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(..), StmtCtxt(..),
16 Match(..), collectMonoBinders, andMonoBinds
18 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
19 import TcHsSyn ( TcMonoBinds, TcId, zonkId, mkHsLet )
22 import Inst ( LIE, emptyLIE, mkLIE, plusLIE, InstOrigin(..),
23 newDicts, tyVarsOfInst, instToId,
24 getAllFunDepsOfLIE, getIPsOfLIE, zonkFunDeps
26 import TcEnv ( tcExtendLocalValEnv,
27 newSpecPragmaId, newLocalId,
29 tcGetGlobalTyVars, tcExtendGlobalTyVars
31 import TcSimplify ( tcSimplify, tcSimplifyAndCheck, tcSimplifyToDicts )
32 import TcImprove ( tcImprove )
33 import TcMonoType ( tcHsSigType, checkSigTyVars,
34 TcSigInfo(..), tcTySig, maybeSig, sigCtxt
36 import TcPat ( tcPat )
37 import TcSimplify ( bindInstsOfLocalFuns )
38 import TcType ( TcThetaType, newTyVarTy, newTyVar,
39 zonkTcTypes, zonkTcThetaType, zonkTcTyVarToTyVar
41 import TcUnify ( unifyTauTy, unifyTauTyLists )
43 import Id ( mkVanillaId, setInlinePragma, idFreeTyVars )
44 import Var ( idType, idName )
45 import IdInfo ( InlinePragInfo(..) )
46 import Name ( Name, getOccName, getSrcLoc )
48 import Type ( mkTyVarTy, tyVarsOfTypes, mkTyConApp,
49 mkForAllTys, mkFunTys,
50 mkPredTy, mkForAllTy, isUnLiftedType,
51 isUnboxedType, unboxedTypeKind, boxedTypeKind, openTypeKind
53 import FunDeps ( tyVarFunDep, oclose )
54 import Var ( tyVarKind )
58 import Maybes ( maybeToBool )
59 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNotTopLevel )
60 import FiniteMap ( listToFM, lookupFM )
61 import PrelNames ( ioTyConKey, mainKey, hasKey )
66 %************************************************************************
68 \subsection{Type-checking bindings}
70 %************************************************************************
72 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
73 it needs to know something about the {\em usage} of the things bound,
74 so that it can create specialisations of them. So @tcBindsAndThen@
75 takes a function which, given an extended environment, E, typechecks
76 the scope of the bindings returning a typechecked thing and (most
77 important) an LIE. It is this LIE which is then used as the basis for
78 specialising the things bound.
80 @tcBindsAndThen@ also takes a "combiner" which glues together the
81 bindings and the "thing" to make a new "thing".
83 The real work is done by @tcBindWithSigsAndThen@.
85 Recursive and non-recursive binds are handled in essentially the same
86 way: because of uniques there are no scoping issues left. The only
87 difference is that non-recursive bindings can bind primitive values.
89 Even for non-recursive binding groups we add typings for each binder
90 to the LVE for the following reason. When each individual binding is
91 checked the type of its LHS is unified with that of its RHS; and
92 type-checking the LHS of course requires that the binder is in scope.
94 At the top-level the LIE is sure to contain nothing but constant
95 dictionaries, which we resolve at the module level.
98 tcTopBindsAndThen, tcBindsAndThen
99 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
104 tcTopBindsAndThen = tc_binds_and_then TopLevel
105 tcBindsAndThen = tc_binds_and_then NotTopLevel
107 tc_binds_and_then top_lvl combiner EmptyBinds do_next
109 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
112 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
113 = tc_binds_and_then top_lvl combiner b1 $
114 tc_binds_and_then top_lvl combiner b2 $
117 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
118 = -- TYPECHECK THE SIGNATURES
119 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
121 tcBindWithSigs top_lvl bind tc_ty_sigs
122 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
124 -- Extend the environment to bind the new polymorphic Ids
125 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
127 -- Build bindings and IdInfos corresponding to user pragmas
128 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
130 -- Now do whatever happens next, in the augmented envt
131 do_next `thenTc` \ (thing, thing_lie) ->
133 -- Create specialisations of functions bound here
134 -- We want to keep non-recursive things non-recursive
135 -- so that we desugar unboxed bindings correctly
136 case (top_lvl, is_rec) of
138 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
139 -- All the top level things are rec'd together anyway, so it's fine to
140 -- leave them to the tcSimplifyTop, and quite a bit faster too
142 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
143 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
145 (NotTopLevel, NonRecursive)
146 -> bindInstsOfLocalFuns
147 (thing_lie `plusLIE` prag_lie)
148 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
151 combiner NonRecursive poly_binds $
152 combiner NonRecursive prag_binds $
153 combiner Recursive lie_binds $
154 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
155 -- aren't guaranteed in dependency order (though we could change
156 -- that); hence the Recursive marker.
