2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcBinds]{TcBinds}
8 module TcBinds ( tcLocalBinds, tcTopBinds,
9 tcHsBootSigs, tcMonoBinds, tcPolyBinds,
10 TcPragFun, tcPrags, mkPragFun,
11 TcSigInfo(..), TcSigFun, mkTcSigFun,
12 badBootDeclErr ) where
14 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
15 import {-# SOURCE #-} TcExpr ( tcMonoExpr )
48 import Data.List( partition )
53 %************************************************************************
55 \subsection{Type-checking bindings}
57 %************************************************************************
59 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
60 it needs to know something about the {\em usage} of the things bound,
61 so that it can create specialisations of them. So @tcBindsAndThen@
62 takes a function which, given an extended environment, E, typechecks
63 the scope of the bindings returning a typechecked thing and (most
64 important) an LIE. It is this LIE which is then used as the basis for
65 specialising the things bound.
67 @tcBindsAndThen@ also takes a "combiner" which glues together the
68 bindings and the "thing" to make a new "thing".
70 The real work is done by @tcBindWithSigsAndThen@.
72 Recursive and non-recursive binds are handled in essentially the same
73 way: because of uniques there are no scoping issues left. The only
74 difference is that non-recursive bindings can bind primitive values.
76 Even for non-recursive binding groups we add typings for each binder
77 to the LVE for the following reason. When each individual binding is
78 checked the type of its LHS is unified with that of its RHS; and
79 type-checking the LHS of course requires that the binder is in scope.
81 At the top-level the LIE is sure to contain nothing but constant
82 dictionaries, which we resolve at the module level.
85 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
86 -- Note: returning the TcLclEnv is more than we really
87 -- want. The bit we care about is the local bindings
88 -- and the free type variables thereof
90 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
91 ; return (foldr (unionBags . snd) emptyBag prs, env) }
92 -- The top level bindings are flattened into a giant
93 -- implicitly-mutually-recursive LHsBinds
95 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
96 -- A hs-boot file has only one BindGroup, and it only has type
97 -- signatures in it. The renamer checked all this
98 tcHsBootSigs (ValBindsOut binds sigs)
99 = do { checkTc (null binds) badBootDeclErr
100 ; mapM (addLocM tc_boot_sig) (filter isTypeLSig sigs) }
102 tc_boot_sig (TypeSig (L _ name) ty)
103 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
104 ; return (mkVanillaGlobal name sigma_ty) }
105 -- Notice that we make GlobalIds, not LocalIds
106 tc_boot_sig s = pprPanic "tcHsBootSigs/tc_boot_sig" (ppr s)
107 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
109 badBootDeclErr :: Message
110 badBootDeclErr = ptext (sLit "Illegal declarations in an hs-boot file")
112 ------------------------
113 tcLocalBinds :: HsLocalBinds Name -> TcM thing
114 -> TcM (HsLocalBinds TcId, thing)
116 tcLocalBinds EmptyLocalBinds thing_inside
117 = do { thing <- thing_inside
118 ; return (EmptyLocalBinds, thing) }
120 tcLocalBinds (HsValBinds binds) thing_inside
121 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
122 ; return (HsValBinds binds', thing) }
124 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
125 = do { (thing, lie) <- getLIE thing_inside
126 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
128 -- If the binding binds ?x = E, we must now
129 -- discharge any ?x constraints in expr_lie
130 ; dict_binds <- tcSimplifyIPs avail_ips lie
131 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
133 -- I wonder if we should do these one at at time
136 tc_ip_bind (IPBind ip expr) = do
137 ty <- newFlexiTyVarTy argTypeKind
138 (ip', ip_inst) <- newIPDict (IPBindOrigin ip) ip ty
139 expr' <- tcMonoExpr expr ty
140 return (ip_inst, (IPBind ip' expr'))
142 ------------------------
143 tcValBinds :: TopLevelFlag
144 -> HsValBinds Name -> TcM thing
145 -> TcM (HsValBinds TcId, thing)
147 tcValBinds _ (ValBindsIn binds _) _
148 = pprPanic "tcValBinds" (ppr binds)
150 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
151 = do { -- Typecheck the signature
152 ; let { prag_fn = mkPragFun sigs
153 ; ty_sigs = filter isTypeLSig sigs
154 ; sig_fn = mkTcSigFun ty_sigs }
156 ; poly_ids <- checkNoErrs (mapAndRecoverM tcTySig ty_sigs)
157 -- No recovery from bad signatures, because the type sigs
158 -- may bind type variables, so proceeding without them
159 -- can lead to a cascade of errors
160 -- ToDo: this means we fall over immediately if any type sig
161 -- is wrong, which is over-conservative, see Trac bug #745
163 -- Extend the envt right away with all
164 -- the Ids declared with type signatures
165 ; poly_rec <- doptM Opt_RelaxedPolyRec
166 ; (binds', thing) <- tcExtendIdEnv poly_ids $
167 tcBindGroups poly_rec top_lvl sig_fn prag_fn
170 ; return (ValBindsOut binds' sigs, thing) }
172 ------------------------
173 tcBindGroups :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
174 -> [(RecFlag, LHsBinds Name)] -> TcM thing
175 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
176 -- Typecheck a whole lot of value bindings,
177 -- one strongly-connected component at a time
178 -- Here a "strongly connected component" has the strightforward
179 -- meaning of a group of bindings that mention each other,
180 -- ignoring type signatures (that part comes later)
182 tcBindGroups _ _ _ _ [] thing_inside
183 = do { thing <- thing_inside
184 ; return ([], thing) }
186 tcBindGroups poly_rec top_lvl sig_fn prag_fn (group : groups) thing_inside
187 = do { (group', (groups', thing))
188 <- tc_group poly_rec top_lvl sig_fn prag_fn group $
189 tcBindGroups poly_rec top_lvl sig_fn prag_fn groups thing_inside
190 ; return (group' ++ groups', thing) }
192 ------------------------
193 tc_group :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
194 -> (RecFlag, LHsBinds Name) -> TcM thing
195 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
197 -- Typecheck one strongly-connected component of the original program.
