2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcLocalBinds, tcTopBinds,
8 tcHsBootSigs, tcMonoBinds,
9 TcPragFun, tcSpecPrag, tcPrags, mkPragFun,
10 badBootDeclErr ) where
12 #include "HsVersions.h"
14 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
15 import {-# SOURCE #-} TcExpr ( tcCheckRho )
17 import DynFlags ( DynFlag(Opt_MonomorphismRestriction, Opt_GlasgowExts) )
18 import HsSyn ( HsExpr(..), HsBind(..), LHsBinds, LHsBind, Sig(..),
19 HsLocalBinds(..), HsValBinds(..), HsIPBinds(..),
20 LSig, Match(..), IPBind(..), Prag(..),
21 HsType(..), LHsType, HsExplicitForAll(..), hsLTyVarNames,
22 isVanillaLSig, sigName, placeHolderNames, isPragLSig,
23 LPat, GRHSs, MatchGroup(..), pprLHsBinds,
24 collectHsBindBinders, collectPatBinders, pprPatBind
26 import TcHsSyn ( zonkId, (<$>) )
29 import Inst ( newDictsAtLoc, newIPDict, instToId )
30 import TcEnv ( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2,
31 tcLookupLocalIds, pprBinders,
33 import TcUnify ( Expected(..), tcInfer, unifyTheta, tcSub,
34 bleatEscapedTvs, sigCtxt )
35 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck,
36 tcSimplifyRestricted, tcSimplifyIPs )
37 import TcHsType ( tcHsSigType, UserTypeCtxt(..), tcAddLetBoundTyVars,
38 TcSigInfo(..), TcSigFun, lookupSig
40 import TcPat ( tcPat, PatCtxt(..) )
41 import TcSimplify ( bindInstsOfLocalFuns )
42 import TcMType ( newTyFlexiVarTy, zonkQuantifiedTyVar,
43 tcInstSigType, zonkTcType, zonkTcTypes, zonkTcTyVar )
44 import TcType ( TcType, TcTyVar, SkolemInfo(SigSkol),
45 TcTauType, TcSigmaType, isUnboxedTupleType,
46 mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
47 mkForAllTy, isUnLiftedType, tcGetTyVar,
48 mkTyVarTys, tidyOpenTyVar )
49 import Kind ( argTypeKind )
50 import VarEnv ( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv, emptyTidyEnv )
51 import TysPrim ( alphaTyVar )
52 import Id ( Id, mkLocalId, mkVanillaGlobal )
53 import IdInfo ( vanillaIdInfo )
54 import Var ( TyVar, idType, idName )
59 import SrcLoc ( Located(..), unLoc, getLoc )
61 import ErrUtils ( Message )
62 import Digraph ( SCC(..), stronglyConnComp )
63 import Maybes ( fromJust, isJust, isNothing, orElse, catMaybes )
64 import Util ( singleton )
65 import BasicTypes ( TopLevelFlag(..), isTopLevel, isNotTopLevel,
66 RecFlag(..), isNonRec, InlineSpec, defaultInlineSpec )
71 %************************************************************************
73 \subsection{Type-checking bindings}
75 %************************************************************************
77 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
78 it needs to know something about the {\em usage} of the things bound,
79 so that it can create specialisations of them. So @tcBindsAndThen@
80 takes a function which, given an extended environment, E, typechecks
81 the scope of the bindings returning a typechecked thing and (most
82 important) an LIE. It is this LIE which is then used as the basis for
83 specialising the things bound.
85 @tcBindsAndThen@ also takes a "combiner" which glues together the
86 bindings and the "thing" to make a new "thing".
88 The real work is done by @tcBindWithSigsAndThen@.
90 Recursive and non-recursive binds are handled in essentially the same
91 way: because of uniques there are no scoping issues left. The only
92 difference is that non-recursive bindings can bind primitive values.
94 Even for non-recursive binding groups we add typings for each binder
95 to the LVE for the following reason. When each individual binding is
96 checked the type of its LHS is unified with that of its RHS; and
97 type-checking the LHS of course requires that the binder is in scope.
99 At the top-level the LIE is sure to contain nothing but constant
100 dictionaries, which we resolve at the module level.
