2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBinds,
8 tcSpecSigs, tcBindWithSigs ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcMatches ( tcGRHSs, tcMatchesFun )
13 import {-# SOURCE #-} TcExpr ( tcExpr )
15 import CmdLineOpts ( opt_NoMonomorphismRestriction )
16 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..),
17 Match(..), HsMatchContext(..),
18 collectMonoBinders, andMonoBinds,
19 collectSigTysFromMonoBinds
21 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
22 import TcHsSyn ( TcMonoBinds, TcId, zonkId, mkHsLet )
25 import Inst ( LIE, emptyLIE, mkLIE, plusLIE, InstOrigin(..),
28 import TcEnv ( tcExtendLocalValEnv,
29 newSpecPragmaId, newLocalId
31 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted, tcSimplifyToDicts )
32 import TcMonoType ( tcHsSigType, UserTypeCtxt(..), checkSigTyVars,
33 TcSigInfo(..), tcTySig, maybeSig, sigCtxt, tcAddScopedTyVars
35 import TcPat ( tcPat )
36 import TcSimplify ( bindInstsOfLocalFuns )
37 import TcMType ( newTyVarTy, newTyVar,
39 unifyTauTy, unifyTauTyLists
41 import TcType ( mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
42 mkPredTy, mkForAllTy, isUnLiftedType,
43 unliftedTypeKind, liftedTypeKind, openTypeKind, eqKind
46 import CoreFVs ( idFreeTyVars )
47 import Id ( mkLocalId, setInlinePragma )
48 import Var ( idType, idName )
49 import Name ( Name, getOccName, getSrcLoc )
51 import Var ( tyVarKind )
54 import Util ( isIn, equalLength )
55 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isNotTopLevel,
57 import FiniteMap ( listToFM, lookupFM )
62 %************************************************************************
64 \subsection{Type-checking bindings}
66 %************************************************************************
68 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
69 it needs to know something about the {\em usage} of the things bound,
70 so that it can create specialisations of them. So @tcBindsAndThen@
71 takes a function which, given an extended environment, E, typechecks
72 the scope of the bindings returning a typechecked thing and (most
73 important) an LIE. It is this LIE which is then used as the basis for
74 specialising the things bound.
76 @tcBindsAndThen@ also takes a "combiner" which glues together the
77 bindings and the "thing" to make a new "thing".
79 The real work is done by @tcBindWithSigsAndThen@.
81 Recursive and non-recursive binds are handled in essentially the same
82 way: because of uniques there are no scoping issues left. The only
83 difference is that non-recursive bindings can bind primitive values.
85 Even for non-recursive binding groups we add typings for each binder
86 to the LVE for the following reason. When each individual binding is
87 checked the type of its LHS is unified with that of its RHS; and
88 type-checking the LHS of course requires that the binder is in scope.
90 At the top-level the LIE is sure to contain nothing but constant
91 dictionaries, which we resolve at the module level.
94 tcTopBinds :: RenamedHsBinds -> TcM ((TcMonoBinds, TcEnv), LIE)
96 = tc_binds_and_then TopLevel glue binds $
97 tcGetEnv `thenNF_Tc` \ env ->
98 returnTc ((EmptyMonoBinds, env), emptyLIE)
100 glue is_rec binds1 (binds2, thing) = (binds1 `AndMonoBinds` binds2, thing)
104 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
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 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
123 -- Notice that they scope over
124 -- a) the type signatures in the binding group
125 -- b) the bindings in the group
126 -- c) the scope of the binding group (the "in" part)
127 tcAddScopedTyVars (collectSigTysFromMonoBinds bind) $
129 -- TYPECHECK THE SIGNATURES
130 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
132 tcBindWithSigs top_lvl bind tc_ty_sigs
133 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
135 -- Extend the environment to bind the new polymorphic Ids
136 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
138 -- Build bindings and IdInfos corresponding to user pragmas
139 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
141 -- Now do whatever happens next, in the augmented envt
142 do_next `thenTc` \ (thing, thing_lie) ->
144 -- Create specialisations of functions bound here
145 -- We want to keep non-recursive things non-recursive
146 -- so that we desugar unlifted bindings correctly
147 case (top_lvl, is_rec) of
149 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
150 -- All the top level things are rec'd together anyway, so it's fine to
151 -- leave them to the tcSimplifyTop, and quite a bit faster too
153 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
154 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
156 (NotTopLevel, NonRecursive)
157 -> bindInstsOfLocalFuns
158 (thing_lie `plusLIE` prag_lie)
159 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
162 combiner NonRecursive poly_binds $
163 combiner NonRecursive prag_binds $
164 combiner Recursive lie_binds $
165 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
166 -- aren't guaranteed in dependency order (though we could change
167 -- that); hence the Recursive marker.
