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(..), isEmptyLHsBinds,
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, flattenSCC )
63 import Maybes ( fromJust, isJust, 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 (ValBindsIn binds sigs)
117 = do { checkTc (isEmptyLHsBinds 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 mkEdges :: (Name -> Bool) -> [LHsBind Name]
161 -> [(LHsBind Name, BKey, [BKey])]
163 type BKey = Int -- Just number off the bindings
165 mkEdges exclude_fn binds
166 = [ (bind, key, [fromJust mb_key | n <- nameSetToList (bind_fvs (unLoc bind)),
167 let mb_key = lookupNameEnv key_map n,
169 not (exclude_fn n) ])
170 | (bind, key) <- keyd_binds
173 keyd_binds = binds `zip` [0::BKey ..]
175 bind_fvs (FunBind _ _ _ fvs) = fvs
176 bind_fvs (PatBind _ _ _ fvs) = fvs
177 bind_fvs bind = pprPanic "mkEdges" (ppr bind)
179 key_map :: NameEnv BKey -- Which binding it comes from
180 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
181 , bndr <- bindersOfHsBind bind ]
183 bindersOfHsBind :: HsBind Name -> [Name]
184 bindersOfHsBind (PatBind pat _ _ _) = collectPatBinders pat
185 bindersOfHsBind (FunBind (L _ f) _ _ _) = [f]
187 ------------------------
188 tcValBinds :: TopLevelFlag
189 -> HsValBinds Name -> TcM thing
190 -> TcM (HsValBinds TcId, thing)
192 tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
193 = tcAddLetBoundTyVars binds $
194 -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
195 -- Notice that they scope over
196 -- a) the type signatures in the binding group
197 -- b) the bindings in the group
198 -- c) the scope of the binding group (the "in" part)
200 do { -- Typecheck the signature
201 tc_ty_sigs <- recoverM (returnM []) (tcTySigs sigs)
203 -- Do the basic strongly-connected component thing
204 ; let { sccs :: [SCC (LHsBind Name)]
205 ; sccs = stronglyConnComp (mkEdges (\n -> False) (bagToList binds))
206 ; prag_fn = mkPragFun sigs
207 ; sig_fn = lookupSig tc_ty_sigs
208 ; sig_ids = map sig_id tc_ty_sigs }
210 -- Extend the envt right away with all
211 -- the Ids declared with type signatures
212 ; (binds', thing) <- tcExtendIdEnv sig_ids $
213 tc_val_binds top_lvl sig_fn prag_fn
216 ; return (ValBindsOut binds', thing) }
218 ------------------------
219 tc_val_binds :: TopLevelFlag -> TcSigFun -> TcPragFun
220 -> [SCC (LHsBind Name)] -> TcM thing
221 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
222 -- Typecheck a whole lot of value bindings,
223 -- one strongly-connected component at a time
225 tc_val_binds top_lvl sig_fn prag_fn [] thing_inside
226 = do { thing <- thing_inside
227 ; return ([], thing) }
229 tc_val_binds top_lvl sig_fn prag_fn (scc : sccs) thing_inside
230 = do { (group', (groups', thing))
231 <- tc_group top_lvl sig_fn prag_fn scc $
232 tc_val_binds top_lvl sig_fn prag_fn sccs thing_inside
233 ; return (group' ++ groups', thing) }
235 ------------------------
236 tc_group :: TopLevelFlag -> TcSigFun -> TcPragFun
237 -> SCC (LHsBind Name) -> TcM thing
238 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
240 -- Typecheck one strongly-connected component of the original program.
241 -- We get a list of groups back, because there may
242 -- be specialisations etc as well
244 tc_group top_lvl sig_fn prag_fn scc@(AcyclicSCC bind) thing_inside
245 = -- A single non-recursive binding
246 -- We want to keep non-recursive things non-recursive
247 -- so that we desugar unlifted bindings correctly
248 do { (binds, thing) <- tcPolyBinds top_lvl NonRecursive
249 sig_fn prag_fn scc thing_inside
250 ; return ([(NonRecursive, b) | b <- binds], thing) }
252 tc_group top_lvl sig_fn prag_fn scc@(CyclicSCC binds) thing_inside
253 = -- A recursive strongly-connected component
254 -- To maximise polymorphism (with -fglasgow-exts), we do a new
255 -- strongly-connected component analysis, this time omitting
256 -- any references to variables with type signatures.
