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 )
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 (Sig (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 (ValBindsOut binds sigs) thing_inside
165 = tcAddLetBoundTyVars binds $
166 -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
167 -- Notice that they scope over
168 -- a) the type signatures in the binding group
169 -- b) the bindings in the group
170 -- c) the scope of the binding group (the "in" part)
172 do { -- Typecheck the signature
173 tc_ty_sigs <- recoverM (returnM []) (tcTySigs sigs)
174 ; let { prag_fn = mkPragFun sigs
175 ; sig_fn = lookupSig tc_ty_sigs
176 ; sig_ids = map sig_id tc_ty_sigs }
178 -- Extend the envt right away with all
179 -- the Ids declared with type signatures
180 ; (binds', thing) <- tcExtendIdEnv sig_ids $
181 tc_val_binds top_lvl sig_fn prag_fn
184 ; return (ValBindsOut binds' sigs, thing) }
186 ------------------------
187 tc_val_binds :: TopLevelFlag -> TcSigFun -> TcPragFun
188 -> [(RecFlag, LHsBinds Name)] -> TcM thing
189 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
190 -- Typecheck a whole lot of value bindings,
191 -- one strongly-connected component at a time
193 tc_val_binds top_lvl sig_fn prag_fn [] thing_inside
194 = do { thing <- thing_inside
195 ; return ([], thing) }
197 tc_val_binds top_lvl sig_fn prag_fn (group : groups) thing_inside
198 = do { (group', (groups', thing))
199 <- tc_group top_lvl sig_fn prag_fn group $
200 tc_val_binds top_lvl sig_fn prag_fn groups thing_inside
201 ; return (group' ++ groups', thing) }
203 ------------------------
204 tc_group :: TopLevelFlag -> TcSigFun -> TcPragFun
205 -> (RecFlag, LHsBinds Name) -> TcM thing
206 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
208 -- Typecheck one strongly-connected component of the original program.
209 -- We get a list of groups back, because there may
210 -- be specialisations etc as well
212 tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
213 = -- A single non-recursive binding
214 -- We want to keep non-recursive things non-recursive
215 -- so that we desugar unlifted bindings correctly
216 do { (binds, thing) <- tcPolyBinds top_lvl NonRecursive NonRecursive
217 sig_fn prag_fn binds thing_inside
218 ; return ([(NonRecursive, b) | b <- binds], thing) }
220 tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
221 = -- A recursive strongly-connected component
222 -- To maximise polymorphism (with -fglasgow-exts), we do a new
223 -- strongly-connected component analysis, this time omitting
224 -- any references to variables with type signatures.
226 -- Then we bring into scope all the variables with type signatures
227 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
228 ; gla_exts <- doptM Opt_GlasgowExts
229 ; (binds,thing) <- if gla_exts
231 else tc_binds Recursive binds thing_inside
232 ; return ([(Recursive, unionManyBags binds)], thing) }
233 -- Rec them all together
235 new_sccs :: [SCC (LHsBind Name)]
236 new_sccs = stronglyConnComp (mkEdges sig_fn binds)
238 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], thing)
239 go (scc:sccs) = do { (binds1, (binds2, thing)) <- go1 scc (go sccs)
240 ; return (binds1 ++ binds2, thing) }
241 go [] = do { thing <- thing_inside; return ([], thing) }
243 go1 (AcyclicSCC bind) = tc_binds NonRecursive (unitBag bind)
244 go1 (CyclicSCC binds) = tc_binds Recursive (listToBag binds)
246 tc_binds rec_tc binds = tcPolyBinds top_lvl Recursive rec_tc sig_fn prag_fn binds
248 ------------------------
249 mkEdges :: TcSigFun -> LHsBinds Name
250 -> [(LHsBind Name, BKey, [BKey])]
252 type BKey = Int -- Just number off the bindings
255 = [ (bind, key, [fromJust mb_key | n <- nameSetToList (bind_fvs (unLoc bind)),
256 let mb_key = lookupNameEnv key_map n,
259 | (bind, key) <- keyd_binds
262 no_sig :: Name -> Bool
263 no_sig n = isNothing (sig_fn n)
265 keyd_binds = bagToList binds `zip` [0::BKey ..]
