2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBindsAndThen,
8 tcSpecSigs, tcBindWithSigs ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcMatches ( tcGRHSs, tcMatchesFun )
13 import {-# SOURCE #-} TcExpr ( tcExpr )
15 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..), InPat(..), StmtCtxt(..),
16 Match(..), collectMonoBinders, andMonoBindList, andMonoBinds
18 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
19 import TcHsSyn ( TcHsBinds, TcMonoBinds, TcId, zonkId, mkHsLet )
22 import Inst ( Inst, LIE, emptyLIE, mkLIE, plusLIE, plusLIEs, InstOrigin(..),
23 newDicts, tyVarsOfInst, instToId,
24 getAllFunDepsOfLIE, getIPsOfLIE, zonkFunDeps
26 import TcEnv ( tcExtendLocalValEnv,
27 newSpecPragmaId, newLocalId,
29 tcGetGlobalTyVars, tcExtendGlobalTyVars
31 import TcSimplify ( tcSimplify, tcSimplifyAndCheck, tcSimplifyToDicts )
32 import TcImprove ( tcImprove )
33 import TcMonoType ( tcHsSigType, checkSigTyVars,
34 TcSigInfo(..), tcTySig, maybeSig, sigCtxt
36 import TcPat ( tcPat )
37 import TcSimplify ( bindInstsOfLocalFuns )
38 import TcType ( TcType, TcThetaType,
40 newTyVarTy, newTyVar, newTyVarTy_OpenKind, tcInstTcType,
41 zonkTcType, zonkTcTypes, zonkTcThetaType, zonkTcTyVarToTyVar
43 import TcUnify ( unifyTauTy, unifyTauTyLists )
45 import PrelInfo ( main_NAME, ioTyCon_NAME )
47 import Id ( Id, mkVanillaId, setInlinePragma, idFreeTyVars )
48 import Var ( idType, idName )
49 import IdInfo ( setInlinePragInfo, InlinePragInfo(..) )
50 import Name ( Name, getName, getOccName, getSrcLoc )
52 import Type ( mkTyVarTy, tyVarsOfTypes, mkTyConApp,
53 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar,
54 mkPredTy, splitRhoTy, mkForAllTy, isUnLiftedType,
55 isUnboxedType, unboxedTypeKind, boxedTypeKind
57 import FunDeps ( tyVarFunDep, oclose )
58 import Var ( TyVar, tyVarKind )
62 import Maybes ( maybeToBool )
63 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNotTopLevel )
64 import FiniteMap ( listToFM, lookupFM )
65 import SrcLoc ( SrcLoc )
70 %************************************************************************
72 \subsection{Type-checking bindings}
74 %************************************************************************
76 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
77 it needs to know something about the {\em usage} of the things bound,
78 so that it can create specialisations of them. So @tcBindsAndThen@
79 takes a function which, given an extended environment, E, typechecks
80 the scope of the bindings returning a typechecked thing and (most
81 important) an LIE. It is this LIE which is then used as the basis for
82 specialising the things bound.
84 @tcBindsAndThen@ also takes a "combiner" which glues together the
85 bindings and the "thing" to make a new "thing".
87 The real work is done by @tcBindWithSigsAndThen@.
89 Recursive and non-recursive binds are handled in essentially the same
90 way: because of uniques there are no scoping issues left. The only
91 difference is that non-recursive bindings can bind primitive values.
93 Even for non-recursive binding groups we add typings for each binder
94 to the LVE for the following reason. When each individual binding is
95 checked the type of its LHS is unified with that of its RHS; and
96 type-checking the LHS of course requires that the binder is in scope.
98 At the top-level the LIE is sure to contain nothing but constant
99 dictionaries, which we resolve at the module level.
