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 TcImprove ( tcImprove )
32 import TcMonoType ( tcHsType, checkSigTyVars,
33 TcSigInfo(..), tcTySig, maybeSig, sigCtxt
35 import TcPat ( tcPat )
36 import TcSimplify ( bindInstsOfLocalFuns )
37 import TcType ( TcType, TcThetaType,
39 newTyVarTy, newTyVar, newTyVarTy_OpenKind, tcInstTcType,
40 zonkTcType, zonkTcTypes, zonkTcThetaType, zonkTcTyVarToTyVar
42 import TcUnify ( unifyTauTy, unifyTauTyLists )
44 import PrelInfo ( main_NAME, ioTyCon_NAME )
46 import Id ( Id, mkVanillaId, setInlinePragma )
47 import Var ( idType, idName )
48 import IdInfo ( IdInfo, vanillaIdInfo, setInlinePragInfo, InlinePragInfo(..) )
49 import Name ( Name, getName, getOccName, getSrcLoc )
51 import Type ( mkTyVarTy, tyVarsOfTypes, mkTyConApp,
52 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar,
53 mkDictTy, splitRhoTy, mkForAllTy, isUnLiftedType,
54 isUnboxedType, unboxedTypeKind, boxedTypeKind
56 import Var ( TyVar, tyVarKind )
60 import Maybes ( maybeToBool )
61 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNotTopLevel )
62 import FiniteMap ( listToFM, lookupFM )
63 import SrcLoc ( SrcLoc )
68 %************************************************************************
70 \subsection{Type-checking bindings}
72 %************************************************************************
74 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
75 it needs to know something about the {\em usage} of the things bound,
76 so that it can create specialisations of them. So @tcBindsAndThen@
77 takes a function which, given an extended environment, E, typechecks
78 the scope of the bindings returning a typechecked thing and (most
79 important) an LIE. It is this LIE which is then used as the basis for
80 specialising the things bound.
82 @tcBindsAndThen@ also takes a "combiner" which glues together the
83 bindings and the "thing" to make a new "thing".
85 The real work is done by @tcBindWithSigsAndThen@.
87 Recursive and non-recursive binds are handled in essentially the same
88 way: because of uniques there are no scoping issues left. The only
89 difference is that non-recursive bindings can bind primitive values.
91 Even for non-recursive binding groups we add typings for each binder
92 to the LVE for the following reason. When each individual binding is
93 checked the type of its LHS is unified with that of its RHS; and
94 type-checking the LHS of course requires that the binder is in scope.
96 At the top-level the LIE is sure to contain nothing but constant
97 dictionaries, which we resolve at the module level.
100 tcTopBindsAndThen, tcBindsAndThen
101 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
103 -> TcM s (thing, LIE)
104 -> TcM s (thing, LIE)
106 tcTopBindsAndThen = tc_binds_and_then TopLevel
107 tcBindsAndThen = tc_binds_and_then NotTopLevel
109 tc_binds_and_then top_lvl combiner EmptyBinds do_next
111 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
114 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
115 = tc_binds_and_then top_lvl combiner b1 $
116 tc_binds_and_then top_lvl combiner b2 $
119 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
120 = -- TYPECHECK THE SIGNATURES
121 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
123 tcBindWithSigs top_lvl bind tc_ty_sigs
124 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
126 -- Extend the environment to bind the new polymorphic Ids
127 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
129 -- Build bindings and IdInfos corresponding to user pragmas
130 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
132 -- Now do whatever happens next, in the augmented envt
133 do_next `thenTc` \ (thing, thing_lie) ->
135 -- Create specialisations of functions bound here
136 -- We want to keep non-recursive things non-recursive
137 -- so that we desugar unboxed bindings correctly
138 case (top_lvl, is_rec) of
140 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
141 -- All the top level things are rec'd together anyway, so it's fine to
142 -- leave them to the tcSimplifyTop, and quite a bit faster too
144 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
145 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
147 (NotTopLevel, NonRecursive)
148 -> bindInstsOfLocalFuns
149 (thing_lie `plusLIE` prag_lie)
150 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
153 combiner NonRecursive poly_binds $
154 combiner NonRecursive prag_binds $
155 combiner Recursive lie_binds $
156 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
157 -- aren't guaranteed in dependency order (though we could change
158 -- that); hence the Recursive marker.
