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, checkSigTyVars,
32 TcSigInfo(..), tcTySig, maybeSig, sigCtxt
34 import TcPat ( tcPat )
35 import TcSimplify ( bindInstsOfLocalFuns )
36 import TcType ( newTyVarTy, newTyVar,
39 import TcUnify ( unifyTauTy, unifyTauTyLists )
41 import CoreFVs ( idFreeTyVars )
42 import Id ( mkLocalId, setInlinePragma )
43 import Var ( idType, idName )
44 import IdInfo ( InlinePragInfo(..) )
45 import Name ( Name, getOccName, getSrcLoc )
47 import Type ( mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
48 mkPredTy, mkForAllTy, isUnLiftedType,
49 unliftedTypeKind, liftedTypeKind, openTypeKind
51 import Var ( tyVarKind )
55 import Maybes ( maybeToBool )
56 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 = -- 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 unlifted 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`
181 %************************************************************************
183 \subsection{tcBindWithSigs}
185 %************************************************************************
187 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
188 so all the clever stuff is in here.
190 * binder_names and mbind must define the same set of Names
192 * The Names in tc_ty_sigs must be a subset of binder_names
194 * The Ids in tc_ty_sigs don't necessarily have to have the same name
195 as the Name in the tc_ty_sig
202 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
204 -> TcM (TcMonoBinds, LIE, [TcId])
206 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
208 -- If typechecking the binds fails, then return with each
209 -- signature-less binder given type (forall a.a), to minimise subsequent
211 newTyVar liftedTypeKind `thenNF_Tc` \ alpha_tv ->
213 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
214 binder_names = collectMonoBinders mbind
215 poly_ids = map mk_dummy binder_names
216 mk_dummy name = case maybeSig tc_ty_sigs name of
217 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
218 Nothing -> mkLocalId name forall_a_a -- No signature
220 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
223 -- TYPECHECK THE BINDINGS
224 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
226 tau_tvs = varSetElems (foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet mono_ids)
230 tcAddSrcLoc (minimum (map getSrcLoc binder_names)) $
231 tcAddErrCtxt (genCtxt binder_names) $
232 generalise binder_names mbind tau_tvs lie_req tc_ty_sigs
233 `thenTc` \ (tc_tyvars_to_gen, lie_free, dict_binds, dict_ids) ->
236 -- ZONK THE GENERALISED TYPE VARIABLES TO REAL TyVars
237 -- This commits any unbound kind variables to boxed kind, by unification
238 -- It's important that the final quanfified type variables
239 -- are fully zonked, *including boxity*, because they'll be
240 -- included in the forall types of the polymorphic Ids.
241 -- At calls of these Ids we'll instantiate fresh type variables from
242 -- them, and we use their boxity then.
243 mapNF_Tc zonkTcTyVarToTyVar tc_tyvars_to_gen `thenNF_Tc` \ real_tyvars_to_gen ->
246 -- It's important that the dict Ids are zonked, including the boxity set
247 -- in the previous step, because they are later used to form the type of
248 -- the polymorphic thing, and forall-types must be zonked so far as
249 -- their bound variables are concerned
250 mapNF_Tc zonkId dict_ids `thenNF_Tc` \ zonked_dict_ids ->
251 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
253 -- CHECK FOR BOGUS UNLIFTED BINDINGS
254 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind zonked_mono_ids `thenTc_`
256 -- BUILD THE POLYMORPHIC RESULT IDs
258 exports = zipWith mk_export binder_names zonked_mono_ids
259 dict_tys = map idType zonked_dict_ids
261 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
262 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
263 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
264 -- "INLINE n foo" means inline foo, but not until at least phase n
265 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
266 -- then only if it is small enough etc.
