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 Id ( Id, mkVanillaId, setInlinePragma, idFreeTyVars )
46 import Var ( idType, idName )
47 import IdInfo ( setInlinePragInfo, InlinePragInfo(..) )
48 import Name ( Name, getName, getOccName, getSrcLoc )
50 import Type ( mkTyVarTy, tyVarsOfTypes, mkTyConApp,
51 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar,
52 mkPredTy, splitRhoTy, mkForAllTy, isUnLiftedType,
53 isUnboxedType, unboxedTypeKind, boxedTypeKind
55 import FunDeps ( tyVarFunDep, oclose )
56 import Var ( TyVar, tyVarKind )
60 import Maybes ( maybeToBool )
61 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNotTopLevel )
62 import FiniteMap ( listToFM, lookupFM )
63 import Unique ( ioTyConKey, mainKey, hasKey, Uniquable(..) )
64 import SrcLoc ( SrcLoc )
69 %************************************************************************
71 \subsection{Type-checking bindings}
73 %************************************************************************
75 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
76 it needs to know something about the {\em usage} of the things bound,
77 so that it can create specialisations of them. So @tcBindsAndThen@
78 takes a function which, given an extended environment, E, typechecks
79 the scope of the bindings returning a typechecked thing and (most
80 important) an LIE. It is this LIE which is then used as the basis for
81 specialising the things bound.
83 @tcBindsAndThen@ also takes a "combiner" which glues together the
84 bindings and the "thing" to make a new "thing".
86 The real work is done by @tcBindWithSigsAndThen@.
88 Recursive and non-recursive binds are handled in essentially the same
89 way: because of uniques there are no scoping issues left. The only
90 difference is that non-recursive bindings can bind primitive values.
92 Even for non-recursive binding groups we add typings for each binder
93 to the LVE for the following reason. When each individual binding is
94 checked the type of its LHS is unified with that of its RHS; and
95 type-checking the LHS of course requires that the binder is in scope.
97 At the top-level the LIE is sure to contain nothing but constant
98 dictionaries, which we resolve at the module level.
101 tcTopBindsAndThen, tcBindsAndThen
102 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
104 -> TcM s (thing, LIE)
105 -> TcM s (thing, LIE)
107 tcTopBindsAndThen = tc_binds_and_then TopLevel
108 tcBindsAndThen = tc_binds_and_then NotTopLevel
110 tc_binds_and_then top_lvl combiner EmptyBinds do_next
112 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
115 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
116 = tc_binds_and_then top_lvl combiner b1 $
117 tc_binds_and_then top_lvl combiner b2 $
120 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
121 = -- TYPECHECK THE SIGNATURES
122 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
124 tcBindWithSigs top_lvl bind tc_ty_sigs
125 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
127 -- Extend the environment to bind the new polymorphic Ids
128 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
130 -- Build bindings and IdInfos corresponding to user pragmas
131 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
133 -- Now do whatever happens next, in the augmented envt
134 do_next `thenTc` \ (thing, thing_lie) ->
136 -- Create specialisations of functions bound here
137 -- We want to keep non-recursive things non-recursive
138 -- so that we desugar unboxed bindings correctly
139 case (top_lvl, is_rec) of
141 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
142 -- All the top level things are rec'd together anyway, so it's fine to
143 -- leave them to the tcSimplifyTop, and quite a bit faster too
145 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
146 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
148 (NotTopLevel, NonRecursive)
149 -> bindInstsOfLocalFuns
150 (thing_lie `plusLIE` prag_lie)
151 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
154 combiner NonRecursive poly_binds $
155 combiner NonRecursive prag_binds $
156 combiner Recursive lie_binds $
157 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
158 -- aren't guaranteed in dependency order (though we could change
159 -- that); hence the Recursive marker.
162 thing_lie' `plusLIE` poly_lie
165 (NotTopLevel, Recursive)
166 -> bindInstsOfLocalFuns
167 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
168 poly_ids `thenTc` \ (final_lie, lie_binds) ->
172 poly_binds `andMonoBinds`
173 lie_binds `andMonoBinds`
179 An aside. The original version of @tcBindsAndThen@ which lacks a
180 combiner function, appears below. Though it is perfectly well
181 behaved, it cannot be typed by Haskell, because the recursive call is
182 at a different type to the definition itself. There aren't too many
183 examples of this, which is why I thought it worth preserving! [SLPJ]
188 % -> TcM s (thing, LIE, thing_ty))
189 % -> TcM s ((TcHsBinds, thing), LIE, thing_ty)
191 % tcBindsAndThen EmptyBinds do_next
192 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
193 % returnTc ((EmptyBinds, thing), lie, thing_ty)
195 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
196 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
197 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
199 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
201 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
202 % = tcBindAndThen bind sigs do_next
206 %************************************************************************
208 \subsection{tcBindWithSigs}
210 %************************************************************************
212 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
213 so all the clever stuff is in here.
