiler, so there
155 -- should be no black-hole problems here.
157 -- TYPECHECK THE SIGNATURES
158 mapTc tcTySig ty_sigs `thenTc` \ tc_ty_sigs ->
160 tcBindWithSigs top_lvl binder_names bind
161 tc_ty_sigs is_rec prag_info_fn `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
163 -- Extend the environment to bind the new polymorphic Ids
164 tcExtendLocalValEnv binder_names poly_ids $
166 -- Build bindings and IdInfos corresponding to user pragmas
167 tcPragmaSigs sigs `thenTc` \ (prag_info_fn, prag_binds, prag_lie) ->
169 -- Catch the environment and return
170 tcGetEnv `thenNF_Tc` \ env ->
171 returnTc (prag_info_fn, (poly_binds `AndMonoBinds` prag_binds,
172 poly_lie `plusLIE` prag_lie,
174 ) ) `thenTc` \ (_, result) ->
177 binder_names = map fst (bagToList (collectMonoBinders bind))
178 ty_sigs = [sig | sig@(Sig name _ _) <- sigs]
181 An aside. The original version of @tcBindsAndThen@ which lacks a
182 combiner function, appears below. Though it is perfectly well
183 behaved, it cannot be typed by Haskell, because the recursive call is
184 at a different type to the definition itself. There aren't too many
185 examples of this, which is why I thought it worth preserving! [SLPJ]
190 -> TcM s (thing, LIE s, thing_ty))
191 -> TcM s ((TcHsBinds s, thing), LIE s, thing_ty)
193 tcBindsAndThen EmptyBinds do_next
194 = do_next `thenTc` \ (thing, lie, thing_ty) ->
195 returnTc ((EmptyBinds, thing), lie, thing_ty)
197 tcBindsAndThen (ThenBinds binds1 binds2) do_next
198 = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
199 `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
201 returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
203 tcBindsAndThen (MonoBind bind sigs is_rec) do_next
204 = tcBindAndThen bind sigs do_next
208 %************************************************************************
210 \subsection{tcBindWithSigs}
212 %************************************************************************
214 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
215 so all the clever stuff is in here.
217 * binder_names and mbind must define the same set of Names
219 * The Names in tc_ty_sigs must be a subset of binder_names
221 * The Ids in tc_ty_sigs don't necessarily have to have the same name
222 as the Name in the tc_ty_sig
232 -> TcM s (TcMonoBinds s, LIE s, [TcIdBndr s])
234 tcBindWithSigs top_lvl binder_names mbind tc_ty_sigs is_rec prag_info_fn
236 -- If typechecking the binds fails, then return with each
237 -- signature-less binder given type (forall a.a), to minimise subsequent
239 newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ alpha_tv ->
241 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
242 poly_ids = map mk_dummy binder_names
243 mk_dummy name = case maybeSig tc_ty_sigs name of
244 Just (TySigInfo _ poly_id _ _ _ _) -> poly_id -- Signature
245 Nothing -> mkUserId name forall_a_a -- No signature
247 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
250 -- Create a new identifier for each binder, with each being given
251 -- a fresh unique, and a type-variable type.
252 -- For "mono_lies" see comments about polymorphic recursion at the
253 -- end of the function.
254 mapAndUnzipNF_Tc mk_mono_id binder_names `thenNF_Tc` \ (mono_lies, mono_ids) ->
256 mono_lie = plusLIEs mono_lies
257 mono_id_tys = map idType mono_ids
260 -- TYPECHECK THE BINDINGS
261 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs `thenTc` \ (mbind', lie) ->
263 -- CHECK THAT THE SIGNATURES MATCH
264 -- (must do this before getTyVarsToGen)
265 checkSigMatch tc_ty_sigs `thenTc` \ sig_theta ->
267 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
268 -- The tyvars_not_to_gen are free in the environment, and hence
269 -- candidates for generalisation, but sometimes the monomorphism
270 -- restriction means we can't generalise them nevertheless
271 getTyVarsToGen is_unrestricted mono_id_tys lie `thenTc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
273 -- DEAL WITH TYPE VARIABLE KINDS
274 -- **** This step can do unification => keep other zonking after this ****
275 mapTc defaultUncommittedTyVar (tyVarSetToList tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
277 real_tyvars_to_gen = mkTyVarSet real_tyvars_to_gen_list
278 -- It's important that the final list
279 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
280 -- zonked, *including boxity*, because they'll be included in the forall types of
281 -- the polymorphic Ids, and instances of these Ids will be generated from them.
