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) )
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 newLocalName, 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 )
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 (CyclicSCC binds) thing_inside
253 = -- A recursive strongly-connected component
254 -- To maximise polymorphism, we do a new strongly-connected
255 -- component analysis, this time omitting any references to
256 -- 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 ; let { sccs :: [SCC (LHsBind Name)]
261 ; sccs = stronglyConnComp (mkEdges has_sig binds) }
262 ; (binds, thing) <- go sccs
263 ; return ([(Recursive, unionManyBags binds)], thing) }
264 -- Rec them all together
266 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], thing)
267 go (scc:sccs) = do { (binds1, (binds2, thing)) <- go1 scc (go sccs)
268 ; return (binds1 ++ binds2, thing) }
269 go [] = do { thing <- thing_inside; return ([], thing) }
271 go1 scc thing_inside = tcPolyBinds top_lvl Recursive
272 sig_fn prag_fn scc thing_inside
274 has_sig :: Name -> Bool
275 has_sig n = isJust (sig_fn n)
277 ------------------------
278 tcPolyBinds :: TopLevelFlag -> RecFlag
279 -> TcSigFun -> TcPragFun
280 -> SCC (LHsBind Name)
282 -> TcM ([LHsBinds TcId], thing)
284 -- Typechecks a single bunch of bindings all together,
285 -- and generalises them. The bunch may be only part of a recursive
286 -- group, because we use type signatures to maximise polymorphism
288 -- Deals with the bindInstsOfLocalFuns thing too
290 tcPolyBinds top_lvl is_rec sig_fn prag_fn scc thing_inside
291 = -- NB: polymorphic recursion means that a function
292 -- may use an instance of itself, we must look at the LIE arising
293 -- from the function's own right hand side. Hence the getLIE
294 -- encloses the tc_poly_binds.
295 do { traceTc (text "tcPolyBinds" <+> ppr scc)
296 ; ((binds1, poly_ids, thing), lie) <- getLIE $
297 do { (binds1, poly_ids) <- tc_poly_binds top_lvl is_rec
299 ; thing <- tcExtendIdEnv poly_ids thing_inside
300 ; return (binds1, poly_ids, thing) }
302 ; if isTopLevel top_lvl
303 then -- For the top level don't bother will all this
304 -- bindInstsOfLocalFuns stuff. All the top level
305 -- things are rec'd together anyway, so it's fine to
306 -- leave them to the tcSimplifyTop,
307 -- and quite a bit faster too
308 do { extendLIEs lie; return (binds1, thing) }
310 else do -- Nested case
311 { lie_binds <- bindInstsOfLocalFuns lie poly_ids
312 ; return (binds1 ++ [lie_binds], thing) }}
314 ------------------------
315 tc_poly_binds :: TopLevelFlag -> RecFlag
316 -> TcSigFun -> TcPragFun
317 -> SCC (LHsBind Name)
318 -> TcM ([LHsBinds TcId], [TcId])
319 -- Typechecks the bindings themselves
320 -- Knows nothing about the scope of the bindings
322 tc_poly_binds top_lvl is_rec sig_fn prag_fn bind_scc
324 non_rec = case bind_scc of { AcyclicSCC _ -> True; CyclicSCC _ -> False }
325 binds = flattenSCC bind_scc
326 binder_names = collectHsBindBinders (listToBag binds)
328 loc = getLoc (head binds)
329 -- TODO: location a bit awkward, but the mbinds have been
330 -- dependency analysed and may no longer be adjacent
332 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
334 recoverM (recoveryCode binder_names sig_fn) $ do
336 { traceTc (ptext SLIT("------------------------------------------------"))
337 ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
339 -- TYPECHECK THE BINDINGS
340 ; ((binds', mono_bind_infos), lie_req)
341 <- getLIE (tcMonoBinds binds sig_fn non_rec)
343 -- CHECK FOR UNLIFTED BINDINGS
344 -- These must be non-recursive etc, and are not generalised
345 -- They desugar to a case expression in the end
346 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
347 ; if any isUnLiftedType zonked_mono_tys then
348 do { -- Unlifted bindings
349 checkUnliftedBinds top_lvl is_rec binds' mono_bind_infos
351 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
352 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
353 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