103 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
104 -- Note: returning the TcLclEnv is more than we really
105 -- want. The bit we care about is the local bindings
106 -- and the free type variables thereof
108 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
109 ; return (foldr (unionBags . snd) emptyBag prs, env) }
110 -- The top level bindings are flattened into a giant
111 -- implicitly-mutually-recursive LHsBinds
113 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
114 -- A hs-boot file has only one BindGroup, and it only has type
115 -- signatures in it. The renamer checked all this
116 tcHsBootSigs (ValBindsOut binds sigs)
117 = do { checkTc (null binds) badBootDeclErr
118 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
120 tc_boot_sig (TypeSig (L _ name) ty)
121 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
122 ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
123 -- Notice that we make GlobalIds, not LocalIds
124 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
126 badBootDeclErr :: Message
127 badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file")
129 ------------------------
130 tcLocalBinds :: HsLocalBinds Name -> TcM thing
131 -> TcM (HsLocalBinds TcId, thing)
133 tcLocalBinds EmptyLocalBinds thing_inside
134 = do { thing <- thing_inside
135 ; return (EmptyLocalBinds, thing) }
137 tcLocalBinds (HsValBinds binds) thing_inside
138 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
139 ; return (HsValBinds binds', thing) }
141 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
142 = do { (thing, lie) <- getLIE thing_inside
143 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
145 -- If the binding binds ?x = E, we must now
146 -- discharge any ?x constraints in expr_lie
147 ; dict_binds <- tcSimplifyIPs avail_ips lie
148 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
150 -- I wonder if we should do these one at at time
153 tc_ip_bind (IPBind ip expr)
154 = newTyFlexiVarTy argTypeKind `thenM` \ ty ->
155 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
156 tcCheckRho expr ty `thenM` \ expr' ->
157 returnM (ip_inst, (IPBind ip' expr'))
159 ------------------------
160 tcValBinds :: TopLevelFlag
161 -> HsValBinds Name -> TcM thing
162 -> TcM (HsValBinds TcId, thing)
164 tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
165 = pprPanic "tcValBinds" (ppr binds)
167 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
168 = tcAddLetBoundTyVars binds $
169 -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
170 -- Notice that they scope over
171 -- a) the type signatures in the binding group
172 -- b) the bindings in the group
173 -- c) the scope of the binding group (the "in" part)
175 do { -- Typecheck the signature
176 tc_ty_sigs <- recoverM (returnM []) (tcTySigs sigs)
177 ; let { prag_fn = mkPragFun sigs
178 ; sig_fn = lookupSig tc_ty_sigs
179 ; sig_ids = map sig_id tc_ty_sigs }
181 -- Extend the envt right away with all
182 -- the Ids declared with type signatures
183 ; (binds', thing) <- tcExtendIdEnv sig_ids $
184 tc_val_binds top_lvl sig_fn prag_fn
187 ; return (ValBindsOut binds' sigs, thing) }
189 ------------------------
190 tc_val_binds :: TopLevelFlag -> TcSigFun -> TcPragFun
191 -> [(RecFlag, LHsBinds Name)] -> TcM thing
192 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
193 -- Typecheck a whole lot of value bindings,
194 -- one strongly-connected component at a time
196 tc_val_binds top_lvl sig_fn prag_fn [] thing_inside
197 = do { thing <- thing_inside
198 ; return ([], thing) }
200 tc_val_binds top_lvl sig_fn prag_fn (group : groups) thing_inside
201 = do { (group', (groups', thing))
202 <- tc_group top_lvl sig_fn prag_fn group $
203 tc_val_binds top_lvl sig_fn prag_fn groups thing_inside
204 ; return (group' ++ groups', thing) }
206 ------------------------
207 tc_group :: TopLevelFlag -> TcSigFun -> TcPragFun
208 -> (RecFlag, LHsBinds Name) -> TcM thing
209 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
211 -- Typecheck one strongly-connected component of the original program.
212 -- We get a list of groups back, because there may
213 -- be specialisations etc as well
215 tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
216 = -- A single non-recursive binding
217 -- We want to keep non-recursive things non-recursive
218 -- so that we desugar unlifted bindings correctly
219 do { (binds, thing) <- tcPolyBinds top_lvl NonRecursive NonRecursive
220 sig_fn prag_fn binds thing_inside
221 ; return ([(NonRecursive, b) | b <- binds], thing) }
223 tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
224 = -- A recursive strongly-connected component
225 -- To maximise polymorphism (with -fglasgow-exts), we do a new
226 -- strongly-connected component analysis, this time omitting
227 -- any references to variables with type signatures.
