2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcBinds]{TcBinds}
7 #include "HsVersions.h"
9 module TcBinds ( tcBindsAndThen, tcPragmaSigs, checkSigTyVars, tcBindWithSigs, TcSigInfo(..) ) where
12 #if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ <= 201
13 IMPORT_DELOOPER(TcLoop) ( tcGRHSsAndBinds )
15 import {-# SOURCE #-} TcGRHSs ( tcGRHSsAndBinds )
18 import HsSyn ( HsBinds(..), Sig(..), MonoBinds(..),
19 Match, HsType, InPat(..), OutPat(..), HsExpr(..),
20 SYN_IE(RecFlag), nonRecursive,
21 GRHSsAndBinds, ArithSeqInfo, HsLit, Fake, Stmt, DoOrListComp, Fixity,
23 import RnHsSyn ( SYN_IE(RenamedHsBinds), RenamedSig(..),
24 SYN_IE(RenamedMonoBinds)
26 import TcHsSyn ( SYN_IE(TcHsBinds), SYN_IE(TcMonoBinds),
32 import Inst ( Inst, SYN_IE(LIE), emptyLIE, plusLIE, InstOrigin(..),
33 newDicts, tyVarsOfInst, instToId
35 import TcEnv ( tcExtendLocalValEnv, tcLookupLocalValueOK, newMonoIds,
36 tcGetGlobalTyVars, tcExtendGlobalTyVars
38 import SpecEnv ( SpecEnv )
39 import TcMatches ( tcMatchesFun )
40 import TcSimplify ( tcSimplify, tcSimplifyAndCheck )
41 import TcMonoType ( tcHsType )
42 import TcPat ( tcPat )
43 import TcSimplify ( bindInstsOfLocalFuns )
44 import TcType ( TcIdOcc(..), SYN_IE(TcIdBndr),
45 SYN_IE(TcType), SYN_IE(TcThetaType), SYN_IE(TcTauType),
46 SYN_IE(TcTyVarSet), SYN_IE(TcTyVar),
47 newTyVarTy, zonkTcType, zonkSigTyVar,
48 newTcTyVar, tcInstSigType, newTyVarTys
50 import Unify ( unifyTauTy, unifyTauTyLists )
52 import Kind ( isUnboxedTypeKind, mkTypeKind, isTypeKind, mkBoxedTypeKind )
53 import Id ( GenId, idType, mkUserLocal, mkUserId )
54 import IdInfo ( noIdInfo )
55 import Maybes ( maybeToBool, assocMaybe, catMaybes )
56 import Name ( getOccName, getSrcLoc, Name )
57 import PragmaInfo ( PragmaInfo(..) )
59 import Type ( mkTyVarTy, mkTyVarTys, isTyVarTy, tyVarsOfTypes, eqSimpleTheta,
60 mkSigmaTy, splitSigmaTy, mkForAllTys, mkFunTys, getTyVar, mkDictTy,
61 splitRhoTy, mkForAllTy, splitForAllTy )
62 import TyVar ( GenTyVar, SYN_IE(TyVar), tyVarKind, mkTyVarSet, minusTyVarSet, emptyTyVarSet,
63 elementOfTyVarSet, unionTyVarSets, tyVarSetToList )
64 import Bag ( bagToList, foldrBag, isEmptyBag )
65 import Util ( isIn, zipEqual, zipWithEqual, zipWith3Equal, hasNoDups, assoc,
66 assertPanic, panic, pprTrace )
67 import PprType ( GenClass, GenType, GenTyVar )
68 import Unique ( Unique )
69 import SrcLoc ( SrcLoc )
71 import Outputable --( interppSP, interpp'SP )
77 %************************************************************************
79 \subsection{Type-checking bindings}
81 %************************************************************************
83 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
84 it needs to know something about the {\em usage} of the things bound,
85 so that it can create specialisations of them. So @tcBindsAndThen@
86 takes a function which, given an extended environment, E, typechecks
87 the scope of the bindings returning a typechecked thing and (most
88 important) an LIE. It is this LIE which is then used as the basis for
89 specialising the things bound.
91 @tcBindsAndThen@ also takes a "combiner" which glues together the
92 bindings and the "thing" to make a new "thing".
94 The real work is done by @tcBindWithSigsAndThen@.
96 Recursive and non-recursive binds are handled in essentially the same
97 way: because of uniques there are no scoping issues left. The only
98 difference is that non-recursive bindings can bind primitive values.
