2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBinds,
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 CoreFVs ( idFreeTyVars )
44 import Id ( mkVanillaId, setInlinePragma )
45 import Var ( idType, idName )
46 import IdInfo ( InlinePragInfo(..) )
47 import Name ( Name, getOccName, getSrcLoc )
49 import Type ( mkTyVarTy, tyVarsOfTypes, mkTyConApp,
50 mkForAllTys, mkFunTys,
51 mkPredTy, mkForAllTy, isUnLiftedType,
52 isUnboxedType, unboxedTypeKind, boxedTypeKind, openTypeKind
54 import FunDeps ( tyVarFunDep, oclose )
55 import Var ( tyVarKind )
59 import Maybes ( maybeToBool )
60 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNotTopLevel )
61 import FiniteMap ( listToFM, lookupFM )
62 import PrelNames ( ioTyConName, mainKey, hasKey )
67 %************************************************************************
69 \subsection{Type-checking bindings}
71 %************************************************************************
73 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
74 it needs to know something about the {\em usage} of the things bound,
75 so that it can create specialisations of them. So @tcBindsAndThen@
76 takes a function which, given an extended environment, E, typechecks
77 the scope of the bindings returning a typechecked thing and (most
78 important) an LIE. It is this LIE which is then used as the basis for
79 specialising the things bound.
81 @tcBindsAndThen@ also takes a "combiner" which glues together the
82 bindings and the "thing" to make a new "thing".
84 The real work is done by @tcBindWithSigsAndThen@.
86 Recursive and non-recursive binds are handled in essentially the same
87 way: because of uniques there are no scoping issues left. The only
88 difference is that non-recursive bindings can bind primitive values.
90 Even for non-recursive binding groups we add typings for each binder
91 to the LVE for the following reason. When each individual binding is
92 checked the type of its LHS is unified with that of its RHS; and
93 type-checking the LHS of course requires that the binder is in scope.
95 At the top-level the LIE is sure to contain nothing but constant
96 dictionaries, which we resolve at the module level.
99 tcTopBinds :: RenamedHsBinds -> TcM ((TcMonoBinds, TcEnv), LIE)
101 = tc_binds_and_then TopLevel glue binds $
102 tcGetEnv `thenNF_Tc` \ env ->
103 returnTc ((EmptyMonoBinds, env), emptyLIE)
105 glue is_rec binds1 (binds2, thing) = (binds1 `AndMonoBinds` binds2, thing)
109 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
114 tcBindsAndThen = tc_binds_and_then NotTopLevel
116 tc_binds_and_then top_lvl combiner EmptyBinds do_next
118 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
121 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
122 = tc_binds_and_then top_lvl combiner b1 $
123 tc_binds_and_then top_lvl combiner b2 $
126 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
127 = -- TYPECHECK THE SIGNATURES
128 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
130 tcBindWithSigs top_lvl bind tc_ty_sigs
131 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
133 -- Extend the environment to bind the new polymorphic Ids
134 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
136 -- Build bindings and IdInfos corresponding to user pragmas
137 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
139 -- Now do whatever happens next, in the augmented envt
140 do_next `thenTc` \ (thing, thing_lie) ->
142 -- Create specialisations of functions bound here
143 -- We want to keep non-recursive things non-recursive
144 -- so that we desugar unboxed bindings correctly
145 case (top_lvl, is_rec) of
147 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
148 -- All the top level things are rec'd together anyway, so it's fine to
149 -- leave them to the tcSimplifyTop, and quite a bit faster too
151 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
152 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
154 (NotTopLevel, NonRecursive)
155 -> bindInstsOfLocalFuns
156 (thing_lie `plusLIE` prag_lie)
157 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
160 combiner NonRecursive poly_binds $
161 combiner NonRecursive prag_binds $
162 combiner Recursive lie_binds $
163 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
164 -- aren't guaranteed in dependency order (though we could change
165 -- that); hence the Recursive marker.
