2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBindsAndThen, bindInstsOfLocalFuns,
8 tcPragmaSigs, checkSigTyVars, tcBindWithSigs,
9 sigCtxt, TcSigInfo(..) ) where
11 #include "HsVersions.h"
13 import {-# SOURCE #-} TcGRHSs ( tcGRHSsAndBinds )
14 import {-# SOURCE #-} TcExpr ( tcExpr )
16 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..), InPat(..),
17 collectMonoBinders, andMonoBinds
19 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
20 import TcHsSyn ( TcHsBinds, TcMonoBinds,
21 TcIdOcc(..), TcIdBndr,
26 import Inst ( Inst, LIE, emptyLIE, plusLIE, plusLIEs, InstOrigin(..),
27 newDicts, tyVarsOfInst, instToId, newMethodWithGivenTy,
30 import TcEnv ( tcExtendLocalValEnv, tcLookupLocalValueOK,
31 newLocalId, newSpecPragmaId,
32 tcGetGlobalTyVars, tcExtendGlobalTyVars
34 import TcMatches ( tcMatchesFun )
35 import TcSimplify ( tcSimplify, tcSimplifyAndCheck )
36 import TcMonoType ( tcHsType )
37 import TcPat ( tcPat )
38 import TcSimplify ( bindInstsOfLocalFuns )
39 import TcType ( TcType, TcThetaType, TcTauType,
41 newTyVarTy, newTcTyVar, tcInstSigType, tcInstSigTcType,
42 zonkTcType, zonkTcTypes, zonkTcThetaType, zonkTcTyVar
44 import Unify ( unifyTauTy, unifyTauTyLists )
46 import Kind ( isUnboxedTypeKind, mkTypeKind, isTypeKind, mkBoxedTypeKind )
47 import MkId ( mkUserId )
48 import Id ( idType, idName, idInfo, replaceIdInfo )
49 import IdInfo ( IdInfo, noIdInfo, setInlinePragInfo, InlinePragInfo(..) )
50 import Maybes ( maybeToBool, assocMaybe )
51 import Name ( getOccName, getSrcLoc, Name )
52 import Type ( mkTyVarTy, mkTyVarTys, isTyVarTy, tyVarsOfTypes,
53 splitSigmaTy, mkForAllTys, mkFunTys, getTyVar, mkDictTy,
54 splitRhoTy, mkForAllTy, splitForAllTys
56 import TyVar ( TyVar, tyVarKind, mkTyVarSet, minusTyVarSet, emptyTyVarSet,
57 elementOfTyVarSet, unionTyVarSets, tyVarSetToList
59 import Bag ( bagToList, foldrBag, )
60 import Util ( isIn, hasNoDups, assoc )
61 import Unique ( Unique )
62 import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
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 s -> this -> that) -- Combinator
103 -> TcM s (this, LIE s)
104 -> TcM s (that, LIE s)
106 tcTopBindsAndThen = tc_binds_and_then TopLevel
107 tcBindsAndThen = tc_binds_and_then NotTopLevel
109 tc_binds_and_then top_lvl combiner binds do_next
110 = tcBinds top_lvl binds `thenTc` \ (mbinds1, binds_lie, env, ids) ->
113 -- Now do whatever happens next, in the augmented envt
114 do_next `thenTc` \ (thing, thing_lie) ->
116 -- Create specialisations of functions bound here
117 -- Nota Bene: we glom the bindings all together in a single
118 -- recursive group ("recursive" passed to combiner, below)
119 -- so that we can do thsi bindInsts thing once for all the bindings
120 -- and the thing inside. This saves a quadratic-cost algorithm
121 -- when there's a long sequence of bindings.
