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, getFunDepsOfLIE,
26 import TcEnv ( tcExtendLocalValEnv,
27 newSpecPragmaId, newLocalId,
29 tcGetGlobalTyVars, tcExtendGlobalTyVars
31 import TcSimplify ( tcSimplify, tcSimplifyAndCheck, tcSimplifyToDicts )
32 import TcImprove ( tcImprove )
33 import TcMonoType ( tcHsType, 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 )
48 import Var ( idType, idName )
49 import IdInfo ( IdInfo, vanillaIdInfo, setInlinePragInfo, InlinePragInfo(..) )
50 import Name ( Name, getName, getOccName, getSrcLoc )
52 import Type ( mkTyVarTy, tyVarsOfTypes, mkTyConApp,
53 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar,
54 mkDictTy, 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 if null real_tyvars_to_gen_list then
294 -- No polymorphism, so no need to simplify context
295 returnTc (lie_req, EmptyMonoBinds, [])
297 case maybe_sig_theta of
299 -- No signatures, so just simplify the lie
300 -- NB: no signatures => no polymorphic recursion, so no
301 -- need to use lie_avail (which will be empty anyway)
302 tcSimplify (text "tcBinds1" <+> ppr binder_names)
303 top_lvl real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
304 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
306 Just (sig_theta, lie_avail) ->
307 -- There are signatures, and their context is sig_theta
308 -- Furthermore, lie_avail is an LIE containing the 'method insts'
309 -- for the things bound here
311 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
312 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
313 -- It's important that sig_theta is zonked, because
314 -- dict_id is later used to form the type of the polymorphic thing,
315 -- and forall-types must be zonked so far as their bound variables
319 -- The "givens" is the stuff available. We get that from
320 -- the context of the type signature, BUT ALSO the lie_avail
321 -- so that polymorphic recursion works right (see comments at end of fn)
322 givens = dicts_sig `plusLIE` lie_avail
325 -- Check that the needed dicts can be expressed in
326 -- terms of the signature ones
327 tcAddErrCtxt (bindSigsCtxt tysig_names) $
329 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
330 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
332 returnTc (lie_free, dict_binds, dict_ids)
334 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
336 -- GET THE FINAL MONO_ID_TYS
337 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
340 -- CHECK FOR BOGUS UNPOINTED BINDINGS
341 (if any isUnLiftedType zonked_mono_id_types then
342 -- Unlifted bindings must be non-recursive,
343 -- not top level, and non-polymorphic
344 checkTc (isNotTopLevel top_lvl)
345 (unliftedBindErr "Top-level" mbind) `thenTc_`
346 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
347 (unliftedBindErr "Recursive" mbind) `thenTc_`
348 checkTc (null real_tyvars_to_gen_list)
349 (unliftedBindErr "Polymorphic" mbind)
354 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
355 -- The instCantBeGeneralised stuff in tcSimplify should have
356 -- already raised an error if we're trying to generalise an
357 -- unboxed tyvar (NB: unboxed tyvars are always introduced
358 -- along with a class constraint) and it's better done there
359 -- because we have more precise origin information.
360 -- That's why we just use an ASSERT here.
363 -- BUILD THE POLYMORPHIC RESULT IDs
364 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
366 exports = zipWith mk_export binder_names zonked_mono_ids
367 dict_tys = map idType dicts_bound
369 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
370 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
371 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
372 -- "INLINE n foo" means inline foo, but not until at least phase n
373 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
374 -- then only if it is small enough etc.