198 -- We get a list of groups back, because there may
199 -- be specialisations etc as well
201 tc_group _ top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
202 -- A single non-recursive binding
203 -- We want to keep non-recursive things non-recursive
204 -- so that we desugar unlifted bindings correctly
205 = do { (binds1, lie_binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn
206 NonRecursive binds thing_inside
207 ; return ( [(NonRecursive, unitBag b) | b <- bagToList binds1]
208 ++ [(Recursive, lie_binds)] -- TcDictBinds have scrambled dependency order
211 tc_group poly_rec top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
212 | not poly_rec -- Recursive group, normal Haskell 98 route
213 = do { (binds1, lie_binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn
214 Recursive binds thing_inside
215 ; return ([(Recursive, binds1 `unionBags` lie_binds)], thing) }
217 | otherwise -- Recursive group, with -XRelaxedPolyRec
218 = -- To maximise polymorphism (with -XRelaxedPolyRec), we do a new
219 -- strongly-connected-component analysis, this time omitting
220 -- any references to variables with type signatures.
222 -- Notice that the bindInsts thing covers *all* the bindings in
223 -- the original group at once; an earlier one may use a later one!
224 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
225 ; (binds1,lie_binds,thing) <- bindLocalInsts top_lvl $
226 go (stronglyConnCompFromEdgedVertices (mkEdges sig_fn binds))
227 ; return ([(Recursive, binds1 `unionBags` lie_binds)], thing) }
228 -- Rec them all together
230 -- go :: SCC (LHsBind Name) -> TcM (LHsBinds TcId, [TcId], thing)
231 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
232 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
233 ; return (binds1 `unionBags` binds2, ids1 ++ ids2, thing) }
234 go [] = do { thing <- thing_inside; return (emptyBag, [], thing) }
236 tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive (unitBag bind)
237 tc_scc (CyclicSCC binds) = tc_sub_group Recursive (listToBag binds)
239 tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
241 tc_haskell98 :: TopLevelFlag -> TcSigFun -> TcPragFun -> RecFlag
242 -> LHsBinds Name -> TcM a -> TcM (LHsBinds TcId, TcDictBinds, a)
243 tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside
244 = bindLocalInsts top_lvl $
245 do { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds
246 ; thing <- tcExtendIdEnv ids thing_inside
247 ; return (binds1, ids, thing) }
249 ------------------------
250 bindLocalInsts :: TopLevelFlag
251 -> TcM (LHsBinds TcId, [TcId], a)
252 -> TcM (LHsBinds TcId, TcDictBinds, a)
253 bindLocalInsts top_lvl thing_inside
255 = do { (binds, _, thing) <- thing_inside; return (binds, emptyBag, thing) }
256 -- For the top level don't bother with all this bindInstsOfLocalFuns stuff.
257 -- All the top level things are rec'd together anyway, so it's fine to
258 -- leave them to the tcSimplifyTop, and quite a bit faster too
260 | otherwise -- Nested case
261 = do { ((binds, ids, thing), lie) <- getLIE thing_inside
262 ; lie_binds <- bindInstsOfLocalFuns lie ids
263 ; return (binds, lie_binds, thing) }
265 ------------------------
266 mkEdges :: TcSigFun -> LHsBinds Name
267 -> [(LHsBind Name, BKey, [BKey])]
269 type BKey = Int -- Just number off the bindings
272 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
273 Just key <- [lookupNameEnv key_map n], no_sig n ])
274 | (bind, key) <- keyd_binds
277 no_sig :: Name -> Bool
278 no_sig n = isNothing (sig_fn n)
280 keyd_binds = bagToList binds `zip` [0::BKey ..]
282 key_map :: NameEnv BKey -- Which binding it comes from
283 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
284 , bndr <- bindersOfHsBind bind ]
286 bindersOfHsBind :: HsBind Name -> [Name]
287 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
288 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
289 bindersOfHsBind (AbsBinds {}) = panic "bindersOfHsBind AbsBinds"
290 bindersOfHsBind (VarBind {}) = panic "bindersOfHsBind VarBind"
292 ------------------------
293 tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragFun
294 -> RecFlag -- Whether the group is really recursive
295 -> RecFlag -- Whether it's recursive after breaking
296 -- dependencies based on type signatures
298 -> TcM (LHsBinds TcId, [TcId])
300 -- Typechecks a single bunch of bindings all together,
301 -- and generalises them. The bunch may be only part of a recursive
302 -- group, because we use type signatures to maximise polymorphism
304 -- Returns a list because the input may be a single non-recursive binding,
305 -- in which case the dependency order of the resulting bindings is
308 -- Knows nothing about the scope of the bindings
310 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds
312 bind_list = bagToList binds
313 binder_names = collectHsBindBinders binds
314 loc = getLoc (head bind_list)
315 -- TODO: location a bit awkward, but the mbinds have been
316 -- dependency analysed and may no longer be adjacent
318 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
320 recoverM (recoveryCode binder_names sig_fn) $ do
322 { traceTc (ptext (sLit "------------------------------------------------"))
323 ; traceTc (ptext (sLit "Bindings for") <+> ppr binder_names)
