2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBindsAndThen,
8 tcSpecSigs, tcBindWithSigs ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcMatches ( tcGRHSs, tcMatchesFun )
13 import {-# SOURCE #-} TcExpr ( tcExpr )
15 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..), InPat(..), StmtCtxt(..),
16 Match(..), collectMonoBinders, andMonoBindList, andMonoBinds
18 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
19 import TcHsSyn ( TcHsBinds, TcMonoBinds, TcId, zonkId, mkHsLet )
22 import Inst ( Inst, LIE, emptyLIE, mkLIE, plusLIE, plusLIEs, InstOrigin(..),
23 newDicts, tyVarsOfInst, instToId,
24 getAllFunDepsOfLIE, getIPsOfLIE, zonkFunDeps
26 import TcEnv ( tcExtendLocalValEnv,
27 newSpecPragmaId, newLocalId,
29 tcGetGlobalTyVars, tcExtendGlobalTyVars
31 import TcSimplify ( tcSimplify, tcSimplifyAndCheck, tcSimplifyToDicts )
32 import TcImprove ( tcImprove )
33 import TcMonoType ( tcHsSigType, checkSigTyVars,
34 TcSigInfo(..), tcTySig, maybeSig, sigCtxt
36 import TcPat ( tcPat )
37 import TcSimplify ( bindInstsOfLocalFuns )
38 import TcType ( TcType, TcThetaType,
40 newTyVarTy, newTyVar, newTyVarTy_OpenKind, tcInstTcType,
41 zonkTcType, zonkTcTypes, zonkTcThetaType, zonkTcTyVarToTyVar
43 import TcUnify ( unifyTauTy, unifyTauTyLists )
45 import Id ( Id, mkVanillaId, setInlinePragma, idFreeTyVars )
46 import Var ( idType, idName )
47 import IdInfo ( setInlinePragInfo, InlinePragInfo(..) )
48 import Name ( Name, getName, getOccName, getSrcLoc )
50 import Type ( mkTyVarTy, tyVarsOfTypes, mkTyConApp,
51 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar,
52 mkPredTy, splitRhoTy, mkForAllTy, isUnLiftedType,
53 isUnboxedType, unboxedTypeKind, boxedTypeKind
55 import FunDeps ( tyVarFunDep, oclose )
56 import Var ( TyVar, tyVarKind )
60 import Maybes ( maybeToBool )
61 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNotTopLevel )
62 import FiniteMap ( listToFM, lookupFM )
63 import Unique ( ioTyConKey, mainKey, hasKey, Uniquable(..) )
64 import SrcLoc ( SrcLoc )
69 %************************************************************************
71 \subsection{Type-checking bindings}
73 %************************************************************************
75 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
76 it needs to know something about the {\em usage} of the things bound,
77 so that it can create specialisations of them. So @tcBindsAndThen@
78 takes a function which, given an extended environment, E, typechecks
79 the scope of the bindings returning a typechecked thing and (most
80 important) an LIE. It is this LIE which is then used as the basis for
81 specialising the things bound.
83 @tcBindsAndThen@ also takes a "combiner" which glues together the
84 bindings and the "thing" to make a new "thing".
86 The real work is done by @tcBindWithSigsAndThen@.
88 Recursive and non-recursive binds are handled in essentially the same
89 way: because of uniques there are no scoping issues left. The only
90 difference is that non-recursive bindings can bind primitive values.
92 Even for non-recursive binding groups we add typings for each binder
93 to the LVE for the following reason. When each individual binding is
94 checked the type of its LHS is unified with that of its RHS; and
95 type-checking the LHS of course requires that the binder is in scope.
97 At the top-level the LIE is sure to contain nothing but constant
98 dictionaries, which we resolve at the module level.
