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(..), StmtCtxt(..),
16 Match(..), collectMonoBinders, andMonoBinds
18 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
19 import TcHsSyn ( TcMonoBinds, TcId, zonkId, mkHsLet )
22 import Inst ( LIE, emptyLIE, mkLIE, plusLIE, 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 ( TcThetaType, newTyVarTy, newTyVar,
39 zonkTcTypes, zonkTcThetaType, zonkTcTyVarToTyVar
41 import TcUnify ( unifyTauTy, unifyTauTyLists )
43 import Id ( mkVanillaId, setInlinePragma, idFreeTyVars )
44 import Var ( idType, idName )
45 import IdInfo ( InlinePragInfo(..) )
46 import Name ( Name, getOccName, getSrcLoc )
48 import Type ( mkTyVarTy, tyVarsOfTypes, mkTyConApp,
49 mkForAllTys, mkFunTys,
50 mkPredTy, mkForAllTy, isUnLiftedType,
51 isUnboxedType, unboxedTypeKind, boxedTypeKind, openTypeKind
53 import FunDeps ( tyVarFunDep, oclose )
54 import Var ( tyVarKind )
58 import Maybes ( maybeToBool )
59 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNotTopLevel )
60 import FiniteMap ( listToFM, lookupFM )
61 import Unique ( ioTyConKey, mainKey, hasKey )
66 %************************************************************************
68 \subsection{Type-checking bindings}
70 %************************************************************************
72 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
73 it needs to know something about the {\em usage} of the things bound,
74 so that it can create specialisations of them. So @tcBindsAndThen@
75 takes a function which, given an extended environment, E, typechecks
76 the scope of the bindings returning a typechecked thing and (most
77 important) an LIE. It is this LIE which is then used as the basis for
78 specialising the things bound.
80 @tcBindsAndThen@ also takes a "combiner" which glues together the
81 bindings and the "thing" to make a new "thing".
83 The real work is done by @tcBindWithSigsAndThen@.
85 Recursive and non-recursive binds are handled in essentially the same
86 way: because of uniques there are no scoping issues left. The only
87 difference is that non-recursive bindings can bind primitive values.
89 Even for non-recursive binding groups we add typings for each binder
90 to the LVE for the following reason. When each individual binding is
91 checked the type of its LHS is unified with that of its RHS; and
92 type-checking the LHS of course requires that the binder is in scope.
94 At the top-level the LIE is sure to contain nothing but constant
95 dictionaries, which we resolve at the module level.
98 tcTopBindsAndThen, tcBindsAndThen
99 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
101 -> TcM s (thing, LIE)
102 -> TcM s (thing, LIE)
104 tcTopBindsAndThen = tc_binds_and_then TopLevel
105 tcBindsAndThen = tc_binds_and_then NotTopLevel
107 tc_binds_and_then top_lvl combiner EmptyBinds do_next
109 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
112 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
113 = tc_binds_and_then top_lvl combiner b1 $
114 tc_binds_and_then top_lvl combiner b2 $
117 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
118 = -- TYPECHECK THE SIGNATURES
119 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
121 tcBindWithSigs top_lvl bind tc_ty_sigs
122 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
124 -- Extend the environment to bind the new polymorphic Ids
125 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
127 -- Build bindings and IdInfos corresponding to user pragmas
128 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
130 -- Now do whatever happens next, in the augmented envt
131 do_next `thenTc` \ (thing, thing_lie) ->
133 -- Create specialisations of functions bound here
134 -- We want to keep non-recursive things non-recursive
135 -- so that we desugar unboxed bindings correctly
136 case (top_lvl, is_rec) of
138 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
139 -- All the top level things are rec'd together anyway, so it's fine to
140 -- leave them to the tcSimplifyTop, and quite a bit faster too
142 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
143 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
145 (NotTopLevel, NonRecursive)
146 -> bindInstsOfLocalFuns
147 (thing_lie `plusLIE` prag_lie)
148 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
151 combiner NonRecursive poly_binds $
152 combiner NonRecursive prag_binds $
153 combiner Recursive lie_binds $
154 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
155 -- aren't guaranteed in dependency order (though we could change
156 -- that); hence the Recursive marker.
