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 SrcLoc ( SrcLoc )
66 %************************************************************************
68 \subsection{Type-checking bindings}
70 %************************************************************************
72 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
73 it needs to know something about the {\em usage} of the things bound,
74 so that it can create specialisations of them. So @tcBindsAndThen@
75 takes a function which, given an extended environment, E, typechecks
76 the scope of the bindings returning a typechecked thing and (most
77 important) an LIE. It is this LIE which is then used as the basis for
78 specialising the things bound.
80 @tcBindsAndThen@ also takes a "combiner" which glues together the
81 bindings and the "thing" to make a new "thing".
83 The real work is done by @tcBindWithSigsAndThen@.
85 Recursive and non-recursive binds are handled in essentially the same
86 way: because of uniques there are no scoping issues left. The only
87 difference is that non-recursive bindings can bind primitive values.
89 Even for non-recursive binding groups we add typings for each binder
90 to the LVE for the following reason. When each individual binding is
91 checked the type of its LHS is unified with that of its RHS; and
92 type-checking the LHS of course requires that the binder is in scope.
94 At the top-level the LIE is sure to contain nothing but constant
95 dictionaries, which we resolve at the module level.
98 tcTopBindsAndThen, tcBindsAndThen
99 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
101 -> TcM s (thing, LIE)
102 -> TcM s (thing, LIE)
104 tcTopBindsAndThen = tc_binds_and_then TopLevel
105 tcBindsAndThen = tc_binds_and_then NotTopLevel
107 tc_binds_and_then top_lvl combiner EmptyBinds do_next
109 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
112 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
113 = tc_binds_and_then top_lvl combiner b1 $
114 tc_binds_and_then top_lvl combiner b2 $
117 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
118 = -- TYPECHECK THE SIGNATURES
119 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
121 tcBindWithSigs top_lvl bind tc_ty_sigs
122 sigs is_rec `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
124 -- Extend the environment to bind the new polymorphic Ids
125 tcExtendLocalValEnv [(idName poly_id, poly_id) | poly_id <- poly_ids] $
127 -- Build bindings and IdInfos corresponding to user pragmas
128 tcSpecSigs sigs `thenTc` \ (prag_binds, prag_lie) ->
130 -- Now do whatever happens next, in the augmented envt
131 do_next `thenTc` \ (thing, thing_lie) ->
133 -- Create specialisations of functions bound here
134 -- We want to keep non-recursive things non-recursive
135 -- so that we desugar unboxed bindings correctly
136 case (top_lvl, is_rec) of
138 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
139 -- All the top level things are rec'd together anyway, so it's fine to
140 -- leave them to the tcSimplifyTop, and quite a bit faster too
142 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
143 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
145 (NotTopLevel, NonRecursive)
146 -> bindInstsOfLocalFuns
147 (thing_lie `plusLIE` prag_lie)
148 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
151 combiner NonRecursive poly_binds $
152 combiner NonRecursive prag_binds $
153 combiner Recursive lie_binds $
154 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
155 -- aren't guaranteed in dependency order (though we could change
156 -- that); hence the Recursive marker.
159 thing_lie' `plusLIE` poly_lie
162 (NotTopLevel, Recursive)
163 -> bindInstsOfLocalFuns
164 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
165 poly_ids `thenTc` \ (final_lie, lie_binds) ->
169 poly_binds `andMonoBinds`
170 lie_binds `andMonoBinds`
176 An aside. The original version of @tcBindsAndThen@ which lacks a
177 combiner function, appears below. Though it is perfectly well
178 behaved, it cannot be typed by Haskell, because the recursive call is
179 at a different type to the definition itself. There aren't too many
180 examples of this, which is why I thought it worth preserving! [SLPJ]
185 % -> TcM s (thing, LIE, thing_ty))
186 % -> TcM s ((TcHsBinds, thing), LIE, thing_ty)
188 % tcBindsAndThen EmptyBinds do_next
189 % = do_next `thenTc` \ (thing, lie, thing_ty) ->
190 % returnTc ((EmptyBinds, thing), lie, thing_ty)
192 % tcBindsAndThen (ThenBinds binds1 binds2) do_next
193 % = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
194 % `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
196 % returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
198 % tcBindsAndThen (MonoBind bind sigs is_rec) do_next
199 % = tcBindAndThen bind sigs do_next
203 %************************************************************************
205 \subsection{tcBindWithSigs}
207 %************************************************************************
209 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
210 so all the clever stuff is in here.