101 tcTopBindsAndThen, tcBindsAndThen
102 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
104 -> TcM s (thing, LIE)
105 -> TcM s (thing, LIE)
107 tcTopBindsAndThen = tc_binds_and_then TopLevel
108 tcBindsAndThen = tc_binds_and_then NotTopLevel
110 tc_binds_and_then top_lvl combiner EmptyBinds do_next
112 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
115 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
116 = tc_binds_and_then top_lvl combiner b1 $
117 tc_binds_and_then top_lvl combiner b2 $
120 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
121 = -- TYPECHECK THE SIGNATURES
122 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
124 tcBindWithSigs top_lvl bind tc_ty_sigs
125 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
127 -- Extend the environment to bind the new polymorphic Ids
128 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
130 -- Build bindings and IdInfos corresponding to user pragmas
131 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
133 -- Now do whatever happens next, in the augmented envt
134 do_next `thenTc` \ (thing, thing_lie) ->
136 -- Create specialisations of functions bound here
137 -- We want to keep non-recursive things non-recursive
138 -- so that we desugar unboxed bindings correctly
139 case (top_lvl, is_rec) of
141 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
142 -- All the top level things are rec'd together anyway, so it's fine to
143 -- leave them to the tcSimplifyTop, and quite a bit faster too
145 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
146 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
148 (NotTopLevel, NonRecursive)
149 -> bindInstsOfLocalFuns
150 (thing_lie `plusLIE` prag_lie)
151 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
154 combiner NonRecursive poly_binds $
155 combiner NonRecursive prag_binds $
156 combiner Recursive lie_binds $
157 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
158 -- aren't guaranteed in dependency order (though we could change
159 -- that); hence the Recursive marker.
162 thing_lie' `plusLIE` poly_lie
165 (NotTopLevel, Recursive)
166 -> bindInstsOfLocalFuns
167 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
168 poly_ids `thenTc` \ (final_lie, lie_binds) ->
172 poly_binds `andMonoBinds`
173 lie_binds `andMonoBinds`
179 An aside. The original version of @tcBindsAndThen@ which lacks a
180 combiner function, appears below. Though it is perfectly well
181 behaved, it cannot be typed by Haskell, because the recursive call is
182 at a different type to the definition itself. There aren't too many
183 examples of this, which is why I thought it worth preserving! [SLPJ]
188 % -> TcM s (thing, LIE, thing_ty))
189 % -> TcM s ((TcHsBinds, thing), LIE, thing_ty)
191 % tcBindsAndThen EmptyBinds do_next
192 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
193 % returnTc ((EmptyBinds, thing), lie, thing_ty)
195 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
196 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
197 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
199 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
201 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
202 % = tcBindAndThen bind sigs do_next
206 %************************************************************************
208 \subsection{tcBindWithSigs}
210 %************************************************************************
212 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
213 so all the clever stuff is in here.
215 * binder_names and mbind must define the same set of Names
217 * The Names in tc_ty_sigs must be a subset of binder_names
219 * The Ids in tc_ty_sigs don't necessarily have to have the same name
220 as the Name in the tc_ty_sig
227 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
229 -> TcM s (TcMonoBinds, LIE, [TcId])
231 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
233 -- If typechecking the binds fails, then return with each
234 -- signature-less binder given type (forall a.a), to minimise subsequent
236 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
238 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
239 binder_names = map fst (bagToList (collectMonoBinders mbind))
240 poly_ids = map mk_dummy binder_names
241 mk_dummy name = case maybeSig tc_ty_sigs name of
242 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
243 Nothing -> mkVanillaId name forall_a_a -- No signature
245 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
248 -- TYPECHECK THE BINDINGS
249 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
251 -- CHECK THAT THE SIGNATURES MATCH
252 -- (must do this before getTyVarsToGen)
253 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
256 -- Force any unifications dictated by functional dependencies.