100 Even for non-recursive binding groups we add typings for each binder
101 to the LVE for the following reason. When each individual binding is
102 checked the type of its LHS is unified with that of its RHS; and
103 type-checking the LHS of course requires that the binder is in scope.
105 At the top-level the LIE is sure to contain nothing but constant
106 dictionaries, which we resolve at the module level.
110 :: (RecFlag -> TcMonoBinds s -> thing -> thing) -- Combinator
112 -> TcM s (thing, LIE s)
113 -> TcM s (thing, LIE s)
115 tcBindsAndThen combiner EmptyBinds do_next
116 = do_next `thenTc` \ (thing, lie) ->
117 returnTc (combiner nonRecursive EmptyMonoBinds thing, lie)
119 tcBindsAndThen combiner (ThenBinds binds1 binds2) do_next
120 = tcBindsAndThen combiner binds1 (tcBindsAndThen combiner binds2 do_next)
122 tcBindsAndThen combiner (MonoBind bind sigs is_rec) do_next
123 = fixTc (\ ~(prag_info_fn, _) ->
124 -- This is the usual prag_info fix; the PragmaInfo field of an Id
125 -- is not inspected till ages later in the compiler, so there
126 -- should be no black-hole problems here.
128 -- TYPECHECK THE SIGNATURES
129 mapTc (tcTySig prag_info_fn) ty_sigs `thenTc` \ tc_ty_sigs ->
131 tcBindWithSigs binder_names bind
132 tc_ty_sigs is_rec prag_info_fn `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
134 -- Extend the environment to bind the new polymorphic Ids
135 tcExtendLocalValEnv binder_names poly_ids $
137 -- Build bindings and IdInfos corresponding to user pragmas
138 tcPragmaSigs sigs `thenTc` \ (prag_info_fn, prag_binds, prag_lie) ->
140 -- Now do whatever happens next, in the augmented envt
141 do_next `thenTc` \ (thing, thing_lie) ->
143 -- Create specialisations of functions bound here
144 bindInstsOfLocalFuns (prag_lie `plusLIE` thing_lie)
145 poly_ids `thenTc` \ (lie2, inst_mbinds) ->
149 final_lie = lie2 `plusLIE` poly_lie
150 final_thing = combiner is_rec poly_binds $
151 combiner nonRecursive inst_mbinds $
152 combiner nonRecursive prag_binds
155 returnTc (prag_info_fn, (final_thing, final_lie))
156 ) `thenTc` \ (_, result) ->
159 binder_names = map fst (bagToList (collectMonoBinders bind))
160 ty_sigs = [sig | sig@(Sig name _ _) <- sigs]
163 An aside. The original version of @tcBindsAndThen@ which lacks a
164 combiner function, appears below. Though it is perfectly well
165 behaved, it cannot be typed by Haskell, because the recursive call is
166 at a different type to the definition itself. There aren't too many
167 examples of this, which is why I thought it worth preserving! [SLPJ]
172 -> TcM s (thing, LIE s, thing_ty))
173 -> TcM s ((TcHsBinds s, thing), LIE s, thing_ty)
175 tcBindsAndThen EmptyBinds do_next
176 = do_next `thenTc` \ (thing, lie, thing_ty) ->
177 returnTc ((EmptyBinds, thing), lie, thing_ty)
179 tcBindsAndThen (ThenBinds binds1 binds2) do_next
180 = tcBindsAndThen binds1 (tcBindsAndThen binds2 do_next)
181 `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
183 returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
185 tcBindsAndThen (MonoBind bind sigs is_rec) do_next
186 = tcBindAndThen bind sigs do_next
190 %************************************************************************
192 \subsection{tcBindWithSigs}
194 %************************************************************************
196 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
197 so all the clever stuff is in here.
199 * binder_names and mbind must define the same set of Names
201 * The Names in tc_ty_sigs must be a subset of binder_names
203 * The Ids in tc_ty_sigs don't necessarily have to have the same name
204 as the Name in the tc_ty_sig
212 -> (Name -> PragmaInfo)
213 -> TcM s (TcMonoBinds s, LIE s, [TcIdBndr s])
215 tcBindWithSigs binder_names mbind tc_ty_sigs is_rec prag_info_fn
217 -- If typechecking the binds fails, then return with each
218 -- signature-less binder given type (forall a.a), to minimise subsequent
220 newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ alpha_tv ->
222 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
223 poly_ids = map mk_dummy binder_names
224 mk_dummy name = case maybeSig tc_ty_sigs name of
225 Just (TySigInfo _ poly_id _ _ _ _) -> poly_id -- Signature
226 Nothing -> mkUserId name forall_a_a NoPragmaInfo -- No signature
228 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
231 -- Create a new identifier for each binder, with each being given
232 -- a fresh unique, and a type-variable type.