267 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
268 -- See comments in CoreUnfold.blackListed for the Authorised Version
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, [idType poly_id | (_, poly_id, _) <- exports])) `thenTc_`
297 AbsBinds real_tyvars_to_gen
301 (dict_binds `andMonoBinds` mbind'),
303 [poly_id | (_, poly_id, _) <- exports]
306 attachNoInlinePrag no_inlines bndr
307 = case lookupFM no_inlines (idName bndr) of
308 Just prag -> bndr `setInlinePragma` prag
311 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind zonked_mono_ids
312 = ASSERT( not (any ((== unliftedTypeKind) . tyVarKind) real_tyvars_to_gen) )
313 -- The instCantBeGeneralised stuff in tcSimplify should have
314 -- already raised an error if we're trying to generalise an
315 -- unboxed tyvar (NB: unboxed tyvars are always introduced
316 -- along with a class constraint) and it's better done there
317 -- because we have more precise origin information.
318 -- That's why we just use an ASSERT here.
320 -- Check that pattern-bound variables are not unlifted
321 (if or [ (idName id `elem` pat_binders) && isUnLiftedType (idType id)
322 | id <- zonked_mono_ids ] then
323 addErrTc (unliftedBindErr "Pattern" mbind)
328 -- Unlifted bindings must be non-recursive,
329 -- not top level, non-polymorphic, and not pattern bound
330 if any (isUnLiftedType . idType) zonked_mono_ids then
331 checkTc (isNotTopLevel top_lvl)
332 (unliftedBindErr "Top-level" mbind) `thenTc_`
333 checkTc (isNonRec is_rec)
334 (unliftedBindErr "Recursive" mbind) `thenTc_`
335 checkTc (null real_tyvars_to_gen)
336 (unliftedBindErr "Polymorphic" mbind)
341 pat_binders :: [Name]
342 pat_binders = collectMonoBinders (justPatBindings mbind EmptyMonoBinds)
344 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
345 justPatBindings (AndMonoBinds b1 b2) binds =
346 justPatBindings b1 (justPatBindings b2 binds)
347 justPatBindings other_bind binds = binds
351 Polymorphic recursion
352 ~~~~~~~~~~~~~~~~~~~~~
353 The game plan for polymorphic recursion in the code above is
355 * Bind any variable for which we have a type signature
356 to an Id with a polymorphic type. Then when type-checking
357 the RHSs we'll make a full polymorphic call.
359 This fine, but if you aren't a bit careful you end up with a horrendous
360 amount of partial application and (worse) a huge space leak. For example:
362 f :: Eq a => [a] -> [a]
365 If we don't take care, after typechecking we get
367 f = /\a -> \d::Eq a -> let f' = f a d
371 Notice the the stupid construction of (f a d), which is of course
372 identical to the function we're executing. In this case, the
373 polymorphic recursion isn't being used (but that's a very common case).
376 f = /\a -> \d::Eq a -> letrec
377 fm = \ys:[a] -> ...fm...
381 This can lead to a massive space leak, from the following top-level defn
387 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
388 f' is another thunk which evaluates to the same thing... and you end
389 up with a chain of identical values all hung onto by the CAF ff.
393 = let f' = f Int dEqInt in \ys. ...f'...
395 = let f' = let f' = f Int dEqInt in \ys. ...f'...
399 Solution: when typechecking the RHSs we always have in hand the
400 *monomorphic* Ids for each binding. So we just need to make sure that
401 if (Method f a d) shows up in the constraints emerging from (...f...)