229 -- Then we bring into scope all the variables with type signatures
230 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
231 ; gla_exts <- doptM Opt_GlasgowExts
232 ; (binds,thing) <- if gla_exts
234 else tc_binds Recursive binds thing_inside
235 ; return ([(Recursive, unionManyBags binds)], thing) }
236 -- Rec them all together
238 new_sccs :: [SCC (LHsBind Name)]
239 new_sccs = stronglyConnComp (mkEdges sig_fn binds)
241 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], thing)
242 go (scc:sccs) = do { (binds1, (binds2, thing)) <- go1 scc (go sccs)
243 ; return (binds1 ++ binds2, thing) }
244 go [] = do { thing <- thing_inside; return ([], thing) }
246 go1 (AcyclicSCC bind) = tc_binds NonRecursive (unitBag bind)
247 go1 (CyclicSCC binds) = tc_binds Recursive (listToBag binds)
249 tc_binds rec_tc binds = tcPolyBinds top_lvl Recursive rec_tc sig_fn prag_fn binds
251 ------------------------
252 mkEdges :: TcSigFun -> LHsBinds Name
253 -> [(LHsBind Name, BKey, [BKey])]
255 type BKey = Int -- Just number off the bindings
258 = [ (bind, key, [fromJust mb_key | n <- nameSetToList (bind_fvs (unLoc bind)),
259 let mb_key = lookupNameEnv key_map n,
262 | (bind, key) <- keyd_binds
265 no_sig :: Name -> Bool
266 no_sig n = isNothing (sig_fn n)
268 keyd_binds = bagToList binds `zip` [0::BKey ..]
270 bind_fvs (FunBind _ _ _ fvs) = fvs
271 bind_fvs (PatBind _ _ _ fvs) = fvs
272 bind_fvs bind = pprPanic "mkEdges" (ppr bind)
274 key_map :: NameEnv BKey -- Which binding it comes from
275 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
276 , bndr <- bindersOfHsBind bind ]
278 bindersOfHsBind :: HsBind Name -> [Name]
279 bindersOfHsBind (PatBind pat _ _ _) = collectPatBinders pat
280 bindersOfHsBind (FunBind (L _ f) _ _ _) = [f]
282 ------------------------
283 tcPolyBinds :: TopLevelFlag
284 -> RecFlag -- Whether the group is really recursive
285 -> RecFlag -- Whether it's recursive for typechecking purposes
286 -> TcSigFun -> TcPragFun
289 -> TcM ([LHsBinds TcId], thing)
291 -- Typechecks a single bunch of bindings all together,
292 -- and generalises them. The bunch may be only part of a recursive
293 -- group, because we use type signatures to maximise polymorphism
295 -- Deals with the bindInstsOfLocalFuns thing too
297 -- Returns a list because the input may be a single non-recursive binding,
298 -- in which case the dependency order of the resulting bindings is
301 tcPolyBinds top_lvl rec_group rec_tc sig_fn prag_fn scc thing_inside
302 = -- NB: polymorphic recursion means that a function
303 -- may use an instance of itself, we must look at the LIE arising
304 -- from the function's own right hand side. Hence the getLIE
305 -- encloses the tc_poly_binds.