161 thing_lie' `plusLIE` poly_lie
164 (NotTopLevel, Recursive)
165 -> bindInstsOfLocalFuns
166 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
167 poly_ids `thenTc` \ (final_lie, lie_binds) ->
171 poly_binds `andMonoBinds`
172 lie_binds `andMonoBinds`
178 An aside. The original version of @tcBindsAndThen@ which lacks a
179 combiner function, appears below. Though it is perfectly well
180 behaved, it cannot be typed by Haskell, because the recursive call is
181 at a different type to the definition itself. There aren't too many
182 examples of this, which is why I thought it worth preserving! [SLPJ]
187 % -> TcM s (thing, LIE, thing_ty))
188 % -> TcM s ((TcHsBinds, thing), LIE, thing_ty)
190 % tcBindsAndThen EmptyBinds do_next
191 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
192 % returnTc ((EmptyBinds, thing), lie, thing_ty)
194 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
195 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
196 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
198 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
200 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
201 % = tcBindAndThen bind sigs do_next
205 %************************************************************************
207 \subsection{tcBindWithSigs}
209 %************************************************************************
211 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
212 so all the clever stuff is in here.
214 * binder_names and mbind must define the same set of Names
216 * The Names in tc_ty_sigs must be a subset of binder_names
218 * The Ids in tc_ty_sigs don't necessarily have to have the same name
219 as the Name in the tc_ty_sig
226 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
228 -> TcM s (TcMonoBinds, LIE, [TcId])
230 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
232 -- If typechecking the binds fails, then return with each
233 -- signature-less binder given type (forall a.a), to minimise subsequent
235 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
237 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
238 binder_names = map fst (bagToList (collectMonoBinders mbind))
239 poly_ids = map mk_dummy binder_names
240 mk_dummy name = case maybeSig tc_ty_sigs name of
241 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
242 Nothing -> mkVanillaId name forall_a_a -- No signature
244 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
247 -- TYPECHECK THE BINDINGS
248 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
250 -- CHECK THAT THE SIGNATURES MATCH
251 -- (must do this before getTyVarsToGen)
252 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
255 -- Force any unifications dictated by functional dependencies.
256 -- Because unification may happen, it's important that this step
258 -- - computing vars over which to quantify
259 -- - zonking the generalized type vars
260 tcImprove lie_req `thenTc_`
262 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
263 -- The tyvars_not_to_gen are free in the environment, and hence
264 -- candidates for generalisation, but sometimes the monomorphism
265 -- restriction means we can't generalise them nevertheless
267 mono_id_tys = map idType mono_ids
269 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
271 -- Finally, zonk the generalised type variables to real TyVars
272 -- This commits any unbound kind variables to boxed kind
273 -- I'm a little worried that such a kind variable might be
274 -- free in the environment, but I don't think it's possible for
275 -- this to happen when the type variable is not free in the envt
276 -- (which it isn't). SLPJ Nov 98
277 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
279 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
280 -- It's important that the final list
281 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
282 -- zonked, *including boxity*, because they'll be included in the forall types of
283 -- the polymorphic Ids, and instances of these Ids will be generated from them.
285 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
286 -- real_tyvars_to_gen
290 tcExtendGlobalTyVars tyvars_not_to_gen (
291 if null real_tyvars_to_gen_list then
292 -- No polymorphism, so no need to simplify context
293 returnTc (lie_req, EmptyMonoBinds, [])
295 case maybe_sig_theta of
297 -- No signatures, so just simplify the lie
298 -- NB: no signatures => no polymorphic recursion, so no
299 -- need to use lie_avail (which will be empty anyway)
300 tcSimplify (text "tcBinds1" <+> ppr binder_names)
301 top_lvl real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
302 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
304 Just (sig_theta, lie_avail) ->
305 -- There are signatures, and their context is sig_theta
306 -- Furthermore, lie_avail is an LIE containing the 'method insts'
307 -- for the things bound here
309 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
310 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
311 -- It's important that sig_theta is zonked, because
312 -- dict_id is later used to form the type of the polymorphic thing,
313 -- and forall-types must be zonked so far as their bound variables
317 -- The "givens" is the stuff available. We get that from
318 -- the context of the type signature, BUT ALSO the lie_avail
319 -- so that polymorphic recursion works right (see comments at end of fn)
320 givens = dicts_sig `plusLIE` lie_avail
323 -- Check that the needed dicts can be expressed in
324 -- terms of the signature ones
325 tcAddErrCtxt (bindSigsCtxt tysig_names) $
327 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
328 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
330 returnTc (lie_free, dict_binds, dict_ids)
332 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
334 -- GET THE FINAL MONO_ID_TYS
335 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
338 -- CHECK FOR BOGUS UNPOINTED BINDINGS
339 (if any isUnLiftedType zonked_mono_id_types then
340 -- Unlifted bindings must be non-recursive,
341 -- not top level, and non-polymorphic
342 checkTc (isNotTopLevel top_lvl)
343 (unliftedBindErr "Top-level" mbind) `thenTc_`
344 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
345 (unliftedBindErr "Recursive" mbind) `thenTc_`
346 checkTc (null real_tyvars_to_gen_list)
347 (unliftedBindErr "Polymorphic" mbind)
352 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
353 -- The instCantBeGeneralised stuff in tcSimplify should have
354 -- already raised an error if we're trying to generalise an
355 -- unboxed tyvar (NB: unboxed tyvars are always introduced
356 -- along with a class constraint) and it's better done there
357 -- because we have more precise origin information.