212 * binder_names and mbind must define the same set of Names
214 * The Names in tc_ty_sigs must be a subset of binder_names
216 * The Ids in tc_ty_sigs don't necessarily have to have the same name
217 as the Name in the tc_ty_sig
224 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
226 -> TcM s (TcMonoBinds, LIE, [TcId])
228 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
230 -- If typechecking the binds fails, then return with each
231 -- signature-less binder given type (forall a.a), to minimise subsequent
233 newTyVar boxedTypeKind `thenNF_Tc` \ alpha_tv ->
235 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
236 binder_names = map fst (bagToList (collectMonoBinders mbind))
237 poly_ids = map mk_dummy binder_names
238 mk_dummy name = case maybeSig tc_ty_sigs name of
239 Just (TySigInfo _ poly_id _ _ _ _ _ _) -> poly_id -- Signature
240 Nothing -> mkVanillaId name forall_a_a -- No signature
242 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
245 -- TYPECHECK THE BINDINGS
246 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
248 -- CHECK THAT THE SIGNATURES MATCH
249 -- (must do this before getTyVarsToGen)
250 checkSigMatch top_lvl binder_names mono_ids tc_ty_sigs `thenTc` \ maybe_sig_theta ->
252 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
253 -- The tyvars_not_to_gen are free in the environment, and hence
254 -- candidates for generalisation, but sometimes the monomorphism
255 -- restriction means we can't generalise them nevertheless
257 mono_id_tys = map idType mono_ids
259 getTyVarsToGen is_unrestricted mono_id_tys lie_req `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
261 -- Finally, zonk the generalised type variables to real TyVars
262 -- This commits any unbound kind variables to boxed kind
263 -- I'm a little worried that such a kind variable might be
264 -- free in the environment, but I don't think it's possible for
265 -- this to happen when the type variable is not free in the envt
266 -- (which it isn't). SLPJ Nov 98
267 mapTc zonkTcTyVarToTyVar (varSetElems tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
269 real_tyvars_to_gen = mkVarSet real_tyvars_to_gen_list
270 -- It's important that the final list
271 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
272 -- zonked, *including boxity*, because they'll be included in the forall types of
273 -- the polymorphic Ids, and instances of these Ids will be generated from them.
275 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
276 -- real_tyvars_to_gen
280 tcExtendGlobalTyVars tyvars_not_to_gen (
281 if null real_tyvars_to_gen_list then
282 -- No polymorphism, so no need to simplify context
283 returnTc (lie_req, EmptyMonoBinds, [])
285 case maybe_sig_theta of
287 -- No signatures, so just simplify the lie
288 -- NB: no signatures => no polymorphic recursion, so no
289 -- need to use lie_avail (which will be empty anyway)
290 tcSimplify (text "tcBinds1" <+> ppr binder_names)
291 top_lvl real_tyvars_to_gen lie_req `thenTc` \ (lie_free, dict_binds, lie_bound) ->
292 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
294 Just (sig_theta, lie_avail) ->
295 -- There are signatures, and their context is sig_theta
296 -- Furthermore, lie_avail is an LIE containing the 'method insts'
297 -- for the things bound here
299 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
300 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
301 -- It's important that sig_theta is zonked, because
302 -- dict_id is later used to form the type of the polymorphic thing,
303 -- and forall-types must be zonked so far as their bound variables
307 -- The "givens" is the stuff available. We get that from
308 -- the context of the type signature, BUT ALSO the lie_avail