283 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
284 -- real_tyvars_to_gen
288 tcExtendGlobalTyVars (tyVarSetToList tyvars_not_to_gen) (
289 if null tc_ty_sigs then
290 -- No signatures, so just simplify the lie
291 -- NB: no signatures => no polymorphic recursion, so no
292 -- need to use mono_lies (which will be empty anyway)
293 tcSimplify (text "tcBinds1" <+> ppr binder_names)
294 top_lvl real_tyvars_to_gen lie `thenTc` \ (lie_free, dict_binds, lie_bound) ->
295 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
298 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
299 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
300 -- It's important that sig_theta is zonked, because
301 -- dict_id is later used to form the type of the polymorphic thing,
302 -- and forall-types must be zonked so far as their bound variables
306 -- The "givens" is the stuff available. We get that from
307 -- the context of the type signature, BUT ALSO the mono_lie
308 -- so that polymorphic recursion works right (see comments at end of fn)
309 givens = dicts_sig `plusLIE` mono_lie
312 -- Check that the needed dicts can be expressed in
313 -- terms of the signature ones
314 tcAddErrCtxt (bindSigsCtxt tysig_names) $
316 (ptext SLIT("type signature for") <+>
317 hsep (punctuate comma (map (quotes . ppr) binder_names)))
318 real_tyvars_to_gen givens lie `thenTc` \ (lie_free, dict_binds) ->
320 returnTc (lie_free, dict_binds, dict_ids)
322 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
324 ASSERT( not (any (isUnboxedTypeKind . tyVarKind) real_tyvars_to_gen_list) )
325 -- The instCantBeGeneralised stuff in tcSimplify should have
326 -- already raised an error if we're trying to generalise an unboxed tyvar
327 -- (NB: unboxed tyvars are always introduced along with a class constraint)
328 -- and it's better done there because we have more precise origin information.
329 -- That's why we just use an ASSERT here.
331 -- BUILD THE POLYMORPHIC RESULT IDs
332 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
334 exports = zipWith3 mk_export binder_names mono_ids zonked_mono_id_types
335 dict_tys = map tcIdType dicts_bound
337 mk_export binder_name mono_id zonked_mono_id_ty
338 = (tyvars, TcId (replaceIdInfo poly_id (prag_info_fn binder_name)), TcId mono_id)
340 (tyvars, poly_id) = case maybeSig tc_ty_sigs binder_name of
341 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _) -> (sig_tyvars, sig_poly_id)
342 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
344 new_poly_id = mkUserId binder_name poly_ty
345 poly_ty = mkForAllTys real_tyvars_to_gen_list $ mkFunTys dict_tys $ zonked_mono_id_ty
346 -- It's important to build a fully-zonked poly_ty, because
347 -- we'll slurp out its free type variables when extending the
348 -- local environment (tcExtendLocalValEnv); if it's not zonked
349 -- it appears to have free tyvars that aren't actually free at all.
