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 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 PprType ( {- instance Outputable Type -} )
58 import FunDeps ( tyVarFunDep, oclose )
59 import Var ( TyVar, tyVarKind )
63 import Maybes ( maybeToBool )
64 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNotTopLevel )
65 import FiniteMap ( listToFM, lookupFM )
66 import SrcLoc ( SrcLoc )
71 %************************************************************************
73 \subsection{Type-checking bindings}
75 %************************************************************************
77 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
78 it needs to know something about the {\em usage} of the things bound,
79 so that it can create specialisations of them. So @tcBindsAndThen@
80 takes a function which, given an extended environment, E, typechecks
81 the scope of the bindings returning a typechecked thing and (most
82 important) an LIE. It is this LIE which is then used as the basis for
83 specialising the things bound.
85 @tcBindsAndThen@ also takes a "combiner" which glues together the
86 bindings and the "thing" to make a new "thing".
88 The real work is done by @tcBindWithSigsAndThen@.
90 Recursive and non-recursive binds are handled in essentially the same
91 way: because of uniques there are no scoping issues left. The only
92 difference is that non-recursive bindings can bind primitive values.
94 Even for non-recursive binding groups we add typings for each binder
95 to the LVE for the following reason. When each individual binding is
96 checked the type of its LHS is unified with that of its RHS; and
97 type-checking the LHS of course requires that the binder is in scope.
99 At the top-level the LIE is sure to contain nothing but constant
100 dictionaries, which we resolve at the module level.
103 tcTopBindsAndThen, tcBindsAndThen
104 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
106 -> TcM s (thing, LIE)
107 -> TcM s (thing, LIE)
109 tcTopBindsAndThen = tc_binds_and_then TopLevel
110 tcBindsAndThen = tc_binds_and_then NotTopLevel
112 tc_binds_and_then top_lvl combiner EmptyBinds do_next
114 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
117 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
118 = tc_binds_and_then top_lvl combiner b1 $
119 tc_binds_and_then top_lvl combiner b2 $
122 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
123 = -- TYPECHECK THE SIGNATURES
124 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
126 tcBindWithSigs top_lvl bind tc_ty_sigs
127 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
129 -- Extend the environment to bind the new polymorphic Ids
130 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
132 -- Build bindings and IdInfos corresponding to user pragmas
133 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
135 -- Now do whatever happens next, in the augmented envt
136 do_next `thenTc` \ (thing, thing_lie) ->
138 -- Create specialisations of functions bound here
139 -- We want to keep non-recursive things non-recursive
140 -- so that we desugar unboxed bindings correctly
141 case (top_lvl, is_rec) of
143 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
144 -- All the top level things are rec'd together anyway, so it's fine to
145 -- leave them to the tcSimplifyTop, and quite a bit faster too
147 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
148 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
150 (NotTopLevel, NonRecursive)
151 -> bindInstsOfLocalFuns
152 (thing_lie `plusLIE` prag_lie)
153 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
156 combiner NonRecursive poly_binds $
157 combiner NonRecursive prag_binds $
158 combiner Recursive lie_binds $
159 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
160 -- aren't guaranteed in dependency order (though we could change
161 -- that); hence the Recursive marker.
164 thing_lie' `plusLIE` poly_lie
167 (NotTopLevel, Recursive)
168 -> bindInstsOfLocalFuns
169 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
170 poly_ids `thenTc` \ (final_lie, lie_binds) ->
174 poly_binds `andMonoBinds`
175 lie_binds `andMonoBinds`
181 An aside. The original version of @tcBindsAndThen@ which lacks a
182 combiner function, appears below. Though it is perfectly well
183 behaved, it cannot be typed by Haskell, because the recursive call is
184 at a different type to the definition itself. There aren't too many
185 examples of this, which is why I thought it worth preserving! [SLPJ]
190 % -> TcM s (thing, LIE, thing_ty))
191 % -> TcM s ((TcHsBinds, thing), LIE, thing_ty)
193 % tcBindsAndThen EmptyBinds do_next
194 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
195 % returnTc ((EmptyBinds, thing), lie, thing_ty)
197 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
198 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
199 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
201 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
203 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
204 % = tcBindAndThen bind sigs do_next
208 %************************************************************************
210 \subsection{tcBindWithSigs}
212 %************************************************************************
214 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
215 so all the clever stuff is in here.