325 -- TYPECHECK THE BINDINGS
326 ; ((binds', mono_bind_infos), lie_req)
327 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
328 ; traceTc (text "temp" <+> (ppr binds' $$ ppr lie_req))
330 -- CHECK FOR UNLIFTED BINDINGS
331 -- These must be non-recursive etc, and are not generalised
332 -- They desugar to a case expression in the end
333 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
334 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
335 zonked_mono_tys mono_bind_infos
337 do { extendLIEs lie_req
338 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
339 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
340 mk_export (_, Just sig, mono_id) _ = ([], sig_id sig, mono_id, [])
341 -- ToDo: prags for unlifted bindings
343 ; return ( unitBag $ L loc $ AbsBinds [] [] exports binds',
344 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
346 else do -- The normal lifted case: GENERALISE
348 ; (tyvars_to_gen, dicts, dict_binds)
349 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
350 generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
352 -- BUILD THE POLYMORPHIC RESULT IDs
353 ; let dict_vars = map instToVar dicts -- May include equality constraints
354 ; exports <- mapM (mkExport top_lvl rec_group (length mono_bind_infos > 1)
355 prag_fn tyvars_to_gen (map varType dict_vars))
358 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
359 ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids))
361 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen
363 (dict_binds `unionBags` binds')
365 ; return (unitBag abs_bind, poly_ids) -- poly_ids are guaranteed zonked by mkExport
370 mkExport :: TopLevelFlag -> RecFlag
371 -> Bool -- More than one variable is bound, so we'll desugar to
372 -- a tuple, so INLINE pragmas won't work
373 -> TcPragFun -> [TyVar] -> [TcType]
375 -> TcM ([TyVar], Id, Id, [LSpecPrag])
376 -- mkExport generates exports with
377 -- zonked type variables,
379 -- The former is just because no further unifications will change
380 -- the quantified type variables, so we can fix their final form
382 -- The latter is needed because the poly_ids are used to extend the
383 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
385 -- Pre-condition: the inferred_tvs are already zonked
387 mkExport top_lvl rec_group multi_bind prag_fn inferred_tvs dict_tys
388 (poly_name, mb_sig, mono_id)
389 = do { warn_missing_sigs <- doptM Opt_WarnMissingSigs
390 ; let warn = isTopLevel top_lvl && warn_missing_sigs
391 ; (tvs, poly_id) <- mk_poly_id warn mb_sig
392 -- poly_id has a zonked type
394 ; (poly_id', spec_prags) <- tcPrags rec_group multi_bind (notNull dict_tys)
395 poly_id (prag_fn poly_name)
396 -- tcPrags requires a zonked poly_id
398 ; return (tvs, poly_id', mono_id, spec_prags) }
400 poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id))
402 mk_poly_id warn Nothing = do { poly_ty' <- zonkTcType poly_ty
403 ; missingSigWarn warn poly_name poly_ty'
404 ; return (inferred_tvs, mkLocalId poly_name poly_ty') }
405 mk_poly_id _ (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
406 ; return (tvs, sig_id sig) }
408 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
410 ------------------------
411 type TcPragFun = Name -> [LSig Name]
413 mkPragFun :: [LSig Name] -> TcPragFun
414 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
416 prs = [(expectJust "mkPragFun" (sigName sig), sig)
417 | sig <- sigs, isPragLSig sig]
418 env = foldl add emptyNameEnv prs
419 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
422 -> Bool -- True <=> AbsBinds binds more than one variable
423 -> Bool -- True <=> function is overloaded
425 -> TcM (Id, [LSpecPrag])
426 -- Add INLINE and SPECLIASE pragmas
427 -- INLINE prags are added to the Id directly
428 -- SPECIALISE prags are passed to the desugarer via [LSpecPrag]
429 -- Pre-condition: the poly_id is zonked
430 -- Reason: required by tcSubExp
431 tcPrags _rec_group _multi_bind _is_overloaded_id poly_id prag_sigs
432 = do { poly_id' <- tc_inl inl_sigs
434 ; spec_prags <- mapM (wrapLocM (tcSpecPrag poly_id')) spec_sigs
436 -- Commented out until bytestring library removes redundant pragmas
437 -- for packWith and unpackWith
438 -- ; unless (null spec_sigs || is_overloaded_id) warn_discarded_spec
440 ; unless (null bad_sigs) warn_discarded_sigs
442 ; return (poly_id', spec_prags) }
444 (inl_sigs, other_sigs) = partition isInlineLSig prag_sigs
445 (spec_sigs, bad_sigs) = partition isSpecLSig other_sigs
447 -- warn_discarded_spec = warnPrags poly_id spec_sigs $
448 -- ptext (sLit "SPECIALISE pragmas for non-overloaded function")
449 warn_dup_inline = warnPrags poly_id inl_sigs $
450 ptext (sLit "Duplicate INLINE pragmas for")
451 warn_discarded_sigs = warnPrags poly_id bad_sigs $
452 ptext (sLit "Discarding unexpected pragmas for")
455 tc_inl [] = return poly_id
456 tc_inl (L loc (InlineSig _ prag) : other_inls)
457 = do { unless (null other_inls) (setSrcSpan loc warn_dup_inline)
458 ; return (poly_id `setInlinePragma` prag) }
459 tc_inl _ = panic "tc_inl"
461 {- Earlier we tried to warn about
462 (a) INLINE for recursive function
463 (b) INLINE for function that is part of a multi-binder group
464 Code fragments below. But we want to allow
468 even though they are mutually recursive.