233 tcGetUniques no_of_binders `thenNF_Tc` \ uniqs ->
234 mapNF_Tc mk_mono_id_ty binder_names `thenNF_Tc` \ mono_id_tys ->
236 mono_ids = zipWith3Equal "tcBindAndSigs" mk_id binder_names uniqs mono_id_tys
237 mk_id name uniq ty = mkUserLocal (getOccName name) uniq ty (getSrcLoc name)
240 -- TYPECHECK THE BINDINGS
241 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs `thenTc` \ (mbind', lie) ->
243 -- CHECK THAT THE SIGNATURES MATCH
244 -- (must do this before getTyVarsToGen)
245 checkSigMatch tc_ty_sigs `thenTc` \ sig_theta ->
247 -- COMPUTE VARIABLES OVER WHICH TO QUANTIFY, namely tyvars_to_gen
248 -- The tyvars_not_to_gen are free in the environment, and hence
249 -- candidates for generalisation, but sometimes the monomorphism
250 -- restriction means we can't generalise them nevertheless
251 getTyVarsToGen is_unrestricted mono_id_tys lie `thenTc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
253 -- DEAL WITH TYPE VARIABLE KINDS
254 mapTc defaultUncommittedTyVar (tyVarSetToList tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
256 real_tyvars_to_gen = mkTyVarSet real_tyvars_to_gen_list
257 -- It's important that the final list (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
258 -- zonked, *including boxity*, because they'll be included in the forall types of
259 -- the polymorphic Ids, and instances of these Ids will be generated from them.
261 -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
262 -- real_tyvars_to_gen
264 -- **** This step can do unification => keep other zonking after this ****
268 tcExtendGlobalTyVars tyvars_not_to_gen (
269 if null tc_ty_sigs then
270 -- No signatures, so just simplify the lie
271 tcSimplify real_tyvars_to_gen lie `thenTc` \ (lie_free, dict_binds, lie_bound) ->
272 returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
275 zonk_theta sig_theta `thenNF_Tc` \ sig_theta' ->
276 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
277 -- It's important that sig_theta is zonked, because
278 -- dict_id is later used to form the type of the polymorphic thing,
279 -- and forall-types must be zonked so far as their bound variables
282 -- Check that the needed dicts can be expressed in
283 -- terms of the signature ones
284 tcAddErrCtxt (sigsCtxt tysig_names) $
285 tcSimplifyAndCheck real_tyvars_to_gen dicts_sig lie `thenTc` \ (lie_free, dict_binds) ->
286 returnTc (lie_free, dict_binds, dict_ids)
288 ) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
290 ASSERT( not (any (isUnboxedTypeKind . tyVarKind) real_tyvars_to_gen_list) )
291 -- The instCantBeGeneralised stuff in tcSimplify should have
292 -- already raised an error if we're trying to generalise an unboxed tyvar
293 -- (NB: unboxed tyvars are always introduced along with a class constraint)
294 -- and it's better done there because we have more precise origin information.
295 -- That's why we just use an ASSERT here.
297 -- BUILD THE POLYMORPHIC RESULT IDs
298 mapNF_Tc zonkTcType mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
300 exports = zipWith3 mk_export binder_names mono_ids zonked_mono_id_types
301 dict_tys = map tcIdType dicts_bound
303 mk_export binder_name mono_id zonked_mono_id_ty
304 | maybeToBool maybe_sig = (sig_tyvars, TcId sig_poly_id, TcId mono_id)
305 | otherwise = (real_tyvars_to_gen_list, TcId poly_id, TcId mono_id)
307 maybe_sig = maybeSig tc_ty_sigs binder_name
308 Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _) = maybe_sig
309 poly_id = mkUserId binder_name poly_ty (prag_info_fn binder_name)
310 poly_ty = mkForAllTys real_tyvars_to_gen_list $ mkFunTys dict_tys $ zonked_mono_id_ty
311 -- It's important to build a fully-zonked poly_ty, because
312 -- we'll slurp out its free type variables when extending the
313 -- local environment (tcExtendLocalValEnv); if it's not zonked
314 -- it appears to have free tyvars that aren't actually free at all.
