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
20 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
21 import TcHsSyn ( TcMonoBinds, TcId, zonkId, mkHsLet )
24 import Inst ( LIE, emptyLIE, mkLIE, plusLIE, InstOrigin(..),
27 import TcEnv ( tcExtendLocalValEnv,
28 newSpecPragmaId, newLocalId
30 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted, tcSimplifyToDicts )
31 import TcMonoType ( tcHsSigType, UserTypeCtxt(..), checkSigTyVars,
32 TcSigInfo(..), tcTySig, maybeSig, sigCtxt
34 import TcPat ( tcPat )
35 import TcSimplify ( bindInstsOfLocalFuns )
36 import TcMType ( newTyVarTy, newTyVar,
38 unifyTauTy, unifyTauTyLists
40 import TcType ( mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
41 mkPredTy, mkForAllTy, isUnLiftedType,
42 unliftedTypeKind, liftedTypeKind, openTypeKind, eqKind
45 import CoreFVs ( idFreeTyVars )
46 import Id ( mkLocalId, setInlinePragma )
47 import Var ( idType, idName )
48 import Name ( Name, getOccName, getSrcLoc )
50 import Var ( tyVarKind )
54 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isNotTopLevel,
56 import FiniteMap ( listToFM, lookupFM )
61 %************************************************************************
63 \subsection{Type-checking bindings}
65 %************************************************************************
67 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
68 it needs to know something about the {\em usage} of the things bound,
69 so that it can create specialisations of them. So @tcBindsAndThen@
70 takes a function which, given an extended environment, E, typechecks
71 the scope of the bindings returning a typechecked thing and (most
72 important) an LIE. It is this LIE which is then used as the basis for
73 specialising the things bound.
75 @tcBindsAndThen@ also takes a "combiner" which glues together the
76 bindings and the "thing" to make a new "thing".
78 The real work is done by @tcBindWithSigsAndThen@.
80 Recursive and non-recursive binds are handled in essentially the same
81 way: because of uniques there are no scoping issues left. The only
82 difference is that non-recursive bindings can bind primitive values.
84 Even for non-recursive binding groups we add typings for each binder
85 to the LVE for the following reason. When each individual binding is
86 checked the type of its LHS is unified with that of its RHS; and
87 type-checking the LHS of course requires that the binder is in scope.
89 At the top-level the LIE is sure to contain nothing but constant
90 dictionaries, which we resolve at the module level.
93 tcTopBinds :: RenamedHsBinds -> TcM ((TcMonoBinds, TcEnv), LIE)
95 = tc_binds_and_then TopLevel glue binds $
96 tcGetEnv `thenNF_Tc` \ env ->
97 returnTc ((EmptyMonoBinds, env), emptyLIE)
99 glue is_rec binds1 (binds2, thing) = (binds1 `AndMonoBinds` binds2, thing)
103 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
108 tcBindsAndThen = tc_binds_and_then NotTopLevel
110 tc_binds_and_then top_lvl combiner EmptyBinds do_next
112 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
115 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
116 = tc_binds_and_then top_lvl combiner b1 $
117 tc_binds_and_then top_lvl combiner b2 $
120 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
121 = -- TYPECHECK THE SIGNATURES
122 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
124 tcBindWithSigs top_lvl bind tc_ty_sigs
125 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
127 -- Extend the environment to bind the new polymorphic Ids
128 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
130 -- Build bindings and IdInfos corresponding to user pragmas
131 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
133 -- Now do whatever happens next, in the augmented envt
134 do_next `thenTc` \ (thing, thing_lie) ->
136 -- Create specialisations of functions bound here
137 -- We want to keep non-recursive things non-recursive
138 -- so that we desugar unlifted bindings correctly
139 case (top_lvl, is_rec) of
141 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
142 -- All the top level things are rec'd together anyway, so it's fine to
143 -- leave them to the tcSimplifyTop, and quite a bit faster too
145 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
146 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
148 (NotTopLevel, NonRecursive)
149 -> bindInstsOfLocalFuns
150 (thing_lie `plusLIE` prag_lie)
151 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
154 combiner NonRecursive poly_binds $
155 combiner NonRecursive prag_binds $
156 combiner Recursive lie_binds $
157 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
158 -- aren't guaranteed in dependency order (though we could change
159 -- that); hence the Recursive marker.
