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, tcSimplifyCheck, 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, tyVarsOfTypes,
48 mkForAllTys, mkFunTys, tyVarsOfType,
49 mkPredTy, mkForAllTy, isUnLiftedType,
50 unliftedTypeKind, liftedTypeKind, openTypeKind
52 import Var ( tyVarKind )
56 import ListSetOps ( minusList )
57 import Maybes ( maybeToBool )
58 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isNotTopLevel )
59 import FiniteMap ( listToFM, lookupFM )
64 %************************************************************************
66 \subsection{Type-checking bindings}
68 %************************************************************************
70 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
71 it needs to know something about the {\em usage} of the things bound,
72 so that it can create specialisations of them. So @tcBindsAndThen@
73 takes a function which, given an extended environment, E, typechecks
74 the scope of the bindings returning a typechecked thing and (most
75 important) an LIE. It is this LIE which is then used as the basis for
76 specialising the things bound.
78 @tcBindsAndThen@ also takes a "combiner" which glues together the
79 bindings and the "thing" to make a new "thing".
81 The real work is done by @tcBindWithSigsAndThen@.
83 Recursive and non-recursive binds are handled in essentially the same
84 way: because of uniques there are no scoping issues left. The only
85 difference is that non-recursive bindings can bind primitive values.
87 Even for non-recursive binding groups we add typings for each binder
88 to the LVE for the following reason. When each individual binding is
89 checked the type of its LHS is unified with that of its RHS; and
90 type-checking the LHS of course requires that the binder is in scope.
92 At the top-level the LIE is sure to contain nothing but constant
93 dictionaries, which we resolve at the module level.
96 tcTopBinds :: RenamedHsBinds -> TcM ((TcMonoBinds, TcEnv), LIE)
98 = tc_binds_and_then TopLevel glue binds $
99 tcGetEnv `thenNF_Tc` \ env ->
100 returnTc ((EmptyMonoBinds, env), emptyLIE)
102 glue is_rec binds1 (binds2, thing) = (binds1 `AndMonoBinds` binds2, thing)
106 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
111 tcBindsAndThen = tc_binds_and_then NotTopLevel
113 tc_binds_and_then top_lvl combiner EmptyBinds do_next
115 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
118 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
119 = tc_binds_and_then top_lvl combiner b1 $
120 tc_binds_and_then top_lvl combiner b2 $
123 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
124 = -- TYPECHECK THE SIGNATURES
125 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
127 tcBindWithSigs top_lvl bind tc_ty_sigs
128 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
130 -- Extend the environment to bind the new polymorphic Ids
131 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
133 -- Build bindings and IdInfos corresponding to user pragmas
134 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
136 -- Now do whatever happens next, in the augmented envt
137 do_next `thenTc` \ (thing, thing_lie) ->
139 -- Create specialisations of functions bound here
140 -- We want to keep non-recursive things non-recursive
141 -- so that we desugar unlifted bindings correctly
142 case (top_lvl, is_rec) of
144 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
145 -- All the top level things are rec'd together anyway, so it's fine to
146 -- leave them to the tcSimplifyTop, and quite a bit faster too
148 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
149 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
151 (NotTopLevel, NonRecursive)
152 -> bindInstsOfLocalFuns
153 (thing_lie `plusLIE` prag_lie)
154 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
157 combiner NonRecursive poly_binds $
158 combiner NonRecursive prag_binds $
159 combiner Recursive lie_binds $
160 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
161 -- aren't guaranteed in dependency order (though we could change
162 -- that); hence the Recursive marker.
165 thing_lie' `plusLIE` poly_lie
168 (NotTopLevel, Recursive)
169 -> bindInstsOfLocalFuns
170 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
171 poly_ids `thenTc` \ (final_lie, lie_binds) ->
175 poly_binds `andMonoBinds`
176 lie_binds `andMonoBinds`
183 %************************************************************************
185 \subsection{tcBindWithSigs}
187 %************************************************************************
189 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
190 so all the clever stuff is in here.