168 thing_lie' `plusLIE` poly_lie
171 (NotTopLevel, Recursive)
172 -> bindInstsOfLocalFuns
173 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
174 poly_ids `thenTc` \ (final_lie, lie_binds) ->
178 poly_binds `andMonoBinds`
179 lie_binds `andMonoBinds`
185 An aside. The original version of @tcBindsAndThen@ which lacks a
186 combiner function, appears below. Though it is perfectly well
187 behaved, it cannot be typed by Haskell, because the recursive call is
188 at a different type to the definition itself. There aren't too many
189 examples of this, which is why I thought it worth preserving! [SLPJ]
194 % -> TcM (thing, LIE, thing_ty))
195 % -> TcM ((TcHsBinds, thing), LIE, thing_ty)
197 % tcBindsAndThen EmptyBinds do_next
198 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
199 % returnTc ((EmptyBinds, thing), lie, thing_ty)
201 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
202 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
203 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
205 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
207 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
208 % = tcBindAndThen bind sigs do_next
212 %************************************************************************
214 \subsection{tcBindWithSigs}
216 %************************************************************************
218 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
219 so all the clever stuff is in here.
221 * binder_names and mbind must define the same set of Names
223 * The Names in tc_ty_sigs must be a subset of binder_names
225 * The Ids in tc_ty_sigs don't necessarily have to have the same name
226 as the Name in the tc_ty_sig
233 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
235 -> TcM (TcMonoBinds, LIE, [TcId])
237 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
239 -- If typechecking the binds fails, then return with each
240 -- signature-less binder given type (forall a.a), to minimise subsequent
242 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
244 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
245 binder_names = collectMonoBinders mbind
246 poly_ids = map mk_dummy binder_names
247 mk_dummy name = case maybeSig tc_ty_sigs name of
248 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
249 Nothing -> mkVanillaId name forall_a_a -- No signature
251 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
254 -- TYPECHECK THE BINDINGS
255 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
257 -- CHECK THAT THE SIGNATURES MATCH
258 -- (must do this before getTyVarsToGen)
259 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
262 -- Force any unifications dictated by functional dependencies.
263 -- Because unification may happen, it's important that this step
265 -- - computing vars over which to quantify
266 -- - zonking the generalized type vars
267 let lie_avail = case maybe_sig_theta of
270 lie_avail_req = lie_avail `plusLIE` lie_req in
271 tcImprove lie_avail_req `thenTc_`
273 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
274 -- The tyvars_not_to_gen are free in the environment, and hence
275 -- candidates for generalisation, but sometimes the monomorphism
276 -- restriction means we can't generalise them nevertheless
278 mono_id_tys = map idType mono_ids
280 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
282 -- Finally, zonk the generalised type variables to real TyVars
283 -- This commits any unbound kind variables to boxed kind
284 -- I'm a little worried that such a kind variable might be
285 -- free in the environment, but I don't think it's possible for
286 -- this to happen when the type variable is not free in the envt
287 -- (which it isn't). SLPJ Nov 98
288 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
290 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
291 -- It's important that the final list
292 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
293 -- zonked, *including boxity*, because they'll be included in the forall types of
294 -- the polymorphic Ids, and instances of these Ids will be generated from them.
296 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
297 -- real_tyvars_to_gen
301 tcExtendGlobalTyVars tyvars_not_to_gen (
302 let ips = getIPsOfLIE lie_avail_req in
303 if null real_tyvars_to_gen_list && (null ips || not is_unrestricted) then
304 -- No polymorphism, and no IPs, so no need to simplify context
305 returnTc (lie_req, EmptyMonoBinds, [])
307 case maybe_sig_theta of
309 -- No signatures, so just simplify the lie
310 -- NB: no signatures => no polymorphic recursion, so no
311 -- need to use lie_avail (which will be empty anyway)
312 tcSimplify (text "tcBinds1" <+> ppr binder_names)
313 real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
314 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
316 Just (sig_theta, lie_avail) ->
317 -- There are signatures, and their context is sig_theta
318 -- Furthermore, lie_avail is an LIE containing the 'method insts'
319 -- for the things bound here
321 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
322 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
323 -- It's important that sig_theta is zonked, because
324 -- dict_id is later used to form the type of the polymorphic thing,
325 -- and forall-types must be zonked so far as their bound variables
329 -- The "givens" is the stuff available. We get that from
330 -- the context of the type signature, BUT ALSO the lie_avail
331 -- so that polymorphic recursion works right (see comments at end of fn)
332 givens = dicts_sig `plusLIE` lie_avail
335 -- Check that the needed dicts can be expressed in
336 -- terms of the signature ones
337 tcAddErrCtxt (bindSigsCtxt tysig_names) $
339 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
340 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
342 returnTc (lie_free, dict_binds, dict_ids)
344 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
346 -- GET THE FINAL MONO_ID_TYS
347 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
350 -- CHECK FOR BOGUS UNPOINTED BINDINGS
351 (if any isUnLiftedType zonked_mono_id_types then
352 -- Unlifted bindings must be non-recursive,
353 -- not top level, and non-polymorphic
354 checkTc (isNotTopLevel top_lvl)
355 (unliftedBindErr "Top-level" mbind) `thenTc_`
356 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
357 (unliftedBindErr "Recursive" mbind) `thenTc_`
358 checkTc (null real_tyvars_to_gen_list)
359 (unliftedBindErr "Polymorphic" mbind)
364 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
365 -- The instCantBeGeneralised stuff in tcSimplify should have
366 -- already raised an error if we're trying to generalise an
367 -- unboxed tyvar (NB: unboxed tyvars are always introduced
368 -- along with a class constraint) and it's better done there
369 -- because we have more precise origin information.