170 thing_lie' `plusLIE` poly_lie
173 (NotTopLevel, Recursive)
174 -> bindInstsOfLocalFuns
175 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
176 poly_ids `thenTc` \ (final_lie, lie_binds) ->
180 poly_binds `andMonoBinds`
181 lie_binds `andMonoBinds`
188 %************************************************************************
190 \subsection{tcBindWithSigs}
192 %************************************************************************
194 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
195 so all the clever stuff is in here.
197 * binder_names and mbind must define the same set of Names
199 * The Names in tc_ty_sigs must be a subset of binder_names
201 * The Ids in tc_ty_sigs don't necessarily have to have the same name
202 as the Name in the tc_ty_sig
209 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
211 -> TcM (TcMonoBinds, LIE, [TcId])
213 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
215 -- If typechecking the binds fails, then return with each
216 -- signature-less binder given type (forall a.a), to minimise subsequent
218 newTyVar liftedTypeKind `thenNF_Tc` \ alpha_tv ->
220 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
221 binder_names = collectMonoBinders mbind
222 poly_ids = map mk_dummy binder_names
223 mk_dummy name = case maybeSig tc_ty_sigs name of
224 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
225 Nothing -> mkLocalId name forall_a_a -- No signature
227 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
230 -- TYPECHECK THE BINDINGS
231 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
233 tau_tvs = foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet mono_ids
237 tcAddSrcLoc (minimum (map getSrcLoc binder_names)) $
238 tcAddErrCtxt (genCtxt binder_names) $
239 generalise binder_names mbind tau_tvs lie_req tc_ty_sigs
240 `thenTc` \ (tc_tyvars_to_gen, lie_free, dict_binds, dict_ids) ->
243 -- ZONK THE GENERALISED TYPE VARIABLES TO REAL TyVars
244 -- This commits any unbound kind variables to boxed kind, by unification
245 -- It's important that the final quanfified type variables
246 -- are fully zonked, *including boxity*, because they'll be
247 -- included in the forall types of the polymorphic Ids.
248 -- At calls of these Ids we'll instantiate fresh type variables from
249 -- them, and we use their boxity then.
250 mapNF_Tc zonkTcTyVarToTyVar tc_tyvars_to_gen `thenNF_Tc` \ real_tyvars_to_gen ->
253 -- It's important that the dict Ids are zonked, including the boxity set
254 -- in the previous step, because they are later used to form the type of
255 -- the polymorphic thing, and forall-types must be zonked so far as
256 -- their bound variables are concerned
257 mapNF_Tc zonkId dict_ids `thenNF_Tc` \ zonked_dict_ids ->
258 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
260 -- CHECK FOR BOGUS UNLIFTED BINDINGS
261 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind zonked_mono_ids `thenTc_`
263 -- BUILD THE POLYMORPHIC RESULT IDs
265 exports = zipWith mk_export binder_names zonked_mono_ids
266 dict_tys = map idType zonked_dict_ids
268 inlines = mkNameSet [name | InlineSig True name _ loc <- inline_sigs]
269 no_inlines = listToFM [(name, phase) | InlineSig _ name phase _ <- inline_sigs,
270 not (isAlwaysActive phase)]
271 -- AlwaysActive is the default, so don't bother with them
273 mk_export binder_name zonked_mono_id
275 attachNoInlinePrag no_inlines poly_id,
279 case maybeSig tc_ty_sigs binder_name of
280 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
281 (sig_tyvars, sig_poly_id)
282 Nothing -> (real_tyvars_to_gen, new_poly_id)
284 new_poly_id = mkLocalId binder_name poly_ty