215 * binder_names and mbind must define the same set of Names
217 * The Names in tc_ty_sigs must be a subset of binder_names
219 * The Ids in tc_ty_sigs don't necessarily have to have the same name
220 as the Name in the tc_ty_sig
227 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
229 -> TcM s (TcMonoBinds, LIE, [TcId])
231 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
233 -- If typechecking the binds fails, then return with each
234 -- signature-less binder given type (forall a.a), to minimise subsequent
236 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
238 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
239 binder_names = map fst (bagToList (collectMonoBinders mbind))
240 poly_ids = map mk_dummy binder_names
241 mk_dummy name = case maybeSig tc_ty_sigs name of
242 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
243 Nothing -> mkVanillaId name forall_a_a -- No signature
245 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
248 -- TYPECHECK THE BINDINGS
249 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
251 -- CHECK THAT THE SIGNATURES MATCH
252 -- (must do this before getTyVarsToGen)
253 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
256 -- Force any unifications dictated by functional dependencies.
257 -- Because unification may happen, it's important that this step
259 -- - computing vars over which to quantify
260 -- - zonking the generalized type vars
261 let lie_avail = case maybe_sig_theta of
263 Just (_, la) -> la in
264 tcImprove (lie_avail `plusLIE` lie_req) `thenTc_`
266 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
267 -- The tyvars_not_to_gen are free in the environment, and hence
268 -- candidates for generalisation, but sometimes the monomorphism
269 -- restriction means we can't generalise them nevertheless
271 mono_id_tys = map idType mono_ids
273 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
275 -- Finally, zonk the generalised type variables to real TyVars
276 -- This commits any unbound kind variables to boxed kind
277 -- I'm a little worried that such a kind variable might be
278 -- free in the environment, but I don't think it's possible for
279 -- this to happen when the type variable is not free in the envt
280 -- (which it isn't). SLPJ Nov 98
281 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
283 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
284 -- It's important that the final list
285 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
286 -- zonked, *including boxity*, because they'll be included in the forall types of
287 -- the polymorphic Ids, and instances of these Ids will be generated from them.
289 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
290 -- real_tyvars_to_gen
294 tcExtendGlobalTyVars tyvars_not_to_gen (
295 let ips = getIPsOfLIE lie_req in
296 if null real_tyvars_to_gen_list && (null ips || not is_unrestricted) then
297 -- No polymorphism, and no IPs, so no need to simplify context
298 returnTc (lie_req, EmptyMonoBinds, [])
300 case maybe_sig_theta of
302 -- No signatures, so just simplify the lie
303 -- NB: no signatures => no polymorphic recursion, so no
304 -- need to use lie_avail (which will be empty anyway)
305 tcSimplify (text "tcBinds1" <+> ppr binder_names)
306 real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
307 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
309 Just (sig_theta, lie_avail) ->
310 -- There are signatures, and their context is sig_theta
311 -- Furthermore, lie_avail is an LIE containing the 'method insts'
312 -- for the things bound here
314 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
315 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
316 -- It's important that sig_theta is zonked, because
317 -- dict_id is later used to form the type of the polymorphic thing,
318 -- and forall-types must be zonked so far as their bound variables
322 -- The "givens" is the stuff available. We get that from
323 -- the context of the type signature, BUT ALSO the lie_avail
324 -- so that polymorphic recursion works right (see comments at end of fn)
325 givens = dicts_sig `plusLIE` lie_avail
328 -- Check that the needed dicts can be expressed in
329 -- terms of the signature ones
330 tcAddErrCtxt (bindSigsCtxt tysig_names) $
332 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
333 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
335 returnTc (lie_free, dict_binds, dict_ids)
337 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
339 -- GET THE FINAL MONO_ID_TYS
340 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
343 -- CHECK FOR BOGUS UNPOINTED BINDINGS
344 (if any isUnLiftedType zonked_mono_id_types then
345 -- Unlifted bindings must be non-recursive,
346 -- not top level, and non-polymorphic
347 checkTc (isNotTopLevel top_lvl)
348 (unliftedBindErr "Top-level" mbind) `thenTc_`
349 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
350 (unliftedBindErr "Recursive" mbind) `thenTc_`
351 checkTc (null real_tyvars_to_gen_list)
352 (unliftedBindErr "Polymorphic" mbind)
357 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
358 -- The instCantBeGeneralised stuff in tcSimplify should have
359 -- already raised an error if we're trying to generalise an
360 -- unboxed tyvar (NB: unboxed tyvars are always introduced
361 -- along with a class constraint) and it's better done there
362 -- because we have more precise origin information.