159 thing_lie' `plusLIE` poly_lie
162 (NotTopLevel, Recursive)
163 -> bindInstsOfLocalFuns
164 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
165 poly_ids `thenTc` \ (final_lie, lie_binds) ->
169 poly_binds `andMonoBinds`
170 lie_binds `andMonoBinds`
176 An aside. The original version of @tcBindsAndThen@ which lacks a
177 combiner function, appears below. Though it is perfectly well
178 behaved, it cannot be typed by Haskell, because the recursive call is
179 at a different type to the definition itself. There aren't too many
180 examples of this, which is why I thought it worth preserving! [SLPJ]
185 % -> TcM (thing, LIE, thing_ty))
186 % -> TcM ((TcHsBinds, thing), LIE, thing_ty)
188 % tcBindsAndThen EmptyBinds do_next
189 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
190 % returnTc ((EmptyBinds, thing), lie, thing_ty)
192 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
193 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
194 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
196 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
198 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
199 % = tcBindAndThen bind sigs do_next
203 %************************************************************************
205 \subsection{tcBindWithSigs}
207 %************************************************************************
209 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
210 so all the clever stuff is in here.
212 * binder_names and mbind must define the same set of Names
214 * The Names in tc_ty_sigs must be a subset of binder_names
216 * The Ids in tc_ty_sigs don't necessarily have to have the same name
217 as the Name in the tc_ty_sig
224 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
226 -> TcM (TcMonoBinds, LIE, [TcId])
228 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
230 -- If typechecking the binds fails, then return with each
231 -- signature-less binder given type (forall a.a), to minimise subsequent
233 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
235 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
236 binder_names = collectMonoBinders mbind
237 poly_ids = map mk_dummy binder_names
238 mk_dummy name = case maybeSig tc_ty_sigs name of
239 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
240 Nothing -> mkVanillaId name forall_a_a -- No signature
242 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
245 -- TYPECHECK THE BINDINGS
246 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
248 -- CHECK THAT THE SIGNATURES MATCH
249 -- (must do this before getTyVarsToGen)
250 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
253 -- Force any unifications dictated by functional dependencies.
254 -- Because unification may happen, it's important that this step
256 -- - computing vars over which to quantify
257 -- - zonking the generalized type vars
258 let lie_avail = case maybe_sig_theta of
261 lie_avail_req = lie_avail `plusLIE` lie_req in
262 tcImprove lie_avail_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_avail_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 = collectMonoBinders (justPatBindings mbind EmptyMonoBinds)
403 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
404 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
405 && isUnboxedType (idType id)))
406 (unboxedPatBindErr id)) zonked_mono_ids
411 -- pprTrace "binding.." (ppr ((dicts_bound, dict_binds), exports, [idType poly_id | (_, poly_id, _) <- exports])) $
412 AbsBinds real_tyvars_to_gen_list
416 (dict_binds `andMonoBinds` mbind'),
418 [poly_id | (_, poly_id, _) <- exports]
421 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
422 is_unrestricted = isUnRestrictedGroup tysig_names mbind
424 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
425 justPatBindings (AndMonoBinds b1 b2) binds =
426 justPatBindings b1 (justPatBindings b2 binds)
427 justPatBindings other_bind binds = binds
429 attachNoInlinePrag no_inlines bndr
430 = case lookupFM no_inlines (idName bndr) of
431 Just prag -> bndr `setInlinePragma` prag
435 Polymorphic recursion
436 ~~~~~~~~~~~~~~~~~~~~~
437 The game plan for polymorphic recursion in the code above is
439 * Bind any variable for which we have a type signature
440 to an Id with a polymorphic type. Then when type-checking
441 the RHSs we'll make a full polymorphic call.
