2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBinds, tcMonoBinds, tcSpecSigs ) where
9 #include "HsVersions.h"
11 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
12 import {-# SOURCE #-} TcExpr ( tcCheckSigma, tcCheckRho )
14 import CmdLineOpts ( DynFlag(Opt_MonomorphismRestriction) )
15 import HsSyn ( HsExpr(..), HsBind(..), LHsBinds, Sig(..),
16 LSig, Match(..), HsBindGroup(..), IPBind(..),
17 LPat, GRHSs, MatchGroup(..), emptyLHsBinds, isEmptyLHsBinds,
18 collectHsBindBinders, collectPatBinders, pprPatBind
20 import TcHsSyn ( TcId, TcDictBinds, zonkId, mkHsLet )
23 import Inst ( InstOrigin(..), newDictsAtLoc, newIPDict, instToId )
24 import TcEnv ( tcExtendIdEnv, tcExtendIdEnv2, newLocalName, tcLookupLocalIds )
25 import TcUnify ( Expected(..), tcInfer, checkSigTyVars, sigCtxt )
26 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted,
27 tcSimplifyToDicts, tcSimplifyIPs )
28 import TcHsType ( tcHsSigType, UserTypeCtxt(..), tcAddLetBoundTyVars,
29 TcSigInfo(..), TcSigFun, mkTcSig, lookupSig
31 import TcPat ( tcPat, PatCtxt(..) )
32 import TcSimplify ( bindInstsOfLocalFuns )
33 import TcMType ( newTyFlexiVarTy, tcSkolType, zonkQuantifiedTyVar, zonkTcTypes )
34 import TcType ( TcTyVar, SkolemInfo(SigSkol),
35 TcTauType, TcSigmaType,
36 TvSubstEnv, mkTvSubst, substTheta, substTy,
37 mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
38 mkForAllTy, isUnLiftedType, tcGetTyVar_maybe,
40 import Unify ( tcMatchPreds )
41 import Kind ( argTypeKind, isUnliftedTypeKind )
42 import VarEnv ( lookupVarEnv )
43 import TysPrim ( alphaTyVar )
44 import Id ( mkLocalId, mkSpecPragmaId, setInlinePragma )
45 import Var ( idType, idName )
48 import Var ( tyVarKind )
50 import SrcLoc ( Located(..), unLoc, noLoc, getLoc )
53 import Maybes ( orElse )
54 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isRec,
55 isNotTopLevel, isAlwaysActive )
56 import FiniteMap ( listToFM, lookupFM )
61 %************************************************************************
63 \subsection{Type-checking bindings}
65 %************************************************************************
67 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
68 it needs to know something about the {\em usage} of the things bound,
69 so that it can create specialisations of them. So @tcBindsAndThen@
70 takes a function which, given an extended environment, E, typechecks
71 the scope of the bindings returning a typechecked thing and (most
72 important) an LIE. It is this LIE which is then used as the basis for
73 specialising the things bound.
75 @tcBindsAndThen@ also takes a "combiner" which glues together the
76 bindings and the "thing" to make a new "thing".
78 The real work is done by @tcBindWithSigsAndThen@.
80 Recursive and non-recursive binds are handled in essentially the same
81 way: because of uniques there are no scoping issues left. The only
82 difference is that non-recursive bindings can bind primitive values.
84 Even for non-recursive binding groups we add typings for each binder
85 to the LVE for the following reason. When each individual binding is
86 checked the type of its LHS is unified with that of its RHS; and
87 type-checking the LHS of course requires that the binder is in scope.
89 At the top-level the LIE is sure to contain nothing but constant
90 dictionaries, which we resolve at the module level.