162 thing_lie' `plusLIE` poly_lie
165 (NotTopLevel, Recursive)
166 -> bindInstsOfLocalFuns
167 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
168 poly_ids `thenTc` \ (final_lie, lie_binds) ->
172 poly_binds `andMonoBinds`
173 lie_binds `andMonoBinds`
180 %************************************************************************
182 \subsection{tcBindWithSigs}
184 %************************************************************************
186 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
187 so all the clever stuff is in here.
189 * binder_names and mbind must define the same set of Names
191 * The Names in tc_ty_sigs must be a subset of binder_names
193 * The Ids in tc_ty_sigs don't necessarily have to have the same name
194 as the Name in the tc_ty_sig
201 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
203 -> TcM (TcMonoBinds, LIE, [TcId])
205 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
207 -- If typechecking the binds fails, then return with each
208 -- signature-less binder given type (forall a.a), to minimise subsequent
210 newTyVar liftedTypeKind `thenNF_Tc` \ alpha_tv ->
212 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
213 binder_names = collectMonoBinders mbind
214 poly_ids = map mk_dummy binder_names
215 mk_dummy name = case maybeSig tc_ty_sigs name of
216 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
217 Nothing -> mkLocalId name forall_a_a -- No signature
219 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
222 -- TYPECHECK THE BINDINGS
223 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
225 tau_tvs = foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet mono_ids
229 tcAddSrcLoc (minimum (map getSrcLoc binder_names)) $
230 tcAddErrCtxt (genCtxt binder_names) $
231 generalise binder_names mbind tau_tvs lie_req tc_ty_sigs
232 `thenTc` \ (tc_tyvars_to_gen, lie_free, dict_binds, dict_ids) ->
235 -- ZONK THE GENERALISED TYPE VARIABLES TO REAL TyVars
236 -- This commits any unbound kind variables to boxed kind, by unification
237 -- It's important that the final quanfified type variables
238 -- are fully zonked, *including boxity*, because they'll be
239 -- included in the forall types of the polymorphic Ids.
240 -- At calls of these Ids we'll instantiate fresh type variables from
241 -- them, and we use their boxity then.
242 mapNF_Tc zonkTcTyVarToTyVar tc_tyvars_to_gen `thenNF_Tc` \ real_tyvars_to_gen ->
245 -- It's important that the dict Ids are zonked, including the boxity set
246 -- in the previous step, because they are later used to form the type of
247 -- the polymorphic thing, and forall-types must be zonked so far as
248 -- their bound variables are concerned
249 mapNF_Tc zonkId dict_ids `thenNF_Tc` \ zonked_dict_ids ->
250 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
252 -- CHECK FOR BOGUS UNLIFTED BINDINGS
253 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind zonked_mono_ids `thenTc_`
255 -- BUILD THE POLYMORPHIC RESULT IDs
257 exports = zipWith mk_export binder_names zonked_mono_ids
258 dict_tys = map idType zonked_dict_ids
260 inlines = mkNameSet [name | InlineSig True name _ loc <- inline_sigs]
261 no_inlines = listToFM [(name, phase) | InlineSig _ name phase _ <- inline_sigs,
262 not (isAlwaysActive phase)]
263 -- AlwaysActive is the default, so don't bother with them
265 mk_export binder_name zonked_mono_id
267 attachNoInlinePrag no_inlines poly_id,
271 case maybeSig tc_ty_sigs binder_name of
272 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
273 (sig_tyvars, sig_poly_id)
274 Nothing -> (real_tyvars_to_gen, new_poly_id)
276 new_poly_id = mkLocalId binder_name poly_ty
277 poly_ty = mkForAllTys real_tyvars_to_gen
279 $ idType zonked_mono_id
280 -- It's important to build a fully-zonked poly_ty, because
281 -- we'll slurp out its free type variables when extending the
282 -- local environment (tcExtendLocalValEnv); if it's not zonked
283 -- it appears to have free tyvars that aren't actually free
287 traceTc (text "binding:" <+> ppr ((zonked_dict_ids, dict_binds),
288 exports, [idType poly_id | (_, poly_id, _) <- exports])) `thenTc_`
292 AbsBinds real_tyvars_to_gen
296 (dict_binds `andMonoBinds` mbind'),
298 [poly_id | (_, poly_id, _) <- exports]
301 attachNoInlinePrag no_inlines bndr
302 = case lookupFM no_inlines (idName bndr) of
303 Just prag -> bndr `setInlinePragma` prag
306 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind zonked_mono_ids
307 = ASSERT( not (any ((eqKind unliftedTypeKind) . tyVarKind) real_tyvars_to_gen) )
308 -- The instCantBeGeneralised stuff in tcSimplify should have
309 -- already raised an error if we're trying to generalise an
310 -- unboxed tyvar (NB: unboxed tyvars are always introduced
311 -- along with a class constraint) and it's better done there
312 -- because we have more precise origin information.