370 -- That's why we just use an ASSERT here.
373 -- BUILD THE POLYMORPHIC RESULT IDs
374 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
376 exports = zipWith mk_export binder_names zonked_mono_ids
377 dict_tys = map idType dicts_bound
379 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
380 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
381 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
382 -- "INLINE n foo" means inline foo, but not until at least phase n
383 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
384 -- then only if it is small enough etc.
385 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
386 -- See comments in CoreUnfold.blackListed for the Authorised Version
388 mk_export binder_name zonked_mono_id
390 attachNoInlinePrag no_inlines poly_id,
394 case maybeSig tc_ty_sigs binder_name of
395 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
396 (sig_tyvars, sig_poly_id)
397 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
399 new_poly_id = mkVanillaId binder_name poly_ty
400 poly_ty = mkForAllTys real_tyvars_to_gen_list
402 $ idType (zonked_mono_id)
403 -- It's important to build a fully-zonked poly_ty, because
404 -- we'll slurp out its free type variables when extending the
405 -- local environment (tcExtendLocalValEnv); if it's not zonked
406 -- it appears to have free tyvars that aren't actually free
409 pat_binders :: [Name]
410 pat_binders = collectMonoBinders (justPatBindings mbind EmptyMonoBinds)
412 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
413 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
414 && isUnboxedType (idType id)))
415 (unboxedPatBindErr id)) zonked_mono_ids
420 -- pprTrace "binding.." (ppr ((dicts_bound, dict_binds), exports, [idType poly_id | (_, poly_id, _) <- exports])) $
421 AbsBinds real_tyvars_to_gen_list
425 (dict_binds `andMonoBinds` mbind'),
427 [poly_id | (_, poly_id, _) <- exports]
430 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
431 is_unrestricted = isUnRestrictedGroup tysig_names mbind
433 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
434 justPatBindings (AndMonoBinds b1 b2) binds =
435 justPatBindings b1 (justPatBindings b2 binds)
436 justPatBindings other_bind binds = binds
438 attachNoInlinePrag no_inlines bndr
439 = case lookupFM no_inlines (idName bndr) of
440 Just prag -> bndr `setInlinePragma` prag
444 Polymorphic recursion
445 ~~~~~~~~~~~~~~~~~~~~~
446 The game plan for polymorphic recursion in the code above is
448 * Bind any variable for which we have a type signature
449 to an Id with a polymorphic type. Then when type-checking
450 the RHSs we'll make a full polymorphic call.
452 This fine, but if you aren't a bit careful you end up with a horrendous
453 amount of partial application and (worse) a huge space leak. For example:
455 f :: Eq a => [a] -> [a]
458 If we don't take care, after typechecking we get
460 f = /\a -> \d::Eq a -> let f' = f a d
464 Notice the the stupid construction of (f a d), which is of course
465 identical to the function we're executing. In this case, the
466 polymorphic recursion isn't being used (but that's a very common case).
469 f = /\a -> \d::Eq a -> letrec
470 fm = \ys:[a] -> ...fm...
474 This can lead to a massive space leak, from the following top-level defn
480 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
481 f' is another thunk which evaluates to the same thing... and you end
482 up with a chain of identical values all hung onto by the CAF ff.
486 = let f' = f Int dEqInt in \ys. ...f'...
488 = let f' = let f' = f Int dEqInt in \ys. ...f'...