159 thing_lie' `plusLIE` poly_lie
162 (NotTopLevel, Recursive)
163 -> bindInstsOfLocalFuns
164 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
165 poly_ids `thenTc` \ (final_lie, lie_binds) ->
169 poly_binds `andMonoBinds`
170 lie_binds `andMonoBinds`
176 An aside. The original version of @tcBindsAndThen@ which lacks a
177 combiner function, appears below. Though it is perfectly well
178 behaved, it cannot be typed by Haskell, because the recursive call is
179 at a different type to the definition itself. There aren't too many
180 examples of this, which is why I thought it worth preserving! [SLPJ]
185 % -> TcM s (thing, LIE, thing_ty))
186 % -> TcM s ((TcHsBinds, thing), LIE, thing_ty)
188 % tcBindsAndThen EmptyBinds do_next
189 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
190 % returnTc ((EmptyBinds, thing), lie, thing_ty)
192 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
193 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
194 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
196 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
198 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
199 % = tcBindAndThen bind sigs do_next
203 %************************************************************************
205 \subsection{tcBindWithSigs}
207 %************************************************************************
209 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
210 so all the clever stuff is in here.
212 * binder_names and mbind must define the same set of Names
214 * The Names in tc_ty_sigs must be a subset of binder_names
216 * The Ids in tc_ty_sigs don't necessarily have to have the same name
217 as the Name in the tc_ty_sig
224 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
226 -> TcM s (TcMonoBinds, LIE, [TcId])
228 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
230 -- If typechecking the binds fails, then return with each
231 -- signature-less binder given type (forall a.a), to minimise subsequent
233 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
235 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
236 binder_names = map fst (bagToList (collectMonoBinders mbind))
237 poly_ids = map mk_dummy binder_names
238 mk_dummy name = case maybeSig tc_ty_sigs name of
239 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
240 Nothing -> mkVanillaId name forall_a_a -- No signature
242 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
245 -- TYPECHECK THE BINDINGS
246 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
248 -- CHECK THAT THE SIGNATURES MATCH
249 -- (must do this before getTyVarsToGen)
250 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
253 -- Force any unifications dictated by functional dependencies.
254 -- Because unification may happen, it's important that this step
256 -- - computing vars over which to quantify
257 -- - zonking the generalized type vars
258 let lie_avail = case maybe_sig_theta of
261 lie_avail_req = lie_avail `plusLIE` lie_req in
262 tcImprove lie_avail_req `thenTc_`
264 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
265 -- The tyvars_not_to_gen are free in the environment, and hence
266 -- candidates for generalisation, but sometimes the monomorphism
267 -- restriction means we can't generalise them nevertheless
269 mono_id_tys = map idType mono_ids
271 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
273 -- Finally, zonk the generalised type variables to real TyVars
274 -- This commits any unbound kind variables to boxed kind
275 -- I'm a little worried that such a kind variable might be
276 -- free in the environment, but I don't think it's possible for
277 -- this to happen when the type variable is not free in the envt
278 -- (which it isn't). SLPJ Nov 98
279 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
281 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
282 -- It's important that the final list
283 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
284 -- zonked, *including boxity*, because they'll be included in the forall types of
285 -- the polymorphic Ids, and instances of these Ids will be generated from them.
287 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
288 -- real_tyvars_to_gen
292 tcExtendGlobalTyVars tyvars_not_to_gen (
293 let ips = getIPsOfLIE lie_avail_req in
294 if null real_tyvars_to_gen_list && (null ips || not is_unrestricted) then
295 -- No polymorphism, and no IPs, so no need to simplify context
296 returnTc (lie_req, EmptyMonoBinds, [])
298 case maybe_sig_theta of
300 -- No signatures, so just simplify the lie
301 -- NB: no signatures => no polymorphic recursion, so no
302 -- need to use lie_avail (which will be empty anyway)
303 tcSimplify (text "tcBinds1" <+> ppr binder_names)
304 real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
305 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
307 Just (sig_theta, lie_avail) ->
308 -- There are signatures, and their context is sig_theta
309 -- Furthermore, lie_avail is an LIE containing the 'method insts'
310 -- for the things bound here
312 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
313 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
314 -- It's important that sig_theta is zonked, because
315 -- dict_id is later used to form the type of the polymorphic thing,
316 -- and forall-types must be zonked so far as their bound variables
320 -- The "givens" is the stuff available. We get that from
321 -- the context of the type signature, BUT ALSO the lie_avail
322 -- so that polymorphic recursion works right (see comments at end of fn)
323 givens = dicts_sig `plusLIE` lie_avail
326 -- Check that the needed dicts can be expressed in
327 -- terms of the signature ones
328 tcAddErrCtxt (bindSigsCtxt tysig_names) $
330 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
331 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
333 returnTc (lie_free, dict_binds, dict_ids)
335 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
337 -- GET THE FINAL MONO_ID_TYS
338 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
341 -- CHECK FOR BOGUS UNPOINTED BINDINGS
342 (if any isUnLiftedType zonked_mono_id_types then
343 -- Unlifted bindings must be non-recursive,
344 -- not top level, and non-polymorphic
345 checkTc (isNotTopLevel top_lvl)
346 (unliftedBindErr "Top-level" mbind) `thenTc_`
347 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
348 (unliftedBindErr "Recursive" mbind) `thenTc_`
349 checkTc (null real_tyvars_to_gen_list)
350 (unliftedBindErr "Polymorphic" mbind)
355 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
356 -- The instCantBeGeneralised stuff in tcSimplify should have
357 -- already raised an error if we're trying to generalise an
358 -- unboxed tyvar (NB: unboxed tyvars are always introduced
359 -- along with a class constraint) and it's better done there
360 -- because we have more precise origin information.