363 -- That's why we just use an ASSERT here.
366 -- BUILD THE POLYMORPHIC RESULT IDs
367 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
369 exports = zipWith mk_export binder_names zonked_mono_ids
370 dict_tys = map idType dicts_bound
372 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
373 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
374 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
375 -- "INLINE n foo" means inline foo, but not until at least phase n
376 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
377 -- then only if it is small enough etc.
378 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
379 -- See comments in CoreUnfold.blackListed for the Authorised Version
381 mk_export binder_name zonked_mono_id
383 attachNoInlinePrag no_inlines poly_id,
387 case maybeSig tc_ty_sigs binder_name of
388 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
389 (sig_tyvars, sig_poly_id)
390 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
392 new_poly_id = mkVanillaId binder_name poly_ty
393 poly_ty = mkForAllTys real_tyvars_to_gen_list
395 $ idType (zonked_mono_id)
396 -- It's important to build a fully-zonked poly_ty, because
397 -- we'll slurp out its free type variables when extending the
398 -- local environment (tcExtendLocalValEnv); if it's not zonked
399 -- it appears to have free tyvars that aren't actually free
402 pat_binders :: [Name]
403 pat_binders = map fst $ bagToList $ collectMonoBinders $
404 (justPatBindings mbind EmptyMonoBinds)
406 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
407 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
408 && isUnboxedType (idType id)))
409 (unboxedPatBindErr id)) zonked_mono_ids
414 -- pprTrace "binding.." (ppr ((dicts_bound, dict_binds), exports, [idType poly_id | (_, poly_id, _) <- exports])) $
415 AbsBinds real_tyvars_to_gen_list
419 (dict_binds `andMonoBinds` mbind'),
421 [poly_id | (_, poly_id, _) <- exports]
424 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
425 is_unrestricted = isUnRestrictedGroup tysig_names mbind
427 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
428 justPatBindings (AndMonoBinds b1 b2) binds =
429 justPatBindings b1 (justPatBindings b2 binds)
430 justPatBindings other_bind binds = binds
432 attachNoInlinePrag no_inlines bndr
433 = case lookupFM no_inlines (idName bndr) of
434 Just prag -> bndr `setInlinePragma` prag
438 Polymorphic recursion
439 ~~~~~~~~~~~~~~~~~~~~~
440 The game plan for polymorphic recursion in the code above is
442 * Bind any variable for which we have a type signature
443 to an Id with a polymorphic type. Then when type-checking
444 the RHSs we'll make a full polymorphic call.
446 This fine, but if you aren't a bit careful you end up with a horrendous
447 amount of partial application and (worse) a huge space leak. For example:
449 f :: Eq a => [a] -> [a]
452 If we don't take care, after typechecking we get
454 f = /\a -> \d::Eq a -> let f' = f a d
458 Notice the the stupid construction of (f a d), which is of course
459 identical to the function we're executing. In this case, the
460 polymorphic recursion isn't being used (but that's a very common case).
463 f = /\a -> \d::Eq a -> letrec
464 fm = \ys:[a] -> ...fm...
468 This can lead to a massive space leak, from the following top-level defn
474 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
475 f' is another thunk which evaluates to the same thing... and you end
476 up with a chain of identical values all hung onto by the CAF ff.
480 = let f' = f Int dEqInt in \ys. ...f'...
482 = let f' = let f' = f Int dEqInt in \ys. ...f'...
486 Solution: when typechecking the RHSs we always have in hand the
487 *monomorphic* Ids for each binding. So we just need to make sure that
488 if (Method f a d) shows up in the constraints emerging from (...f...)
489 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
490 to the "givens" when simplifying constraints. That's what the "lies_avail"
494 %************************************************************************
496 \subsection{getTyVarsToGen}
498 %************************************************************************
500 @getTyVarsToGen@ decides what type variables to generalise over.
