2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBinds, tcMonoBinds,
8 tcSpecSigs, tcBindWithSigs ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcMatches ( tcGRHSs, tcMatchesFun )
13 import {-# SOURCE #-} TcExpr ( tcExpr )
15 import CmdLineOpts ( DynFlag(Opt_NoMonomorphismRestriction) )
16 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..),
17 Match(..), HsMatchContext(..),
18 collectMonoBinders, andMonoBinds,
19 collectSigTysFromMonoBinds
21 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds,
23 import TcHsSyn ( TcMonoBinds, TcId, zonkId, mkHsLet )
26 import Inst ( LIE, emptyLIE, mkLIE, plusLIE, InstOrigin(..),
29 import TcEnv ( tcExtendLocalValEnv, tcExtendLocalValEnv2, newLocalName )
30 import TcUnify ( unifyTauTyLists, checkSigTyVarsWrt, sigCtxt )
31 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted, tcSimplifyToDicts )
32 import TcMonoType ( tcHsSigType, UserTypeCtxt(..), TcSigInfo(..),
33 tcTySig, maybeSig, tcSigPolyId, tcSigMonoId, tcAddScopedTyVars
35 import TcPat ( tcPat, tcSubPat, tcMonoPatBndr )
36 import TcSimplify ( bindInstsOfLocalFuns )
37 import TcMType ( newTyVar, newTyVarTy, newHoleTyVarTy,
38 zonkTcTyVarToTyVar, readHoleResult
40 import TcType ( mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
41 mkPredTy, mkForAllTy, isUnLiftedType,
42 unliftedTypeKind, liftedTypeKind, openTypeKind, eqKind
45 import CoreFVs ( idFreeTyVars )
46 import Id ( mkLocalId, mkSpecPragmaId, setInlinePragma )
47 import Var ( idType, idName )
48 import Name ( Name, getSrcLoc )
50 import Var ( tyVarKind )
53 import Util ( isIn, equalLength )
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 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
122 -- Notice that they scope over
123 -- a) the type signatures in the binding group
124 -- b) the bindings in the group
125 -- c) the scope of the binding group (the "in" part)
126 tcAddScopedTyVars (collectSigTysFromMonoBinds bind) $
128 -- TYPECHECK THE SIGNATURES
129 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
131 tcBindWithSigs top_lvl bind tc_ty_sigs
132 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
134 -- Extend the environment to bind the new polymorphic Ids
135 tcExtendLocalValEnv poly_ids $
137 -- Build bindings and IdInfos corresponding to user pragmas
138 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
140 -- Now do whatever happens next, in the augmented envt
141 do_next `thenTc` \ (thing, thing_lie) ->
143 -- Create specialisations of functions bound here
144 -- We want to keep non-recursive things non-recursive
145 -- so that we desugar unlifted bindings correctly
146 case (top_lvl, is_rec) of
148 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
149 -- All the top level things are rec'd together anyway, so it's fine to
150 -- leave them to the tcSimplifyTop, and quite a bit faster too
152 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
153 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
155 (NotTopLevel, NonRecursive)
156 -> bindInstsOfLocalFuns
157 (thing_lie `plusLIE` prag_lie)
158 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
161 combiner NonRecursive poly_binds $
162 combiner NonRecursive prag_binds $
163 combiner Recursive lie_binds $
164 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
165 -- aren't guaranteed in dependency order (though we could change
166 -- that); hence the Recursive marker.
169 thing_lie' `plusLIE` poly_lie
172 (NotTopLevel, Recursive)
173 -> bindInstsOfLocalFuns
174 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
175 poly_ids `thenTc` \ (final_lie, lie_binds) ->
179 poly_binds `andMonoBinds`
180 lie_binds `andMonoBinds`
187 %************************************************************************
189 \subsection{tcBindWithSigs}
191 %************************************************************************
193 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
194 so all the clever stuff is in here.