192 * binder_names and mbind must define the same set of Names
194 * The Names in tc_ty_sigs must be a subset of binder_names
196 * The Ids in tc_ty_sigs don't necessarily have to have the same name
197 as the Name in the tc_ty_sig
204 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
206 -> TcM (TcMonoBinds, LIE, [TcId])
208 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
210 -- If typechecking the binds fails, then return with each
211 -- signature-less binder given type (forall a.a), to minimise subsequent
213 newTyVar liftedTypeKind `thenNF_Tc` \ alpha_tv ->
215 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
216 binder_names = collectMonoBinders mbind
217 poly_ids = map mk_dummy binder_names
218 mk_dummy name = case maybeSig tc_ty_sigs name of
219 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
220 Nothing -> mkLocalId name forall_a_a -- No signature
222 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
225 -- TYPECHECK THE BINDINGS
226 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
228 tau_tvs = varSetElems (foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet mono_ids)
232 tcAddSrcLoc (minimum (map getSrcLoc binder_names)) $
233 tcAddErrCtxt (genCtxt binder_names) $
234 generalise binder_names mbind tau_tvs lie_req tc_ty_sigs
235 `thenTc` \ (tc_tyvars_to_gen, lie_free, dict_binds, dict_ids) ->
238 -- ZONK THE GENERALISED TYPE VARIABLES TO REAL TyVars
239 -- This commits any unbound kind variables to boxed kind, by unification
240 -- It's important that the final quanfified type variables
241 -- are fully zonked, *including boxity*, because they'll be
242 -- included in the forall types of the polymorphic Ids.
243 -- At calls of these Ids we'll instantiate fresh type variables from
244 -- them, and we use their boxity then.
245 mapNF_Tc zonkTcTyVarToTyVar tc_tyvars_to_gen `thenNF_Tc` \ real_tyvars_to_gen ->
248 -- It's important that the dict Ids are zonked, including the boxity set
249 -- in the previous step, because they are later used to form the type of
250 -- the polymorphic thing, and forall-types must be zonked so far as
251 -- their bound variables are concerned
252 mapNF_Tc zonkId dict_ids `thenNF_Tc` \ zonked_dict_ids ->
253 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
255 -- CHECK FOR BOGUS UNLIFTED BINDINGS
256 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind zonked_mono_ids `thenTc_`
258 -- BUILD THE POLYMORPHIC RESULT IDs
260 exports = zipWith mk_export binder_names zonked_mono_ids
261 dict_tys = map idType zonked_dict_ids
263 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
264 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
265 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
266 -- "INLINE n foo" means inline foo, but not until at least phase n
267 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
268 -- then only if it is small enough etc.
269 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
270 -- See comments in CoreUnfold.blackListed for the Authorised Version
272 mk_export binder_name zonked_mono_id
274 attachNoInlinePrag no_inlines poly_id,
278 case maybeSig tc_ty_sigs binder_name of
279 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
280 (sig_tyvars, sig_poly_id)
281 Nothing -> (real_tyvars_to_gen, new_poly_id)
283 new_poly_id = mkLocalId binder_name poly_ty
284 poly_ty = mkForAllTys real_tyvars_to_gen
286 $ idType zonked_mono_id
287 -- It's important to build a fully-zonked poly_ty, because
288 -- we'll slurp out its free type variables when extending the
289 -- local environment (tcExtendLocalValEnv); if it's not zonked
290 -- it appears to have free tyvars that aren't actually free
294 traceTc (text "binding:" <+> ppr ((zonked_dict_ids, dict_binds),
295 exports, [idType poly_id | (_, poly_id, _) <- exports])) `thenTc_`
299 AbsBinds real_tyvars_to_gen
303 (dict_binds `andMonoBinds` mbind'),
305 [poly_id | (_, poly_id, _) <- exports]
308 attachNoInlinePrag no_inlines bndr
309 = case lookupFM no_inlines (idName bndr) of
310 Just prag -> bndr `setInlinePragma` prag
313 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind zonked_mono_ids
314 = ASSERT( not (any ((== unliftedTypeKind) . tyVarKind) real_tyvars_to_gen) )
315 -- The instCantBeGeneralised stuff in tcSimplify should have
316 -- already raised an error if we're trying to generalise an
317 -- unboxed tyvar (NB: unboxed tyvars are always introduced
318 -- along with a class constraint) and it's better done there
319 -- because we have more precise origin information.
