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,
10 TcPragFun, tcSpecPrag, tcPrags, mkPragFun,
11 TcSigInfo(..), TcSigFun, mkTcSigFun,
12 badBootDeclErr ) where
14 #include "HsVersions.h"
16 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
17 import {-# SOURCE #-} TcExpr ( tcMonoExpr )
32 import {- Kind parts of -} Type
55 %************************************************************************
57 \subsection{Type-checking bindings}
59 %************************************************************************
61 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
62 it needs to know something about the {\em usage} of the things bound,
63 so that it can create specialisations of them. So @tcBindsAndThen@
64 takes a function which, given an extended environment, E, typechecks
65 the scope of the bindings returning a typechecked thing and (most
66 important) an LIE. It is this LIE which is then used as the basis for
67 specialising the things bound.
69 @tcBindsAndThen@ also takes a "combiner" which glues together the
70 bindings and the "thing" to make a new "thing".
72 The real work is done by @tcBindWithSigsAndThen@.
74 Recursive and non-recursive binds are handled in essentially the same
75 way: because of uniques there are no scoping issues left. The only
76 difference is that non-recursive bindings can bind primitive values.
78 Even for non-recursive binding groups we add typings for each binder
79 to the LVE for the following reason. When each individual binding is
80 checked the type of its LHS is unified with that of its RHS; and
81 type-checking the LHS of course requires that the binder is in scope.
83 At the top-level the LIE is sure to contain nothing but constant
84 dictionaries, which we resolve at the module level.
87 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
88 -- Note: returning the TcLclEnv is more than we really
89 -- want. The bit we care about is the local bindings
90 -- and the free type variables thereof
92 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
93 ; return (foldr (unionBags . snd) emptyBag prs, env) }
94 -- The top level bindings are flattened into a giant
95 -- implicitly-mutually-recursive LHsBinds
97 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
98 -- A hs-boot file has only one BindGroup, and it only has type
99 -- signatures in it. The renamer checked all this
100 tcHsBootSigs (ValBindsOut binds sigs)
101 = do { checkTc (null binds) badBootDeclErr
102 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
104 tc_boot_sig (TypeSig (L _ name) ty)
105 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
106 ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
107 -- Notice that we make GlobalIds, not LocalIds
108 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
110 badBootDeclErr :: Message
111 badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file")
113 ------------------------
114 tcLocalBinds :: HsLocalBinds Name -> TcM thing
115 -> TcM (HsLocalBinds TcId, thing)
117 tcLocalBinds EmptyLocalBinds thing_inside
118 = do { thing <- thing_inside
119 ; return (EmptyLocalBinds, thing) }
121 tcLocalBinds (HsValBinds binds) thing_inside
122 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
123 ; return (HsValBinds binds', thing) }
125 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
126 = do { (thing, lie) <- getLIE thing_inside
127 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
129 -- If the binding binds ?x = E, we must now
130 -- discharge any ?x constraints in expr_lie
131 ; dict_binds <- tcSimplifyIPs avail_ips lie
132 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
134 -- I wonder if we should do these one at at time
137 tc_ip_bind (IPBind ip expr)
138 = newFlexiTyVarTy argTypeKind `thenM` \ ty ->
139 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
140 tcMonoExpr expr ty `thenM` \ expr' ->
141 returnM (ip_inst, (IPBind ip' expr'))
143 ------------------------
144 tcValBinds :: TopLevelFlag
145 -> HsValBinds Name -> TcM thing
146 -> TcM (HsValBinds TcId, thing)
148 tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
149 = pprPanic "tcValBinds" (ppr binds)
151 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
152 = do { -- Typecheck the signature
153 ; let { prag_fn = mkPragFun sigs
154 ; ty_sigs = filter isVanillaLSig sigs
155 ; sig_fn = mkTcSigFun ty_sigs }
157 ; poly_ids <- mapM tcTySig ty_sigs
158 -- No recovery from bad signatures, because the type sigs
159 -- may bind type variables, so proceeding without them
160 -- can lead to a cascade of errors
161 -- ToDo: this means we fall over immediately if any type sig
162 -- is wrong, which is over-conservative, see Trac bug #745
164 -- Extend the envt right away with all
165 -- the Ids declared with type signatures
166 ; poly_rec <- doptM Opt_RelaxedPolyRec
167 ; (binds', thing) <- tcExtendIdEnv poly_ids $
168 tc_val_binds poly_rec top_lvl sig_fn prag_fn
171 ; return (ValBindsOut binds' sigs, thing) }
173 ------------------------
174 tc_val_binds :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
175 -> [(RecFlag, LHsBinds Name)] -> TcM thing
176 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
177 -- Typecheck a whole lot of value bindings,
178 -- one strongly-connected component at a time
180 tc_val_binds poly_rec top_lvl sig_fn prag_fn [] thing_inside
181 = do { thing <- thing_inside
182 ; return ([], thing) }
184 tc_val_binds poly_rec top_lvl sig_fn prag_fn (group : groups) thing_inside
185 = do { (group', (groups', thing))
186 <- tc_group poly_rec top_lvl sig_fn prag_fn group $
187 tc_val_binds poly_rec top_lvl sig_fn prag_fn groups thing_inside
188 ; return (group' ++ groups', thing) }
190 ------------------------
191 tc_group :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
192 -> (RecFlag, LHsBinds Name) -> TcM thing
193 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
195 -- Typecheck one strongly-connected component of the original program.