93 tcTopBinds :: [HsBindGroup Name] -> TcM (LHsBinds TcId, TcLclEnv)
94 -- Note: returning the TcLclEnv is more than we really
95 -- want. The bit we care about is the local bindings
96 -- and the free type variables thereof
98 = tc_binds_and_then TopLevel glue binds $
99 getLclEnv `thenM` \ env ->
100 returnM (emptyLHsBinds, env)
102 -- The top level bindings are flattened into a giant
103 -- implicitly-mutually-recursive MonoBinds
104 glue (HsBindGroup binds1 _ _) (binds2, env) = (binds1 `unionBags` binds2, env)
105 -- Can't have a HsIPBinds at top level
109 :: (HsBindGroup TcId -> thing -> thing) -- Combinator
110 -> [HsBindGroup Name]
114 tcBindsAndThen = tc_binds_and_then NotTopLevel
116 tc_binds_and_then top_lvl combiner [] do_next
118 tc_binds_and_then top_lvl combiner (group : groups) do_next
119 = tc_bind_and_then top_lvl combiner group $
120 tc_binds_and_then top_lvl combiner groups do_next
122 tc_bind_and_then top_lvl combiner (HsIPBinds binds) do_next
123 = getLIE do_next `thenM` \ (result, expr_lie) ->
124 mapAndUnzipM (wrapLocSndM tc_ip_bind) binds `thenM` \ (avail_ips, binds') ->
126 -- If the binding binds ?x = E, we must now
127 -- discharge any ?x constraints in expr_lie
128 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
130 returnM (combiner (HsIPBinds binds') $
131 combiner (HsBindGroup dict_binds [] Recursive) result)
133 -- I wonder if we should do these one at at time
136 tc_ip_bind (IPBind ip expr)
137 = newTyFlexiVarTy argTypeKind `thenM` \ ty ->
138 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
139 tcCheckRho expr ty `thenM` \ expr' ->
140 returnM (ip_inst, (IPBind ip' expr'))
142 tc_bind_and_then top_lvl combiner (HsBindGroup binds sigs is_rec) do_next
143 | isEmptyLHsBinds binds
146 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
147 -- Notice that they scope over
148 -- a) the type signatures in the binding group
149 -- b) the bindings in the group
150 -- c) the scope of the binding group (the "in" part)
151 tcAddLetBoundTyVars binds $
154 TopLevel -- For the top level don't bother will all this
155 -- bindInstsOfLocalFuns stuff. All the top level
156 -- things are rec'd together anyway, so it's fine to
157 -- leave them to the tcSimplifyTop, and quite a bit faster too
158 -> tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
159 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
160 returnM (combiner (HsBindGroup
161 (poly_binds `unionBags` prag_binds)
166 NotTopLevel -- For nested bindings we must do the bindInstsOfLocalFuns thing.
167 | not (isRec is_rec) -- Non-recursive group
168 -> -- We want to keep non-recursive things non-recursive
169 -- so that we desugar unlifted bindings correctly
170 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
171 getLIE (tc_body poly_ids) `thenM` \ ((prag_binds, thing), lie) ->
173 -- Create specialisations of functions bound here
174 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
177 combiner (HsBindGroup poly_binds [] NonRecursive) $
178 combiner (HsBindGroup prag_binds [] NonRecursive) $
179 combiner (HsBindGroup lie_binds [] Recursive) $
180 -- NB: the binds returned by tcSimplify and
181 -- bindInstsOfLocalFuns aren't guaranteed in
182 -- dependency order (though we could change that);
183 -- hence the Recursive marker.
187 -> -- NB: polymorphic recursion means that a function
188 -- may use an instance of itself, we must look at the LIE arising
189 -- from the function's own right hand side. Hence the getLIE
190 -- encloses the tcBindWithSigs.
193 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
194 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
195 returnM (poly_ids, poly_binds `unionBags` prag_binds, thing)
196 ) `thenM` \ ((poly_ids, extra_binds, thing), lie) ->
198 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
200 returnM (combiner (HsBindGroup
201 (extra_binds `unionBags` lie_binds)
205 tc_body poly_ids -- Type check the pragmas and "thing inside"
206 = -- Extend the environment to bind the new polymorphic Ids
207 tcExtendIdEnv poly_ids $
209 -- Build bindings and IdInfos corresponding to user pragmas
210 tcSpecSigs sigs `thenM` \ prag_binds ->
212 -- Now do whatever happens next, in the augmented envt
213 do_next `thenM` \ thing ->
215 returnM (prag_binds, thing)
219 %************************************************************************
221 \subsection{tcBindWithSigs}
223 %************************************************************************
225 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
226 so all the clever stuff is in here.