356 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
357 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
359 else do -- The normal lifted case: GENERALISE
360 { is_unres <- isUnRestrictedGroup binds sig_fn
361 ; (tyvars_to_gen, dict_binds, dict_ids)
362 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
363 generalise top_lvl is_unres mono_bind_infos lie_req
365 -- FINALISE THE QUANTIFIED TYPE VARIABLES
366 -- The quantified type variables often include meta type variables
367 -- we want to freeze them into ordinary type variables, and
368 -- default their kind (e.g. from OpenTypeKind to TypeKind)
369 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
371 -- BUILD THE POLYMORPHIC RESULT IDs
372 ; exports <- mapM (mkExport prag_fn tyvars_to_gen' (map idType dict_ids))
375 -- ZONK THE poly_ids, because they are used to extend the type
376 -- environment; see the invariant on TcEnv.tcExtendIdEnv
377 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
378 ; zonked_poly_ids <- mappM zonkId poly_ids
380 ; traceTc (text "binding:" <+> ppr ((dict_ids, dict_binds),
381 map idType zonked_poly_ids))
383 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen'
385 (dict_binds `unionBags` binds')
387 ; return ([unitBag abs_bind], zonked_poly_ids)
392 mkExport :: TcPragFun -> [TyVar] -> [TcType] -> MonoBindInfo
393 -> TcM ([TyVar], Id, Id, [Prag])
394 mkExport prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
395 = do { prags <- tcPrags poly_id (prag_fn poly_name)
396 ; return (tvs, poly_id, mono_id, prags) }
398 (tvs, poly_id) = case mb_sig of
399 Just sig -> (sig_tvs sig, sig_id sig)
400 Nothing -> (inferred_tvs, mkLocalId poly_name poly_ty)
402 poly_ty = mkForAllTys inferred_tvs
406 ------------------------
407 type TcPragFun = Name -> [LSig Name]
409 mkPragFun :: [LSig Name] -> TcPragFun
410 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
412 prs = [(fromJust (sigName sig), sig) | sig <- sigs, isPragLSig sig]
413 env = foldl add emptyNameEnv prs
414 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
416 tcPrags :: Id -> [LSig Name] -> TcM [Prag]
417 tcPrags poly_id prags = mapM tc_prag prags
419 tc_prag (L loc prag) = setSrcSpan loc $
420 addErrCtxt (pragSigCtxt prag) $
423 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
425 tcPrag :: TcId -> Sig Name -> TcM Prag
426 tcPrag poly_id (SpecSig orig_name hs_ty) = tcSpecPrag poly_id hs_ty
427 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty
428 tcPrag poly_id (InlineSig inl _ act) = return (InlinePrag inl act)
431 tcSpecPrag :: TcId -> LHsType Name -> TcM Prag
432 tcSpecPrag poly_id hs_ty
433 = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
434 ; (co_fn, lie) <- getLIE (tcSub spec_ty (idType poly_id))
436 ; let const_dicts = map instToId lie
437 ; return (SpecPrag (co_fn <$> (HsVar poly_id)) spec_ty const_dicts) }
440 -- If typechecking the binds fails, then return with each
441 -- signature-less binder given type (forall a.a), to minimise
442 -- subsequent error messages
443 recoveryCode binder_names sig_fn
444 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
445 ; return ([], poly_ids) }
447 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
448 poly_ids = map mk_dummy binder_names
449 mk_dummy name = case sig_fn name of
450 Just sig -> sig_id sig -- Signature
451 Nothing -> mkLocalId name forall_a_a -- No signature
453 -- Check that non-overloaded unlifted bindings are
456 -- c) not a multiple-binding group (more or less implied by (a))
458 checkUnliftedBinds :: TopLevelFlag -> RecFlag
459 -> LHsBinds TcId -> [MonoBindInfo] -> TcM ()
460 checkUnliftedBinds top_lvl is_rec mbind infos
461 = do { checkTc (isNotTopLevel top_lvl)
462 (unliftedBindErr "Top-level" mbind)
463 ; checkTc (isNonRec is_rec)
464 (unliftedBindErr "Recursive" mbind)
465 ; checkTc (isSingletonBag mbind)
466 (unliftedBindErr "Multiple" mbind)
467 ; mapM_ check_sig infos }
469 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
471 check_sig other = return ()