122 bindInstsOfLocalFuns (binds_lie `plusLIE` thing_lie) ids `thenTc` \ (final_lie, mbinds2) ->
126 final_mbinds = mbinds1 `AndMonoBinds` mbinds2
128 returnTc (combiner Recursive final_mbinds thing, final_lie)
130 tcBinds :: TopLevelFlag
132 -> TcM s (TcMonoBinds s, LIE s, TcEnv s, [TcIdBndr s])
133 -- The envt is the envt with binders in scope
134 -- The binders are those bound by this group of bindings
136 tcBinds top_lvl EmptyBinds
137 = tcGetEnv `thenNF_Tc` \ env ->
138 returnTc (EmptyMonoBinds, emptyLIE, env, [])
140 -- Short-cut for the rather common case of an empty bunch of bindings
141 tcBinds top_lvl (MonoBind EmptyMonoBinds sigs is_rec)
142 = tcGetEnv `thenNF_Tc` \ env ->
143 returnTc (EmptyMonoBinds, emptyLIE, env, [])
145 tcBinds top_lvl (ThenBinds binds1 binds2)
146 = tcBinds top_lvl binds1 `thenTc` \ (mbinds1, lie1, env1, ids1) ->
148 tcBinds top_lvl binds2 `thenTc` \ (mbinds2, lie2, env2, ids2) ->
149 returnTc (mbinds1 `AndMonoBinds` mbinds2, lie1 `plusLIE` lie2, env2, ids1++ids2)
151 tcBinds top_lvl (MonoBind bind sigs is_rec)
152 = fixTc (\ ~(prag_info_fn, _) ->
153 -- This is the usual prag_info fix; the PragmaInfo field of an Id
154 -- is not inspected till ages later in the compiler, so there
155 -- should be no black-hole problems here.
157 -- TYPECHECK THE SIGNATURES
158 mapTc tcTySig ty_sigs `thenTc` \ tc_ty_sigs ->
160 tcBindWithSigs top_lvl binder_names bind
161 tc_ty_sigs is_rec prag_info_fn `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
163 -- Extend the environment to bind the new polymorphic Ids
164 tcExtendLocalValEnv binder_names poly_ids $
166 -- Build bindings and IdInfos corresponding to user pragmas
167 tcPragmaSigs sigs `thenTc` \ (prag_info_fn, prag_binds, prag_lie) ->
169 -- Catch the environment and return
170 tcGetEnv `thenNF_Tc` \ env ->
171 returnTc (prag_info_fn, (poly_binds `AndMonoBinds` prag_binds,
172 poly_lie `plusLIE` prag_lie,
174 ) ) `thenTc` \ (_, result) ->
177 binder_names = map fst (bagToList (collectMonoBinders bind))
178 ty_sigs = [sig | sig@(Sig name _ _) <- sigs]
181 An aside. The original version of @tcBindsAndThen@ which lacks a
182 combiner function, appears below. Though it is perfectly well
183 behaved, it cannot be typed by Haskell, because the recursive call is
184 at a different type to the definition itself. There aren't too many
185 examples of this, which is why I thought it worth preserving! [SLPJ]
190 -> TcM s (thing, LIE s, thing_ty))
191 -> TcM s ((TcHsBinds s, thing), LIE s, thing_ty)
193 tcBindsAndThen EmptyBinds do_next
194 = do_next `thenTc` \ (thing, lie, thing_ty) ->
195 returnTc ((EmptyBinds, thing), lie, thing_ty)
197 tcBindsAndThen (ThenBinds binds1 binds2) do_next
198 = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
199 `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
201 returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
203 tcBindsAndThen (MonoBind bind sigs is_rec) do_next
204 = tcBindAndThen bind sigs do_next
208 %************************************************************************
210 \subsection{tcBindWithSigs}
212 %************************************************************************
214 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
215 so all the clever stuff is in here.
217 * binder_names and mbind must define the same set of Names
219 * The Names in tc_ty_sigs must be a subset of binder_names
221 * The Ids in tc_ty_sigs don't necessarily have to have the same name
222 as the Name in the tc_ty_sig
232 -> TcM s (TcMonoBinds s, LIE s, [TcIdBndr s])
234 tcBindWithSigs top_lvl binder_names mbind tc_ty_sigs is_rec prag_info_fn
236 -- If typechecking the binds fails, then return with each
237 -- signature-less binder given type (forall a.a), to minimise subsequent
239 newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ alpha_tv ->
241 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
242 poly_ids = map mk_dummy binder_names
243 mk_dummy name = case maybeSig tc_ty_sigs name of
244 Just (TySigInfo _ poly_id _ _ _ _) -> poly_id -- Signature
245 Nothing -> mkUserId name forall_a_a -- No signature
247 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
250 -- Create a new identifier for each binder, with each being given
251 -- a fresh unique, and a type-variable type.
252 -- For "mono_lies" see comments about polymorphic recursion at the
253 -- end of the function.