402 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
403 to the "givens" when simplifying constraints. That's what the "lies_avail"
407 %************************************************************************
409 \subsection{getTyVarsToGen}
411 %************************************************************************
414 generalise binder_names mbind tau_tvs lie_req sigs
415 | not is_unrestricted -- RESTRICTED CASE
416 = -- Check signature contexts are empty
417 checkTc (all is_mono_sig sigs)
418 (restrictedBindCtxtErr binder_names) `thenTc_`
420 -- Now simplify with exactly that set of tyvars
421 -- We have to squash those Methods
422 tcSimplifyRestricted doc tau_tvs lie_req `thenTc` \ (qtvs, lie_free, binds) ->
424 -- Check that signature type variables are OK
425 checkSigsTyVars sigs `thenTc_`
427 returnTc (qtvs, lie_free, binds, [])
429 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
430 = tcSimplifyInfer doc tau_tvs lie_req
432 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
433 = -- CHECKING CASE: Unrestricted group, there are type signatures
434 -- Check signature contexts are empty
435 checkSigsCtxts sigs `thenTc` \ (sig_avails, sig_dicts) ->
437 -- Check that the needed dicts can be
438 -- expressed in terms of the signature ones
439 tcSimplifyInferCheck doc tau_tvs sig_avails lie_req `thenTc` \ (forall_tvs, lie_free, dict_binds) ->
441 -- Check that signature type variables are OK
442 checkSigsTyVars sigs `thenTc_`
444 returnTc (forall_tvs, lie_free, dict_binds, sig_dicts)
447 is_unrestricted | opt_NoMonomorphismRestriction = True
448 | otherwise = isUnRestrictedGroup tysig_names mbind
450 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- sigs]
451 is_mono_sig (TySigInfo _ _ _ theta _ _ _ _) = null theta
453 doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
455 -----------------------
456 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
457 -- The type signatures on a mutually-recursive group of definitions
458 -- must all have the same context (or none).
460 -- We unify them because, with polymorphic recursion, their types
461 -- might not otherwise be related. This is a rather subtle issue.
463 checkSigsCtxts sigs@(TySigInfo _ id1 sig_tvs theta1 _ _ _ src_loc : other_sigs)
464 = tcAddSrcLoc src_loc $
465 mapTc_ check_one other_sigs `thenTc_`
467 returnTc ([], []) -- Non-overloaded type signatures
469 newDicts SignatureOrigin theta1 `thenNF_Tc` \ sig_dicts ->
471 -- The "sig_avails" is the stuff available. We get that from
472 -- the context of the type signature, BUT ALSO the lie_avail
473 -- so that polymorphic recursion works right (see comments at end of fn)
474 sig_avails = sig_dicts ++ sig_meths
476 returnTc (sig_avails, map instToId sig_dicts)
478 sig1_dict_tys = map mkPredTy theta1
479 n_sig1_theta = length theta1
480 sig_meths = concat [insts | TySigInfo _ _ _ _ _ _ insts _ <- sigs]
482 check_one sig@(TySigInfo _ id _ theta _ _ _ src_loc)
483 = tcAddErrCtxt (sigContextsCtxt id1 id) $
484 checkTc (length theta == n_sig1_theta) sigContextsErr `thenTc_`
485 unifyTauTyLists sig1_dict_tys (map mkPredTy theta)
487 checkSigsTyVars sigs = mapTc_ check_one sigs
489 check_one (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
490 = tcAddSrcLoc src_loc $
491 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
492 checkSigTyVars sig_tyvars (idFreeTyVars id)
494 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
497 @getTyVarsToGen@ decides what type variables to generalise over.
499 For a "restricted group" -- see the monomorphism restriction
500 for a definition -- we bind no dictionaries, and
501 remove from tyvars_to_gen any constrained type variables
503 *Don't* simplify dicts at this point, because we aren't going
504 to generalise over these dicts. By the time we do simplify them
505 we may well know more. For example (this actually came up)
507 f x = array ... xs where xs = [1,2,3,4,5]
508 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
509 stuff. If we simplify only at the f-binding (not the xs-binding)
510 we'll know that the literals are all Ints, and we can just produce
513 Find all the type variables involved in overloading, the
514 "constrained_tyvars". These are the ones we *aren't* going to
515 generalise. We must be careful about doing this:
517 (a) If we fail to generalise a tyvar which is not actually
518 constrained, then it will never, ever get bound, and lands
519 up printed out in interface files! Notorious example:
520 instance Eq a => Eq (Foo a b) where ..