443 This fine, but if you aren't a bit careful you end up with a horrendous
444 amount of partial application and (worse) a huge space leak. For example:
446 f :: Eq a => [a] -> [a]
449 If we don't take care, after typechecking we get
451 f = /\a -> \d::Eq a -> let f' = f a d
455 Notice the the stupid construction of (f a d), which is of course
456 identical to the function we're executing. In this case, the
457 polymorphic recursion isn't being used (but that's a very common case).
460 f = /\a -> \d::Eq a -> letrec
461 fm = \ys:[a] -> ...fm...
465 This can lead to a massive space leak, from the following top-level defn
471 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
472 f' is another thunk which evaluates to the same thing... and you end
473 up with a chain of identical values all hung onto by the CAF ff.
477 = let f' = f Int dEqInt in \ys. ...f'...
479 = let f' = let f' = f Int dEqInt in \ys. ...f'...
483 Solution: when typechecking the RHSs we always have in hand the
484 *monomorphic* Ids for each binding. So we just need to make sure that
485 if (Method f a d) shows up in the constraints emerging from (...f...)
486 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
487 to the "givens" when simplifying constraints. That's what the "lies_avail"
491 %************************************************************************
493 \subsection{getTyVarsToGen}
495 %************************************************************************
497 @getTyVarsToGen@ decides what type variables to generalise over.
499 For a "restricted group" -- see the monomorphism restriction
500 for a definition -- we bind no dictionaries, and
501 remove from tyvars_to_gen any constrained type variables
503 *Don't* simplify dicts at this point, because we aren't going
504 to generalise over these dicts. By the time we do simplify them
505 we may well know more. For example (this actually came up)
507 f x = array ... xs where xs = [1,2,3,4,5]
508 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
509 stuff. If we simplify only at the f-binding (not the xs-binding)
510 we'll know that the literals are all Ints, and we can just produce
513 Find all the type variables involved in overloading, the
514 "constrained_tyvars". These are the ones we *aren't* going to
515 generalise. We must be careful about doing this:
517 (a) If we fail to generalise a tyvar which is not actually
518 constrained, then it will never, ever get bound, and lands
519 up printed out in interface files! Notorious example:
520 instance Eq a => Eq (Foo a b) where ..
521 Here, b is not constrained, even though it looks as if it is.
522 Another, more common, example is when there's a Method inst in
523 the LIE, whose type might very well involve non-overloaded
526 (b) On the other hand, we mustn't generalise tyvars which are constrained,
527 because we are going to pass on out the unmodified LIE, with those
528 tyvars in it. They won't be in scope if we've generalised them.
530 So we are careful, and do a complete simplification just to find the
531 constrained tyvars. We don't use any of the results, except to
532 find which tyvars are constrained.
535 getTyVarsToGen is_unrestricted mono_id_tys lie
536 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
537 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
539 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
540 fds = getAllFunDepsOfLIE lie
544 -- We need to augment the type variables that appear explicitly in
545 -- the type by those that are determined by the functional dependencies.
546 -- e.g. suppose our type is C a b => a -> a
547 -- with the fun-dep a->b
548 -- Then we should generalise over b too; otherwise it will be
549 -- reported as ambiguous.
550 zonkFunDeps fds `thenNF_Tc` \ fds' ->
551 let tvFundep = tyVarFunDep fds'
552 extended_tyvars = oclose tvFundep body_tyvars
554 returnNF_Tc (emptyVarSet, extended_tyvars)
556 -- This recover and discard-errs is to avoid duplicate error
557 -- messages; this, after all, is an "extra" call to tcSimplify
558 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
561 tcSimplify (text "getTVG") body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
563 -- ASSERT: dicts_sig is already zonked!
564 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
565 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
567 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
572 isUnRestrictedGroup :: [Name] -- Signatures given for these
576 is_elem v vs = isIn "isUnResMono" v vs
578 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
579 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
580 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
582 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
583 isUnRestrictedGroup sigs mb2
584 isUnRestrictedGroup sigs EmptyMonoBinds = True
586 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
587 isUnRestrictedMatch other = True -- Some args or a signature
591 %************************************************************************
593 \subsection{tcMonoBind}
595 %************************************************************************
597 @tcMonoBinds@ deals with a single @MonoBind@.
