2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBindsAndThen,
8 tcSpecSigs, tcBindWithSigs ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcMatches ( tcGRHSs, tcMatchesFun )
13 import {-# SOURCE #-} TcExpr ( tcExpr )
15 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..), InPat(..), StmtCtxt(..),
16 collectMonoBinders, andMonoBindList, andMonoBinds
18 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
19 import TcHsSyn ( TcHsBinds, TcMonoBinds, TcId, zonkId, mkHsLet )
22 import Inst ( Inst, LIE, emptyLIE, mkLIE, plusLIE, plusLIEs, InstOrigin(..),
23 newDicts, tyVarsOfInst, instToId,
25 import TcEnv ( tcExtendLocalValEnv,
26 newSpecPragmaId, newLocalId,
28 tcGetGlobalTyVars, tcExtendGlobalTyVars
30 import TcSimplify ( tcSimplify, tcSimplifyAndCheck, tcSimplifyToDicts )
31 import TcMonoType ( tcHsType, checkSigTyVars,
32 TcSigInfo(..), tcTySig, maybeSig, sigCtxt
34 import TcPat ( tcPat )
35 import TcSimplify ( bindInstsOfLocalFuns )
36 import TcType ( TcType, TcThetaType,
38 newTyVarTy, newTyVar, newTyVarTy_OpenKind, tcInstTcType,
39 zonkTcType, zonkTcTypes, zonkTcThetaType, zonkTcTyVarToTyVar
41 import TcUnify ( unifyTauTy, unifyTauTyLists )
43 import PrelInfo ( main_NAME, ioTyCon_NAME )
45 import Id ( Id, mkVanillaId, setInlinePragma )
46 import Var ( idType, idName )
47 import IdInfo ( IdInfo, vanillaIdInfo, setInlinePragInfo, InlinePragInfo(..) )
48 import Name ( Name, getName, getOccName, getSrcLoc )
50 import Type ( mkTyVarTy, tyVarsOfTypes, mkTyConApp,
51 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar,
52 mkDictTy, splitRhoTy, mkForAllTy, isUnLiftedType,
53 isUnboxedType, unboxedTypeKind, boxedTypeKind
55 import Var ( TyVar, tyVarKind )
59 import Maybes ( maybeToBool )
60 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNotTopLevel )
61 import FiniteMap ( listToFM, lookupFM )
62 import SrcLoc ( SrcLoc )
67 %************************************************************************
69 \subsection{Type-checking bindings}
71 %************************************************************************
73 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
74 it needs to know something about the {\em usage} of the things bound,
75 so that it can create specialisations of them. So @tcBindsAndThen@
76 takes a function which, given an extended environment, E, typechecks
77 the scope of the bindings returning a typechecked thing and (most
78 important) an LIE. It is this LIE which is then used as the basis for
79 specialising the things bound.
81 @tcBindsAndThen@ also takes a "combiner" which glues together the
82 bindings and the "thing" to make a new "thing".
84 The real work is done by @tcBindWithSigsAndThen@.
86 Recursive and non-recursive binds are handled in essentially the same
87 way: because of uniques there are no scoping issues left. The only
88 difference is that non-recursive bindings can bind primitive values.
90 Even for non-recursive binding groups we add typings for each binder
91 to the LVE for the following reason. When each individual binding is
92 checked the type of its LHS is unified with that of its RHS; and
93 type-checking the LHS of course requires that the binder is in scope.
95 At the top-level the LIE is sure to contain nothing but constant
96 dictionaries, which we resolve at the module level.
99 tcTopBindsAndThen, tcBindsAndThen
100 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
102 -> TcM s (thing, LIE)
103 -> TcM s (thing, LIE)
105 tcTopBindsAndThen = tc_binds_and_then TopLevel
106 tcBindsAndThen = tc_binds_and_then NotTopLevel
108 tc_binds_and_then top_lvl combiner EmptyBinds do_next
110 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
113 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
114 = tc_binds_and_then top_lvl combiner b1 $
115 tc_binds_and_then top_lvl combiner b2 $
118 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
119 = -- TYPECHECK THE SIGNATURES
120 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
122 tcBindWithSigs top_lvl bind tc_ty_sigs
123 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
125 -- Extend the environment to bind the new polymorphic Ids
126 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
128 -- Build bindings and IdInfos corresponding to user pragmas
129 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
131 -- Now do whatever happens next, in the augmented envt
132 do_next `thenTc` \ (thing, thing_lie) ->
134 -- Create specialisations of functions bound here
135 -- We want to keep non-recursive things non-recursive
136 -- so that we desugar unboxed bindings correctly
137 case (top_lvl, is_rec) of
139 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
140 -- All the top level things are rec'd together anyway, so it's fine to
141 -- leave them to the tcSimplifyTop, and quite a bit faster too
143 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
144 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
146 (NotTopLevel, NonRecursive)
147 -> bindInstsOfLocalFuns
148 (thing_lie `plusLIE` prag_lie)
149 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
152 combiner NonRecursive poly_binds $
153 combiner NonRecursive prag_binds $
154 combiner Recursive lie_binds $
155 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
156 -- aren't guaranteed in dependency order (though we could change
157 -- that); hence the Recursive marker.