196 * binder_names and mbind must define the same set of Names
198 * The Names in tc_ty_sigs must be a subset of binder_names
200 * The Ids in tc_ty_sigs don't necessarily have to have the same name
201 as the Name in the tc_ty_sig
208 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
210 -> TcM (TcMonoBinds, LIE, [TcId])
212 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
214 -- If typechecking the binds fails, then return with each
215 -- signature-less binder given type (forall a.a), to minimise subsequent
217 newTyVar liftedTypeKind `thenNF_Tc` \ alpha_tv ->
219 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
220 binder_names = collectMonoBinders mbind
221 poly_ids = map mk_dummy binder_names
222 mk_dummy name = case maybeSig tc_ty_sigs name of
223 Just sig -> tcSigPolyId sig -- Signature
224 Nothing -> mkLocalId name forall_a_a -- No signature
226 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
229 -- TYPECHECK THE BINDINGS
230 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
232 tau_tvs = foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet mono_ids
236 tcAddSrcLoc (minimum (map getSrcLoc binder_names)) $
237 tcAddErrCtxt (genCtxt binder_names) $
238 generalise binder_names mbind tau_tvs lie_req tc_ty_sigs
239 `thenTc` \ (tc_tyvars_to_gen, lie_free, dict_binds, dict_ids) ->
242 -- ZONK THE GENERALISED TYPE VARIABLES TO REAL TyVars
243 -- This commits any unbound kind variables to boxed kind, by unification
244 -- It's important that the final quanfified type variables
245 -- are fully zonked, *including boxity*, because they'll be
246 -- included in the forall types of the polymorphic Ids.
247 -- At calls of these Ids we'll instantiate fresh type variables from
248 -- them, and we use their boxity then.
249 mapNF_Tc zonkTcTyVarToTyVar tc_tyvars_to_gen `thenNF_Tc` \ real_tyvars_to_gen ->
252 -- It's important that the dict Ids are zonked, including the boxity set
253 -- in the previous step, because they are later used to form the type of
254 -- the polymorphic thing, and forall-types must be zonked so far as
255 -- their bound variables are concerned
256 mapNF_Tc zonkId dict_ids `thenNF_Tc` \ zonked_dict_ids ->
257 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
259 -- BUILD THE POLYMORPHIC RESULT IDs
261 exports = zipWith mk_export binder_names zonked_mono_ids
262 poly_ids = [poly_id | (_, poly_id, _) <- exports]
263 dict_tys = map idType zonked_dict_ids
265 inlines = mkNameSet [name | InlineSig True name _ loc <- inline_sigs]
266 no_inlines = listToFM [(name, phase) | InlineSig _ name phase _ <- inline_sigs,
267 not (isAlwaysActive phase)]
268 -- AlwaysActive is the default, so don't bother with them
270 mk_export binder_name zonked_mono_id
272 attachNoInlinePrag no_inlines poly_id,
276 case maybeSig tc_ty_sigs binder_name of
277 Just (TySigInfo sig_poly_id sig_tyvars _ _ _ _ _) ->
278 (sig_tyvars, sig_poly_id)
279 Nothing -> (real_tyvars_to_gen, new_poly_id)
281 new_poly_id = mkLocalId binder_name poly_ty
282 poly_ty = mkForAllTys real_tyvars_to_gen
284 $ idType zonked_mono_id
285 -- It's important to build a fully-zonked poly_ty, because
286 -- we'll slurp out its free type variables when extending the
287 -- local environment (tcExtendLocalValEnv); if it's not zonked
288 -- it appears to have free tyvars that aren't actually free
292 traceTc (text "binding:" <+> ppr ((zonked_dict_ids, dict_binds),
293 exports, map idType poly_ids)) `thenTc_`
295 -- Check for an unlifted, non-overloaded group
296 -- In that case we must make extra checks
297 if any (isUnLiftedType . idType) zonked_mono_ids && null zonked_dict_ids
298 then -- Some bindings are unlifted
299 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind `thenTc_`
302 AbsBinds [] [] exports inlines mbind',
303 lie_req, -- Do not generate even any x=y bindings
307 else -- The normal case
309 AbsBinds real_tyvars_to_gen
313 (dict_binds `andMonoBinds` mbind'),
317 attachNoInlinePrag no_inlines bndr
318 = case lookupFM no_inlines (idName bndr) of
319 Just prag -> bndr `setInlinePragma` prag
322 -- Check that non-overloaded unlifted bindings are
325 -- c) non-polymorphic
326 -- d) not a multiple-binding group (more or less implied by (a))
328 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind
329 = ASSERT( not (any ((eqKind unliftedTypeKind) . tyVarKind) real_tyvars_to_gen) )
330 -- The instCantBeGeneralised stuff in tcSimplify should have
331 -- already raised an error if we're trying to generalise an
332 -- unboxed tyvar (NB: unboxed tyvars are always introduced
333 -- along with a class constraint) and it's better done there
334 -- because we have more precise origin information.