306 do { traceTc (text "tcPolyBinds" <+> ppr scc)
307 ; ((binds1, poly_ids, thing), lie) <- getLIE $
308 do { (binds1, poly_ids) <- tc_poly_binds top_lvl rec_group rec_tc
310 ; thing <- tcExtendIdEnv poly_ids thing_inside
311 ; return (binds1, poly_ids, thing) }
313 ; if isTopLevel top_lvl
314 then -- For the top level don't bother will all this
315 -- bindInstsOfLocalFuns stuff. All the top level
316 -- things are rec'd together anyway, so it's fine to
317 -- leave them to the tcSimplifyTop,
318 -- and quite a bit faster too
319 do { extendLIEs lie; return (binds1, thing) }
321 else do -- Nested case
322 { lie_binds <- bindInstsOfLocalFuns lie poly_ids
323 ; return (binds1 ++ [lie_binds], thing) }}
325 ------------------------
326 tc_poly_binds :: TopLevelFlag -- See comments on tcPolyBinds
327 -> RecFlag -> RecFlag
328 -> TcSigFun -> TcPragFun
330 -> TcM ([LHsBinds TcId], [TcId])
331 -- Typechecks the bindings themselves
332 -- Knows nothing about the scope of the bindings
334 tc_poly_binds top_lvl rec_group rec_tc sig_fn prag_fn binds
336 binder_names = collectHsBindBinders binds
337 bind_list = bagToList binds
339 loc = getLoc (head bind_list)
340 -- TODO: location a bit awkward, but the mbinds have been
341 -- dependency analysed and may no longer be adjacent
343 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
345 recoverM (recoveryCode binder_names sig_fn) $ do
347 { traceTc (ptext SLIT("------------------------------------------------"))
348 ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
350 -- TYPECHECK THE BINDINGS
351 ; ((binds', mono_bind_infos), lie_req)
352 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
354 -- CHECK FOR UNLIFTED BINDINGS
355 -- These must be non-recursive etc, and are not generalised
356 -- They desugar to a case expression in the end
357 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
358 ; if any isUnLiftedType zonked_mono_tys then
359 do { -- Unlifted bindings
360 checkUnliftedBinds top_lvl rec_group binds' mono_bind_infos
362 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
363 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
364 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
367 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
368 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
370 else do -- The normal lifted case: GENERALISE
371 { is_unres <- isUnRestrictedGroup bind_list sig_fn
372 ; (tyvars_to_gen, dict_binds, dict_ids)
373 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
374 generalise top_lvl is_unres mono_bind_infos lie_req
376 -- FINALISE THE QUANTIFIED TYPE VARIABLES
377 -- The quantified type variables often include meta type variables
378 -- we want to freeze them into ordinary type variables, and
379 -- default their kind (e.g. from OpenTypeKind to TypeKind)
380 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
382 -- BUILD THE POLYMORPHIC RESULT IDs
383 ; exports <- mapM (mkExport prag_fn tyvars_to_gen' (map idType dict_ids))
386 -- ZONK THE poly_ids, because they are used to extend the type
387 -- environment; see the invariant on TcEnv.tcExtendIdEnv
388 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
389 ; zonked_poly_ids <- mappM zonkId poly_ids
391 ; traceTc (text "binding:" <+> ppr ((dict_ids, dict_binds),
392 map idType zonked_poly_ids))
394 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen'
396 (dict_binds `unionBags` binds')
398 ; return ([unitBag abs_bind], zonked_poly_ids)
403 mkExport :: TcPragFun -> [TyVar] -> [TcType] -> MonoBindInfo
404 -> TcM ([TyVar], Id, Id, [Prag])
405 mkExport prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
406 = do { prags <- tcPrags poly_id (prag_fn poly_name)
407 ; return (tvs, poly_id, mono_id, prags) }
409 (tvs, poly_id) = case mb_sig of
410 Just sig -> (sig_tvs sig, sig_id sig)
411 Nothing -> (inferred_tvs, mkLocalId poly_name poly_ty)
413 poly_ty = mkForAllTys inferred_tvs
417 ------------------------
418 type TcPragFun = Name -> [LSig Name]
420 mkPragFun :: [LSig Name] -> TcPragFun
421 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
423 prs = [(fromJust (sigName sig), sig) | sig <- sigs, isPragLSig sig]
424 env = foldl add emptyNameEnv prs
425 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
427 tcPrags :: Id -> [LSig Name] -> TcM [Prag]
428 tcPrags poly_id prags = mapM tc_prag prags
430 tc_prag (L loc prag) = setSrcSpan loc $
431 addErrCtxt (pragSigCtxt prag) $
434 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
436 tcPrag :: TcId -> Sig Name -> TcM Prag
437 tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
438 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
439 tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
442 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
443 tcSpecPrag poly_id hs_ty inl
444 = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
445 ; (co_fn, lie) <- getLIE (tcSub spec_ty (idType poly_id))
447 ; let const_dicts = map instToId lie
448 ; return (SpecPrag (co_fn <$> (HsVar poly_id)) spec_ty const_dicts inl) }
451 -- If typechecking the binds fails, then return with each
452 -- signature-less binder given type (forall a.a), to minimise
453 -- subsequent error messages
454 recoveryCode binder_names sig_fn
455 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
456 ; return ([], poly_ids) }
458 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
459 poly_ids = map mk_dummy binder_names
460 mk_dummy name = case sig_fn name of
461 Just sig -> sig_id sig -- Signature
462 Nothing -> mkLocalId name forall_a_a -- No signature
464 -- Check that non-overloaded unlifted bindings are
467 -- c) not a multiple-binding group (more or less implied by (a))
469 checkUnliftedBinds :: TopLevelFlag -> RecFlag
470 -> LHsBinds TcId -> [MonoBindInfo] -> TcM ()
471 checkUnliftedBinds top_lvl rec_group mbind infos
472 = do { checkTc (isNotTopLevel top_lvl)
473 (unliftedBindErr "Top-level" mbind)
474 ; checkTc (isNonRec rec_group)
475 (unliftedBindErr "Recursive" mbind)
476 ; checkTc (isSingletonBag mbind)
477 (unliftedBindErr "Multiple" mbind)
478 ; mapM_ check_sig infos }
480 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
482 check_sig other = return ()