375 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
376 -- See comments in CoreUnfold.blackListed for the Authorised Version
378 mk_export binder_name zonked_mono_id
380 attachNoInlinePrag no_inlines poly_id,
384 case maybeSig tc_ty_sigs binder_name of
385 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
386 (sig_tyvars, sig_poly_id)
387 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
389 new_poly_id = mkVanillaId binder_name poly_ty
390 poly_ty = mkForAllTys real_tyvars_to_gen_list
392 $ idType (zonked_mono_id)
393 -- It's important to build a fully-zonked poly_ty, because
394 -- we'll slurp out its free type variables when extending the
395 -- local environment (tcExtendLocalValEnv); if it's not zonked
396 -- it appears to have free tyvars that aren't actually free
399 pat_binders :: [Name]
400 pat_binders = map fst $ bagToList $ collectMonoBinders $
401 (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 AbsBinds real_tyvars_to_gen_list
415 (dict_binds `andMonoBinds` mbind'),
417 [poly_id | (_, poly_id, _) <- exports]
420 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
421 is_unrestricted = isUnRestrictedGroup tysig_names mbind
423 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
424 justPatBindings (AndMonoBinds b1 b2) binds =
425 justPatBindings b1 (justPatBindings b2 binds)
426 justPatBindings other_bind binds = binds
428 attachNoInlinePrag no_inlines bndr
429 = case lookupFM no_inlines (idName bndr) of
430 Just prag -> bndr `setInlinePragma` prag
434 Polymorphic recursion
435 ~~~~~~~~~~~~~~~~~~~~~
436 The game plan for polymorphic recursion in the code above is
438 * Bind any variable for which we have a type signature
439 to an Id with a polymorphic type. Then when type-checking
440 the RHSs we'll make a full polymorphic call.
442 This fine, but if you aren't a bit careful you end up with a horrendous
443 amount of partial application and (worse) a huge space leak. For example:
445 f :: Eq a => [a] -> [a]
448 If we don't take care, after typechecking we get
450 f = /\a -> \d::Eq a -> let f' = f a d
454 Notice the the stupid construction of (f a d), which is of course
455 identical to the function we're executing. In this case, the
456 polymorphic recursion isn't being used (but that's a very common case).
459 f = /\a -> \d::Eq a -> letrec
460 fm = \ys:[a] -> ...fm...
464 This can lead to a massive space leak, from the following top-level defn
470 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
471 f' is another thunk which evaluates to the same thing... and you end
472 up with a chain of identical values all hung onto by the CAF ff.
476 = let f' = f Int dEqInt in \ys. ...f'...
478 = let f' = let f' = f Int dEqInt in \ys. ...f'...
482 Solution: when typechecking the RHSs we always have in hand the
483 *monomorphic* Ids for each binding. So we just need to make sure that
484 if (Method f a d) shows up in the constraints emerging from (...f...)
485 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
486 to the "givens" when simplifying constraints. That's what the "lies_avail"
490 %************************************************************************
492 \subsection{getTyVarsToGen}
494 %************************************************************************
496 @getTyVarsToGen@ decides what type variables to generalise over.
498 For a "restricted group" -- see the monomorphism restriction
499 for a definition -- we bind no dictionaries, and
500 remove from tyvars_to_gen any constrained type variables
502 *Don't* simplify dicts at this point, because we aren't going
503 to generalise over these dicts. By the time we do simplify them
504 we may well know more. For example (this actually came up)
506 f x = array ... xs where xs = [1,2,3,4,5]
507 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
508 stuff. If we simplify only at the f-binding (not the xs-binding)
509 we'll know that the literals are all Ints, and we can just produce
512 Find all the type variables involved in overloading, the
513 "constrained_tyvars". These are the ones we *aren't* going to
514 generalise. We must be careful about doing this:
516 (a) If we fail to generalise a tyvar which is not actually
517 constrained, then it will never, ever get bound, and lands
518 up printed out in interface files! Notorious example:
519 instance Eq a => Eq (Foo a b) where ..
520 Here, b is not constrained, even though it looks as if it is.
521 Another, more common, example is when there's a Method inst in
522 the LIE, whose type might very well involve non-overloaded
525 (b) On the other hand, we mustn't generalise tyvars which are constrained,
526 because we are going to pass on out the unmodified LIE, with those
527 tyvars in it. They won't be in scope if we've generalised them.
529 So we are careful, and do a complete simplification just to find the
530 constrained tyvars. We don't use any of the results, except to
531 find which tyvars are constrained.