257 -- Because unification may happen, it's important that this step
259 -- - computing vars over which to quantify
260 -- - zonking the generalized type vars
261 let lie_avail = case maybe_sig_theta of
264 lie_avail_req = lie_avail `plusLIE` lie_req in
265 tcImprove lie_avail_req `thenTc_`
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
272 mono_id_tys = map idType mono_ids
274 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
276 -- Finally, zonk the generalised type variables to real TyVars
277 -- This commits any unbound kind variables to boxed kind
278 -- I'm a little worried that such a kind variable might be
279 -- free in the environment, but I don't think it's possible for
280 -- this to happen when the type variable is not free in the envt
281 -- (which it isn't). SLPJ Nov 98
282 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
284 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
285 -- It's important that the final list
286 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
287 -- zonked, *including boxity*, because they'll be included in the forall types of
288 -- the polymorphic Ids, and instances of these Ids will be generated from them.
290 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
291 -- real_tyvars_to_gen
295 tcExtendGlobalTyVars tyvars_not_to_gen (
296 let ips = getIPsOfLIE lie_avail_req in
297 if null real_tyvars_to_gen_list && (null ips || not is_unrestricted) then
298 -- No polymorphism, and no IPs, so no need to simplify context
299 returnTc (lie_req, EmptyMonoBinds, [])
301 case maybe_sig_theta of
303 -- No signatures, so just simplify the lie
304 -- NB: no signatures => no polymorphic recursion, so no
305 -- need to use lie_avail (which will be empty anyway)
306 tcSimplify (text "tcBinds1" <+> ppr binder_names)
307 real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
308 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
310 Just (sig_theta, lie_avail) ->
311 -- There are signatures, and their context is sig_theta
312 -- Furthermore, lie_avail is an LIE containing the 'method insts'
313 -- for the things bound here
315 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
316 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
317 -- It's important that sig_theta is zonked, because
318 -- dict_id is later used to form the type of the polymorphic thing,
319 -- and forall-types must be zonked so far as their bound variables
323 -- The "givens" is the stuff available. We get that from
324 -- the context of the type signature, BUT ALSO the lie_avail
325 -- so that polymorphic recursion works right (see comments at end of fn)
326 givens = dicts_sig `plusLIE` lie_avail
329 -- Check that the needed dicts can be expressed in
330 -- terms of the signature ones
331 tcAddErrCtxt (bindSigsCtxt tysig_names) $
333 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
334 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
336 returnTc (lie_free, dict_binds, dict_ids)
338 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
340 -- GET THE FINAL MONO_ID_TYS
341 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
344 -- CHECK FOR BOGUS UNPOINTED BINDINGS
345 (if any isUnLiftedType zonked_mono_id_types then
346 -- Unlifted bindings must be non-recursive,
347 -- not top level, and non-polymorphic
348 checkTc (isNotTopLevel top_lvl)
349 (unliftedBindErr "Top-level" mbind) `thenTc_`
350 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
351 (unliftedBindErr "Recursive" mbind) `thenTc_`
352 checkTc (null real_tyvars_to_gen_list)
353 (unliftedBindErr "Polymorphic" mbind)
358 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
359 -- The instCantBeGeneralised stuff in tcSimplify should have
360 -- already raised an error if we're trying to generalise an
361 -- unboxed tyvar (NB: unboxed tyvars are always introduced
362 -- along with a class constraint) and it's better done there
363 -- because we have more precise origin information.
364 -- That's why we just use an ASSERT here.
367 -- BUILD THE POLYMORPHIC RESULT IDs
368 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
370 exports = zipWith mk_export binder_names zonked_mono_ids
371 dict_tys = map idType dicts_bound
373 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
374 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
375 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
376 -- "INLINE n foo" means inline foo, but not until at least phase n
377 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
378 -- then only if it is small enough etc.