469 So I'm just omitting the warnings for now
471 | multi_bind && isInlinePragma prag
472 = do { setSrcSpan loc $ addWarnTc multi_bind_warn
475 ; when (isInlinePragma prag && isRec rec_group)
476 (setSrcSpan loc (addWarnTc rec_inline_warn))
478 rec_inline_warn = ptext (sLit "INLINE pragma for recursive binder")
479 <+> quotes (ppr poly_id) <+> ptext (sLit "may be discarded")
481 multi_bind_warn = hang (ptext (sLit "Discarding INLINE pragma for") <+> quotes (ppr poly_id))
482 2 (ptext (sLit "because it is bound by a pattern, or mutual recursion") )
486 warnPrags :: Id -> [LSig Name] -> SDoc -> TcM ()
487 warnPrags id bad_sigs herald
488 = addWarnTc (hang (herald <+> quotes (ppr id))
489 2 (ppr_sigs bad_sigs))
491 ppr_sigs sigs = vcat (map (ppr . getLoc) sigs)
494 tcSpecPrag :: TcId -> Sig Name -> TcM SpecPrag
495 tcSpecPrag poly_id prag@(SpecSig _ hs_ty inl)
496 = addErrCtxt (spec_ctxt prag) $
497 do { let name = idName poly_id
498 ; spec_ty <- tcHsSigType (FunSigCtxt name) hs_ty
499 ; co_fn <- tcSubExp (SpecPragOrigin name) (idType poly_id) spec_ty
500 ; return (SpecPrag co_fn inl) }
502 spec_ctxt prag = hang (ptext (sLit "In the SPECIALISE pragma")) 2 (ppr prag)
503 tcSpecPrag _ sig = pprPanic "tcSpecPrag" (ppr sig)
507 -- If typechecking the binds fails, then return with each
508 -- signature-less binder given type (forall a.a), to minimise
509 -- subsequent error messages
510 recoveryCode :: [Name] -> (Name -> Maybe [Name])
511 -> TcM (LHsBinds TcId, [Id])
512 recoveryCode binder_names sig_fn
513 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
514 ; poly_ids <- mapM mk_dummy binder_names
515 ; return (emptyBag, poly_ids) }
518 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
519 | otherwise = return (mkLocalId name forall_a_a) -- No signature
522 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
525 -- Check that non-overloaded unlifted bindings are
528 -- c) not a multiple-binding group (more or less implied by (a))
530 checkStrictBinds :: TopLevelFlag -> RecFlag
531 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
533 checkStrictBinds top_lvl rec_group mbind mono_tys infos
534 | unlifted || bang_pat
535 = do { checkTc (isNotTopLevel top_lvl)
536 (strictBindErr "Top-level" unlifted mbind)
537 ; checkTc (isNonRec rec_group)
538 (strictBindErr "Recursive" unlifted mbind)
539 ; checkTc (isSingletonBag mbind)
540 (strictBindErr "Multiple" unlifted mbind)
541 -- This should be a checkTc, not a warnTc, but as of GHC 6.11
542 -- the versions of alex and happy available have non-conforming
543 -- templates, so the GHC build fails if it's an error:
544 ; warnUnlifted <- doptM Opt_WarnLazyUnliftedBindings
545 ; warnTc (warnUnlifted && not bang_pat)
546 (unliftedMustBeBang mbind)
547 ; mapM_ check_sig infos
552 unlifted = any isUnLiftedType mono_tys
553 bang_pat = anyBag (isBangHsBind . unLoc) mbind
554 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
555 (badStrictSig unlifted sig)
556 check_sig _ = return ()
558 unliftedMustBeBang :: LHsBindsLR Var Var -> SDoc
559 unliftedMustBeBang mbind
560 = hang (text "Bindings containing unlifted types must use an outermost bang pattern:")
561 4 (pprLHsBinds mbind)
562 $$ text "*** This will be an error in GHC 6.14! Fix your code now!"
564 strictBindErr :: String -> Bool -> LHsBindsLR Var Var -> SDoc
565 strictBindErr flavour unlifted mbind
566 = hang (text flavour <+> msg <+> ptext (sLit "aren't allowed:"))
567 4 (pprLHsBinds mbind)
569 msg | unlifted = ptext (sLit "bindings for unlifted types")
570 | otherwise = ptext (sLit "bang-pattern bindings")
572 badStrictSig :: Bool -> TcSigInfo -> SDoc
573 badStrictSig unlifted sig
574 = hang (ptext (sLit "Illegal polymorphic signature in") <+> msg)
577 msg | unlifted = ptext (sLit "an unlifted binding")
578 | otherwise = ptext (sLit "a bang-pattern binding")
582 %************************************************************************
584 \subsection{tcMonoBind}
586 %************************************************************************
588 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
589 The signatures have been dealt with already.
592 tcMonoBinds :: [LHsBind Name]
594 -> RecFlag -- Whether the binding is recursive for typechecking purposes
595 -- i.e. the binders are mentioned in their RHSs, and
596 -- we are not resuced by a type signature
597 -> TcM (LHsBinds TcId, [MonoBindInfo])
599 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
600 fun_matches = matches, bind_fvs = fvs })]
601 sig_fn -- Single function binding,
602 NonRecursive -- binder isn't mentioned in RHS,
603 | Nothing <- sig_fn name -- ...with no type signature
604 = -- In this very special case we infer the type of the
605 -- right hand side first (it may have a higher-rank type)
606 -- and *then* make the monomorphic Id for the LHS
607 -- e.g. f = \(x::forall a. a->a) -> <body>
608 -- We want to infer a higher-rank type for f
610 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
612 -- Check for an unboxed tuple type
613 -- f = (# True, False #)
614 -- Zonk first just in case it's hidden inside a meta type variable
615 -- (This shows up as a (more obscure) kind error
616 -- in the 'otherwise' case of tcMonoBinds.)
617 ; zonked_rhs_ty <- zonkTcType rhs_ty
618 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
619 (unboxedTupleErr name zonked_rhs_ty)
621 ; mono_name <- newLocalName name
622 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
623 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
624 fun_matches = matches', bind_fvs = fvs,
625 fun_co_fn = co_fn, fun_tick = Nothing })),
626 [(name, Nothing, mono_id)]) }
628 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
629 fun_matches = matches })]
630 sig_fn -- Single function binding
632 | Just scoped_tvs <- sig_fn name -- ...with a type signature
633 = -- When we have a single function binding, with a type signature
634 -- we can (a) use genuine, rigid skolem constants for the type variables
635 -- (b) bring (rigid) scoped type variables into scope
637 do { tc_sig <- tcInstSig True name
638 ; mono_name <- newLocalName name
639 ; let mono_ty = sig_tau tc_sig
640 mono_id = mkLocalId mono_name mono_ty
641 rhs_tvs = [ (name, mkTyVarTy tv)
642 | (name, tv) <- scoped_tvs `zip` sig_tvs tc_sig ]
643 -- See Note [More instantiated than scoped]
644 -- Note that the scoped_tvs and the (sig_tvs sig)
645 -- may have different Names. That's quite ok.