313 -- That's why we just use an ASSERT here.
315 -- Check that pattern-bound variables are not unlifted
316 (if or [ (idName id `elem` pat_binders) && isUnLiftedType (idType id)
317 | id <- zonked_mono_ids ] then
318 addErrTc (unliftedBindErr "Pattern" mbind)
323 -- Unlifted bindings must be non-recursive,
324 -- not top level, non-polymorphic, and not pattern bound
325 if any (isUnLiftedType . idType) zonked_mono_ids then
326 checkTc (isNotTopLevel top_lvl)
327 (unliftedBindErr "Top-level" mbind) `thenTc_`
328 checkTc (isNonRec is_rec)
329 (unliftedBindErr "Recursive" mbind) `thenTc_`
330 checkTc (null real_tyvars_to_gen)
331 (unliftedBindErr "Polymorphic" mbind)
336 pat_binders :: [Name]
337 pat_binders = collectMonoBinders (justPatBindings mbind EmptyMonoBinds)
339 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
340 justPatBindings (AndMonoBinds b1 b2) binds =
341 justPatBindings b1 (justPatBindings b2 binds)
342 justPatBindings other_bind binds = binds
346 Polymorphic recursion
347 ~~~~~~~~~~~~~~~~~~~~~
348 The game plan for polymorphic recursion in the code above is
350 * Bind any variable for which we have a type signature
351 to an Id with a polymorphic type. Then when type-checking
352 the RHSs we'll make a full polymorphic call.
354 This fine, but if you aren't a bit careful you end up with a horrendous
355 amount of partial application and (worse) a huge space leak. For example:
357 f :: Eq a => [a] -> [a]
360 If we don't take care, after typechecking we get
362 f = /\a -> \d::Eq a -> let f' = f a d
366 Notice the the stupid construction of (f a d), which is of course
367 identical to the function we're executing. In this case, the
368 polymorphic recursion isn't being used (but that's a very common case).
371 f = /\a -> \d::Eq a -> letrec
372 fm = \ys:[a] -> ...fm...
376 This can lead to a massive space leak, from the following top-level defn
382 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
383 f' is another thunk which evaluates to the same thing... and you end
384 up with a chain of identical values all hung onto by the CAF ff.
388 = let f' = f Int dEqInt in \ys. ...f'...
390 = let f' = let f' = f Int dEqInt in \ys. ...f'...
394 Solution: when typechecking the RHSs we always have in hand the
395 *monomorphic* Ids for each binding. So we just need to make sure that
396 if (Method f a d) shows up in the constraints emerging from (...f...)