354 AbsBinds real_tyvars_to_gen_list
357 (dict_binds `AndMonoBinds` mbind'),
359 [poly_id | (_, TcId poly_id, _) <- exports]
362 no_of_binders = length binder_names
364 mk_mono_id binder_name
365 | theres_a_signature -- There's a signature; and it's overloaded,
366 && not (null sig_theta) -- so make a Method
367 = tcAddSrcLoc sig_loc $
368 newMethodWithGivenTy SignatureOrigin
369 (TcId poly_id) (mkTyVarTys sig_tyvars)
370 sig_theta sig_tau `thenNF_Tc` \ (mono_lie, TcId mono_id) ->
371 -- A bit turgid to have to strip the TcId
372 returnNF_Tc (mono_lie, mono_id)
374 | otherwise -- No signature or not overloaded;
375 = tcAddSrcLoc (getSrcLoc binder_name) $
376 (if theres_a_signature then
377 returnNF_Tc sig_tau -- Non-overloaded signature; use its type
379 newTyVarTy kind -- No signature; use a new type variable
380 ) `thenNF_Tc` \ mono_id_ty ->
382 newLocalId (getOccName binder_name) mono_id_ty `thenNF_Tc` \ mono_id ->
383 returnNF_Tc (emptyLIE, mono_id)
385 maybe_sig = maybeSig tc_ty_sigs binder_name
386 theres_a_signature = maybeToBool maybe_sig
387 Just (TySigInfo name poly_id sig_tyvars sig_theta sig_tau sig_loc) = maybe_sig
389 tysig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
390 is_unrestricted = isUnRestrictedGroup tysig_names mbind
392 kind = case is_rec of
393 Recursive -> mkBoxedTypeKind -- Recursive, so no unboxed types
394 NonRecursive -> mkTypeKind -- Non-recursive, so we permit unboxed types
397 Polymorphic recursion
398 ~~~~~~~~~~~~~~~~~~~~~
399 The game plan for polymorphic recursion in the code above is
401 * Bind any variable for which we have a type signature
402 to an Id with a polymorphic type. Then when type-checking
403 the RHSs we'll make a full polymorphic call.
405 This fine, but if you aren't a bit careful you end up with a horrendous
406 amount of partial application and (worse) a huge space leak. For example:
408 f :: Eq a => [a] -> [a]
411 If we don't take care, after typechecking we get
413 f = /\a -> \d::Eq a -> let f' = f a d
417 Notice the the stupid construction of (f a d), which is of course
418 identical to the function we're executing. In this case, the
419 polymorphic recursion ins't being used (but that's a very common case).
421 This can lead to a massive space leak, from the following top-level defn:
426 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
427 f' is another thunk which evaluates to the same thing... and you end
428 up with a chain of identical values all hung onto by the CAF ff.
430 Solution: when typechecking the RHSs we always have in hand the
431 *monomorphic* Ids for each binding. So we just need to make sure that
432 if (Method f a d) shows up in the constraints emerging from (...f...)
433 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
434 to the "givens" when simplifying constraints. Thats' what the "mono_lies"
438 %************************************************************************
440 \subsection{getTyVarsToGen}
442 %************************************************************************
444 @getTyVarsToGen@ decides what type variables generalise over.
446 For a "restricted group" -- see the monomorphism restriction
447 for a definition -- we bind no dictionaries, and
448 remove from tyvars_to_gen any constrained type variables
450 *Don't* simplify dicts at this point, because we aren't going
451 to generalise over these dicts. By the time we do simplify them
452 we may well know more. For example (this actually came up)
454 f x = array ... xs where xs = [1,2,3,4,5]
455 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
456 stuff. If we simplify only at the f-binding (not the xs-binding)
457 we'll know that the literals are all Ints, and we can just produce
460 Find all the type variables involved in overloading, the
461 "constrained_tyvars". These are the ones we *aren't* going to
462 generalise. We must be careful about doing this:
464 (a) If we fail to generalise a tyvar which is not actually
465 constrained, then it will never, ever get bound, and lands
466 up printed out in interface files! Notorious example:
467 instance Eq a => Eq (Foo a b) where ..
468 Here, b is not constrained, even though it looks as if it is.
469 Another, more common, example is when there's a Method inst in
470 the LIE, whose type might very well involve non-overloaded
473 (b) On the other hand, we mustn't generalise tyvars which are constrained,
474 because we are going to pass on out the unmodified LIE, with those
475 tyvars in it. They won't be in scope if we've generalised them.
477 So we are careful, and do a complete simplification just to find the
478 constrained tyvars. We don't use any of the results, except to
479 find which tyvars are constrained.
482 getTyVarsToGen is_unrestricted mono_id_tys lie
483 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
484 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
486 tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusTyVarSet` free_tyvars
490 returnTc (emptyTyVarSet, tyvars_to_gen)
492 tcSimplify (text "getTVG") NotTopLevel tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
494 -- ASSERT: dicts_sig is already zonked!