285 poly_ty = mkForAllTys real_tyvars_to_gen
287 $ idType zonked_mono_id
288 -- It's important to build a fully-zonked poly_ty, because
289 -- we'll slurp out its free type variables when extending the
290 -- local environment (tcExtendLocalValEnv); if it's not zonked
291 -- it appears to have free tyvars that aren't actually free
295 traceTc (text "binding:" <+> ppr ((zonked_dict_ids, dict_binds),
296 exports, [idType poly_id | (_, poly_id, _) <- exports])) `thenTc_`
300 AbsBinds real_tyvars_to_gen
304 (dict_binds `andMonoBinds` mbind'),
306 [poly_id | (_, poly_id, _) <- exports]
309 attachNoInlinePrag no_inlines bndr
310 = case lookupFM no_inlines (idName bndr) of
311 Just prag -> bndr `setInlinePragma` prag
314 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind zonked_mono_ids
315 = ASSERT( not (any ((eqKind unliftedTypeKind) . tyVarKind) real_tyvars_to_gen) )
316 -- The instCantBeGeneralised stuff in tcSimplify should have
317 -- already raised an error if we're trying to generalise an
318 -- unboxed tyvar (NB: unboxed tyvars are always introduced
319 -- along with a class constraint) and it's better done there
320 -- because we have more precise origin information.
321 -- That's why we just use an ASSERT here.
323 -- Check that pattern-bound variables are not unlifted
324 (if or [ (idName id `elem` pat_binders) && isUnLiftedType (idType id)
325 | id <- zonked_mono_ids ] then
326 addErrTc (unliftedBindErr "Pattern" mbind)
331 -- Unlifted bindings must be non-recursive,
332 -- not top level, non-polymorphic, and not pattern bound
333 if any (isUnLiftedType . idType) zonked_mono_ids then
334 checkTc (isNotTopLevel top_lvl)
335 (unliftedBindErr "Top-level" mbind) `thenTc_`
336 checkTc (isNonRec is_rec)
337 (unliftedBindErr "Recursive" mbind) `thenTc_`
338 checkTc (null real_tyvars_to_gen)
339 (unliftedBindErr "Polymorphic" mbind)
344 pat_binders :: [Name]
345 pat_binders = collectMonoBinders (justPatBindings mbind EmptyMonoBinds)
347 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
348 justPatBindings (AndMonoBinds b1 b2) binds =
349 justPatBindings b1 (justPatBindings b2 binds)
350 justPatBindings other_bind binds = binds
354 Polymorphic recursion
355 ~~~~~~~~~~~~~~~~~~~~~
356 The game plan for polymorphic recursion in the code above is
358 * Bind any variable for which we have a type signature
359 to an Id with a polymorphic type. Then when type-checking
360 the RHSs we'll make a full polymorphic call.
362 This fine, but if you aren't a bit careful you end up with a horrendous
363 amount of partial application and (worse) a huge space leak. For example:
365 f :: Eq a => [a] -> [a]
368 If we don't take care, after typechecking we get
370 f = /\a -> \d::Eq a -> let f' = f a d
374 Notice the the stupid construction of (f a d), which is of course
375 identical to the function we're executing. In this case, the
376 polymorphic recursion isn't being used (but that's a very common case).
379 f = /\a -> \d::Eq a -> letrec
380 fm = \ys:[a] -> ...fm...
384 This can lead to a massive space leak, from the following top-level defn
390 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
391 f' is another thunk which evaluates to the same thing... and you end
392 up with a chain of identical values all hung onto by the CAF ff.
396 = let f' = f Int dEqInt in \ys. ...f'...
398 = let f' = let f' = f Int dEqInt in \ys. ...f'...
402 Solution: when typechecking the RHSs we always have in hand the
403 *monomorphic* Ids for each binding. So we just need to make sure that
404 if (Method f a d) shows up in the constraints emerging from (...f...)