320 -- That's why we just use an ASSERT here.
322 -- Check that pattern-bound variables are not unlifted
323 (if or [ (idName id `elem` pat_binders) && isUnLiftedType (idType id)
324 | id <- zonked_mono_ids ] then
325 addErrTc (unliftedBindErr "Pattern" mbind)
330 -- Unlifted bindings must be non-recursive,
331 -- not top level, non-polymorphic, and not pattern bound
332 if any (isUnLiftedType . idType) zonked_mono_ids then
333 checkTc (isNotTopLevel top_lvl)
334 (unliftedBindErr "Top-level" mbind) `thenTc_`
335 checkTc (isNonRec is_rec)
336 (unliftedBindErr "Recursive" mbind) `thenTc_`
337 checkTc (null real_tyvars_to_gen)
338 (unliftedBindErr "Polymorphic" mbind)
343 pat_binders :: [Name]
344 pat_binders = collectMonoBinders (justPatBindings mbind EmptyMonoBinds)
346 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
347 justPatBindings (AndMonoBinds b1 b2) binds =
348 justPatBindings b1 (justPatBindings b2 binds)
349 justPatBindings other_bind binds = binds
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_help doc tau_tvs lie_req sigs
418 -----------------------
420 = -- INFERENCE CASE: Unrestricted group, no type signatures
421 tcSimplifyInfer doc tau_tvs lie_req
423 -----------------------
425 = -- CHECKING CASE: Unrestricted group, there are type signatures
426 -- Check signature contexts are empty
427 checkSigsCtxts sigs `thenTc` \ (sig_avails, sig_dicts) ->
429 -- Check that the needed dicts can be
430 -- expressed in terms of the signature ones
431 tcSimplifyInferCheck doc tau_tvs sig_avails lie_req `thenTc` \ (forall_tvs, lie_free, dict_binds) ->
433 -- Check that signature type variables are OK
434 checkSigsTyVars sigs `thenTc_`
436 returnTc (forall_tvs, lie_free, dict_binds, sig_dicts)
438 generalise binder_names mbind tau_tvs lie_req sigs
439 | is_unrestricted -- UNRESTRICTED CASE
440 = generalise_help doc tau_tvs lie_req sigs
442 | otherwise -- RESTRICTED CASE
443 = -- Do a simplification to decide what type variables
444 -- are constrained. We can't just take the free vars
445 -- of lie_req because that'll have methods that may
446 -- incidentally mention entirely unconstrained variables
447 -- e.g. a call to f :: Eq a => a -> b -> b
448 -- Here, b is unconstrained. A good example would be
450 -- We want to infer the polymorphic type
451 -- foo :: forall b. b -> b
452 generalise_help doc tau_tvs lie_req sigs `thenTc` \ (forall_tvs, lie_free, dict_binds, dict_ids) ->
454 -- Check signature contexts are empty
455 checkTc (null sigs || null dict_ids)
456 (restrictedBindCtxtErr binder_names) `thenTc_`
458 -- Identify constrained tyvars
460 constrained_tvs = varSetElems (tyVarsOfTypes (map idType dict_ids))
461 -- The dict_ids are fully zonked
462 final_forall_tvs = forall_tvs `minusList` constrained_tvs
465 -- Now simplify with exactly that set of tyvars
466 -- We have to squash those Methods
467 tcSimplifyRestricted doc final_forall_tvs [] lie_req `thenTc` \ (lie_free, binds) ->
469 returnTc (final_forall_tvs, lie_free, binds, [])
472 is_unrestricted | opt_NoMonomorphismRestriction = True
473 | otherwise = isUnRestrictedGroup tysig_names mbind
475 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- sigs]
477 doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
479 -----------------------
480 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
481 -- The type signatures on a mutually-recursive group of definitions
482 -- must all have the same context (or none).