102 tcTopBindsAndThen, tcBindsAndThen
103 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
105 -> TcM s (thing, LIE)
106 -> TcM s (thing, LIE)
108 tcTopBindsAndThen = tc_binds_and_then TopLevel
109 tcBindsAndThen = tc_binds_and_then NotTopLevel
111 tc_binds_and_then top_lvl combiner EmptyBinds do_next
113 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
116 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
117 = tc_binds_and_then top_lvl combiner b1 $
118 tc_binds_and_then top_lvl combiner b2 $
121 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
122 = -- TYPECHECK THE SIGNATURES
123 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
125 tcBindWithSigs top_lvl bind tc_ty_sigs
126 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
128 -- Extend the environment to bind the new polymorphic Ids
129 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
131 -- Build bindings and IdInfos corresponding to user pragmas
132 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
134 -- Now do whatever happens next, in the augmented envt
135 do_next `thenTc` \ (thing, thing_lie) ->
137 -- Create specialisations of functions bound here
138 -- We want to keep non-recursive things non-recursive
139 -- so that we desugar unboxed bindings correctly
140 case (top_lvl, is_rec) of
142 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
143 -- All the top level things are rec'd together anyway, so it's fine to
144 -- leave them to the tcSimplifyTop, and quite a bit faster too
146 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
147 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
149 (NotTopLevel, NonRecursive)
150 -> bindInstsOfLocalFuns
151 (thing_lie `plusLIE` prag_lie)
152 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
155 combiner NonRecursive poly_binds $
156 combiner NonRecursive prag_binds $
157 combiner Recursive lie_binds $
158 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
159 -- aren't guaranteed in dependency order (though we could change
160 -- that); hence the Recursive marker.
163 thing_lie' `plusLIE` poly_lie
166 (NotTopLevel, Recursive)
167 -> bindInstsOfLocalFuns
168 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
169 poly_ids `thenTc` \ (final_lie, lie_binds) ->
173 poly_binds `andMonoBinds`
174 lie_binds `andMonoBinds`
180 An aside. The original version of @tcBindsAndThen@ which lacks a
181 combiner function, appears below. Though it is perfectly well
182 behaved, it cannot be typed by Haskell, because the recursive call is
183 at a different type to the definition itself. There aren't too many
184 examples of this, which is why I thought it worth preserving! [SLPJ]
189 % -> TcM s (thing, LIE, thing_ty))
190 % -> TcM s ((TcHsBinds, thing), LIE, thing_ty)
192 % tcBindsAndThen EmptyBinds do_next
193 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
194 % returnTc ((EmptyBinds, thing), lie, thing_ty)
196 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
197 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
198 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
200 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
202 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
203 % = tcBindAndThen bind sigs do_next
207 %************************************************************************
209 \subsection{tcBindWithSigs}
211 %************************************************************************
213 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
214 so all the clever stuff is in here.
216 * binder_names and mbind must define the same set of Names
218 * The Names in tc_ty_sigs must be a subset of binder_names
220 * The Ids in tc_ty_sigs don't necessarily have to have the same name
221 as the Name in the tc_ty_sig
228 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
230 -> TcM s (TcMonoBinds, LIE, [TcId])
232 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
234 -- If typechecking the binds fails, then return with each
235 -- signature-less binder given type (forall a.a), to minimise subsequent
237 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
239 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
240 binder_names = map fst (bagToList (collectMonoBinders mbind))
241 poly_ids = map mk_dummy binder_names
242 mk_dummy name = case maybeSig tc_ty_sigs name of
243 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
244 Nothing -> mkVanillaId name forall_a_a -- No signature
246 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
249 -- TYPECHECK THE BINDINGS
250 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
252 -- CHECK THAT THE SIGNATURES MATCH
253 -- (must do this before getTyVarsToGen)
254 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
257 -- Force any unifications dictated by functional dependencies.