309 -- so that polymorphic recursion works right (see comments at end of fn)
310 givens = dicts_sig `plusLIE` lie_avail
313 -- Check that the needed dicts can be expressed in
314 -- terms of the signature ones
315 tcAddErrCtxt (bindSigsCtxt tysig_names) $
317 (ptext SLIT("type signature for") <+> pprQuotedList binder_names)
318 real_tyvars_to_gen givens lie_req `thenTc` \ (lie_free, dict_binds) ->
320 returnTc (lie_free, dict_binds, dict_ids)
322 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
324 -- GET THE FINAL MONO_ID_TYS
325 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
328 -- CHECK FOR BOGUS UNPOINTED BINDINGS
329 (if any isUnLiftedType zonked_mono_id_types then
330 -- Unlifted bindings must be non-recursive,
331 -- not top level, and non-polymorphic
332 checkTc (isNotTopLevel top_lvl)
333 (unliftedBindErr "Top-level" mbind) `thenTc_`
334 checkTc (case is_rec of {Recursive -> False; NonRecursive -> True})
335 (unliftedBindErr "Recursive" mbind) `thenTc_`
336 checkTc (null real_tyvars_to_gen_list)
337 (unliftedBindErr "Polymorphic" mbind)
342 ASSERT( not (any ((== unboxedTypeKind) . tyVarKind) real_tyvars_to_gen_list) )
343 -- The instCantBeGeneralised stuff in tcSimplify should have
344 -- already raised an error if we're trying to generalise an
345 -- unboxed tyvar (NB: unboxed tyvars are always introduced
346 -- along with a class constraint) and it's better done there
347 -- because we have more precise origin information.
348 -- That's why we just use an ASSERT here.
351 -- BUILD THE POLYMORPHIC RESULT IDs
352 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
354 exports = zipWith mk_export binder_names zonked_mono_ids
355 dict_tys = map idType dicts_bound
357 inlines = mkNameSet [name | InlineSig name loc <- inline_sigs]
358 no_inlines = mkNameSet [name | NoInlineSig name loc <- inline_sigs]
360 mk_export binder_name zonked_mono_id
362 attachNoInlinePrag no_inlines poly_id,
366 case maybeSig tc_ty_sigs binder_name of
367 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _ _ _) ->
368 (sig_tyvars, sig_poly_id)
369 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
371 new_poly_id = mkVanillaId binder_name poly_ty
372 poly_ty = mkForAllTys real_tyvars_to_gen_list
374 $ idType (zonked_mono_id)
375 -- It's important to build a fully-zonked poly_ty, because
376 -- we'll slurp out its free type variables when extending the
377 -- local environment (tcExtendLocalValEnv); if it's not zonked
378 -- it appears to have free tyvars that aren't actually free
381 pat_binders :: [Name]
382 pat_binders = map fst $ bagToList $ collectMonoBinders $
383 (justPatBindings mbind EmptyMonoBinds)
385 -- CHECK FOR UNBOXED BINDERS IN PATTERN BINDINGS
386 mapTc (\id -> checkTc (not (idName id `elem` pat_binders
387 && isUnboxedType (idType id)))
388 (unboxedPatBindErr id)) zonked_mono_ids
393 AbsBinds real_tyvars_to_gen_list
397 (dict_binds `andMonoBinds` mbind'),
399 [poly_id | (_, poly_id, _) <- exports]
402 tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- tc_ty_sigs]
403 is_unrestricted = isUnRestrictedGroup tysig_names mbind
405 justPatBindings bind@(PatMonoBind _ _ _) binds = bind `andMonoBinds` binds
406 justPatBindings (AndMonoBinds b1 b2) binds =
407 justPatBindings b1 (justPatBindings b2 binds)
408 justPatBindings other_bind binds = binds
410 attachNoInlinePrag no_inlines bndr
411 | idName bndr `elemNameSet` no_inlines = bndr `setInlinePragma` IMustNotBeINLINEd
415 Polymorphic recursion
416 ~~~~~~~~~~~~~~~~~~~~~
417 The game plan for polymorphic recursion in the code above is
419 * Bind any variable for which we have a type signature
420 to an Id with a polymorphic type. Then when type-checking
421 the RHSs we'll make a full polymorphic call.