521 Here, b is not constrained, even though it looks as if it is.
522 Another, more common, example is when there's a Method inst in
523 the LIE, whose type might very well involve non-overloaded
525 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
526 the simple thing instead]
528 (b) On the other hand, we mustn't generalise tyvars which are constrained,
529 because we are going to pass on out the unmodified LIE, with those
530 tyvars in it. They won't be in scope if we've generalised them.
532 So we are careful, and do a complete simplification just to find the
533 constrained tyvars. We don't use any of the results, except to
534 find which tyvars are constrained.
537 isUnRestrictedGroup :: [Name] -- Signatures given for these
541 is_elem v vs = isIn "isUnResMono" v vs
543 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
544 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
545 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
547 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
548 isUnRestrictedGroup sigs mb2
549 isUnRestrictedGroup sigs EmptyMonoBinds = True
551 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
552 isUnRestrictedMatch other = True -- Some args or a signature
556 %************************************************************************
558 \subsection{tcMonoBind}
560 %************************************************************************
562 @tcMonoBinds@ deals with a single @MonoBind@.
563 The signatures have been dealt with already.
566 tcMonoBinds :: RenamedMonoBinds
571 [Name], -- Bound names
572 [TcId]) -- Corresponding monomorphic bound things
574 tcMonoBinds mbinds tc_ty_sigs is_rec
575 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
577 id_list = bagToList ids
578 (names, mono_ids) = unzip id_list
580 -- This last defn is the key one:
581 -- extend the val envt with bindings for the
582 -- things bound in this group, overriding the monomorphic
583 -- ids with the polymorphic ones from the pattern
584 extra_val_env = case is_rec of
585 Recursive -> map mk_bind id_list
588 -- Don't know how to deal with pattern-bound existentials yet
589 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
590 (existentialExplode mbinds) `thenTc_`
592 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
593 -- extend the envt with bindings for all the bound ids;
594 -- and *then* override with the polymorphic Ids from the signatures
595 -- That is the whole point of the "complete_it" stuff.
597 -- There's a further wrinkle: we have to delay extending the environment
598 -- until after we've dealt with any pattern-bound signature type variables
599 -- Consider f (x::a) = ...f...
600 -- We're going to check that a isn't unified with anything in the envt,
601 -- so f itself had better not be! So we pass the envt binding f into
602 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
603 -- dealing with the signature tyvars
605 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
607 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
610 -- This function is used when dealing with a LHS binder;
611 -- we make a monomorphic version of the Id.
612 -- We check for a type signature; if there is one, we use the mono_id
613 -- from the signature. This is how we make sure the tau part of the
614 -- signature actually maatches the type of the LHS; then tc_mb_pats
615 -- ensures the LHS and RHS have the same type
617 tc_pat_bndr name pat_ty
618 = case maybeSig tc_ty_sigs name of
620 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
622 Just (TySigInfo _ _ _ _ _ mono_id _ _)
623 -> tcAddSrcLoc (getSrcLoc name) $
624 unifyTauTy (idType mono_id) pat_ty `thenTc_`
627 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
628 Nothing -> (name, mono_id)
629 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
631 tc_mb_pats EmptyMonoBinds
632 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
634 tc_mb_pats (AndMonoBinds mb1 mb2)
635 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
636 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
638 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
639 complete_it2 xve `thenTc` \ (mb2', lie2) ->
640 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
642 returnTc (complete_it,
643 lie_req1 `plusLIE` lie_req2,
644 tvs1 `unionBags` tvs2,
645 ids1 `unionBags` ids2,
646 lie_avail1 `plusLIE` lie_avail2)
648 tc_mb_pats (FunMonoBind name inf matches locn)
649 = newTyVarTy kind `thenNF_Tc` \ bndr_ty ->
650 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
652 complete_it xve = tcAddSrcLoc locn $
653 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
654 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
656 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
658 tc_mb_pats bind@(PatMonoBind pat grhss locn)
660 newTyVarTy kind `thenNF_Tc` \ pat_ty ->
662 -- Now typecheck the pattern
663 -- We don't support binding fresh type variables in the
664 -- pattern of a pattern binding. For example, this is illegal:
666 -- whereas this is ok
667 -- (x::Int, y::Bool) = e
669 -- We don't check explicitly for this problem. Instead, we simply
670 -- type check the pattern with tcPat. If the pattern mentions any
671 -- fresh tyvars we simply get an out-of-scope type variable error
672 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
674 complete_it xve = tcAddSrcLoc locn $
675 tcAddErrCtxt (patMonoBindsCtxt bind) $
676 tcExtendLocalValEnv xve $
677 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
678 returnTc (PatMonoBind pat' grhss' locn, lie)
680 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
682 -- Figure out the appropriate kind for the pattern,
683 -- and generate a suitable type variable
684 kind = case is_rec of
685 Recursive -> liftedTypeKind -- Recursive, so no unlifted types
686 NonRecursive -> openTypeKind -- Non-recursive, so we permit unlifted types
690 %************************************************************************
692 \subsection{SPECIALIZE pragmas}
694 %************************************************************************
696 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
697 pragmas. It is convenient for them to appear in the @[RenamedSig]@
698 part of a binding because then the same machinery can be used for
699 moving them into place as is done for type signatures.
