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 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 PrelNames ( ioTyConName, 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 tcTopBinds :: RenamedHsBinds -> TcM ((TcMonoBinds, TcEnv), LIE)
100 = tc_binds_and_then TopLevel glue binds $
101 tcGetEnv `thenNF_Tc` \ env ->
102 returnTc ((EmptyMonoBinds, env), emptyLIE)
104 glue is_rec binds1 (binds2, thing) = (binds1 `AndMonoBinds` binds2, thing)
108 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
113 tcBindsAndThen = tc_binds_and_then NotTopLevel
115 tc_binds_and_then top_lvl combiner EmptyBinds do_next
117 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
120 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
121 = tc_binds_and_then top_lvl combiner b1 $
122 tc_binds_and_then top_lvl combiner b2 $
125 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
126 = -- TYPECHECK THE SIGNATURES
127 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
129 tcBindWithSigs top_lvl bind tc_ty_sigs
130 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
132 -- Extend the environment to bind the new polymorphic Ids
133 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
135 -- Build bindings and IdInfos corresponding to user pragmas
136 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
138 -- Now do whatever happens next, in the augmented envt
139 do_next `thenTc` \ (thing, thing_lie) ->
141 -- Create specialisations of functions bound here
142 -- We want to keep non-recursive things non-recursive
143 -- so that we desugar unboxed bindings correctly
144 case (top_lvl, is_rec) of
146 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
147 -- All the top level things are rec'd together anyway, so it's fine to
148 -- leave them to the tcSimplifyTop, and quite a bit faster too
150 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
151 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
153 (NotTopLevel, NonRecursive)
154 -> bindInstsOfLocalFuns
155 (thing_lie `plusLIE` prag_lie)
156 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
159 combiner NonRecursive poly_binds $
160 combiner NonRecursive prag_binds $
161 combiner Recursive lie_binds $
162 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
163 -- aren't guaranteed in dependency order (though we could change
164 -- that); hence the Recursive marker.
167 thing_lie' `plusLIE` poly_lie
170 (NotTopLevel, Recursive)
171 -> bindInstsOfLocalFuns
172 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
173 poly_ids `thenTc` \ (final_lie, lie_binds) ->
177 poly_binds `andMonoBinds`
178 lie_binds `andMonoBinds`
184 An aside. The original version of @tcBindsAndThen@ which lacks a
185 combiner function, appears below. Though it is perfectly well
186 behaved, it cannot be typed by Haskell, because the recursive call is
187 at a different type to the definition itself. There aren't too many
188 examples of this, which is why I thought it worth preserving! [SLPJ]
193 % -> TcM (thing, LIE, thing_ty))
194 % -> TcM ((TcHsBinds, thing), LIE, thing_ty)
196 % tcBindsAndThen EmptyBinds do_next
197 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
198 % returnTc ((EmptyBinds, thing), lie, thing_ty)
200 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
201 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
202 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
204 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
206 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
207 % = tcBindAndThen bind sigs do_next
211 %************************************************************************
213 \subsection{tcBindWithSigs}
215 %************************************************************************
217 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
218 so all the clever stuff is in here.
220 * binder_names and mbind must define the same set of Names
222 * The Names in tc_ty_sigs must be a subset of binder_names
224 * The Ids in tc_ty_sigs don't necessarily have to have the same name
225 as the Name in the tc_ty_sig
232 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
234 -> TcM (TcMonoBinds, LIE, [TcId])
236 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
238 -- If typechecking the binds fails, then return with each
239 -- signature-less binder given type (forall a.a), to minimise subsequent
241 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
243 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
244 binder_names = collectMonoBinders mbind
245 poly_ids = map mk_dummy binder_names
246 mk_dummy name = case maybeSig tc_ty_sigs name of
247 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
248 Nothing -> mkVanillaId name forall_a_a -- No signature
250 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
253 -- TYPECHECK THE BINDINGS
254 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
256 -- CHECK THAT THE SIGNATURES MATCH
257 -- (must do this before getTyVarsToGen)
258 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
261 -- Force any unifications dictated by functional dependencies.
262 -- Because unification may happen, it's important that this step
264 -- - computing vars over which to quantify
265 -- - zonking the generalized type vars
266 let lie_avail = case maybe_sig_theta of
269 lie_avail_req = lie_avail `plusLIE` lie_req in
270 tcImprove lie_avail_req `thenTc_`
272 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
273 -- The tyvars_not_to_gen are free in the environment, and hence
274 -- candidates for generalisation, but sometimes the monomorphism
275 -- restriction means we can't generalise them nevertheless
277 mono_id_tys = map idType mono_ids
279 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
281 -- Finally, zonk the generalised type variables to real TyVars
282 -- This commits any unbound kind variables to boxed kind
283 -- I'm a little worried that such a kind variable might be
284 -- free in the environment, but I don't think it's possible for
285 -- this to happen when the type variable is not free in the envt
286 -- (which it isn't). SLPJ Nov 98
287 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
289 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
290 -- It's important that the final list
291 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
292 -- zonked, *including boxity*, because they'll be included in the forall types of
293 -- the polymorphic Ids, and instances of these Ids will be generated from them.