228 * binder_names and mbind must define the same set of Names
230 * The Names in tc_ty_sigs must be a subset of binder_names
232 * The Ids in tc_ty_sigs don't necessarily have to have the same name
233 as the Name in the tc_ty_sig
236 tcBindWithSigs :: TopLevelFlag
240 -> TcM (LHsBinds TcId, [TcId])
241 -- The returned TcIds are guaranteed zonked
243 tcBindWithSigs top_lvl mbind sigs is_rec = do
244 { -- TYPECHECK THE SIGNATURES
245 tc_ty_sigs <- recoverM (returnM []) $
246 tcTySigs [sig | sig@(L _(Sig name _)) <- sigs]
247 ; let lookup_sig = lookupSig tc_ty_sigs
249 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
250 ; recoverM (recoveryCode mbind lookup_sig) $ do
252 { traceTc (ptext SLIT("--------------------------------------------------------"))
253 ; traceTc (ptext SLIT("Bindings for") <+> ppr (collectHsBindBinders mbind))
255 -- TYPECHECK THE BINDINGS
256 ; ((mbind', mono_bind_infos), lie_req)
257 <- getLIE (tcMonoBinds mbind lookup_sig is_rec)
259 -- CHECK FOR UNLIFTED BINDINGS
260 -- These must be non-recursive etc, and are not generalised
261 -- They desugar to a case expression in the end
262 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
263 ; if any isUnLiftedType zonked_mono_tys then
264 do { -- Unlifted bindings
265 checkUnliftedBinds top_lvl is_rec mbind
267 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
268 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id)
269 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id)
271 ; return ( unitBag $ noLoc $ AbsBinds [] [] exports emptyNameSet mbind',
272 [poly_id | (_, poly_id, _) <- exports]) } -- Guaranteed zonked
274 else do -- The normal lifted case: GENERALISE
275 { is_unres <- isUnRestrictedGroup mbind tc_ty_sigs
276 ; (tyvars_to_gen, dict_binds, dict_ids)
277 <- setSrcSpan (getLoc (head (bagToList mbind))) $
278 -- TODO: location a bit awkward, but the mbinds have been
279 -- dependency analysed and may no longer be adjacent
280 addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
281 generalise is_unres mono_bind_infos tc_ty_sigs lie_req
283 -- FINALISE THE QUANTIFIED TYPE VARIABLES
284 -- The quantified type variables often include meta type variables
285 -- we want to freeze them into ordinary type variables, and
286 -- default their kind (e.g. from OpenTypeKind to TypeKind)
287 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
289 -- BUILD THE POLYMORPHIC RESULT IDs
291 exports = map mk_export mono_bind_infos
292 poly_ids = [poly_id | (_, poly_id, _) <- exports]
293 dict_tys = map idType dict_ids
295 inlines = mkNameSet [ name
296 | L _ (InlineSig True (L _ name) _) <- sigs]
297 -- Any INLINE sig (regardless of phase control)
298 -- makes the RHS look small
299 inline_phases = listToFM [ (name, phase)
300 | L _ (InlineSig _ (L _ name) phase) <- sigs,
301 not (isAlwaysActive phase)]
302 -- Set the IdInfo field to control the inline phase
303 -- AlwaysActive is the default, so don't bother with them
304 add_inlines id = attachInlinePhase inline_phases id
306 mk_export (binder_name, mb_sig, mono_id)
308 Just sig -> (sig_tvs sig, add_inlines (sig_id sig), mono_id)
309 Nothing -> (tyvars_to_gen', add_inlines new_poly_id, mono_id)
311 new_poly_id = mkLocalId binder_name poly_ty
312 poly_ty = mkForAllTys tyvars_to_gen'
316 -- ZONK THE poly_ids, because they are used to extend the type
317 -- environment; see the invariant on TcEnv.tcExtendIdEnv
318 ; zonked_poly_ids <- mappM zonkId poly_ids
320 ; traceTc (text "binding:" <+> ppr ((dict_ids, dict_binds),
321 exports, map idType zonked_poly_ids))
325 AbsBinds tyvars_to_gen'
329 (dict_binds `unionBags` mbind'),
334 -- If typechecking the binds fails, then return with each
335 -- signature-less binder given type (forall a.a), to minimise
336 -- subsequent error messages
337 recoveryCode mbind lookup_sig
338 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
339 ; return (emptyLHsBinds, poly_ids) }
341 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
342 binder_names = collectHsBindBinders mbind
343 poly_ids = map mk_dummy binder_names
344 mk_dummy name = case lookup_sig name of
345 Just sig -> sig_id sig -- Signature
346 Nothing -> mkLocalId name forall_a_a -- No signature
348 attachInlinePhase inline_phases bndr
349 = case lookupFM inline_phases (idName bndr) of
350 Just prag -> bndr `setInlinePragma` prag
353 -- Check that non-overloaded unlifted bindings are
356 -- c) not a multiple-binding group (more or less implied by (a))
358 checkUnliftedBinds top_lvl is_rec mbind
359 = checkTc (isNotTopLevel top_lvl)
360 (unliftedBindErr "Top-level" mbind) `thenM_`
361 checkTc (isNonRec is_rec)
362 (unliftedBindErr "Recursive" mbind) `thenM_`
363 checkTc (isSingletonBag mbind)
364 (unliftedBindErr "Multiple" mbind)
368 Polymorphic recursion
369 ~~~~~~~~~~~~~~~~~~~~~
370 The game plan for polymorphic recursion in the code above is
372 * Bind any variable for which we have a type signature
373 to an Id with a polymorphic type. Then when type-checking
374 the RHSs we'll make a full polymorphic call.