267 bind_fvs (FunBind _ _ _ fvs) = fvs
268 bind_fvs (PatBind _ _ _ fvs) = fvs
269 bind_fvs bind = pprPanic "mkEdges" (ppr bind)
271 key_map :: NameEnv BKey -- Which binding it comes from
272 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
273 , bndr <- bindersOfHsBind bind ]
275 bindersOfHsBind :: HsBind Name -> [Name]
276 bindersOfHsBind (PatBind pat _ _ _) = collectPatBinders pat
277 bindersOfHsBind (FunBind (L _ f) _ _ _) = [f]
279 ------------------------
280 tcPolyBinds :: TopLevelFlag
281 -> RecFlag -- Whether the group is really recursive
282 -> RecFlag -- Whether it's recursive for typechecking purposes
283 -> TcSigFun -> TcPragFun
286 -> TcM ([LHsBinds TcId], thing)
288 -- Typechecks a single bunch of bindings all together,
289 -- and generalises them. The bunch may be only part of a recursive
290 -- group, because we use type signatures to maximise polymorphism
292 -- Deals with the bindInstsOfLocalFuns thing too
294 -- Returns a list because the input may be a single non-recursive binding,
295 -- in which case the dependency order of the resulting bindings is
298 tcPolyBinds top_lvl rec_group rec_tc sig_fn prag_fn scc thing_inside
299 = -- NB: polymorphic recursion means that a function
300 -- may use an instance of itself, we must look at the LIE arising
301 -- from the function's own right hand side. Hence the getLIE
302 -- encloses the tc_poly_binds.
303 do { traceTc (text "tcPolyBinds" <+> ppr scc)
304 ; ((binds1, poly_ids, thing), lie) <- getLIE $
305 do { (binds1, poly_ids) <- tc_poly_binds top_lvl rec_group rec_tc
307 ; thing <- tcExtendIdEnv poly_ids thing_inside
308 ; return (binds1, poly_ids, thing) }
310 ; if isTopLevel top_lvl
311 then -- For the top level don't bother will all this
312 -- bindInstsOfLocalFuns stuff. All the top level
313 -- things are rec'd together anyway, so it's fine to
314 -- leave them to the tcSimplifyTop,
315 -- and quite a bit faster too
316 do { extendLIEs lie; return (binds1, thing) }
318 else do -- Nested case
319 { lie_binds <- bindInstsOfLocalFuns lie poly_ids
320 ; return (binds1 ++ [lie_binds], thing) }}
322 ------------------------
323 tc_poly_binds :: TopLevelFlag -- See comments on tcPolyBinds
324 -> RecFlag -> RecFlag
325 -> TcSigFun -> TcPragFun
327 -> TcM ([LHsBinds TcId], [TcId])
328 -- Typechecks the bindings themselves
329 -- Knows nothing about the scope of the bindings
331 tc_poly_binds top_lvl rec_group rec_tc sig_fn prag_fn binds
333 binder_names = collectHsBindBinders binds
334 bind_list = bagToList binds
336 loc = getLoc (head bind_list)
337 -- TODO: location a bit awkward, but the mbinds have been
338 -- dependency analysed and may no longer be adjacent
340 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
342 recoverM (recoveryCode binder_names sig_fn) $ do
344 { traceTc (ptext SLIT("------------------------------------------------"))
345 ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
347 -- TYPECHECK THE BINDINGS
348 ; ((binds', mono_bind_infos), lie_req)
349 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
351 -- CHECK FOR UNLIFTED BINDINGS
352 -- These must be non-recursive etc, and are not generalised
353 -- They desugar to a case expression in the end
354 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
355 ; if any isUnLiftedType zonked_mono_tys then
356 do { -- Unlifted bindings
357 checkUnliftedBinds top_lvl rec_group binds' mono_bind_infos
359 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
360 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
361 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
364 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
365 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
367 else do -- The normal lifted case: GENERALISE
368 { is_unres <- isUnRestrictedGroup bind_list sig_fn