361 -- That's why we just use an ASSERT here.
364 -- BUILD THE POLYMORPHIC RESULT IDs
365 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
367 exports = zipWith mk_export binder_names zonked_mono_ids
368 dict_tys = map idType dicts_bound
370 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
371 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
372 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
373 -- "INLINE n foo" means inline foo, but not until at least phase n
374 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
375 -- then only if it is small enough etc.
376 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
377 -- See comments in CoreUnfold.blackListed for the Authorised Version
379 mk_export binder_name zonked_mono_id
381 attachNoInlinePrag no_inlines poly_id,
385 case maybeSig tc_ty_sigs binder_name of
386 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
387 (sig_tyvars, sig_poly_id)
388 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
390 new_poly_id = mkVanillaId binder_name poly_ty
391 poly_ty = mkForAllTys real_tyvars_to_gen_list
393 $ idType (zonked_mono_id)
394 -- It's important to build a fully-zonked poly_ty, because
395 -- we'll slurp out its free type variables when extending the
396 -- local environment (tcExtendLocalValEnv); if it's not zonked
397 -- it appears to have free tyvars that aren't actually free
400 pat_binders :: [Name]
401 pat_binders = map fst $ bagToList $ collectMonoBinders $
402 (justPatBindings mbind EmptyMonoBinds)
404 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
405 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
406 && isUnboxedType (idType id)))
407 (unboxedPatBindErr id)) zonked_mono_ids
412 -- pprTrace "binding.." (ppr ((dicts_bound, dict_binds), exports, [idType poly_id | (_, poly_id, _) <- exports])) $
413 AbsBinds real_tyvars_to_gen_list
417 (dict_binds `andMonoBinds` mbind'),
419 [poly_id | (_, poly_id, _) <- exports]
422 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
423 is_unrestricted = isUnRestrictedGroup tysig_names mbind
425 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
426 justPatBindings (AndMonoBinds b1 b2) binds =
427 justPatBindings b1 (justPatBindings b2 binds)
428 justPatBindings other_bind binds = binds
430 attachNoInlinePrag no_inlines bndr
431 = case lookupFM no_inlines (idName bndr) of
432 Just prag -> bndr `setInlinePragma` prag
436 Polymorphic recursion
437 ~~~~~~~~~~~~~~~~~~~~~
438 The game plan for polymorphic recursion in the code above is
440 * Bind any variable for which we have a type signature
441 to an Id with a polymorphic type. Then when type-checking
442 the RHSs we'll make a full polymorphic call.
444 This fine, but if you aren't a bit careful you end up with a horrendous
445 amount of partial application and (worse) a huge space leak. For example:
447 f :: Eq a => [a] -> [a]
450 If we don't take care, after typechecking we get
452 f = /\a -> \d::Eq a -> let f' = f a d
456 Notice the the stupid construction of (f a d), which is of course
457 identical to the function we're executing. In this case, the
458 polymorphic recursion isn't being used (but that's a very common case).
461 f = /\a -> \d::Eq a -> letrec
462 fm = \ys:[a] -> ...fm...
466 This can lead to a massive space leak, from the following top-level defn
472 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
473 f' is another thunk which evaluates to the same thing... and you end
474 up with a chain of identical values all hung onto by the CAF ff.