492 Solution: when typechecking the RHSs we always have in hand the
493 *monomorphic* Ids for each binding. So we just need to make sure that
494 if (Method f a d) shows up in the constraints emerging from (...f...)
495 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
496 to the "givens" when simplifying constraints. That's what the "lies_avail"
500 %************************************************************************
502 \subsection{getTyVarsToGen}
504 %************************************************************************
506 @getTyVarsToGen@ decides what type variables to generalise over.
508 For a "restricted group" -- see the monomorphism restriction
509 for a definition -- we bind no dictionaries, and
510 remove from tyvars_to_gen any constrained type variables
512 *Don't* simplify dicts at this point, because we aren't going
513 to generalise over these dicts. By the time we do simplify them
514 we may well know more. For example (this actually came up)
516 f x = array ... xs where xs = [1,2,3,4,5]
517 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
518 stuff. If we simplify only at the f-binding (not the xs-binding)
519 we'll know that the literals are all Ints, and we can just produce
522 Find all the type variables involved in overloading, the
523 "constrained_tyvars". These are the ones we *aren't* going to
524 generalise. We must be careful about doing this:
526 (a) If we fail to generalise a tyvar which is not actually
527 constrained, then it will never, ever get bound, and lands
528 up printed out in interface files! Notorious example:
529 instance Eq a => Eq (Foo a b) where ..
530 Here, b is not constrained, even though it looks as if it is.
531 Another, more common, example is when there's a Method inst in
532 the LIE, whose type might very well involve non-overloaded
535 (b) On the other hand, we mustn't generalise tyvars which are constrained,
536 because we are going to pass on out the unmodified LIE, with those
537 tyvars in it. They won't be in scope if we've generalised them.
539 So we are careful, and do a complete simplification just to find the
540 constrained tyvars. We don't use any of the results, except to
541 find which tyvars are constrained.
544 getTyVarsToGen is_unrestricted mono_id_tys lie
545 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
546 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
548 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
549 fds = getAllFunDepsOfLIE lie
553 -- We need to augment the type variables that appear explicitly in
554 -- the type by those that are determined by the functional dependencies.
555 -- e.g. suppose our type is C a b => a -> a
556 -- with the fun-dep a->b
557 -- Then we should generalise over b too; otherwise it will be
558 -- reported as ambiguous.
559 zonkFunDeps fds `thenNF_Tc` \ fds' ->
560 let tvFundep = tyVarFunDep fds'
561 extended_tyvars = oclose tvFundep body_tyvars
563 returnNF_Tc (emptyVarSet, extended_tyvars)
565 -- This recover and discard-errs is to avoid duplicate error
566 -- messages; this, after all, is an "extra" call to tcSimplify
567 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
570 tcSimplify (text "getTVG") body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
572 -- ASSERT: dicts_sig is already zonked!
573 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
574 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
576 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
581 isUnRestrictedGroup :: [Name] -- Signatures given for these
585 is_elem v vs = isIn "isUnResMono" v vs
587 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
588 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
589 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
591 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
592 isUnRestrictedGroup sigs mb2
593 isUnRestrictedGroup sigs EmptyMonoBinds = True
595 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
596 isUnRestrictedMatch other = True -- Some args or a signature
600 %************************************************************************
602 \subsection{tcMonoBind}
604 %************************************************************************
606 @tcMonoBinds@ deals with a single @MonoBind@.
607 The signatures have been dealt with already.
610 tcMonoBinds :: RenamedMonoBinds
615 [Name], -- Bound names
616 [TcId]) -- Corresponding monomorphic bound things
618 tcMonoBinds mbinds tc_ty_sigs is_rec
619 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
621 id_list = bagToList ids
622 (names, mono_ids) = unzip id_list
624 -- This last defn is the key one:
625 -- extend the val envt with bindings for the
626 -- things bound in this group, overriding the monomorphic
627 -- ids with the polymorphic ones from the pattern
628 extra_val_env = case is_rec of
629 Recursive -> map mk_bind id_list
632 -- Don't know how to deal with pattern-bound existentials yet
633 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
634 (existentialExplode mbinds) `thenTc_`
636 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
637 -- extend the envt with bindings for all the bound ids;
638 -- and *then* override with the polymorphic Ids from the signatures
639 -- That is the whole point of the "complete_it" stuff.
641 -- There's a further wrinkle: we have to delay extending the environment
642 -- until after we've dealt with any pattern-bound signature type variables
643 -- Consider f (x::a) = ...f...
