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 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 tcImprove lie_req `thenTc_`
264 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
265 -- The tyvars_not_to_gen are free in the environment, and hence
266 -- candidates for generalisation, but sometimes the monomorphism
267 -- restriction means we can't generalise them nevertheless
269 mono_id_tys = map idType mono_ids
271 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
273 -- Finally, zonk the generalised type variables to real TyVars
274 -- This commits any unbound kind variables to boxed kind
275 -- I'm a little worried that such a kind variable might be
276 -- free in the environment, but I don't think it's possible for
277 -- this to happen when the type variable is not free in the envt
278 -- (which it isn't). SLPJ Nov 98
279 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
281 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
282 -- It's important that the final list
283 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
284 -- zonked, *including boxity*, because they'll be included in the forall types of
285 -- the polymorphic Ids, and instances of these Ids will be generated from them.
287 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
288 -- real_tyvars_to_gen
292 tcExtendGlobalTyVars tyvars_not_to_gen (
293 let ips = getIPsOfLIE lie_req in
294 if null real_tyvars_to_gen_list && (null ips || not is_unrestricted) then
295 -- No polymorphism, and no IPs, so no need to simplify context
296 returnTc (lie_req, EmptyMonoBinds, [])
298 case maybe_sig_theta of
300 -- No signatures, so just simplify the lie
301 -- NB: no signatures => no polymorphic recursion, so no
302 -- need to use lie_avail (which will be empty anyway)
303 tcSimplify (text "tcBinds1" <+> ppr binder_names)
304 real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
305 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
307 Just (sig_theta, lie_avail) ->
308 -- There are signatures, and their context is sig_theta
309 -- Furthermore, lie_avail is an LIE containing the 'method insts'
310 -- for the things bound here
312 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
313 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
314 -- It's important that sig_theta is zonked, because
315 -- dict_id is later used to form the type of the polymorphic thing,
316 -- and forall-types must be zonked so far as their bound variables
320 -- The "givens" is the stuff available. We get that from
321 -- the context of the type signature, BUT ALSO the lie_avail
322 -- so that polymorphic recursion works right (see comments at end of fn)
323 givens = dicts_sig `plusLIE` lie_avail
326 -- Check that the needed dicts can be expressed in
327 -- terms of the signature ones
328 tcAddErrCtxt (bindSigsCtxt tysig_names) $
330 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
331 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
333 returnTc (lie_free, dict_binds, dict_ids)
335 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
337 -- GET THE FINAL MONO_ID_TYS
338 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
341 -- CHECK FOR BOGUS UNPOINTED BINDINGS
342 (if any isUnLiftedType zonked_mono_id_types then
343 -- Unlifted bindings must be non-recursive,
344 -- not top level, and non-polymorphic
345 checkTc (isNotTopLevel top_lvl)
346 (unliftedBindErr "Top-level" mbind) `thenTc_`
347 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
348 (unliftedBindErr "Recursive" mbind) `thenTc_`
349 checkTc (null real_tyvars_to_gen_list)
350 (unliftedBindErr "Polymorphic" mbind)
355 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
356 -- The instCantBeGeneralised stuff in tcSimplify should have
357 -- already raised an error if we're trying to generalise an
358 -- unboxed tyvar (NB: unboxed tyvars are always introduced
359 -- along with a class constraint) and it's better done there
360 -- because we have more precise origin information.
361 -- That's why we just use an ASSERT here.
364 -- BUILD THE POLYMORPHIC RESULT IDs
365 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
367 exports = zipWith mk_export binder_names zonked_mono_ids
368 dict_tys = map idType dicts_bound
370 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
371 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
372 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
373 -- "INLINE n foo" means inline foo, but not until at least phase n
374 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
375 -- then only if it is small enough etc.