254 mapAndUnzipNF_Tc mk_mono_id binder_names `thenNF_Tc` \ (mono_lies, mono_ids) ->
256 mono_lie = plusLIEs mono_lies
257 mono_id_tys = map idType mono_ids
260 -- TYPECHECK THE BINDINGS
261 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs `thenTc` \ (mbind', lie) ->
263 -- CHECK THAT THE SIGNATURES MATCH
264 -- (must do this before getTyVarsToGen)
265 checkSigMatch tc_ty_sigs `thenTc` \ sig_theta ->
267 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
268 -- The tyvars_not_to_gen are free in the environment, and hence
269 -- candidates for generalisation, but sometimes the monomorphism
270 -- restriction means we can't generalise them nevertheless
271 getTyVarsToGen is_unrestricted mono_id_tys lie `thenNF_Tc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
273 -- DEAL WITH TYPE VARIABLE KINDS
274 -- **** This step can do unification => keep other zonking after this ****
275 mapTc defaultUncommittedTyVar (tyVarSetToList tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
277 real_tyvars_to_gen = mkTyVarSet real_tyvars_to_gen_list
278 -- It's important that the final list
279 -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
280 -- zonked, *including boxity*, because they'll be included in the forall types of
281 -- the polymorphic Ids, and instances of these Ids will be generated from them.
283 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
284 -- real_tyvars_to_gen
288 tcExtendGlobalTyVars (tyVarSetToList tyvars_not_to_gen) (
289 if null tc_ty_sigs then
290 -- No signatures, so just simplify the lie
291 -- NB: no signatures => no polymorphic recursion, so no
292 -- need to use mono_lies (which will be empty anyway)
293 tcSimplify (text "tcBinds1" <+> ppr binder_names)
294 top_lvl real_tyvars_to_gen lie `thenTc` \ (lie_free, dict_binds, lie_bound) ->
295 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
298 zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
299 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
300 -- It's important that sig_theta is zonked, because
301 -- dict_id is later used to form the type of the polymorphic thing,
302 -- and forall-types must be zonked so far as their bound variables
306 -- The "givens" is the stuff available. We get that from
307 -- the context of the type signature, BUT ALSO the mono_lie
308 -- so that polymorphic recursion works right (see comments at end of fn)
309 givens = dicts_sig `plusLIE` mono_lie
312 -- Check that the needed dicts can be expressed in
313 -- terms of the signature ones
314 tcAddErrCtxt (bindSigsCtxt tysig_names) $
316 (ptext SLIT("type signature for") <+>
317 hsep (punctuate comma (map (quotes . ppr) binder_names)))
318 real_tyvars_to_gen givens lie `thenTc` \ (lie_free, dict_binds) ->
320 returnTc (lie_free, dict_binds, dict_ids)
322 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
324 ASSERT( not (any (isUnboxedTypeKind . tyVarKind) real_tyvars_to_gen_list) )
325 -- The instCantBeGeneralised stuff in tcSimplify should have
326 -- already raised an error if we're trying to generalise an unboxed tyvar
327 -- (NB: unboxed tyvars are always introduced along with a class constraint)
328 -- and it's better done there because we have more precise origin information.
329 -- That's why we just use an ASSERT here.
331 -- BUILD THE POLYMORPHIC RESULT IDs
332 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
334 exports = zipWith3 mk_export binder_names mono_ids zonked_mono_id_types
335 dict_tys = map tcIdType dicts_bound
337 mk_export binder_name mono_id zonked_mono_id_ty
338 = (tyvars, TcId (replaceIdInfo poly_id (prag_info_fn binder_name)), TcId mono_id)
341 case maybeSig tc_ty_sigs binder_name of
342 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _) -> (sig_tyvars, sig_poly_id)
343 Nothing -> (real_tyvars_to_gen_list, new_poly_id)
345 new_poly_id = mkUserId binder_name poly_ty
346 poly_ty = mkForAllTys real_tyvars_to_gen_list $ mkFunTys dict_tys zonked_mono_id_ty
347 -- It's important to build a fully-zonked poly_ty, because
348 -- we'll slurp out its free type variables when extending the
349 -- local environment (tcExtendLocalValEnv); if it's not zonked
350 -- it appears to have free tyvars that aren't actually free at all.