423 This fine, but if you aren't a bit careful you end up with a horrendous
424 amount of partial application and (worse) a huge space leak. For example:
426 f :: Eq a => [a] -> [a]
429 If we don't take care, after typechecking we get
431 f = /\a -> \d::Eq a -> let f' = f a d
435 Notice the the stupid construction of (f a d), which is of course
436 identical to the function we're executing. In this case, the
437 polymorphic recursion isn't being used (but that's a very common case).
440 f = /\a -> \d::Eq a -> letrec
441 fm = \ys:[a] -> ...fm...
445 This can lead to a massive space leak, from the following top-level defn
451 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
452 f' is another thunk which evaluates to the same thing... and you end
453 up with a chain of identical values all hung onto by the CAF ff.
457 = let f' = f Int dEqInt in \ys. ...f'...
459 = let f' = let f' = f Int dEqInt in \ys. ...f'...
463 Solution: when typechecking the RHSs we always have in hand the
464 *monomorphic* Ids for each binding. So we just need to make sure that
465 if (Method f a d) shows up in the constraints emerging from (...f...)
466 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
467 to the "givens" when simplifying constraints. That's what the "lies_avail"
471 %************************************************************************
473 \subsection{getTyVarsToGen}
475 %************************************************************************
477 @getTyVarsToGen@ decides what type variables generalise over.
479 For a "restricted group" -- see the monomorphism restriction
480 for a definition -- we bind no dictionaries, and
481 remove from tyvars_to_gen any constrained type variables
483 *Don't* simplify dicts at this point, because we aren't going
484 to generalise over these dicts. By the time we do simplify them
485 we may well know more. For example (this actually came up)
487 f x = array ... xs where xs = [1,2,3,4,5]
488 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
489 stuff. If we simplify only at the f-binding (not the xs-binding)
490 we'll know that the literals are all Ints, and we can just produce
493 Find all the type variables involved in overloading, the
494 "constrained_tyvars". These are the ones we *aren't* going to
495 generalise. We must be careful about doing this:
497 (a) If we fail to generalise a tyvar which is not actually
498 constrained, then it will never, ever get bound, and lands
499 up printed out in interface files! Notorious example:
500 instance Eq a => Eq (Foo a b) where ..
501 Here, b is not constrained, even though it looks as if it is.
502 Another, more common, example is when there's a Method inst in
503 the LIE, whose type might very well involve non-overloaded
506 (b) On the other hand, we mustn't generalise tyvars which are constrained,
507 because we are going to pass on out the unmodified LIE, with those
508 tyvars in it. They won't be in scope if we've generalised them.
510 So we are careful, and do a complete simplification just to find the
511 constrained tyvars. We don't use any of the results, except to
512 find which tyvars are constrained.
515 getTyVarsToGen is_unrestricted mono_id_tys lie
516 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
517 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
519 tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusVarSet` free_tyvars
523 returnNF_Tc (emptyVarSet, tyvars_to_gen)
525 -- This recover and discard-errs is to avoid duplicate error
526 -- messages; this, after all, is an "extra" call to tcSimplify
527 recoverNF_Tc (returnNF_Tc (emptyVarSet, tyvars_to_gen)) $
530 tcSimplify (text "getTVG") NotTopLevel tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
532 -- ASSERT: dicts_sig is already zonked!
533 constrained_tyvars = foldrBag (unionVarSet . tyVarsOfInst) emptyVarSet constrained_dicts
534 reduced_tyvars_to_gen = tyvars_to_gen `minusVarSet` constrained_tyvars
536 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
541 isUnRestrictedGroup :: [Name] -- Signatures given for these
545 is_elem v vs = isIn "isUnResMono" v vs
547 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
548 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
549 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
550 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
551 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
552 isUnRestrictedGroup sigs mb2
553 isUnRestrictedGroup sigs EmptyMonoBinds = True
557 %************************************************************************
559 \subsection{tcMonoBind}
561 %************************************************************************
563 @tcMonoBinds@ deals with a single @MonoBind@.