335 -- That's why we just use an ASSERT here.
337 checkTc (isNotTopLevel top_lvl)
338 (unliftedBindErr "Top-level" mbind) `thenTc_`
339 checkTc (isNonRec is_rec)
340 (unliftedBindErr "Recursive" mbind) `thenTc_`
341 checkTc (single_bind mbind)
342 (unliftedBindErr "Multiple" mbind) `thenTc_`
343 checkTc (null real_tyvars_to_gen)
344 (unliftedBindErr "Polymorphic" mbind)
347 single_bind (PatMonoBind _ _ _) = True
348 single_bind (FunMonoBind _ _ _ _) = True
349 single_bind other = False
353 Polymorphic recursion
354 ~~~~~~~~~~~~~~~~~~~~~
355 The game plan for polymorphic recursion in the code above is
357 * Bind any variable for which we have a type signature
358 to an Id with a polymorphic type. Then when type-checking
359 the RHSs we'll make a full polymorphic call.
361 This fine, but if you aren't a bit careful you end up with a horrendous
362 amount of partial application and (worse) a huge space leak. For example:
364 f :: Eq a => [a] -> [a]
367 If we don't take care, after typechecking we get
369 f = /\a -> \d::Eq a -> let f' = f a d
373 Notice the the stupid construction of (f a d), which is of course
374 identical to the function we're executing. In this case, the
375 polymorphic recursion isn't being used (but that's a very common case).
378 f = /\a -> \d::Eq a -> letrec
379 fm = \ys:[a] -> ...fm...
383 This can lead to a massive space leak, from the following top-level defn
389 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
390 f' is another thunk which evaluates to the same thing... and you end
391 up with a chain of identical values all hung onto by the CAF ff.
395 = let f' = f Int dEqInt in \ys. ...f'...
397 = let f' = let f' = f Int dEqInt in \ys. ...f'...
401 Solution: when typechecking the RHSs we always have in hand the
402 *monomorphic* Ids for each binding. So we just need to make sure that
403 if (Method f a d) shows up in the constraints emerging from (...f...)
404 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
405 to the "givens" when simplifying constraints. That's what the "lies_avail"
409 %************************************************************************
411 \subsection{getTyVarsToGen}
413 %************************************************************************
416 generalise binder_names mbind tau_tvs lie_req sigs =
418 -- check for -fno-monomorphism-restriction
419 doptsTc Opt_NoMonomorphismRestriction `thenTc` \ no_MR ->
420 let is_unrestricted | no_MR = True
421 | otherwise = isUnRestrictedGroup tysig_names mbind
424 if not is_unrestricted then -- RESTRICTED CASE
425 -- Check signature contexts are empty
426 checkTc (all is_mono_sig sigs)
427 (restrictedBindCtxtErr binder_names) `thenTc_`
429 -- Now simplify with exactly that set of tyvars
430 -- We have to squash those Methods
431 tcSimplifyRestricted doc tau_tvs lie_req `thenTc` \ (qtvs, lie_free, binds) ->
433 -- Check that signature type variables are OK
434 checkSigsTyVars sigs `thenTc_`
436 returnTc (qtvs, lie_free, binds, [])
438 else if null sigs then -- UNRESTRICTED CASE, NO TYPE SIGS
439 tcSimplifyInfer doc tau_tvs lie_req
441 else -- UNRESTRICTED CASE, WITH TYPE SIGS
442 -- CHECKING CASE: Unrestricted group, there are type signatures
443 -- Check signature contexts are empty
444 checkSigsCtxts sigs `thenTc` \ (sig_avails, sig_dicts) ->
446 -- Check that the needed dicts can be
447 -- expressed in terms of the signature ones
448 tcSimplifyInferCheck doc tau_tvs sig_avails lie_req `thenTc` \ (forall_tvs, lie_free, dict_binds) ->
450 -- Check that signature type variables are OK
451 checkSigsTyVars sigs `thenTc_`
453 returnTc (forall_tvs, lie_free, dict_binds, sig_dicts)
456 tysig_names = map (idName . tcSigPolyId) sigs
457 is_mono_sig (TySigInfo _ _ theta _ _ _ _) = null theta
459 doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
461 -----------------------
462 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
463 -- The type signatures on a mutually-recursive group of definitions
464 -- must all have the same context (or none).
