2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcBinds]{TcBinds}
9 -- The above warning supression flag is a temporary kludge.
10 -- While working on this module you are encouraged to remove it and fix
11 -- any warnings in the module. See
12 -- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings
15 module TcBinds ( tcLocalBinds, tcTopBinds,
16 tcHsBootSigs, tcMonoBinds,
17 TcPragFun, tcSpecPrag, tcPrags, mkPragFun,
18 TcSigInfo(..), TcSigFun, mkTcSigFun,
19 badBootDeclErr ) where
21 #include "HsVersions.h"
23 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
24 import {-# SOURCE #-} TcExpr ( tcMonoExpr )
39 import {- Kind parts of -} Type
62 %************************************************************************
64 \subsection{Type-checking bindings}
66 %************************************************************************
68 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
69 it needs to know something about the {\em usage} of the things bound,
70 so that it can create specialisations of them. So @tcBindsAndThen@
71 takes a function which, given an extended environment, E, typechecks
72 the scope of the bindings returning a typechecked thing and (most
73 important) an LIE. It is this LIE which is then used as the basis for
74 specialising the things bound.
76 @tcBindsAndThen@ also takes a "combiner" which glues together the
77 bindings and the "thing" to make a new "thing".
79 The real work is done by @tcBindWithSigsAndThen@.
81 Recursive and non-recursive binds are handled in essentially the same
82 way: because of uniques there are no scoping issues left. The only
83 difference is that non-recursive bindings can bind primitive values.
85 Even for non-recursive binding groups we add typings for each binder
86 to the LVE for the following reason. When each individual binding is
87 checked the type of its LHS is unified with that of its RHS; and
88 type-checking the LHS of course requires that the binder is in scope.
90 At the top-level the LIE is sure to contain nothing but constant
91 dictionaries, which we resolve at the module level.
94 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
95 -- Note: returning the TcLclEnv is more than we really
96 -- want. The bit we care about is the local bindings
97 -- and the free type variables thereof
99 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
100 ; return (foldr (unionBags . snd) emptyBag prs, env) }
101 -- The top level bindings are flattened into a giant
102 -- implicitly-mutually-recursive LHsBinds
104 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
105 -- A hs-boot file has only one BindGroup, and it only has type
106 -- signatures in it. The renamer checked all this
107 tcHsBootSigs (ValBindsOut binds sigs)
108 = do { checkTc (null binds) badBootDeclErr
109 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
111 tc_boot_sig (TypeSig (L _ name) ty)
112 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
113 ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
114 -- Notice that we make GlobalIds, not LocalIds
115 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
117 badBootDeclErr :: Message
118 badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file")
120 ------------------------
121 tcLocalBinds :: HsLocalBinds Name -> TcM thing
122 -> TcM (HsLocalBinds TcId, thing)
124 tcLocalBinds EmptyLocalBinds thing_inside
125 = do { thing <- thing_inside
126 ; return (EmptyLocalBinds, thing) }
128 tcLocalBinds (HsValBinds binds) thing_inside
129 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
130 ; return (HsValBinds binds', thing) }
132 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
133 = do { (thing, lie) <- getLIE thing_inside
134 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
136 -- If the binding binds ?x = E, we must now
137 -- discharge any ?x constraints in expr_lie
138 ; dict_binds <- tcSimplifyIPs avail_ips lie
139 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
141 -- I wonder if we should do these one at at time
144 tc_ip_bind (IPBind ip expr)
145 = newFlexiTyVarTy argTypeKind `thenM` \ ty ->
146 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
147 tcMonoExpr expr ty `thenM` \ expr' ->
148 returnM (ip_inst, (IPBind ip' expr'))
150 ------------------------
151 tcValBinds :: TopLevelFlag
152 -> HsValBinds Name -> TcM thing
153 -> TcM (HsValBinds TcId, thing)
155 tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
156 = pprPanic "tcValBinds" (ppr binds)
158 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
159 = do { -- Typecheck the signature
160 ; let { prag_fn = mkPragFun sigs
161 ; ty_sigs = filter isVanillaLSig sigs
162 ; sig_fn = mkTcSigFun ty_sigs }
164 ; poly_ids <- mapM tcTySig ty_sigs
165 -- No recovery from bad signatures, because the type sigs
166 -- may bind type variables, so proceeding without them
167 -- can lead to a cascade of errors
168 -- ToDo: this means we fall over immediately if any type sig
169 -- is wrong, which is over-conservative, see Trac bug #745
171 -- Extend the envt right away with all
172 -- the Ids declared with type signatures
173 ; poly_rec <- doptM Opt_RelaxedPolyRec
174 ; (binds', thing) <- tcExtendIdEnv poly_ids $
175 tc_val_binds poly_rec top_lvl sig_fn prag_fn
178 ; return (ValBindsOut binds' sigs, thing) }
180 ------------------------
181 tc_val_binds :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
182 -> [(RecFlag, LHsBinds Name)] -> TcM thing
183 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
184 -- Typecheck a whole lot of value bindings,
185 -- one strongly-connected component at a time
187 tc_val_binds poly_rec top_lvl sig_fn prag_fn [] thing_inside
188 = do { thing <- thing_inside
189 ; return ([], thing) }
191 tc_val_binds poly_rec top_lvl sig_fn prag_fn (group : groups) thing_inside
192 = do { (group', (groups', thing))
193 <- tc_group poly_rec top_lvl sig_fn prag_fn group $
194 tc_val_binds poly_rec top_lvl sig_fn prag_fn groups thing_inside
195 ; return (group' ++ groups', thing) }
197 ------------------------
198 tc_group :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
199 -> (RecFlag, LHsBinds Name) -> TcM thing
200 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
202 -- Typecheck one strongly-connected component of the original program.