502 For a "restricted group" -- see the monomorphism restriction
503 for a definition -- we bind no dictionaries, and
504 remove from tyvars_to_gen any constrained type variables
506 *Don't* simplify dicts at this point, because we aren't going
507 to generalise over these dicts. By the time we do simplify them
508 we may well know more. For example (this actually came up)
510 f x = array ... xs where xs = [1,2,3,4,5]
511 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
512 stuff. If we simplify only at the f-binding (not the xs-binding)
513 we'll know that the literals are all Ints, and we can just produce
516 Find all the type variables involved in overloading, the
517 "constrained_tyvars". These are the ones we *aren't* going to
518 generalise. We must be careful about doing this:
520 (a) If we fail to generalise a tyvar which is not actually
521 constrained, then it will never, ever get bound, and lands
522 up printed out in interface files! Notorious example:
523 instance Eq a => Eq (Foo a b) where ..
524 Here, b is not constrained, even though it looks as if it is.
525 Another, more common, example is when there's a Method inst in
526 the LIE, whose type might very well involve non-overloaded
529 (b) On the other hand, we mustn't generalise tyvars which are constrained,
530 because we are going to pass on out the unmodified LIE, with those
531 tyvars in it. They won't be in scope if we've generalised them.
533 So we are careful, and do a complete simplification just to find the
534 constrained tyvars. We don't use any of the results, except to
535 find which tyvars are constrained.
538 getTyVarsToGen is_unrestricted mono_id_tys lie
539 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
540 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
542 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
543 fds = getAllFunDepsOfLIE lie
547 -- We need to augment the type variables that appear explicitly in
548 -- the type by those that are determined by the functional dependencies.
549 -- e.g. suppose our type is C a b => a -> a
550 -- with the fun-dep a->b
551 -- Then we should generalise over b too; otherwise it will be
552 -- reported as ambiguous.
553 zonkFunDeps fds `thenNF_Tc` \ fds' ->
554 let tvFundep = tyVarFunDep fds'
555 extended_tyvars = oclose tvFundep body_tyvars
557 returnNF_Tc (emptyVarSet, extended_tyvars)
559 -- This recover and discard-errs is to avoid duplicate error
560 -- messages; this, after all, is an "extra" call to tcSimplify
561 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
564 tcSimplify (text "getTVG") body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
566 -- ASSERT: dicts_sig is already zonked!
567 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
568 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
570 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
575 isUnRestrictedGroup :: [Name] -- Signatures given for these
579 is_elem v vs = isIn "isUnResMono" v vs
581 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
582 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
583 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
585 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
586 isUnRestrictedGroup sigs mb2
587 isUnRestrictedGroup sigs EmptyMonoBinds = True
589 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
590 isUnRestrictedMatch other = True -- Some args or a signature
594 %************************************************************************
596 \subsection{tcMonoBind}
598 %************************************************************************
600 @tcMonoBinds@ deals with a single @MonoBind@.
601 The signatures have been dealt with already.
604 tcMonoBinds :: RenamedMonoBinds
607 -> TcM s (TcMonoBinds,
609 [Name], -- Bound names
610 [TcId]) -- Corresponding monomorphic bound things
612 tcMonoBinds mbinds tc_ty_sigs is_rec
613 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
615 tv_list = bagToList tvs
616 id_list = bagToList ids
617 (names, mono_ids) = unzip id_list
619 -- This last defn is the key one:
620 -- extend the val envt with bindings for the
621 -- things bound in this group, overriding the monomorphic
622 -- ids with the polymorphic ones from the pattern
623 extra_val_env = case is_rec of
624 Recursive -> map mk_bind id_list
627 -- Don't know how to deal with pattern-bound existentials yet
628 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
629 (existentialExplode mbinds) `thenTc_`
631 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
632 -- extend the envt with bindings for all the bound ids;
633 -- and *then* override with the polymorphic Ids from the signatures
634 -- That is the whole point of the "complete_it" stuff.
636 -- There's a further wrinkle: we have to delay extending the environment
637 -- until after we've dealt with any pattern-bound signature type variables
638 -- Consider f (x::a) = ...f...