295 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
296 -- real_tyvars_to_gen
300 tcExtendGlobalTyVars tyvars_not_to_gen (
301 let ips = getIPsOfLIE lie_avail_req in
302 if null real_tyvars_to_gen_list && (null ips || not is_unrestricted) then
303 -- No polymorphism, and no IPs, so no need to simplify context
304 returnTc (lie_req, EmptyMonoBinds, [])
306 case maybe_sig_theta of
308 -- No signatures, so just simplify the lie
309 -- NB: no signatures => no polymorphic recursion, so no
310 -- need to use lie_avail (which will be empty anyway)
311 tcSimplify (text "tcBinds1" <+> ppr binder_names)
312 real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
313 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
315 Just (sig_theta, lie_avail) ->
316 -- There are signatures, and their context is sig_theta
317 -- Furthermore, lie_avail is an LIE containing the 'method insts'
318 -- for the things bound here
320 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
321 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
322 -- It's important that sig_theta is zonked, because
323 -- dict_id is later used to form the type of the polymorphic thing,
324 -- and forall-types must be zonked so far as their bound variables
328 -- The "givens" is the stuff available. We get that from
329 -- the context of the type signature, BUT ALSO the lie_avail
330 -- so that polymorphic recursion works right (see comments at end of fn)
331 givens = dicts_sig `plusLIE` lie_avail
334 -- Check that the needed dicts can be expressed in
335 -- terms of the signature ones
336 tcAddErrCtxt (bindSigsCtxt tysig_names) $
338 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
339 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
341 returnTc (lie_free, dict_binds, dict_ids)
343 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
345 -- GET THE FINAL MONO_ID_TYS
346 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
349 -- CHECK FOR BOGUS UNPOINTED BINDINGS
350 (if any isUnLiftedType zonked_mono_id_types then
351 -- Unlifted bindings must be non-recursive,
352 -- not top level, and non-polymorphic
353 checkTc (isNotTopLevel top_lvl)
354 (unliftedBindErr "Top-level" mbind) `thenTc_`
355 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
356 (unliftedBindErr "Recursive" mbind) `thenTc_`
357 checkTc (null real_tyvars_to_gen_list)
358 (unliftedBindErr "Polymorphic" mbind)
363 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
364 -- The instCantBeGeneralised stuff in tcSimplify should have
365 -- already raised an error if we're trying to generalise an
366 -- unboxed tyvar (NB: unboxed tyvars are always introduced
367 -- along with a class constraint) and it's better done there
368 -- because we have more precise origin information.
369 -- That's why we just use an ASSERT here.
372 -- BUILD THE POLYMORPHIC RESULT IDs
373 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
375 exports = zipWith mk_export binder_names zonked_mono_ids
376 dict_tys = map idType dicts_bound
378 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
379 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
380 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
381 -- "INLINE n foo" means inline foo, but not until at least phase n
382 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
383 -- then only if it is small enough etc.
384 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
385 -- See comments in CoreUnfold.blackListed for the Authorised Version
387 mk_export binder_name zonked_mono_id
389 attachNoInlinePrag no_inlines poly_id,
393 case maybeSig tc_ty_sigs binder_name of
394 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
395 (sig_tyvars, sig_poly_id)
396 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
398 new_poly_id = mkVanillaId binder_name poly_ty
399 poly_ty = mkForAllTys real_tyvars_to_gen_list
401 $ idType (zonked_mono_id)
402 -- It's important to build a fully-zonked poly_ty, because
403 -- we'll slurp out its free type variables when extending the
404 -- local environment (tcExtendLocalValEnv); if it's not zonked
405 -- it appears to have free tyvars that aren't actually free
408 pat_binders :: [Name]
409 pat_binders = collectMonoBinders (justPatBindings mbind EmptyMonoBinds)
411 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
412 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
413 && isUnboxedType (idType id)))
414 (unboxedPatBindErr id)) zonked_mono_ids
419 -- pprTrace "binding.." (ppr ((dicts_bound, dict_binds), exports, [idType poly_id | (_, poly_id, _) <- exports])) $
420 AbsBinds real_tyvars_to_gen_list
424 (dict_binds `andMonoBinds` mbind'),
426 [poly_id | (_, poly_id, _) <- exports]
429 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
430 is_unrestricted = isUnRestrictedGroup tysig_names mbind
432 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
433 justPatBindings (AndMonoBinds b1 b2) binds =
434 justPatBindings b1 (justPatBindings b2 binds)
435 justPatBindings other_bind binds = binds
437 attachNoInlinePrag no_inlines bndr
438 = case lookupFM no_inlines (idName bndr) of
439 Just prag -> bndr `setInlinePragma` prag
443 Polymorphic recursion
444 ~~~~~~~~~~~~~~~~~~~~~
445 The game plan for polymorphic recursion in the code above is
447 * Bind any variable for which we have a type signature
448 to an Id with a polymorphic type. Then when type-checking
449 the RHSs we'll make a full polymorphic call.