405 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
406 to the "givens" when simplifying constraints. That's what the "lies_avail"
410 %************************************************************************
412 \subsection{getTyVarsToGen}
414 %************************************************************************
417 generalise binder_names mbind tau_tvs lie_req sigs
418 | not is_unrestricted -- RESTRICTED CASE
419 = -- Check signature contexts are empty
420 checkTc (all is_mono_sig sigs)
421 (restrictedBindCtxtErr binder_names) `thenTc_`
423 -- Now simplify with exactly that set of tyvars
424 -- We have to squash those Methods
425 tcSimplifyRestricted doc tau_tvs lie_req `thenTc` \ (qtvs, lie_free, binds) ->
427 -- Check that signature type variables are OK
428 checkSigsTyVars sigs `thenTc_`
430 returnTc (qtvs, lie_free, binds, [])
432 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
433 = tcSimplifyInfer doc tau_tvs lie_req
435 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
436 = -- CHECKING CASE: Unrestricted group, there are type signatures
437 -- Check signature contexts are empty
438 checkSigsCtxts sigs `thenTc` \ (sig_avails, sig_dicts) ->
440 -- Check that the needed dicts can be
441 -- expressed in terms of the signature ones
442 tcSimplifyInferCheck doc tau_tvs sig_avails lie_req `thenTc` \ (forall_tvs, lie_free, dict_binds) ->
444 -- Check that signature type variables are OK
445 checkSigsTyVars sigs `thenTc_`
447 returnTc (forall_tvs, lie_free, dict_binds, sig_dicts)
450 is_unrestricted | opt_NoMonomorphismRestriction = True
451 | otherwise = isUnRestrictedGroup tysig_names mbind
453 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- sigs]
454 is_mono_sig (TySigInfo _ _ _ theta _ _ _ _) = null theta
456 doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
458 -----------------------
459 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
460 -- The type signatures on a mutually-recursive group of definitions
461 -- must all have the same context (or none).
463 -- We unify them because, with polymorphic recursion, their types
464 -- might not otherwise be related. This is a rather subtle issue.
466 checkSigsCtxts sigs@(TySigInfo _ id1 sig_tvs theta1 _ _ _ src_loc : other_sigs)
467 = tcAddSrcLoc src_loc $
468 mapTc_ check_one other_sigs `thenTc_`
470 returnTc ([], []) -- Non-overloaded type signatures
472 newDicts SignatureOrigin theta1 `thenNF_Tc` \ sig_dicts ->
474 -- The "sig_avails" is the stuff available. We get that from
475 -- the context of the type signature, BUT ALSO the lie_avail
476 -- so that polymorphic recursion works right (see comments at end of fn)
477 sig_avails = sig_dicts ++ sig_meths
479 returnTc (sig_avails, map instToId sig_dicts)
481 sig1_dict_tys = map mkPredTy theta1
482 sig_meths = concat [insts | TySigInfo _ _ _ _ _ _ insts _ <- sigs]
484 check_one sig@(TySigInfo _ id _ theta _ _ _ src_loc)
485 = tcAddErrCtxt (sigContextsCtxt id1 id) $
486 checkTc (equalLength theta theta1) sigContextsErr `thenTc_`
487 unifyTauTyLists sig1_dict_tys (map mkPredTy theta)
489 checkSigsTyVars sigs = mapTc_ check_one sigs
491 check_one (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
492 = tcAddSrcLoc src_loc $
493 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
494 checkSigTyVars sig_tyvars (idFreeTyVars id)
496 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
499 @getTyVarsToGen@ decides what type variables to generalise over.
501 For a "restricted group" -- see the monomorphism restriction
502 for a definition -- we bind no dictionaries, and
503 remove from tyvars_to_gen any constrained type variables
505 *Don't* simplify dicts at this point, because we aren't going
506 to generalise over these dicts. By the time we do simplify them
507 we may well know more. For example (this actually came up)
509 f x = array ... xs where xs = [1,2,3,4,5]
510 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
511 stuff. If we simplify only at the f-binding (not the xs-binding)
512 we'll know that the literals are all Ints, and we can just produce
515 Find all the type variables involved in overloading, the
516 "constrained_tyvars". These are the ones we *aren't* going to
517 generalise. We must be careful about doing this:
519 (a) If we fail to generalise a tyvar which is not actually
520 constrained, then it will never, ever get bound, and lands
521 up printed out in interface files! Notorious example:
522 instance Eq a => Eq (Foo a b) where ..