319 AbsBinds real_tyvars_to_gen_list
322 (dict_binds `AndMonoBinds` mbind'),
324 [poly_id | (_, TcId poly_id, _) <- exports]
327 no_of_binders = length binder_names
329 mk_mono_id_ty binder_name = case maybeSig tc_ty_sigs binder_name of
330 Just (TySigInfo name _ _ _ tau_ty _) -> returnNF_Tc tau_ty -- There's a signature
331 otherwise -> newTyVarTy kind -- No signature
333 tysig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
334 is_unrestricted = isUnRestrictedGroup tysig_names mbind
336 kind | is_rec = mkBoxedTypeKind -- Recursive, so no unboxed types
337 | otherwise = mkTypeKind -- Non-recursive, so we permit unboxed types
339 zonk_theta theta = mapNF_Tc zonk theta
341 zonk (c,t) = zonkTcType t `thenNF_Tc` \ t' ->
345 @getImplicitStuffToGen@ decides what type variables generalise over.
347 For a "restricted group" -- see the monomorphism restriction
348 for a definition -- we bind no dictionaries, and
349 remove from tyvars_to_gen any constrained type variables
351 *Don't* simplify dicts at this point, because we aren't going
352 to generalise over these dicts. By the time we do simplify them
353 we may well know more. For example (this actually came up)
355 f x = array ... xs where xs = [1,2,3,4,5]
356 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
357 stuff. If we simplify only at the f-binding (not the xs-binding)
358 we'll know that the literals are all Ints, and we can just produce
361 Find all the type variables involved in overloading, the
362 "constrained_tyvars". These are the ones we *aren't* going to
363 generalise. We must be careful about doing this:
365 (a) If we fail to generalise a tyvar which is not actually
366 constrained, then it will never, ever get bound, and lands
367 up printed out in interface files! Notorious example:
368 instance Eq a => Eq (Foo a b) where ..
369 Here, b is not constrained, even though it looks as if it is.
370 Another, more common, example is when there's a Method inst in
371 the LIE, whose type might very well involve non-overloaded
374 (b) On the other hand, we mustn't generalise tyvars which are constrained,
375 because we are going to pass on out the unmodified LIE, with those
376 tyvars in it. They won't be in scope if we've generalised them.
378 So we are careful, and do a complete simplification just to find the
379 constrained tyvars. We don't use any of the results, except to
380 find which tyvars are constrained.
383 getTyVarsToGen is_unrestricted mono_id_tys lie
384 = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
385 mapNF_Tc zonkTcType mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
387 tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusTyVarSet` free_tyvars
391 returnTc (emptyTyVarSet, tyvars_to_gen)
393 tcSimplify tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
395 -- ASSERT: dicts_sig is already zonked!
396 constrained_tyvars = foldrBag (unionTyVarSets . tyVarsOfInst) emptyTyVarSet constrained_dicts
397 reduced_tyvars_to_gen = tyvars_to_gen `minusTyVarSet` constrained_tyvars
399 returnTc (constrained_tyvars, reduced_tyvars_to_gen)
404 isUnRestrictedGroup :: [Name] -- Signatures given for these
408 is_elem v vs = isIn "isUnResMono" v vs
410 isUnRestrictedGroup sigs (PatMonoBind (VarPatIn v) _ _) = v `is_elem` sigs
411 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
412 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
413 isUnRestrictedGroup sigs (FunMonoBind _ _ _ _) = True
414 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
415 isUnRestrictedGroup sigs mb2
416 isUnRestrictedGroup sigs EmptyMonoBinds = True
419 @defaultUncommittedTyVar@ checks for generalisation over unboxed
420 types, and defaults any TypeKind TyVars to BoxedTypeKind.
423 defaultUncommittedTyVar tyvar
424 | isTypeKind (tyVarKind tyvar)
425 = newTcTyVar mkBoxedTypeKind `thenNF_Tc` \ boxed_tyvar ->
426 unifyTauTy (mkTyVarTy boxed_tyvar) (mkTyVarTy tyvar) `thenTc_`
434 %************************************************************************
436 \subsection{tcMonoBind}
438 %************************************************************************
440 @tcMonoBinds@ deals with a single @MonoBind@.