534 getTyVarsToGen is_unrestricted mono_id_tys lie
535 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
536 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
538 body_tyvars = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
542 let fds = concatMap snd (getFunDepsOfLIE lie) in
543 zonkFunDeps fds `thenNF_Tc` \ fds' ->
544 let tvFundep = tyVarFunDep fds'
545 extended_tyvars = oclose tvFundep body_tyvars in
546 -- pprTrace "gTVTG" (ppr (lie, body_tyvars, extended_tyvars)) $
547 returnNF_Tc (emptyVarSet, extended_tyvars)
549 -- This recover and discard-errs is to avoid duplicate error
550 -- messages; this, after all, is an "extra" call to tcSimplify
551 recoverNF_Tc (returnNF_Tc (emptyVarSet, body_tyvars)) $
554 tcSimplify (text "getTVG") NotTopLevel body_tyvars lie `thenTc` \ (_, _, constrained_dicts) ->
556 -- ASSERT: dicts_sig is already zonked!
557 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
558 reduced_tyvars_to_gen = body_tyvars `minusVarSet` constrained_tyvars
560 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
565 isUnRestrictedGroup :: [Name] -- Signatures given for these
569 is_elem v vs = isIn "isUnResMono" v vs
571 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
572 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
573 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
574 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
575 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
576 isUnRestrictedGroup sigs mb2
577 isUnRestrictedGroup sigs EmptyMonoBinds = True
581 %************************************************************************
583 \subsection{tcMonoBind}
585 %************************************************************************
587 @tcMonoBinds@ deals with a single @MonoBind@.
588 The signatures have been dealt with already.
591 tcMonoBinds :: RenamedMonoBinds
594 -> TcM s (TcMonoBinds,
596 [Name], -- Bound names
597 [TcId]) -- Corresponding monomorphic bound things
599 tcMonoBinds mbinds tc_ty_sigs is_rec
600 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
602 tv_list = bagToList tvs
603 id_list = bagToList ids
604 (names, mono_ids) = unzip id_list
606 -- This last defn is the key one:
607 -- extend the val envt with bindings for the
608 -- things bound in this group, overriding the monomorphic
609 -- ids with the polymorphic ones from the pattern
610 extra_val_env = case is_rec of
611 Recursive -> map mk_bind id_list
614 -- Don't know how to deal with pattern-bound existentials yet
615 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
616 (existentialExplode mbinds) `thenTc_`
618 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
619 -- extend the envt with bindings for all the bound ids;
620 -- and *then* override with the polymorphic Ids from the signatures
621 -- That is the whole point of the "complete_it" stuff.
623 -- There's a further wrinkle: we have to delay extending the environment
624 -- until after we've dealt with any pattern-bound signature type variables
625 -- Consider f (x::a) = ...f...