217 * binder_names and mbind must define the same set of Names
219 * The Names in tc_ty_sigs must be a subset of binder_names
221 * The Ids in tc_ty_sigs don't necessarily have to have the same name
222 as the Name in the tc_ty_sig
229 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
231 -> TcM s (TcMonoBinds, LIE, [TcId])
233 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
235 -- If typechecking the binds fails, then return with each
236 -- signature-less binder given type (forall a.a), to minimise subsequent
238 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
240 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
241 binder_names = map fst (bagToList (collectMonoBinders mbind))
242 poly_ids = map mk_dummy binder_names
243 mk_dummy name = case maybeSig tc_ty_sigs name of
244 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
245 Nothing -> mkVanillaId name forall_a_a -- No signature
247 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
250 -- TYPECHECK THE BINDINGS
251 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
253 -- CHECK THAT THE SIGNATURES MATCH
254 -- (must do this before getTyVarsToGen)
255 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
258 -- Force any unifications dictated by functional dependencies.
259 -- Because unification may happen, it's important that this step
261 -- - computing vars over which to quantify
262 -- - zonking the generalized type vars
263 tcImprove lie_req `thenTc_`
265 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
266 -- The tyvars_not_to_gen are free in the environment, and hence
267 -- candidates for generalisation, but sometimes the monomorphism
268 -- restriction means we can't generalise them nevertheless
270 mono_id_tys = map idType mono_ids
272 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
274 -- Finally, zonk the generalised type variables to real TyVars
275 -- This commits any unbound kind variables to boxed kind
276 -- I'm a little worried that such a kind variable might be
277 -- free in the environment, but I don't think it's possible for
278 -- this to happen when the type variable is not free in the envt
279 -- (which it isn't). SLPJ Nov 98
280 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
282 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
283 -- It's important that the final list
284 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
285 -- zonked, *including boxity*, because they'll be included in the forall types of
286 -- the polymorphic Ids, and instances of these Ids will be generated from them.
288 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
289 -- real_tyvars_to_gen
293 tcExtendGlobalTyVars tyvars_not_to_gen (
294 let ips = getIPsOfLIE lie_req in
295 if null real_tyvars_to_gen_list && (null ips || not is_unrestricted) then
296 -- No polymorphism, and no IPs, so no need to simplify context
297 returnTc (lie_req, EmptyMonoBinds, [])
299 case maybe_sig_theta of
301 -- No signatures, so just simplify the lie
302 -- NB: no signatures => no polymorphic recursion, so no
303 -- need to use lie_avail (which will be empty anyway)
304 tcSimplify (text "tcBinds1" <+> ppr binder_names)
305 real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
306 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
308 Just (sig_theta, lie_avail) ->
309 -- There are signatures, and their context is sig_theta
310 -- Furthermore, lie_avail is an LIE containing the 'method insts'
311 -- for the things bound here
313 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
314 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
315 -- It's important that sig_theta is zonked, because
316 -- dict_id is later used to form the type of the polymorphic thing,
317 -- and forall-types must be zonked so far as their bound variables
321 -- The "givens" is the stuff available. We get that from
322 -- the context of the type signature, BUT ALSO the lie_avail
323 -- so that polymorphic recursion works right (see comments at end of fn)
324 givens = dicts_sig `plusLIE` lie_avail
327 -- Check that the needed dicts can be expressed in
328 -- terms of the signature ones
329 tcAddErrCtxt (bindSigsCtxt tysig_names) $
331 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
332 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
334 returnTc (lie_free, dict_binds, dict_ids)
336 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
338 -- GET THE FINAL MONO_ID_TYS
339 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
342 -- CHECK FOR BOGUS UNPOINTED BINDINGS
343 (if any isUnLiftedType zonked_mono_id_types then
344 -- Unlifted bindings must be non-recursive,
345 -- not top level, and non-polymorphic
346 checkTc (isNotTopLevel top_lvl)
347 (unliftedBindErr "Top-level" mbind) `thenTc_`
348 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
349 (unliftedBindErr "Recursive" mbind) `thenTc_`
350 checkTc (null real_tyvars_to_gen_list)
351 (unliftedBindErr "Polymorphic" mbind)
356 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
357 -- The instCantBeGeneralised stuff in tcSimplify should have
358 -- already raised an error if we're trying to generalise an
359 -- unboxed tyvar (NB: unboxed tyvars are always introduced
360 -- along with a class constraint) and it's better done there
361 -- because we have more precise origin information.