475 %************************************************************************
477 \subsection{tcMonoBind}
479 %************************************************************************
481 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
482 The signatures have been dealt with already.
485 tcMonoBinds :: [LHsBind Name]
487 -> Bool -- True <=> either the binders are not mentioned
488 -- in their RHSs or they have type sigs
489 -> TcM (LHsBinds TcId, [MonoBindInfo])
491 tcMonoBinds [L b_loc (FunBind (L nm_loc name) inf matches fvs)]
492 sig_fn -- Single function binding,
493 True -- binder isn't mentioned in RHS,
494 | Nothing <- sig_fn name -- ...with no type signature
495 = -- In this very special case we infer the type of the
496 -- right hand side first (it may have a higher-rank type)
497 -- and *then* make the monomorphic Id for the LHS
498 -- e.g. f = \(x::forall a. a->a) -> <body>
499 -- We want to infer a higher-rank type for f
501 do { (matches', rhs_ty) <- tcInfer (tcMatchesFun name matches)
503 -- Check for an unboxed tuple type
504 -- f = (# True, False #)
505 -- Zonk first just in case it's hidden inside a meta type variable
506 -- (This shows up as a (more obscure) kind error
507 -- in the 'otherwise' case of tcMonoBinds.)
508 ; zonked_rhs_ty <- zonkTcType rhs_ty
509 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
510 (unboxedTupleErr name zonked_rhs_ty)
512 ; mono_name <- newLocalName name
513 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
514 ; return (unitBag (L b_loc (FunBind (L nm_loc mono_id) inf matches' fvs)),
515 [(name, Nothing, mono_id)]) }
517 tcMonoBinds binds sig_fn non_rec
518 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
520 -- Bring (a) the scoped type variables, and (b) the Ids, into scope for the RHSs
521 -- For (a) it's ok to bring them all into scope at once, even
522 -- though each type sig should scope only over its own RHS,
523 -- because the renamer has sorted all that out.
524 ; let mono_info = getMonoBindInfo tc_binds
525 rhs_tvs = [ (name, mkTyVarTy tv)
526 | (_, Just sig, _) <- mono_info,
527 (name, tv) <- sig_scoped sig `zip` sig_tvs sig ]
528 rhs_id_env = map mk mono_info -- A binding for each term variable
530 ; binds' <- tcExtendTyVarEnv2 rhs_tvs $
531 tcExtendIdEnv2 rhs_id_env $
532 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
533 | (n,id) <- rhs_id_env]) `thenM_`
534 mapM (wrapLocM tcRhs) tc_binds
535 ; return (listToBag binds', mono_info) }
537 mk (name, Just sig, _) = (name, sig_id sig) -- Use the type sig if there is one
538 mk (name, Nothing, mono_id) = (name, mono_id) -- otherwise use a monomorphic version
540 ------------------------
541 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
542 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
543 -- if there's a signature for it, use the instantiated signature type
544 -- otherwise invent a type variable
545 -- You see that quite directly in the FunBind case.
547 -- But there's a complication for pattern bindings:
548 -- data T = MkT (forall a. a->a)
550 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
551 -- but we want to get (f::forall a. a->a) as the RHS environment.