376 This fine, but if you aren't a bit careful you end up with a horrendous
377 amount of partial application and (worse) a huge space leak. For example:
379 f :: Eq a => [a] -> [a]
382 If we don't take care, after typechecking we get
384 f = /\a -> \d::Eq a -> let f' = f a d
388 Notice the the stupid construction of (f a d), which is of course
389 identical to the function we're executing. In this case, the
390 polymorphic recursion isn't being used (but that's a very common case).
393 f = /\a -> \d::Eq a -> letrec
394 fm = \ys:[a] -> ...fm...
398 This can lead to a massive space leak, from the following top-level defn
404 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
405 f' is another thunk which evaluates to the same thing... and you end
406 up with a chain of identical values all hung onto by the CAF ff.
410 = let f' = f Int dEqInt in \ys. ...f'...
412 = let f' = let f' = f Int dEqInt in \ys. ...f'...
416 Solution: when typechecking the RHSs we always have in hand the
417 *monomorphic* Ids for each binding. So we just need to make sure that
418 if (Method f a d) shows up in the constraints emerging from (...f...)
419 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
420 to the "givens" when simplifying constraints. That's what the "lies_avail"
424 %************************************************************************
426 \subsection{tcMonoBind}
428 %************************************************************************
430 @tcMonoBinds@ deals with a single @MonoBind@.
431 The signatures have been dealt with already.
434 tcMonoBinds :: LHsBinds Name
435 -> TcSigFun -> RecFlag
436 -> TcM (LHsBinds TcId, [MonoBindInfo])
438 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
439 -- Type signature (if any), and
440 -- the monomorphic bound things
442 bndrNames :: [MonoBindInfo] -> [Name]
443 bndrNames mbi = [n | (n,_,_) <- mbi]
445 getMonoType :: MonoBindInfo -> TcTauType
446 getMonoType (_,_,mono_id) = idType mono_id
448 tcMonoBinds binds lookup_sig is_rec
449 = do { tc_binds <- mapBagM (wrapLocM (tcLhs lookup_sig)) binds
450 ; let mono_info = getMonoBindInfo tc_binds
451 ; binds' <- tcExtendIdEnv2 (rhsEnvExtension mono_info) $
452 mapBagM (wrapLocM tcRhs) tc_binds
453 ; return (binds', mono_info) }
455 ------------------------
456 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
457 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
458 -- if there's a signature for it, use the instantiated signature type
459 -- otherwise invent a type variable
460 -- You see that quite directly in the FunBind case.
462 -- But there's a complication for pattern bindings:
463 -- data T = MkT (forall a. a->a)
465 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
466 -- but we want to get (f::forall a. a->a) as the RHS environment.