258 -- Then we bring into scope all the variables with type signatures
259 do { traceTc (text "tc_group rec" <+> vcat [ppr b $$ text "--and--" | b <- binds])
260 ; gla_exts <- doptM Opt_GlasgowExts
261 ; (binds,thing) <- if gla_exts
263 else go1 scc thing_inside
264 ; return ([(Recursive, unionManyBags binds)], thing) }
265 -- Rec them all together
267 new_sccs :: [SCC (LHsBind Name)]
268 new_sccs = stronglyConnComp (mkEdges has_sig binds)
270 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], thing)
271 go (scc:sccs) = do { (binds1, (binds2, thing)) <- go1 scc (go sccs)
272 ; return (binds1 ++ binds2, thing) }
273 go [] = do { thing <- thing_inside; return ([], thing) }
275 go1 scc thing_inside = tcPolyBinds top_lvl Recursive
276 sig_fn prag_fn scc thing_inside
278 has_sig :: Name -> Bool
279 has_sig n = isJust (sig_fn n)
281 ------------------------
282 tcPolyBinds :: TopLevelFlag -> RecFlag
283 -> TcSigFun -> TcPragFun
284 -> SCC (LHsBind Name)
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 is_rec 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 is_rec
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 -> RecFlag
324 -> TcSigFun -> TcPragFun
325 -> SCC (LHsBind Name)
326 -> TcM ([LHsBinds TcId], [TcId])
327 -- Typechecks the bindings themselves
328 -- Knows nothing about the scope of the bindings
330 tc_poly_binds top_lvl is_rec sig_fn prag_fn bind_scc
332 non_rec = case bind_scc of { AcyclicSCC _ -> True; CyclicSCC _ -> False }
333 binds = flattenSCC bind_scc
334 binder_names = collectHsBindBinders (listToBag binds)
336 loc = getLoc (head binds)
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 binds sig_fn non_rec)
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 is_rec 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 binds 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 is_rec mbind infos
469 = do { checkTc (isNotTopLevel top_lvl)
470 (unliftedBindErr "Top-level" mbind)
471 ; checkTc (isNonRec is_rec)
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 -> Bool -- True <=> either the binders are not mentioned
496 -- in their RHSs or they have type sigs
497 -> TcM (LHsBinds TcId, [MonoBindInfo])
499 tcMonoBinds [L b_loc (FunBind (L nm_loc name) inf matches fvs)]
500 sig_fn -- Single function binding,
501 True -- binder isn't mentioned in RHS,
502 | Nothing <- sig_fn name -- ...with no type signature
503 = -- In this very special case we infer the type of the
504 -- right hand side first (it may have a higher-rank type)
505 -- and *then* make the monomorphic Id for the LHS
506 -- e.g. f = \(x::forall a. a->a) -> <body>
507 -- We want to infer a higher-rank type for f
509 do { (matches', rhs_ty) <- tcInfer (tcMatchesFun name matches)
511 -- Check for an unboxed tuple type
512 -- f = (# True, False #)
513 -- Zonk first just in case it's hidden inside a meta type variable
514 -- (This shows up as a (more obscure) kind error
515 -- in the 'otherwise' case of tcMonoBinds.)
516 ; zonked_rhs_ty <- zonkTcType rhs_ty
517 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
518 (unboxedTupleErr name zonked_rhs_ty)
520 ; mono_name <- newLocalName name
521 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
522 ; return (unitBag (L b_loc (FunBind (L nm_loc mono_id) inf matches' fvs)),
523 [(name, Nothing, mono_id)]) }
525 tcMonoBinds binds sig_fn non_rec
526 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
528 -- Bring (a) the scoped type variables, and (b) the Ids, into scope for the RHSs
529 -- For (a) it's ok to bring them all into scope at once, even
530 -- though each type sig should scope only over its own RHS,
531 -- because the renamer has sorted all that out.
532 ; let mono_info = getMonoBindInfo tc_binds
533 rhs_tvs = [ (name, mkTyVarTy tv)
534 | (_, Just sig, _) <- mono_info,
535 (name, tv) <- sig_scoped sig `zip` sig_tvs sig ]
536 rhs_id_env = map mk mono_info -- A binding for each term variable
538 ; binds' <- tcExtendTyVarEnv2 rhs_tvs $
539 tcExtendIdEnv2 rhs_id_env $
540 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
541 | (n,id) <- rhs_id_env]) `thenM_`
542 mapM (wrapLocM tcRhs) tc_binds
543 ; return (listToBag binds', mono_info) }
545 mk (name, Just sig, _) = (name, sig_id sig) -- Use the type sig if there is one
546 mk (name, Nothing, mono_id) = (name, mono_id) -- otherwise use a monomorphic version
548 ------------------------
549 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
550 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
551 -- if there's a signature for it, use the instantiated signature type
552 -- otherwise invent a type variable
553 -- You see that quite directly in the FunBind case.