486 %************************************************************************
488 \subsection{tcMonoBind}
490 %************************************************************************
492 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
493 The signatures have been dealt with already.
496 tcMonoBinds :: [LHsBind Name]
498 -> RecFlag -- True <=> the binding is recursive for typechecking purposes
499 -- i.e. the binders are mentioned in their RHSs, and
500 -- we are not resuced by a type signature
501 -> TcM (LHsBinds TcId, [MonoBindInfo])
503 tcMonoBinds [L b_loc (FunBind (L nm_loc name) inf matches fvs)]
504 sig_fn -- Single function binding,
505 NonRecursive -- binder isn't mentioned in RHS,
506 | Nothing <- sig_fn name -- ...with no type signature
507 = -- In this very special case we infer the type of the
508 -- right hand side first (it may have a higher-rank type)
509 -- and *then* make the monomorphic Id for the LHS
510 -- e.g. f = \(x::forall a. a->a) -> <body>
511 -- We want to infer a higher-rank type for f
513 do { (matches', rhs_ty) <- tcInfer (tcMatchesFun name matches)
515 -- Check for an unboxed tuple type
516 -- f = (# True, False #)
517 -- Zonk first just in case it's hidden inside a meta type variable
518 -- (This shows up as a (more obscure) kind error
519 -- in the 'otherwise' case of tcMonoBinds.)
520 ; zonked_rhs_ty <- zonkTcType rhs_ty
521 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
522 (unboxedTupleErr name zonked_rhs_ty)
524 ; mono_name <- newLocalName name
525 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
526 ; return (unitBag (L b_loc (FunBind (L nm_loc mono_id) inf matches' fvs)),
527 [(name, Nothing, mono_id)]) }
529 tcMonoBinds binds sig_fn non_rec
530 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
532 -- Bring (a) the scoped type variables, and (b) the Ids, into scope for the RHSs
533 -- For (a) it's ok to bring them all into scope at once, even
534 -- though each type sig should scope only over its own RHS,
535 -- because the renamer has sorted all that out.
536 ; let mono_info = getMonoBindInfo tc_binds
537 rhs_tvs = [ (name, mkTyVarTy tv)
538 | (_, Just sig, _) <- mono_info,
539 (name, tv) <- sig_scoped sig `zip` sig_tvs sig ]
540 rhs_id_env = map mk mono_info -- A binding for each term variable
542 ; binds' <- tcExtendTyVarEnv2 rhs_tvs $
543 tcExtendIdEnv2 rhs_id_env $
544 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
545 | (n,id) <- rhs_id_env]) `thenM_`
546 mapM (wrapLocM tcRhs) tc_binds
547 ; return (listToBag binds', mono_info) }
549 mk (name, Just sig, _) = (name, sig_id sig) -- Use the type sig if there is one
550 mk (name, Nothing, mono_id) = (name, mono_id) -- otherwise use a monomorphic version
552 ------------------------
553 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
554 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
555 -- if there's a signature for it, use the instantiated signature type
556 -- otherwise invent a type variable
557 -- You see that quite directly in the FunBind case.
559 -- But there's a complication for pattern bindings:
560 -- data T = MkT (forall a. a->a)
562 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
563 -- but we want to get (f::forall a. a->a) as the RHS environment.