355 AbsBinds real_tyvars_to_gen_list
358 (dict_binds `AndMonoBinds` mbind'),
360 [poly_id | (_, TcId poly_id, _) <- exports]
363 no_of_binders = length binder_names
365 mk_mono_id binder_name
366 | theres_a_signature -- There's a signature; and it's overloaded,
367 && not (null sig_theta) -- so make a Method
368 = tcAddSrcLoc sig_loc $
369 newMethodWithGivenTy SignatureOrigin
370 (TcId poly_id) (mkTyVarTys sig_tyvars)
371 sig_theta sig_tau `thenNF_Tc` \ (mono_lie, TcId mono_id) ->
372 -- A bit turgid to have to strip the TcId
373 returnNF_Tc (mono_lie, mono_id)
375 | otherwise -- No signature or not overloaded;
376 = tcAddSrcLoc (getSrcLoc binder_name) $
377 (if theres_a_signature then
378 returnNF_Tc sig_tau -- Non-overloaded signature; use its type
380 newTyVarTy kind -- No signature; use a new type variable
381 ) `thenNF_Tc` \ mono_id_ty ->
383 newLocalId (getOccName binder_name) mono_id_ty `thenNF_Tc` \ mono_id ->
384 returnNF_Tc (emptyLIE, mono_id)
386 maybe_sig = maybeSig tc_ty_sigs binder_name
387 theres_a_signature = maybeToBool maybe_sig
388 Just (TySigInfo name poly_id sig_tyvars sig_theta sig_tau sig_loc) = maybe_sig
390 tysig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
391 is_unrestricted = isUnRestrictedGroup tysig_names mbind
393 kind = case is_rec of
394 Recursive -> mkBoxedTypeKind -- Recursive, so no unboxed types
395 NonRecursive -> mkTypeKind -- Non-recursive, so we permit unboxed types
398 Polymorphic recursion
399 ~~~~~~~~~~~~~~~~~~~~~
400 The game plan for polymorphic recursion in the code above is
402 * Bind any variable for which we have a type signature
403 to an Id with a polymorphic type. Then when type-checking
404 the RHSs we'll make a full polymorphic call.
406 This fine, but if you aren't a bit careful you end up with a horrendous
407 amount of partial application and (worse) a huge space leak. For example:
409 f :: Eq a => [a] -> [a]
412 If we don't take care, after typechecking we get
414 f = /\a -> \d::Eq a -> let f' = f a d
418 Notice the the stupid construction of (f a d), which is of course
419 identical to the function we're executing. In this case, the
420 polymorphic recursion ins't being used (but that's a very common case).
422 This can lead to a massive space leak, from the following top-level defn:
427 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
428 f' is another thunk which evaluates to the same thing... and you end
429 up with a chain of identical values all hung onto by the CAF ff.
431 Solution: when typechecking the RHSs we always have in hand the
432 *monomorphic* Ids for each binding. So we just need to make sure that
433 if (Method f a d) shows up in the constraints emerging from (...f...)
434 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
435 to the "givens" when simplifying constraints. Thats' what the "mono_lies"
439 %************************************************************************
441 \subsection{getTyVarsToGen}
443 %************************************************************************
445 @getTyVarsToGen@ decides what type variables generalise over.
447 For a "restricted group" -- see the monomorphism restriction
448 for a definition -- we bind no dictionaries, and
449 remove from tyvars_to_gen any constrained type variables
451 *Don't* simplify dicts at this point, because we aren't going
452 to generalise over these dicts. By the time we do simplify them
453 we may well know more. For example (this actually came up)
455 f x = array ... xs where xs = [1,2,3,4,5]
456 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
457 stuff. If we simplify only at the f-binding (not the xs-binding)
458 we'll know that the literals are all Ints, and we can just produce
461 Find all the type variables involved in overloading, the
462 "constrained_tyvars". These are the ones we *aren't* going to
463 generalise. We must be careful about doing this:
465 (a) If we fail to generalise a tyvar which is not actually
466 constrained, then it will never, ever get bound, and lands
467 up printed out in interface files! Notorious example:
468 instance Eq a => Eq (Foo a b) where ..
469 Here, b is not constrained, even though it looks as if it is.
470 Another, more common, example is when there's a Method inst in
471 the LIE, whose type might very well involve non-overloaded
474 (b) On the other hand, we mustn't generalise tyvars which are constrained,
475 because we are going to pass on out the unmodified LIE, with those
476 tyvars in it. They won't be in scope if we've generalised them.
478 So we are careful, and do a complete simplification just to find the
479 constrained tyvars. We don't use any of the results, except to
480 find which tyvars are constrained.