451 This fine, but if you aren't a bit careful you end up with a horrendous
452 amount of partial application and (worse) a huge space leak. For example:
454 f :: Eq a => [a] -> [a]
457 If we don't take care, after typechecking we get
459 f = /\a -> \d::Eq a -> let f' = f a d
463 Notice the the stupid construction of (f a d), which is of course
464 identical to the function we're executing. In this case, the
465 polymorphic recursion isn't being used (but that's a very common case).
468 f = /\a -> \d::Eq a -> letrec
469 fm = \ys:[a] -> ...fm...
473 This can lead to a massive space leak, from the following top-level defn
479 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
480 f' is another thunk which evaluates to the same thing... and you end
481 up with a chain of identical values all hung onto by the CAF ff.
485 = let f' = f Int dEqInt in \ys. ...f'...
487 = let f' = let f' = f Int dEqInt in \ys. ...f'...
491 Solution: when typechecking the RHSs we always have in hand the
492 *monomorphic* Ids for each binding. So we just need to make sure that
493 if (Method f a d) shows up in the constraints emerging from (...f...)
494 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
495 to the "givens" when simplifying constraints. That's what the "lies_avail"
499 %************************************************************************
501 \subsection{getTyVarsToGen}
503 %************************************************************************
505 @getTyVarsToGen@ decides what type variables to generalise over.
507 For a "restricted group" -- see the monomorphism restriction
508 for a definition -- we bind no dictionaries, and
509 remove from tyvars_to_gen any constrained type variables
511 *Don't* simplify dicts at this point, because we aren't going
512 to generalise over these dicts. By the time we do simplify them
513 we may well know more. For example (this actually came up)
515 f x = array ... xs where xs = [1,2,3,4,5]
516 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
517 stuff. If we simplify only at the f-binding (not the xs-binding)
518 we'll know that the literals are all Ints, and we can just produce
521 Find all the type variables involved in overloading, the
522 "constrained_tyvars". These are the ones we *aren't* going to
523 generalise. We must be careful about doing this:
525 (a) If we fail to generalise a tyvar which is not actually
526 constrained, then it will never, ever get bound, and lands
527 up printed out in interface files! Notorious example:
528 instance Eq a => Eq (Foo a b) where ..
529 Here, b is not constrained, even though it looks as if it is.
530 Another, more common, example is when there's a Method inst in
531 the LIE, whose type might very well involve non-overloaded
534 (b) On the other hand, we mustn't generalise tyvars which are constrained,
535 because we are going to pass on out the unmodified LIE, with those
536 tyvars in it. They won't be in scope if we've generalised them.
538 So we are careful, and do a complete simplification just to find the
539 constrained tyvars. We don't use any of the results, except to
540 find which tyvars are constrained.
543 getTyVarsToGen is_unrestricted mono_id_tys lie
544 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
545 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
547 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
548 fds = getAllFunDepsOfLIE lie
552 -- We need to augment the type variables that appear explicitly in
553 -- the type by those that are determined by the functional dependencies.
554 -- e.g. suppose our type is C a b => a -> a
555 -- with the fun-dep a->b
556 -- Then we should generalise over b too; otherwise it will be
557 -- reported as ambiguous.
558 zonkFunDeps fds `thenNF_Tc` \ fds' ->
559 let tvFundep = tyVarFunDep fds'
560 extended_tyvars = oclose tvFundep body_tyvars
562 returnNF_Tc (emptyVarSet, extended_tyvars)
564 -- This recover and discard-errs is to avoid duplicate error
565 -- messages; this, after all, is an "extra" call to tcSimplify
566 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
569 tcSimplify (text "getTVG") body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
571 -- ASSERT: dicts_sig is already zonked!
572 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
573 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
575 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
580 isUnRestrictedGroup :: [Name] -- Signatures given for these
584 is_elem v vs = isIn "isUnResMono" v vs
586 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
587 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
588 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
590 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
591 isUnRestrictedGroup sigs mb2
592 isUnRestrictedGroup sigs EmptyMonoBinds = True
594 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
595 isUnRestrictedMatch other = True -- Some args or a signature
599 %************************************************************************
601 \subsection{tcMonoBind}
603 %************************************************************************
605 @tcMonoBinds@ deals with a single @MonoBind@.