358 -- That's why we just use an ASSERT here.
361 -- BUILD THE POLYMORPHIC RESULT IDs
362 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
364 exports = zipWith mk_export binder_names zonked_mono_ids
365 dict_tys = map idType dicts_bound
367 inlines = mkNameSet [name | InlineSig name _ loc <- inline_sigs]
368 no_inlines = listToFM ([(name, IMustNotBeINLINEd False phase) | NoInlineSig name phase loc <- inline_sigs] ++
369 [(name, IMustNotBeINLINEd True phase) | InlineSig name phase loc <- inline_sigs, maybeToBool phase])
370 -- "INLINE n foo" means inline foo, but not until at least phase n
371 -- "NOINLINE n foo" means don't inline foo until at least phase n, and even
372 -- then only if it is small enough etc.
373 -- "NOINLINE foo" means don't inline foo ever, which we signal with a (IMustNotBeINLINEd Nothing)
374 -- See comments in CoreUnfold.blackListed for the Authorised Version
376 mk_export binder_name zonked_mono_id
378 attachNoInlinePrag no_inlines poly_id,
382 case maybeSig tc_ty_sigs binder_name of
383 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
384 (sig_tyvars, sig_poly_id)
385 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
387 new_poly_id = mkVanillaId binder_name poly_ty
388 poly_ty = mkForAllTys real_tyvars_to_gen_list
390 $ idType (zonked_mono_id)
391 -- It's important to build a fully-zonked poly_ty, because
392 -- we'll slurp out its free type variables when extending the
393 -- local environment (tcExtendLocalValEnv); if it's not zonked
394 -- it appears to have free tyvars that aren't actually free
397 pat_binders :: [Name]
398 pat_binders = map fst $ bagToList $ collectMonoBinders $
399 (justPatBindings mbind EmptyMonoBinds)
401 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
402 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
403 && isUnboxedType (idType id)))
404 (unboxedPatBindErr id)) zonked_mono_ids
409 AbsBinds real_tyvars_to_gen_list
413 (dict_binds `andMonoBinds` mbind'),
415 [poly_id | (_, poly_id, _) <- exports]
418 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
419 is_unrestricted = isUnRestrictedGroup tysig_names mbind
421 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
422 justPatBindings (AndMonoBinds b1 b2) binds =
423 justPatBindings b1 (justPatBindings b2 binds)
424 justPatBindings other_bind binds = binds
426 attachNoInlinePrag no_inlines bndr
427 = case lookupFM no_inlines (idName bndr) of
428 Just prag -> bndr `setInlinePragma` prag
432 Polymorphic recursion
433 ~~~~~~~~~~~~~~~~~~~~~
434 The game plan for polymorphic recursion in the code above is
436 * Bind any variable for which we have a type signature
437 to an Id with a polymorphic type. Then when type-checking
438 the RHSs we'll make a full polymorphic call.
440 This fine, but if you aren't a bit careful you end up with a horrendous
441 amount of partial application and (worse) a huge space leak. For example:
443 f :: Eq a => [a] -> [a]
446 If we don't take care, after typechecking we get
448 f = /\a -> \d::Eq a -> let f' = f a d
452 Notice the the stupid construction of (f a d), which is of course
453 identical to the function we're executing. In this case, the
454 polymorphic recursion isn't being used (but that's a very common case).
457 f = /\a -> \d::Eq a -> letrec
458 fm = \ys:[a] -> ...fm...
462 This can lead to a massive space leak, from the following top-level defn
468 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
469 f' is another thunk which evaluates to the same thing... and you end
470 up with a chain of identical values all hung onto by the CAF ff.