564 -- The simplest way to do this is to typecheck the pattern, and then look up the
565 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
566 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
568 data TcMonoBind -- Half completed; LHS done, RHS not done
569 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
570 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
572 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
573 -- Type signature (if any), and
574 -- the monomorphic bound things
576 bndrNames :: [MonoBindInfo] -> [Name]
577 bndrNames mbi = [n | (n,_,_) <- mbi]
579 getMonoType :: MonoBindInfo -> TcTauType
580 getMonoType (_,_,mono_id) = idType mono_id
582 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
583 tcLhs sig_fn (FunBind (L nm_loc name) inf matches _)
584 = do { let mb_sig = sig_fn name
585 ; mono_name <- newLocalName name
586 ; mono_ty <- mk_mono_ty mb_sig
587 ; let mono_id = mkLocalId mono_name mono_ty
588 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
590 mk_mono_ty (Just sig) = return (sig_tau sig)
591 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
593 tcLhs sig_fn bind@(PatBind pat grhss _ _)
594 = do { let tc_pat exp_ty = tcPat (LetPat sig_fn) pat exp_ty lookup_infos
595 ; ((pat', ex_tvs, infos), pat_ty)
596 <- addErrCtxt (patMonoBindsCtxt pat grhss)
599 -- Don't know how to deal with pattern-bound existentials yet
600 ; checkTc (null ex_tvs) (existentialExplode bind)
602 ; return (TcPatBind infos pat' grhss pat_ty) }
604 names = collectPatBinders pat
606 -- After typechecking the pattern, look up the binder
607 -- names, which the pattern has brought into scope.
608 lookup_infos :: TcM [MonoBindInfo]
609 lookup_infos = do { mono_ids <- tcLookupLocalIds names
610 ; return [ (name, sig_fn name, mono_id)
611 | (name, mono_id) <- names `zip` mono_ids] }
613 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
614 -- AbsBind, VarBind impossible
617 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
618 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
619 = do { matches' <- tcMatchesFun (idName mono_id) matches
620 (Check (idType mono_id))
621 ; return (FunBind fun' inf matches' placeHolderNames) }
623 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
624 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
625 tcGRHSsPat grhss (Check pat_ty)
626 ; return (PatBind pat' grhss' pat_ty placeHolderNames) }
629 ---------------------
630 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
631 getMonoBindInfo tc_binds
632 = foldr (get_info . unLoc) [] tc_binds
634 get_info (TcFunBind info _ _ _) rest = info : rest
635 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
639 %************************************************************************
643 %************************************************************************
646 generalise :: TopLevelFlag -> Bool
647 -> [MonoBindInfo] -> [Inst]
648 -> TcM ([TcTyVar], TcDictBinds, [TcId])
649 generalise top_lvl is_unrestricted mono_infos lie_req
650 | not is_unrestricted -- RESTRICTED CASE
651 = -- Check signature contexts are empty
652 do { checkTc (all is_mono_sig sigs)
653 (restrictedBindCtxtErr bndrs)
655 -- Now simplify with exactly that set of tyvars
656 -- We have to squash those Methods
657 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
660 -- Check that signature type variables are OK
661 ; final_qtvs <- checkSigsTyVars qtvs sigs
663 ; return (final_qtvs, binds, []) }
665 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
666 = tcSimplifyInfer doc tau_tvs lie_req
668 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
669 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty
670 ; let -- The "sig_avails" is the stuff available. We get that from
671 -- the context of the type signature, BUT ALSO the lie_avail
672 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
673 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
674 sig_avails = sig_lie ++ local_meths
676 -- Check that the needed dicts can be
677 -- expressed in terms of the signature ones
678 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
680 -- Check that signature type variables are OK
681 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
683 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
685 bndrs = bndrNames mono_infos
686 sigs = [sig | (_, Just sig, _) <- mono_infos]
687 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
688 is_mono_sig sig = null (sig_theta sig)
689 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
691 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
692 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
693 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
696 -- Check that all the signature contexts are the same
697 -- The type signatures on a mutually-recursive group of definitions
698 -- must all have the same context (or none).