203 -- We get a list of groups back, because there may
204 -- be specialisations etc as well
206 tc_group poly_rec top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
207 -- A single non-recursive binding
208 -- We want to keep non-recursive things non-recursive
209 -- so that we desugar unlifted bindings correctly
210 = do { (binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn NonRecursive binds thing_inside
211 ; return ([(NonRecursive, b) | b <- binds], thing) }
213 tc_group poly_rec top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
214 | not poly_rec -- Recursive group, normal Haskell 98 route
215 = do { (binds1, thing) <- tc_haskell98 top_lvl sig_fn prag_fn Recursive binds thing_inside
216 ; return ([(Recursive, unionManyBags binds1)], thing) }
218 | otherwise -- Recursive group, with gla-exts
219 = -- To maximise polymorphism (with -fglasgow-exts), we do a new
220 -- strongly-connected-component analysis, this time omitting
221 -- any references to variables with type signatures.
223 -- Notice that the bindInsts thing covers *all* the bindings in the original
224 -- group at once; an earlier one may use a later one!
225 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
226 ; (binds1,thing) <- bindLocalInsts top_lvl $
227 go (stronglyConnComp (mkEdges sig_fn binds))
228 ; return ([(Recursive, unionManyBags binds1)], thing) }
229 -- Rec them all together
231 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], [TcId], thing)
232 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
233 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
234 ; return (binds1 ++ binds2, ids1 ++ ids2, thing) }
235 go [] = do { thing <- thing_inside; return ([], [], thing) }
237 tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive (unitBag bind)
238 tc_scc (CyclicSCC binds) = tc_sub_group Recursive (listToBag binds)
240 tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
242 tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside
243 = bindLocalInsts top_lvl $ do
244 { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds
245 ; thing <- tcExtendIdEnv ids thing_inside
246 ; return (binds1, ids, thing) }
248 ------------------------
249 bindLocalInsts :: TopLevelFlag -> TcM ([LHsBinds TcId], [TcId], a) -> TcM ([LHsBinds TcId], a)
250 bindLocalInsts top_lvl thing_inside
251 | isTopLevel top_lvl = do { (binds, ids, thing) <- thing_inside; return (binds, thing) }
252 -- For the top level don't bother with all this bindInstsOfLocalFuns stuff.
253 -- All the top level things are rec'd together anyway, so it's fine to
254 -- leave them to the tcSimplifyTop, and quite a bit faster too
256 | otherwise -- Nested case
257 = do { ((binds, ids, thing), lie) <- getLIE thing_inside
258 ; lie_binds <- bindInstsOfLocalFuns lie ids
259 ; return (binds ++ [lie_binds], thing) }
261 ------------------------
262 mkEdges :: TcSigFun -> LHsBinds Name
263 -> [(LHsBind Name, BKey, [BKey])]
265 type BKey = Int -- Just number off the bindings
268 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
269 Just key <- [lookupNameEnv key_map n], no_sig n ])
270 | (bind, key) <- keyd_binds
273 no_sig :: Name -> Bool
274 no_sig n = isNothing (sig_fn n)
276 keyd_binds = bagToList binds `zip` [0::BKey ..]