598 The signatures have been dealt with already.
601 tcMonoBinds :: RenamedMonoBinds
606 [Name], -- Bound names
607 [TcId]) -- Corresponding monomorphic bound things
609 tcMonoBinds mbinds tc_ty_sigs is_rec
610 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
612 id_list = bagToList ids
613 (names, mono_ids) = unzip id_list
615 -- This last defn is the key one:
616 -- extend the val envt with bindings for the
617 -- things bound in this group, overriding the monomorphic
618 -- ids with the polymorphic ones from the pattern
619 extra_val_env = case is_rec of
620 Recursive -> map mk_bind id_list
623 -- Don't know how to deal with pattern-bound existentials yet
624 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
625 (existentialExplode mbinds) `thenTc_`
627 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
628 -- extend the envt with bindings for all the bound ids;
629 -- and *then* override with the polymorphic Ids from the signatures
630 -- That is the whole point of the "complete_it" stuff.
632 -- There's a further wrinkle: we have to delay extending the environment
633 -- until after we've dealt with any pattern-bound signature type variables
634 -- Consider f (x::a) = ...f...
635 -- We're going to check that a isn't unified with anything in the envt,
636 -- so f itself had better not be! So we pass the envt binding f into
637 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
638 -- dealing with the signature tyvars
640 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
642 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
645 -- This function is used when dealing with a LHS binder; we make a monomorphic
646 -- version of the Id. We check for type signatures
647 tc_pat_bndr name pat_ty
648 = case maybeSig tc_ty_sigs name of
650 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
652 Just (TySigInfo _ _ _ _ _ mono_id _ _)
653 -> tcAddSrcLoc (getSrcLoc name) $
654 unifyTauTy (idType mono_id) pat_ty `thenTc_`
657 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
658 Nothing -> (name, mono_id)
659 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
661 tc_mb_pats EmptyMonoBinds
662 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
664 tc_mb_pats (AndMonoBinds mb1 mb2)
665 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
666 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
668 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
669 complete_it2 xve `thenTc` \ (mb2', lie2) ->
670 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
672 returnTc (complete_it,
673 lie_req1 `plusLIE` lie_req2,
674 tvs1 `unionBags` tvs2,
675 ids1 `unionBags` ids2,
676 lie_avail1 `plusLIE` lie_avail2)
678 tc_mb_pats (FunMonoBind name inf matches locn)
679 = newTyVarTy kind `thenNF_Tc` \ bndr_ty ->
680 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
682 complete_it xve = tcAddSrcLoc locn $
683 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
684 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
686 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
688 tc_mb_pats bind@(PatMonoBind pat grhss locn)
690 newTyVarTy kind `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)
712 -- Figure out the appropriate kind for the pattern,
713 -- and generate a suitable type variable
714 kind = case is_rec of
715 Recursive -> boxedTypeKind -- Recursive, so no unboxed types
716 NonRecursive -> openTypeKind -- Non-recursive, so we permit unboxed types
719 %************************************************************************
721 \subsection{Signatures}
723 %************************************************************************
725 @checkSigMatch@ does the next step in checking signature matching.
726 The tau-type part has already been unified. What we do here is to
727 check that this unification has not over-constrained the (polymorphic)
728 type variables of the original signature type.
730 The error message here is somewhat unsatisfactory, but it'll do for
734 checkSigMatch :: TopLevelFlag -> [Name] -> [TcId] -> [TcSigInfo] -> TcM (Maybe (TcThetaType, LIE))
735 checkSigMatch top_lvl binder_names mono_ids sigs
737 = -- First unify the main_id with IO t, for any old t
738 tcSetErrCtxt mainTyCheckCtxt (
739 tcLookupTyCon ioTyConName `thenTc` \ ioTyCon ->
740 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
741 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
742 (idType main_mono_id)
745 -- Now check the signatures
746 -- Must do this after the unification with IO t,
747 -- in case of a silly signature like
748 -- main :: forall a. a
749 -- The unification to IO t will bind the type variable 'a',
750 -- which is just waht check_one_sig looks for
751 mapTc check_one_sig sigs `thenTc_`
752 mapTc check_main_ctxt sigs `thenTc_`
754 returnTc (Just ([], emptyLIE))
757 = mapTc check_one_sig sigs `thenTc_`
758 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
759 returnTc (Just (theta1, sig_lie))
762 = returnTc Nothing -- No constraints from type sigs
765 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
767 sig1_dict_tys = mk_dict_tys theta1
768 n_sig1_dict_tys = length sig1_dict_tys
769 sig_lie = mkLIE (concat [insts | TySigInfo _ _ _ _ _ _ insts _ <- sigs])
771 maybe_main = find_main top_lvl binder_names mono_ids
772 main_bound_here = maybeToBool maybe_main
773 Just main_mono_id = maybe_main
775 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
776 -- Doesn't affect substitution
777 check_one_sig (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
778 = tcAddSrcLoc src_loc $
779 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
780 checkSigTyVars sig_tyvars (idFreeTyVars id)
783 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
784 -- The type signatures on a mutually-recursive group of definitions
785 -- must all have the same context (or none).