474 = let f' = f Int dEqInt in \ys. ...f'...
476 = let f' = let f' = f Int dEqInt in \ys. ...f'...
480 Solution: when typechecking the RHSs we always have in hand the
481 *monomorphic* Ids for each binding. So we just need to make sure that
482 if (Method f a d) shows up in the constraints emerging from (...f...)
483 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
484 to the "givens" when simplifying constraints. That's what the "lies_avail"
488 %************************************************************************
490 \subsection{getTyVarsToGen}
492 %************************************************************************
494 @getTyVarsToGen@ decides what type variables to generalise over.
496 For a "restricted group" -- see the monomorphism restriction
497 for a definition -- we bind no dictionaries, and
498 remove from tyvars_to_gen any constrained type variables
500 *Don't* simplify dicts at this point, because we aren't going
501 to generalise over these dicts. By the time we do simplify them
502 we may well know more. For example (this actually came up)
504 f x = array ... xs where xs = [1,2,3,4,5]
505 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
506 stuff. If we simplify only at the f-binding (not the xs-binding)
507 we'll know that the literals are all Ints, and we can just produce
510 Find all the type variables involved in overloading, the
511 "constrained_tyvars". These are the ones we *aren't* going to
512 generalise. We must be careful about doing this:
514 (a) If we fail to generalise a tyvar which is not actually
515 constrained, then it will never, ever get bound, and lands
516 up printed out in interface files! Notorious example:
517 instance Eq a => Eq (Foo a b) where ..
518 Here, b is not constrained, even though it looks as if it is.
519 Another, more common, example is when there's a Method inst in
520 the LIE, whose type might very well involve non-overloaded
523 (b) On the other hand, we mustn't generalise tyvars which are constrained,
524 because we are going to pass on out the unmodified LIE, with those
525 tyvars in it. They won't be in scope if we've generalised them.
527 So we are careful, and do a complete simplification just to find the
528 constrained tyvars. We don't use any of the results, except to
529 find which tyvars are constrained.
532 getTyVarsToGen is_unrestricted mono_id_tys lie
533 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
534 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
536 tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
540 returnNF_Tc (emptyVarSet, tyvars_to_gen)
542 -- This recover and discard-errs is to avoid duplicate error
543 -- messages; this, after all, is an "extra" call to tcSimplify
544 recoverNF_Tc (returnNF_Tc (emptyVarSet, tyvars_to_gen)) $
547 tcSimplify (text "getTVG") NotTopLevel tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
549 -- ASSERT: dicts_sig is already zonked!
550 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
551 reduced_tyvars_to_gen = tyvars_to_gen `minusVarSet` constrained_tyvars
553 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
558 isUnRestrictedGroup :: [Name] -- Signatures given for these
562 is_elem v vs = isIn "isUnResMono" v vs
564 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
565 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
566 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
567 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
568 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
569 isUnRestrictedGroup sigs mb2
570 isUnRestrictedGroup sigs EmptyMonoBinds = True
574 %************************************************************************
576 \subsection{tcMonoBind}
578 %************************************************************************
580 @tcMonoBinds@ deals with a single @MonoBind@.
581 The signatures have been dealt with already.
584 tcMonoBinds :: RenamedMonoBinds
587 -> TcM s (TcMonoBinds,
589 [Name], -- Bound names
590 [TcId]) -- Corresponding monomorphic bound things
592 tcMonoBinds mbinds tc_ty_sigs is_rec
593 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
595 tv_list = bagToList tvs
596 id_list = bagToList ids
597 (names, mono_ids) = unzip id_list
599 -- This last defn is the key one:
600 -- extend the val envt with bindings for the
601 -- things bound in this group, overriding the monomorphic
602 -- ids with the polymorphic ones from the pattern
603 extra_val_env = case is_rec of
604 Recursive -> map mk_bind id_list
607 -- Don't know how to deal with pattern-bound existentials yet
608 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
609 (existentialExplode mbinds) `thenTc_`
611 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
612 -- extend the envt with bindings for all the bound ids;
613 -- and *then* override with the polymorphic Ids from the signatures
614 -- That is the whole point of the "complete_it" stuff.
616 -- There's a further wrinkle: we have to delay extending the environment
617 -- until after we've dealt with any pattern-bound signature type variables
618 -- Consider f (x::a) = ...f...