278 key_map :: NameEnv BKey -- Which binding it comes from
279 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
280 , bndr <- bindersOfHsBind bind ]
282 bindersOfHsBind :: HsBind Name -> [Name]
283 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
284 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
286 ------------------------
287 tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragFun
288 -> RecFlag -- Whether the group is really recursive
289 -> RecFlag -- Whether it's recursive after breaking
290 -- dependencies based on type signatures
292 -> TcM ([LHsBinds TcId], [TcId])
294 -- Typechecks a single bunch of bindings all together,
295 -- and generalises them. The bunch may be only part of a recursive
296 -- group, because we use type signatures to maximise polymorphism
298 -- Returns a list because the input may be a single non-recursive binding,
299 -- in which case the dependency order of the resulting bindings is
302 -- Knows nothing about the scope of the bindings
304 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds
306 bind_list = bagToList binds
307 binder_names = collectHsBindBinders binds
308 loc = getLoc (head bind_list)
309 -- TODO: location a bit awkward, but the mbinds have been
310 -- dependency analysed and may no longer be adjacent
312 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
314 recoverM (recoveryCode binder_names sig_fn) $ do
316 { traceTc (ptext SLIT("------------------------------------------------"))
317 ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
319 -- TYPECHECK THE BINDINGS
320 ; ((binds', mono_bind_infos), lie_req)
321 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
322 ; traceTc (text "temp" <+> (ppr binds' $$ ppr lie_req))
324 -- CHECK FOR UNLIFTED BINDINGS
325 -- These must be non-recursive etc, and are not generalised
326 -- They desugar to a case expression in the end
327 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
328 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
329 zonked_mono_tys mono_bind_infos
331 do { extendLIEs lie_req
332 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
333 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
334 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
335 -- ToDo: prags for unlifted bindings
337 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
338 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
340 else do -- The normal lifted case: GENERALISE
342 ; (tyvars_to_gen, dicts, dict_binds)
343 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
344 generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
346 -- BUILD THE POLYMORPHIC RESULT IDs
347 ; let dict_ids = map instToId dicts
348 ; exports <- mapM (mkExport top_lvl prag_fn tyvars_to_gen (map idType dict_ids))
351 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
352 ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids))
354 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen
356 (dict_binds `unionBags` binds')
358 ; return ([unitBag abs_bind], poly_ids) -- poly_ids are guaranteed zonked by mkExport
363 mkExport :: TopLevelFlag -> TcPragFun -> [TyVar] -> [TcType]
365 -> TcM ([TyVar], Id, Id, [LPrag])
366 -- mkExport generates exports with
367 -- zonked type variables,
369 -- The former is just because no further unifications will change
370 -- the quantified type variables, so we can fix their final form
372 -- The latter is needed because the poly_ids are used to extend the
373 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
375 -- Pre-condition: the inferred_tvs are already zonked
377 mkExport top_lvl prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
378 = do { warn_missing_sigs <- doptM Opt_WarnMissingSigs
379 ; let warn = isTopLevel top_lvl && warn_missing_sigs
380 ; (tvs, poly_id) <- mk_poly_id warn mb_sig
382 ; poly_id' <- zonkId poly_id
383 ; prags <- tcPrags poly_id' (prag_fn poly_name)
384 -- tcPrags requires a zonked poly_id
386 ; return (tvs, poly_id', mono_id, prags) }
388 poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id))
390 mk_poly_id warn Nothing = do { missingSigWarn warn poly_name poly_ty
391 ; return (inferred_tvs, mkLocalId poly_name poly_ty) }
392 mk_poly_id warn (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
393 ; return (tvs, sig_id sig) }
395 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
397 ------------------------
398 type TcPragFun = Name -> [LSig Name]
400 mkPragFun :: [LSig Name] -> TcPragFun
401 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
403 prs = [(expectJust "mkPragFun" (sigName sig), sig)
404 | sig <- sigs, isPragLSig sig]
405 env = foldl add emptyNameEnv prs
406 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
408 tcPrags :: Id -> [LSig Name] -> TcM [LPrag]
409 tcPrags poly_id prags = mapM (wrapLocM tc_prag) prags
411 tc_prag prag = addErrCtxt (pragSigCtxt prag) $
414 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
416 tcPrag :: TcId -> Sig Name -> TcM Prag
417 -- Pre-condition: the poly_id is zonked
418 -- Reason: required by tcSubExp
419 tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
420 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
421 tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
424 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
425 tcSpecPrag poly_id hs_ty inl
426 = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
427 ; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty)
429 ; let const_dicts = map instToId lie
430 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty const_dicts inl) }