552 -- The simplest way to do this is to typecheck the pattern, and then look up the
553 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
554 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
556 data TcMonoBind -- Half completed; LHS done, RHS not done
557 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
558 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
560 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
561 -- Type signature (if any), and
562 -- the monomorphic bound things
564 bndrNames :: [MonoBindInfo] -> [Name]
565 bndrNames mbi = [n | (n,_,_) <- mbi]
567 getMonoType :: MonoBindInfo -> TcTauType
568 getMonoType (_,_,mono_id) = idType mono_id
570 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
571 tcLhs sig_fn (FunBind (L nm_loc name) inf matches _)
572 = do { let mb_sig = sig_fn name
573 ; mono_name <- newLocalName name
574 ; mono_ty <- mk_mono_ty mb_sig
575 ; let mono_id = mkLocalId mono_name mono_ty
576 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
578 mk_mono_ty (Just sig) = return (sig_tau sig)
579 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
581 tcLhs sig_fn bind@(PatBind pat grhss _ _)
582 = do { let tc_pat exp_ty = tcPat (LetPat sig_fn) pat exp_ty lookup_infos
583 ; ((pat', ex_tvs, infos), pat_ty)
584 <- addErrCtxt (patMonoBindsCtxt pat grhss)
587 -- Don't know how to deal with pattern-bound existentials yet
588 ; checkTc (null ex_tvs) (existentialExplode bind)
590 ; return (TcPatBind infos pat' grhss pat_ty) }
592 names = collectPatBinders pat
594 -- After typechecking the pattern, look up the binder
595 -- names, which the pattern has brought into scope.
596 lookup_infos :: TcM [MonoBindInfo]
597 lookup_infos = do { mono_ids <- tcLookupLocalIds names
598 ; return [ (name, sig_fn name, mono_id)
599 | (name, mono_id) <- names `zip` mono_ids] }
601 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
602 -- AbsBind, VarBind impossible
605 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
606 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
607 = do { matches' <- tcMatchesFun (idName mono_id) matches
608 (Check (idType mono_id))
609 ; return (FunBind fun' inf matches' placeHolderNames) }
611 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
612 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
613 tcGRHSsPat grhss (Check pat_ty)
614 ; return (PatBind pat' grhss' pat_ty placeHolderNames) }
617 ---------------------
618 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
619 getMonoBindInfo tc_binds
620 = foldr (get_info . unLoc) [] tc_binds
622 get_info (TcFunBind info _ _ _) rest = info : rest
623 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
627 %************************************************************************
631 %************************************************************************
634 generalise :: TopLevelFlag -> Bool
635 -> [MonoBindInfo] -> [Inst]
636 -> TcM ([TcTyVar], TcDictBinds, [TcId])
637 generalise top_lvl is_unrestricted mono_infos lie_req
638 | not is_unrestricted -- RESTRICTED CASE
639 = -- Check signature contexts are empty
640 do { checkTc (all is_mono_sig sigs)
641 (restrictedBindCtxtErr bndrs)
643 -- Now simplify with exactly that set of tyvars
644 -- We have to squash those Methods
645 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
648 -- Check that signature type variables are OK
649 ; final_qtvs <- checkSigsTyVars qtvs sigs
651 ; return (final_qtvs, binds, []) }
653 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
654 = tcSimplifyInfer doc tau_tvs lie_req
656 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
657 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty
658 ; let -- The "sig_avails" is the stuff available. We get that from
659 -- the context of the type signature, BUT ALSO the lie_avail
660 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
661 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
662 sig_avails = sig_lie ++ local_meths
664 -- Check that the needed dicts can be
665 -- expressed in terms of the signature ones
666 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
668 -- Check that signature type variables are OK
669 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
671 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
673 bndrs = bndrNames mono_infos
674 sigs = [sig | (_, Just sig, _) <- mono_infos]
675 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
676 is_mono_sig sig = null (sig_theta sig)
677 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
679 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
680 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
681 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
684 -- Check that all the signature contexts are the same
685 -- The type signatures on a mutually-recursive group of definitions
686 -- must all have the same context (or none).
688 -- The trick here is that all the signatures should have the same
689 -- context, and we want to share type variables for that context, so that
690 -- all the right hand sides agree a common vocabulary for their type
693 -- We unify them because, with polymorphic recursion, their types
694 -- might not otherwise be related. This is a rather subtle issue.