160 thing_lie' `plusLIE` poly_lie
163 (NotTopLevel, Recursive)
164 -> bindInstsOfLocalFuns
165 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
166 poly_ids `thenTc` \ (final_lie, lie_binds) ->
170 poly_binds `andMonoBinds`
171 lie_binds `andMonoBinds`
177 An aside. The original version of @tcBindsAndThen@ which lacks a
178 combiner function, appears below. Though it is perfectly well
179 behaved, it cannot be typed by Haskell, because the recursive call is
180 at a different type to the definition itself. There aren't too many
181 examples of this, which is why I thought it worth preserving! [SLPJ]
186 % -> TcM s (thing, LIE, thing_ty))
187 % -> TcM s ((TcHsBinds, thing), LIE, thing_ty)
189 % tcBindsAndThen EmptyBinds do_next
190 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
191 % returnTc ((EmptyBinds, thing), lie, thing_ty)
193 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
194 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
195 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
197 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
199 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
200 % = tcBindAndThen bind sigs do_next
204 %************************************************************************
206 \subsection{tcBindWithSigs}
208 %************************************************************************
210 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
211 so all the clever stuff is in here.
213 * binder_names and mbind must define the same set of Names
215 * The Names in tc_ty_sigs must be a subset of binder_names
217 * The Ids in tc_ty_sigs don't necessarily have to have the same name
218 as the Name in the tc_ty_sig
225 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
227 -> TcM s (TcMonoBinds, LIE, [TcId])
229 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
231 -- If typechecking the binds fails, then return with each
232 -- signature-less binder given type (forall a.a), to minimise subsequent
234 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
236 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
237 binder_names = map fst (bagToList (collectMonoBinders mbind))
238 poly_ids = map mk_dummy binder_names
239 mk_dummy name = case maybeSig tc_ty_sigs name of
240 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
241 Nothing -> mkVanillaId name forall_a_a -- No signature
243 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
246 -- TYPECHECK THE BINDINGS
247 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
249 -- CHECK THAT THE SIGNATURES MATCH
250 -- (must do this before getTyVarsToGen)
251 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
253 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
254 -- The tyvars_not_to_gen are free in the environment, and hence
255 -- candidates for generalisation, but sometimes the monomorphism
256 -- restriction means we can't generalise them nevertheless
258 mono_id_tys = map idType mono_ids
260 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
262 -- Finally, zonk the generalised type variables to real TyVars
263 -- This commits any unbound kind variables to boxed kind
264 -- I'm a little worried that such a kind variable might be
265 -- free in the environment, but I don't think it's possible for
266 -- this to happen when the type variable is not free in the envt
267 -- (which it isn't). SLPJ Nov 98
268 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
270 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
271 -- It's important that the final list
272 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
273 -- zonked, *including boxity*, because they'll be included in the forall types of
274 -- the polymorphic Ids, and instances of these Ids will be generated from them.