379 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
380 -- See comments in CoreUnfold.blackListed for the Authorised Version
382 mk_export binder_name zonked_mono_id
384 attachNoInlinePrag no_inlines poly_id,
388 case maybeSig tc_ty_sigs binder_name of
389 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
390 (sig_tyvars, sig_poly_id)
391 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
393 new_poly_id = mkVanillaId binder_name poly_ty
394 poly_ty = mkForAllTys real_tyvars_to_gen_list
396 $ idType (zonked_mono_id)
397 -- It's important to build a fully-zonked poly_ty, because
398 -- we'll slurp out its free type variables when extending the
399 -- local environment (tcExtendLocalValEnv); if it's not zonked
400 -- it appears to have free tyvars that aren't actually free
403 pat_binders :: [Name]
404 pat_binders = map fst $ bagToList $ collectMonoBinders $
405 (justPatBindings mbind EmptyMonoBinds)
407 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
408 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
409 && isUnboxedType (idType id)))
410 (unboxedPatBindErr id)) zonked_mono_ids
415 -- pprTrace "binding.." (ppr ((dicts_bound, dict_binds), exports, [idType poly_id | (_, poly_id, _) <- exports])) $
416 AbsBinds real_tyvars_to_gen_list
420 (dict_binds `andMonoBinds` mbind'),
422 [poly_id | (_, poly_id, _) <- exports]
425 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
426 is_unrestricted = isUnRestrictedGroup tysig_names mbind
428 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
429 justPatBindings (AndMonoBinds b1 b2) binds =
430 justPatBindings b1 (justPatBindings b2 binds)
431 justPatBindings other_bind binds = binds
433 attachNoInlinePrag no_inlines bndr
434 = case lookupFM no_inlines (idName bndr) of
435 Just prag -> bndr `setInlinePragma` prag
439 Polymorphic recursion
440 ~~~~~~~~~~~~~~~~~~~~~
441 The game plan for polymorphic recursion in the code above is
443 * Bind any variable for which we have a type signature
444 to an Id with a polymorphic type. Then when type-checking
445 the RHSs we'll make a full polymorphic call.
447 This fine, but if you aren't a bit careful you end up with a horrendous
448 amount of partial application and (worse) a huge space leak. For example:
450 f :: Eq a => [a] -> [a]
453 If we don't take care, after typechecking we get
455 f = /\a -> \d::Eq a -> let f' = f a d
459 Notice the the stupid construction of (f a d), which is of course
460 identical to the function we're executing. In this case, the
461 polymorphic recursion isn't being used (but that's a very common case).
464 f = /\a -> \d::Eq a -> letrec
465 fm = \ys:[a] -> ...fm...
469 This can lead to a massive space leak, from the following top-level defn
475 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
476 f' is another thunk which evaluates to the same thing... and you end
477 up with a chain of identical values all hung onto by the CAF ff.
481 = let f' = f Int dEqInt in \ys. ...f'...
483 = let f' = let f' = f Int dEqInt in \ys. ...f'...
487 Solution: when typechecking the RHSs we always have in hand the
488 *monomorphic* Ids for each binding. So we just need to make sure that
489 if (Method f a d) shows up in the constraints emerging from (...f...)
490 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
491 to the "givens" when simplifying constraints. That's what the "lies_avail"
495 %************************************************************************
497 \subsection{getTyVarsToGen}
499 %************************************************************************
501 @getTyVarsToGen@ decides what type variables to generalise over.
503 For a "restricted group" -- see the monomorphism restriction
504 for a definition -- we bind no dictionaries, and
505 remove from tyvars_to_gen any constrained type variables
507 *Don't* simplify dicts at this point, because we aren't going
508 to generalise over these dicts. By the time we do simplify them
509 we may well know more. For example (this actually came up)
511 f x = array ... xs where xs = [1,2,3,4,5]
512 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
513 stuff. If we simplify only at the f-binding (not the xs-binding)
514 we'll know that the literals are all Ints, and we can just produce
517 Find all the type variables involved in overloading, the
518 "constrained_tyvars". These are the ones we *aren't* going to
519 generalise. We must be careful about doing this:
521 (a) If we fail to generalise a tyvar which is not actually
522 constrained, then it will never, ever get bound, and lands
523 up printed out in interface files! Notorious example:
524 instance Eq a => Eq (Foo a b) where ..
525 Here, b is not constrained, even though it looks as if it is.
526 Another, more common, example is when there's a Method inst in
527 the LIE, whose type might very well involve non-overloaded
530 (b) On the other hand, we mustn't generalise tyvars which are constrained,
531 because we are going to pass on out the unmodified LIE, with those
532 tyvars in it. They won't be in scope if we've generalised them.