376 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
377 -- See comments in CoreUnfold.blackListed for the Authorised Version
379 mk_export binder_name zonked_mono_id
381 attachNoInlinePrag no_inlines poly_id,
385 case maybeSig tc_ty_sigs binder_name of
386 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
387 (sig_tyvars, sig_poly_id)
388 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
390 new_poly_id = mkVanillaId binder_name poly_ty
391 poly_ty = mkForAllTys real_tyvars_to_gen_list
393 $ idType (zonked_mono_id)
394 -- It's important to build a fully-zonked poly_ty, because
395 -- we'll slurp out its free type variables when extending the
396 -- local environment (tcExtendLocalValEnv); if it's not zonked
397 -- it appears to have free tyvars that aren't actually free
400 pat_binders :: [Name]
401 pat_binders = map fst $ bagToList $ collectMonoBinders $
402 (justPatBindings mbind EmptyMonoBinds)
404 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
405 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
406 && isUnboxedType (idType id)))
407 (unboxedPatBindErr id)) zonked_mono_ids
412 -- pprTrace "binding.." (ppr ((dicts_bound, dict_binds), exports, [idType poly_id | (_, poly_id, _) <- exports])) $
413 AbsBinds real_tyvars_to_gen_list
417 (dict_binds `andMonoBinds` mbind'),
419 [poly_id | (_, poly_id, _) <- exports]
422 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
423 is_unrestricted = isUnRestrictedGroup tysig_names mbind
425 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
426 justPatBindings (AndMonoBinds b1 b2) binds =
427 justPatBindings b1 (justPatBindings b2 binds)
428 justPatBindings other_bind binds = binds
430 attachNoInlinePrag no_inlines bndr
431 = case lookupFM no_inlines (idName bndr) of
432 Just prag -> bndr `setInlinePragma` prag
436 Polymorphic recursion
437 ~~~~~~~~~~~~~~~~~~~~~
438 The game plan for polymorphic recursion in the code above is
440 * Bind any variable for which we have a type signature
441 to an Id with a polymorphic type. Then when type-checking
442 the RHSs we'll make a full polymorphic call.
444 This fine, but if you aren't a bit careful you end up with a horrendous
445 amount of partial application and (worse) a huge space leak. For example:
447 f :: Eq a => [a] -> [a]
450 If we don't take care, after typechecking we get
452 f = /\a -> \d::Eq a -> let f' = f a d
456 Notice the the stupid construction of (f a d), which is of course
457 identical to the function we're executing. In this case, the
458 polymorphic recursion isn't being used (but that's a very common case).
461 f = /\a -> \d::Eq a -> letrec
462 fm = \ys:[a] -> ...fm...
466 This can lead to a massive space leak, from the following top-level defn
472 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
473 f' is another thunk which evaluates to the same thing... and you end
474 up with a chain of identical values all hung onto by the CAF ff.
478 = let f' = f Int dEqInt in \ys. ...f'...
480 = let f' = let f' = f Int dEqInt in \ys. ...f'...
484 Solution: when typechecking the RHSs we always have in hand the
485 *monomorphic* Ids for each binding. So we just need to make sure that
486 if (Method f a d) shows up in the constraints emerging from (...f...)
487 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
488 to the "givens" when simplifying constraints. That's what the "lies_avail"
492 %************************************************************************
494 \subsection{getTyVarsToGen}
496 %************************************************************************
498 @getTyVarsToGen@ decides what type variables to generalise over.
500 For a "restricted group" -- see the monomorphism restriction
501 for a definition -- we bind no dictionaries, and
502 remove from tyvars_to_gen any constrained type variables
504 *Don't* simplify dicts at this point, because we aren't going
505 to generalise over these dicts. By the time we do simplify them
506 we may well know more. For example (this actually came up)
508 f x = array ... xs where xs = [1,2,3,4,5]
509 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
510 stuff. If we simplify only at the f-binding (not the xs-binding)
511 we'll know that the literals are all Ints, and we can just produce
514 Find all the type variables involved in overloading, the
515 "constrained_tyvars". These are the ones we *aren't* going to
516 generalise. We must be careful about doing this:
518 (a) If we fail to generalise a tyvar which is not actually
519 constrained, then it will never, ever get bound, and lands
520 up printed out in interface files! Notorious example:
521 instance Eq a => Eq (Foo a b) where ..