484 -- We unify them because, with polymorphic recursion, their types
485 -- might not otherwise be related. This is a rather subtle issue.
487 checkSigsCtxts sigs@(TySigInfo _ id1 sig_tvs theta1 _ _ _ src_loc : other_sigs)
488 = tcAddSrcLoc src_loc $
489 mapTc_ check_one other_sigs `thenTc_`
491 returnTc ([], []) -- Non-overloaded type signatures
493 newDicts SignatureOrigin theta1 `thenNF_Tc` \ sig_dicts ->
495 -- The "sig_avails" is the stuff available. We get that from
496 -- the context of the type signature, BUT ALSO the lie_avail
497 -- so that polymorphic recursion works right (see comments at end of fn)
498 sig_avails = sig_dicts ++ sig_meths
500 returnTc (sig_avails, map instToId sig_dicts)
502 sig1_dict_tys = map mkPredTy theta1
503 n_sig1_theta = length theta1
504 sig_meths = concat [insts | TySigInfo _ _ _ _ _ _ insts _ <- sigs]
506 check_one sig@(TySigInfo _ id _ theta _ _ _ src_loc)
507 = tcAddErrCtxt (sigContextsCtxt id1 id) $
508 checkTc (length theta == n_sig1_theta) sigContextsErr `thenTc_`
509 unifyTauTyLists sig1_dict_tys (map mkPredTy theta)
511 checkSigsTyVars sigs = mapTc_ check_one sigs
513 check_one (TySigInfo _ id sig_tyvars sig_theta sig_tau _ _ src_loc)
514 = tcAddSrcLoc src_loc $
515 tcAddErrCtxtM (sigCtxt (sig_msg id) sig_tyvars sig_theta sig_tau) $
516 checkSigTyVars sig_tyvars (idFreeTyVars id)
518 sig_msg id = ptext SLIT("When checking the type signature for") <+> quotes (ppr id)
521 @getTyVarsToGen@ decides what type variables to generalise over.
523 For a "restricted group" -- see the monomorphism restriction
524 for a definition -- we bind no dictionaries, and
525 remove from tyvars_to_gen any constrained type variables
527 *Don't* simplify dicts at this point, because we aren't going
528 to generalise over these dicts. By the time we do simplify them
529 we may well know more. For example (this actually came up)
531 f x = array ... xs where xs = [1,2,3,4,5]
532 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
533 stuff. If we simplify only at the f-binding (not the xs-binding)
534 we'll know that the literals are all Ints, and we can just produce
537 Find all the type variables involved in overloading, the
538 "constrained_tyvars". These are the ones we *aren't* going to
539 generalise. We must be careful about doing this:
541 (a) If we fail to generalise a tyvar which is not actually
542 constrained, then it will never, ever get bound, and lands
543 up printed out in interface files! Notorious example:
544 instance Eq a => Eq (Foo a b) where ..
545 Here, b is not constrained, even though it looks as if it is.
546 Another, more common, example is when there's a Method inst in
547 the LIE, whose type might very well involve non-overloaded
549 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
550 the simple thing instead]
552 (b) On the other hand, we mustn't generalise tyvars which are constrained,
553 because we are going to pass on out the unmodified LIE, with those
554 tyvars in it. They won't be in scope if we've generalised them.