258 -- Because unification may happen, it's important that this step
260 -- - computing vars over which to quantify
261 -- - zonking the generalized type vars
262 let lie_avail = case maybe_sig_theta of
264 Just (_, la) -> la in
265 tcImprove (lie_avail `plusLIE` lie_req) `thenTc_`
267 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
268 -- The tyvars_not_to_gen are free in the environment, and hence
269 -- candidates for generalisation, but sometimes the monomorphism
270 -- restriction means we can't generalise them nevertheless
272 mono_id_tys = map idType mono_ids
274 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
276 -- Finally, zonk the generalised type variables to real TyVars
277 -- This commits any unbound kind variables to boxed kind
278 -- I'm a little worried that such a kind variable might be
279 -- free in the environment, but I don't think it's possible for
280 -- this to happen when the type variable is not free in the envt
281 -- (which it isn't). SLPJ Nov 98
282 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
284 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
285 -- It's important that the final list
286 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
287 -- zonked, *including boxity*, because they'll be included in the forall types of
288 -- the polymorphic Ids, and instances of these Ids will be generated from them.
290 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
291 -- real_tyvars_to_gen
295 tcExtendGlobalTyVars tyvars_not_to_gen (
296 let ips = getIPsOfLIE lie_req in
297 if null real_tyvars_to_gen_list && (null ips || not is_unrestricted) then
298 -- No polymorphism, and no IPs, so no need to simplify context
299 returnTc (lie_req, EmptyMonoBinds, [])
301 case maybe_sig_theta of
303 -- No signatures, so just simplify the lie
304 -- NB: no signatures => no polymorphic recursion, so no
305 -- need to use lie_avail (which will be empty anyway)
306 tcSimplify (text "tcBinds1" <+> ppr binder_names)
307 real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
308 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
310 Just (sig_theta, lie_avail) ->
311 -- There are signatures, and their context is sig_theta
312 -- Furthermore, lie_avail is an LIE containing the 'method insts'
313 -- for the things bound here
315 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
316 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
317 -- It's important that sig_theta is zonked, because
318 -- dict_id is later used to form the type of the polymorphic thing,
319 -- and forall-types must be zonked so far as their bound variables
323 -- The "givens" is the stuff available. We get that from
324 -- the context of the type signature, BUT ALSO the lie_avail
325 -- so that polymorphic recursion works right (see comments at end of fn)
326 givens = dicts_sig `plusLIE` lie_avail
329 -- Check that the needed dicts can be expressed in
330 -- terms of the signature ones
331 tcAddErrCtxt (bindSigsCtxt tysig_names) $
333 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
334 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
336 returnTc (lie_free, dict_binds, dict_ids)
338 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
340 -- GET THE FINAL MONO_ID_TYS
341 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
344 -- CHECK FOR BOGUS UNPOINTED BINDINGS
345 (if any isUnLiftedType zonked_mono_id_types then
346 -- Unlifted bindings must be non-recursive,
347 -- not top level, and non-polymorphic
348 checkTc (isNotTopLevel top_lvl)
349 (unliftedBindErr "Top-level" mbind) `thenTc_`
350 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
351 (unliftedBindErr "Recursive" mbind) `thenTc_`
352 checkTc (null real_tyvars_to_gen_list)
353 (unliftedBindErr "Polymorphic" mbind)
358 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
359 -- The instCantBeGeneralised stuff in tcSimplify should have
360 -- already raised an error if we're trying to generalise an
361 -- unboxed tyvar (NB: unboxed tyvars are always introduced
362 -- along with a class constraint) and it's better done there
363 -- because we have more precise origin information.
364 -- That's why we just use an ASSERT here.
367 -- BUILD THE POLYMORPHIC RESULT IDs
368 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
370 exports = zipWith mk_export binder_names zonked_mono_ids
371 dict_tys = map idType dicts_bound
373 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
374 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
375 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
376 -- "INLINE n foo" means inline foo, but not until at least phase n
377 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
378 -- then only if it is small enough etc.