397 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
398 to the "givens" when simplifying constraints. That's what the "lies_avail"
402 %************************************************************************
404 \subsection{getTyVarsToGen}
406 %************************************************************************
409 generalise binder_names mbind tau_tvs lie_req sigs
410 | not is_unrestricted -- RESTRICTED CASE
411 = -- Check signature contexts are empty
412 checkTc (all is_mono_sig sigs)
413 (restrictedBindCtxtErr binder_names) `thenTc_`
415 -- Now simplify with exactly that set of tyvars
416 -- We have to squash those Methods
417 tcSimplifyRestricted doc tau_tvs lie_req `thenTc` \ (qtvs, lie_free, binds) ->
419 -- Check that signature type variables are OK
420 checkSigsTyVars sigs `thenTc_`
422 returnTc (qtvs, lie_free, binds, [])
424 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
425 = tcSimplifyInfer doc tau_tvs lie_req
427 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
428 = -- CHECKING CASE: Unrestricted group, there are type signatures
429 -- Check signature contexts are empty
430 checkSigsCtxts sigs `thenTc` \ (sig_avails, sig_dicts) ->
432 -- Check that the needed dicts can be
433 -- expressed in terms of the signature ones
434 tcSimplifyInferCheck doc tau_tvs sig_avails lie_req `thenTc` \ (forall_tvs, lie_free, dict_binds) ->
436 -- Check that signature type variables are OK
437 checkSigsTyVars sigs `thenTc_`
439 returnTc (forall_tvs, lie_free, dict_binds, sig_dicts)
442 is_unrestricted | opt_NoMonomorphismRestriction = True
443 | otherwise = isUnRestrictedGroup tysig_names mbind
445 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- sigs]
446 is_mono_sig (TySigInfo _ _ _ theta _ _ _ _) = null theta
448 doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
450 -----------------------
451 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
452 -- The type signatures on a mutually-recursive group of definitions
453 -- must all have the same context (or none).
455 -- We unify them because, with polymorphic recursion, their types
456 -- might not otherwise be related. This is a rather subtle issue.
458 checkSigsCtxts sigs@(TySigInfo _ id1 sig_tvs theta1 _ _ _ src_loc : other_sigs)
459 = tcAddSrcLoc src_loc $
460 mapTc_ check_one other_sigs `thenTc_`
462 returnTc ([], []) -- Non-overloaded type signatures
464 newDicts SignatureOrigin theta1 `thenNF_Tc` \ sig_dicts ->
466 -- The "sig_avails" is the stuff available. We get that from
467 -- the context of the type signature, BUT ALSO the lie_avail
468 -- so that polymorphic recursion works right (see comments at end of fn)
469 sig_avails = sig_dicts ++ sig_meths
471 returnTc (sig_avails, map instToId sig_dicts)
473 sig1_dict_tys = map mkPredTy theta1
474 n_sig1_theta = length theta1
475 sig_meths = concat [insts | TySigInfo _ _ _ _ _ _ insts _ <- sigs]
477 check_one sig@(TySigInfo _ id _ theta _ _ _ src_loc)
478 = tcAddErrCtxt (sigContextsCtxt id1 id) $
479 checkTc (length theta == n_sig1_theta) sigContextsErr `thenTc_`
480 unifyTauTyLists sig1_dict_tys (map mkPredTy theta)
482 checkSigsTyVars sigs = mapTc_ check_one sigs
484 check_one (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
485 = tcAddSrcLoc src_loc $
486 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
487 checkSigTyVars sig_tyvars (idFreeTyVars id)
489 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
492 @getTyVarsToGen@ decides what type variables to generalise over.
494 For a "restricted group" -- see the monomorphism restriction
495 for a definition -- we bind no dictionaries, and
496 remove from tyvars_to_gen any constrained type variables
498 *Don't* simplify dicts at this point, because we aren't going
499 to generalise over these dicts. By the time we do simplify them
500 we may well know more. For example (this actually came up)
502 f x = array ... xs where xs = [1,2,3,4,5]
503 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
504 stuff. If we simplify only at the f-binding (not the xs-binding)
505 we'll know that the literals are all Ints, and we can just produce
508 Find all the type variables involved in overloading, the
509 "constrained_tyvars". These are the ones we *aren't* going to
510 generalise. We must be careful about doing this:
512 (a) If we fail to generalise a tyvar which is not actually
513 constrained, then it will never, ever get bound, and lands
514 up printed out in interface files! Notorious example:
515 instance Eq a => Eq (Foo a b) where ..