647 ; traceTc (text "tcMoonBinds" <+> ppr scoped_tvs $$ ppr tc_sig)
648 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
649 tcMatchesFun mono_name inf matches mono_ty
650 -- Note that "mono_ty" might actually be a polymorphic type,
651 -- if the original function had a signature like
652 -- forall a. Eq a => forall b. Ord b => ....
653 -- But that's ok: tcMatchesFun can deal with that
654 -- It happens, too! See Note [Polymorphic methods] in TcClassDcl.
656 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
657 fun_infix = inf, fun_matches = matches',
658 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
660 ; return (unitBag (L b_loc fun_bind'),
661 [(name, Just tc_sig, mono_id)]) }
663 tcMonoBinds binds sig_fn _
664 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
666 -- Bring the monomorphic Ids, into scope for the RHSs
667 ; let mono_info = getMonoBindInfo tc_binds
668 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
669 -- A monomorphic binding for each term variable that lacks
670 -- a type sig. (Ones with a sig are already in scope.)
672 ; binds' <- tcExtendIdEnv2 rhs_id_env $ do
673 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
674 | (n,id) <- rhs_id_env])
675 mapM (wrapLocM tcRhs) tc_binds
676 ; return (listToBag binds', mono_info) }
678 ------------------------
679 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
680 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
681 -- if there's a signature for it, use the instantiated signature type
682 -- otherwise invent a type variable
683 -- You see that quite directly in the FunBind case.
685 -- But there's a complication for pattern bindings:
686 -- data T = MkT (forall a. a->a)
688 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
689 -- but we want to get (f::forall a. a->a) as the RHS environment.
690 -- The simplest way to do this is to typecheck the pattern, and then look up the
691 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
692 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
694 data TcMonoBind -- Half completed; LHS done, RHS not done
695 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
696 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
698 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
699 -- Type signature (if any), and
700 -- the monomorphic bound things
702 bndrNames :: [MonoBindInfo] -> [Name]
703 bndrNames mbi = [n | (n,_,_) <- mbi]
705 getMonoType :: MonoBindInfo -> TcTauType
706 getMonoType (_,_,mono_id) = idType mono_id
708 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
709 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
710 = do { mb_sig <- tcInstSig_maybe sig_fn name
711 ; mono_name <- newLocalName name
712 ; mono_ty <- mk_mono_ty mb_sig
713 ; let mono_id = mkLocalId mono_name mono_ty
714 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
716 mk_mono_ty (Just sig) = return (sig_tau sig)
717 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
719 tcLhs sig_fn (PatBind { pat_lhs = pat, pat_rhs = grhss })
720 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
721 ; mono_pat_binds <- doptM Opt_MonoPatBinds
722 -- With -XMonoPatBinds, we do no generalisation of pattern bindings
723 -- But the signature can still be polymoprhic!
724 -- data T = MkT (forall a. a->a)
725 -- x :: forall a. a->a
727 -- The function get_sig_ty decides whether the pattern-bound variables
728 -- should have exactly the type in the type signature (-XMonoPatBinds),
729 -- or the instantiated version (-XMonoPatBinds)
731 ; let nm_sig_prs = names `zip` mb_sigs
732 get_sig_ty | mono_pat_binds = idType . sig_id
733 | otherwise = sig_tau
734 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
735 | (name, Just sig) <- nm_sig_prs]
736 sig_tau_fn = lookupNameEnv tau_sig_env
738 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
739 mapM lookup_info nm_sig_prs
741 -- After typechecking the pattern, look up the binder
742 -- names, which the pattern has brought into scope.
743 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
744 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
745 ; return (name, mb_sig, mono_id) }
747 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
750 ; return (TcPatBind infos pat' grhss pat_ty) }
752 names = collectPatBinders pat
755 tcLhs _ other_bind = pprPanic "tcLhs" (ppr other_bind)
756 -- AbsBind, VarBind impossible
759 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
760 -- When we are doing pattern bindings, or multiple function bindings at a time
761 -- we *don't* bring any scoped type variables into scope
762 -- Wny not? They are not completely rigid.