379 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
380 -- See comments in CoreUnfold.blackListed for the Authorised Version
382 mk_export binder_name zonked_mono_id
384 attachNoInlinePrag no_inlines poly_id,
388 case maybeSig tc_ty_sigs binder_name of
389 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
390 (sig_tyvars, sig_poly_id)
391 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
393 new_poly_id = mkVanillaId binder_name poly_ty
394 poly_ty = mkForAllTys real_tyvars_to_gen_list
396 $ idType (zonked_mono_id)
397 -- It's important to build a fully-zonked poly_ty, because
398 -- we'll slurp out its free type variables when extending the
399 -- local environment (tcExtendLocalValEnv); if it's not zonked
400 -- it appears to have free tyvars that aren't actually free
403 pat_binders :: [Name]
404 pat_binders = map fst $ bagToList $ collectMonoBinders $
405 (justPatBindings mbind EmptyMonoBinds)
407 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
408 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
409 && isUnboxedType (idType id)))
410 (unboxedPatBindErr id)) zonked_mono_ids
415 -- pprTrace "binding.." (ppr ((dicts_bound, dict_binds), exports, [idType poly_id | (_, poly_id, _) <- exports])) $
416 AbsBinds real_tyvars_to_gen_list
420 (dict_binds `andMonoBinds` mbind'),
422 [poly_id | (_, poly_id, _) <- exports]
425 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
426 is_unrestricted = isUnRestrictedGroup tysig_names mbind
428 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
429 justPatBindings (AndMonoBinds b1 b2) binds =
430 justPatBindings b1 (justPatBindings b2 binds)
431 justPatBindings other_bind binds = binds
433 attachNoInlinePrag no_inlines bndr
434 = case lookupFM no_inlines (idName bndr) of
435 Just prag -> bndr `setInlinePragma` prag
439 Polymorphic recursion
440 ~~~~~~~~~~~~~~~~~~~~~
441 The game plan for polymorphic recursion in the code above is
443 * Bind any variable for which we have a type signature
444 to an Id with a polymorphic type. Then when type-checking
445 the RHSs we'll make a full polymorphic call.
447 This fine, but if you aren't a bit careful you end up with a horrendous
448 amount of partial application and (worse) a huge space leak. For example:
450 f :: Eq a => [a] -> [a]
453 If we don't take care, after typechecking we get
455 f = /\a -> \d::Eq a -> let f' = f a d
459 Notice the the stupid construction of (f a d), which is of course
460 identical to the function we're executing. In this case, the
461 polymorphic recursion isn't being used (but that's a very common case).
464 f = /\a -> \d::Eq a -> letrec
465 fm = \ys:[a] -> ...fm...
469 This can lead to a massive space leak, from the following top-level defn
475 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
476 f' is another thunk which evaluates to the same thing... and you end
477 up with a chain of identical values all hung onto by the CAF ff.
481 = let f' = f Int dEqInt in \ys. ...f'...
483 = let f' = let f' = f Int dEqInt in \ys. ...f'...
487 Solution: when typechecking the RHSs we always have in hand the
488 *monomorphic* Ids for each binding. So we just need to make sure that
489 if (Method f a d) shows up in the constraints emerging from (...f...)
490 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
491 to the "givens" when simplifying constraints. That's what the "lies_avail"
495 %************************************************************************
497 \subsection{getTyVarsToGen}
499 %************************************************************************
501 @getTyVarsToGen@ decides what type variables to generalise over.
503 For a "restricted group" -- see the monomorphism restriction
504 for a definition -- we bind no dictionaries, and
505 remove from tyvars_to_gen any constrained type variables
507 *Don't* simplify dicts at this point, because we aren't going
508 to generalise over these dicts. By the time we do simplify them
509 we may well know more. For example (this actually came up)
511 f x = array ... xs where xs = [1,2,3,4,5]
512 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
513 stuff. If we simplify only at the f-binding (not the xs-binding)
514 we'll know that the literals are all Ints, and we can just produce
517 Find all the type variables involved in overloading, the
518 "constrained_tyvars". These are the ones we *aren't* going to
519 generalise. We must be careful about doing this:
521 (a) If we fail to generalise a tyvar which is not actually
522 constrained, then it will never, ever get bound, and lands
523 up printed out in interface files! Notorious example:
524 instance Eq a => Eq (Foo a b) where ..