495 constrained_tyvars = foldrBag (unionTyVarSets . tyVarsOfInst) emptyTyVarSet constrained_dicts
496 reduced_tyvars_to_gen = tyvars_to_gen `minusTyVarSet` constrained_tyvars
498 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
503 isUnRestrictedGroup :: [Name] -- Signatures given for these
507 is_elem v vs = isIn "isUnResMono" v vs
509 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
510 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
511 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
512 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
513 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
514 isUnRestrictedGroup sigs mb2
515 isUnRestrictedGroup sigs EmptyMonoBinds = True
518 @defaultUncommittedTyVar@ checks for generalisation over unboxed
519 types, and defaults any TypeKind TyVars to BoxedTypeKind.
522 defaultUncommittedTyVar tyvar
523 | isTypeKind (tyVarKind tyvar)
524 = newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ boxed_tyvar ->
525 unifyTauTy (mkTyVarTy boxed_tyvar) (mkTyVarTy tyvar) `thenTc_`
533 %************************************************************************
535 \subsection{tcMonoBind}
537 %************************************************************************
539 @tcMonoBinds@ deals with a single @MonoBind@.
540 The signatures have been dealt with already.
543 tcMonoBinds :: RenamedMonoBinds
544 -> [Name] -> [TcIdBndr s]
546 -> TcM s (TcMonoBinds s, LIE s)
548 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs
549 = tcExtendLocalValEnv binder_names mono_ids (
553 sig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
554 sig_ids = [id | (TySigInfo _ id _ _ _ _) <- tc_ty_sigs]
556 tc_mono_binds EmptyMonoBinds = returnTc (EmptyMonoBinds, emptyLIE)
558 tc_mono_binds (AndMonoBinds mb1 mb2)
559 = tc_mono_binds mb1 `thenTc` \ (mb1a, lie1) ->
560 tc_mono_binds mb2 `thenTc` \ (mb2a, lie2) ->
561 returnTc (AndMonoBinds mb1a mb2a, lie1 `plusLIE` lie2)
563 tc_mono_binds (FunMonoBind name inf matches locn)
565 tcLookupLocalValueOK "tc_mono_binds" name `thenNF_Tc` \ id ->
567 -- Before checking the RHS, extend the envt with
568 -- bindings for the *polymorphic* Ids from any type signatures
569 tcExtendLocalValEnv sig_names sig_ids $
570 tcMatchesFun name (idType id) matches `thenTc` \ (matches', lie) ->
572 returnTc (FunMonoBind (TcId id) inf matches' locn, lie)
574 tc_mono_binds bind@(PatMonoBind pat grhss_and_binds locn)
576 tcAddErrCtxt (patMonoBindsCtxt bind) $
577 tcPat pat `thenTc` \ (pat2, lie_pat, pat_ty) ->
579 -- Before checking the RHS, but after the pattern, extend the envt with
580 -- bindings for the *polymorphic* Ids from any type signatures
581 tcExtendLocalValEnv sig_names sig_ids $
582 tcGRHSsAndBinds pat_ty grhss_and_binds `thenTc` \ (grhss_and_binds2, lie) ->
583 returnTc (PatMonoBind pat2 grhss_and_binds2 locn,
587 %************************************************************************
589 \subsection{Signatures}
591 %************************************************************************
593 @tcSigs@ checks the signatures for validity, and returns a list of
594 {\em freshly-instantiated} signatures. That is, the types are already
595 split up, and have fresh type variables installed. All non-type-signature
596 "RenamedSigs" are ignored.
598 The @TcSigInfo@ contains @TcTypes@ because they are unified with
599 the variable's type, and after that checked to see whether they've
605 Name -- N, the Name in corresponding binding
606 (TcIdBndr s) -- *Polymorphic* binder for this value...
607 -- Usually has name = N, but doesn't have to.