523 Here, b is not constrained, even though it looks as if it is.
524 Another, more common, example is when there's a Method inst in
525 the LIE, whose type might very well involve non-overloaded
527 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
528 the simple thing instead]
530 (b) On the other hand, we mustn't generalise tyvars which are constrained,
531 because we are going to pass on out the unmodified LIE, with those
532 tyvars in it. They won't be in scope if we've generalised them.
534 So we are careful, and do a complete simplification just to find the
535 constrained tyvars. We don't use any of the results, except to
536 find which tyvars are constrained.
539 isUnRestrictedGroup :: [Name] -- Signatures given for these
543 is_elem v vs = isIn "isUnResMono" v vs
545 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
546 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
547 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = isUnRestrictedMatch matches ||
549 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
550 isUnRestrictedGroup sigs mb2
551 isUnRestrictedGroup sigs EmptyMonoBinds = True
553 isUnRestrictedMatch (Match [] _ _ : _) = False -- No args => like a pattern binding
554 isUnRestrictedMatch other = True -- Some args => a function binding
558 %************************************************************************
560 \subsection{tcMonoBind}
562 %************************************************************************
564 @tcMonoBinds@ deals with a single @MonoBind@.
565 The signatures have been dealt with already.
568 tcMonoBinds :: RenamedMonoBinds
573 [Name], -- Bound names
574 [TcId]) -- Corresponding monomorphic bound things
576 tcMonoBinds mbinds tc_ty_sigs is_rec
577 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
579 id_list = bagToList ids
580 (names, mono_ids) = unzip id_list
582 -- This last defn is the key one:
583 -- extend the val envt with bindings for the
584 -- things bound in this group, overriding the monomorphic
585 -- ids with the polymorphic ones from the pattern
586 extra_val_env = case is_rec of
587 Recursive -> map mk_bind id_list
590 -- Don't know how to deal with pattern-bound existentials yet
591 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
592 (existentialExplode mbinds) `thenTc_`
594 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
595 -- extend the envt with bindings for all the bound ids;
596 -- and *then* override with the polymorphic Ids from the signatures
597 -- That is the whole point of the "complete_it" stuff.
599 -- There's a further wrinkle: we have to delay extending the environment
600 -- until after we've dealt with any pattern-bound signature type variables
601 -- Consider f (x::a) = ...f...
602 -- We're going to check that a isn't unified with anything in the envt,
603 -- so f itself had better not be! So we pass the envt binding f into
604 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
605 -- dealing with the signature tyvars
607 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
609 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
612 -- This function is used when dealing with a LHS binder;
613 -- we make a monomorphic version of the Id.
614 -- We check for a type signature; if there is one, we use the mono_id
615 -- from the signature. This is how we make sure the tau part of the
616 -- signature actually maatches the type of the LHS; then tc_mb_pats
617 -- ensures the LHS and RHS have the same type
619 tc_pat_bndr name pat_ty
620 = case maybeSig tc_ty_sigs name of
622 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
624 Just (TySigInfo _ _ _ _ _ mono_id _ _)
625 -> tcAddSrcLoc (getSrcLoc name) $
626 unifyTauTy (idType mono_id) pat_ty `thenTc_`
629 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
630 Nothing -> (name, mono_id)
631 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
633 tc_mb_pats EmptyMonoBinds
634 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
636 tc_mb_pats (AndMonoBinds mb1 mb2)
637 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
638 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
640 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
641 complete_it2 xve `thenTc` \ (mb2', lie2) ->
642 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
644 returnTc (complete_it,
645 lie_req1 `plusLIE` lie_req2,
646 tvs1 `unionBags` tvs2,
647 ids1 `unionBags` ids2,
648 lie_avail1 `plusLIE` lie_avail2)
650 tc_mb_pats (FunMonoBind name inf matches locn)
651 = newTyVarTy kind `thenNF_Tc` \ bndr_ty ->
652 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
654 complete_it xve = tcAddSrcLoc locn $
655 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
656 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
658 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
660 tc_mb_pats bind@(PatMonoBind pat grhss locn)
662 newTyVarTy kind `thenNF_Tc` \ pat_ty ->
664 -- Now typecheck the pattern
665 -- We don't support binding fresh (not-already-in-scope) scoped
666 -- type variables in the pattern of a pattern binding.