362 -- That's why we just use an ASSERT here.
365 -- BUILD THE POLYMORPHIC RESULT IDs
366 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
368 exports = zipWith mk_export binder_names zonked_mono_ids
369 dict_tys = map idType dicts_bound
371 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
372 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
373 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
374 -- "INLINE n foo" means inline foo, but not until at least phase n
375 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
376 -- then only if it is small enough etc.
377 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
378 -- See comments in CoreUnfold.blackListed for the Authorised Version
380 mk_export binder_name zonked_mono_id
382 attachNoInlinePrag no_inlines poly_id,
386 case maybeSig tc_ty_sigs binder_name of
387 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
388 (sig_tyvars, sig_poly_id)
389 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
391 new_poly_id = mkVanillaId binder_name poly_ty
392 poly_ty = mkForAllTys real_tyvars_to_gen_list
394 $ idType (zonked_mono_id)
395 -- It's important to build a fully-zonked poly_ty, because
396 -- we'll slurp out its free type variables when extending the
397 -- local environment (tcExtendLocalValEnv); if it's not zonked
398 -- it appears to have free tyvars that aren't actually free
401 pat_binders :: [Name]
402 pat_binders = map fst $ bagToList $ collectMonoBinders $
403 (justPatBindings mbind EmptyMonoBinds)
405 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
406 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
407 && isUnboxedType (idType id)))
408 (unboxedPatBindErr id)) zonked_mono_ids
413 -- pprTrace "binding.." (ppr ((dicts_bound, dict_binds), exports, [idType poly_id | (_, poly_id, _) <- exports])) $
414 AbsBinds real_tyvars_to_gen_list
418 (dict_binds `andMonoBinds` mbind'),
420 [poly_id | (_, poly_id, _) <- exports]
423 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
424 is_unrestricted = isUnRestrictedGroup tysig_names mbind
426 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
427 justPatBindings (AndMonoBinds b1 b2) binds =
428 justPatBindings b1 (justPatBindings b2 binds)
429 justPatBindings other_bind binds = binds
431 attachNoInlinePrag no_inlines bndr
432 = case lookupFM no_inlines (idName bndr) of
433 Just prag -> bndr `setInlinePragma` prag
437 Polymorphic recursion
438 ~~~~~~~~~~~~~~~~~~~~~
439 The game plan for polymorphic recursion in the code above is
441 * Bind any variable for which we have a type signature
442 to an Id with a polymorphic type. Then when type-checking
443 the RHSs we'll make a full polymorphic call.
445 This fine, but if you aren't a bit careful you end up with a horrendous
446 amount of partial application and (worse) a huge space leak. For example:
448 f :: Eq a => [a] -> [a]
451 If we don't take care, after typechecking we get
453 f = /\a -> \d::Eq a -> let f' = f a d
457 Notice the the stupid construction of (f a d), which is of course
458 identical to the function we're executing. In this case, the
459 polymorphic recursion isn't being used (but that's a very common case).
462 f = /\a -> \d::Eq a -> letrec
463 fm = \ys:[a] -> ...fm...
467 This can lead to a massive space leak, from the following top-level defn
473 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
474 f' is another thunk which evaluates to the same thing... and you end
475 up with a chain of identical values all hung onto by the CAF ff.
479 = let f' = f Int dEqInt in \ys. ...f'...
481 = let f' = let f' = f Int dEqInt in \ys. ...f'...
485 Solution: when typechecking the RHSs we always have in hand the
486 *monomorphic* Ids for each binding. So we just need to make sure that
487 if (Method f a d) shows up in the constraints emerging from (...f...)