483 getTyVarsToGen is_unrestricted mono_id_tys lie
484 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
485 zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
487 tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusTyVarSet` free_tyvars
491 returnNF_Tc (emptyTyVarSet, tyvars_to_gen)
493 -- This recover and discard-errs is to avoid duplicate error
494 -- messages; this, after all, is an "extra" call to tcSimplify
495 recoverNF_Tc (returnNF_Tc (emptyTyVarSet, tyvars_to_gen)) $
498 tcSimplify (text "getTVG") NotTopLevel tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
500 -- ASSERT: dicts_sig is already zonked!
501 constrained_tyvars = foldrBag (unionTyVarSets . tyVarsOfInst) emptyTyVarSet constrained_dicts
502 reduced_tyvars_to_gen = tyvars_to_gen `minusTyVarSet` constrained_tyvars
504 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
509 isUnRestrictedGroup :: [Name] -- Signatures given for these
513 is_elem v vs = isIn "isUnResMono" v vs
515 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
516 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
517 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
518 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
519 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
520 isUnRestrictedGroup sigs mb2
521 isUnRestrictedGroup sigs EmptyMonoBinds = True
524 @defaultUncommittedTyVar@ checks for generalisation over unboxed
525 types, and defaults any TypeKind TyVars to BoxedTypeKind.
528 defaultUncommittedTyVar tyvar
529 | isTypeKind (tyVarKind tyvar)
530 = newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ boxed_tyvar ->
531 unifyTauTy (mkTyVarTy boxed_tyvar) (mkTyVarTy tyvar) `thenTc_`
539 %************************************************************************
541 \subsection{tcMonoBind}
543 %************************************************************************
545 @tcMonoBinds@ deals with a single @MonoBind@.
546 The signatures have been dealt with already.
549 tcMonoBinds :: RenamedMonoBinds
550 -> [Name] -> [TcIdBndr s]
552 -> TcM s (TcMonoBinds s, LIE s)
554 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs
555 = tcExtendLocalValEnv binder_names mono_ids (
559 sig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
560 sig_ids = [id | (TySigInfo _ id _ _ _ _) <- tc_ty_sigs]
562 tc_mono_binds EmptyMonoBinds = returnTc (EmptyMonoBinds, emptyLIE)
564 tc_mono_binds (AndMonoBinds mb1 mb2)
565 = tc_mono_binds mb1 `thenTc` \ (mb1a, lie1) ->
566 tc_mono_binds mb2 `thenTc` \ (mb2a, lie2) ->
567 returnTc (AndMonoBinds mb1a mb2a, lie1 `plusLIE` lie2)
569 tc_mono_binds (FunMonoBind name inf matches locn)
571 tcLookupLocalValueOK "tc_mono_binds" name `thenNF_Tc` \ id ->
573 -- Before checking the RHS, extend the envt with
574 -- bindings for the *polymorphic* Ids from any type signatures
575 tcExtendLocalValEnv sig_names sig_ids $
576 tcMatchesFun name (idType id) matches `thenTc` \ (matches', lie) ->
578 returnTc (FunMonoBind (TcId id) inf matches' locn, lie)
580 tc_mono_binds bind@(PatMonoBind pat grhss_and_binds locn)
582 tcAddErrCtxt (patMonoBindsCtxt bind) $
583 tcPat pat `thenTc` \ (pat2, lie_pat, pat_ty) ->
585 -- Before checking the RHS, but after the pattern, extend the envt with
586 -- bindings for the *polymorphic* Ids from any type signatures
587 tcExtendLocalValEnv sig_names sig_ids $
588 tcGRHSsAndBinds pat_ty grhss_and_binds `thenTc` \ (grhss_and_binds2, lie) ->
589 returnTc (PatMonoBind pat2 grhss_and_binds2 locn,
593 %************************************************************************
595 \subsection{Signatures}
597 %************************************************************************
599 @tcSigs@ checks the signatures for validity, and returns a list of
600 {\em freshly-instantiated} signatures. That is, the types are already
601 split up, and have fresh type variables installed. All non-type-signature
602 "RenamedSigs" are ignored.
604 The @TcSigInfo@ contains @TcTypes@ because they are unified with
605 the variable's type, and after that checked to see whether they've
611 Name -- N, the Name in corresponding binding
612 (TcIdBndr s) -- *Polymorphic* binder for this value...
613 -- Usually has name = N, but doesn't have to.