196 -- We get a list of groups back, because there may
197 -- be specialisations etc as well
199 tc_group poly_rec top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
200 -- A single non-recursive binding
201 -- We want to keep non-recursive things non-recursive
202 -- so that we desugar unlifted bindings correctly
203 = do { (binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn NonRecursive binds thing_inside
204 ; return ([(NonRecursive, b) | b <- binds], thing) }
206 tc_group poly_rec top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
207 | not poly_rec -- Recursive group, normal Haskell 98 route
208 = do { (binds1, thing) <- tc_haskell98 top_lvl sig_fn prag_fn Recursive binds thing_inside
209 ; return ([(Recursive, unionManyBags binds1)], thing) }
211 | otherwise -- Recursive group, with gla-exts
212 = -- To maximise polymorphism (with -fglasgow-exts), we do a new
213 -- strongly-connected-component analysis, this time omitting
214 -- any references to variables with type signatures.
216 -- Notice that the bindInsts thing covers *all* the bindings in the original
217 -- group at once; an earlier one may use a later one!
218 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
219 ; (binds1,thing) <- bindLocalInsts top_lvl $
220 go (stronglyConnComp (mkEdges sig_fn binds))
221 ; return ([(Recursive, unionManyBags binds1)], thing) }
222 -- Rec them all together
224 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], [TcId], thing)
225 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
226 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
227 ; return (binds1 ++ binds2, ids1 ++ ids2, thing) }
228 go [] = do { thing <- thing_inside; return ([], [], thing) }
230 tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive (unitBag bind)
231 tc_scc (CyclicSCC binds) = tc_sub_group Recursive (listToBag binds)
233 tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
235 tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside
236 = bindLocalInsts top_lvl $ do
237 { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds
238 ; thing <- tcExtendIdEnv ids thing_inside
239 ; return (binds1, ids, thing) }
241 ------------------------
242 bindLocalInsts :: TopLevelFlag -> TcM ([LHsBinds TcId], [TcId], a) -> TcM ([LHsBinds TcId], a)
243 bindLocalInsts top_lvl thing_inside
244 | isTopLevel top_lvl = do { (binds, ids, thing) <- thing_inside; return (binds, thing) }
245 -- For the top level don't bother with all this bindInstsOfLocalFuns stuff.
246 -- All the top level things are rec'd together anyway, so it's fine to
247 -- leave them to the tcSimplifyTop, and quite a bit faster too
249 | otherwise -- Nested case
250 = do { ((binds, ids, thing), lie) <- getLIE thing_inside
251 ; lie_binds <- bindInstsOfLocalFuns lie ids
252 ; return (binds ++ [lie_binds], thing) }
254 ------------------------
255 mkEdges :: TcSigFun -> LHsBinds Name
256 -> [(LHsBind Name, BKey, [BKey])]
258 type BKey = Int -- Just number off the bindings
261 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
262 Just key <- [lookupNameEnv key_map n], no_sig n ])
263 | (bind, key) <- keyd_binds
266 no_sig :: Name -> Bool
267 no_sig n = isNothing (sig_fn n)
269 keyd_binds = bagToList binds `zip` [0::BKey ..]
271 key_map :: NameEnv BKey -- Which binding it comes from
272 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
273 , bndr <- bindersOfHsBind bind ]
275 bindersOfHsBind :: HsBind Name -> [Name]
276 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
277 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
279 ------------------------
280 tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragFun
281 -> RecFlag -- Whether the group is really recursive
282 -> RecFlag -- Whether it's recursive after breaking
283 -- dependencies based on type signatures
285 -> TcM ([LHsBinds TcId], [TcId])
287 -- Typechecks a single bunch of bindings all together,
288 -- and generalises them. The bunch may be only part of a recursive
289 -- group, because we use type signatures to maximise polymorphism
291 -- Returns a list because the input may be a single non-recursive binding,
292 -- in which case the dependency order of the resulting bindings is
295 -- Knows nothing about the scope of the bindings
297 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds
299 bind_list = bagToList binds
300 binder_names = collectHsBindBinders binds
301 loc = getLoc (head bind_list)
302 -- TODO: location a bit awkward, but the mbinds have been
303 -- dependency analysed and may no longer be adjacent
305 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
307 recoverM (recoveryCode binder_names sig_fn) $ do
309 { traceTc (ptext SLIT("------------------------------------------------"))
310 ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
312 -- TYPECHECK THE BINDINGS
313 ; ((binds', mono_bind_infos), lie_req)
314 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
315 ; traceTc (text "temp" <+> (ppr binds' $$ ppr lie_req))
317 -- CHECK FOR UNLIFTED BINDINGS
318 -- These must be non-recursive etc, and are not generalised
319 -- They desugar to a case expression in the end
320 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
321 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
322 zonked_mono_tys mono_bind_infos
324 do { extendLIEs lie_req
325 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
326 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
327 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
328 -- ToDo: prags for unlifted bindings
330 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