466 -- We unify them because, with polymorphic recursion, their types
467 -- might not otherwise be related. This is a rather subtle issue.
469 checkSigsCtxts sigs@(TySigInfo id1 sig_tvs theta1 _ _ _ src_loc : other_sigs)
470 = tcAddSrcLoc src_loc $
471 mapTc_ check_one other_sigs `thenTc_`
473 returnTc ([], []) -- Non-overloaded type signatures
475 newDicts SignatureOrigin theta1 `thenNF_Tc` \ sig_dicts ->
477 -- The "sig_avails" is the stuff available. We get that from
478 -- the context of the type signature, BUT ALSO the lie_avail
479 -- so that polymorphic recursion works right (see comments at end of fn)
480 sig_avails = sig_dicts ++ sig_meths
482 returnTc (sig_avails, map instToId sig_dicts)
484 sig1_dict_tys = map mkPredTy theta1
485 sig_meths = concat [insts | TySigInfo _ _ _ _ _ insts _ <- sigs]
487 check_one sig@(TySigInfo id _ theta _ _ _ _)
488 = tcAddErrCtxt (sigContextsCtxt id1 id) $
489 checkTc (equalLength theta theta1) sigContextsErr `thenTc_`
490 unifyTauTyLists sig1_dict_tys (map mkPredTy theta)
492 checkSigsTyVars sigs = mapTc_ check_one sigs
494 check_one (TySigInfo id sig_tyvars sig_theta sig_tau _ _ src_loc)
495 = tcAddSrcLoc src_loc $
496 tcAddErrCtxt (ptext SLIT("When checking the type signature for")
497 <+> quotes (ppr id)) $
498 tcAddErrCtxtM (sigCtxt id sig_tyvars sig_theta sig_tau) $
499 checkSigTyVarsWrt (idFreeTyVars id) sig_tyvars
502 @getTyVarsToGen@ decides what type variables to generalise over.
504 For a "restricted group" -- see the monomorphism restriction
505 for a definition -- we bind no dictionaries, and
506 remove from tyvars_to_gen any constrained type variables
508 *Don't* simplify dicts at this point, because we aren't going
509 to generalise over these dicts. By the time we do simplify them
510 we may well know more. For example (this actually came up)
512 f x = array ... xs where xs = [1,2,3,4,5]
513 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
514 stuff. If we simplify only at the f-binding (not the xs-binding)
515 we'll know that the literals are all Ints, and we can just produce
518 Find all the type variables involved in overloading, the
519 "constrained_tyvars". These are the ones we *aren't* going to
520 generalise. We must be careful about doing this:
522 (a) If we fail to generalise a tyvar which is not actually
523 constrained, then it will never, ever get bound, and lands
524 up printed out in interface files! Notorious example:
525 instance Eq a => Eq (Foo a b) where ..
526 Here, b is not constrained, even though it looks as if it is.
527 Another, more common, example is when there's a Method inst in
528 the LIE, whose type might very well involve non-overloaded
530 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
531 the simple thing instead]
533 (b) On the other hand, we mustn't generalise tyvars which are constrained,
534 because we are going to pass on out the unmodified LIE, with those
535 tyvars in it. They won't be in scope if we've generalised them.
537 So we are careful, and do a complete simplification just to find the
538 constrained tyvars. We don't use any of the results, except to
539 find which tyvars are constrained.
542 isUnRestrictedGroup :: [Name] -- Signatures given for these
546 is_elem v vs = isIn "isUnResMono" v vs
548 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
549 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
550 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = isUnRestrictedMatch matches ||
552 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
553 isUnRestrictedGroup sigs mb2
554 isUnRestrictedGroup sigs EmptyMonoBinds = True
556 isUnRestrictedMatch (Match [] _ _ : _) = False -- No args => like a pattern binding
557 isUnRestrictedMatch other = True -- Some args => a function binding
561 %************************************************************************
563 \subsection{tcMonoBind}
565 %************************************************************************
567 @tcMonoBinds@ deals with a single @MonoBind@.