431 -- Most of the work of specialisation is done by
432 -- the desugarer, guided by the SpecPrag
435 -- If typechecking the binds fails, then return with each
436 -- signature-less binder given type (forall a.a), to minimise
437 -- subsequent error messages
438 recoveryCode binder_names sig_fn
439 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
440 ; poly_ids <- mapM mk_dummy binder_names
441 ; return ([], poly_ids) }
444 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
445 | otherwise = return (mkLocalId name forall_a_a) -- No signature
448 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
451 -- Check that non-overloaded unlifted bindings are
454 -- c) not a multiple-binding group (more or less implied by (a))
456 checkStrictBinds :: TopLevelFlag -> RecFlag
457 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
459 checkStrictBinds top_lvl rec_group mbind mono_tys infos
460 | unlifted || bang_pat
461 = do { checkTc (isNotTopLevel top_lvl)
462 (strictBindErr "Top-level" unlifted mbind)
463 ; checkTc (isNonRec rec_group)
464 (strictBindErr "Recursive" unlifted mbind)
465 ; checkTc (isSingletonBag mbind)
466 (strictBindErr "Multiple" unlifted mbind)
467 ; mapM_ check_sig infos
472 unlifted = any isUnLiftedType mono_tys
473 bang_pat = anyBag (isBangHsBind . unLoc) mbind
474 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
475 (badStrictSig unlifted sig)
476 check_sig other = return ()
478 strictBindErr flavour unlifted mbind
479 = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:"))
480 4 (pprLHsBinds mbind)
482 msg | unlifted = ptext SLIT("bindings for unlifted types")
483 | otherwise = ptext SLIT("bang-pattern bindings")
485 badStrictSig unlifted sig
486 = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
489 msg | unlifted = ptext SLIT("an unlifted binding")
490 | otherwise = ptext SLIT("a bang-pattern binding")
494 %************************************************************************
496 \subsection{tcMonoBind}
498 %************************************************************************
500 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
501 The signatures have been dealt with already.
504 tcMonoBinds :: [LHsBind Name]
506 -> RecFlag -- Whether the binding is recursive for typechecking purposes
507 -- i.e. the binders are mentioned in their RHSs, and
508 -- we are not resuced by a type signature
509 -> TcM (LHsBinds TcId, [MonoBindInfo])
511 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
512 fun_matches = matches, bind_fvs = fvs })]
513 sig_fn -- Single function binding,
514 NonRecursive -- binder isn't mentioned in RHS,
515 | Nothing <- sig_fn name -- ...with no type signature
516 = -- In this very special case we infer the type of the
517 -- right hand side first (it may have a higher-rank type)
518 -- and *then* make the monomorphic Id for the LHS
519 -- e.g. f = \(x::forall a. a->a) -> <body>
520 -- We want to infer a higher-rank type for f
522 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
524 -- Check for an unboxed tuple type
525 -- f = (# True, False #)
526 -- Zonk first just in case it's hidden inside a meta type variable
527 -- (This shows up as a (more obscure) kind error
528 -- in the 'otherwise' case of tcMonoBinds.)
529 ; zonked_rhs_ty <- zonkTcType rhs_ty
530 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
531 (unboxedTupleErr name zonked_rhs_ty)
533 ; mono_name <- newLocalName name
534 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
535 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
536 fun_matches = matches', bind_fvs = fvs,
537 fun_co_fn = co_fn, fun_tick = Nothing })),
538 [(name, Nothing, mono_id)]) }
540 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
541 fun_matches = matches, bind_fvs = fvs })]
542 sig_fn -- Single function binding
544 | Just scoped_tvs <- sig_fn name -- ...with a type signature
545 = -- When we have a single function binding, with a type signature
546 -- we can (a) use genuine, rigid skolem constants for the type variables
547 -- (b) bring (rigid) scoped type variables into scope
549 do { tc_sig <- tcInstSig True name scoped_tvs
550 ; mono_name <- newLocalName name
551 ; let mono_ty = sig_tau tc_sig
552 mono_id = mkLocalId mono_name mono_ty
553 rhs_tvs = [ (name, mkTyVarTy tv)
554 | (name, tv) <- sig_scoped tc_sig `zip` sig_tvs tc_sig ]
556 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
557 tcMatchesFun mono_name inf matches mono_ty
559 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
560 fun_infix = inf, fun_matches = matches',
561 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
563 ; return (unitBag (L b_loc fun_bind'),
564 [(name, Just tc_sig, mono_id)]) }
566 tcMonoBinds binds sig_fn non_rec
567 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
569 -- Bring the monomorphic Ids, into scope for the RHSs
570 ; let mono_info = getMonoBindInfo tc_binds
571 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
572 -- A monomorphic binding for each term variable that lacks
573 -- a type sig. (Ones with a sig are already in scope.)
575 ; binds' <- tcExtendIdEnv2 rhs_id_env $
576 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
577 | (n,id) <- rhs_id_env]) `thenM_`
578 mapM (wrapLocM tcRhs) tc_binds
579 ; return (listToBag binds', mono_info) }
581 ------------------------
582 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
583 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
584 -- if there's a signature for it, use the instantiated signature type
585 -- otherwise invent a type variable
586 -- You see that quite directly in the FunBind case.