369 ; (tyvars_to_gen, dict_binds, dict_ids)
370 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
371 generalise top_lvl is_unres mono_bind_infos lie_req
373 -- FINALISE THE QUANTIFIED TYPE VARIABLES
374 -- The quantified type variables often include meta type variables
375 -- we want to freeze them into ordinary type variables, and
376 -- default their kind (e.g. from OpenTypeKind to TypeKind)
377 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
379 -- BUILD THE POLYMORPHIC RESULT IDs
380 ; exports <- mapM (mkExport prag_fn tyvars_to_gen' (map idType dict_ids))
383 -- ZONK THE poly_ids, because they are used to extend the type
384 -- environment; see the invariant on TcEnv.tcExtendIdEnv
385 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
386 ; zonked_poly_ids <- mappM zonkId poly_ids
388 ; traceTc (text "binding:" <+> ppr ((dict_ids, dict_binds),
389 map idType zonked_poly_ids))
391 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen'
393 (dict_binds `unionBags` binds')
395 ; return ([unitBag abs_bind], zonked_poly_ids)
400 mkExport :: TcPragFun -> [TyVar] -> [TcType] -> MonoBindInfo
401 -> TcM ([TyVar], Id, Id, [Prag])
402 mkExport prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
403 = do { prags <- tcPrags poly_id (prag_fn poly_name)
404 ; return (tvs, poly_id, mono_id, prags) }
406 (tvs, poly_id) = case mb_sig of
407 Just sig -> (sig_tvs sig, sig_id sig)
408 Nothing -> (inferred_tvs, mkLocalId poly_name poly_ty)
410 poly_ty = mkForAllTys inferred_tvs
414 ------------------------
415 type TcPragFun = Name -> [LSig Name]
417 mkPragFun :: [LSig Name] -> TcPragFun
418 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
420 prs = [(fromJust (sigName sig), sig) | sig <- sigs, isPragLSig sig]
421 env = foldl add emptyNameEnv prs
422 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
424 tcPrags :: Id -> [LSig Name] -> TcM [Prag]
425 tcPrags poly_id prags = mapM tc_prag prags
427 tc_prag (L loc prag) = setSrcSpan loc $
428 addErrCtxt (pragSigCtxt prag) $
431 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
433 tcPrag :: TcId -> Sig Name -> TcM Prag
434 tcPrag poly_id (SpecSig orig_name hs_ty) = tcSpecPrag poly_id hs_ty
435 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty
436 tcPrag poly_id (InlineSig inl _ act) = return (InlinePrag inl act)
439 tcSpecPrag :: TcId -> LHsType Name -> TcM Prag
440 tcSpecPrag poly_id hs_ty
441 = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
442 ; (co_fn, lie) <- getLIE (tcSub spec_ty (idType poly_id))
444 ; let const_dicts = map instToId lie
445 ; return (SpecPrag (co_fn <$> (HsVar poly_id)) spec_ty const_dicts) }
448 -- If typechecking the binds fails, then return with each
449 -- signature-less binder given type (forall a.a), to minimise
450 -- subsequent error messages
451 recoveryCode binder_names sig_fn
452 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
453 ; return ([], poly_ids) }
455 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
456 poly_ids = map mk_dummy binder_names
457 mk_dummy name = case sig_fn name of
458 Just sig -> sig_id sig -- Signature
459 Nothing -> mkLocalId name forall_a_a -- No signature
461 -- Check that non-overloaded unlifted bindings are
464 -- c) not a multiple-binding group (more or less implied by (a))
466 checkUnliftedBinds :: TopLevelFlag -> RecFlag
467 -> LHsBinds TcId -> [MonoBindInfo] -> TcM ()
468 checkUnliftedBinds top_lvl rec_group mbind infos
469 = do { checkTc (isNotTopLevel top_lvl)
470 (unliftedBindErr "Top-level" mbind)
471 ; checkTc (isNonRec rec_group)
472 (unliftedBindErr "Recursive" mbind)
473 ; checkTc (isSingletonBag mbind)
474 (unliftedBindErr "Multiple" mbind)
475 ; mapM_ check_sig infos }
477 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
479 check_sig other = return ()