763 -- That's why we have the special case for a single FunBind in tcMonoBinds
764 tcRhs (TcFunBind (_,_,mono_id) fun' inf matches)
765 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
766 matches (idType mono_id)
767 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
768 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
769 fun_tick = Nothing }) }
771 tcRhs (TcPatBind _ pat' grhss pat_ty)
772 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
773 tcGRHSsPat grhss pat_ty
774 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
775 bind_fvs = placeHolderNames }) }
778 ---------------------
779 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
780 getMonoBindInfo tc_binds
781 = foldr (get_info . unLoc) [] tc_binds
783 get_info (TcFunBind info _ _ _) rest = info : rest
784 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
788 %************************************************************************
792 %************************************************************************
795 generalise :: DynFlags -> TopLevelFlag
796 -> [LHsBind Name] -> TcSigFun
797 -> [MonoBindInfo] -> [Inst]
798 -> TcM ([TyVar], [Inst], TcDictBinds)
799 -- The returned [TyVar] are all ready to quantify
801 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
802 | isMonoGroup dflags top_lvl bind_list sigs
803 = do { extendLIEs lie_req
804 ; return ([], [], emptyBag) }
806 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
807 = -- Check signature contexts are empty
808 do { checkTc (all is_mono_sig sigs)
809 (restrictedBindCtxtErr bndrs)
811 -- Now simplify with exactly that set of tyvars
812 -- We have to squash those Methods
813 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
816 -- Check that signature type variables are OK
817 ; final_qtvs <- checkSigsTyVars qtvs sigs
819 ; return (final_qtvs, [], binds) }
821 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
822 = tcSimplifyInfer doc tau_tvs lie_req
824 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
825 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
826 ; let -- The "sig_avails" is the stuff available. We get that from
827 -- the context of the type signature, BUT ALSO the lie_avail
828 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
829 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
830 sig_avails = sig_lie ++ local_meths
831 loc = sig_loc (head sigs)
833 -- Check that the needed dicts can be
834 -- expressed in terms of the signature ones
835 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
837 -- Check that signature type variables are OK
838 ; final_qtvs <- checkSigsTyVars qtvs sigs
840 ; return (final_qtvs, sig_lie, binds) }
842 bndrs = bndrNames mono_infos
843 sigs = [sig | (_, Just sig, _) <- mono_infos]
844 get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
845 | otherwise = exactTyVarsOfType
846 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
847 is_mono_sig sig = null (sig_theta sig)
848 doc = ptext (sLit "type signature(s) for") <+> pprBinders bndrs
850 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
851 sig_theta = theta, sig_loc = loc }) mono_id
852 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
853 tci_theta = theta, tci_loc = loc}
856 unifyCtxts checks that all the signature contexts are the same
857 The type signatures on a mutually-recursive group of definitions
858 must all have the same context (or none).
860 The trick here is that all the signatures should have the same
861 context, and we want to share type variables for that context, so that
862 all the right hand sides agree a common vocabulary for their type
865 We unify them because, with polymorphic recursion, their types
866 might not otherwise be related. This is a rather subtle issue.
869 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
870 -- Post-condition: the returned Insts are full zonked
871 unifyCtxts [] = panic "unifyCtxts []"
872 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
873 = do { traceTc $ text "unifyCtxts" <+> ppr (sig1 : sigs)
874 ; mapM_ unify_ctxt sigs
875 ; theta <- zonkTcThetaType (sig_theta sig1)
876 ; newDictBndrs (sig_loc sig1) theta }
878 theta1 = sig_theta sig1
879 unify_ctxt :: TcSigInfo -> TcM ()
880 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
881 = setSrcSpan (instLocSpan (sig_loc sig)) $
882 addErrCtxt (sigContextsCtxt sig1 sig) $
883 do { cois <- unifyTheta theta1 theta
884 ; -- Check whether all coercions are identity coercions
885 -- That can happen if we have, say
887 -- g :: C (F a) => ...
888 -- where F is a type function and (F a ~ [a])
889 -- Then unification might succeed with a coercion. But it's much
890 -- much simpler to require that such signatures have identical contexts
891 checkTc (all isIdentityCoI cois)
892 (ptext (sLit "Mutually dependent functions have syntactically distinct contexts"))
895 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
896 checkSigsTyVars qtvs sigs
897 = do { gbl_tvs <- tcGetGlobalTyVars
898 ; sig_tvs_s <- mapM (check_sig gbl_tvs) sigs
900 ; let -- Sigh. Make sure that all the tyvars in the type sigs
901 -- appear in the returned ty var list, which is what we are
902 -- going to generalise over. Reason: we occasionally get
904 -- type T a = () -> ()
907 -- Here, 'a' won't appear in qtvs, so we have to add it
908 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
909 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
912 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
913 sig_theta = theta, sig_tau = tau})
914 = addErrCtxt (ptext (sLit "In the type signature for") <+> quotes (ppr id)) $
915 addErrCtxtM (sigCtxt id tvs theta tau) $
916 do { tvs' <- checkDistinctTyVars tvs
917 ; when (any (`elemVarSet` gbl_tvs) tvs')
918 (bleatEscapedTvs gbl_tvs tvs tvs')
921 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
922 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
923 -- are still all type variables, and all distinct from each other.
924 -- It returns a zonked set of type variables.
925 -- For example, if the type sig is
926 -- f :: forall a b. a -> b -> b
927 -- we want to check that 'a' and 'b' haven't
928 -- (a) been unified with a non-tyvar type
929 -- (b) been unified with each other (all distinct)
931 checkDistinctTyVars sig_tvs
932 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
933 ; foldlM_ check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
934 ; return zonked_tvs }
936 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
937 -- The TyVarEnv maps each zonked type variable back to its
938 -- corresponding user-written signature type variable
939 check_dup acc (sig_tv, zonked_tv)
940 = case lookupVarEnv acc zonked_tv of
941 Just sig_tv' -> bomb_out sig_tv sig_tv'
943 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
945 bomb_out sig_tv1 sig_tv2
946 = do { env0 <- tcInitTidyEnv
947 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
948 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
949 msg = ptext (sLit "Quantified type variable") <+> quotes (ppr tidy_tv1)
950 <+> ptext (sLit "is unified with another quantified type variable")
951 <+> quotes (ppr tidy_tv2)
952 ; failWithTcM (env2, msg) }
956 @getTyVarsToGen@ decides what type variables to generalise over.
958 For a "restricted group" -- see the monomorphism restriction
959 for a definition -- we bind no dictionaries, and
960 remove from tyvars_to_gen any constrained type variables
962 *Don't* simplify dicts at this point, because we aren't going
963 to generalise over these dicts. By the time we do simplify them
964 we may well know more. For example (this actually came up)
966 f x = array ... xs where xs = [1,2,3,4,5]
967 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
968 stuff. If we simplify only at the f-binding (not the xs-binding)
969 we'll know that the literals are all Ints, and we can just produce
972 Find all the type variables involved in overloading, the
973 "constrained_tyvars". These are the ones we *aren't* going to
974 generalise. We must be careful about doing this:
976 (a) If we fail to generalise a tyvar which is not actually
977 constrained, then it will never, ever get bound, and lands
978 up printed out in interface files! Notorious example:
979 instance Eq a => Eq (Foo a b) where ..