588 -- But there's a complication for pattern bindings:
589 -- data T = MkT (forall a. a->a)
591 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
592 -- but we want to get (f::forall a. a->a) as the RHS environment.
593 -- The simplest way to do this is to typecheck the pattern, and then look up the
594 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
595 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
597 data TcMonoBind -- Half completed; LHS done, RHS not done
598 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
599 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
601 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
602 -- Type signature (if any), and
603 -- the monomorphic bound things
605 bndrNames :: [MonoBindInfo] -> [Name]
606 bndrNames mbi = [n | (n,_,_) <- mbi]
608 getMonoType :: MonoBindInfo -> TcTauType
609 getMonoType (_,_,mono_id) = idType mono_id
611 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
612 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
613 = do { mb_sig <- tcInstSig_maybe sig_fn name
614 ; mono_name <- newLocalName name
615 ; mono_ty <- mk_mono_ty mb_sig
616 ; let mono_id = mkLocalId mono_name mono_ty
617 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
619 mk_mono_ty (Just sig) = return (sig_tau sig)
620 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
622 tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
623 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
624 ; mono_pat_binds <- doptM Opt_MonoPatBinds
625 -- With -fmono-pat-binds, we do no generalisation of pattern bindings
626 -- But the signature can still be polymoprhic!
627 -- data T = MkT (forall a. a->a)
628 -- x :: forall a. a->a
630 -- The function get_sig_ty decides whether the pattern-bound variables
631 -- should have exactly the type in the type signature (-fmono-pat-binds),
632 -- or the instantiated version (-fmono-pat-binds)
634 ; let nm_sig_prs = names `zip` mb_sigs
635 get_sig_ty | mono_pat_binds = idType . sig_id
636 | otherwise = sig_tau
637 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
638 | (name, Just sig) <- nm_sig_prs]
639 sig_tau_fn = lookupNameEnv tau_sig_env
641 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
642 mapM lookup_info nm_sig_prs
644 -- After typechecking the pattern, look up the binder
645 -- names, which the pattern has brought into scope.
646 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
647 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
648 ; return (name, mb_sig, mono_id) }
650 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
653 ; return (TcPatBind infos pat' grhss pat_ty) }
655 names = collectPatBinders pat
658 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
659 -- AbsBind, VarBind impossible
662 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
663 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
664 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
665 matches (idType mono_id)
666 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
667 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
668 fun_tick = Nothing }) }
670 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
671 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
672 tcGRHSsPat grhss pat_ty
673 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
674 bind_fvs = placeHolderNames }) }
677 ---------------------
678 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
679 getMonoBindInfo tc_binds
680 = foldr (get_info . unLoc) [] tc_binds
682 get_info (TcFunBind info _ _ _) rest = info : rest
683 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
687 %************************************************************************
691 %************************************************************************
694 generalise :: DynFlags -> TopLevelFlag
695 -> [LHsBind Name] -> TcSigFun
696 -> [MonoBindInfo] -> [Inst]
697 -> TcM ([TyVar], [Inst], TcDictBinds)
698 -- The returned [TyVar] are all ready to quantify
700 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
701 | isMonoGroup dflags bind_list
702 = do { extendLIEs lie_req
703 ; return ([], [], emptyBag) }
705 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
706 = -- Check signature contexts are empty
707 do { checkTc (all is_mono_sig sigs)
708 (restrictedBindCtxtErr bndrs)
710 -- Now simplify with exactly that set of tyvars
711 -- We have to squash those Methods
712 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
715 -- Check that signature type variables are OK
716 ; final_qtvs <- checkSigsTyVars qtvs sigs
718 ; return (final_qtvs, [], binds) }
720 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
721 = tcSimplifyInfer doc tau_tvs lie_req
723 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
724 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
725 ; let -- The "sig_avails" is the stuff available. We get that from
726 -- the context of the type signature, BUT ALSO the lie_avail
727 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
728 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
729 sig_avails = sig_lie ++ local_meths
730 loc = sig_loc (head sigs)
732 -- Check that the needed dicts can be
733 -- expressed in terms of the signature ones
734 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
736 -- Check that signature type variables are OK
737 ; final_qtvs <- checkSigsTyVars qtvs sigs
739 ; returnM (final_qtvs, sig_lie, binds) }
741 bndrs = bndrNames mono_infos
742 sigs = [sig | (_, Just sig, _) <- mono_infos]
743 tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos
744 -- NB: exactTyVarsOfType; see Note [Silly type synonym]
745 -- near defn of TcType.exactTyVarsOfType
746 is_mono_sig sig = null (sig_theta sig)
747 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
749 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
750 sig_theta = theta, sig_loc = loc }) mono_id
751 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
752 tci_theta = theta, tci_loc = loc}
755 unifyCtxts checks that all the signature contexts are the same
756 The type signatures on a mutually-recursive group of definitions
757 must all have the same context (or none).