619 -- We're going to check that a isn't unified with anything in the envt,
620 -- so f itself had better not be! So we pass the envt binding f into
621 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
622 -- dealing with the signature tyvars
624 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
626 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
629 -- This function is used when dealing with a LHS binder; we make a monomorphic
630 -- version of the Id. We check for type signatures
631 tc_pat_bndr name pat_ty
632 = case maybeSig tc_ty_sigs name of
634 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
636 Just (TySigInfo _ _ _ _ _ mono_id _ _)
637 -> tcAddSrcLoc (getSrcLoc name) $
638 unifyTauTy (idType mono_id) pat_ty `thenTc_`
641 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
642 Nothing -> (name, mono_id)
643 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
645 tc_mb_pats EmptyMonoBinds
646 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
648 tc_mb_pats (AndMonoBinds mb1 mb2)
649 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
650 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
652 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
653 complete_it2 xve `thenTc` \ (mb2', lie2) ->
654 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
656 returnTc (complete_it,
657 lie_req1 `plusLIE` lie_req2,
658 tvs1 `unionBags` tvs2,
659 ids1 `unionBags` ids2,
660 lie_avail1 `plusLIE` lie_avail2)
662 tc_mb_pats (FunMonoBind name inf matches locn)
663 = newTyVarTy boxedTypeKind `thenNF_Tc` \ bndr_ty ->
664 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
666 complete_it xve = tcAddSrcLoc locn $
667 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
668 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
670 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
672 tc_mb_pats bind@(PatMonoBind pat grhss locn)
675 -- Figure out the appropriate kind for the pattern,
676 -- and generate a suitable type variable
678 Recursive -> newTyVarTy boxedTypeKind -- Recursive, so no unboxed types
679 NonRecursive -> newTyVarTy_OpenKind -- Non-recursive, so we permit unboxed types
680 ) `thenNF_Tc` \ pat_ty ->
682 -- Now typecheck the pattern
683 -- We don't support binding fresh type variables in the
684 -- pattern of a pattern binding. For example, this is illegal:
686 -- whereas this is ok
687 -- (x::Int, y::Bool) = e
689 -- We don't check explicitly for this problem. Instead, we simply
690 -- type check the pattern with tcPat. If the pattern mentions any
691 -- fresh tyvars we simply get an out-of-scope type variable error
692 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
694 complete_it xve = tcAddSrcLoc locn $
695 tcAddErrCtxt (patMonoBindsCtxt bind) $
696 tcExtendLocalValEnv xve $
697 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
698 returnTc (PatMonoBind pat' grhss' locn, lie)
700 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
703 %************************************************************************
705 \subsection{Signatures}
707 %************************************************************************
709 @checkSigMatch@ does the next step in checking signature matching.
710 The tau-type part has already been unified. What we do here is to
711 check that this unification has not over-constrained the (polymorphic)
712 type variables of the original signature type.
714 The error message here is somewhat unsatisfactory, but it'll do for
718 checkSigMatch top_lvl binder_names mono_ids sigs
720 = -- First unify the main_id with IO t, for any old t
721 tcSetErrCtxt mainTyCheckCtxt (
722 tcLookupTyCon ioTyCon_NAME `thenTc` \ ioTyCon ->
723 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
724 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
725 (idType main_mono_id)
728 -- Now check the signatures
729 -- Must do this after the unification with IO t,
730 -- in case of a silly signature like
731 -- main :: forall a. a
732 -- The unification to IO t will bind the type variable 'a',
733 -- which is just waht check_one_sig looks for
734 mapTc check_one_sig sigs `thenTc_`
735 mapTc check_main_ctxt sigs `thenTc_`
737 returnTc (Just ([], emptyLIE))
740 = mapTc check_one_sig sigs `thenTc_`
741 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
742 returnTc (Just (theta1, sig_lie))
745 = returnTc Nothing -- No constraints from type sigs
748 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
750 sig1_dict_tys = mk_dict_tys theta1
751 n_sig1_dict_tys = length sig1_dict_tys
752 sig_lie = mkLIE [inst | TySigInfo _ _ _ _ _ _ inst _ <- sigs]
754 maybe_main = find_main top_lvl binder_names mono_ids
755 main_bound_here = maybeToBool maybe_main
756 Just main_mono_id = maybe_main
758 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
759 -- Doesn't affect substitution
760 check_one_sig (TySigInfo _ id sig_tyvars _ sig_tau _ _ src_loc)
761 = tcAddSrcLoc src_loc $
762 tcAddErrCtxtM (sigCtxt (sig_msg id) (idType id)) $
763 checkSigTyVars sig_tyvars
766 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
767 -- The type signatures on a mutually-recursive group of definitions
768 -- must all have the same context (or none).