522 Here, b is not constrained, even though it looks as if it is.
523 Another, more common, example is when there's a Method inst in
524 the LIE, whose type might very well involve non-overloaded
527 (b) On the other hand, we mustn't generalise tyvars which are constrained,
528 because we are going to pass on out the unmodified LIE, with those
529 tyvars in it. They won't be in scope if we've generalised them.
531 So we are careful, and do a complete simplification just to find the
532 constrained tyvars. We don't use any of the results, except to
533 find which tyvars are constrained.
536 getTyVarsToGen is_unrestricted mono_id_tys lie
537 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
538 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
540 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
544 let fds = getAllFunDepsOfLIE lie in
545 zonkFunDeps fds `thenNF_Tc` \ fds' ->
546 let tvFundep = tyVarFunDep fds'
547 extended_tyvars = oclose tvFundep body_tyvars in
548 -- pprTrace "gTVTG" (ppr (lie, body_tyvars, extended_tyvars)) $
549 returnNF_Tc (emptyVarSet, extended_tyvars)
551 -- This recover and discard-errs is to avoid duplicate error
552 -- messages; this, after all, is an "extra" call to tcSimplify
553 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
556 tcSimplify (text "getTVG") body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
558 -- ASSERT: dicts_sig is already zonked!
559 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
560 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
562 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
567 isUnRestrictedGroup :: [Name] -- Signatures given for these
571 is_elem v vs = isIn "isUnResMono" v vs
573 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
574 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
575 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
576 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
577 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
578 isUnRestrictedGroup sigs mb2
579 isUnRestrictedGroup sigs EmptyMonoBinds = True
583 %************************************************************************
585 \subsection{tcMonoBind}
587 %************************************************************************
589 @tcMonoBinds@ deals with a single @MonoBind@.
590 The signatures have been dealt with already.
593 tcMonoBinds :: RenamedMonoBinds
596 -> TcM s (TcMonoBinds,
598 [Name], -- Bound names
599 [TcId]) -- Corresponding monomorphic bound things
601 tcMonoBinds mbinds tc_ty_sigs is_rec
602 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
604 tv_list = bagToList tvs
605 id_list = bagToList ids
606 (names, mono_ids) = unzip id_list
608 -- This last defn is the key one:
609 -- extend the val envt with bindings for the
610 -- things bound in this group, overriding the monomorphic
611 -- ids with the polymorphic ones from the pattern
612 extra_val_env = case is_rec of
613 Recursive -> map mk_bind id_list
616 -- Don't know how to deal with pattern-bound existentials yet
617 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
618 (existentialExplode mbinds) `thenTc_`
620 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
621 -- extend the envt with bindings for all the bound ids;
622 -- and *then* override with the polymorphic Ids from the signatures
623 -- That is the whole point of the "complete_it" stuff.
625 -- There's a further wrinkle: we have to delay extending the environment
626 -- until after we've dealt with any pattern-bound signature type variables
627 -- Consider f (x::a) = ...f...