516 Here, b is not constrained, even though it looks as if it is.
517 Another, more common, example is when there's a Method inst in
518 the LIE, whose type might very well involve non-overloaded
520 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
521 the simple thing instead]
523 (b) On the other hand, we mustn't generalise tyvars which are constrained,
524 because we are going to pass on out the unmodified LIE, with those
525 tyvars in it. They won't be in scope if we've generalised them.
527 So we are careful, and do a complete simplification just to find the
528 constrained tyvars. We don't use any of the results, except to
529 find which tyvars are constrained.
532 isUnRestrictedGroup :: [Name] -- Signatures given for these
536 is_elem v vs = isIn "isUnResMono" v vs
538 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
539 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
540 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
542 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
543 isUnRestrictedGroup sigs mb2
544 isUnRestrictedGroup sigs EmptyMonoBinds = True
546 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
547 isUnRestrictedMatch other = True -- Some args or a signature
551 %************************************************************************
553 \subsection{tcMonoBind}
555 %************************************************************************
557 @tcMonoBinds@ deals with a single @MonoBind@.
558 The signatures have been dealt with already.
561 tcMonoBinds :: RenamedMonoBinds
566 [Name], -- Bound names
567 [TcId]) -- Corresponding monomorphic bound things
569 tcMonoBinds mbinds tc_ty_sigs is_rec
570 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
572 id_list = bagToList ids
573 (names, mono_ids) = unzip id_list
575 -- This last defn is the key one:
576 -- extend the val envt with bindings for the
577 -- things bound in this group, overriding the monomorphic
578 -- ids with the polymorphic ones from the pattern
579 extra_val_env = case is_rec of
580 Recursive -> map mk_bind id_list
583 -- Don't know how to deal with pattern-bound existentials yet
584 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
585 (existentialExplode mbinds) `thenTc_`
587 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
588 -- extend the envt with bindings for all the bound ids;
589 -- and *then* override with the polymorphic Ids from the signatures
590 -- That is the whole point of the "complete_it" stuff.
592 -- There's a further wrinkle: we have to delay extending the environment
593 -- until after we've dealt with any pattern-bound signature type variables
594 -- Consider f (x::a) = ...f...
595 -- We're going to check that a isn't unified with anything in the envt,
596 -- so f itself had better not be! So we pass the envt binding f into
597 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
598 -- dealing with the signature tyvars
600 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
602 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
605 -- This function is used when dealing with a LHS binder;
606 -- we make a monomorphic version of the Id.
607 -- We check for a type signature; if there is one, we use the mono_id
608 -- from the signature. This is how we make sure the tau part of the
609 -- signature actually maatches the type of the LHS; then tc_mb_pats
610 -- ensures the LHS and RHS have the same type
612 tc_pat_bndr name pat_ty
613 = case maybeSig tc_ty_sigs name of
615 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
617 Just (TySigInfo _ _ _ _ _ mono_id _ _)
618 -> tcAddSrcLoc (getSrcLoc name) $
619 unifyTauTy (idType mono_id) pat_ty `thenTc_`
622 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
623 Nothing -> (name, mono_id)
624 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
626 tc_mb_pats EmptyMonoBinds
627 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
629 tc_mb_pats (AndMonoBinds mb1 mb2)
630 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
631 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
633 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
634 complete_it2 xve `thenTc` \ (mb2', lie2) ->
635 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
637 returnTc (complete_it,
638 lie_req1 `plusLIE` lie_req2,
639 tvs1 `unionBags` tvs2,
640 ids1 `unionBags` ids2,
641 lie_avail1 `plusLIE` lie_avail2)
643 tc_mb_pats (FunMonoBind name inf matches locn)
644 = newTyVarTy kind `thenNF_Tc` \ bndr_ty ->
645 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
647 complete_it xve = tcAddSrcLoc locn $
648 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
649 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
651 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
653 tc_mb_pats bind@(PatMonoBind pat grhss locn)
655 newTyVarTy kind `thenNF_Tc` \ pat_ty ->
657 -- Now typecheck the pattern
658 -- We don't support binding fresh (not-already-in-scope) scoped
659 -- type variables in the pattern of a pattern binding.