467 -- The simplest way to do this is to typecheck the pattern, and then look up the
468 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
469 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
471 data TcMonoBind -- Half completed; LHS done, RHS not done
472 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
473 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
475 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
476 tcLhs lookup_sig (FunBind (L nm_loc name) inf matches)
477 = do { let mb_sig = lookup_sig name
478 ; mono_name <- newLocalName name
479 ; mono_ty <- mk_mono_ty mb_sig
480 ; let mono_id = mkLocalId mono_name mono_ty
481 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
483 mk_mono_ty (Just sig) = return (sig_tau sig)
484 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
486 tcLhs lookup_sig bind@(PatBind pat grhss _)
487 = do { let tc_pat exp_ty = tcPat (LetPat lookup_sig) pat exp_ty lookup_infos
488 ; ((pat', ex_tvs, infos), pat_ty)
489 <- addErrCtxt (patMonoBindsCtxt pat grhss)
492 -- Don't know how to deal with pattern-bound existentials yet
493 ; checkTc (null ex_tvs) (existentialExplode bind)
495 ; return (TcPatBind infos pat' grhss pat_ty) }
497 names = collectPatBinders pat
499 -- After typechecking the pattern, look up the binder
500 -- names, which the pattern has brought into scope.
501 lookup_infos :: TcM [MonoBindInfo]
502 lookup_infos = do { mono_ids <- tcLookupLocalIds names
503 ; return [ (name, lookup_sig name, mono_id)
504 | (name, mono_id) <- names `zip` mono_ids] }
507 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
508 tcRhs (TcFunBind _ fun'@(L _ mono_id) inf matches)
509 = do { matches' <- tcMatchesFun (idName mono_id) matches
510 (Check (idType mono_id))
511 ; return (FunBind fun' inf matches') }
513 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
514 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
515 tcGRHSsPat grhss (Check pat_ty)
516 ; return (PatBind pat' grhss' pat_ty) }
519 ---------------------
520 getMonoBindInfo :: Bag (Located TcMonoBind) -> [MonoBindInfo]
521 getMonoBindInfo tc_binds
522 = foldrBag (get_info . unLoc) [] tc_binds
524 get_info (TcFunBind info _ _ _) rest = info : rest
525 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
527 ---------------------
528 rhsEnvExtension :: [MonoBindInfo] -> [(Name, TcId)]
529 -- Environment for RHS of definitions: use type sig if there is one
530 rhsEnvExtension mono_info
533 mk (name, Just sig, _) = (name, sig_id sig)
534 mk (name, Nothing, mono_id) = (name, mono_id)
538 %************************************************************************
540 \subsection{getTyVarsToGen}
542 %************************************************************************
545 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
546 -- The trick here is that all the signatures should have the same
547 -- context, and we want to share type variables for that context, so that
548 -- all the right hand sides agree a common vocabulary for their type
550 tcTySigs [] = return []
551 tcTySigs (L span (Sig (L _ name) ty) : sigs)
552 = do { -- Typecheck the first signature
553 ; sigma1 <- setSrcSpan span $
554 tcHsSigType (FunSigCtxt name) ty
555 ; let id1 = mkLocalId name sigma1
556 ; tc_sig1 <- mkTcSig id1
558 ; tc_sigs <- mapM (tcTySig tc_sig1) sigs
559 ; return (tc_sig1 : tc_sigs) }
561 tcTySig sig1 (L span (Sig (L _ name) ty))
563 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
564 ; (tvs, theta, tau) <- tcSkolType rigid_info sigma_ty
565 ; let poly_id = mkLocalId name sigma_ty
566 bale_out = failWithTc $
567 sigContextsErr (sig_id sig1) name sigma_ty
569 -- Try to match the context of this signature with
570 -- that of the first signature
571 ; case tcMatchPreds tvs theta (sig_theta sig1) of {
574 ; case check_tvs tenv tvs of
578 let subst = mkTvSubst tenv
579 theta' = substTheta subst theta
580 tau' = substTy subst tau
581 ; loc <- getInstLoc (SigOrigin rigid_info)
582 ; return (TcSigInfo { sig_id = poly_id, sig_tvs = tvs',
583 sig_theta = theta', sig_tau = tau',
586 rigid_info = SigSkol name
588 -- Rather tedious check that the type variables
589 -- have been matched only with another type variable,
590 -- and that two type variables have not been matched
592 -- A return of Nothing indicates that one of the bad
593 -- things has happened
594 check_tvs :: TvSubstEnv -> [TcTyVar] -> Maybe [TcTyVar]
595 check_tvs tenv [] = Just []
596 check_tvs tenv (tv:tvs)
597 = do { let ty = lookupVarEnv tenv tv `orElse` mkTyVarTy tv