478 = let f' = f Int dEqInt in \ys. ...f'...
480 = let f' = let f' = f Int dEqInt in \ys. ...f'...
484 Solution: when typechecking the RHSs we always have in hand the
485 *monomorphic* Ids for each binding. So we just need to make sure that
486 if (Method f a d) shows up in the constraints emerging from (...f...)
487 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
488 to the "givens" when simplifying constraints. That's what the "lies_avail"
492 %************************************************************************
494 \subsection{getTyVarsToGen}
496 %************************************************************************
498 @getTyVarsToGen@ decides what type variables to generalise over.
500 For a "restricted group" -- see the monomorphism restriction
501 for a definition -- we bind no dictionaries, and
502 remove from tyvars_to_gen any constrained type variables
504 *Don't* simplify dicts at this point, because we aren't going
505 to generalise over these dicts. By the time we do simplify them
506 we may well know more. For example (this actually came up)
508 f x = array ... xs where xs = [1,2,3,4,5]
509 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
510 stuff. If we simplify only at the f-binding (not the xs-binding)
511 we'll know that the literals are all Ints, and we can just produce
514 Find all the type variables involved in overloading, the
515 "constrained_tyvars". These are the ones we *aren't* going to
516 generalise. We must be careful about doing this:
518 (a) If we fail to generalise a tyvar which is not actually
519 constrained, then it will never, ever get bound, and lands
520 up printed out in interface files! Notorious example:
521 instance Eq a => Eq (Foo a b) where ..
522 Here, b is not constrained, even though it looks as if it is.
523 Another, more common, example is when there's a Method inst in
524 the LIE, whose type might very well involve non-overloaded
527 (b) On the other hand, we mustn't generalise tyvars which are constrained,
528 because we are going to pass on out the unmodified LIE, with those
529 tyvars in it. They won't be in scope if we've generalised them.
531 So we are careful, and do a complete simplification just to find the
532 constrained tyvars. We don't use any of the results, except to
533 find which tyvars are constrained.
536 getTyVarsToGen is_unrestricted mono_id_tys lie
537 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
538 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
540 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
541 fds = getAllFunDepsOfLIE lie
545 -- We need to augment the type variables that appear explicitly in
546 -- the type by those that are determined by the functional dependencies.
547 -- e.g. suppose our type is C a b => a -> a
548 -- with the fun-dep a->b
549 -- Then we should generalise over b too; otherwise it will be
550 -- reported as ambiguous.
551 zonkFunDeps fds `thenNF_Tc` \ fds' ->
552 let tvFundep = tyVarFunDep fds'
553 extended_tyvars = oclose tvFundep body_tyvars
555 returnNF_Tc (emptyVarSet, extended_tyvars)
557 -- This recover and discard-errs is to avoid duplicate error
558 -- messages; this, after all, is an "extra" call to tcSimplify
559 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
562 tcSimplify (text "getTVG") body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
564 -- ASSERT: dicts_sig is already zonked!
565 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
566 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
568 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
573 isUnRestrictedGroup :: [Name] -- Signatures given for these
577 is_elem v vs = isIn "isUnResMono" v vs
579 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
580 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
581 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
583 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
584 isUnRestrictedGroup sigs mb2
585 isUnRestrictedGroup sigs EmptyMonoBinds = True
587 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
588 isUnRestrictedMatch other = True -- Some args or a signature
592 %************************************************************************
594 \subsection{tcMonoBind}
596 %************************************************************************
598 @tcMonoBinds@ deals with a single @MonoBind@.
599 The signatures have been dealt with already.
602 tcMonoBinds :: RenamedMonoBinds
605 -> TcM s (TcMonoBinds,
607 [Name], -- Bound names
608 [TcId]) -- Corresponding monomorphic bound things
610 tcMonoBinds mbinds tc_ty_sigs is_rec
611 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
613 id_list = bagToList ids
614 (names, mono_ids) = unzip id_list
616 -- This last defn is the key one:
617 -- extend the val envt with bindings for the
618 -- things bound in this group, overriding the monomorphic
619 -- ids with the polymorphic ones from the pattern
620 extra_val_env = case is_rec of
621 Recursive -> map mk_bind id_list
624 -- Don't know how to deal with pattern-bound existentials yet
625 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
626 (existentialExplode mbinds) `thenTc_`
628 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
629 -- extend the envt with bindings for all the bound ids;
630 -- and *then* override with the polymorphic Ids from the signatures
631 -- That is the whole point of the "complete_it" stuff.