980 Here, b is not constrained, even though it looks as if it is.
981 Another, more common, example is when there's a Method inst in
982 the LIE, whose type might very well involve non-overloaded
984 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
985 the simple thing instead]
987 (b) On the other hand, we mustn't generalise tyvars which are constrained,
988 because we are going to pass on out the unmodified LIE, with those
989 tyvars in it. They won't be in scope if we've generalised them.
991 So we are careful, and do a complete simplification just to find the
992 constrained tyvars. We don't use any of the results, except to
993 find which tyvars are constrained.
995 Note [Polymorphic recursion]
996 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
997 The game plan for polymorphic recursion in the code above is
999 * Bind any variable for which we have a type signature
1000 to an Id with a polymorphic type. Then when type-checking
1001 the RHSs we'll make a full polymorphic call.
1003 This fine, but if you aren't a bit careful you end up with a horrendous
1004 amount of partial application and (worse) a huge space leak. For example:
1006 f :: Eq a => [a] -> [a]
1009 If we don't take care, after typechecking we get
1011 f = /\a -> \d::Eq a -> let f' = f a d
1015 Notice the the stupid construction of (f a d), which is of course
1016 identical to the function we're executing. In this case, the
1017 polymorphic recursion isn't being used (but that's a very common case).
1018 This can lead to a massive space leak, from the following top-level defn
1021 ff :: [Int] -> [Int]
1024 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
1025 f' is another thunk which evaluates to the same thing... and you end
1026 up with a chain of identical values all hung onto by the CAF ff.
1030 = let f' = f Int dEqInt in \ys. ...f'...
1032 = let f' = let f' = f Int dEqInt in \ys. ...f'...
1037 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
1038 which would make the space leak go away in this case
1040 Solution: when typechecking the RHSs we always have in hand the
1041 *monomorphic* Ids for each binding. So we just need to make sure that
1042 if (Method f a d) shows up in the constraints emerging from (...f...)
1043 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
1044 to the "givens" when simplifying constraints. That's what the "lies_avail"
1049 f = /\a -> \d::Eq a -> letrec
1050 fm = \ys:[a] -> ...fm...
1056 %************************************************************************
1060 %************************************************************************
1062 Type signatures are tricky. See Note [Signature skolems] in TcType
1064 @tcSigs@ checks the signatures for validity, and returns a list of
1065 {\em freshly-instantiated} signatures. That is, the types are already
1066 split up, and have fresh type variables installed. All non-type-signature
1067 "RenamedSigs" are ignored.
1069 The @TcSigInfo@ contains @TcTypes@ because they are unified with
1070 the variable's type, and after that checked to see whether they've
1073 Note [Scoped tyvars]
1074 ~~~~~~~~~~~~~~~~~~~~
1075 The -XScopedTypeVariables flag brings lexically-scoped type variables
1076 into scope for any explicitly forall-quantified type variables:
1077 f :: forall a. a -> a
1079 Then 'a' is in scope inside 'e'.
1081 However, we do *not* support this
1082 - For pattern bindings e.g
1086 - For multiple function bindings, unless Opt_RelaxedPolyRec is on
1087 f :: forall a. a -> a
1089 g :: forall b. b -> b
1091 Reason: we use mutable variables for 'a' and 'b', since they may
1092 unify to each other, and that means the scoped type variable would
1093 not stand for a completely rigid variable.
1095 Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
1098 Note [More instantiated than scoped]
1099 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1100 There may be more instantiated type variables than lexically-scoped
1102 type T a = forall b. b -> (a,b)
1104 Here, the signature for f will have one scoped type variable, c,
1105 but two instantiated type variables, c' and b'.
1107 We assume that the scoped ones are at the *front* of sig_tvs,
1108 and remember the names from the original HsForAllTy in the TcSigFun.
1112 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
1113 -- type variables brought into scope
1114 -- by its type signature.
1115 -- Nothing => no type signature
1117 mkTcSigFun :: [LSig Name] -> TcSigFun
1118 -- Search for a particular type signature
1119 -- Precondition: the sigs are all type sigs
1120 -- Precondition: no duplicates
1121 mkTcSigFun sigs = lookupNameEnv env
1123 env = mkNameEnv (mapCatMaybes mk_pair sigs)
1124 mk_pair (L _ (TypeSig (L _ name) lhs_ty)) = Just (name, hsExplicitTvs lhs_ty)
1125 mk_pair (L _ (IdSig id)) = Just (idName id, [])
1127 -- The scoped names are the ones explicitly mentioned
1128 -- in the HsForAll. (There may be more in sigma_ty, because
1129 -- of nested type synonyms. See Note [More instantiated than scoped].)
1130 -- See Note [Only scoped tyvars are in the TyVarEnv]
1135 sig_id :: TcId, -- *Polymorphic* binder for this value...
1137 sig_tvs :: [TcTyVar], -- Instantiated type variables
1138 -- See Note [Instantiate sig]
1140 sig_theta :: TcThetaType, -- Instantiated theta
1141 sig_tau :: TcTauType, -- Instantiated tau
1142 sig_loc :: InstLoc -- The location of the signature
1146 -- Note [Only scoped tyvars are in the TyVarEnv]
1147 -- We are careful to keep only the *lexically scoped* type variables in
1148 -- the type environment. Why? After all, the renamer has ensured
1149 -- that only legal occurrences occur, so we could put all type variables
1150 -- into the type env.
1152 -- But we want to check that two distinct lexically scoped type variables
1153 -- do not map to the same internal type variable. So we need to know which
1154 -- the lexically-scoped ones are... and at the moment we do that by putting
1155 -- only the lexically scoped ones into the environment.
1158 -- Note [Instantiate sig]
1159 -- It's vital to instantiate a type signature with fresh variables.