276 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
277 -- real_tyvars_to_gen
281 tcExtendGlobalTyVars tyvars_not_to_gen (
282 if null real_tyvars_to_gen_list then
283 -- No polymorphism, so no need to simplify context
284 returnTc (lie_req, EmptyMonoBinds, [])
286 case maybe_sig_theta of
288 -- No signatures, so just simplify the lie
289 -- NB: no signatures => no polymorphic recursion, so no
290 -- need to use lie_avail (which will be empty anyway)
291 tcSimplify (text "tcBinds1" <+> ppr binder_names)
292 top_lvl real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
293 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
295 Just (sig_theta, lie_avail) ->
296 -- There are signatures, and their context is sig_theta
297 -- Furthermore, lie_avail is an LIE containing the 'method insts'
298 -- for the things bound here
300 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
301 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
302 -- It's important that sig_theta is zonked, because
303 -- dict_id is later used to form the type of the polymorphic thing,
304 -- and forall-types must be zonked so far as their bound variables
308 -- The "givens" is the stuff available. We get that from
309 -- the context of the type signature, BUT ALSO the lie_avail
310 -- so that polymorphic recursion works right (see comments at end of fn)
311 givens = dicts_sig `plusLIE` lie_avail
314 -- Check that the needed dicts can be expressed in
315 -- terms of the signature ones
316 tcAddErrCtxt (bindSigsCtxt tysig_names) $
318 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
319 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
321 returnTc (lie_free, dict_binds, dict_ids)
323 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
325 -- GET THE FINAL MONO_ID_TYS
326 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
329 -- CHECK FOR BOGUS UNPOINTED BINDINGS
330 (if any isUnLiftedType zonked_mono_id_types then
331 -- Unlifted bindings must be non-recursive,
332 -- not top level, and non-polymorphic
333 checkTc (isNotTopLevel top_lvl)
334 (unliftedBindErr "Top-level" mbind) `thenTc_`
335 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
336 (unliftedBindErr "Recursive" mbind) `thenTc_`
337 checkTc (null real_tyvars_to_gen_list)
338 (unliftedBindErr "Polymorphic" mbind)
343 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
344 -- The instCantBeGeneralised stuff in tcSimplify should have
345 -- already raised an error if we're trying to generalise an
346 -- unboxed tyvar (NB: unboxed tyvars are always introduced
347 -- along with a class constraint) and it's better done there
348 -- because we have more precise origin information.
349 -- That's why we just use an ASSERT here.
352 -- BUILD THE POLYMORPHIC RESULT IDs
353 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
355 exports = zipWith mk_export binder_names zonked_mono_ids
356 dict_tys = map idType dicts_bound
358 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
359 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
360 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
361 -- "INLINE n foo" means inline foo, but not until at least phase n
362 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
363 -- then only if it is small enough etc.
364 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
365 -- See comments in CoreUnfold.blackListed for the Authorised Version
367 mk_export binder_name zonked_mono_id
369 attachNoInlinePrag no_inlines poly_id,
373 case maybeSig tc_ty_sigs binder_name of
374 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
375 (sig_tyvars, sig_poly_id)
376 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
378 new_poly_id = mkVanillaId binder_name poly_ty
379 poly_ty = mkForAllTys real_tyvars_to_gen_list
381 $ idType (zonked_mono_id)
382 -- It's important to build a fully-zonked poly_ty, because
383 -- we'll slurp out its free type variables when extending the
384 -- local environment (tcExtendLocalValEnv); if it's not zonked
385 -- it appears to have free tyvars that aren't actually free
388 pat_binders :: [Name]
389 pat_binders = map fst $ bagToList $ collectMonoBinders $
390 (justPatBindings mbind EmptyMonoBinds)
392 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
393 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
394 && isUnboxedType (idType id)))
395 (unboxedPatBindErr id)) zonked_mono_ids
400 AbsBinds real_tyvars_to_gen_list
404 (dict_binds `andMonoBinds` mbind'),
406 [poly_id | (_, poly_id, _) <- exports]
409 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
410 is_unrestricted = isUnRestrictedGroup tysig_names mbind
412 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
413 justPatBindings (AndMonoBinds b1 b2) binds =
414 justPatBindings b1 (justPatBindings b2 binds)
415 justPatBindings other_bind binds = binds
417 attachNoInlinePrag no_inlines bndr
418 = case lookupFM no_inlines (idName bndr) of
419 Just prag -> bndr `setInlinePragma` prag
423 Polymorphic recursion
424 ~~~~~~~~~~~~~~~~~~~~~
425 The game plan for polymorphic recursion in the code above is
427 * Bind any variable for which we have a type signature
428 to an Id with a polymorphic type. Then when type-checking
429 the RHSs we'll make a full polymorphic call.
431 This fine, but if you aren't a bit careful you end up with a horrendous
432 amount of partial application and (worse) a huge space leak. For example:
434 f :: Eq a => [a] -> [a]
437 If we don't take care, after typechecking we get
439 f = /\a -> \d::Eq a -> let f' = f a d
443 Notice the the stupid construction of (f a d), which is of course
444 identical to the function we're executing. In this case, the
445 polymorphic recursion isn't being used (but that's a very common case).
448 f = /\a -> \d::Eq a -> letrec
449 fm = \ys:[a] -> ...fm...