614 maybeSig :: [TcSigInfo s] -> Name -> Maybe (TcSigInfo s)
615 -- Search for a particular signature
616 maybeSig [] name = Nothing
617 maybeSig (sig@(TySigInfo sig_name _ _ _ _ _) : sigs) name
618 | name == sig_name = Just sig
619 | otherwise = maybeSig sigs name
624 tcTySig :: RenamedSig
625 -> TcM s (TcSigInfo s)
627 tcTySig (Sig v ty src_loc)
628 = tcAddSrcLoc src_loc $
629 tcHsType ty `thenTc` \ sigma_ty ->
631 -- Convert from Type to TcType
632 tcInstSigType sigma_ty `thenNF_Tc` \ sigma_tc_ty ->
634 poly_id = mkUserId v sigma_tc_ty
636 -- Instantiate this type
637 -- It's important to do this even though in the error-free case
638 -- we could just split the sigma_tc_ty (since the tyvars don't
639 -- unified with anything). But in the case of an error, when
640 -- the tyvars *do* get unified with something, we want to carry on
641 -- typechecking the rest of the program with the function bound
642 -- to a pristine type, namely sigma_tc_ty
643 tcInstSigTcType sigma_tc_ty `thenNF_Tc` \ (tyvars, rho) ->
645 (theta, tau) = splitRhoTy rho
646 -- This splitSigmaTy tries hard to make sure that tau' is a type synonym
647 -- wherever possible, which can improve interface files.
649 returnTc (TySigInfo v poly_id tyvars theta tau src_loc)
652 @checkSigMatch@ does the next step in checking signature matching.
653 The tau-type part has already been unified. What we do here is to
654 check that this unification has not over-constrained the (polymorphic)
655 type variables of the original signature type.
657 The error message here is somewhat unsatisfactory, but it'll do for
662 = returnTc (error "checkSigMatch")
664 checkSigMatch tc_ty_sigs@( sig1@(TySigInfo _ id1 _ theta1 _ _) : all_sigs_but_first )
665 = -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
666 -- Doesn't affect substitution
667 mapTc check_one_sig tc_ty_sigs `thenTc_`
669 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
670 -- The type signatures on a mutually-recursive group of definitions
671 -- must all have the same context (or none).
673 -- We unify them because, with polymorphic recursion, their types
674 -- might not otherwise be related. This is a rather subtle issue.
676 mapTc check_one_cxt all_sigs_but_first `thenTc_`
680 sig1_dict_tys = mk_dict_tys theta1
681 n_sig1_dict_tys = length sig1_dict_tys
683 check_one_cxt sig@(TySigInfo _ id _ theta _ src_loc)
684 = tcAddSrcLoc src_loc $
685 tcAddErrCtxt (sigContextsCtxt id1 id) $
686 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
687 sigContextsErr `thenTc_`
688 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
690 this_sig_dict_tys = mk_dict_tys theta
692 check_one_sig (TySigInfo name id sig_tyvars _ sig_tau src_loc)
693 = tcAddSrcLoc src_loc $
694 tcAddErrCtxt (sigCtxt id) $
695 checkSigTyVars sig_tyvars sig_tau
697 mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
701 @checkSigTyVars@ is used after the type in a type signature has been unified with
702 the actual type found. It then checks that the type variables of the type signature
704 (a) still all type variables
705 eg matching signature [a] against inferred type [(p,q)]
706 [then a will be unified to a non-type variable]
708 (b) still all distinct
709 eg matching signature [(a,b)] against inferred type [(p,p)]
710 [then a and b will be unified together]
712 (c) not mentioned in the environment
713 eg the signature for f in this:
719 Here, f is forced to be monorphic by the free occurence of x.
721 Before doing this, the substitution is applied to the signature type variable.
723 We used to have the notion of a "DontBind" type variable, which would
724 only be bound to itself or nothing. Then points (a) and (b) were
725 self-checking. But it gave rise to bogus consequential error messages.
728 f = (*) -- Monomorphic
733 Here, we get a complaint when checking the type signature for g,
734 that g isn't polymorphic enough; but then we get another one when
735 dealing with the (Num x) context arising from f's definition;
736 we try to unify x with Int (to default it), but find that x has already
737 been unified with the DontBind variable "a" from g's signature.
738 This is really a problem with side-effecting unification; we'd like to
739 undo g's effects when its type signature fails, but unification is done
740 by side effect, so we can't (easily).
742 So we revert to ordinary type variables for signatures, and try to
743 give a helpful message in checkSigTyVars.