488 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
489 to the "givens" when simplifying constraints. That's what the "lies_avail"
493 %************************************************************************
495 \subsection{getTyVarsToGen}
497 %************************************************************************
499 @getTyVarsToGen@ decides what type variables to generalise over.
501 For a "restricted group" -- see the monomorphism restriction
502 for a definition -- we bind no dictionaries, and
503 remove from tyvars_to_gen any constrained type variables
505 *Don't* simplify dicts at this point, because we aren't going
506 to generalise over these dicts. By the time we do simplify them
507 we may well know more. For example (this actually came up)
509 f x = array ... xs where xs = [1,2,3,4,5]
510 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
511 stuff. If we simplify only at the f-binding (not the xs-binding)
512 we'll know that the literals are all Ints, and we can just produce
515 Find all the type variables involved in overloading, the
516 "constrained_tyvars". These are the ones we *aren't* going to
517 generalise. We must be careful about doing this:
519 (a) If we fail to generalise a tyvar which is not actually
520 constrained, then it will never, ever get bound, and lands
521 up printed out in interface files! Notorious example:
522 instance Eq a => Eq (Foo a b) where ..
523 Here, b is not constrained, even though it looks as if it is.
524 Another, more common, example is when there's a Method inst in
525 the LIE, whose type might very well involve non-overloaded
528 (b) On the other hand, we mustn't generalise tyvars which are constrained,
529 because we are going to pass on out the unmodified LIE, with those
530 tyvars in it. They won't be in scope if we've generalised them.
532 So we are careful, and do a complete simplification just to find the
533 constrained tyvars. We don't use any of the results, except to
534 find which tyvars are constrained.
537 getTyVarsToGen is_unrestricted mono_id_tys lie
538 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
539 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
541 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
545 let fds = getAllFunDepsOfLIE lie in
546 zonkFunDeps fds `thenNF_Tc` \ fds' ->
547 let tvFundep = tyVarFunDep fds'
548 extended_tyvars = oclose tvFundep body_tyvars in
549 -- pprTrace "gTVTG" (ppr (lie, body_tyvars, extended_tyvars)) $
550 returnNF_Tc (emptyVarSet, extended_tyvars)
552 -- This recover and discard-errs is to avoid duplicate error
553 -- messages; this, after all, is an "extra" call to tcSimplify
554 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
557 tcSimplify (text "getTVG") body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
559 -- ASSERT: dicts_sig is already zonked!
560 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
561 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
563 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
568 isUnRestrictedGroup :: [Name] -- Signatures given for these
572 is_elem v vs = isIn "isUnResMono" v vs
574 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
575 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
576 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
577 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
578 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
579 isUnRestrictedGroup sigs mb2
580 isUnRestrictedGroup sigs EmptyMonoBinds = True
584 %************************************************************************
586 \subsection{tcMonoBind}
588 %************************************************************************
590 @tcMonoBinds@ deals with a single @MonoBind@.
591 The signatures have been dealt with already.
594 tcMonoBinds :: RenamedMonoBinds
597 -> TcM s (TcMonoBinds,
599 [Name], -- Bound names
600 [TcId]) -- Corresponding monomorphic bound things
602 tcMonoBinds mbinds tc_ty_sigs is_rec
603 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
605 tv_list = bagToList tvs
606 id_list = bagToList ids
607 (names, mono_ids) = unzip id_list
609 -- This last defn is the key one:
610 -- extend the val envt with bindings for the
611 -- things bound in this group, overriding the monomorphic
612 -- ids with the polymorphic ones from the pattern
613 extra_val_env = case is_rec of
614 Recursive -> map mk_bind id_list
617 -- Don't know how to deal with pattern-bound existentials yet
618 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
619 (existentialExplode mbinds) `thenTc_`
621 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
622 -- extend the envt with bindings for all the bound ids;
623 -- and *then* override with the polymorphic Ids from the signatures
624 -- That is the whole point of the "complete_it" stuff.
626 -- There's a further wrinkle: we have to delay extending the environment
627 -- until after we've dealt with any pattern-bound signature type variables
628 -- Consider f (x::a) = ...f...