453 This can lead to a massive space leak, from the following top-level defn
459 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
460 f' is another thunk which evaluates to the same thing... and you end
461 up with a chain of identical values all hung onto by the CAF ff.
465 = let f' = f Int dEqInt in \ys. ...f'...
467 = let f' = let f' = f Int dEqInt in \ys. ...f'...
471 Solution: when typechecking the RHSs we always have in hand the
472 *monomorphic* Ids for each binding. So we just need to make sure that
473 if (Method f a d) shows up in the constraints emerging from (...f...)
474 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
475 to the "givens" when simplifying constraints. That's what the "lies_avail"
479 %************************************************************************
481 \subsection{getTyVarsToGen}
483 %************************************************************************
485 @getTyVarsToGen@ decides what type variables generalise over.
487 For a "restricted group" -- see the monomorphism restriction
488 for a definition -- we bind no dictionaries, and
489 remove from tyvars_to_gen any constrained type variables
491 *Don't* simplify dicts at this point, because we aren't going
492 to generalise over these dicts. By the time we do simplify them
493 we may well know more. For example (this actually came up)
495 f x = array ... xs where xs = [1,2,3,4,5]
496 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
497 stuff. If we simplify only at the f-binding (not the xs-binding)
498 we'll know that the literals are all Ints, and we can just produce
501 Find all the type variables involved in overloading, the
502 "constrained_tyvars". These are the ones we *aren't* going to
503 generalise. We must be careful about doing this:
505 (a) If we fail to generalise a tyvar which is not actually
506 constrained, then it will never, ever get bound, and lands
507 up printed out in interface files! Notorious example:
508 instance Eq a => Eq (Foo a b) where ..
509 Here, b is not constrained, even though it looks as if it is.
510 Another, more common, example is when there's a Method inst in
511 the LIE, whose type might very well involve non-overloaded
514 (b) On the other hand, we mustn't generalise tyvars which are constrained,
515 because we are going to pass on out the unmodified LIE, with those
516 tyvars in it. They won't be in scope if we've generalised them.
518 So we are careful, and do a complete simplification just to find the
519 constrained tyvars. We don't use any of the results, except to
520 find which tyvars are constrained.
523 getTyVarsToGen is_unrestricted mono_id_tys lie
524 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
525 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
527 tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
531 returnNF_Tc (emptyVarSet, tyvars_to_gen)
533 -- This recover and discard-errs is to avoid duplicate error
534 -- messages; this, after all, is an "extra" call to tcSimplify
535 recoverNF_Tc (returnNF_Tc (emptyVarSet, tyvars_to_gen)) $
538 tcSimplify (text "getTVG") NotTopLevel tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
540 -- ASSERT: dicts_sig is already zonked!
541 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
542 reduced_tyvars_to_gen = tyvars_to_gen `minusVarSet` constrained_tyvars
544 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
549 isUnRestrictedGroup :: [Name] -- Signatures given for these
553 is_elem v vs = isIn "isUnResMono" v vs
555 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
556 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
557 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
558 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
559 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
560 isUnRestrictedGroup sigs mb2
561 isUnRestrictedGroup sigs EmptyMonoBinds = True
565 %************************************************************************
567 \subsection{tcMonoBind}
569 %************************************************************************
571 @tcMonoBinds@ deals with a single @MonoBind@.
572 The signatures have been dealt with already.
575 tcMonoBinds :: RenamedMonoBinds
578 -> TcM s (TcMonoBinds,
580 [Name], -- Bound names
581 [TcId]) -- Corresponding monomorphic bound things
583 tcMonoBinds mbinds tc_ty_sigs is_rec
584 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
586 tv_list = bagToList tvs
587 id_list = bagToList ids
588 (names, mono_ids) = unzip id_list
590 -- This last defn is the key one:
591 -- extend the val envt with bindings for the
592 -- things bound in this group, overriding the monomorphic
593 -- ids with the polymorphic ones from the pattern
594 extra_val_env = case is_rec of
595 Recursive -> map mk_bind id_list
598 -- Don't know how to deal with pattern-bound existentials yet
599 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
600 (existentialExplode mbinds) `thenTc_`
602 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
603 -- extend the envt with bindings for all the bound ids;
604 -- and *then* override with the polymorphic Ids from the signatures
605 -- That is the whole point of the "complete_it" stuff.
607 -- There's a further wrinkle: we have to delay extending the environment
608 -- until after we've dealt with any pattern-bound signature type variables
609 -- Consider f (x::a) = ...f...