441 The signatures have been dealt with already.
444 tcMonoBinds :: RenamedMonoBinds
445 -> [Name] -> [TcIdBndr s]
447 -> TcM s (TcMonoBinds s, LIE s)
449 tcMonoBinds mbind binder_names mono_ids tc_ty_sigs
450 = tcExtendLocalValEnv binder_names mono_ids (
454 sig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
455 sig_ids = [id | (TySigInfo _ id _ _ _ _) <- tc_ty_sigs]
457 tc_mono_binds EmptyMonoBinds = returnTc (EmptyMonoBinds, emptyLIE)
459 tc_mono_binds (AndMonoBinds mb1 mb2)
460 = tc_mono_binds mb1 `thenTc` \ (mb1a, lie1) ->
461 tc_mono_binds mb2 `thenTc` \ (mb2a, lie2) ->
462 returnTc (AndMonoBinds mb1a mb2a, lie1 `plusLIE` lie2)
464 tc_mono_binds (FunMonoBind name inf matches locn)
466 tcLookupLocalValueOK "tc_mono_binds" name `thenNF_Tc` \ id ->
468 -- Before checking the RHS, extend the envt with
469 -- bindings for the *polymorphic* Ids from any type signatures
470 tcExtendLocalValEnv sig_names sig_ids $
471 tcMatchesFun name (idType id) matches `thenTc` \ (matches', lie) ->
473 returnTc (FunMonoBind (TcId id) inf matches' locn, lie)
475 tc_mono_binds bind@(PatMonoBind pat grhss_and_binds locn)
477 tcAddErrCtxt (patMonoBindsCtxt bind) $
478 tcPat pat `thenTc` \ (pat2, lie_pat, pat_ty) ->
480 -- Before checking the RHS, but after the pattern, extend the envt with
481 -- bindings for the *polymorphic* Ids from any type signatures
482 tcExtendLocalValEnv sig_names sig_ids $
483 tcGRHSsAndBinds pat_ty grhss_and_binds `thenTc` \ (grhss_and_binds2, lie) ->
484 returnTc (PatMonoBind pat2 grhss_and_binds2 locn,
488 %************************************************************************
490 \subsection{Signatures}
492 %************************************************************************
494 @tcSigs@ checks the signatures for validity, and returns a list of
495 {\em freshly-instantiated} signatures. That is, the types are already
496 split up, and have fresh type variables installed. All non-type-signature
497 "RenamedSigs" are ignored.
499 The @TcSigInfo@ contains @TcTypes@ because they are unified with
500 the variable's type, and after that checked to see whether they've
506 Name -- N, the Name in corresponding binding
507 (TcIdBndr s) -- *Polymorphic* binder for this value...
508 -- Usually has name = N, but doesn't have to.
515 maybeSig :: [TcSigInfo s] -> Name -> Maybe (TcSigInfo s)
516 -- Search for a particular signature
517 maybeSig [] name = Nothing
518 maybeSig (sig@(TySigInfo sig_name _ _ _ _ _) : sigs) name
519 | name == sig_name = Just sig
520 | otherwise = maybeSig sigs name
525 tcTySig :: (Name -> PragmaInfo)
527 -> TcM s (TcSigInfo s)
529 tcTySig prag_info_fn (Sig v ty src_loc)
530 = tcAddSrcLoc src_loc $
531 tcHsType ty `thenTc` \ sigma_ty ->
532 tcInstSigType sigma_ty `thenNF_Tc` \ sigma_ty' ->
534 poly_id = mkUserId v sigma_ty' (prag_info_fn v)
535 (tyvars', theta', tau') = splitSigmaTy sigma_ty'
536 -- This splitSigmaTy tries hard to make sure that tau' is a type synonym
537 -- wherever possible, which can improve interface files.
539 returnTc (TySigInfo v poly_id tyvars' theta' tau' src_loc)
542 @checkSigMatch@ does the next step in checking signature matching.
543 The tau-type part has already been unified. What we do here is to
544 check that this unification has not over-constrained the (polymorphic)
545 type variables of the original signature type.
547 The error message here is somewhat unsatisfactory, but it'll do for
552 = returnTc (error "checkSigMatch")
554 checkSigMatch tc_ty_sigs@( sig1@(TySigInfo _ id1 _ theta1 _ _) : all_sigs_but_first )
555 = -- CHECK THAT THE SIGNATURE TYVARS AND TAU_TYPES ARE OK
556 -- Doesn't affect substitution
557 mapTc check_one_sig tc_ty_sigs `thenTc_`
559 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
560 -- The type signatures on a mutually-recursive group of definitions
561 -- must all have the same context (or none).
563 -- We unify them because, with polymorphic recursion, their types
564 -- might not otherwise be related. This is a rather subtle issue.