633 -- There's a further wrinkle: we have to delay extending the environment
634 -- until after we've dealt with any pattern-bound signature type variables
635 -- Consider f (x::a) = ...f...
636 -- We're going to check that a isn't unified with anything in the envt,
637 -- so f itself had better not be! So we pass the envt binding f into
638 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
639 -- dealing with the signature tyvars
641 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
643 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
646 -- This function is used when dealing with a LHS binder; we make a monomorphic
647 -- version of the Id. We check for type signatures
648 tc_pat_bndr name pat_ty
649 = case maybeSig tc_ty_sigs name of
651 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
653 Just (TySigInfo _ _ _ _ _ mono_id _ _)
654 -> tcAddSrcLoc (getSrcLoc name) $
655 unifyTauTy (idType mono_id) pat_ty `thenTc_`
658 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
659 Nothing -> (name, mono_id)
660 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
662 tc_mb_pats EmptyMonoBinds
663 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
665 tc_mb_pats (AndMonoBinds mb1 mb2)
666 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
667 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
669 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
670 complete_it2 xve `thenTc` \ (mb2', lie2) ->
671 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
673 returnTc (complete_it,
674 lie_req1 `plusLIE` lie_req2,
675 tvs1 `unionBags` tvs2,
676 ids1 `unionBags` ids2,
677 lie_avail1 `plusLIE` lie_avail2)
679 tc_mb_pats (FunMonoBind name inf matches locn)
680 = newTyVarTy kind `thenNF_Tc` \ bndr_ty ->
681 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
683 complete_it xve = tcAddSrcLoc locn $
684 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
685 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
687 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
689 tc_mb_pats bind@(PatMonoBind pat grhss locn)
691 newTyVarTy kind `thenNF_Tc` \ pat_ty ->
693 -- Now typecheck the pattern
694 -- We don't support binding fresh type variables in the
695 -- pattern of a pattern binding. For example, this is illegal:
697 -- whereas this is ok
698 -- (x::Int, y::Bool) = e
700 -- We don't check explicitly for this problem. Instead, we simply
701 -- type check the pattern with tcPat. If the pattern mentions any
702 -- fresh tyvars we simply get an out-of-scope type variable error
703 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
705 complete_it xve = tcAddSrcLoc locn $
706 tcAddErrCtxt (patMonoBindsCtxt bind) $
707 tcExtendLocalValEnv xve $
708 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
709 returnTc (PatMonoBind pat' grhss' locn, lie)
711 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
713 -- Figure out the appropriate kind for the pattern,
714 -- and generate a suitable type variable
715 kind = case is_rec of
716 Recursive -> boxedTypeKind -- Recursive, so no unboxed types
717 NonRecursive -> openTypeKind -- Non-recursive, so we permit unboxed types
720 %************************************************************************
722 \subsection{Signatures}
724 %************************************************************************
726 @checkSigMatch@ does the next step in checking signature matching.
727 The tau-type part has already been unified. What we do here is to
728 check that this unification has not over-constrained the (polymorphic)
729 type variables of the original signature type.
731 The error message here is somewhat unsatisfactory, but it'll do for
735 checkSigMatch :: TopLevelFlag -> [Name] -> [TcId] -> [TcSigInfo] -> TcM s (Maybe (TcThetaType, LIE))
736 checkSigMatch top_lvl binder_names mono_ids sigs
738 = -- First unify the main_id with IO t, for any old t
739 tcSetErrCtxt mainTyCheckCtxt (
740 tcLookupTyConByKey ioTyConKey `thenTc` \ ioTyCon ->
741 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
742 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
743 (idType main_mono_id)
746 -- Now check the signatures
747 -- Must do this after the unification with IO t,
748 -- in case of a silly signature like
749 -- main :: forall a. a
750 -- The unification to IO t will bind the type variable 'a',
751 -- which is just waht check_one_sig looks for
752 mapTc check_one_sig sigs `thenTc_`
753 mapTc check_main_ctxt sigs `thenTc_`
755 returnTc (Just ([], emptyLIE))
758 = mapTc check_one_sig sigs `thenTc_`
759 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
760 returnTc (Just (theta1, sig_lie))
763 = returnTc Nothing -- No constraints from type sigs
766 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
768 sig1_dict_tys = mk_dict_tys theta1
769 n_sig1_dict_tys = length sig1_dict_tys
770 sig_lie = mkLIE (concat [insts | TySigInfo _ _ _ _ _ _ insts _ <- sigs])
772 maybe_main = find_main top_lvl binder_names mono_ids
773 main_bound_here = maybeToBool maybe_main
774 Just main_mono_id = maybe_main
776 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
777 -- Doesn't affect substitution
778 check_one_sig (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
779 = tcAddSrcLoc src_loc $
780 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
781 checkSigTyVars sig_tyvars (idFreeTyVars id)
784 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
785 -- The type signatures on a mutually-recursive group of definitions
786 -- must all have the same context (or none).