606 The signatures have been dealt with already.
609 tcMonoBinds :: RenamedMonoBinds
614 [Name], -- Bound names
615 [TcId]) -- Corresponding monomorphic bound things
617 tcMonoBinds mbinds tc_ty_sigs is_rec
618 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
620 id_list = bagToList ids
621 (names, mono_ids) = unzip id_list
623 -- This last defn is the key one:
624 -- extend the val envt with bindings for the
625 -- things bound in this group, overriding the monomorphic
626 -- ids with the polymorphic ones from the pattern
627 extra_val_env = case is_rec of
628 Recursive -> map mk_bind id_list
631 -- Don't know how to deal with pattern-bound existentials yet
632 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
633 (existentialExplode mbinds) `thenTc_`
635 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
636 -- extend the envt with bindings for all the bound ids;
637 -- and *then* override with the polymorphic Ids from the signatures
638 -- That is the whole point of the "complete_it" stuff.
640 -- There's a further wrinkle: we have to delay extending the environment
641 -- until after we've dealt with any pattern-bound signature type variables
642 -- Consider f (x::a) = ...f...
643 -- We're going to check that a isn't unified with anything in the envt,
644 -- so f itself had better not be! So we pass the envt binding f into
645 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
646 -- dealing with the signature tyvars
648 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
650 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
653 -- This function is used when dealing with a LHS binder; we make a monomorphic
654 -- version of the Id. We check for type signatures
655 tc_pat_bndr name pat_ty
656 = case maybeSig tc_ty_sigs name of
658 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
660 Just (TySigInfo _ _ _ _ _ mono_id _ _)
661 -> tcAddSrcLoc (getSrcLoc name) $
662 unifyTauTy (idType mono_id) pat_ty `thenTc_`
665 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
666 Nothing -> (name, mono_id)
667 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
669 tc_mb_pats EmptyMonoBinds
670 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
672 tc_mb_pats (AndMonoBinds mb1 mb2)
673 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
674 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
676 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
677 complete_it2 xve `thenTc` \ (mb2', lie2) ->
678 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
680 returnTc (complete_it,
681 lie_req1 `plusLIE` lie_req2,
682 tvs1 `unionBags` tvs2,
683 ids1 `unionBags` ids2,
684 lie_avail1 `plusLIE` lie_avail2)
686 tc_mb_pats (FunMonoBind name inf matches locn)
687 = newTyVarTy kind `thenNF_Tc` \ bndr_ty ->
688 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
690 complete_it xve = tcAddSrcLoc locn $
691 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
692 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
694 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
696 tc_mb_pats bind@(PatMonoBind pat grhss locn)
698 newTyVarTy kind `thenNF_Tc` \ pat_ty ->
700 -- Now typecheck the pattern
701 -- We don't support binding fresh type variables in the
702 -- pattern of a pattern binding. For example, this is illegal:
704 -- whereas this is ok
705 -- (x::Int, y::Bool) = e
707 -- We don't check explicitly for this problem. Instead, we simply
708 -- type check the pattern with tcPat. If the pattern mentions any
709 -- fresh tyvars we simply get an out-of-scope type variable error
710 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
712 complete_it xve = tcAddSrcLoc locn $
713 tcAddErrCtxt (patMonoBindsCtxt bind) $
714 tcExtendLocalValEnv xve $
715 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
716 returnTc (PatMonoBind pat' grhss' locn, lie)
718 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
720 -- Figure out the appropriate kind for the pattern,
721 -- and generate a suitable type variable
722 kind = case is_rec of
723 Recursive -> boxedTypeKind -- Recursive, so no unboxed types
724 NonRecursive -> openTypeKind -- Non-recursive, so we permit unboxed types
727 %************************************************************************
729 \subsection{Signatures}
731 %************************************************************************
733 @checkSigMatch@ does the next step in checking signature matching.
734 The tau-type part has already been unified. What we do here is to
735 check that this unification has not over-constrained the (polymorphic)
736 type variables of the original signature type.
738 The error message here is somewhat unsatisfactory, but it'll do for
742 checkSigMatch :: TopLevelFlag -> [Name] -> [TcId] -> [TcSigInfo] -> TcM (Maybe (TcThetaType, LIE))
743 checkSigMatch top_lvl binder_names mono_ids sigs
745 = -- First unify the main_id with IO t, for any old t
746 tcSetErrCtxt mainTyCheckCtxt (
747 tcLookupTyCon ioTyConName `thenTc` \ ioTyCon ->
748 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
749 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
750 (idType main_mono_id)
753 -- Now check the signatures
754 -- Must do this after the unification with IO t,
755 -- in case of a silly signature like
756 -- main :: forall a. a
757 -- The unification to IO t will bind the type variable 'a',
758 -- which is just waht check_one_sig looks for
759 mapTc check_one_sig sigs `thenTc_`
760 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"])