695 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
696 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
697 = do { mapM unify_ctxt sigs
698 ; newDictsAtLoc (sig_loc sig1) (sig_theta sig1) }
700 theta1 = sig_theta sig1
701 unify_ctxt :: TcSigInfo -> TcM ()
702 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
703 = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
704 addErrCtxt (sigContextsCtxt sig1 sig) $
705 unifyTheta theta1 theta
707 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
708 checkSigsTyVars qtvs sigs
709 = do { gbl_tvs <- tcGetGlobalTyVars
710 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
712 ; let -- Sigh. Make sure that all the tyvars in the type sigs
713 -- appear in the returned ty var list, which is what we are
714 -- going to generalise over. Reason: we occasionally get
716 -- type T a = () -> ()
719 -- Here, 'a' won't appear in qtvs, so we have to add it
720 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
721 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
724 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
725 sig_theta = theta, sig_tau = tau})
726 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
727 addErrCtxtM (sigCtxt id tvs theta tau) $
728 do { tvs' <- checkDistinctTyVars tvs
729 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
730 (bleatEscapedTvs gbl_tvs tvs tvs')
733 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
734 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
735 -- are still all type variables, and all distinct from each other.
736 -- It returns a zonked set of type variables.
737 -- For example, if the type sig is
738 -- f :: forall a b. a -> b -> b
739 -- we want to check that 'a' and 'b' haven't
740 -- (a) been unified with a non-tyvar type
741 -- (b) been unified with each other (all distinct)
743 checkDistinctTyVars sig_tvs
744 = do { zonked_tvs <- mapM zonk_one sig_tvs
745 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
746 ; return zonked_tvs }
748 zonk_one sig_tv = do { ty <- zonkTcTyVar sig_tv
749 ; return (tcGetTyVar "checkDistinctTyVars" ty) }
750 -- 'ty' is bound to be a type variable, because SigSkolTvs
751 -- can only be unified with type variables
753 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
754 -- The TyVarEnv maps each zonked type variable back to its
755 -- corresponding user-written signature type variable
756 check_dup acc (sig_tv, zonked_tv)
757 = case lookupVarEnv acc zonked_tv of
758 Just sig_tv' -> bomb_out sig_tv sig_tv'
760 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
762 bomb_out sig_tv1 sig_tv2
763 = failWithTc (ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
764 <+> ptext SLIT("is unified with another quantified type variable")
765 <+> quotes (ppr tidy_tv2))
767 (env1, tidy_tv1) = tidyOpenTyVar emptyTidyEnv sig_tv1
768 (_env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
772 @getTyVarsToGen@ decides what type variables to generalise over.
774 For a "restricted group" -- see the monomorphism restriction
775 for a definition -- we bind no dictionaries, and
776 remove from tyvars_to_gen any constrained type variables
778 *Don't* simplify dicts at this point, because we aren't going
779 to generalise over these dicts. By the time we do simplify them
780 we may well know more. For example (this actually came up)
782 f x = array ... xs where xs = [1,2,3,4,5]
783 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
784 stuff. If we simplify only at the f-binding (not the xs-binding)
785 we'll know that the literals are all Ints, and we can just produce
788 Find all the type variables involved in overloading, the
789 "constrained_tyvars". These are the ones we *aren't* going to
790 generalise. We must be careful about doing this:
792 (a) If we fail to generalise a tyvar which is not actually
793 constrained, then it will never, ever get bound, and lands
794 up printed out in interface files! Notorious example:
795 instance Eq a => Eq (Foo a b) where ..
796 Here, b is not constrained, even though it looks as if it is.
797 Another, more common, example is when there's a Method inst in
798 the LIE, whose type might very well involve non-overloaded
800 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
801 the simple thing instead]
803 (b) On the other hand, we mustn't generalise tyvars which are constrained,
804 because we are going to pass on out the unmodified LIE, with those
805 tyvars in it. They won't be in scope if we've generalised them.
807 So we are careful, and do a complete simplification just to find the
808 constrained tyvars. We don't use any of the results, except to
809 find which tyvars are constrained.
811 Note [Polymorphic recursion]
812 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
813 The game plan for polymorphic recursion in the code above is
815 * Bind any variable for which we have a type signature
816 to an Id with a polymorphic type. Then when type-checking
817 the RHSs we'll make a full polymorphic call.