759 The trick here is that all the signatures should have the same
760 context, and we want to share type variables for that context, so that
761 all the right hand sides agree a common vocabulary for their type
764 We unify them because, with polymorphic recursion, their types
765 might not otherwise be related. This is a rather subtle issue.
768 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
769 -- Post-condition: the returned Insts are full zonked
770 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
771 = do { mapM unify_ctxt sigs
772 ; theta <- zonkTcThetaType (sig_theta sig1)
773 ; newDictBndrs (sig_loc sig1) theta }
775 theta1 = sig_theta sig1
776 unify_ctxt :: TcSigInfo -> TcM ()
777 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
778 = setSrcSpan (instLocSpan (sig_loc sig)) $
779 addErrCtxt (sigContextsCtxt sig1 sig) $
780 do { cois <- unifyTheta theta1 theta
781 ; -- Check whether all coercions are identity coercions
782 -- That can happen if we have, say
784 -- g :: C (F a) => ...
785 -- where F is a type function and (F a ~ [a])
786 -- Then unification might succeed with a coercion. But it's much
787 -- much simpler to require that such signatures have identical contexts
788 checkTc (all isIdentityCoercion cois)
789 (ptext SLIT("Mutually dependent functions have syntactically distinct contexts"))
792 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
793 checkSigsTyVars qtvs sigs
794 = do { gbl_tvs <- tcGetGlobalTyVars
795 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
797 ; let -- Sigh. Make sure that all the tyvars in the type sigs
798 -- appear in the returned ty var list, which is what we are
799 -- going to generalise over. Reason: we occasionally get
801 -- type T a = () -> ()
804 -- Here, 'a' won't appear in qtvs, so we have to add it
805 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
806 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
809 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
810 sig_theta = theta, sig_tau = tau})
811 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
812 addErrCtxtM (sigCtxt id tvs theta tau) $
813 do { tvs' <- checkDistinctTyVars tvs
814 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
815 (bleatEscapedTvs gbl_tvs tvs tvs')
818 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
819 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
820 -- are still all type variables, and all distinct from each other.
821 -- It returns a zonked set of type variables.
822 -- For example, if the type sig is
823 -- f :: forall a b. a -> b -> b
824 -- we want to check that 'a' and 'b' haven't
825 -- (a) been unified with a non-tyvar type
826 -- (b) been unified with each other (all distinct)
828 checkDistinctTyVars sig_tvs
829 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
830 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
831 ; return zonked_tvs }
833 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
834 -- The TyVarEnv maps each zonked type variable back to its
835 -- corresponding user-written signature type variable
836 check_dup acc (sig_tv, zonked_tv)
837 = case lookupVarEnv acc zonked_tv of
838 Just sig_tv' -> bomb_out sig_tv sig_tv'
840 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
842 bomb_out sig_tv1 sig_tv2
843 = do { env0 <- tcInitTidyEnv
844 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
845 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
846 msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
847 <+> ptext SLIT("is unified with another quantified type variable")
848 <+> quotes (ppr tidy_tv2)
849 ; failWithTcM (env2, msg) }
854 @getTyVarsToGen@ decides what type variables to generalise over.
856 For a "restricted group" -- see the monomorphism restriction
857 for a definition -- we bind no dictionaries, and
858 remove from tyvars_to_gen any constrained type variables
860 *Don't* simplify dicts at this point, because we aren't going
861 to generalise over these dicts. By the time we do simplify them
862 we may well know more. For example (this actually came up)
864 f x = array ... xs where xs = [1,2,3,4,5]
865 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
866 stuff. If we simplify only at the f-binding (not the xs-binding)
867 we'll know that the literals are all Ints, and we can just produce
870 Find all the type variables involved in overloading, the
871 "constrained_tyvars". These are the ones we *aren't* going to
872 generalise. We must be careful about doing this:
874 (a) If we fail to generalise a tyvar which is not actually
875 constrained, then it will never, ever get bound, and lands
876 up printed out in interface files! Notorious example:
877 instance Eq a => Eq (Foo a b) where ..