525 Here, b is not constrained, even though it looks as if it is.
526 Another, more common, example is when there's a Method inst in
527 the LIE, whose type might very well involve non-overloaded
530 (b) On the other hand, we mustn't generalise tyvars which are constrained,
531 because we are going to pass on out the unmodified LIE, with those
532 tyvars in it. They won't be in scope if we've generalised them.
534 So we are careful, and do a complete simplification just to find the
535 constrained tyvars. We don't use any of the results, except to
536 find which tyvars are constrained.
539 getTyVarsToGen is_unrestricted mono_id_tys lie
540 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
541 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
543 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
547 let fds = getAllFunDepsOfLIE lie in
548 zonkFunDeps fds `thenNF_Tc` \ fds' ->
549 let tvFundep = tyVarFunDep fds'
550 extended_tyvars = oclose tvFundep body_tyvars in
551 -- pprTrace "gTVTG" (ppr (lie, body_tyvars, extended_tyvars)) $
552 returnNF_Tc (emptyVarSet, extended_tyvars)
554 -- This recover and discard-errs is to avoid duplicate error
555 -- messages; this, after all, is an "extra" call to tcSimplify
556 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
559 tcSimplify (text "getTVG") body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
561 -- ASSERT: dicts_sig is already zonked!
562 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
563 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
565 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
570 isUnRestrictedGroup :: [Name] -- Signatures given for these
574 is_elem v vs = isIn "isUnResMono" v vs
576 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
577 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
578 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
580 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
581 isUnRestrictedGroup sigs mb2
582 isUnRestrictedGroup sigs EmptyMonoBinds = True
584 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
585 isUnRestrictedMatch other = True -- Some args or a signature
589 %************************************************************************
591 \subsection{tcMonoBind}
593 %************************************************************************
595 @tcMonoBinds@ deals with a single @MonoBind@.
596 The signatures have been dealt with already.
599 tcMonoBinds :: RenamedMonoBinds
602 -> TcM s (TcMonoBinds,
604 [Name], -- Bound names
605 [TcId]) -- Corresponding monomorphic bound things
607 tcMonoBinds mbinds tc_ty_sigs is_rec
608 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
610 tv_list = bagToList tvs
611 id_list = bagToList ids
612 (names, mono_ids) = unzip id_list
614 -- This last defn is the key one:
615 -- extend the val envt with bindings for the
616 -- things bound in this group, overriding the monomorphic
617 -- ids with the polymorphic ones from the pattern
618 extra_val_env = case is_rec of
619 Recursive -> map mk_bind id_list
622 -- Don't know how to deal with pattern-bound existentials yet
623 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
624 (existentialExplode mbinds) `thenTc_`
626 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
627 -- extend the envt with bindings for all the bound ids;
628 -- and *then* override with the polymorphic Ids from the signatures
629 -- That is the whole point of the "complete_it" stuff.
631 -- There's a further wrinkle: we have to delay extending the environment
632 -- until after we've dealt with any pattern-bound signature type variables
633 -- Consider f (x::a) = ...f...