483 %************************************************************************
485 \subsection{tcMonoBind}
487 %************************************************************************
489 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
490 The signatures have been dealt with already.
493 tcMonoBinds :: [LHsBind Name]
495 -> RecFlag -- True <=> the binding is recursive for typechecking purposes
496 -- i.e. the binders are mentioned in their RHSs, and
497 -- we are not resuced by a type signature
498 -> TcM (LHsBinds TcId, [MonoBindInfo])
500 tcMonoBinds [L b_loc (FunBind (L nm_loc name) inf matches fvs)]
501 sig_fn -- Single function binding,
502 NonRecursive -- binder isn't mentioned in RHS,
503 | Nothing <- sig_fn name -- ...with no type signature
504 = -- In this very special case we infer the type of the
505 -- right hand side first (it may have a higher-rank type)
506 -- and *then* make the monomorphic Id for the LHS
507 -- e.g. f = \(x::forall a. a->a) -> <body>
508 -- We want to infer a higher-rank type for f
510 do { (matches', rhs_ty) <- tcInfer (tcMatchesFun name matches)
512 -- Check for an unboxed tuple type
513 -- f = (# True, False #)
514 -- Zonk first just in case it's hidden inside a meta type variable
515 -- (This shows up as a (more obscure) kind error
516 -- in the 'otherwise' case of tcMonoBinds.)
517 ; zonked_rhs_ty <- zonkTcType rhs_ty
518 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
519 (unboxedTupleErr name zonked_rhs_ty)
521 ; mono_name <- newLocalName name
522 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
523 ; return (unitBag (L b_loc (FunBind (L nm_loc mono_id) inf matches' fvs)),
524 [(name, Nothing, mono_id)]) }
526 tcMonoBinds binds sig_fn non_rec
527 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
529 -- Bring (a) the scoped type variables, and (b) the Ids, into scope for the RHSs
530 -- For (a) it's ok to bring them all into scope at once, even
531 -- though each type sig should scope only over its own RHS,
532 -- because the renamer has sorted all that out.
533 ; let mono_info = getMonoBindInfo tc_binds
534 rhs_tvs = [ (name, mkTyVarTy tv)
535 | (_, Just sig, _) <- mono_info,
536 (name, tv) <- sig_scoped sig `zip` sig_tvs sig ]
537 rhs_id_env = map mk mono_info -- A binding for each term variable
539 ; binds' <- tcExtendTyVarEnv2 rhs_tvs $
540 tcExtendIdEnv2 rhs_id_env $
541 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
542 | (n,id) <- rhs_id_env]) `thenM_`
543 mapM (wrapLocM tcRhs) tc_binds
544 ; return (listToBag binds', mono_info) }
546 mk (name, Just sig, _) = (name, sig_id sig) -- Use the type sig if there is one
547 mk (name, Nothing, mono_id) = (name, mono_id) -- otherwise use a monomorphic version
549 ------------------------
550 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
551 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
552 -- if there's a signature for it, use the instantiated signature type
553 -- otherwise invent a type variable
554 -- You see that quite directly in the FunBind case.
556 -- But there's a complication for pattern bindings:
557 -- data T = MkT (forall a. a->a)
559 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
560 -- but we want to get (f::forall a. a->a) as the RHS environment.