704 f :: Ord a => [a] -> b -> b
705 {-# SPECIALIZE f :: [Int] -> b -> b #-}
708 For this we generate:
710 f* = /\ b -> let d1 = ...
714 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
715 retain a right-hand-side that the simplifier will otherwise discard as
716 dead code... the simplifier has a flag that tells it not to discard
717 SpecPragmaId bindings.
719 In this case the f* retains a call-instance of the overloaded
720 function, f, (including appropriate dictionaries) so that the
721 specialiser will subsequently discover that there's a call of @f@ at
722 Int, and will create a specialisation for @f@. After that, the
723 binding for @f*@ can be discarded.
725 We used to have a form
726 {-# SPECIALISE f :: <type> = g #-}
727 which promised that g implemented f at <type>, but we do that with
729 {-# SPECIALISE (f::<type) = g #-}
732 tcSpecSigs :: [RenamedSig] -> TcM (TcMonoBinds, LIE)
733 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
734 = -- SPECIALISE f :: forall b. theta => tau = g
735 tcAddSrcLoc src_loc $
736 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
738 -- Get and instantiate its alleged specialised type
739 tcHsSigType poly_ty `thenTc` \ sig_ty ->
741 -- Check that f has a more general type, and build a RHS for
742 -- the spec-pragma-id at the same time
743 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
745 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
746 tcSimplifyToDicts spec_lie `thenTc` \ (spec_dicts, spec_binds) ->
748 -- Just specialise "f" by building a SpecPragmaId binding
749 -- It is the thing that makes sure we don't prematurely
750 -- dead-code-eliminate the binding we are really interested in.
751 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
753 -- Do the rest and combine
754 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
755 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
756 lie_rest `plusLIE` mkLIE spec_dicts)
758 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
759 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
763 %************************************************************************
765 \subsection[TcBinds-errors]{Error contexts and messages}
767 %************************************************************************
771 patMonoBindsCtxt bind
772 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
774 -----------------------------------------------
776 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
777 nest 4 (ppr v <+> dcolon <+> ppr ty)]
779 -----------------------------------------------
780 sigContextsErr = ptext SLIT("Mismatched contexts")
782 sigContextsCtxt s1 s2
783 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
784 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
785 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
787 -----------------------------------------------
788 unliftedBindErr flavour mbind
789 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
792 -----------------------------------------------
793 existentialExplode mbinds
794 = hang (vcat [text "My brain just exploded.",
795 text "I can't handle pattern bindings for existentially-quantified constructors.",
796 text "In the binding group"])
799 -----------------------------------------------
800 restrictedBindCtxtErr binder_names
801 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
802 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
803 ptext SLIT("that falls under the monomorphism restriction")])
806 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
808 -- Used in error messages
809 pprBinders bndrs = pprWithCommas ppr bndrs