568 The signatures have been dealt with already.
571 tcMonoBinds :: RenamedMonoBinds
576 [Name], -- Bound names
577 [TcId]) -- Corresponding monomorphic bound things
579 tcMonoBinds mbinds tc_ty_sigs is_rec
580 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
582 id_list = bagToList ids
583 (names, mono_ids) = unzip id_list
585 -- This last defn is the key one:
586 -- extend the val envt with bindings for the
587 -- things bound in this group, overriding the monomorphic
588 -- ids with the polymorphic ones from the pattern
589 extra_val_env = case is_rec of
590 Recursive -> map mk_bind id_list
593 -- Don't know how to deal with pattern-bound existentials yet
594 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
595 (existentialExplode mbinds) `thenTc_`
597 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
598 -- extend the envt with bindings for all the bound ids;
599 -- and *then* override with the polymorphic Ids from the signatures
600 -- That is the whole point of the "complete_it" stuff.
602 -- There's a further wrinkle: we have to delay extending the environment
603 -- until after we've dealt with any pattern-bound signature type variables
604 -- Consider f (x::a) = ...f...
605 -- We're going to check that a isn't unified with anything in the envt,
606 -- so f itself had better not be! So we pass the envt binding f into
607 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
608 -- dealing with the signature tyvars
610 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
612 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
615 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
616 Nothing -> (name, mono_id)
617 Just sig -> (idName poly_id, poly_id)
619 poly_id = tcSigPolyId sig
621 tc_mb_pats EmptyMonoBinds
622 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
624 tc_mb_pats (AndMonoBinds mb1 mb2)
625 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
626 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
628 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
629 complete_it2 xve `thenTc` \ (mb2', lie2) ->
630 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
632 returnTc (complete_it,
633 lie_req1 `plusLIE` lie_req2,
634 tvs1 `unionBags` tvs2,
635 ids1 `unionBags` ids2,
636 lie_avail1 `plusLIE` lie_avail2)
638 tc_mb_pats (FunMonoBind name inf matches locn)
639 = (case maybeSig tc_ty_sigs name of
640 Just sig -> returnNF_Tc (tcSigMonoId sig)
641 Nothing -> newLocalName name `thenNF_Tc` \ bndr_name ->
642 newTyVarTy openTypeKind `thenNF_Tc` \ bndr_ty ->
643 -- NB: not a 'hole' tyvar; since there is no type
644 -- signature, we revert to ordinary H-M typechecking
645 -- which means the variable gets an inferred tau-type
646 returnNF_Tc (mkLocalId bndr_name bndr_ty)
647 ) `thenNF_Tc` \ bndr_id ->
649 bndr_ty = idType bndr_id
650 complete_it xve = tcAddSrcLoc locn $
651 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
652 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
654 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
656 tc_mb_pats bind@(PatMonoBind pat grhss locn)
658 newHoleTyVarTy `thenNF_Tc` \ pat_ty ->
660 -- Now typecheck the pattern
661 -- We do now support binding fresh (not-already-in-scope) scoped
662 -- type variables in the pattern of a pattern binding.
663 -- For example, this is now legal:
665 -- The type variables are brought into scope in tc_binds_and_then,
666 -- so we don't have to do anything here.
668 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
669 readHoleResult pat_ty `thenTc` \ pat_ty' ->
671 complete_it xve = tcAddSrcLoc locn $
672 tcAddErrCtxt (patMonoBindsCtxt bind) $
673 tcExtendLocalValEnv2 xve $
674 tcGRHSs PatBindRhs grhss pat_ty' `thenTc` \ (grhss', lie) ->
675 returnTc (PatMonoBind pat' grhss' locn, lie)
677 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
679 -- tc_pat_bndr is used when dealing with a LHS binder in a pattern.
680 -- If there was a type sig for that Id, we want to make it much
681 -- as if that type signature had been on the binder as a SigPatIn.