534 So we are careful, and do a complete simplification just to find the
535 constrained tyvars. We don't use any of the results, except to
536 find which tyvars are constrained.
539 getTyVarsToGen is_unrestricted mono_id_tys lie
540 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
541 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
543 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
544 fds = getAllFunDepsOfLIE lie
548 -- We need to augment the type variables that appear explicitly in
549 -- the type by those that are determined by the functional dependencies.
550 -- e.g. suppose our type is C a b => a -> a
551 -- with the fun-dep a->b
552 -- Then we should generalise over b too; otherwise it will be
553 -- reported as ambiguous.
554 zonkFunDeps fds `thenNF_Tc` \ fds' ->
555 let tvFundep = tyVarFunDep fds'
556 extended_tyvars = oclose tvFundep body_tyvars
558 returnNF_Tc (emptyVarSet, extended_tyvars)
560 -- This recover and discard-errs is to avoid duplicate error
561 -- messages; this, after all, is an "extra" call to tcSimplify
562 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
565 tcSimplify (text "getTVG") body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
567 -- ASSERT: dicts_sig is already zonked!
568 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
569 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
571 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
576 isUnRestrictedGroup :: [Name] -- Signatures given for these
580 is_elem v vs = isIn "isUnResMono" v vs
582 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
583 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
584 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
586 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
587 isUnRestrictedGroup sigs mb2
588 isUnRestrictedGroup sigs EmptyMonoBinds = True
590 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
591 isUnRestrictedMatch other = True -- Some args or a signature
595 %************************************************************************
597 \subsection{tcMonoBind}
599 %************************************************************************
601 @tcMonoBinds@ deals with a single @MonoBind@.
602 The signatures have been dealt with already.
605 tcMonoBinds :: RenamedMonoBinds
608 -> TcM s (TcMonoBinds,
610 [Name], -- Bound names
611 [TcId]) -- Corresponding monomorphic bound things
613 tcMonoBinds mbinds tc_ty_sigs is_rec
614 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
616 tv_list = bagToList tvs
617 id_list = bagToList ids
618 (names, mono_ids) = unzip id_list
620 -- This last defn is the key one:
621 -- extend the val envt with bindings for the
622 -- things bound in this group, overriding the monomorphic
623 -- ids with the polymorphic ones from the pattern
624 extra_val_env = case is_rec of
625 Recursive -> map mk_bind id_list
628 -- Don't know how to deal with pattern-bound existentials yet
629 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
630 (existentialExplode mbinds) `thenTc_`
632 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
633 -- extend the envt with bindings for all the bound ids;
634 -- and *then* override with the polymorphic Ids from the signatures
635 -- That is the whole point of the "complete_it" stuff.
637 -- There's a further wrinkle: we have to delay extending the environment
638 -- until after we've dealt with any pattern-bound signature type variables
639 -- Consider f (x::a) = ...f...