566 mapTc check_one_cxt all_sigs_but_first `thenTc_`
570 sig1_dict_tys = mk_dict_tys theta1
571 n_sig1_dict_tys = length sig1_dict_tys
573 check_one_cxt sig@(TySigInfo _ id _ theta _ src_loc)
574 = tcAddSrcLoc src_loc $
575 tcAddErrCtxt (sigContextsCtxt id1 id) $
576 checkTc (length this_sig_dict_tys == n_sig1_dict_tys)
577 sigContextsErr `thenTc_`
578 unifyTauTyLists sig1_dict_tys this_sig_dict_tys
580 this_sig_dict_tys = mk_dict_tys theta
582 check_one_sig (TySigInfo name id sig_tyvars _ sig_tau src_loc)
583 = tcAddSrcLoc src_loc $
584 tcAddErrCtxt (sigCtxt id) $
585 checkSigTyVars sig_tyvars sig_tau
587 mk_dict_tys theta = [mkDictTy c t | (c,t) <- theta]
591 @checkSigTyVars@ is used after the type in a type signature has been unified with
592 the actual type found. It then checks that the type variables of the type signature
594 (a) still all type variables
595 eg matching signature [a] against inferred type [(p,q)]
596 [then a will be unified to a non-type variable]
598 (b) still all distinct
599 eg matching signature [(a,b)] against inferred type [(p,p)]
600 [then a and b will be unified together]
602 BUT ACTUALLY THESE FIRST TWO ARE FORCED BY USING DontBind TYVARS
604 (c) not mentioned in the environment
605 eg the signature for f in this:
611 Here, f is forced to be monorphic by the free occurence of x.
613 Before doing this, the substitution is applied to the signature type variable.
616 checkSigTyVars :: [TcTyVar s] -- The original signature type variables
617 -> TcType s -- signature type (for err msg)
620 checkSigTyVars sig_tyvars sig_tau
621 = -- Several type signatures in the same bindings group can
622 -- cause the signature type variable from the different
623 -- signatures to be unified. So we need to zonk them.
624 mapNF_Tc zonkSigTyVar sig_tyvars `thenNF_Tc` \ sig_tyvars' ->
626 -- Point (a) is forced by the fact that they are signature type
627 -- variables, so the unifer won't bind them to a type.
630 checkTcM (hasNoDups sig_tyvars')
631 (zonkTcType sig_tau `thenNF_Tc` \ sig_tau' ->
632 failTc (badMatchErr sig_tau sig_tau')
636 -- We want to report errors in terms of the original signature tyvars,
637 -- ie sig_tyvars, NOT sig_tyvars'. sig_tyvars' correspond
638 -- 1-1 with sig_tyvars, so we can just map back.
639 tcGetGlobalTyVars `thenNF_Tc` \ globals ->
641 -- mono_tyvars = [sig_tv | (sig_tv, sig_tv') <- sig_tyvars `zip` sig_tyvars',
642 -- sig_tv' `elementOfTyVarSet` globals
644 mono_tyvars' = [sig_tv' | sig_tv' <- sig_tyvars',
645 sig_tv' `elementOfTyVarSet` globals]
647 checkTcM (null mono_tyvars')
648 (zonkTcType sig_tau `thenNF_Tc` \ sig_tau' ->
649 failTc (notAsPolyAsSigErr sig_tau' mono_tyvars'))
653 %************************************************************************
655 \subsection{SPECIALIZE pragmas}
657 %************************************************************************
660 @tcPragmaSigs@ munches up the "signatures" that arise through *user*
661 pragmas. It is convenient for them to appear in the @[RenamedSig]@
662 part of a binding because then the same machinery can be used for
663 moving them into place as is done for type signatures.