819 This fine, but if you aren't a bit careful you end up with a horrendous
820 amount of partial application and (worse) a huge space leak. For example:
822 f :: Eq a => [a] -> [a]
825 If we don't take care, after typechecking we get
827 f = /\a -> \d::Eq a -> let f' = f a d
831 Notice the the stupid construction of (f a d), which is of course
832 identical to the function we're executing. In this case, the
833 polymorphic recursion isn't being used (but that's a very common case).
836 f = /\a -> \d::Eq a -> letrec
837 fm = \ys:[a] -> ...fm...
841 This can lead to a massive space leak, from the following top-level defn
847 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
848 f' is another thunk which evaluates to the same thing... and you end
849 up with a chain of identical values all hung onto by the CAF ff.
853 = let f' = f Int dEqInt in \ys. ...f'...
855 = let f' = let f' = f Int dEqInt in \ys. ...f'...
859 Solution: when typechecking the RHSs we always have in hand the
860 *monomorphic* Ids for each binding. So we just need to make sure that
861 if (Method f a d) shows up in the constraints emerging from (...f...)
862 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
863 to the "givens" when simplifying constraints. That's what the "lies_avail"
867 %************************************************************************
871 %************************************************************************
873 Type signatures are tricky. See Note [Signature skolems] in TcType
876 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
877 tcTySigs sigs = mappM tcTySig (filter isVanillaLSig sigs)
879 tcTySig :: LSig Name -> TcM TcSigInfo
880 tcTySig (L span (Sig (L _ name) ty))
882 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
883 ; (tvs, theta, tau) <- tcInstSigType name scoped_names sigma_ty
884 ; loc <- getInstLoc (SigOrigin (SigSkol name))
885 ; return (TcSigInfo { sig_id = mkLocalId name sigma_ty,
886 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
887 sig_scoped = scoped_names, sig_loc = loc }) }
889 -- The scoped names are the ones explicitly mentioned
890 -- in the HsForAll. (There may be more in sigma_ty, because
891 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
892 scoped_names = case ty of
893 L _ (HsForAllTy Explicit tvs _ _) -> hsLTyVarNames tvs
896 isUnRestrictedGroup :: [LHsBind Name] -> TcSigFun -> TcM Bool
897 isUnRestrictedGroup binds sig_fn
898 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
899 ; return (not mono_restriction || all_unrestricted) }
901 all_unrestricted = all (unrestricted . unLoc) binds
902 has_sig n = isJust (sig_fn n)
904 unrestricted (PatBind other _ _ _) = False
905 unrestricted (VarBind v _) = has_sig v
906 unrestricted (FunBind v _ matches _) = unrestricted_match matches
909 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
910 -- No args => like a pattern binding
911 unrestricted_match other = True
912 -- Some args => a function binding
916 %************************************************************************
918 \subsection[TcBinds-errors]{Error contexts and messages}
920 %************************************************************************
924 -- This one is called on LHS, when pat and grhss are both Name
925 -- and on RHS, when pat is TcId and grhss is still Name
926 patMonoBindsCtxt pat grhss
927 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
929 -----------------------------------------------
930 sigContextsCtxt sig1 sig2
931 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
932 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
933 ppr id2 <+> dcolon <+> ppr (idType id2)]),
934 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
940 -----------------------------------------------
941 unliftedBindErr flavour mbind
942 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
946 = hang (ptext SLIT("Illegal polymorphic signature in an unlifted binding"))
949 -----------------------------------------------
950 unboxedTupleErr name ty
951 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
952 4 (ppr name <+> dcolon <+> ppr ty)
954 -----------------------------------------------
955 existentialExplode mbinds
956 = hang (vcat [text "My brain just exploded.",
957 text "I can't handle pattern bindings for existentially-quantified constructors.",
958 text "In the binding group"])
961 -----------------------------------------------
962 restrictedBindCtxtErr binder_names
963 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
964 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
965 ptext SLIT("that falls under the monomorphism restriction")])
968 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names