640 -- We're going to check that a isn't unified with anything in the envt,
641 -- so f itself had better not be! So we pass the envt binding f into
642 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
643 -- dealing with the signature tyvars
645 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
647 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
650 -- This function is used when dealing with a LHS binder; we make a monomorphic
651 -- version of the Id. We check for type signatures
652 tc_pat_bndr name pat_ty
653 = case maybeSig tc_ty_sigs name of
655 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
657 Just (TySigInfo _ _ _ _ _ mono_id _ _)
658 -> tcAddSrcLoc (getSrcLoc name) $
659 unifyTauTy (idType mono_id) pat_ty `thenTc_`
662 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
663 Nothing -> (name, mono_id)
664 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
666 tc_mb_pats EmptyMonoBinds
667 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
669 tc_mb_pats (AndMonoBinds mb1 mb2)
670 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
671 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
673 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
674 complete_it2 xve `thenTc` \ (mb2', lie2) ->
675 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
677 returnTc (complete_it,
678 lie_req1 `plusLIE` lie_req2,
679 tvs1 `unionBags` tvs2,
680 ids1 `unionBags` ids2,
681 lie_avail1 `plusLIE` lie_avail2)
683 tc_mb_pats (FunMonoBind name inf matches locn)
684 = new_lhs_ty `thenNF_Tc` \ bndr_ty ->
685 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
687 complete_it xve = tcAddSrcLoc locn $
688 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
689 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
691 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
693 tc_mb_pats bind@(PatMonoBind pat grhss locn)
695 new_lhs_ty `thenNF_Tc` \ pat_ty ->
697 -- Now typecheck the pattern
698 -- We don't support binding fresh type variables in the
699 -- pattern of a pattern binding. For example, this is illegal:
701 -- whereas this is ok
702 -- (x::Int, y::Bool) = e
704 -- We don't check explicitly for this problem. Instead, we simply
705 -- type check the pattern with tcPat. If the pattern mentions any
706 -- fresh tyvars we simply get an out-of-scope type variable error
707 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
709 complete_it xve = tcAddSrcLoc locn $
710 tcAddErrCtxt (patMonoBindsCtxt bind) $
711 tcExtendLocalValEnv xve $
712 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
713 returnTc (PatMonoBind pat' grhss' locn, lie)
715 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
717 -- Figure out the appropriate kind for the pattern,
718 -- and generate a suitable type variable
719 new_lhs_ty = case is_rec of
720 Recursive -> newTyVarTy boxedTypeKind -- Recursive, so no unboxed types
721 NonRecursive -> newTyVarTy_OpenKind -- Non-recursive, so we permit unboxed types
724 %************************************************************************
726 \subsection{Signatures}
728 %************************************************************************
730 @checkSigMatch@ does the next step in checking signature matching.
731 The tau-type part has already been unified. What we do here is to
732 check that this unification has not over-constrained the (polymorphic)
733 type variables of the original signature type.
735 The error message here is somewhat unsatisfactory, but it'll do for
739 checkSigMatch :: TopLevelFlag -> [Name] -> [TcId] -> [TcSigInfo] -> TcM s (Maybe (TcThetaType, LIE))
740 checkSigMatch top_lvl binder_names mono_ids sigs
742 = -- First unify the main_id with IO t, for any old t
743 tcSetErrCtxt mainTyCheckCtxt (
744 tcLookupTyConByKey ioTyConKey `thenTc` \ ioTyCon ->
745 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
746 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
747 (idType main_mono_id)
750 -- Now check the signatures
751 -- Must do this after the unification with IO t,
752 -- in case of a silly signature like
753 -- main :: forall a. a
754 -- The unification to IO t will bind the type variable 'a',
755 -- which is just waht check_one_sig looks for
756 mapTc check_one_sig sigs `thenTc_`
757 mapTc check_main_ctxt sigs `thenTc_`
759 returnTc (Just ([], emptyLIE))
762 = mapTc check_one_sig sigs `thenTc_`
763 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
764 returnTc (Just (theta1, sig_lie))
767 = returnTc Nothing -- No constraints from type sigs
770 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
772 sig1_dict_tys = mk_dict_tys theta1
773 n_sig1_dict_tys = length sig1_dict_tys
774 sig_lie = mkLIE (concat [insts | TySigInfo _ _ _ _ _ _ insts _ <- sigs])
776 maybe_main = find_main top_lvl binder_names mono_ids
777 main_bound_here = maybeToBool maybe_main
778 Just main_mono_id = maybe_main
780 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
781 -- Doesn't affect substitution
782 check_one_sig (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
783 = tcAddSrcLoc src_loc $
784 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
785 checkSigTyVars sig_tyvars (idFreeTyVars id)
788 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
789 -- The type signatures on a mutually-recursive group of definitions
790 -- must all have the same context (or none).
792 -- We unify them because, with polymorphic recursion, their types
793 -- might not otherwise be related. This is a rather subtle issue.