878 Here, b is not constrained, even though it looks as if it is.
879 Another, more common, example is when there's a Method inst in
880 the LIE, whose type might very well involve non-overloaded
882 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
883 the simple thing instead]
885 (b) On the other hand, we mustn't generalise tyvars which are constrained,
886 because we are going to pass on out the unmodified LIE, with those
887 tyvars in it. They won't be in scope if we've generalised them.
889 So we are careful, and do a complete simplification just to find the
890 constrained tyvars. We don't use any of the results, except to
891 find which tyvars are constrained.
893 Note [Polymorphic recursion]
894 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
895 The game plan for polymorphic recursion in the code above is
897 * Bind any variable for which we have a type signature
898 to an Id with a polymorphic type. Then when type-checking
899 the RHSs we'll make a full polymorphic call.
901 This fine, but if you aren't a bit careful you end up with a horrendous
902 amount of partial application and (worse) a huge space leak. For example:
904 f :: Eq a => [a] -> [a]
907 If we don't take care, after typechecking we get
909 f = /\a -> \d::Eq a -> let f' = f a d
913 Notice the the stupid construction of (f a d), which is of course
914 identical to the function we're executing. In this case, the
915 polymorphic recursion isn't being used (but that's a very common case).
916 This can lead to a massive space leak, from the following top-level defn
922 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
923 f' is another thunk which evaluates to the same thing... and you end
924 up with a chain of identical values all hung onto by the CAF ff.
928 = let f' = f Int dEqInt in \ys. ...f'...
930 = let f' = let f' = f Int dEqInt in \ys. ...f'...
935 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
936 which would make the space leak go away in this case
938 Solution: when typechecking the RHSs we always have in hand the
939 *monomorphic* Ids for each binding. So we just need to make sure that
940 if (Method f a d) shows up in the constraints emerging from (...f...)
941 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
942 to the "givens" when simplifying constraints. That's what the "lies_avail"
947 f = /\a -> \d::Eq a -> letrec
948 fm = \ys:[a] -> ...fm...
954 %************************************************************************
958 %************************************************************************
960 Type signatures are tricky. See Note [Signature skolems] in TcType
962 @tcSigs@ checks the signatures for validity, and returns a list of
963 {\em freshly-instantiated} signatures. That is, the types are already
964 split up, and have fresh type variables installed. All non-type-signature
965 "RenamedSigs" are ignored.
967 The @TcSigInfo@ contains @TcTypes@ because they are unified with
968 the variable's type, and after that checked to see whether they've
972 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
973 -- type variables brought into scope
974 -- by its type signature.
975 -- Nothing => no type signature
977 mkTcSigFun :: [LSig Name] -> TcSigFun
978 -- Search for a particular type signature
979 -- Precondition: the sigs are all type sigs
980 -- Precondition: no duplicates
981 mkTcSigFun sigs = lookupNameEnv env
983 env = mkNameEnv [(name, hsExplicitTvs lhs_ty)
984 | L span (TypeSig (L _ name) lhs_ty) <- sigs]
985 -- The scoped names are the ones explicitly mentioned
986 -- in the HsForAll. (There may be more in sigma_ty, because
987 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
988 -- See Note [Only scoped tyvars are in the TyVarEnv]
993 sig_id :: TcId, -- *Polymorphic* binder for this value...
995 sig_scoped :: [Name], -- Names for any scoped type variables
996 -- Invariant: correspond 1-1 with an initial
997 -- segment of sig_tvs (see Note [Scoped])
999 sig_tvs :: [TcTyVar], -- Instantiated type variables
1000 -- See Note [Instantiate sig]
1002 sig_theta :: TcThetaType, -- Instantiated theta
1003 sig_tau :: TcTauType, -- Instantiated tau
1004 sig_loc :: InstLoc -- The location of the signature
1008 -- Note [Only scoped tyvars are in the TyVarEnv]
1009 -- We are careful to keep only the *lexically scoped* type variables in
1010 -- the type environment. Why? After all, the renamer has ensured
1011 -- that only legal occurrences occur, so we could put all type variables
1012 -- into the type env.
1014 -- But we want to check that two distinct lexically scoped type variables
1015 -- do not map to the same internal type variable. So we need to know which
1016 -- the lexically-scoped ones are... and at the moment we do that by putting
1017 -- only the lexically scoped ones into the environment.
1021 -- There may be more instantiated type variables than scoped
1022 -- ones. For example:
1023 -- type T a = forall b. b -> (a,b)
1024 -- f :: forall c. T c
1025 -- Here, the signature for f will have one scoped type variable, c,
1026 -- but two instantiated type variables, c' and b'.
1028 -- We assume that the scoped ones are at the *front* of sig_tvs,
1029 -- and remember the names from the original HsForAllTy in sig_scoped
1031 -- Note [Instantiate sig]
1032 -- It's vital to instantiate a type signature with fresh variables.