555 -- But there's a complication for pattern bindings:
556 -- data T = MkT (forall a. a->a)
558 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
559 -- but we want to get (f::forall a. a->a) as the RHS environment.
560 -- The simplest way to do this is to typecheck the pattern, and then look up the
561 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
562 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
564 data TcMonoBind -- Half completed; LHS done, RHS not done
565 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
566 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
568 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
569 -- Type signature (if any), and
570 -- the monomorphic bound things
572 bndrNames :: [MonoBindInfo] -> [Name]
573 bndrNames mbi = [n | (n,_,_) <- mbi]
575 getMonoType :: MonoBindInfo -> TcTauType
576 getMonoType (_,_,mono_id) = idType mono_id
578 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
579 tcLhs sig_fn (FunBind (L nm_loc name) inf matches _)
580 = do { let mb_sig = sig_fn name
581 ; mono_name <- newLocalName name
582 ; mono_ty <- mk_mono_ty mb_sig
583 ; let mono_id = mkLocalId mono_name mono_ty
584 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
586 mk_mono_ty (Just sig) = return (sig_tau sig)
587 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
589 tcLhs sig_fn bind@(PatBind pat grhss _ _)
590 = do { let tc_pat exp_ty = tcPat (LetPat sig_fn) pat exp_ty lookup_infos
591 ; ((pat', ex_tvs, infos), pat_ty)
592 <- addErrCtxt (patMonoBindsCtxt pat grhss)
595 -- Don't know how to deal with pattern-bound existentials yet
596 ; checkTc (null ex_tvs) (existentialExplode bind)
598 ; return (TcPatBind infos pat' grhss pat_ty) }
600 names = collectPatBinders pat
602 -- After typechecking the pattern, look up the binder
603 -- names, which the pattern has brought into scope.
604 lookup_infos :: TcM [MonoBindInfo]
605 lookup_infos = do { mono_ids <- tcLookupLocalIds names
606 ; return [ (name, sig_fn name, mono_id)
607 | (name, mono_id) <- names `zip` mono_ids] }
609 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
610 -- AbsBind, VarBind impossible
613 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
614 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
615 = do { matches' <- tcMatchesFun (idName mono_id) matches
616 (Check (idType mono_id))
617 ; return (FunBind fun' inf matches' placeHolderNames) }
619 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
620 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
621 tcGRHSsPat grhss (Check pat_ty)
622 ; return (PatBind pat' grhss' pat_ty placeHolderNames) }
625 ---------------------
626 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
627 getMonoBindInfo tc_binds
628 = foldr (get_info . unLoc) [] tc_binds
630 get_info (TcFunBind info _ _ _) rest = info : rest
631 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
635 %************************************************************************
639 %************************************************************************
642 generalise :: TopLevelFlag -> Bool
643 -> [MonoBindInfo] -> [Inst]
644 -> TcM ([TcTyVar], TcDictBinds, [TcId])
645 generalise top_lvl is_unrestricted mono_infos lie_req
646 | not is_unrestricted -- RESTRICTED CASE
647 = -- Check signature contexts are empty
648 do { checkTc (all is_mono_sig sigs)
649 (restrictedBindCtxtErr bndrs)
651 -- Now simplify with exactly that set of tyvars
652 -- We have to squash those Methods
653 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
656 -- Check that signature type variables are OK
657 ; final_qtvs <- checkSigsTyVars qtvs sigs
659 ; return (final_qtvs, binds, []) }
661 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
662 = tcSimplifyInfer doc tau_tvs lie_req
664 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
665 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty
666 ; let -- The "sig_avails" is the stuff available. We get that from
667 -- the context of the type signature, BUT ALSO the lie_avail
668 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
669 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
670 sig_avails = sig_lie ++ local_meths
672 -- Check that the needed dicts can be
673 -- expressed in terms of the signature ones
674 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
676 -- Check that signature type variables are OK
677 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
679 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
681 bndrs = bndrNames mono_infos
682 sigs = [sig | (_, Just sig, _) <- mono_infos]
683 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
684 is_mono_sig sig = null (sig_theta sig)
685 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
687 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
688 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
689 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
692 -- Check that all the signature contexts are the same
693 -- The type signatures on a mutually-recursive group of definitions
694 -- must all have the same context (or none).