644 -- We're going to check that a isn't unified with anything in the envt,
645 -- so f itself had better not be! So we pass the envt binding f into
646 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
647 -- dealing with the signature tyvars
649 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
651 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
654 -- This function is used when dealing with a LHS binder; we make a monomorphic
655 -- version of the Id. We check for type signatures
656 tc_pat_bndr name pat_ty
657 = case maybeSig tc_ty_sigs name of
659 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
661 Just (TySigInfo _ _ _ _ _ mono_id _ _)
662 -> tcAddSrcLoc (getSrcLoc name) $
663 unifyTauTy (idType mono_id) pat_ty `thenTc_`
666 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
667 Nothing -> (name, mono_id)
668 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
670 tc_mb_pats EmptyMonoBinds
671 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
673 tc_mb_pats (AndMonoBinds mb1 mb2)
674 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
675 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
677 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
678 complete_it2 xve `thenTc` \ (mb2', lie2) ->
679 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
681 returnTc (complete_it,
682 lie_req1 `plusLIE` lie_req2,
683 tvs1 `unionBags` tvs2,
684 ids1 `unionBags` ids2,
685 lie_avail1 `plusLIE` lie_avail2)
687 tc_mb_pats (FunMonoBind name inf matches locn)
688 = newTyVarTy kind `thenNF_Tc` \ bndr_ty ->
689 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
691 complete_it xve = tcAddSrcLoc locn $
692 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
693 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
695 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
697 tc_mb_pats bind@(PatMonoBind pat grhss locn)
699 newTyVarTy kind `thenNF_Tc` \ pat_ty ->
701 -- Now typecheck the pattern
702 -- We don't support binding fresh type variables in the
703 -- pattern of a pattern binding. For example, this is illegal:
705 -- whereas this is ok
706 -- (x::Int, y::Bool) = e
708 -- We don't check explicitly for this problem. Instead, we simply
709 -- type check the pattern with tcPat. If the pattern mentions any
710 -- fresh tyvars we simply get an out-of-scope type variable error
711 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
713 complete_it xve = tcAddSrcLoc locn $
714 tcAddErrCtxt (patMonoBindsCtxt bind) $
715 tcExtendLocalValEnv xve $
716 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
717 returnTc (PatMonoBind pat' grhss' locn, lie)
719 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
721 -- Figure out the appropriate kind for the pattern,
722 -- and generate a suitable type variable
723 kind = case is_rec of
724 Recursive -> boxedTypeKind -- Recursive, so no unboxed types
725 NonRecursive -> openTypeKind -- Non-recursive, so we permit unboxed types
728 %************************************************************************
730 \subsection{Signatures}
732 %************************************************************************
734 @checkSigMatch@ does the next step in checking signature matching.
735 The tau-type part has already been unified. What we do here is to
736 check that this unification has not over-constrained the (polymorphic)
737 type variables of the original signature type.
739 The error message here is somewhat unsatisfactory, but it'll do for
743 checkSigMatch :: TopLevelFlag -> [Name] -> [TcId] -> [TcSigInfo] -> TcM (Maybe (TcThetaType, LIE))
744 checkSigMatch top_lvl binder_names mono_ids sigs
746 = -- First unify the main_id with IO t, for any old t
747 tcSetErrCtxt mainTyCheckCtxt (
748 tcLookupTyCon ioTyConName `thenTc` \ ioTyCon ->
749 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
750 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
751 (idType main_mono_id)
754 -- Now check the signatures
755 -- Must do this after the unification with IO t,
756 -- in case of a silly signature like
757 -- main :: forall a. a
758 -- The unification to IO t will bind the type variable 'a',
759 -- which is just waht check_one_sig looks for
760 mapTc check_one_sig sigs `thenTc_`
761 mapTc check_main_ctxt sigs `thenTc_`
762 returnTc (Just ([], emptyLIE))
765 = mapTc check_one_sig sigs `thenTc_`
766 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
767 returnTc (Just (theta1, sig_lie))
770 = returnTc Nothing -- No constraints from type sigs
773 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
775 sig1_dict_tys = mk_dict_tys theta1
776 n_sig1_dict_tys = length sig1_dict_tys
777 sig_lie = mkLIE (concat [insts | TySigInfo _ _ _ _ _ _ insts _ <- sigs])
779 maybe_main = find_main top_lvl binder_names mono_ids
780 main_bound_here = maybeToBool maybe_main
781 Just main_mono_id = maybe_main
783 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
784 -- Doesn't affect substitution
785 check_one_sig (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
786 = tcAddSrcLoc src_loc $
787 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
788 checkSigTyVars sig_tyvars (idFreeTyVars id)
791 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
792 -- The type signatures on a mutually-recursive group of definitions
793 -- must all have the same context (or none).