1034 -- type S = forall a. a->a
1038 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1039 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1040 -- it's all cool; each signature has distinct type variables from the renamer.)
1042 instance Outputable TcSigInfo where
1043 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1044 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
1048 tcTySig :: LSig Name -> TcM TcId
1049 tcTySig (L span (TypeSig (L _ name) ty))
1051 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1052 ; return (mkLocalId name sigma_ty) }
1055 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1056 -- Instantiate with *meta* type variables;
1057 -- this signature is part of a multi-signature group
1058 tcInstSig_maybe sig_fn name
1059 = case sig_fn name of
1060 Nothing -> return Nothing
1061 Just tvs -> do { tc_sig <- tcInstSig False name tvs
1062 ; return (Just tc_sig) }
1064 tcInstSig :: Bool -> Name -> [Name] -> TcM TcSigInfo
1065 -- Instantiate the signature, with either skolems or meta-type variables
1066 -- depending on the use_skols boolean. This variable is set True
1067 -- when we are typechecking a single function binding; and False for
1068 -- pattern bindings and a group of several function bindings.
1069 -- Reason: in the latter cases, the "skolems" can be unified together,
1070 -- so they aren't properly rigid in the type-refinement sense.
1071 -- NB: unless we are doing H98, each function with a sig will be done
1072 -- separately, even if it's mutually recursive, so use_skols will be True
1074 -- We always instantiate with fresh uniques,
1075 -- although we keep the same print-name
1077 -- type T = forall a. [a] -> [a]
1079 -- f = g where { g :: T; g = <rhs> }
1081 -- We must not use the same 'a' from the defn of T at both places!!
1083 tcInstSig use_skols name scoped_names
1084 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1085 -- scope when starting the binding group
1086 ; let skol_info = SigSkol (FunSigCtxt name)
1087 inst_tyvars = tcInstSigTyVars use_skols skol_info
1088 ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
1089 ; loc <- getInstLoc (SigOrigin skol_info)
1090 ; return (TcSigInfo { sig_id = poly_id,
1091 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1092 sig_scoped = final_scoped_names, sig_loc = loc }) }
1093 -- Note that the scoped_names and the sig_tvs will have
1094 -- different Names. That's quite ok; when we bring the
1095 -- scoped_names into scope, we just bind them to the sig_tvs
1097 -- We also only have scoped type variables when we are instantiating
1098 -- with true skolems
1099 final_scoped_names | use_skols = scoped_names
1103 isMonoGroup :: DynFlags -> [LHsBind Name] -> Bool
1104 -- No generalisation at all
1105 isMonoGroup dflags binds
1106 = dopt Opt_MonoPatBinds dflags && any is_pat_bind binds
1108 is_pat_bind (L _ (PatBind {})) = True
1109 is_pat_bind other = False
1112 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1113 isRestrictedGroup dflags binds sig_fn
1114 = mono_restriction && not all_unrestricted
1116 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1117 all_unrestricted = all (unrestricted . unLoc) binds
1118 has_sig n = isJust (sig_fn n)
1120 unrestricted (PatBind {}) = False
1121 unrestricted (VarBind { var_id = v }) = has_sig v
1122 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1123 || has_sig (unLoc v)
1125 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1126 -- No args => like a pattern binding
1127 unrestricted_match other = True
1128 -- Some args => a function binding
1132 %************************************************************************
1134 \subsection[TcBinds-errors]{Error contexts and messages}
1136 %************************************************************************
1140 -- This one is called on LHS, when pat and grhss are both Name
1141 -- and on RHS, when pat is TcId and grhss is still Name
1142 patMonoBindsCtxt pat grhss
1143 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
1145 -----------------------------------------------
1146 sigContextsCtxt sig1 sig2
1147 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
1148 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1149 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1150 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
1156 -----------------------------------------------
1157 unboxedTupleErr name ty
1158 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
1159 4 (ppr name <+> dcolon <+> ppr ty)
1161 -----------------------------------------------
1162 restrictedBindCtxtErr binder_names
1163 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
1164 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
1165 ptext SLIT("that falls under the monomorphism restriction")])
1167 genCtxt binder_names
1168 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
1170 missingSigWarn False name ty = return ()
1171 missingSigWarn True name ty
1172 = do { env0 <- tcInitTidyEnv
1173 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1174 ; addWarnTcM (env1, mk_msg tidy_ty) }
1176 mk_msg ty = vcat [ptext SLIT("Definition but no type signature for") <+> quotes (ppr name),
1177 sep [ptext SLIT("Inferred type:") <+> ppr name <+> dcolon <+> ppr ty]]