634 -- We're going to check that a isn't unified with anything in the envt,
635 -- so f itself had better not be! So we pass the envt binding f into
636 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
637 -- dealing with the signature tyvars
639 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
641 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
644 -- This function is used when dealing with a LHS binder; we make a monomorphic
645 -- version of the Id. We check for type signatures
646 tc_pat_bndr name pat_ty
647 = case maybeSig tc_ty_sigs name of
649 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
651 Just (TySigInfo _ _ _ _ _ mono_id _ _)
652 -> tcAddSrcLoc (getSrcLoc name) $
653 unifyTauTy (idType mono_id) pat_ty `thenTc_`
656 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
657 Nothing -> (name, mono_id)
658 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
660 tc_mb_pats EmptyMonoBinds
661 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
663 tc_mb_pats (AndMonoBinds mb1 mb2)
664 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
665 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
667 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
668 complete_it2 xve `thenTc` \ (mb2', lie2) ->
669 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
671 returnTc (complete_it,
672 lie_req1 `plusLIE` lie_req2,
673 tvs1 `unionBags` tvs2,
674 ids1 `unionBags` ids2,
675 lie_avail1 `plusLIE` lie_avail2)
677 tc_mb_pats (FunMonoBind name inf matches locn)
678 = newTyVarTy boxedTypeKind `thenNF_Tc` \ bndr_ty ->
679 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
681 complete_it xve = tcAddSrcLoc locn $
682 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
683 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
685 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
687 tc_mb_pats bind@(PatMonoBind pat grhss locn)
690 -- Figure out the appropriate kind for the pattern,
691 -- and generate a suitable type variable
693 Recursive -> newTyVarTy boxedTypeKind -- Recursive, so no unboxed types
694 NonRecursive -> newTyVarTy_OpenKind -- Non-recursive, so we permit unboxed types
695 ) `thenNF_Tc` \ pat_ty ->
697 -- Now typecheck the pattern
698 -- We don't support binding fresh type variables in the
699 -- pattern of a pattern binding. For example, this is illegal:
701 -- whereas this is ok
702 -- (x::Int, y::Bool) = e
704 -- We don't check explicitly for this problem. Instead, we simply
705 -- type check the pattern with tcPat. If the pattern mentions any
706 -- fresh tyvars we simply get an out-of-scope type variable error
707 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
709 complete_it xve = tcAddSrcLoc locn $
710 tcAddErrCtxt (patMonoBindsCtxt bind) $
711 tcExtendLocalValEnv xve $
712 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
713 returnTc (PatMonoBind pat' grhss' locn, lie)
715 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
718 %************************************************************************
720 \subsection{Signatures}
722 %************************************************************************
724 @checkSigMatch@ does the next step in checking signature matching.
725 The tau-type part has already been unified. What we do here is to
726 check that this unification has not over-constrained the (polymorphic)
727 type variables of the original signature type.
729 The error message here is somewhat unsatisfactory, but it'll do for
733 checkSigMatch top_lvl binder_names mono_ids sigs
735 = -- First unify the main_id with IO t, for any old t
736 tcSetErrCtxt mainTyCheckCtxt (
737 tcLookupTyCon ioTyCon_NAME `thenTc` \ ioTyCon ->
738 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
739 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
740 (idType main_mono_id)
743 -- Now check the signatures
744 -- Must do this after the unification with IO t,
745 -- in case of a silly signature like
746 -- main :: forall a. a
747 -- The unification to IO t will bind the type variable 'a',
748 -- which is just waht check_one_sig looks for
749 mapTc check_one_sig sigs `thenTc_`
750 mapTc check_main_ctxt sigs `thenTc_`
752 returnTc (Just ([], emptyLIE))
755 = mapTc check_one_sig sigs `thenTc_`
756 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
757 returnTc (Just (theta1, sig_lie))
760 = returnTc Nothing -- No constraints from type sigs
763 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
765 sig1_dict_tys = mk_dict_tys theta1
766 n_sig1_dict_tys = length sig1_dict_tys
767 sig_lie = mkLIE [inst | TySigInfo _ _ _ _ _ _ inst _ <- sigs]
769 maybe_main = find_main top_lvl binder_names mono_ids
770 main_bound_here = maybeToBool maybe_main
771 Just main_mono_id = maybe_main
773 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
774 -- Doesn't affect substitution
775 check_one_sig (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
776 = tcAddSrcLoc src_loc $
777 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
778 checkSigTyVars sig_tyvars (idFreeTyVars id)
781 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
782 -- The type signatures on a mutually-recursive group of definitions
783 -- must all have the same context (or none).
785 -- We unify them because, with polymorphic recursion, their types
786 -- might not otherwise be related. This is a rather subtle issue.