564 The signatures have been dealt with already.
567 tcMonoBinds :: RenamedMonoBinds
570 -> TcM s (TcMonoBinds,
572 [Name], -- Bound names
573 [TcId]) -- Corresponding monomorphic bound things
575 tcMonoBinds mbinds tc_ty_sigs is_rec
576 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
578 tv_list = bagToList tvs
579 id_list = bagToList ids
580 (names, mono_ids) = unzip id_list
582 -- This last defn is the key one:
583 -- extend the val envt with bindings for the
584 -- things bound in this group, overriding the monomorphic
585 -- ids with the polymorphic ones from the pattern
586 extra_val_env = case is_rec of
587 Recursive -> map mk_bind id_list
590 -- Don't know how to deal with pattern-bound existentials yet
591 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
592 (existentialExplode mbinds) `thenTc_`
594 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
595 -- extend the envt with bindings for all the bound ids;
596 -- and *then* override with the polymorphic Ids from the signatures
597 -- That is the whole point of the "complete_it" stuff.
599 -- There's a further wrinkle: we have to delay extending the environment
600 -- until after we've dealt with any pattern-bound signature type variables
601 -- Consider f (x::a) = ...f...
602 -- We're going to check that a isn't unified with anything in the envt,
603 -- so f itself had better not be! So we pass the envt binding f into
604 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
605 -- dealing with the signature tyvars
607 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
609 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
612 -- This function is used when dealing with a LHS binder; we make a monomorphic
613 -- version of the Id. We check for type signatures
614 tc_pat_bndr name pat_ty
615 = case maybeSig tc_ty_sigs name of
617 -> newLocalId (getOccName name) pat_ty (getSrcLoc name)
619 Just (TySigInfo _ _ _ _ _ mono_id _ _)
620 -> tcAddSrcLoc (getSrcLoc name) $
621 unifyTauTy (idType mono_id) pat_ty `thenTc_`
624 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
625 Nothing -> (name, mono_id)
626 Just (TySigInfo name poly_id _ _ _ _ _ _) -> (name, poly_id)
628 tc_mb_pats EmptyMonoBinds
629 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
631 tc_mb_pats (AndMonoBinds mb1 mb2)
632 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
633 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
635 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
636 complete_it2 xve `thenTc` \ (mb2', lie2) ->
637 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
639 returnTc (complete_it,
640 lie_req1 `plusLIE` lie_req2,
641 tvs1 `unionBags` tvs2,
642 ids1 `unionBags` ids2,
643 lie_avail1 `plusLIE` lie_avail2)
645 tc_mb_pats (FunMonoBind name inf matches locn)
646 = newTyVarTy boxedTypeKind `thenNF_Tc` \ bndr_ty ->
647 tc_pat_bndr name bndr_ty `thenTc` \ bndr_id ->
649 complete_it xve = tcAddSrcLoc locn $
650 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
651 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
653 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
655 tc_mb_pats bind@(PatMonoBind pat grhss locn)
658 -- Figure out the appropriate kind for the pattern,
659 -- and generate a suitable type variable
661 Recursive -> newTyVarTy boxedTypeKind -- Recursive, so no unboxed types
662 NonRecursive -> newTyVarTy_OpenKind -- Non-recursive, so we permit unboxed types
663 ) `thenNF_Tc` \ pat_ty ->
665 -- Now typecheck the pattern
666 -- We don't support binding fresh type variables in the
667 -- pattern of a pattern binding. For example, this is illegal:
669 -- whereas this is ok
670 -- (x::Int, y::Bool) = e
672 -- We don't check explicitly for this problem. Instead, we simply
673 -- type check the pattern with tcPat. If the pattern mentions any
674 -- fresh tyvars we simply get an out-of-scope type variable error
675 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
677 complete_it xve = tcAddSrcLoc locn $
678 tcAddErrCtxt (patMonoBindsCtxt bind) $
679 tcExtendLocalValEnv xve $
680 tcGRHSs grhss pat_ty PatBindRhs `thenTc` \ (grhss', lie) ->
681 returnTc (PatMonoBind pat' grhss' locn, lie)
683 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
686 %************************************************************************
688 \subsection{Signatures}
690 %************************************************************************
692 @checkSigMatch@ does the next step in checking signature matching.