667 -- For example, this is illegal:
669 -- whereas this is ok
670 -- (x::Int, y::Bool) = e
672 -- We don't check explicitly for this problem. Instead, we simply
673 -- type check the pattern with tcPat. If the pattern mentions any
674 -- fresh tyvars we simply get an out-of-scope type variable error
675 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
677 complete_it xve = tcAddSrcLoc locn $
678 tcAddErrCtxt (patMonoBindsCtxt bind) $
679 tcExtendLocalValEnv xve $
680 tcGRHSs PatBindRhs grhss pat_ty `thenTc` \ (grhss', lie) ->
681 returnTc (PatMonoBind pat' grhss' locn, lie)
683 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
685 -- Figure out the appropriate kind for the pattern,
686 -- and generate a suitable type variable
687 kind = case is_rec of
688 Recursive -> liftedTypeKind -- Recursive, so no unlifted types
689 NonRecursive -> openTypeKind -- Non-recursive, so we permit unlifted types
693 %************************************************************************
695 \subsection{SPECIALIZE pragmas}
697 %************************************************************************
699 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
700 pragmas. It is convenient for them to appear in the @[RenamedSig]@
701 part of a binding because then the same machinery can be used for
702 moving them into place as is done for type signatures.
707 f :: Ord a => [a] -> b -> b
708 {-# SPECIALIZE f :: [Int] -> b -> b #-}
711 For this we generate:
713 f* = /\ b -> let d1 = ...
717 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
718 retain a right-hand-side that the simplifier will otherwise discard as
719 dead code... the simplifier has a flag that tells it not to discard
720 SpecPragmaId bindings.
722 In this case the f* retains a call-instance of the overloaded
723 function, f, (including appropriate dictionaries) so that the
724 specialiser will subsequently discover that there's a call of @f@ at
725 Int, and will create a specialisation for @f@. After that, the
726 binding for @f*@ can be discarded.
728 We used to have a form
729 {-# SPECIALISE f :: <type> = g #-}
730 which promised that g implemented f at <type>, but we do that with
732 {-# SPECIALISE (f::<type) = g #-}
735 tcSpecSigs :: [RenamedSig] -> TcM (TcMonoBinds, LIE)
736 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
737 = -- SPECIALISE f :: forall b. theta => tau = g
738 tcAddSrcLoc src_loc $
739 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
741 -- Get and instantiate its alleged specialised type
742 tcHsSigType (FunSigCtxt name) poly_ty `thenTc` \ sig_ty ->
744 -- Check that f has a more general type, and build a RHS for
745 -- the spec-pragma-id at the same time
746 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
748 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
749 tcSimplifyToDicts spec_lie `thenTc` \ (spec_dicts, spec_binds) ->
751 -- Just specialise "f" by building a SpecPragmaId binding
752 -- It is the thing that makes sure we don't prematurely
753 -- dead-code-eliminate the binding we are really interested in.
754 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
756 -- Do the rest and combine
757 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
758 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
759 lie_rest `plusLIE` mkLIE spec_dicts)
761 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
762 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
766 %************************************************************************
768 \subsection[TcBinds-errors]{Error contexts and messages}
770 %************************************************************************
774 patMonoBindsCtxt bind
775 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
777 -----------------------------------------------
779 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
780 nest 4 (ppr v <+> dcolon <+> ppr ty)]
782 -----------------------------------------------
783 sigContextsErr = ptext SLIT("Mismatched contexts")
785 sigContextsCtxt s1 s2
786 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
787 nest 2 (vcat [ppr s1 <+> dcolon <+> ppr (idType s1),
788 ppr s2 <+> dcolon <+> ppr (idType s2)]),
789 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
791 -----------------------------------------------
792 unliftedBindErr flavour mbind
793 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
796 -----------------------------------------------
797 existentialExplode mbinds
798 = hang (vcat [text "My brain just exploded.",
799 text "I can't handle pattern bindings for existentially-quantified constructors.",
800 text "In the binding group"])
803 -----------------------------------------------
804 restrictedBindCtxtErr binder_names
805 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
806 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
807 ptext SLIT("that falls under the monomorphism restriction")])
810 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
812 -- Used in error messages
813 pprBinders bndrs = pprWithCommas ppr bndrs