626 -- We're going to check that a isn't unified with anything in the envt,
627 -- so f itself had better not be! So we pass the envt binding f into
628 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
629 -- dealing with the signature tyvars
631 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
633 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
636 -- This function is used when dealing with a LHS binder; we make a monomorphic
637 -- version of the Id. We check for type signatures
638 tc_pat_bndr name pat_ty
639 = case maybeSig tc_ty_sigs name of
641 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
643 Just (TySigInfo _ _ _ _ _ mono_id _ _)
644 -> tcAddSrcLoc (getSrcLoc name) $
645 unifyTauTy (idType mono_id) pat_ty `thenTc_`
648 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
649 Nothing -> (name, mono_id)
650 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
652 tc_mb_pats EmptyMonoBinds
653 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
655 tc_mb_pats (AndMonoBinds mb1 mb2)
656 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
657 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
659 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
660 complete_it2 xve `thenTc` \ (mb2', lie2) ->
661 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
663 returnTc (complete_it,
664 lie_req1 `plusLIE` lie_req2,
665 tvs1 `unionBags` tvs2,
666 ids1 `unionBags` ids2,
667 lie_avail1 `plusLIE` lie_avail2)
669 tc_mb_pats (FunMonoBind name inf matches locn)
670 = newTyVarTy boxedTypeKind `thenNF_Tc` \ bndr_ty ->
671 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
673 complete_it xve = tcAddSrcLoc locn $
674 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
675 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
677 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
679 tc_mb_pats bind@(PatMonoBind pat grhss locn)
682 -- Figure out the appropriate kind for the pattern,
683 -- and generate a suitable type variable
685 Recursive -> newTyVarTy boxedTypeKind -- Recursive, so no unboxed types
686 NonRecursive -> newTyVarTy_OpenKind -- Non-recursive, so we permit unboxed types
687 ) `thenNF_Tc` \ pat_ty ->
689 -- Now typecheck the pattern
690 -- We don't support binding fresh type variables in the
691 -- pattern of a pattern binding. For example, this is illegal:
693 -- whereas this is ok
694 -- (x::Int, y::Bool) = e
696 -- We don't check explicitly for this problem. Instead, we simply
697 -- type check the pattern with tcPat. If the pattern mentions any
698 -- fresh tyvars we simply get an out-of-scope type variable error
699 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
701 complete_it xve = tcAddSrcLoc locn $
702 tcAddErrCtxt (patMonoBindsCtxt bind) $
703 tcExtendLocalValEnv xve $
704 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
705 returnTc (PatMonoBind pat' grhss' locn, lie)
707 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
710 %************************************************************************
712 \subsection{Signatures}
714 %************************************************************************
716 @checkSigMatch@ does the next step in checking signature matching.
717 The tau-type part has already been unified. What we do here is to
718 check that this unification has not over-constrained the (polymorphic)
719 type variables of the original signature type.
721 The error message here is somewhat unsatisfactory, but it'll do for
725 checkSigMatch top_lvl binder_names mono_ids sigs
727 = -- First unify the main_id with IO t, for any old t
728 tcSetErrCtxt mainTyCheckCtxt (
729 tcLookupTyCon ioTyCon_NAME `thenTc` \ ioTyCon ->
730 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
731 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
732 (idType main_mono_id)
735 -- Now check the signatures
736 -- Must do this after the unification with IO t,
737 -- in case of a silly signature like
738 -- main :: forall a. a
739 -- The unification to IO t will bind the type variable 'a',
740 -- which is just waht check_one_sig looks for
741 mapTc check_one_sig sigs `thenTc_`
742 mapTc check_main_ctxt sigs `thenTc_`
744 returnTc (Just ([], emptyLIE))
747 = mapTc check_one_sig sigs `thenTc_`
748 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
749 returnTc (Just (theta1, sig_lie))
752 = returnTc Nothing -- No constraints from type sigs
755 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
757 sig1_dict_tys = mk_dict_tys theta1
758 n_sig1_dict_tys = length sig1_dict_tys
759 sig_lie = mkLIE [inst | TySigInfo _ _ _ _ _ _ inst _ <- sigs]
761 maybe_main = find_main top_lvl binder_names mono_ids
762 main_bound_here = maybeToBool maybe_main
763 Just main_mono_id = maybe_main
765 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
766 -- Doesn't affect substitution
767 check_one_sig (TySigInfo _ id sig_tyvars _ sig_tau _ _ src_loc)
768 = tcAddSrcLoc src_loc $
769 tcAddErrCtxtM (sigCtxt (sig_msg id) (idType id)) $
770 checkSigTyVars sig_tyvars
773 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
774 -- The type signatures on a mutually-recursive group of definitions
775 -- must all have the same context (or none).
777 -- We unify them because, with polymorphic recursion, their types
778 -- might not otherwise be related. This is a rather subtle issue.