628 -- We're going to check that a isn't unified with anything in the envt,
629 -- so f itself had better not be! So we pass the envt binding f into
630 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
631 -- dealing with the signature tyvars
633 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
635 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
638 -- This function is used when dealing with a LHS binder; we make a monomorphic
639 -- version of the Id. We check for type signatures
640 tc_pat_bndr name pat_ty
641 = case maybeSig tc_ty_sigs name of
643 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
645 Just (TySigInfo _ _ _ _ _ mono_id _ _)
646 -> tcAddSrcLoc (getSrcLoc name) $
647 unifyTauTy (idType mono_id) pat_ty `thenTc_`
650 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
651 Nothing -> (name, mono_id)
652 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
654 tc_mb_pats EmptyMonoBinds
655 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
657 tc_mb_pats (AndMonoBinds mb1 mb2)
658 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
659 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
661 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
662 complete_it2 xve `thenTc` \ (mb2', lie2) ->
663 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
665 returnTc (complete_it,
666 lie_req1 `plusLIE` lie_req2,
667 tvs1 `unionBags` tvs2,
668 ids1 `unionBags` ids2,
669 lie_avail1 `plusLIE` lie_avail2)
671 tc_mb_pats (FunMonoBind name inf matches locn)
672 = newTyVarTy boxedTypeKind `thenNF_Tc` \ bndr_ty ->
673 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
675 complete_it xve = tcAddSrcLoc locn $
676 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
677 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
679 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
681 tc_mb_pats bind@(PatMonoBind pat grhss locn)
684 -- Figure out the appropriate kind for the pattern,
685 -- and generate a suitable type variable
687 Recursive -> newTyVarTy boxedTypeKind -- Recursive, so no unboxed types
688 NonRecursive -> newTyVarTy_OpenKind -- Non-recursive, so we permit unboxed types
689 ) `thenNF_Tc` \ pat_ty ->
691 -- Now typecheck the pattern
692 -- We don't support binding fresh type variables in the
693 -- pattern of a pattern binding. For example, this is illegal:
695 -- whereas this is ok
696 -- (x::Int, y::Bool) = e
698 -- We don't check explicitly for this problem. Instead, we simply
699 -- type check the pattern with tcPat. If the pattern mentions any
700 -- fresh tyvars we simply get an out-of-scope type variable error
701 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
703 complete_it xve = tcAddSrcLoc locn $
704 tcAddErrCtxt (patMonoBindsCtxt bind) $
705 tcExtendLocalValEnv xve $
706 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
707 returnTc (PatMonoBind pat' grhss' locn, lie)
709 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
712 %************************************************************************
714 \subsection{Signatures}
716 %************************************************************************
718 @checkSigMatch@ does the next step in checking signature matching.
719 The tau-type part has already been unified. What we do here is to
720 check that this unification has not over-constrained the (polymorphic)
721 type variables of the original signature type.
723 The error message here is somewhat unsatisfactory, but it'll do for
727 checkSigMatch top_lvl binder_names mono_ids sigs
729 = -- First unify the main_id with IO t, for any old t
730 tcSetErrCtxt mainTyCheckCtxt (
731 tcLookupTyCon ioTyCon_NAME `thenTc` \ ioTyCon ->
732 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
733 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
734 (idType main_mono_id)
737 -- Now check the signatures
738 -- Must do this after the unification with IO t,
739 -- in case of a silly signature like
740 -- main :: forall a. a
741 -- The unification to IO t will bind the type variable 'a',
742 -- which is just waht check_one_sig looks for
743 mapTc check_one_sig sigs `thenTc_`
744 mapTc check_main_ctxt sigs `thenTc_`
746 returnTc (Just ([], emptyLIE))
749 = mapTc check_one_sig sigs `thenTc_`
750 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
751 returnTc (Just (theta1, sig_lie))
754 = returnTc Nothing -- No constraints from type sigs
757 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
759 sig1_dict_tys = mk_dict_tys theta1
760 n_sig1_dict_tys = length sig1_dict_tys
761 sig_lie = mkLIE [inst | TySigInfo _ _ _ _ _ _ inst _ <- sigs]
763 maybe_main = find_main top_lvl binder_names mono_ids
764 main_bound_here = maybeToBool maybe_main
765 Just main_mono_id = maybe_main
767 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
768 -- Doesn't affect substitution
769 check_one_sig (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
770 = tcAddSrcLoc src_loc $
771 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
772 checkSigTyVars sig_tyvars (idFreeTyVars id)
775 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
776 -- The type signatures on a mutually-recursive group of definitions
777 -- must all have the same context (or none).
779 -- We unify them because, with polymorphic recursion, their types
780 -- might not otherwise be related. This is a rather subtle issue.