561 -- The simplest way to do this is to typecheck the pattern, and then look up the
562 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
563 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
565 data TcMonoBind -- Half completed; LHS done, RHS not done
566 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
567 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
569 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
570 -- Type signature (if any), and
571 -- the monomorphic bound things
573 bndrNames :: [MonoBindInfo] -> [Name]
574 bndrNames mbi = [n | (n,_,_) <- mbi]
576 getMonoType :: MonoBindInfo -> TcTauType
577 getMonoType (_,_,mono_id) = idType mono_id
579 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
580 tcLhs sig_fn (FunBind (L nm_loc name) inf matches _)
581 = do { let mb_sig = sig_fn name
582 ; mono_name <- newLocalName name
583 ; mono_ty <- mk_mono_ty mb_sig
584 ; let mono_id = mkLocalId mono_name mono_ty
585 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
587 mk_mono_ty (Just sig) = return (sig_tau sig)
588 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
590 tcLhs sig_fn bind@(PatBind pat grhss _ _)
591 = do { let tc_pat exp_ty = tcPat (LetPat sig_fn) pat exp_ty lookup_infos
592 ; ((pat', ex_tvs, infos), pat_ty)
593 <- addErrCtxt (patMonoBindsCtxt pat grhss)
596 -- Don't know how to deal with pattern-bound existentials yet
597 ; checkTc (null ex_tvs) (existentialExplode bind)
599 ; return (TcPatBind infos pat' grhss pat_ty) }
601 names = collectPatBinders pat
603 -- After typechecking the pattern, look up the binder
604 -- names, which the pattern has brought into scope.
605 lookup_infos :: TcM [MonoBindInfo]
606 lookup_infos = do { mono_ids <- tcLookupLocalIds names
607 ; return [ (name, sig_fn name, mono_id)
608 | (name, mono_id) <- names `zip` mono_ids] }
610 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
611 -- AbsBind, VarBind impossible
614 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
615 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
616 = do { matches' <- tcMatchesFun (idName mono_id) matches
617 (Check (idType mono_id))
618 ; return (FunBind fun' inf matches' placeHolderNames) }
620 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
621 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
622 tcGRHSsPat grhss (Check pat_ty)
623 ; return (PatBind pat' grhss' pat_ty placeHolderNames) }
626 ---------------------
627 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
628 getMonoBindInfo tc_binds
629 = foldr (get_info . unLoc) [] tc_binds
631 get_info (TcFunBind info _ _ _) rest = info : rest
632 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
636 %************************************************************************
640 %************************************************************************
643 generalise :: TopLevelFlag -> Bool
644 -> [MonoBindInfo] -> [Inst]
645 -> TcM ([TcTyVar], TcDictBinds, [TcId])
646 generalise top_lvl is_unrestricted mono_infos lie_req
647 | not is_unrestricted -- RESTRICTED CASE
648 = -- Check signature contexts are empty
649 do { checkTc (all is_mono_sig sigs)
650 (restrictedBindCtxtErr bndrs)
652 -- Now simplify with exactly that set of tyvars
653 -- We have to squash those Methods
654 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
657 -- Check that signature type variables are OK
658 ; final_qtvs <- checkSigsTyVars qtvs sigs
660 ; return (final_qtvs, binds, []) }
662 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
663 = tcSimplifyInfer doc tau_tvs lie_req
665 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
666 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty
667 ; let -- The "sig_avails" is the stuff available. We get that from
668 -- the context of the type signature, BUT ALSO the lie_avail
669 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
670 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
671 sig_avails = sig_lie ++ local_meths
673 -- Check that the needed dicts can be
674 -- expressed in terms of the signature ones
675 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
677 -- Check that signature type variables are OK
678 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
680 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
682 bndrs = bndrNames mono_infos
683 sigs = [sig | (_, Just sig, _) <- mono_infos]
684 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
685 is_mono_sig sig = null (sig_theta sig)
686 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
688 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
689 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
690 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
693 -- Check that all the signature contexts are the same
694 -- The type signatures on a mutually-recursive group of definitions
695 -- must all have the same context (or none).
697 -- The trick here is that all the signatures should have the same
698 -- context, and we want to share type variables for that context, so that
699 -- all the right hand sides agree a common vocabulary for their type
702 -- We unify them because, with polymorphic recursion, their types
703 -- might not otherwise be related. This is a rather subtle issue.