696 -- The trick here is that all the signatures should have the same
697 -- context, and we want to share type variables for that context, so that
698 -- all the right hand sides agree a common vocabulary for their type
701 -- We unify them because, with polymorphic recursion, their types
702 -- might not otherwise be related. This is a rather subtle issue.
703 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
704 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
705 = do { mapM unify_ctxt sigs
706 ; newDictsAtLoc (sig_loc sig1) (sig_theta sig1) }
708 theta1 = sig_theta sig1
709 unify_ctxt :: TcSigInfo -> TcM ()
710 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
711 = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
712 addErrCtxt (sigContextsCtxt sig1 sig) $
713 unifyTheta theta1 theta
715 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
716 checkSigsTyVars qtvs sigs
717 = do { gbl_tvs <- tcGetGlobalTyVars
718 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
720 ; let -- Sigh. Make sure that all the tyvars in the type sigs
721 -- appear in the returned ty var list, which is what we are
722 -- going to generalise over. Reason: we occasionally get
724 -- type T a = () -> ()
727 -- Here, 'a' won't appear in qtvs, so we have to add it
728 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
729 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
732 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
733 sig_theta = theta, sig_tau = tau})
734 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
735 addErrCtxtM (sigCtxt id tvs theta tau) $
736 do { tvs' <- checkDistinctTyVars tvs
737 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
738 (bleatEscapedTvs gbl_tvs tvs tvs')
741 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
742 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
743 -- are still all type variables, and all distinct from each other.
744 -- It returns a zonked set of type variables.
745 -- For example, if the type sig is
746 -- f :: forall a b. a -> b -> b
747 -- we want to check that 'a' and 'b' haven't
748 -- (a) been unified with a non-tyvar type
749 -- (b) been unified with each other (all distinct)
751 checkDistinctTyVars sig_tvs
752 = do { zonked_tvs <- mapM zonk_one sig_tvs
753 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
754 ; return zonked_tvs }
756 zonk_one sig_tv = do { ty <- zonkTcTyVar sig_tv
757 ; return (tcGetTyVar "checkDistinctTyVars" ty) }
758 -- 'ty' is bound to be a type variable, because SigSkolTvs
759 -- can only be unified with type variables
761 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
762 -- The TyVarEnv maps each zonked type variable back to its
763 -- corresponding user-written signature type variable
764 check_dup acc (sig_tv, zonked_tv)
765 = case lookupVarEnv acc zonked_tv of
766 Just sig_tv' -> bomb_out sig_tv sig_tv'
768 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
770 bomb_out sig_tv1 sig_tv2
771 = failWithTc (ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
772 <+> ptext SLIT("is unified with another quantified type variable")
773 <+> quotes (ppr tidy_tv2))
775 (env1, tidy_tv1) = tidyOpenTyVar emptyTidyEnv sig_tv1
776 (_env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
780 @getTyVarsToGen@ decides what type variables to generalise over.
782 For a "restricted group" -- see the monomorphism restriction
783 for a definition -- we bind no dictionaries, and
784 remove from tyvars_to_gen any constrained type variables
786 *Don't* simplify dicts at this point, because we aren't going
787 to generalise over these dicts. By the time we do simplify them
788 we may well know more. For example (this actually came up)
790 f x = array ... xs where xs = [1,2,3,4,5]
791 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
792 stuff. If we simplify only at the f-binding (not the xs-binding)
793 we'll know that the literals are all Ints, and we can just produce
796 Find all the type variables involved in overloading, the
797 "constrained_tyvars". These are the ones we *aren't* going to
798 generalise. We must be careful about doing this:
800 (a) If we fail to generalise a tyvar which is not actually
801 constrained, then it will never, ever get bound, and lands
802 up printed out in interface files! Notorious example:
803 instance Eq a => Eq (Foo a b) where ..
804 Here, b is not constrained, even though it looks as if it is.
805 Another, more common, example is when there's a Method inst in
806 the LIE, whose type might very well involve non-overloaded
808 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
809 the simple thing instead]
811 (b) On the other hand, we mustn't generalise tyvars which are constrained,
812 because we are going to pass on out the unmodified LIE, with those
813 tyvars in it. They won't be in scope if we've generalised them.