787 -- We unify them because, with polymorphic recursion, their types
788 -- might not otherwise be related. This is a rather subtle issue.
790 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
791 = tcAddSrcLoc src_loc $
792 tcAddErrCtxt (sigContextsCtxt id1 id) $
793 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
794 sigContextsErr `thenTc_`
795 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
797 this_sig_dict_tys = mk_dict_tys theta
799 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
800 -- the signature contexts are empty (what a bore)
801 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
802 = tcAddSrcLoc src_loc $
803 checkTc (null theta) (mainContextsErr id)
805 mk_dict_tys theta = map mkPredTy theta
807 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
809 -- Search for Main.main in the binder_names, return corresponding mono_id
810 find_main NotTopLevel binder_names mono_ids = Nothing
811 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
813 go (n:ns) (m:ms) | n `hasKey` mainKey = Just m
814 | otherwise = go ns ms
818 %************************************************************************
820 \subsection{SPECIALIZE pragmas}
822 %************************************************************************
824 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
825 pragmas. It is convenient for them to appear in the @[RenamedSig]@
826 part of a binding because then the same machinery can be used for
827 moving them into place as is done for type signatures.
832 f :: Ord a => [a] -> b -> b
833 {-# SPECIALIZE f :: [Int] -> b -> b #-}
836 For this we generate:
838 f* = /\ b -> let d1 = ...
842 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
843 retain a right-hand-side that the simplifier will otherwise discard as
844 dead code... the simplifier has a flag that tells it not to discard
845 SpecPragmaId bindings.
847 In this case the f* retains a call-instance of the overloaded
848 function, f, (including appropriate dictionaries) so that the
849 specialiser will subsequently discover that there's a call of @f@ at
850 Int, and will create a specialisation for @f@. After that, the
851 binding for @f*@ can be discarded.
853 We used to have a form
854 {-# SPECIALISE f :: <type> = g #-}
855 which promised that g implemented f at <type>, but we do that with
857 {-# SPECIALISE (f::<type) = g #-}
860 tcSpecSigs :: [RenamedSig] -> TcM (TcMonoBinds, LIE)
861 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
862 = -- SPECIALISE f :: forall b. theta => tau = g
863 tcAddSrcLoc src_loc $
864 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
866 -- Get and instantiate its alleged specialised type
867 tcHsSigType poly_ty `thenTc` \ sig_ty ->
869 -- Check that f has a more general type, and build a RHS for
870 -- the spec-pragma-id at the same time
871 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
873 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
874 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
876 -- Just specialise "f" by building a SpecPragmaId binding
877 -- It is the thing that makes sure we don't prematurely
878 -- dead-code-eliminate the binding we are really interested in.
879 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
881 -- Do the rest and combine
882 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
883 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
884 lie_rest `plusLIE` spec_lie1)
886 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
887 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
891 %************************************************************************
893 \subsection[TcBinds-errors]{Error contexts and messages}
895 %************************************************************************
899 patMonoBindsCtxt bind
900 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
902 -----------------------------------------------
904 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
905 nest 4 (ppr v <+> dcolon <+> ppr ty)]
907 -----------------------------------------------
909 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
912 -----------------------------------------------
914 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
916 -----------------------------------------------
918 = ptext SLIT("Mismatched contexts")
920 sigContextsCtxt s1 s2
921 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
922 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
923 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
926 | id `hasKey` mainKey = ptext SLIT("Main.main cannot be overloaded")
928 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
929 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
932 = hsep [ptext SLIT("When checking that"), quotes (ptext SLIT("main")),
933 ptext SLIT("has the required type")]
935 -----------------------------------------------
936 unliftedBindErr flavour mbind
937 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
940 existentialExplode mbinds
941 = hang (vcat [text "My brain just exploded.",
942 text "I can't handle pattern bindings for existentially-quantified constructors.",
943 text "In the binding group"])