780 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
781 = tcAddSrcLoc src_loc $
782 tcAddErrCtxt (sigContextsCtxt id1 id) $
783 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
784 sigContextsErr `thenTc_`
785 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
787 this_sig_dict_tys = mk_dict_tys theta
789 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
790 -- the signature contexts are empty (what a bore)
791 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
792 = tcAddSrcLoc src_loc $
793 checkTc (null theta) (mainContextsErr id)
795 mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
797 sig_msg id tidy_ty = sep [ptext SLIT("When checking the type signature"),
798 nest 4 (ppr id <+> dcolon <+> ppr tidy_ty)]
800 -- Search for Main.main in the binder_names, return corresponding mono_id
801 find_main NotTopLevel binder_names mono_ids = Nothing
802 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
804 go (n:ns) (m:ms) | n == main_NAME = Just m
805 | otherwise = go ns ms
809 %************************************************************************
811 \subsection{SPECIALIZE pragmas}
813 %************************************************************************
815 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
816 pragmas. It is convenient for them to appear in the @[RenamedSig]@
817 part of a binding because then the same machinery can be used for
818 moving them into place as is done for type signatures.
823 f :: Ord a => [a] -> b -> b
824 {-# SPECIALIZE f :: [Int] -> b -> b #-}
827 For this we generate:
829 f* = /\ b -> let d1 = ...
833 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
834 retain a right-hand-side that the simplifier will otherwise discard as
835 dead code... the simplifier has a flag that tells it not to discard
836 SpecPragmaId bindings.
838 In this case the f* retains a call-instance of the overloaded
839 function, f, (including appropriate dictionaries) so that the
840 specialiser will subsequently discover that there's a call of @f@ at
841 Int, and will create a specialisation for @f@. After that, the
842 binding for @f*@ can be discarded.
844 We used to have a form
845 {-# SPECIALISE f :: <type> = g #-}
846 which promised that g implemented f at <type>, but we do that with
848 {-# SPECIALISE (f::<type) = g #-}
851 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
852 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
853 = -- SPECIALISE f :: forall b. theta => tau = g
854 tcAddSrcLoc src_loc $
855 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
857 -- Get and instantiate its alleged specialised type
858 tcHsType poly_ty `thenTc` \ sig_ty ->
860 -- Check that f has a more general type, and build a RHS for
861 -- the spec-pragma-id at the same time
862 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
864 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
865 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
867 -- Just specialise "f" by building a SpecPragmaId binding
868 -- It is the thing that makes sure we don't prematurely
869 -- dead-code-eliminate the binding we are really interested in.
870 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
872 -- Do the rest and combine
873 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
874 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
875 lie_rest `plusLIE` spec_lie1)
877 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
878 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
882 %************************************************************************
884 \subsection[TcBinds-errors]{Error contexts and messages}
886 %************************************************************************
890 patMonoBindsCtxt bind
891 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
893 -----------------------------------------------
895 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
896 nest 4 (ppr v <+> dcolon <+> ppr ty)]
898 -----------------------------------------------
899 notAsPolyAsSigErr sig_tau mono_tyvars
900 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
901 4 (vcat [text "Can't for-all the type variable(s)" <+>
902 pprQuotedList mono_tyvars,
903 text "in the type" <+> quotes (ppr sig_tau)
906 -----------------------------------------------
907 badMatchErr sig_ty inferred_ty
908 = hang (ptext SLIT("Type signature doesn't match inferred type"))
909 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
910 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
913 -----------------------------------------------
915 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
918 -----------------------------------------------
920 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
922 -----------------------------------------------
924 = ptext SLIT("Mismatched contexts")
926 sigContextsCtxt s1 s2
927 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
928 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
929 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
932 | getName id == main_NAME = ptext SLIT("Main.main cannot be overloaded")
934 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
935 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
938 = hsep [ptext SLIT("When checking that"), quotes (ppr main_NAME),
939 ptext SLIT("has the required type")]
941 -----------------------------------------------
942 unliftedBindErr flavour mbind
943 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
946 existentialExplode mbinds
947 = hang (vcat [text "My brain just exploded.",
948 text "I can't handle pattern bindings for existentially-quantified constructors.",
949 text "In the binding group"])