620 maybeSig :: [TcSigInfo s] -> Name -> Maybe (TcSigInfo s)
621 -- Search for a particular signature
622 maybeSig [] name = Nothing
623 maybeSig (sig@(TySigInfo sig_name _ _ _ _ _) : sigs) name
624 | name == sig_name = Just sig
625 | otherwise = maybeSig sigs name
630 tcTySig :: RenamedSig
631 -> TcM s (TcSigInfo s)
633 tcTySig (Sig v ty src_loc)
634 = tcAddSrcLoc src_loc $
635 tcHsType ty `thenTc` \ sigma_ty ->
637 -- Convert from Type to TcType
638 tcInstSigType sigma_ty `thenNF_Tc` \ sigma_tc_ty ->
640 poly_id = mkUserId v sigma_tc_ty
642 -- Instantiate this type
643 -- It's important to do this even though in the error-free case
644 -- we could just split the sigma_tc_ty (since the tyvars don't
645 -- unified with anything). But in the case of an error, when
646 -- the tyvars *do* get unified with something, we want to carry on
647 -- typechecking the rest of the program with the function bound
648 -- to a pristine type, namely sigma_tc_ty
649 tcInstSigTcType sigma_tc_ty `thenNF_Tc` \ (tyvars, rho) ->
651 (theta, tau) = splitRhoTy rho
652 -- This splitSigmaTy tries hard to make sure that tau' is a type synonym
653 -- wherever possible, which can improve interface files.
655 returnTc (TySigInfo v poly_id tyvars theta tau src_loc)
658 @checkSigMatch@ does the next step in checking signature matching.
659 The tau-type part has already been unified. What we do here is to
660 check that this unification has not over-constrained the (polymorphic)
661 type variables of the original signature type.
663 The error message here is somewhat unsatisfactory, but it'll do for
668 = returnTc (error "checkSigMatch")
670 checkSigMatch tc_ty_sigs@( sig1@(TySigInfo _ id1 _ theta1 _ _) : all_sigs_but_first )
671 = -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
672 -- Doesn't affect substitution
673 mapTc check_one_sig tc_ty_sigs `thenTc_`
675 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
676 -- The type signatures on a mutually-recursive group of definitions
677 -- must all have the same context (or none).
679 -- We unify them because, with polymorphic recursion, their types
680 -- might not otherwise be related. This is a rather subtle issue.
682 mapTc check_one_cxt all_sigs_but_first `thenTc_`
686 sig1_dict_tys = mk_dict_tys theta1
687 n_sig1_dict_tys = length sig1_dict_tys
689 check_one_cxt sig@(TySigInfo _ id _ theta _ src_loc)
690 = tcAddSrcLoc src_loc $
691 tcAddErrCtxt (sigContextsCtxt id1 id) $
692 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
693 sigContextsErr `thenTc_`
694 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
696 this_sig_dict_tys = mk_dict_tys theta
698 check_one_sig (TySigInfo name id sig_tyvars _ sig_tau src_loc)
699 = tcAddSrcLoc src_loc $
700 tcAddErrCtxt (sigCtxt id) $
701 checkSigTyVars sig_tyvars sig_tau
703 mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
707 @checkSigTyVars@ is used after the type in a type signature has been unified with
708 the actual type found. It then checks that the type variables of the type signature
710 (a) still all type variables
711 eg matching signature [a] against inferred type [(p,q)]
712 [then a will be unified to a non-type variable]
714 (b) still all distinct
715 eg matching signature [(a,b)] against inferred type [(p,p)]
716 [then a and b will be unified together]
718 (c) not mentioned in the environment
719 eg the signature for f in this:
725 Here, f is forced to be monorphic by the free occurence of x.
727 Before doing this, the substitution is applied to the signature type variable.
729 We used to have the notion of a "DontBind" type variable, which would
730 only be bound to itself or nothing. Then points (a) and (b) were
731 self-checking. But it gave rise to bogus consequential error messages.
734 f = (*) -- Monomorphic
739 Here, we get a complaint when checking the type signature for g,
740 that g isn't polymorphic enough; but then we get another one when
741 dealing with the (Num x) context arising from f's definition;
742 we try to unify x with Int (to default it), but find that x has already
743 been unified with the DontBind variable "a" from g's signature.
744 This is really a problem with side-effecting unification; we'd like to
745 undo g's effects when its type signature fails, but unification is done
746 by side effect, so we can't (easily).
748 So we revert to ordinary type variables for signatures, and try to
749 give a helpful message in checkSigTyVars.