700 -- The trick here is that all the signatures should have the same
701 -- context, and we want to share type variables for that context, so that
702 -- all the right hand sides agree a common vocabulary for their type
705 -- We unify them because, with polymorphic recursion, their types
706 -- might not otherwise be related. This is a rather subtle issue.
707 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
708 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
709 = do { mapM unify_ctxt sigs
710 ; newDictsAtLoc (sig_loc sig1) (sig_theta sig1) }
712 theta1 = sig_theta sig1
713 unify_ctxt :: TcSigInfo -> TcM ()
714 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
715 = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
716 addErrCtxt (sigContextsCtxt sig1 sig) $
717 unifyTheta theta1 theta
719 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
720 checkSigsTyVars qtvs sigs
721 = do { gbl_tvs <- tcGetGlobalTyVars
722 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
724 ; let -- Sigh. Make sure that all the tyvars in the type sigs
725 -- appear in the returned ty var list, which is what we are
726 -- going to generalise over. Reason: we occasionally get
728 -- type T a = () -> ()
731 -- Here, 'a' won't appear in qtvs, so we have to add it
732 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
733 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
736 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
737 sig_theta = theta, sig_tau = tau})
738 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
739 addErrCtxtM (sigCtxt id tvs theta tau) $
740 do { tvs' <- checkDistinctTyVars tvs
741 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
742 (bleatEscapedTvs gbl_tvs tvs tvs')
745 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
746 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
747 -- are still all type variables, and all distinct from each other.
748 -- It returns a zonked set of type variables.
749 -- For example, if the type sig is
750 -- f :: forall a b. a -> b -> b
751 -- we want to check that 'a' and 'b' haven't
752 -- (a) been unified with a non-tyvar type
753 -- (b) been unified with each other (all distinct)
755 checkDistinctTyVars sig_tvs
756 = do { zonked_tvs <- mapM zonk_one sig_tvs
757 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
758 ; return zonked_tvs }
760 zonk_one sig_tv = do { ty <- zonkTcTyVar sig_tv
761 ; return (tcGetTyVar "checkDistinctTyVars" ty) }
762 -- 'ty' is bound to be a type variable, because SigSkolTvs
763 -- can only be unified with type variables
765 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
766 -- The TyVarEnv maps each zonked type variable back to its
767 -- corresponding user-written signature type variable
768 check_dup acc (sig_tv, zonked_tv)
769 = case lookupVarEnv acc zonked_tv of
770 Just sig_tv' -> bomb_out sig_tv sig_tv'
772 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
774 bomb_out sig_tv1 sig_tv2
775 = failWithTc (ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
776 <+> ptext SLIT("is unified with another quantified type variable")
777 <+> quotes (ppr tidy_tv2))
779 (env1, tidy_tv1) = tidyOpenTyVar emptyTidyEnv sig_tv1
780 (_env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
784 @getTyVarsToGen@ decides what type variables to generalise over.
786 For a "restricted group" -- see the monomorphism restriction
787 for a definition -- we bind no dictionaries, and
788 remove from tyvars_to_gen any constrained type variables
790 *Don't* simplify dicts at this point, because we aren't going
791 to generalise over these dicts. By the time we do simplify them
792 we may well know more. For example (this actually came up)
794 f x = array ... xs where xs = [1,2,3,4,5]
795 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
796 stuff. If we simplify only at the f-binding (not the xs-binding)
797 we'll know that the literals are all Ints, and we can just produce
800 Find all the type variables involved in overloading, the
801 "constrained_tyvars". These are the ones we *aren't* going to
802 generalise. We must be careful about doing this:
804 (a) If we fail to generalise a tyvar which is not actually
805 constrained, then it will never, ever get bound, and lands
806 up printed out in interface files! Notorious example:
807 instance Eq a => Eq (Foo a b) where ..
808 Here, b is not constrained, even though it looks as if it is.
809 Another, more common, example is when there's a Method inst in
810 the LIE, whose type might very well involve non-overloaded
812 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
813 the simple thing instead]
815 (b) On the other hand, we mustn't generalise tyvars which are constrained,
816 because we are going to pass on out the unmodified LIE, with those
817 tyvars in it. They won't be in scope if we've generalised them.
819 So we are careful, and do a complete simplification just to find the
820 constrained tyvars. We don't use any of the results, except to
821 find which tyvars are constrained.