660 -- For example, this is illegal:
662 -- whereas this is ok
663 -- (x::Int, y::Bool) = e
665 -- We don't check explicitly for this problem. Instead, we simply
666 -- type check the pattern with tcPat. If the pattern mentions any
667 -- fresh tyvars we simply get an out-of-scope type variable error
668 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
670 complete_it xve = tcAddSrcLoc locn $
671 tcAddErrCtxt (patMonoBindsCtxt bind) $
672 tcExtendLocalValEnv xve $
673 tcGRHSs PatBindRhs grhss pat_ty `thenTc` \ (grhss', lie) ->
674 returnTc (PatMonoBind pat' grhss' locn, lie)
676 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
678 -- Figure out the appropriate kind for the pattern,
679 -- and generate a suitable type variable
680 kind = case is_rec of
681 Recursive -> liftedTypeKind -- Recursive, so no unlifted types
682 NonRecursive -> openTypeKind -- Non-recursive, so we permit unlifted types
686 %************************************************************************
688 \subsection{SPECIALIZE pragmas}
690 %************************************************************************
692 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
693 pragmas. It is convenient for them to appear in the @[RenamedSig]@
694 part of a binding because then the same machinery can be used for
695 moving them into place as is done for type signatures.
700 f :: Ord a => [a] -> b -> b
701 {-# SPECIALIZE f :: [Int] -> b -> b #-}
704 For this we generate:
706 f* = /\ b -> let d1 = ...
710 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
711 retain a right-hand-side that the simplifier will otherwise discard as
712 dead code... the simplifier has a flag that tells it not to discard
713 SpecPragmaId bindings.
715 In this case the f* retains a call-instance of the overloaded
716 function, f, (including appropriate dictionaries) so that the
717 specialiser will subsequently discover that there's a call of @f@ at
718 Int, and will create a specialisation for @f@. After that, the
719 binding for @f*@ can be discarded.
721 We used to have a form
722 {-# SPECIALISE f :: <type> = g #-}
723 which promised that g implemented f at <type>, but we do that with
725 {-# SPECIALISE (f::<type) = g #-}
728 tcSpecSigs :: [RenamedSig] -> TcM (TcMonoBinds, LIE)
729 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
730 = -- SPECIALISE f :: forall b. theta => tau = g
731 tcAddSrcLoc src_loc $
732 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
734 -- Get and instantiate its alleged specialised type
735 tcHsSigType (FunSigCtxt name) poly_ty `thenTc` \ sig_ty ->
737 -- Check that f has a more general type, and build a RHS for
738 -- the spec-pragma-id at the same time
739 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
741 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
742 tcSimplifyToDicts spec_lie `thenTc` \ (spec_dicts, spec_binds) ->
744 -- Just specialise "f" by building a SpecPragmaId binding
745 -- It is the thing that makes sure we don't prematurely
746 -- dead-code-eliminate the binding we are really interested in.
747 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
749 -- Do the rest and combine
750 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
751 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
752 lie_rest `plusLIE` mkLIE spec_dicts)
754 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
755 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
759 %************************************************************************
761 \subsection[TcBinds-errors]{Error contexts and messages}
763 %************************************************************************
767 patMonoBindsCtxt bind
768 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
770 -----------------------------------------------
772 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
773 nest 4 (ppr v <+> dcolon <+> ppr ty)]
775 -----------------------------------------------
776 sigContextsErr = ptext SLIT("Mismatched contexts")
778 sigContextsCtxt s1 s2
779 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
780 nest 2 (vcat [ppr s1 <+> dcolon <+> ppr (idType s1),
781 ppr s2 <+> dcolon <+> ppr (idType s2)]),
782 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
784 -----------------------------------------------
785 unliftedBindErr flavour mbind
786 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
789 -----------------------------------------------
790 existentialExplode mbinds
791 = hang (vcat [text "My brain just exploded.",
792 text "I can't handle pattern bindings for existentially-quantified constructors.",
793 text "In the binding group"])
796 -----------------------------------------------
797 restrictedBindCtxtErr binder_names
798 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
799 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
800 ptext SLIT("that falls under the monomorphism restriction")])
803 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
805 -- Used in error messages
806 pprBinders bndrs = pprWithCommas ppr bndrs