746 checkSigTyVars :: [TcTyVar s] -- The original signature type variables
747 -> TcType s -- signature type (for err msg)
748 -> TcM s [TcTyVar s] -- Zonked signature type variables
750 checkSigTyVars sig_tyvars sig_tau
751 = mapNF_Tc zonkTcTyVar sig_tyvars `thenNF_Tc` \ sig_tys ->
753 sig_tyvars' = map (getTyVar "checkSigTyVars") sig_tys
756 -- Check points (a) and (b)
757 checkTcM (all isTyVarTy sig_tys && hasNoDups sig_tyvars')
758 (zonkTcType sig_tau `thenNF_Tc` \ sig_tau' ->
759 failWithTc (badMatchErr sig_tau sig_tau')
763 -- We want to report errors in terms of the original signature tyvars,
764 -- ie sig_tyvars, NOT sig_tyvars'. sig_tyvars' correspond
765 -- 1-1 with sig_tyvars, so we can just map back.
766 tcGetGlobalTyVars `thenNF_Tc` \ globals ->
768 mono_tyvars' = [sig_tv' | sig_tv' <- sig_tyvars',
769 sig_tv' `elementOfTyVarSet` globals]
771 mono_tyvars = map (assoc "checkSigTyVars" (sig_tyvars' `zip` sig_tyvars)) mono_tyvars'
773 checkTcM (null mono_tyvars')
774 (failWithTc (notAsPolyAsSigErr sig_tau mono_tyvars)) `thenTc_`
780 %************************************************************************
782 \subsection{SPECIALIZE pragmas}
784 %************************************************************************
787 @tcPragmaSigs@ munches up the "signatures" that arise through *user*
788 pragmas. It is convenient for them to appear in the @[RenamedSig]@
789 part of a binding because then the same machinery can be used for
790 moving them into place as is done for type signatures.
793 tcPragmaSigs :: [RenamedSig] -- The pragma signatures
794 -> TcM s (Name -> IdInfo, -- Maps name to the appropriate IdInfo
799 = mapAndUnzip3Tc tcPragmaSig sigs `thenTc` \ (maybe_info_modifiers, binds, lies) ->
801 prag_fn name = foldr ($) noIdInfo [f | Just (n,f) <- maybe_info_modifiers, n==name]
803 returnTc (prag_fn, andMonoBinds binds, plusLIEs lies)
806 The interesting case is for SPECIALISE pragmas. There are two forms.
807 Here's the first form:
809 f :: Ord a => [a] -> b -> b
810 {-# SPECIALIZE f :: [Int] -> b -> b #-}
813 For this we generate:
815 f* = /\ b -> let d1 = ...
819 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
820 retain a right-hand-side that the simplifier will otherwise discard as
821 dead code... the simplifier has a flag that tells it not to discard
822 SpecPragmaId bindings.
824 In this case the f* retains a call-instance of the overloaded
825 function, f, (including appropriate dictionaries) so that the
826 specialiser will subsequently discover that there's a call of @f@ at
827 Int, and will create a specialisation for @f@. After that, the
828 binding for @f*@ can be discarded.
830 The second form is this:
832 f :: Ord a => [a] -> b -> b
833 {-# SPECIALIZE f :: [Int] -> b -> b = g #-}
836 Here @g@ is specified as a function that implements the specialised
837 version of @f@. Suppose that g has type (a->b->b); that is, g's type
838 is more general than that required. For this we generate
840 f@Int = /\b -> g Int b
844 Here @f@@Int@ is a SpecId, the specialised version of @f@. It inherits
845 f's export status etc. @f*@ is a SpecPragmaId, as before, which just serves
846 to prevent @f@@Int@ from being discarded prematurely. After specialisation,
847 if @f@@Int@ is going to be used at all it will be used explicitly, so the simplifier can
848 discard the f* binding.