598 ; tv' <- tcGetTyVar_maybe ty
599 ; tvs' <- check_tvs tenv tvs
602 else Just (tv':tvs') }
606 generalise :: Bool -> [MonoBindInfo] -> [TcSigInfo] -> [Inst]
607 -> TcM ([TcTyVar], TcDictBinds, [TcId])
608 generalise is_unrestricted mono_infos sigs lie_req
609 | not is_unrestricted -- RESTRICTED CASE
610 = -- Check signature contexts are empty
611 do { checkTc (all is_mono_sig sigs)
612 (restrictedBindCtxtErr bndr_names)
614 -- Now simplify with exactly that set of tyvars
615 -- We have to squash those Methods
616 ; (qtvs, binds) <- tcSimplifyRestricted doc tau_tvs lie_req
618 -- Check that signature type variables are OK
619 ; final_qtvs <- checkSigsTyVars qtvs sigs
621 ; return (final_qtvs, binds, []) }
623 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
624 = tcSimplifyInfer doc tau_tvs lie_req
626 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
627 = do { let sig1 = head sigs
628 ; sig_lie <- newDictsAtLoc (sig_loc sig1) (sig_theta sig1)
629 ; let -- The "sig_avails" is the stuff available. We get that from
630 -- the context of the type signature, BUT ALSO the lie_avail
631 -- so that polymorphic recursion works right (see comments at end of fn)
632 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
633 sig_avails = sig_lie ++ local_meths
635 -- Check that the needed dicts can be
636 -- expressed in terms of the signature ones
637 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
639 -- Check that signature type variables are OK
640 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
642 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
645 bndr_names = bndrNames mono_infos
646 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
647 is_mono_sig sig = null (sig_theta sig)
648 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndr_names
650 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
651 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
652 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
654 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
655 checkSigsTyVars qtvs sigs
656 = mappM check_one sigs `thenM` \ sig_tvs_s ->
658 -- Sigh. Make sure that all the tyvars in the type sigs
659 -- appear in the returned ty var list, which is what we are
660 -- going to generalise over. Reason: we occasionally get
662 -- type T a = () -> ()
665 -- Here, 'a' won't appear in qtvs, so we have to add it
667 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
668 all_tvs = extendVarSetList sig_tvs qtvs
670 returnM (varSetElems all_tvs)
672 check_one (TcSigInfo {sig_id = id, sig_tvs = tvs, sig_theta = theta, sig_tau = tau})
673 = addErrCtxt (ptext SLIT("In the type signature for")
674 <+> quotes (ppr id)) $
675 addErrCtxtM (sigCtxt id tvs theta tau) $
676 do { checkSigTyVars tvs; return tvs }
679 @getTyVarsToGen@ decides what type variables to generalise over.
681 For a "restricted group" -- see the monomorphism restriction
682 for a definition -- we bind no dictionaries, and
683 remove from tyvars_to_gen any constrained type variables
685 *Don't* simplify dicts at this point, because we aren't going
686 to generalise over these dicts. By the time we do simplify them
687 we may well know more. For example (this actually came up)
689 f x = array ... xs where xs = [1,2,3,4,5]
690 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
691 stuff. If we simplify only at the f-binding (not the xs-binding)
692 we'll know that the literals are all Ints, and we can just produce
695 Find all the type variables involved in overloading, the
696 "constrained_tyvars". These are the ones we *aren't* going to
697 generalise. We must be careful about doing this:
699 (a) If we fail to generalise a tyvar which is not actually
700 constrained, then it will never, ever get bound, and lands
701 up printed out in interface files! Notorious example:
702 instance Eq a => Eq (Foo a b) where ..
703 Here, b is not constrained, even though it looks as if it is.
704 Another, more common, example is when there's a Method inst in
705 the LIE, whose type might very well involve non-overloaded
707 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
708 the simple thing instead]
710 (b) On the other hand, we mustn't generalise tyvars which are constrained,
711 because we are going to pass on out the unmodified LIE, with those
712 tyvars in it. They won't be in scope if we've generalised them.
714 So we are careful, and do a complete simplification just to find the
715 constrained tyvars. We don't use any of the results, except to
716 find which tyvars are constrained.