693 The tau-type part has already been unified. What we do here is to
694 check that this unification has not over-constrained the (polymorphic)
695 type variables of the original signature type.
697 The error message here is somewhat unsatisfactory, but it'll do for
701 checkSigMatch top_lvl binder_names mono_ids sigs
703 = -- First unify the main_id with IO t, for any old t
704 tcSetErrCtxt mainTyCheckCtxt (
705 tcLookupTyCon ioTyCon_NAME `thenTc` \ ioTyCon ->
706 newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
707 unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
708 (idType main_mono_id)
711 -- Now check the signatures
712 -- Must do this after the unification with IO t,
713 -- in case of a silly signature like
714 -- main :: forall a. a
715 -- The unification to IO t will bind the type variable 'a',
716 -- which is just waht check_one_sig looks for
717 mapTc check_one_sig sigs `thenTc_`
718 mapTc check_main_ctxt sigs `thenTc_`
720 returnTc (Just ([], emptyLIE))
723 = mapTc check_one_sig sigs `thenTc_`
724 mapTc check_one_ctxt all_sigs_but_first `thenTc_`
725 returnTc (Just (theta1, sig_lie))
728 = returnTc Nothing -- No constraints from type sigs
731 (TySigInfo _ id1 _ theta1 _ _ _ _ : all_sigs_but_first) = sigs
733 sig1_dict_tys = mk_dict_tys theta1
734 n_sig1_dict_tys = length sig1_dict_tys
735 sig_lie = mkLIE [inst | TySigInfo _ _ _ _ _ _ inst _ <- sigs]
737 maybe_main = find_main top_lvl binder_names mono_ids
738 main_bound_here = maybeToBool maybe_main
739 Just main_mono_id = maybe_main
741 -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
742 -- Doesn't affect substitution
743 check_one_sig (TySigInfo _ id sig_tyvars _ sig_tau _ _ src_loc)
744 = tcAddSrcLoc src_loc $
745 tcAddErrCtxtM (sigCtxt (sig_msg id) (idType id)) $
746 checkSigTyVars sig_tyvars
749 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
750 -- The type signatures on a mutually-recursive group of definitions
751 -- must all have the same context (or none).
753 -- We unify them because, with polymorphic recursion, their types
754 -- might not otherwise be related. This is a rather subtle issue.
756 check_one_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
757 = tcAddSrcLoc src_loc $
758 tcAddErrCtxt (sigContextsCtxt id1 id) $
759 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
760 sigContextsErr `thenTc_`
761 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
763 this_sig_dict_tys = mk_dict_tys theta
765 -- CHECK THAT FOR A GROUP INVOLVING Main.main, all
766 -- the signature contexts are empty (what a bore)
767 check_main_ctxt sig@(TySigInfo _ id _ theta _ _ _ src_loc)
768 = tcAddSrcLoc src_loc $
769 checkTc (null theta) (mainContextsErr id)
771 mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
773 sig_msg id tidy_ty = sep [ptext SLIT("When checking the type signature"),
774 nest 4 (ppr id <+> dcolon <+> ppr tidy_ty)]
776 -- Search for Main.main in the binder_names, return corresponding mono_id
777 find_main NotTopLevel binder_names mono_ids = Nothing
778 find_main TopLevel binder_names mono_ids = go binder_names mono_ids
780 go (n:ns) (m:ms) | n == main_NAME = Just m
781 | otherwise = go ns ms
785 %************************************************************************
787 \subsection{SPECIALIZE pragmas}
789 %************************************************************************
791 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
792 pragmas. It is convenient for them to appear in the @[RenamedSig]@
793 part of a binding because then the same machinery can be used for
794 moving them into place as is done for type signatures.