666 tcPragmaSigs :: [RenamedSig] -- The pragma signatures
667 -> TcM s (Name -> PragmaInfo, -- Maps name to the appropriate PragmaInfo
671 -- For now we just deal with INLINE pragmas
672 tcPragmaSigs sigs = returnTc (prag_fn, EmptyMonoBinds, emptyLIE )
674 prag_fn name | any has_inline sigs = IWantToBeINLINEd
675 | otherwise = NoPragmaInfo
677 has_inline (InlineSig n _) = (n == name)
678 has_inline other = False
683 = mapAndUnzip3Tc tcPragmaSig sigs `thenTc` \ (names_w_id_infos, binds, lies) ->
685 name_to_info name = foldr ($) noIdInfo
686 [info_fn | (n,info_fn) <- names_w_id_infos, n==name]
688 returnTc (name_to_info,
689 foldr ThenBinds EmptyBinds binds,
690 foldr plusLIE emptyLIE lies)
693 Here are the easy cases for tcPragmaSigs
696 tcPragmaSig (DeforestSig name loc)
697 = returnTc ((name, addDeforestInfo DoDeforest),EmptyBinds,emptyLIE)
698 tcPragmaSig (InlineSig name loc)
699 = returnTc ((name, addUnfoldInfo (iWantToBeINLINEd UnfoldAlways)), EmptyBinds, emptyLIE)
700 tcPragmaSig (MagicUnfoldingSig name string loc)
701 = returnTc ((name, addUnfoldInfo (mkMagicUnfolding string)), EmptyBinds, emptyLIE)
704 The interesting case is for SPECIALISE pragmas. There are two forms.
705 Here's the first form:
707 f :: Ord a => [a] -> b -> b
708 {-# SPECIALIZE f :: [Int] -> b -> b #-}
711 For this we generate:
713 f* = /\ b -> let d1 = ...
717 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
718 retain a right-hand-side that the simplifier will otherwise discard as
719 dead code... the simplifier has a flag that tells it not to discard
720 SpecPragmaId bindings.
722 In this case the f* retains a call-instance of the overloaded
723 function, f, (including appropriate dictionaries) so that the
724 specialiser will subsequently discover that there's a call of @f@ at
725 Int, and will create a specialisation for @f@. After that, the
726 binding for @f*@ can be discarded.
728 The second form is this:
730 f :: Ord a => [a] -> b -> b
731 {-# SPECIALIZE f :: [Int] -> b -> b = g #-}
734 Here @g@ is specified as a function that implements the specialised
735 version of @f@. Suppose that g has type (a->b->b); that is, g's type
736 is more general than that required. For this we generate
738 f@Int = /\b -> g Int b
742 Here @f@@Int@ is a SpecId, the specialised version of @f@. It inherits
743 f's export status etc. @f*@ is a SpecPragmaId, as before, which just serves
744 to prevent @f@@Int@ from being discarded prematurely. After specialisation,
745 if @f@@Int@ is going to be used at all it will be used explicitly, so the simplifier can
746 discard the f* binding.
748 Actually, there is really only point in giving a SPECIALISE pragma on exported things,
749 and the simplifer won't discard SpecIds for exporte things anyway, so maybe this is
753 tcPragmaSig (SpecSig name poly_ty maybe_spec_name src_loc)
754 = tcAddSrcLoc src_loc $
755 tcAddErrCtxt (valSpecSigCtxt name spec_ty) $
757 -- Get and instantiate its alleged specialised type
758 tcHsType poly_ty `thenTc` \ sig_sigma ->
759 tcInstSigType sig_sigma `thenNF_Tc` \ sig_ty ->
761 (sig_tyvars, sig_theta, sig_tau) = splitSigmaTy sig_ty
762 origin = ValSpecOrigin name
765 -- Check that the SPECIALIZE pragma had an empty context
766 checkTc (null sig_theta)
767 (panic "SPECIALIZE non-empty context (ToDo: msg)") `thenTc_`
769 -- Get and instantiate the type of the id mentioned
770 tcLookupLocalValueOK "tcPragmaSig" name `thenNF_Tc` \ main_id ->
771 tcInstSigType [] (idType main_id) `thenNF_Tc` \ main_ty ->
773 (main_tyvars, main_rho) = splitForAllTy main_ty
774 (main_theta,main_tau) = splitRhoTy main_rho
775 main_arg_tys = mkTyVarTys main_tyvars
778 -- Check that the specialised type is indeed an instance of
779 -- the type of the main function.
780 unifyTauTy sig_tau main_tau `thenTc_`
781 checkSigTyVars sig_tyvars sig_tau `thenTc_`
783 -- Check that the type variables of the polymorphic function are
784 -- either left polymorphic, or instantiate to ground type.
785 -- Also check that the overloaded type variables are instantiated to
786 -- ground type; or equivalently that all dictionaries have ground type
787 mapTc zonkTcType main_arg_tys `thenNF_Tc` \ main_arg_tys' ->
788 zonkTcThetaType main_theta `thenNF_Tc` \ main_theta' ->
789 tcAddErrCtxt (specGroundnessCtxt main_arg_tys')
790 (checkTc (all isGroundOrTyVarTy main_arg_tys')) `thenTc_`
791 tcAddErrCtxt (specContextGroundnessCtxt main_theta')
792 (checkTc (and [isGroundTy ty | (_,ty) <- theta'])) `thenTc_`
794 -- Build the SpecPragmaId; it is the thing that makes sure we
795 -- don't prematurely dead-code-eliminate the binding we are really interested in.