788 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
789 = tcAddSrcLoc src_loc $
790 tcAddErrCtxt (sigContextsCtxt id1 id) $
791 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
792 sigContextsErr `thenTc_`
793 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
795 this_sig_dict_tys = mk_dict_tys theta
797 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
798 -- the signature contexts are empty (what a bore)
799 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
800 = tcAddSrcLoc src_loc $
801 checkTc (null theta) (mainContextsErr id)
803 mk_dict_tys theta = map mkPredTy theta
805 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
807 -- Search for Main.main in the binder_names, return corresponding mono_id
808 find_main NotTopLevel binder_names mono_ids = Nothing
809 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
811 go (n:ns) (m:ms) | n == main_NAME = Just m
812 | otherwise = go ns ms
816 %************************************************************************
818 \subsection{SPECIALIZE pragmas}
820 %************************************************************************
822 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
823 pragmas. It is convenient for them to appear in the @[RenamedSig]@
824 part of a binding because then the same machinery can be used for
825 moving them into place as is done for type signatures.
830 f :: Ord a => [a] -> b -> b
831 {-# SPECIALIZE f :: [Int] -> b -> b #-}
834 For this we generate:
836 f* = /\ b -> let d1 = ...
840 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
841 retain a right-hand-side that the simplifier will otherwise discard as
842 dead code... the simplifier has a flag that tells it not to discard
843 SpecPragmaId bindings.
845 In this case the f* retains a call-instance of the overloaded
846 function, f, (including appropriate dictionaries) so that the
847 specialiser will subsequently discover that there's a call of @f@ at
848 Int, and will create a specialisation for @f@. After that, the
849 binding for @f*@ can be discarded.
851 We used to have a form
852 {-# SPECIALISE f :: <type> = g #-}
853 which promised that g implemented f at <type>, but we do that with
855 {-# SPECIALISE (f::<type) = g #-}
858 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
859 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
860 = -- SPECIALISE f :: forall b. theta => tau = g
861 tcAddSrcLoc src_loc $
862 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
864 -- Get and instantiate its alleged specialised type
865 tcHsSigType poly_ty `thenTc` \ sig_ty ->
867 -- Check that f has a more general type, and build a RHS for
868 -- the spec-pragma-id at the same time
869 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
871 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
872 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
874 -- Just specialise "f" by building a SpecPragmaId binding
875 -- It is the thing that makes sure we don't prematurely
876 -- dead-code-eliminate the binding we are really interested in.
877 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
879 -- Do the rest and combine
880 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
881 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
882 lie_rest `plusLIE` spec_lie1)
884 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
885 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
889 %************************************************************************
891 \subsection[TcBinds-errors]{Error contexts and messages}
893 %************************************************************************
897 patMonoBindsCtxt bind
898 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
900 -----------------------------------------------
902 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
903 nest 4 (ppr v <+> dcolon <+> ppr ty)]
905 -----------------------------------------------
906 notAsPolyAsSigErr sig_tau mono_tyvars
907 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
908 4 (vcat [text "Can't for-all the type variable(s)" <+>
909 pprQuotedList mono_tyvars,
910 text "in the type" <+> quotes (ppr sig_tau)
913 -----------------------------------------------
914 badMatchErr sig_ty inferred_ty
915 = hang (ptext SLIT("Type signature doesn't match inferred type"))
916 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
917 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
920 -----------------------------------------------
922 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
925 -----------------------------------------------
927 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
929 -----------------------------------------------
931 = ptext SLIT("Mismatched contexts")
933 sigContextsCtxt s1 s2
934 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
935 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
936 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
939 | getName id == main_NAME = ptext SLIT("Main.main cannot be overloaded")
941 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
942 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
945 = hsep [ptext SLIT("When checking that"), quotes (ppr main_NAME),
946 ptext SLIT("has the required type")]
948 -----------------------------------------------
949 unliftedBindErr flavour mbind
950 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
953 existentialExplode mbinds
954 = hang (vcat [text "My brain just exploded.",
955 text "I can't handle pattern bindings for existentially-quantified constructors.",
956 text "In the binding group"])