610 -- We're going to check that a isn't unified with anything in the envt,
611 -- so f itself had better not be! So we pass the envt binding f into
612 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
613 -- dealing with the signature tyvars
615 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
617 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
620 -- This function is used when dealing with a LHS binder; we make a monomorphic
621 -- version of the Id. We check for type signatures
622 tc_pat_bndr name pat_ty
623 = case maybeSig tc_ty_sigs name of
625 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
627 Just (TySigInfo _ _ _ _ _ mono_id _ _)
628 -> tcAddSrcLoc (getSrcLoc name) $
629 unifyTauTy (idType mono_id) pat_ty `thenTc_`
632 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
633 Nothing -> (name, mono_id)
634 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
636 tc_mb_pats EmptyMonoBinds
637 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
639 tc_mb_pats (AndMonoBinds mb1 mb2)
640 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
641 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
643 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
644 complete_it2 xve `thenTc` \ (mb2', lie2) ->
645 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
647 returnTc (complete_it,
648 lie_req1 `plusLIE` lie_req2,
649 tvs1 `unionBags` tvs2,
650 ids1 `unionBags` ids2,
651 lie_avail1 `plusLIE` lie_avail2)
653 tc_mb_pats (FunMonoBind name inf matches locn)
654 = newTyVarTy boxedTypeKind `thenNF_Tc` \ bndr_ty ->
655 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
657 complete_it xve = tcAddSrcLoc locn $
658 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
659 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
661 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
663 tc_mb_pats bind@(PatMonoBind pat grhss locn)
666 -- Figure out the appropriate kind for the pattern,
667 -- and generate a suitable type variable
669 Recursive -> newTyVarTy boxedTypeKind -- Recursive, so no unboxed types
670 NonRecursive -> newTyVarTy_OpenKind -- Non-recursive, so we permit unboxed types
671 ) `thenNF_Tc` \ pat_ty ->
673 -- Now typecheck the pattern
674 -- We don't support binding fresh type variables in the
675 -- pattern of a pattern binding. For example, this is illegal:
677 -- whereas this is ok
678 -- (x::Int, y::Bool) = e
680 -- We don't check explicitly for this problem. Instead, we simply
681 -- type check the pattern with tcPat. If the pattern mentions any
682 -- fresh tyvars we simply get an out-of-scope type variable error
683 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
685 complete_it xve = tcAddSrcLoc locn $
686 tcAddErrCtxt (patMonoBindsCtxt bind) $
687 tcExtendLocalValEnv xve $
688 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
689 returnTc (PatMonoBind pat' grhss' locn, lie)
691 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
694 %************************************************************************
696 \subsection{Signatures}
698 %************************************************************************
700 @checkSigMatch@ does the next step in checking signature matching.
701 The tau-type part has already been unified. What we do here is to
702 check that this unification has not over-constrained the (polymorphic)
703 type variables of the original signature type.
705 The error message here is somewhat unsatisfactory, but it'll do for
709 checkSigMatch top_lvl binder_names mono_ids sigs
711 = -- First unify the main_id with IO t, for any old t
712 tcSetErrCtxt mainTyCheckCtxt (
713 tcLookupTyCon ioTyCon_NAME `thenTc` \ ioTyCon ->
714 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
715 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
716 (idType main_mono_id)
719 -- Now check the signatures
720 -- Must do this after the unification with IO t,
721 -- in case of a silly signature like
722 -- main :: forall a. a
723 -- The unification to IO t will bind the type variable 'a',
724 -- which is just waht check_one_sig looks for
725 mapTc check_one_sig sigs `thenTc_`
726 mapTc check_main_ctxt sigs `thenTc_`
728 returnTc (Just ([], emptyLIE))
731 = mapTc check_one_sig sigs `thenTc_`
732 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
733 returnTc (Just (theta1, sig_lie))
736 = returnTc Nothing -- No constraints from type sigs
739 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
741 sig1_dict_tys = mk_dict_tys theta1
742 n_sig1_dict_tys = length sig1_dict_tys
743 sig_lie = mkLIE [inst | TySigInfo _ _ _ _ _ _ inst _ <- sigs]
745 maybe_main = find_main top_lvl binder_names mono_ids
746 main_bound_here = maybeToBool maybe_main
747 Just main_mono_id = maybe_main
749 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
750 -- Doesn't affect substitution
751 check_one_sig (TySigInfo _ id sig_tyvars _ sig_tau _ _ src_loc)
752 = tcAddSrcLoc src_loc $
753 tcAddErrCtxtM (sigCtxt (sig_msg id) (idType id)) $
754 checkSigTyVars sig_tyvars
757 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
758 -- The type signatures on a mutually-recursive group of definitions
759 -- must all have the same context (or none).