752 checkSigTyVars :: [TcTyVar s] -- The original signature type variables
753 -> TcType s -- signature type (for err msg)
754 -> TcM s [TcTyVar s] -- Zonked signature type variables
756 checkSigTyVars sig_tyvars sig_tau
757 = mapNF_Tc zonkTcTyVar sig_tyvars `thenNF_Tc` \ sig_tys ->
759 sig_tyvars' = map (getTyVar "checkSigTyVars") sig_tys
762 -- Check points (a) and (b)
763 checkTcM (all isTyVarTy sig_tys && hasNoDups sig_tyvars')
764 (zonkTcType sig_tau `thenNF_Tc` \ sig_tau' ->
765 failWithTc (badMatchErr sig_tau sig_tau')
769 -- We want to report errors in terms of the original signature tyvars,
770 -- ie sig_tyvars, NOT sig_tyvars'. sig_tyvars' correspond
771 -- 1-1 with sig_tyvars, so we can just map back.
772 tcGetGlobalTyVars `thenNF_Tc` \ globals ->
774 mono_tyvars' = [sig_tv' | sig_tv' <- sig_tyvars',
775 sig_tv' `elementOfTyVarSet` globals]
777 mono_tyvars = map (assoc "checkSigTyVars" (sig_tyvars' `zip` sig_tyvars)) mono_tyvars'
779 checkTcM (null mono_tyvars')
780 (failWithTc (notAsPolyAsSigErr sig_tau mono_tyvars)) `thenTc_`
786 %************************************************************************
788 \subsection{SPECIALIZE pragmas}
790 %************************************************************************
793 @tcPragmaSigs@ munches up the "signatures" that arise through *user*
794 pragmas. It is convenient for them to appear in the @[RenamedSig]@
795 part of a binding because then the same machinery can be used for
796 moving them into place as is done for type signatures.
799 tcPragmaSigs :: [RenamedSig] -- The pragma signatures
800 -> TcM s (Name -> IdInfo, -- Maps name to the appropriate IdInfo
805 = mapAndUnzip3Tc tcPragmaSig sigs `thenTc` \ (maybe_info_modifiers, binds, lies) ->
807 prag_fn name = foldr ($) noIdInfo [f | Just (n,f) <- maybe_info_modifiers, n==name]
809 returnTc (prag_fn, andMonoBinds binds, plusLIEs lies)
812 The interesting case is for SPECIALISE pragmas. There are two forms.
813 Here's the first form:
815 f :: Ord a => [a] -> b -> b
816 {-# SPECIALIZE f :: [Int] -> b -> b #-}
819 For this we generate:
821 f* = /\ b -> let d1 = ...
825 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
826 retain a right-hand-side that the simplifier will otherwise discard as
827 dead code... the simplifier has a flag that tells it not to discard
828 SpecPragmaId bindings.
830 In this case the f* retains a call-instance of the overloaded
831 function, f, (including appropriate dictionaries) so that the
832 specialiser will subsequently discover that there's a call of @f@ at
833 Int, and will create a specialisation for @f@. After that, the
834 binding for @f*@ can be discarded.
836 The second form is this:
838 f :: Ord a => [a] -> b -> b
839 {-# SPECIALIZE f :: [Int] -> b -> b = g #-}
842 Here @g@ is specified as a function that implements the specialised
843 version of @f@. Suppose that g has type (a->b->b); that is, g's type
844 is more general than that required. For this we generate
846 f@Int = /\b -> g Int b
850 Here @f@@Int@ is a SpecId, the specialised version of @f@. It inherits
851 f's export status etc. @f*@ is a SpecPragmaId, as before, which just serves
852 to prevent @f@@Int@ from being discarded prematurely. After specialisation,
853 if @f@@Int@ is going to be used at all it will be used explicitly, so the simplifier can
854 discard the f* binding.