799 f :: Ord a => [a] -> b -> b
800 {-# SPECIALIZE f :: [Int] -> b -> b #-}
803 For this we generate:
805 f* = /\ b -> let d1 = ...
809 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
810 retain a right-hand-side that the simplifier will otherwise discard as
811 dead code... the simplifier has a flag that tells it not to discard
812 SpecPragmaId bindings.
814 In this case the f* retains a call-instance of the overloaded
815 function, f, (including appropriate dictionaries) so that the
816 specialiser will subsequently discover that there's a call of @f@ at
817 Int, and will create a specialisation for @f@. After that, the
818 binding for @f*@ can be discarded.
820 We used to have a form
821 {-# SPECIALISE f :: <type> = g #-}
822 which promised that g implemented f at <type>, but we do that with
824 {-# SPECIALISE (f::<type) = g #-}
827 tcSpecSigs :: [RenamedSig] -> TcM s (TcMonoBinds, LIE)
828 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
829 = -- SPECIALISE f :: forall b. theta => tau = g
830 tcAddSrcLoc src_loc $
831 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
833 -- Get and instantiate its alleged specialised type
834 tcHsType poly_ty `thenTc` \ sig_ty ->
836 -- Check that f has a more general type, and build a RHS for
837 -- the spec-pragma-id at the same time
838 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
840 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
841 tcSimplifyToDicts spec_lie `thenTc` \ (spec_lie1, spec_binds) ->
843 -- Just specialise "f" by building a SpecPragmaId binding
844 -- It is the thing that makes sure we don't prematurely
845 -- dead-code-eliminate the binding we are really interested in.
846 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
848 -- Do the rest and combine
849 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
850 returnTc (binds_rest `andMonoBinds` VarMonoBind spec_id (mkHsLet spec_binds spec_expr),
851 lie_rest `plusLIE` spec_lie1)
853 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
854 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
858 %************************************************************************
860 \subsection[TcBinds-errors]{Error contexts and messages}
862 %************************************************************************
866 patMonoBindsCtxt bind
867 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
869 -----------------------------------------------
871 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
872 nest 4 (ppr v <+> dcolon <+> ppr ty)]
874 -----------------------------------------------
875 notAsPolyAsSigErr sig_tau mono_tyvars
876 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
877 4 (vcat [text "Can't for-all the type variable(s)" <+>
878 pprQuotedList mono_tyvars,
879 text "in the type" <+> quotes (ppr sig_tau)
882 -----------------------------------------------
883 badMatchErr sig_ty inferred_ty
884 = hang (ptext SLIT("Type signature doesn't match inferred type"))
885 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
886 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
889 -----------------------------------------------
891 = ptext SLIT("variable in a lazy pattern binding has unboxed type: ")
894 -----------------------------------------------
896 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
898 -----------------------------------------------
900 = ptext SLIT("Mismatched contexts")
902 sigContextsCtxt s1 s2
903 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
904 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
905 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
908 | getName id == main_NAME = ptext SLIT("Main.main cannot be overloaded")
910 = quotes (ppr id) <+> ptext SLIT("cannot be overloaded") <> char ',' <> -- sigh; workaround for cpp's inability to deal
911 ptext SLIT("because it is mutually recursive with Main.main") -- with commas inside SLIT strings.
914 = hsep [ptext SLIT("When checking that"), quotes (ppr main_NAME),
915 ptext SLIT("has the required type")]
917 -----------------------------------------------
918 unliftedBindErr flavour mbind
919 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed"))
922 existentialExplode mbinds
923 = hang (vcat [text "My brain just exploded.",
924 text "I can't handle pattern bindings for existentially-quantified constructors.",
925 text "In the binding group"])