629 -- We're going to check that a isn't unified with anything in the envt,
630 -- so f itself had better not be! So we pass the envt binding f into
631 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
632 -- dealing with the signature tyvars
634 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
636 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
639 -- This function is used when dealing with a LHS binder; we make a monomorphic
640 -- version of the Id. We check for type signatures
641 tc_pat_bndr name pat_ty
642 = case maybeSig tc_ty_sigs name of
644 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
646 Just (TySigInfo _ _ _ _ _ mono_id _ _)
647 -> tcAddSrcLoc (getSrcLoc name) $
648 unifyTauTy (idType mono_id) pat_ty `thenTc_`
651 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
652 Nothing -> (name, mono_id)
653 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
655 tc_mb_pats EmptyMonoBinds
656 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
658 tc_mb_pats (AndMonoBinds mb1 mb2)
659 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
660 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
662 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
663 complete_it2 xve `thenTc` \ (mb2', lie2) ->
664 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
666 returnTc (complete_it,
667 lie_req1 `plusLIE` lie_req2,
668 tvs1 `unionBags` tvs2,
669 ids1 `unionBags` ids2,
670 lie_avail1 `plusLIE` lie_avail2)
672 tc_mb_pats (FunMonoBind name inf matches locn)
673 = newTyVarTy boxedTypeKind `thenNF_Tc` \ bndr_ty ->
674 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
676 complete_it xve = tcAddSrcLoc locn $
677 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
678 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
680 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
682 tc_mb_pats bind@(PatMonoBind pat grhss locn)
685 -- Figure out the appropriate kind for the pattern,
686 -- and generate a suitable type variable
688 Recursive -> newTyVarTy boxedTypeKind -- Recursive, so no unboxed types
689 NonRecursive -> newTyVarTy_OpenKind -- Non-recursive, so we permit unboxed types
690 ) `thenNF_Tc` \ pat_ty ->
692 -- Now typecheck the pattern
693 -- We don't support binding fresh type variables in the
694 -- pattern of a pattern binding. For example, this is illegal:
696 -- whereas this is ok
697 -- (x::Int, y::Bool) = e
699 -- We don't check explicitly for this problem. Instead, we simply
700 -- type check the pattern with tcPat. If the pattern mentions any
701 -- fresh tyvars we simply get an out-of-scope type variable error
702 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
704 complete_it xve = tcAddSrcLoc locn $
705 tcAddErrCtxt (patMonoBindsCtxt bind) $
706 tcExtendLocalValEnv xve $
707 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
708 returnTc (PatMonoBind pat' grhss' locn, lie)
710 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
713 %************************************************************************
715 \subsection{Signatures}
717 %************************************************************************
719 @checkSigMatch@ does the next step in checking signature matching.
720 The tau-type part has already been unified. What we do here is to
721 check that this unification has not over-constrained the (polymorphic)
722 type variables of the original signature type.
724 The error message here is somewhat unsatisfactory, but it'll do for
728 checkSigMatch top_lvl binder_names mono_ids sigs
730 = -- First unify the main_id with IO t, for any old t
731 tcSetErrCtxt mainTyCheckCtxt (
732 tcLookupTyCon ioTyCon_NAME `thenTc` \ ioTyCon ->
733 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
734 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
735 (idType main_mono_id)
738 -- Now check the signatures
739 -- Must do this after the unification with IO t,
740 -- in case of a silly signature like
741 -- main :: forall a. a
742 -- The unification to IO t will bind the type variable 'a',
743 -- which is just waht check_one_sig looks for
744 mapTc check_one_sig sigs `thenTc_`
745 mapTc check_main_ctxt sigs `thenTc_`
747 returnTc (Just ([], emptyLIE))
750 = mapTc check_one_sig sigs `thenTc_`
751 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
752 returnTc (Just (theta1, sig_lie))
755 = returnTc Nothing -- No constraints from type sigs
758 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
760 sig1_dict_tys = mk_dict_tys theta1
761 n_sig1_dict_tys = length sig1_dict_tys
762 sig_lie = mkLIE [inst | TySigInfo _ _ _ _ _ _ inst _ <- sigs]
764 maybe_main = find_main top_lvl binder_names mono_ids
765 main_bound_here = maybeToBool maybe_main
766 Just main_mono_id = maybe_main
768 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
769 -- Doesn't affect substitution
770 check_one_sig (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
771 = tcAddSrcLoc src_loc $
772 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
773 checkSigTyVars sig_tyvars (idFreeTyVars id)
776 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
777 -- The type signatures on a mutually-recursive group of definitions
778 -- must all have the same context (or none).