856 Actually, there is really only point in giving a SPECIALISE pragma on exported things,
857 and the simplifer won't discard SpecIds for exporte things anyway, so maybe this is
861 tcPragmaSig :: RenamedSig -> TcM s (Maybe (Name, IdInfo -> IdInfo), TcMonoBinds s, LIE s)
862 tcPragmaSig (Sig _ _ _) = returnTc (Nothing, EmptyMonoBinds, emptyLIE)
863 tcPragmaSig (SpecInstSig _ _) = returnTc (Nothing, EmptyMonoBinds, emptyLIE)
865 tcPragmaSig (InlineSig name loc)
866 = returnTc (Just (name, setInlinePragInfo IWantToBeINLINEd), EmptyMonoBinds, emptyLIE)
868 tcPragmaSig (NoInlineSig name loc)
869 = returnTc (Just (name, setInlinePragInfo IDontWantToBeINLINEd), EmptyMonoBinds, emptyLIE)
871 tcPragmaSig (SpecSig name poly_ty maybe_spec_name src_loc)
872 = -- SPECIALISE f :: forall b. theta => tau = g
873 tcAddSrcLoc src_loc $
874 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
876 -- Get and instantiate its alleged specialised type
877 tcHsType poly_ty `thenTc` \ sig_sigma ->
878 tcInstSigType sig_sigma `thenNF_Tc` \ sig_ty ->
880 -- Check that f has a more general type, and build a RHS for
881 -- the spec-pragma-id at the same time
882 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
884 case maybe_spec_name of
885 Nothing -> -- Just specialise "f" by building a SpecPragmaId binding
886 -- It is the thing that makes sure we don't prematurely
887 -- dead-code-eliminate the binding we are really interested in.
888 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_id ->
889 returnTc (Nothing, VarMonoBind (TcId spec_id) spec_expr, spec_lie)
891 Just g_name -> -- Don't create a SpecPragmaId. Instead add some suitable IdIfo
893 panic "Can't handle SPECIALISE with a '= g' part"
895 {- Not yet. Because we're still in the TcType world we
896 can't really add to the SpecEnv of the Id. Instead we have to
897 record the information in a different sort of Sig, and add it to
898 the IdInfo after zonking.
900 For now we just leave out this case
902 -- Get the type of f, and find out what types
903 -- f has to be instantiated at to give the signature type
904 tcLookupLocalValueOK "tcPragmaSig" name `thenNF_Tc` \ f_id ->
905 tcInstSigTcType (idType f_id) `thenNF_Tc` \ (f_tyvars, f_rho) ->
908 (sig_tyvars, sig_theta, sig_tau) = splitSigmaTy sig_ty
909 (f_theta, f_tau) = splitRhoTy f_rho
910 sig_tyvar_set = mkTyVarSet sig_tyvars
912 unifyTauTy sig_tau f_tau `thenTc_`
914 tcPolyExpr str (HsVar g_name) (mkSigmaTy sig_tyvars f_theta sig_tau) `thenTc` \ (_, _,
917 tcPragmaSig other = pprTrace "tcPragmaSig: ignoring" (ppr other) $
918 returnTc (Nothing, EmptyMonoBinds, emptyLIE)
922 %************************************************************************
924 \subsection[TcBinds-errors]{Error contexts and messages}
926 %************************************************************************
930 patMonoBindsCtxt bind
931 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
933 -----------------------------------------------
935 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
936 nest 4 (ppr v <+> ptext SLIT(" ::") <+> ppr ty)]
938 -----------------------------------------------
939 notAsPolyAsSigErr sig_tau mono_tyvars
940 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
941 4 (vcat [text "Can't for-all the type variable(s)" <+>
942 pprQuotedList mono_tyvars,
943 text "in the type" <+> quotes (ppr sig_tau)
946 -----------------------------------------------
947 badMatchErr sig_ty inferred_ty
948 = hang (ptext SLIT("Type signature doesn't match inferred type"))
949 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
950 hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
953 -----------------------------------------------
955 = sep [ptext SLIT("When checking the type signature for"), quotes (ppr id)]
958 = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
960 -----------------------------------------------
962 = ptext SLIT("Mismatched contexts")
963 sigContextsCtxt s1 s2
964 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
965 quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
966 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
968 -----------------------------------------------
970 = panic "specGroundnessCtxt"
972 --------------------------------------------
973 specContextGroundnessCtxt -- err_ctxt dicts
974 = panic "specContextGroundnessCtxt"
977 sep [hsep [ptext SLIT("In the SPECIALIZE pragma for"), ppr name],
978 hcat [ptext SLIT(" specialised to the type"), ppr spec_ty],
980 ptext SLIT("... not all overloaded type variables were instantiated"),
981 ptext SLIT("to ground types:")])
982 4 (vcat [hsep [ppr c, ppr t]
983 | (c,t) <- map getDictClassAndType dicts])
985 (name, spec_ty, locn, pp_spec_id)
987 ValSpecSigCtxt n ty loc -> (n, ty, loc, \ x -> empty)
988 ValSpecSpecIdCtxt n ty spec loc ->
990 hsep [ptext SLIT("... type of explicit id"), ppr spec])