639 -- We're going to check that a isn't unified with anything in the envt,
640 -- so f itself had better not be! So we pass the envt binding f into
641 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
642 -- dealing with the signature tyvars
644 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
646 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
649 -- This function is used when dealing with a LHS binder; we make a monomorphic
650 -- version of the Id. We check for type signatures
651 tc_pat_bndr name pat_ty
652 = case maybeSig tc_ty_sigs name of
654 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
656 Just (TySigInfo _ _ _ _ _ mono_id _ _)
657 -> tcAddSrcLoc (getSrcLoc name) $
658 unifyTauTy (idType mono_id) pat_ty `thenTc_`
661 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
662 Nothing -> (name, mono_id)
663 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
665 tc_mb_pats EmptyMonoBinds
666 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
668 tc_mb_pats (AndMonoBinds mb1 mb2)
669 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
670 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
672 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
673 complete_it2 xve `thenTc` \ (mb2', lie2) ->
674 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
676 returnTc (complete_it,
677 lie_req1 `plusLIE` lie_req2,
678 tvs1 `unionBags` tvs2,
679 ids1 `unionBags` ids2,
680 lie_avail1 `plusLIE` lie_avail2)
682 tc_mb_pats (FunMonoBind name inf matches locn)
683 = new_lhs_ty `thenNF_Tc` \ bndr_ty ->
684 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
686 complete_it xve = tcAddSrcLoc locn $
687 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
688 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
690 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
692 tc_mb_pats bind@(PatMonoBind pat grhss locn)
694 new_lhs_ty `thenNF_Tc` \ pat_ty ->
696 -- Now typecheck the pattern
697 -- We don't support binding fresh type variables in the
698 -- pattern of a pattern binding. For example, this is illegal:
700 -- whereas this is ok
701 -- (x::Int, y::Bool) = e
703 -- We don't check explicitly for this problem. Instead, we simply
704 -- type check the pattern with tcPat. If the pattern mentions any
705 -- fresh tyvars we simply get an out-of-scope type variable error
706 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
708 complete_it xve = tcAddSrcLoc locn $
709 tcAddErrCtxt (patMonoBindsCtxt bind) $
710 tcExtendLocalValEnv xve $
711 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
712 returnTc (PatMonoBind pat' grhss' locn, lie)
714 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
716 -- Figure out the appropriate kind for the pattern,
717 -- and generate a suitable type variable
718 new_lhs_ty = case is_rec of
719 Recursive -> newTyVarTy boxedTypeKind -- Recursive, so no unboxed types
720 NonRecursive -> newTyVarTy_OpenKind -- Non-recursive, so we permit unboxed types
723 %************************************************************************
725 \subsection{Signatures}
727 %************************************************************************
729 @checkSigMatch@ does the next step in checking signature matching.
730 The tau-type part has already been unified. What we do here is to
731 check that this unification has not over-constrained the (polymorphic)
732 type variables of the original signature type.
734 The error message here is somewhat unsatisfactory, but it'll do for
738 checkSigMatch :: TopLevelFlag -> [Name] -> [TcId] -> [TcSigInfo] -> TcM s (Maybe (TcThetaType, LIE))
739 checkSigMatch top_lvl binder_names mono_ids sigs
741 = -- First unify the main_id with IO t, for any old t
742 tcSetErrCtxt mainTyCheckCtxt (
743 tcLookupTyConByKey ioTyConKey `thenTc` \ ioTyCon ->
744 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
745 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
746 (idType main_mono_id)
749 -- Now check the signatures
750 -- Must do this after the unification with IO t,
751 -- in case of a silly signature like
752 -- main :: forall a. a
753 -- The unification to IO t will bind the type variable 'a',
754 -- which is just waht check_one_sig looks for
755 mapTc check_one_sig sigs `thenTc_`
756 mapTc check_main_ctxt sigs `thenTc_`
758 returnTc (Just ([], emptyLIE))
761 = mapTc check_one_sig sigs `thenTc_`
762 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
763 returnTc (Just (theta1, sig_lie))
766 = returnTc Nothing -- No constraints from type sigs
769 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
771 sig1_dict_tys = mk_dict_tys theta1
772 n_sig1_dict_tys = length sig1_dict_tys
773 sig_lie = mkLIE (concat [insts | TySigInfo _ _ _ _ _ _ insts _ <- sigs])
775 maybe_main = find_main top_lvl binder_names mono_ids
776 main_bound_here = maybeToBool maybe_main
777 Just main_mono_id = maybe_main
779 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
780 -- Doesn't affect substitution
781 check_one_sig (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
782 = tcAddSrcLoc src_loc $
783 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
784 checkSigTyVars sig_tyvars (idFreeTyVars id)
787 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
788 -- The type signatures on a mutually-recursive group of definitions
789 -- must all have the same context (or none).