780 -- We unify them because, with polymorphic recursion, their types
781 -- might not otherwise be related. This is a rather subtle issue.
783 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
784 = tcAddSrcLoc src_loc $
785 tcAddErrCtxt (sigContextsCtxt id1 id) $
786 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
787 sigContextsErr `thenTc_`
788 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
790 this_sig_dict_tys = mk_dict_tys theta
792 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
793 -- the signature contexts are empty (what a bore)
794 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
795 = tcAddSrcLoc src_loc $
796 checkTc (null theta) (mainContextsErr id)
798 mk_dict_tys theta = map mkPredTy theta
800 sig_msg id = ptext SLIT("When checking the type signature for") <+> ppr id
802 -- Search for Main.main in the binder_names, return corresponding mono_id
803 find_main NotTopLevel binder_names mono_ids = Nothing
804 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
806 go (n:ns) (m:ms) | n == main_NAME = Just m
807 | otherwise = go ns ms
811 %************************************************************************
813 \subsection{SPECIALIZE pragmas}
815 %************************************************************************
817 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
818 pragmas. It is convenient for them to appear in the @[RenamedSig]@
819 part of a binding because then the same machinery can be used for
820 moving them into place as is done for type signatures.
825 f :: Ord a => [a] -> b -> b
826 {-# SPECIALIZE f :: [Int] -> b -> b #-}
829 For this we generate:
831 f* = /\ b -> let d1 = ...
835 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
836 retain a right-hand-side that the simplifier will otherwise discard as
837 dead code... the simplifier has a flag that tells it not to discard
838 SpecPragmaId bindings.
840 In this case the f* retains a call-instance of the overloaded
841 function, f, (including appropriate dictionaries) so that the
842 specialiser will subsequently discover that there's a call of @f@ at
843 Int, and will create a specialisation for @f@. After that, the
844 binding for @f*@ can be discarded.
846 We used to have a form
847 {-# SPECIALISE f :: <type> = g #-}
848 which promised that g implemented f at <type>, but we do that with
850 {-# SPECIALISE (f::<type) = g #-}
853 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
854 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
855 = -- SPECIALISE f :: forall b. theta => tau = g
856 tcAddSrcLoc src_loc $
857 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
859 -- Get and instantiate its alleged specialised type
860 tcHsSigType poly_ty `thenTc` \ sig_ty ->
862 -- Check that f has a more general type, and build a RHS for
863 -- the spec-pragma-id at the same time
864 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
866 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
867 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
869 -- Just specialise "f" by building a SpecPragmaId binding
870 -- It is the thing that makes sure we don't prematurely
871 -- dead-code-eliminate the binding we are really interested in.
872 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
874 -- Do the rest and combine
875 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
876 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
877 lie_rest `plusLIE` spec_lie1)
879 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
880 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
884 %************************************************************************
886 \subsection[TcBinds-errors]{Error contexts and messages}
888 %************************************************************************
892 patMonoBindsCtxt bind
893 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
895 -----------------------------------------------
897 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
898 nest 4 (ppr v <+> dcolon <+> ppr ty)]
900 -----------------------------------------------
901 notAsPolyAsSigErr sig_tau mono_tyvars
902 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
903 4 (vcat [text "Can't for-all the type variable(s)" <+>
904 pprQuotedList mono_tyvars,
905 text "in the type" <+> quotes (ppr sig_tau)
908 -----------------------------------------------
909 badMatchErr sig_ty inferred_ty
910 = hang (ptext SLIT("Type signature doesn't match inferred type"))
911 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
912 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_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 | getName id == main_NAME = 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 (ppr main_NAME),
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"])