556 So we are careful, and do a complete simplification just to find the
557 constrained tyvars. We don't use any of the results, except to
558 find which tyvars are constrained.
561 isUnRestrictedGroup :: [Name] -- Signatures given for these
565 is_elem v vs = isIn "isUnResMono" v vs
567 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
568 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
569 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = any isUnRestrictedMatch matches ||
571 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
572 isUnRestrictedGroup sigs mb2
573 isUnRestrictedGroup sigs EmptyMonoBinds = True
575 isUnRestrictedMatch (Match _ [] Nothing _) = False -- No args, no signature
576 isUnRestrictedMatch other = True -- Some args or a signature
580 %************************************************************************
582 \subsection{tcMonoBind}
584 %************************************************************************
586 @tcMonoBinds@ deals with a single @MonoBind@.
587 The signatures have been dealt with already.
590 tcMonoBinds :: RenamedMonoBinds
595 [Name], -- Bound names
596 [TcId]) -- Corresponding monomorphic bound things
598 tcMonoBinds mbinds tc_ty_sigs is_rec
599 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
601 id_list = bagToList ids
602 (names, mono_ids) = unzip id_list
604 -- This last defn is the key one:
605 -- extend the val envt with bindings for the
606 -- things bound in this group, overriding the monomorphic
607 -- ids with the polymorphic ones from the pattern
608 extra_val_env = case is_rec of
609 Recursive -> map mk_bind id_list
612 -- Don't know how to deal with pattern-bound existentials yet
613 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
614 (existentialExplode mbinds) `thenTc_`
616 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
617 -- extend the envt with bindings for all the bound ids;
618 -- and *then* override with the polymorphic Ids from the signatures
619 -- That is the whole point of the "complete_it" stuff.
621 -- There's a further wrinkle: we have to delay extending the environment
622 -- until after we've dealt with any pattern-bound signature type variables
623 -- Consider f (x::a) = ...f...
624 -- We're going to check that a isn't unified with anything in the envt,
625 -- so f itself had better not be! So we pass the envt binding f into
626 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
627 -- dealing with the signature tyvars
629 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
631 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
634 -- This function is used when dealing with a LHS binder;
635 -- we make a monomorphic version of the Id.
636 -- We check for a type signature; if there is one, we use the mono_id
637 -- from the signature. This is how we make sure the tau part of the
638 -- signature actually maatches the type of the LHS; then tc_mb_pats
639 -- ensures the LHS and RHS have the same type
641 tc_pat_bndr name pat_ty
642 = case maybeSig tc_ty_sigs name of
644 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
646 Just (TySigInfo _ _ _ _ _ mono_id _ _)
647 -> tcAddSrcLoc (getSrcLoc name) $
648 unifyTauTy (idType mono_id) pat_ty `thenTc_`
651 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
652 Nothing -> (name, mono_id)
653 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
655 tc_mb_pats EmptyMonoBinds
656 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
658 tc_mb_pats (AndMonoBinds mb1 mb2)
659 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
660 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
662 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
663 complete_it2 xve `thenTc` \ (mb2', lie2) ->
664 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
666 returnTc (complete_it,
667 lie_req1 `plusLIE` lie_req2,
668 tvs1 `unionBags` tvs2,
669 ids1 `unionBags` ids2,
670 lie_avail1 `plusLIE` lie_avail2)
672 tc_mb_pats (FunMonoBind name inf matches locn)
673 = newTyVarTy kind `thenNF_Tc` \ bndr_ty ->
674 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
676 complete_it xve = tcAddSrcLoc locn $
677 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
678 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
680 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
682 tc_mb_pats bind@(PatMonoBind pat grhss locn)
684 newTyVarTy kind `thenNF_Tc` \ pat_ty ->
686 -- Now typecheck the pattern
687 -- We don't support binding fresh type variables in the
688 -- pattern of a pattern binding. For example, this is illegal:
690 -- whereas this is ok
691 -- (x::Int, y::Bool) = e
693 -- We don't check explicitly for this problem. Instead, we simply
694 -- type check the pattern with tcPat. If the pattern mentions any
695 -- fresh tyvars we simply get an out-of-scope type variable error
696 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
698 complete_it xve = tcAddSrcLoc locn $
699 tcAddErrCtxt (patMonoBindsCtxt bind) $
700 tcExtendLocalValEnv xve $
701 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
702 returnTc (PatMonoBind pat' grhss' locn, lie)
704 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
706 -- Figure out the appropriate kind for the pattern,
707 -- and generate a suitable type variable
708 kind = case is_rec of
709 Recursive -> liftedTypeKind -- Recursive, so no unlifted types
710 NonRecursive -> openTypeKind -- Non-recursive, so we permit unlifted types
714 %************************************************************************
716 \subsection{SPECIALIZE pragmas}
718 %************************************************************************
720 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
721 pragmas. It is convenient for them to appear in the @[RenamedSig]@
722 part of a binding because then the same machinery can be used for
723 moving them into place as is done for type signatures.