791 -- We unify them because, with polymorphic recursion, their types
792 -- might not otherwise be related. This is a rather subtle issue.
794 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
795 = tcAddSrcLoc src_loc $
796 tcAddErrCtxt (sigContextsCtxt id1 id) $
797 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
798 sigContextsErr `thenTc_`
799 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
801 this_sig_dict_tys = mk_dict_tys theta
803 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
804 -- the signature contexts are empty (what a bore)
805 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
806 = tcAddSrcLoc src_loc $
807 checkTc (null theta) (mainContextsErr id)
809 mk_dict_tys theta = map mkPredTy theta
811 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
813 -- Search for Main.main in the binder_names, return corresponding mono_id
814 find_main NotTopLevel binder_names mono_ids = Nothing
815 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
817 go (n:ns) (m:ms) | n `hasKey` mainKey = Just m
818 | otherwise = go ns ms
822 %************************************************************************
824 \subsection{SPECIALIZE pragmas}
826 %************************************************************************
828 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
829 pragmas. It is convenient for them to appear in the @[RenamedSig]@
830 part of a binding because then the same machinery can be used for
831 moving them into place as is done for type signatures.
836 f :: Ord a => [a] -> b -> b
837 {-# SPECIALIZE f :: [Int] -> b -> b #-}
840 For this we generate:
842 f* = /\ b -> let d1 = ...
846 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
847 retain a right-hand-side that the simplifier will otherwise discard as
848 dead code... the simplifier has a flag that tells it not to discard
849 SpecPragmaId bindings.
851 In this case the f* retains a call-instance of the overloaded
852 function, f, (including appropriate dictionaries) so that the
853 specialiser will subsequently discover that there's a call of @f@ at
854 Int, and will create a specialisation for @f@. After that, the
855 binding for @f*@ can be discarded.
857 We used to have a form
858 {-# SPECIALISE f :: <type> = g #-}
859 which promised that g implemented f at <type>, but we do that with
861 {-# SPECIALISE (f::<type) = g #-}
864 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
865 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
866 = -- SPECIALISE f :: forall b. theta => tau = g
867 tcAddSrcLoc src_loc $
868 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
870 -- Get and instantiate its alleged specialised type
871 tcHsSigType poly_ty `thenTc` \ sig_ty ->
873 -- Check that f has a more general type, and build a RHS for
874 -- the spec-pragma-id at the same time
875 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
877 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
878 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
880 -- Just specialise "f" by building a SpecPragmaId binding
881 -- It is the thing that makes sure we don't prematurely
882 -- dead-code-eliminate the binding we are really interested in.
883 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
885 -- Do the rest and combine
886 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
887 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
888 lie_rest `plusLIE` spec_lie1)
890 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
891 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
895 %************************************************************************
897 \subsection[TcBinds-errors]{Error contexts and messages}
899 %************************************************************************
903 patMonoBindsCtxt bind
904 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
906 -----------------------------------------------
908 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
909 nest 4 (ppr v <+> dcolon <+> ppr ty)]
911 -----------------------------------------------
912 notAsPolyAsSigErr sig_tau mono_tyvars
913 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
914 4 (vcat [text "Can't for-all the type variable(s)" <+>
915 pprQuotedList mono_tyvars,
916 text "in the type" <+> quotes (ppr sig_tau)
919 -----------------------------------------------
920 badMatchErr sig_ty inferred_ty
921 = hang (ptext SLIT("Type signature doesn't match inferred type"))
922 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
923 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
926 -----------------------------------------------
928 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
931 -----------------------------------------------
933 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
935 -----------------------------------------------
937 = ptext SLIT("Mismatched contexts")
939 sigContextsCtxt s1 s2
940 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
941 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
942 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
945 | id `hasKey` mainKey = ptext SLIT("Main.main cannot be overloaded")
947 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
948 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
951 = hsep [ptext SLIT("When checking that"), quotes (ptext SLIT("main")),
952 ptext SLIT("has the required type")]
954 -----------------------------------------------
955 unliftedBindErr flavour mbind
956 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
959 existentialExplode mbinds
960 = hang (vcat [text "My brain just exploded.",
961 text "I can't handle pattern bindings for existentially-quantified constructors.",
962 text "In the binding group"])