795 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
796 = tcAddSrcLoc src_loc $
797 tcAddErrCtxt (sigContextsCtxt id1 id) $
798 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
799 sigContextsErr `thenTc_`
800 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
802 this_sig_dict_tys = mk_dict_tys theta
804 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
805 -- the signature contexts are empty (what a bore)
806 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
807 = tcAddSrcLoc src_loc $
808 checkTc (null theta) (mainContextsErr id)
810 mk_dict_tys theta = map mkPredTy theta
812 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
814 -- Search for Main.main in the binder_names, return corresponding mono_id
815 find_main NotTopLevel binder_names mono_ids = Nothing
816 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
818 go (n:ns) (m:ms) | n `hasKey` mainKey = Just m
819 | otherwise = go ns ms
823 %************************************************************************
825 \subsection{SPECIALIZE pragmas}
827 %************************************************************************
829 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
830 pragmas. It is convenient for them to appear in the @[RenamedSig]@
831 part of a binding because then the same machinery can be used for
832 moving them into place as is done for type signatures.
837 f :: Ord a => [a] -> b -> b
838 {-# SPECIALIZE f :: [Int] -> b -> b #-}
841 For this we generate:
843 f* = /\ b -> let d1 = ...
847 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
848 retain a right-hand-side that the simplifier will otherwise discard as
849 dead code... the simplifier has a flag that tells it not to discard
850 SpecPragmaId bindings.
852 In this case the f* retains a call-instance of the overloaded
853 function, f, (including appropriate dictionaries) so that the
854 specialiser will subsequently discover that there's a call of @f@ at
855 Int, and will create a specialisation for @f@. After that, the
856 binding for @f*@ can be discarded.
858 We used to have a form
859 {-# SPECIALISE f :: <type> = g #-}
860 which promised that g implemented f at <type>, but we do that with
862 {-# SPECIALISE (f::<type) = g #-}
865 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
866 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
867 = -- SPECIALISE f :: forall b. theta => tau = g
868 tcAddSrcLoc src_loc $
869 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
871 -- Get and instantiate its alleged specialised type
872 tcHsSigType poly_ty `thenTc` \ 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 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
879 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
881 -- Just specialise "f" by building a SpecPragmaId binding
882 -- It is the thing that makes sure we don't prematurely
883 -- dead-code-eliminate the binding we are really interested in.
884 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
886 -- Do the rest and combine
887 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
888 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
889 lie_rest `plusLIE` spec_lie1)
891 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
892 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
896 %************************************************************************
898 \subsection[TcBinds-errors]{Error contexts and messages}
900 %************************************************************************
904 patMonoBindsCtxt bind
905 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
907 -----------------------------------------------
909 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
910 nest 4 (ppr v <+> dcolon <+> ppr ty)]
912 -----------------------------------------------
913 notAsPolyAsSigErr sig_tau mono_tyvars
914 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
915 4 (vcat [text "Can't for-all the type variable(s)" <+>
916 pprQuotedList mono_tyvars,
917 text "in the type" <+> quotes (ppr sig_tau)
920 -----------------------------------------------
921 badMatchErr sig_ty inferred_ty
922 = hang (ptext SLIT("Type signature doesn't match inferred type"))
923 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
924 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
927 -----------------------------------------------
929 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
932 -----------------------------------------------
934 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
936 -----------------------------------------------
938 = ptext SLIT("Mismatched contexts")
940 sigContextsCtxt s1 s2
941 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
942 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
943 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
946 | id `hasKey` mainKey = ptext SLIT("Main.main cannot be overloaded")
948 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
949 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
952 = hsep [ptext SLIT("When checking that"), quotes (ptext SLIT("main")),
953 ptext SLIT("has the required type")]
955 -----------------------------------------------
956 unliftedBindErr flavour mbind
957 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
960 existentialExplode mbinds
961 = hang (vcat [text "My brain just exploded.",
962 text "I can't handle pattern bindings for existentially-quantified constructors.",
963 text "In the binding group"])