796 newSpecPragmaId name sig_ty `thenNF_Tc` \ spec_pragma_id ->
798 -- Build a suitable binding; depending on whether we were given
799 -- a value (Maybe Name) to be used as the specialisation.
801 Nothing -> -- No implementation function specified
803 -- Make a Method inst for the occurrence of the overloaded function
804 newMethodWithGivenTy (OccurrenceOf name)
805 (TcId main_id) main_arg_tys main_rho `thenNF_Tc` \ (lie, meth_id) ->
808 pseudo_bind = VarMonoBind spec_pragma_id pseudo_rhs
809 pseudo_rhs = mkHsTyLam sig_tyvars (HsVar (TcId meth_id))
811 returnTc (pseudo_bind, lie, \ info -> info)
813 Just spec_name -> -- Use spec_name as the specialisation value ...
815 -- Type check a simple occurrence of the specialised Id
816 tcId spec_name `thenTc` \ (spec_body, spec_lie, spec_tau) ->
818 -- Check that it has the correct type, and doesn't constrain the
819 -- signature variables at all
820 unifyTauTy sig_tau spec_tau `thenTc_`
821 checkSigTyVars sig_tyvars sig_tau `thenTc_`
823 -- Make a local SpecId to bind to applied spec_id
824 newSpecId main_id main_arg_tys sig_ty `thenNF_Tc` \ local_spec_id ->
827 spec_rhs = mkHsTyLam sig_tyvars spec_body
828 spec_binds = VarMonoBind local_spec_id spec_rhs
830 VarMonoBind spec_pragma_id (HsVar (TcId local_spec_id))
831 spec_info = SpecInfo spec_tys (length main_theta) local_spec_id
833 returnTc ((name, addSpecInfo spec_info), spec_binds, spec_lie)
838 %************************************************************************
840 \subsection[TcBinds-errors]{Error contexts and messages}
842 %************************************************************************
846 patMonoBindsCtxt bind sty
847 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr sty bind)
849 -----------------------------------------------
850 valSpecSigCtxt v ty sty
851 = hang (ptext SLIT("In a SPECIALIZE pragma for a value:"))
852 4 (sep [(<>) (ppr sty v) (ptext SLIT(" ::")),
857 -----------------------------------------------
858 notAsPolyAsSigErr sig_tau mono_tyvars sty
859 = hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
860 4 (vcat [text "Can't for-all the type variable(s)" <+> interpp'SP sty mono_tyvars,
861 text "in the inferred type" <+> ppr sty sig_tau
864 -----------------------------------------------
865 badMatchErr sig_ty inferred_ty sty
866 = hang (ptext SLIT("Type signature doesn't match inferred type"))
867 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sty sig_ty),
868 hang (ptext SLIT("Inferred :")) 4 (ppr sty inferred_ty)
871 -----------------------------------------------
873 = sep [ptext SLIT("When checking signature for"), ppr sty id]
875 = sep [ptext SLIT("When checking signature(s) for:"), interpp'SP sty ids]
877 -----------------------------------------------
879 = ptext SLIT("Mismatched contexts")
880 sigContextsCtxt s1 s2 sty
881 = hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
882 ppr sty s1, ptext SLIT("and"), ppr sty s2])
883 4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
885 -----------------------------------------------
887 = panic "specGroundnessCtxt"
889 --------------------------------------------
890 specContextGroundnessCtxt -- err_ctxt dicts sty
891 = panic "specContextGroundnessCtxt"
894 sep [hsep [ptext SLIT("In the SPECIALIZE pragma for"), ppr sty name],
895 hcat [ptext SLIT(" specialised to the type"), ppr sty spec_ty],
897 ptext SLIT("... not all overloaded type variables were instantiated"),
898 ptext SLIT("to ground types:")])
899 4 (vcat [hsep [ppr sty c, ppr sty t]
900 | (c,t) <- map getDictClassAndType dicts])
902 (name, spec_ty, locn, pp_spec_id)
904 ValSpecSigCtxt n ty loc -> (n, ty, loc, \ x -> empty)
905 ValSpecSpecIdCtxt n ty spec loc ->
907 \ sty -> hsep [ptext SLIT("... type of explicit id"), ppr sty spec])