704 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
705 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
706 = do { mapM unify_ctxt sigs
707 ; newDictsAtLoc (sig_loc sig1) (sig_theta sig1) }
709 theta1 = sig_theta sig1
710 unify_ctxt :: TcSigInfo -> TcM ()
711 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
712 = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
713 addErrCtxt (sigContextsCtxt sig1 sig) $
714 unifyTheta theta1 theta
716 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
717 checkSigsTyVars qtvs sigs
718 = do { gbl_tvs <- tcGetGlobalTyVars
719 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
721 ; let -- Sigh. Make sure that all the tyvars in the type sigs
722 -- appear in the returned ty var list, which is what we are
723 -- going to generalise over. Reason: we occasionally get
725 -- type T a = () -> ()
728 -- Here, 'a' won't appear in qtvs, so we have to add it
729 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
730 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
733 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
734 sig_theta = theta, sig_tau = tau})
735 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
736 addErrCtxtM (sigCtxt id tvs theta tau) $
737 do { tvs' <- checkDistinctTyVars tvs
738 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
739 (bleatEscapedTvs gbl_tvs tvs tvs')
742 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
743 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
744 -- are still all type variables, and all distinct from each other.
745 -- It returns a zonked set of type variables.
746 -- For example, if the type sig is
747 -- f :: forall a b. a -> b -> b
748 -- we want to check that 'a' and 'b' haven't
749 -- (a) been unified with a non-tyvar type
750 -- (b) been unified with each other (all distinct)
752 checkDistinctTyVars sig_tvs
753 = do { zonked_tvs <- mapM zonk_one sig_tvs
754 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
755 ; return zonked_tvs }
757 zonk_one sig_tv = do { ty <- zonkTcTyVar sig_tv
758 ; return (tcGetTyVar "checkDistinctTyVars" ty) }
759 -- 'ty' is bound to be a type variable, because SigSkolTvs
760 -- can only be unified with type variables
762 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
763 -- The TyVarEnv maps each zonked type variable back to its
764 -- corresponding user-written signature type variable
765 check_dup acc (sig_tv, zonked_tv)
766 = case lookupVarEnv acc zonked_tv of
767 Just sig_tv' -> bomb_out sig_tv sig_tv'
769 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
771 bomb_out sig_tv1 sig_tv2
772 = failWithTc (ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
773 <+> ptext SLIT("is unified with another quantified type variable")
774 <+> quotes (ppr tidy_tv2))
776 (env1, tidy_tv1) = tidyOpenTyVar emptyTidyEnv sig_tv1
777 (_env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
781 @getTyVarsToGen@ decides what type variables to generalise over.
783 For a "restricted group" -- see the monomorphism restriction
784 for a definition -- we bind no dictionaries, and
785 remove from tyvars_to_gen any constrained type variables
787 *Don't* simplify dicts at this point, because we aren't going
788 to generalise over these dicts. By the time we do simplify them
789 we may well know more. For example (this actually came up)
791 f x = array ... xs where xs = [1,2,3,4,5]
792 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
793 stuff. If we simplify only at the f-binding (not the xs-binding)
794 we'll know that the literals are all Ints, and we can just produce
797 Find all the type variables involved in overloading, the
798 "constrained_tyvars". These are the ones we *aren't* going to
799 generalise. We must be careful about doing this:
801 (a) If we fail to generalise a tyvar which is not actually
802 constrained, then it will never, ever get bound, and lands
803 up printed out in interface files! Notorious example:
804 instance Eq a => Eq (Foo a b) where ..
805 Here, b is not constrained, even though it looks as if it is.
806 Another, more common, example is when there's a Method inst in
807 the LIE, whose type might very well involve non-overloaded
809 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
810 the simple thing instead]
812 (b) On the other hand, we mustn't generalise tyvars which are constrained,
813 because we are going to pass on out the unmodified LIE, with those
814 tyvars in it. They won't be in scope if we've generalised them.
816 So we are careful, and do a complete simplification just to find the
817 constrained tyvars. We don't use any of the results, except to
818 find which tyvars are constrained.
820 Note [Polymorphic recursion]
821 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
822 The game plan for polymorphic recursion in the code above is
824 * Bind any variable for which we have a type signature
825 to an Id with a polymorphic type. Then when type-checking
826 the RHSs we'll make a full polymorphic call.