795 -- We unify them because, with polymorphic recursion, their types
796 -- might not otherwise be related. This is a rather subtle issue.
798 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
799 = tcAddSrcLoc src_loc $
800 tcAddErrCtxt (sigContextsCtxt id1 id) $
801 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
802 sigContextsErr `thenTc_`
803 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
805 this_sig_dict_tys = mk_dict_tys theta
807 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
808 -- the signature contexts are empty (what a bore)
809 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
810 = tcAddSrcLoc src_loc $
811 checkTc (null theta) (mainContextsErr id)
813 mk_dict_tys theta = map mkPredTy theta
815 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
817 -- Search for Main.main in the binder_names, return corresponding mono_id
818 find_main NotTopLevel binder_names mono_ids = Nothing
819 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
821 go (n:ns) (m:ms) | n `hasKey` mainKey = Just m
822 | otherwise = go ns ms
826 %************************************************************************
828 \subsection{SPECIALIZE pragmas}
830 %************************************************************************
832 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
833 pragmas. It is convenient for them to appear in the @[RenamedSig]@
834 part of a binding because then the same machinery can be used for
835 moving them into place as is done for type signatures.
840 f :: Ord a => [a] -> b -> b
841 {-# SPECIALIZE f :: [Int] -> b -> b #-}
844 For this we generate:
846 f* = /\ b -> let d1 = ...
850 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
851 retain a right-hand-side that the simplifier will otherwise discard as
852 dead code... the simplifier has a flag that tells it not to discard
853 SpecPragmaId bindings.
855 In this case the f* retains a call-instance of the overloaded
856 function, f, (including appropriate dictionaries) so that the
857 specialiser will subsequently discover that there's a call of @f@ at
858 Int, and will create a specialisation for @f@. After that, the
859 binding for @f*@ can be discarded.
861 We used to have a form
862 {-# SPECIALISE f :: <type> = g #-}
863 which promised that g implemented f at <type>, but we do that with
865 {-# SPECIALISE (f::<type) = g #-}
868 tcSpecSigs :: [RenamedSig] -> TcM (TcMonoBinds, LIE)
869 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
870 = -- SPECIALISE f :: forall b. theta => tau = g
871 tcAddSrcLoc src_loc $
872 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
874 -- Get and instantiate its alleged specialised type
875 tcHsSigType poly_ty `thenTc` \ sig_ty ->
877 -- Check that f has a more general type, and build a RHS for
878 -- the spec-pragma-id at the same time
879 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
881 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
882 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
884 -- Just specialise "f" by building a SpecPragmaId binding
885 -- It is the thing that makes sure we don't prematurely
886 -- dead-code-eliminate the binding we are really interested in.
887 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
889 -- Do the rest and combine
890 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
891 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
892 lie_rest `plusLIE` spec_lie1)
894 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
895 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
899 %************************************************************************
901 \subsection[TcBinds-errors]{Error contexts and messages}
903 %************************************************************************
907 patMonoBindsCtxt bind
908 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
910 -----------------------------------------------
912 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
913 nest 4 (ppr v <+> dcolon <+> ppr ty)]
915 -----------------------------------------------
917 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
920 -----------------------------------------------
922 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
924 -----------------------------------------------
926 = ptext SLIT("Mismatched contexts")
928 sigContextsCtxt s1 s2
929 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
930 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
931 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
934 | id `hasKey` mainKey = ptext SLIT("Main.main cannot be overloaded")
936 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
937 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
940 = hsep [ptext SLIT("When checking that"), quotes (ptext SLIT("main")),
941 ptext SLIT("has the required type")]
943 -----------------------------------------------
944 unliftedBindErr flavour mbind
945 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
948 existentialExplode mbinds
949 = hang (vcat [text "My brain just exploded.",
950 text "I can't handle pattern bindings for existentially-quantified constructors.",
951 text "In the binding group"])