788 -- We unify them because, with polymorphic recursion, their types
789 -- might not otherwise be related. This is a rather subtle issue.
791 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
792 = tcAddSrcLoc src_loc $
793 tcAddErrCtxt (sigContextsCtxt id1 id) $
794 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
795 sigContextsErr `thenTc_`
796 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
798 this_sig_dict_tys = mk_dict_tys theta
800 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
801 -- the signature contexts are empty (what a bore)
802 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
803 = tcAddSrcLoc src_loc $
804 checkTc (null theta) (mainContextsErr id)
806 mk_dict_tys theta = map mkPredTy theta
808 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
810 -- Search for Main.main in the binder_names, return corresponding mono_id
811 find_main NotTopLevel binder_names mono_ids = Nothing
812 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
814 go (n:ns) (m:ms) | n `hasKey` mainKey = Just m
815 | otherwise = go ns ms
819 %************************************************************************
821 \subsection{SPECIALIZE pragmas}
823 %************************************************************************
825 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
826 pragmas. It is convenient for them to appear in the @[RenamedSig]@
827 part of a binding because then the same machinery can be used for
828 moving them into place as is done for type signatures.
833 f :: Ord a => [a] -> b -> b
834 {-# SPECIALIZE f :: [Int] -> b -> b #-}
837 For this we generate:
839 f* = /\ b -> let d1 = ...
843 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
844 retain a right-hand-side that the simplifier will otherwise discard as
845 dead code... the simplifier has a flag that tells it not to discard
846 SpecPragmaId bindings.
848 In this case the f* retains a call-instance of the overloaded
849 function, f, (including appropriate dictionaries) so that the
850 specialiser will subsequently discover that there's a call of @f@ at
851 Int, and will create a specialisation for @f@. After that, the
852 binding for @f*@ can be discarded.
854 We used to have a form
855 {-# SPECIALISE f :: <type> = g #-}
856 which promised that g implemented f at <type>, but we do that with
858 {-# SPECIALISE (f::<type) = g #-}
861 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
862 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
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 tcHsSigType poly_ty `thenTc` \ sig_ty ->
870 -- Check that f has a more general type, and build a RHS for
871 -- the spec-pragma-id at the same time
872 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
874 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
875 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
877 -- Just specialise "f" by building a SpecPragmaId binding
878 -- It is the thing that makes sure we don't prematurely
879 -- dead-code-eliminate the binding we are really interested in.
880 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
882 -- Do the rest and combine
883 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
884 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
885 lie_rest `plusLIE` spec_lie1)
887 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
888 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
892 %************************************************************************
894 \subsection[TcBinds-errors]{Error contexts and messages}
896 %************************************************************************
900 patMonoBindsCtxt bind
901 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
903 -----------------------------------------------
905 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
906 nest 4 (ppr v <+> dcolon <+> ppr ty)]
908 -----------------------------------------------
910 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
913 -----------------------------------------------
915 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
917 -----------------------------------------------
919 = ptext SLIT("Mismatched contexts")
921 sigContextsCtxt s1 s2
922 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
923 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
924 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
927 | id `hasKey` mainKey = ptext SLIT("Main.main cannot be overloaded")
929 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
930 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
933 = hsep [ptext SLIT("When checking that"), quotes (ptext SLIT("main")),
934 ptext SLIT("has the required type")]
936 -----------------------------------------------
937 unliftedBindErr flavour mbind
938 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
941 existentialExplode mbinds
942 = hang (vcat [text "My brain just exploded.",
943 text "I can't handle pattern bindings for existentially-quantified constructors.",
944 text "In the binding group"])