728 f :: Ord a => [a] -> b -> b
729 {-# SPECIALIZE f :: [Int] -> b -> b #-}
732 For this we generate:
734 f* = /\ b -> let d1 = ...
738 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
739 retain a right-hand-side that the simplifier will otherwise discard as
740 dead code... the simplifier has a flag that tells it not to discard
741 SpecPragmaId bindings.
743 In this case the f* retains a call-instance of the overloaded
744 function, f, (including appropriate dictionaries) so that the
745 specialiser will subsequently discover that there's a call of @f@ at
746 Int, and will create a specialisation for @f@. After that, the
747 binding for @f*@ can be discarded.
749 We used to have a form
750 {-# SPECIALISE f :: <type> = g #-}
751 which promised that g implemented f at <type>, but we do that with
753 {-# SPECIALISE (f::<type) = g #-}
756 tcSpecSigs :: [RenamedSig] -> TcM (TcMonoBinds, LIE)
757 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
758 = -- SPECIALISE f :: forall b. theta => tau = g
759 tcAddSrcLoc src_loc $
760 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
762 -- Get and instantiate its alleged specialised type
763 tcHsSigType poly_ty `thenTc` \ sig_ty ->
765 -- Check that f has a more general type, and build a RHS for
766 -- the spec-pragma-id at the same time
767 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
769 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
770 tcSimplifyToDicts spec_lie `thenTc` \ (spec_dicts, spec_binds) ->
772 -- Just specialise "f" by building a SpecPragmaId binding
773 -- It is the thing that makes sure we don't prematurely
774 -- dead-code-eliminate the binding we are really interested in.
775 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
777 -- Do the rest and combine
778 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
779 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
780 lie_rest `plusLIE` mkLIE spec_dicts)
782 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
783 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
787 %************************************************************************
789 \subsection[TcBinds-errors]{Error contexts and messages}
791 %************************************************************************
795 patMonoBindsCtxt bind
796 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
798 -----------------------------------------------
800 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
801 nest 4 (ppr v <+> dcolon <+> ppr ty)]
803 -----------------------------------------------
804 sigContextsErr = ptext SLIT("Mismatched contexts")
806 sigContextsCtxt s1 s2
807 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
808 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
809 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
811 -----------------------------------------------
812 unliftedBindErr flavour mbind
813 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
816 -----------------------------------------------
817 existentialExplode mbinds
818 = hang (vcat [text "My brain just exploded.",
819 text "I can't handle pattern bindings for existentially-quantified constructors.",
820 text "In the binding group"])
823 -----------------------------------------------
824 restrictedBindCtxtErr binder_names
825 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
826 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
827 ptext SLIT("that falls under the monomorphism restriction")])
830 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
832 -- Used in error messages
833 pprBinders bndrs = pprWithCommas ppr bndrs