761 -- We unify them because, with polymorphic recursion, their types
762 -- might not otherwise be related. This is a rather subtle issue.
764 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
765 = tcAddSrcLoc src_loc $
766 tcAddErrCtxt (sigContextsCtxt id1 id) $
767 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
768 sigContextsErr `thenTc_`
769 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
771 this_sig_dict_tys = mk_dict_tys theta
773 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
774 -- the signature contexts are empty (what a bore)
775 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
776 = tcAddSrcLoc src_loc $
777 checkTc (null theta) (mainContextsErr id)
779 mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
781 sig_msg id tidy_ty = sep [ptext SLIT("When checking the type signature"),
782 nest 4 (ppr id <+> dcolon <+> ppr tidy_ty)]
784 -- Search for Main.main in the binder_names, return corresponding mono_id
785 find_main NotTopLevel binder_names mono_ids = Nothing
786 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
788 go (n:ns) (m:ms) | n == main_NAME = Just m
789 | otherwise = go ns ms
793 %************************************************************************
795 \subsection{SPECIALIZE pragmas}
797 %************************************************************************
799 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
800 pragmas. It is convenient for them to appear in the @[RenamedSig]@
801 part of a binding because then the same machinery can be used for
802 moving them into place as is done for type signatures.
807 f :: Ord a => [a] -> b -> b
808 {-# SPECIALIZE f :: [Int] -> b -> b #-}
811 For this we generate:
813 f* = /\ b -> let d1 = ...
817 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
818 retain a right-hand-side that the simplifier will otherwise discard as
819 dead code... the simplifier has a flag that tells it not to discard
820 SpecPragmaId bindings.
822 In this case the f* retains a call-instance of the overloaded
823 function, f, (including appropriate dictionaries) so that the
824 specialiser will subsequently discover that there's a call of @f@ at
825 Int, and will create a specialisation for @f@. After that, the
826 binding for @f*@ can be discarded.
828 We used to have a form
829 {-# SPECIALISE f :: <type> = g #-}
830 which promised that g implemented f at <type>, but we do that with
832 {-# SPECIALISE (f::<type) = g #-}
835 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
836 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
837 = -- SPECIALISE f :: forall b. theta => tau = g
838 tcAddSrcLoc src_loc $
839 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
841 -- Get and instantiate its alleged specialised type
842 tcHsType poly_ty `thenTc` \ sig_ty ->
844 -- Check that f has a more general type, and build a RHS for
845 -- the spec-pragma-id at the same time
846 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
848 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
849 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
851 -- Just specialise "f" by building a SpecPragmaId binding
852 -- It is the thing that makes sure we don't prematurely
853 -- dead-code-eliminate the binding we are really interested in.
854 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
856 -- Do the rest and combine
857 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
858 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
859 lie_rest `plusLIE` spec_lie1)
861 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
862 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
866 %************************************************************************
868 \subsection[TcBinds-errors]{Error contexts and messages}
870 %************************************************************************
874 patMonoBindsCtxt bind
875 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
877 -----------------------------------------------
879 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
880 nest 4 (ppr v <+> dcolon <+> ppr ty)]
882 -----------------------------------------------
883 notAsPolyAsSigErr sig_tau mono_tyvars
884 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
885 4 (vcat [text "Can't for-all the type variable(s)" <+>
886 pprQuotedList mono_tyvars,
887 text "in the type" <+> quotes (ppr sig_tau)
890 -----------------------------------------------
891 badMatchErr sig_ty inferred_ty
892 = hang (ptext SLIT("Type signature doesn't match inferred type"))
893 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
894 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
897 -----------------------------------------------
899 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
902 -----------------------------------------------
904 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
906 -----------------------------------------------
908 = ptext SLIT("Mismatched contexts")
910 sigContextsCtxt s1 s2
911 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
912 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
913 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
916 | getName id == main_NAME = ptext SLIT("Main.main cannot be overloaded")
918 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
919 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
922 = hsep [ptext SLIT("When checking that"), quotes (ppr main_NAME),
923 ptext SLIT("has the required type")]
925 -----------------------------------------------
926 unliftedBindErr flavour mbind
927 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
930 existentialExplode mbinds
931 = hang (vcat [text "My brain just exploded.",
932 text "I can't handle pattern bindings for existentially-quantified constructors.",
933 text "In the binding group"])