682 -- We check for a type signature; if there is one, we use the mono_id
683 -- from the signature. This is how we make sure the tau part of the
684 -- signature actually matches the type of the LHS; then tc_mb_pats
685 -- ensures the LHS and RHS have the same type
687 tc_pat_bndr name pat_ty
688 = case maybeSig tc_ty_sigs name of
690 -> newLocalName name `thenNF_Tc` \ bndr_name ->
691 tcMonoPatBndr bndr_name pat_ty
693 Just sig -> tcAddSrcLoc (getSrcLoc name) $
694 tcSubPat (idType mono_id) pat_ty `thenTc` \ (co_fn, lie) ->
695 returnTc (co_fn, lie, mono_id)
697 mono_id = tcSigMonoId sig
701 %************************************************************************
703 \subsection{SPECIALIZE pragmas}
705 %************************************************************************
707 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
708 pragmas. It is convenient for them to appear in the @[RenamedSig]@
709 part of a binding because then the same machinery can be used for
710 moving them into place as is done for type signatures.
715 f :: Ord a => [a] -> b -> b
716 {-# SPECIALIZE f :: [Int] -> b -> b #-}
719 For this we generate:
721 f* = /\ b -> let d1 = ...
725 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
726 retain a right-hand-side that the simplifier will otherwise discard as
727 dead code... the simplifier has a flag that tells it not to discard
728 SpecPragmaId bindings.
730 In this case the f* retains a call-instance of the overloaded
731 function, f, (including appropriate dictionaries) so that the
732 specialiser will subsequently discover that there's a call of @f@ at
733 Int, and will create a specialisation for @f@. After that, the
734 binding for @f*@ can be discarded.
736 We used to have a form
737 {-# SPECIALISE f :: <type> = g #-}
738 which promised that g implemented f at <type>, but we do that with
740 {-# SPECIALISE (f::<type) = g #-}
743 tcSpecSigs :: [RenamedSig] -> TcM (TcMonoBinds, LIE)
744 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
745 = -- SPECIALISE f :: forall b. theta => tau = g
746 tcAddSrcLoc src_loc $
747 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
749 -- Get and instantiate its alleged specialised type
750 tcHsSigType (FunSigCtxt name) poly_ty `thenTc` \ sig_ty ->
752 -- Check that f has a more general type, and build a RHS for
753 -- the spec-pragma-id at the same time
754 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
756 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
757 tcSimplifyToDicts spec_lie `thenTc` \ (spec_dicts, spec_binds) ->
759 -- Just specialise "f" by building a SpecPragmaId binding
760 -- It is the thing that makes sure we don't prematurely
761 -- dead-code-eliminate the binding we are really interested in.
762 newLocalName name `thenNF_Tc` \ spec_name ->
764 spec_bind = VarMonoBind (mkSpecPragmaId spec_name sig_ty)
765 (mkHsLet spec_binds spec_expr)
768 -- Do the rest and combine
769 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
770 returnTc (binds_rest `andMonoBinds` spec_bind,
771 lie_rest `plusLIE` mkLIE spec_dicts)
773 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
774 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
778 %************************************************************************
780 \subsection[TcBinds-errors]{Error contexts and messages}
782 %************************************************************************
786 patMonoBindsCtxt bind
787 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
789 -----------------------------------------------
791 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
792 nest 4 (ppr v <+> dcolon <+> ppr ty)]
794 -----------------------------------------------
795 sigContextsErr = ptext SLIT("Mismatched contexts")
797 sigContextsCtxt s1 s2
798 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
799 nest 2 (vcat [ppr s1 <+> dcolon <+> ppr (idType s1),
800 ppr s2 <+> dcolon <+> ppr (idType s2)]),
801 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
803 -----------------------------------------------
804 unliftedBindErr flavour mbind
805 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
808 -----------------------------------------------
809 existentialExplode mbinds
810 = hang (vcat [text "My brain just exploded.",
811 text "I can't handle pattern bindings for existentially-quantified constructors.",
812 text "In the binding group"])
815 -----------------------------------------------
816 restrictedBindCtxtErr binder_names
817 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
818 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
819 ptext SLIT("that falls under the monomorphism restriction")])
822 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
824 -- Used in error messages
825 -- Use quotes for a single one; they look a bit "busy" for several
826 pprBinders [bndr] = quotes (ppr bndr)
827 pprBinders bndrs = pprWithCommas ppr bndrs