828 This fine, but if you aren't a bit careful you end up with a horrendous
829 amount of partial application and (worse) a huge space leak. For example:
831 f :: Eq a => [a] -> [a]
834 If we don't take care, after typechecking we get
836 f = /\a -> \d::Eq a -> let f' = f a d
840 Notice the the stupid construction of (f a d), which is of course
841 identical to the function we're executing. In this case, the
842 polymorphic recursion isn't being used (but that's a very common case).
845 f = /\a -> \d::Eq a -> letrec
846 fm = \ys:[a] -> ...fm...
850 This can lead to a massive space leak, from the following top-level defn
856 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
857 f' is another thunk which evaluates to the same thing... and you end
858 up with a chain of identical values all hung onto by the CAF ff.
862 = let f' = f Int dEqInt in \ys. ...f'...
864 = let f' = let f' = f Int dEqInt in \ys. ...f'...
868 Solution: when typechecking the RHSs we always have in hand the
869 *monomorphic* Ids for each binding. So we just need to make sure that
870 if (Method f a d) shows up in the constraints emerging from (...f...)
871 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
872 to the "givens" when simplifying constraints. That's what the "lies_avail"
876 %************************************************************************
880 %************************************************************************
882 Type signatures are tricky. See Note [Signature skolems] in TcType
885 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
886 tcTySigs sigs = do { mb_sigs <- mappM tcTySig (filter isVanillaLSig sigs)
887 ; return (catMaybes mb_sigs) }
889 tcTySig :: LSig Name -> TcM (Maybe TcSigInfo)
890 tcTySig (L span (Sig (L _ name) ty))
891 = recoverM (return Nothing) $
893 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
894 ; (tvs, theta, tau) <- tcInstSigType name scoped_names sigma_ty
895 ; loc <- getInstLoc (SigOrigin (SigSkol name))
896 ; return (Just (TcSigInfo { sig_id = mkLocalId name sigma_ty,
897 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
898 sig_scoped = scoped_names, sig_loc = loc })) }
900 -- The scoped names are the ones explicitly mentioned
901 -- in the HsForAll. (There may be more in sigma_ty, because
902 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
903 scoped_names = case ty of
904 L _ (HsForAllTy Explicit tvs _ _) -> hsLTyVarNames tvs
907 isUnRestrictedGroup :: [LHsBind Name] -> TcSigFun -> TcM Bool
908 isUnRestrictedGroup binds sig_fn
909 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
910 ; return (not mono_restriction || all_unrestricted) }
912 all_unrestricted = all (unrestricted . unLoc) binds
913 has_sig n = isJust (sig_fn n)
915 unrestricted (PatBind other _ _ _) = False
916 unrestricted (VarBind v _) = has_sig v
917 unrestricted (FunBind v _ matches _) = unrestricted_match matches
920 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
921 -- No args => like a pattern binding
922 unrestricted_match other = True
923 -- Some args => a function binding
927 %************************************************************************
929 \subsection[TcBinds-errors]{Error contexts and messages}
931 %************************************************************************
935 -- This one is called on LHS, when pat and grhss are both Name
936 -- and on RHS, when pat is TcId and grhss is still Name
937 patMonoBindsCtxt pat grhss
938 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
940 -----------------------------------------------
941 sigContextsCtxt sig1 sig2
942 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
943 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
944 ppr id2 <+> dcolon <+> ppr (idType id2)]),
945 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
951 -----------------------------------------------
952 unliftedBindErr flavour mbind
953 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
957 = hang (ptext SLIT("Illegal polymorphic signature in an unlifted binding"))
960 -----------------------------------------------
961 unboxedTupleErr name ty
962 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
963 4 (ppr name <+> dcolon <+> ppr ty)
965 -----------------------------------------------
966 existentialExplode mbinds
967 = hang (vcat [text "My brain just exploded.",
968 text "I can't handle pattern bindings for existentially-quantified constructors.",
969 text "In the binding group"])
972 -----------------------------------------------
973 restrictedBindCtxtErr binder_names
974 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
975 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
976 ptext SLIT("that falls under the monomorphism restriction")])
979 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names