770 -- We unify them because, with polymorphic recursion, their types
771 -- might not otherwise be related. This is a rather subtle issue.
773 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
774 = tcAddSrcLoc src_loc $
775 tcAddErrCtxt (sigContextsCtxt id1 id) $
776 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
777 sigContextsErr `thenTc_`
778 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
780 this_sig_dict_tys = mk_dict_tys theta
782 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
783 -- the signature contexts are empty (what a bore)
784 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
785 = tcAddSrcLoc src_loc $
786 checkTc (null theta) (mainContextsErr id)
788 mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
790 sig_msg id tidy_ty = sep [ptext SLIT("When checking the type signature"),
791 nest 4 (ppr id <+> dcolon <+> ppr tidy_ty)]
793 -- Search for Main.main in the binder_names, return corresponding mono_id
794 find_main NotTopLevel binder_names mono_ids = Nothing
795 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
797 go (n:ns) (m:ms) | n == main_NAME = Just m
798 | otherwise = go ns ms
802 %************************************************************************
804 \subsection{SPECIALIZE pragmas}
806 %************************************************************************
808 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
809 pragmas. It is convenient for them to appear in the @[RenamedSig]@
810 part of a binding because then the same machinery can be used for
811 moving them into place as is done for type signatures.
816 f :: Ord a => [a] -> b -> b
817 {-# SPECIALIZE f :: [Int] -> b -> b #-}
820 For this we generate:
822 f* = /\ b -> let d1 = ...
826 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
827 retain a right-hand-side that the simplifier will otherwise discard as
828 dead code... the simplifier has a flag that tells it not to discard
829 SpecPragmaId bindings.
831 In this case the f* retains a call-instance of the overloaded
832 function, f, (including appropriate dictionaries) so that the
833 specialiser will subsequently discover that there's a call of @f@ at
834 Int, and will create a specialisation for @f@. After that, the
835 binding for @f*@ can be discarded.
837 We used to have a form
838 {-# SPECIALISE f :: <type> = g #-}
839 which promised that g implemented f at <type>, but we do that with
841 {-# SPECIALISE (f::<type) = g #-}
844 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
845 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
846 = -- SPECIALISE f :: forall b. theta => tau = g
847 tcAddSrcLoc src_loc $
848 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
850 -- Get and instantiate its alleged specialised type
851 tcHsType poly_ty `thenTc` \ sig_ty ->
853 -- Check that f has a more general type, and build a RHS for
854 -- the spec-pragma-id at the same time
855 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
857 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
858 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
860 -- Just specialise "f" by building a SpecPragmaId binding
861 -- It is the thing that makes sure we don't prematurely
862 -- dead-code-eliminate the binding we are really interested in.
863 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
865 -- Do the rest and combine
866 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
867 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
868 lie_rest `plusLIE` spec_lie1)
870 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
871 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
875 %************************************************************************
877 \subsection[TcBinds-errors]{Error contexts and messages}
879 %************************************************************************
883 patMonoBindsCtxt bind
884 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
886 -----------------------------------------------
888 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
889 nest 4 (ppr v <+> dcolon <+> ppr ty)]
891 -----------------------------------------------
892 notAsPolyAsSigErr sig_tau mono_tyvars
893 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
894 4 (vcat [text "Can't for-all the type variable(s)" <+>
895 pprQuotedList mono_tyvars,
896 text "in the type" <+> quotes (ppr sig_tau)
899 -----------------------------------------------
900 badMatchErr sig_ty inferred_ty
901 = hang (ptext SLIT("Type signature doesn't match inferred type"))
902 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
903 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
906 -----------------------------------------------
908 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
911 -----------------------------------------------
913 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
915 -----------------------------------------------
917 = ptext SLIT("Mismatched contexts")
919 sigContextsCtxt s1 s2
920 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
921 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
922 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
925 | getName id == main_NAME = ptext SLIT("Main.main cannot be overloaded")
927 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
928 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
931 = hsep [ptext SLIT("When checking that"), quotes (ppr main_NAME),
932 ptext SLIT("has the required type")]
934 -----------------------------------------------
935 unliftedBindErr flavour mbind
936 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
939 existentialExplode mbinds
940 = hang (vcat [text "My brain just exploded.",
941 text "I can't handle pattern bindings for existentially-quantified constructors.",
942 text "In the binding group"])