815 So we are careful, and do a complete simplification just to find the
816 constrained tyvars. We don't use any of the results, except to
817 find which tyvars are constrained.
819 Note [Polymorphic recursion]
820 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
821 The game plan for polymorphic recursion in the code above is
823 * Bind any variable for which we have a type signature
824 to an Id with a polymorphic type. Then when type-checking
825 the RHSs we'll make a full polymorphic call.
827 This fine, but if you aren't a bit careful you end up with a horrendous
828 amount of partial application and (worse) a huge space leak. For example:
830 f :: Eq a => [a] -> [a]
833 If we don't take care, after typechecking we get
835 f = /\a -> \d::Eq a -> let f' = f a d
839 Notice the the stupid construction of (f a d), which is of course
840 identical to the function we're executing. In this case, the
841 polymorphic recursion isn't being used (but that's a very common case).
844 f = /\a -> \d::Eq a -> letrec
845 fm = \ys:[a] -> ...fm...
849 This can lead to a massive space leak, from the following top-level defn
855 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
856 f' is another thunk which evaluates to the same thing... and you end
857 up with a chain of identical values all hung onto by the CAF ff.
861 = let f' = f Int dEqInt in \ys. ...f'...
863 = let f' = let f' = f Int dEqInt in \ys. ...f'...
867 Solution: when typechecking the RHSs we always have in hand the
868 *monomorphic* Ids for each binding. So we just need to make sure that
869 if (Method f a d) shows up in the constraints emerging from (...f...)
870 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
871 to the "givens" when simplifying constraints. That's what the "lies_avail"
875 %************************************************************************
879 %************************************************************************
881 Type signatures are tricky. See Note [Signature skolems] in TcType
884 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
885 tcTySigs sigs = do { mb_sigs <- mappM tcTySig (filter isVanillaLSig sigs)
886 ; return (catMaybes mb_sigs) }
888 tcTySig :: LSig Name -> TcM (Maybe TcSigInfo)
889 tcTySig (L span (Sig (L _ name) ty))
890 = recoverM (return Nothing) $
892 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
893 ; (tvs, theta, tau) <- tcInstSigType name scoped_names sigma_ty
894 ; loc <- getInstLoc (SigOrigin (SigSkol name))
895 ; return (Just (TcSigInfo { sig_id = mkLocalId name sigma_ty,
896 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
897 sig_scoped = scoped_names, sig_loc = loc })) }
899 -- The scoped names are the ones explicitly mentioned
900 -- in the HsForAll. (There may be more in sigma_ty, because
901 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
902 scoped_names = case ty of
903 L _ (HsForAllTy Explicit tvs _ _) -> hsLTyVarNames tvs
906 isUnRestrictedGroup :: [LHsBind Name] -> TcSigFun -> TcM Bool
907 isUnRestrictedGroup binds sig_fn
908 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
909 ; return (not mono_restriction || all_unrestricted) }
911 all_unrestricted = all (unrestricted . unLoc) binds
912 has_sig n = isJust (sig_fn n)
914 unrestricted (PatBind other _ _ _) = False
915 unrestricted (VarBind v _) = has_sig v
916 unrestricted (FunBind v _ matches _) = unrestricted_match matches
919 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
920 -- No args => like a pattern binding
921 unrestricted_match other = True
922 -- Some args => a function binding
926 %************************************************************************
928 \subsection[TcBinds-errors]{Error contexts and messages}
930 %************************************************************************
934 -- This one is called on LHS, when pat and grhss are both Name
935 -- and on RHS, when pat is TcId and grhss is still Name
936 patMonoBindsCtxt pat grhss
937 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
939 -----------------------------------------------
940 sigContextsCtxt sig1 sig2
941 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
942 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
943 ppr id2 <+> dcolon <+> ppr (idType id2)]),
944 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
950 -----------------------------------------------
951 unliftedBindErr flavour mbind
952 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
956 = hang (ptext SLIT("Illegal polymorphic signature in an unlifted binding"))
959 -----------------------------------------------
960 unboxedTupleErr name ty
961 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
962 4 (ppr name <+> dcolon <+> ppr ty)
964 -----------------------------------------------
965 existentialExplode mbinds
966 = hang (vcat [text "My brain just exploded.",
967 text "I can't handle pattern bindings for existentially-quantified constructors.",
968 text "In the binding group"])
971 -----------------------------------------------
972 restrictedBindCtxtErr binder_names
973 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
974 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
975 ptext SLIT("that falls under the monomorphism restriction")])
978 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names