823 Note [Polymorphic recursion]
824 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
825 The game plan for polymorphic recursion in the code above is
827 * Bind any variable for which we have a type signature
828 to an Id with a polymorphic type. Then when type-checking
829 the RHSs we'll make a full polymorphic call.
831 This fine, but if you aren't a bit careful you end up with a horrendous
832 amount of partial application and (worse) a huge space leak. For example:
834 f :: Eq a => [a] -> [a]
837 If we don't take care, after typechecking we get
839 f = /\a -> \d::Eq a -> let f' = f a d
843 Notice the the stupid construction of (f a d), which is of course
844 identical to the function we're executing. In this case, the
845 polymorphic recursion isn't being used (but that's a very common case).
848 f = /\a -> \d::Eq a -> letrec
849 fm = \ys:[a] -> ...fm...
853 This can lead to a massive space leak, from the following top-level defn
859 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
860 f' is another thunk which evaluates to the same thing... and you end
861 up with a chain of identical values all hung onto by the CAF ff.
865 = let f' = f Int dEqInt in \ys. ...f'...
867 = let f' = let f' = f Int dEqInt in \ys. ...f'...
871 Solution: when typechecking the RHSs we always have in hand the
872 *monomorphic* Ids for each binding. So we just need to make sure that
873 if (Method f a d) shows up in the constraints emerging from (...f...)
874 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
875 to the "givens" when simplifying constraints. That's what the "lies_avail"
879 %************************************************************************
883 %************************************************************************
885 Type signatures are tricky. See Note [Signature skolems] in TcType
888 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
889 tcTySigs sigs = do { mb_sigs <- mappM tcTySig (filter isVanillaLSig sigs)
890 ; return (catMaybes mb_sigs) }
892 tcTySig :: LSig Name -> TcM (Maybe TcSigInfo)
893 tcTySig (L span (TypeSig (L _ name) ty))
894 = recoverM (return Nothing) $
896 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
897 ; (tvs, theta, tau) <- tcInstSigType name scoped_names sigma_ty
898 ; loc <- getInstLoc (SigOrigin (SigSkol name))
899 ; return (Just (TcSigInfo { sig_id = mkLocalId name sigma_ty,
900 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
901 sig_scoped = scoped_names, sig_loc = loc })) }
903 -- The scoped names are the ones explicitly mentioned
904 -- in the HsForAll. (There may be more in sigma_ty, because
905 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
906 scoped_names = case ty of
907 L _ (HsForAllTy Explicit tvs _ _) -> hsLTyVarNames tvs
910 isUnRestrictedGroup :: [LHsBind Name] -> TcSigFun -> TcM Bool
911 isUnRestrictedGroup binds sig_fn
912 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
913 ; return (not mono_restriction || all_unrestricted) }
915 all_unrestricted = all (unrestricted . unLoc) binds
916 has_sig n = isJust (sig_fn n)
918 unrestricted (PatBind other _ _ _) = False
919 unrestricted (VarBind v _) = has_sig v
920 unrestricted (FunBind v _ matches _) = unrestricted_match matches
923 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
924 -- No args => like a pattern binding
925 unrestricted_match other = True
926 -- Some args => a function binding
930 %************************************************************************
932 \subsection[TcBinds-errors]{Error contexts and messages}
934 %************************************************************************
938 -- This one is called on LHS, when pat and grhss are both Name
939 -- and on RHS, when pat is TcId and grhss is still Name
940 patMonoBindsCtxt pat grhss
941 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
943 -----------------------------------------------
944 sigContextsCtxt sig1 sig2
945 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
946 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
947 ppr id2 <+> dcolon <+> ppr (idType id2)]),
948 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
954 -----------------------------------------------
955 unliftedBindErr flavour mbind
956 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
960 = hang (ptext SLIT("Illegal polymorphic signature in an unlifted binding"))
963 -----------------------------------------------
964 unboxedTupleErr name ty
965 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
966 4 (ppr name <+> dcolon <+> ppr ty)
968 -----------------------------------------------
969 existentialExplode mbinds
970 = hang (vcat [text "My brain just exploded.",
971 text "I can't handle pattern bindings for existentially-quantified constructors.",
972 text "In the binding group"])
975 -----------------------------------------------
976 restrictedBindCtxtErr binder_names
977 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
978 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
979 ptext SLIT("that falls under the monomorphism restriction")])
982 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names