719 isUnRestrictedGroup :: LHsBinds Name -> [TcSigInfo] -> TcM Bool
720 isUnRestrictedGroup binds sigs
721 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
722 ; return (not mono_restriction || all_unrestricted) }
724 all_unrestricted = all (unrestricted . unLoc) (bagToList binds)
725 tysig_names = map (idName . sig_id) sigs
727 unrestricted (PatBind other _ _) = False
728 unrestricted (VarBind v _) = v `is_elem` tysig_names
729 unrestricted (FunBind v _ matches) = unrestricted_match matches
730 || unLoc v `is_elem` tysig_names
732 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
733 -- No args => like a pattern binding
734 unrestricted_match other = True
735 -- Some args => a function binding
737 is_elem v vs = isIn "isUnResMono" v vs
741 %************************************************************************
743 \subsection{SPECIALIZE pragmas}
745 %************************************************************************
747 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
748 pragmas. It is convenient for them to appear in the @[RenamedSig]@
749 part of a binding because then the same machinery can be used for
750 moving them into place as is done for type signatures.
755 f :: Ord a => [a] -> b -> b
756 {-# SPECIALIZE f :: [Int] -> b -> b #-}
759 For this we generate:
761 f* = /\ b -> let d1 = ...
765 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
766 retain a right-hand-side that the simplifier will otherwise discard as
767 dead code... the simplifier has a flag that tells it not to discard
768 SpecPragmaId bindings.
770 In this case the f* retains a call-instance of the overloaded
771 function, f, (including appropriate dictionaries) so that the
772 specialiser will subsequently discover that there's a call of @f@ at
773 Int, and will create a specialisation for @f@. After that, the
774 binding for @f*@ can be discarded.
776 We used to have a form
777 {-# SPECIALISE f :: <type> = g #-}
778 which promised that g implemented f at <type>, but we do that with
780 {-# RULES (f::<type>) = g #-}
783 tcSpecSigs :: [LSig Name] -> TcM (LHsBinds TcId)
784 tcSpecSigs (L loc (SpecSig (L nm_loc name) poly_ty) : sigs)
785 = -- SPECIALISE f :: forall b. theta => tau = g
787 addErrCtxt (valSpecSigCtxt name poly_ty) $
789 -- Get and instantiate its alleged specialised type
790 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
792 -- Check that f has a more general type, and build a RHS for
793 -- the spec-pragma-id at the same time
794 getLIE (tcCheckSigma (L nm_loc (HsVar name)) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
796 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
797 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
799 -- Just specialise "f" by building a SpecPragmaId binding
800 -- It is the thing that makes sure we don't prematurely
801 -- dead-code-eliminate the binding we are really interested in.
802 newLocalName name `thenM` \ spec_name ->
804 spec_bind = VarBind (mkSpecPragmaId spec_name sig_ty)
805 (mkHsLet spec_binds spec_expr)
808 -- Do the rest and combine
809 tcSpecSigs sigs `thenM` \ binds_rest ->
810 returnM (binds_rest `snocBag` L loc spec_bind)
812 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
813 tcSpecSigs [] = returnM emptyLHsBinds
816 %************************************************************************
818 \subsection[TcBinds-errors]{Error contexts and messages}
820 %************************************************************************
824 -- This one is called on LHS, when pat and grhss are both Name
825 -- and on RHS, when pat is TcId and grhss is still Name
826 patMonoBindsCtxt pat grhss
827 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
829 -----------------------------------------------
831 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
832 nest 4 (ppr v <+> dcolon <+> ppr ty)]
834 -----------------------------------------------
835 sigContextsErr id1 name ty
836 = vcat [ptext SLIT("Mis-match between the contexts of the signatures for"),
837 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
838 ppr name <+> dcolon <+> ppr ty]),
839 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
842 -----------------------------------------------
843 unliftedBindErr flavour mbind
844 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
847 -----------------------------------------------
848 existentialExplode mbinds
849 = hang (vcat [text "My brain just exploded.",
850 text "I can't handle pattern bindings for existentially-quantified constructors.",
851 text "In the binding group"])
854 -----------------------------------------------
855 restrictedBindCtxtErr binder_names
856 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
857 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
858 ptext SLIT("that falls under the monomorphism restriction")])
861 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
863 -- Used in error messages
864 -- Use quotes for a single one; they look a bit "busy" for several
865 pprBinders [bndr] = quotes (ppr bndr)
866 pprBinders bndrs = pprWithCommas ppr bndrs