1161 -- type S = forall a. a->a
1165 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1166 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1167 -- it's all cool; each signature has distinct type variables from the renamer.)
1169 instance Outputable TcSigInfo where
1170 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1171 = ppr id <+> ptext (sLit "::") <+> ppr tyvars <+> ppr theta <+> ptext (sLit "=>") <+> ppr tau
1175 tcTySig :: LSig Name -> TcM TcId
1176 tcTySig (L span (TypeSig (L _ name) ty))
1178 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1179 ; return (mkLocalId name sigma_ty) }
1180 tcTySig (L _ (IdSig id))
1182 tcTySig s = pprPanic "tcTySig" (ppr s)
1185 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1186 -- Instantiate with *meta* type variables;
1187 -- this signature is part of a multi-signature group
1188 tcInstSig_maybe sig_fn name
1189 = case sig_fn name of
1190 Nothing -> return Nothing
1191 Just _scoped_tvs -> do { tc_sig <- tcInstSig False name
1192 ; return (Just tc_sig) }
1193 -- NB: the _scoped_tvs may be non-empty, but we can
1194 -- just ignore them. See Note [Scoped tyvars].
1196 tcInstSig :: Bool -> Name -> TcM TcSigInfo
1197 -- Instantiate the signature, with either skolems or meta-type variables
1198 -- depending on the use_skols boolean. This variable is set True
1199 -- when we are typechecking a single function binding; and False for
1200 -- pattern bindings and a group of several function bindings.
1201 -- Reason: in the latter cases, the "skolems" can be unified together,
1202 -- so they aren't properly rigid in the type-refinement sense.
1203 -- NB: unless we are doing H98, each function with a sig will be done
1204 -- separately, even if it's mutually recursive, so use_skols will be True
1206 -- We always instantiate with fresh uniques,
1207 -- although we keep the same print-name
1209 -- type T = forall a. [a] -> [a]
1211 -- f = g where { g :: T; g = <rhs> }
1213 -- We must not use the same 'a' from the defn of T at both places!!
1215 tcInstSig use_skols name
1216 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1217 -- scope when starting the binding group
1218 ; let skol_info = SigSkol (FunSigCtxt name)
1219 ; (tvs, theta, tau) <- tcInstSigType use_skols skol_info (idType poly_id)
1220 ; loc <- getInstLoc (SigOrigin skol_info)
1221 ; return (TcSigInfo { sig_id = poly_id,
1222 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1226 isMonoGroup :: DynFlags -> TopLevelFlag -> [LHsBind Name]
1227 -> [TcSigInfo] -> Bool
1228 -- No generalisation at all
1229 isMonoGroup dflags top_lvl binds sigs
1230 = (dopt Opt_MonoPatBinds dflags && any is_pat_bind binds)
1231 || (dopt Opt_MonoLocalBinds dflags && null sigs && not (isTopLevel top_lvl))
1233 is_pat_bind (L _ (PatBind {})) = True
1234 is_pat_bind _ = False
1237 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1238 isRestrictedGroup dflags binds sig_fn
1239 = mono_restriction && not all_unrestricted
1241 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1242 all_unrestricted = all (unrestricted . unLoc) binds
1243 has_sig n = isJust (sig_fn n)
1245 unrestricted (PatBind {}) = False
1246 unrestricted (VarBind { var_id = v }) = has_sig v
1247 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1248 || has_sig (unLoc v)
1249 unrestricted (AbsBinds {})
1250 = panic "isRestrictedGroup/unrestricted AbsBinds"
1252 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1253 -- No args => like a pattern binding
1254 unrestricted_match _ = True
1255 -- Some args => a function binding
1259 %************************************************************************
1261 \subsection[TcBinds-errors]{Error contexts and messages}
1263 %************************************************************************
1267 -- This one is called on LHS, when pat and grhss are both Name
1268 -- and on RHS, when pat is TcId and grhss is still Name
1269 patMonoBindsCtxt :: OutputableBndr id => LPat id -> GRHSs Name -> SDoc
1270 patMonoBindsCtxt pat grhss
1271 = hang (ptext (sLit "In a pattern binding:")) 4 (pprPatBind pat grhss)
1273 -----------------------------------------------
1274 sigContextsCtxt :: TcSigInfo -> TcSigInfo -> SDoc
1275 sigContextsCtxt sig1 sig2
1276 = vcat [ptext (sLit "When matching the contexts of the signatures for"),
1277 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1278 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1279 ptext (sLit "The signature contexts in a mutually recursive group should all be identical")]
1285 -----------------------------------------------
1286 unboxedTupleErr :: Name -> Type -> SDoc
1287 unboxedTupleErr name ty
1288 = hang (ptext (sLit "Illegal binding of unboxed tuple"))
1289 4 (ppr name <+> dcolon <+> ppr ty)
1291 -----------------------------------------------
1292 restrictedBindCtxtErr :: [Name] -> SDoc
1293 restrictedBindCtxtErr binder_names
1294 = hang (ptext (sLit "Illegal overloaded type signature(s)"))
1295 4 (vcat [ptext (sLit "in a binding group for") <+> pprBinders binder_names,
1296 ptext (sLit "that falls under the monomorphism restriction")])
1298 genCtxt :: [Name] -> SDoc
1299 genCtxt binder_names
1300 = ptext (sLit "When generalising the type(s) for") <+> pprBinders binder_names
1302 missingSigWarn :: Bool -> Name -> Type -> TcM ()
1303 missingSigWarn False _ _ = return ()
1304 missingSigWarn True name ty
1305 = do { env0 <- tcInitTidyEnv
1306 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1307 ; addWarnTcM (env1, mk_msg tidy_ty) }
1309 mk_msg ty = vcat [ptext (sLit "Definition but no type signature for") <+> quotes (ppr name),
1310 sep [ptext (sLit "Inferred type:") <+> pprHsVar name <+> dcolon <+> ppr ty]]