850 Actually, there is really only point in giving a SPECIALISE pragma on exported things,
851 and the simplifer won't discard SpecIds for exporte things anyway, so maybe this is
855 tcPragmaSig :: RenamedSig -> TcM s (Maybe (Name, IdInfo -> IdInfo), TcMonoBinds s, LIE s)
856 tcPragmaSig (Sig _ _ _) = returnTc (Nothing, EmptyMonoBinds, emptyLIE)
857 tcPragmaSig (SpecInstSig _ _) = returnTc (Nothing, EmptyMonoBinds, emptyLIE)
859 tcPragmaSig (InlineSig name loc)
860 = returnTc (Just (name, setInlinePragInfo IWantToBeINLINEd), EmptyMonoBinds, emptyLIE)
862 tcPragmaSig (SpecSig name poly_ty maybe_spec_name src_loc)
863 = -- SPECIALISE f :: forall b. theta => tau = g
864 tcAddSrcLoc src_loc $
865 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
867 -- Get and instantiate its alleged specialised type
868 tcHsType poly_ty `thenTc` \ sig_sigma ->
869 tcInstSigType sig_sigma `thenNF_Tc` \ sig_ty ->
871 -- Check that f has a more general type, and build a RHS for
872 -- the spec-pragma-id at the same time
873 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
875 case maybe_spec_name of
876 Nothing -> -- Just specialise "f" by building a SpecPragmaId binding
877 -- It is the thing that makes sure we don't prematurely
878 -- dead-code-eliminate the binding we are really interested in.
879 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
880 returnTc (Nothing, VarMonoBind (TcId spec_id) spec_expr, spec_lie)
882 Just g_name -> -- Don't create a SpecPragmaId. Instead add some suitable IdIfo
884 panic "Can't handle SPECIALISE with a '= g' part"
886 {- Not yet. Because we're still in the TcType world we
887 can't really add to the SpecEnv of the Id. Instead we have to
888 record the information in a different sort of Sig, and add it to
889 the IdInfo after zonking.
891 For now we just leave out this case
893 -- Get the type of f, and find out what types
894 -- f has to be instantiated at to give the signature type
895 tcLookupLocalValueOK "tcPragmaSig" name `thenNF_Tc` \ f_id ->
896 tcInstSigTcType (idType f_id) `thenNF_Tc` \ (f_tyvars, f_rho) ->
899 (sig_tyvars, sig_theta, sig_tau) = splitSigmaTy sig_ty
900 (f_theta, f_tau) = splitRhoTy f_rho
901 sig_tyvar_set = mkTyVarSet sig_tyvars
903 unifyTauTy sig_tau f_tau `thenTc_`
905 tcPolyExpr str (HsVar g_name) (mkSigmaTy sig_tyvars f_theta sig_tau) `thenTc` \ (_, _,
908 tcPragmaSig other = pprTrace "tcPragmaSig: ignoring" (ppr other) $
909 returnTc (Nothing, EmptyMonoBinds, emptyLIE)
913 %************************************************************************
915 \subsection[TcBinds-errors]{Error contexts and messages}
917 %************************************************************************
921 patMonoBindsCtxt bind
922 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
924 -----------------------------------------------
926 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
927 nest 4 (ppr v <+> ptext SLIT(" ::") <+> ppr ty)]
929 -----------------------------------------------
930 notAsPolyAsSigErr sig_tau mono_tyvars
931 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
932 4 (vcat [text "Can't for-all the type variable(s)" <+>
933 pprQuotedList mono_tyvars,
934 text "in the type" <+> quotes (ppr sig_tau)
937 -----------------------------------------------
938 badMatchErr sig_ty inferred_ty
939 = hang (ptext SLIT("Type signature doesn't match inferred type"))
940 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
941 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
944 -----------------------------------------------
946 = sep [ptext SLIT("When checking the type signature for"), quotes (ppr id)]
949 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
951 -----------------------------------------------
953 = ptext SLIT("Mismatched contexts")
954 sigContextsCtxt s1 s2
955 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
956 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
957 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
959 -----------------------------------------------
961 = panic "specGroundnessCtxt"
963 --------------------------------------------
964 specContextGroundnessCtxt -- err_ctxt dicts
965 = panic "specContextGroundnessCtxt"
968 sep [hsep [ptext SLIT("In the SPECIALIZE pragma for"), ppr name],
969 hcat [ptext SLIT(" specialised to the type"), ppr spec_ty],
971 ptext SLIT("... not all overloaded type variables were instantiated"),
972 ptext SLIT("to ground types:")])
973 4 (vcat [hsep [ppr c, ppr t]
974 | (c,t) <- map getDictClassAndType dicts])
976 (name, spec_ty, locn, pp_spec_id)
978 ValSpecSigCtxt n ty loc -> (n, ty, loc, \ x -> empty)
979 ValSpecSpecIdCtxt n ty spec loc ->
981 hsep [ptext SLIT("... type of explicit id"), ppr spec])