782 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
783 = tcAddSrcLoc src_loc $
784 tcAddErrCtxt (sigContextsCtxt id1 id) $
785 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
786 sigContextsErr `thenTc_`
787 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
789 this_sig_dict_tys = mk_dict_tys theta
791 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
792 -- the signature contexts are empty (what a bore)
793 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
794 = tcAddSrcLoc src_loc $
795 checkTc (null theta) (mainContextsErr id)
797 mk_dict_tys theta = map mkPredTy theta
799 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
801 -- Search for Main.main in the binder_names, return corresponding mono_id
802 find_main NotTopLevel binder_names mono_ids = Nothing
803 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
805 go (n:ns) (m:ms) | n == main_NAME = Just m
806 | otherwise = go ns ms
810 %************************************************************************
812 \subsection{SPECIALIZE pragmas}
814 %************************************************************************
816 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
817 pragmas. It is convenient for them to appear in the @[RenamedSig]@
818 part of a binding because then the same machinery can be used for
819 moving them into place as is done for type signatures.
824 f :: Ord a => [a] -> b -> b
825 {-# SPECIALIZE f :: [Int] -> b -> b #-}
828 For this we generate:
830 f* = /\ b -> let d1 = ...
834 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
835 retain a right-hand-side that the simplifier will otherwise discard as
836 dead code... the simplifier has a flag that tells it not to discard
837 SpecPragmaId bindings.
839 In this case the f* retains a call-instance of the overloaded
840 function, f, (including appropriate dictionaries) so that the
841 specialiser will subsequently discover that there's a call of @f@ at
842 Int, and will create a specialisation for @f@. After that, the
843 binding for @f*@ can be discarded.
845 We used to have a form
846 {-# SPECIALISE f :: <type> = g #-}
847 which promised that g implemented f at <type>, but we do that with
849 {-# SPECIALISE (f::<type) = g #-}
852 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
853 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
854 = -- SPECIALISE f :: forall b. theta => tau = g
855 tcAddSrcLoc src_loc $
856 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
858 -- Get and instantiate its alleged specialised type
859 tcHsSigType poly_ty `thenTc` \ sig_ty ->
861 -- Check that f has a more general type, and build a RHS for
862 -- the spec-pragma-id at the same time
863 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
865 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
866 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
868 -- Just specialise "f" by building a SpecPragmaId binding
869 -- It is the thing that makes sure we don't prematurely
870 -- dead-code-eliminate the binding we are really interested in.
871 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
873 -- Do the rest and combine
874 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
875 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
876 lie_rest `plusLIE` spec_lie1)
878 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
879 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
883 %************************************************************************
885 \subsection[TcBinds-errors]{Error contexts and messages}
887 %************************************************************************
891 patMonoBindsCtxt bind
892 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
894 -----------------------------------------------
896 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
897 nest 4 (ppr v <+> dcolon <+> ppr ty)]
899 -----------------------------------------------
900 notAsPolyAsSigErr sig_tau mono_tyvars
901 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
902 4 (vcat [text "Can't for-all the type variable(s)" <+>
903 pprQuotedList mono_tyvars,
904 text "in the type" <+> quotes (ppr sig_tau)
907 -----------------------------------------------
908 badMatchErr sig_ty inferred_ty
909 = hang (ptext SLIT("Type signature doesn't match inferred type"))
910 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
911 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
914 -----------------------------------------------
916 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
919 -----------------------------------------------
921 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
923 -----------------------------------------------
925 = ptext SLIT("Mismatched contexts")
927 sigContextsCtxt s1 s2
928 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
929 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
930 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
933 | getName id == main_NAME = ptext SLIT("Main.main cannot be overloaded")
935 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
936 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
939 = hsep [ptext SLIT("When checking that"), quotes (ppr main_NAME),
940 ptext SLIT("has the required type")]
942 -----------------------------------------------
943 unliftedBindErr flavour mbind
944 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
947 existentialExplode mbinds
948 = hang (vcat [text "My brain just exploded.",
949 text "I can't handle pattern bindings for existentially-quantified constructors.",
950 text "In the binding group"])