331 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
333 else do -- The normal lifted case: GENERALISE
335 ; (tyvars_to_gen, dicts, dict_binds)
336 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
337 generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
339 -- BUILD THE POLYMORPHIC RESULT IDs
340 ; let dict_ids = map instToId dicts
341 ; exports <- mapM (mkExport top_lvl prag_fn tyvars_to_gen (map idType dict_ids))
344 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
345 ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids))
347 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen
349 (dict_binds `unionBags` binds')
351 ; return ([unitBag abs_bind], poly_ids) -- poly_ids are guaranteed zonked by mkExport
356 mkExport :: TopLevelFlag -> TcPragFun -> [TyVar] -> [TcType]
358 -> TcM ([TyVar], Id, Id, [LPrag])
359 -- mkExport generates exports with
360 -- zonked type variables,
362 -- The former is just because no further unifications will change
363 -- the quantified type variables, so we can fix their final form
365 -- The latter is needed because the poly_ids are used to extend the
366 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
368 -- Pre-condition: the inferred_tvs are already zonked
370 mkExport top_lvl prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
371 = do { warn_missing_sigs <- doptM Opt_WarnMissingSigs
372 ; let warn = isTopLevel top_lvl && warn_missing_sigs
373 ; (tvs, poly_id) <- mk_poly_id warn mb_sig
375 ; poly_id' <- zonkId poly_id
376 ; prags <- tcPrags poly_id' (prag_fn poly_name)
377 -- tcPrags requires a zonked poly_id
379 ; return (tvs, poly_id', mono_id, prags) }
381 poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id))
383 mk_poly_id warn Nothing = do { missingSigWarn warn poly_name poly_ty
384 ; return (inferred_tvs, mkLocalId poly_name poly_ty) }
385 mk_poly_id warn (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
386 ; return (tvs, sig_id sig) }
388 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
390 ------------------------
391 type TcPragFun = Name -> [LSig Name]
393 mkPragFun :: [LSig Name] -> TcPragFun
394 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
396 prs = [(expectJust "mkPragFun" (sigName sig), sig)
397 | sig <- sigs, isPragLSig sig]
398 env = foldl add emptyNameEnv prs
399 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
401 tcPrags :: Id -> [LSig Name] -> TcM [LPrag]
402 tcPrags poly_id prags = mapM (wrapLocM tc_prag) prags
404 tc_prag prag = addErrCtxt (pragSigCtxt prag) $
407 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
409 tcPrag :: TcId -> Sig Name -> TcM Prag
410 -- Pre-condition: the poly_id is zonked
411 -- Reason: required by tcSubExp
412 tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
413 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
414 tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
417 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
418 tcSpecPrag poly_id hs_ty inl
419 = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
420 ; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty)
422 ; let const_dicts = map instToId lie
423 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty const_dicts inl) }
424 -- Most of the work of specialisation is done by
425 -- the desugarer, guided by the SpecPrag
428 -- If typechecking the binds fails, then return with each
429 -- signature-less binder given type (forall a.a), to minimise
430 -- subsequent error messages
431 recoveryCode binder_names sig_fn
432 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
433 ; poly_ids <- mapM mk_dummy binder_names
434 ; return ([], poly_ids) }
437 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
438 | otherwise = return (mkLocalId name forall_a_a) -- No signature
441 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
444 -- Check that non-overloaded unlifted bindings are
447 -- c) not a multiple-binding group (more or less implied by (a))
449 checkStrictBinds :: TopLevelFlag -> RecFlag
450 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
452 checkStrictBinds top_lvl rec_group mbind mono_tys infos
453 | unlifted || bang_pat
454 = do { checkTc (isNotTopLevel top_lvl)
455 (strictBindErr "Top-level" unlifted mbind)
456 ; checkTc (isNonRec rec_group)
457 (strictBindErr "Recursive" unlifted mbind)
458 ; checkTc (isSingletonBag mbind)
459 (strictBindErr "Multiple" unlifted mbind)
460 ; mapM_ check_sig infos
465 unlifted = any isUnLiftedType mono_tys
466 bang_pat = anyBag (isBangHsBind . unLoc) mbind
467 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
468 (badStrictSig unlifted sig)
469 check_sig other = return ()
471 strictBindErr flavour unlifted mbind
472 = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:"))
473 4 (pprLHsBinds mbind)
475 msg | unlifted = ptext SLIT("bindings for unlifted types")
476 | otherwise = ptext SLIT("bang-pattern bindings")
478 badStrictSig unlifted sig
479 = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
482 msg | unlifted = ptext SLIT("an unlifted binding")
483 | otherwise = ptext SLIT("a bang-pattern binding")
487 %************************************************************************
489 \subsection{tcMonoBind}
491 %************************************************************************
493 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
494 The signatures have been dealt with already.
497 tcMonoBinds :: [LHsBind Name]
499 -> RecFlag -- Whether the binding is recursive for typechecking purposes
500 -- i.e. the binders are mentioned in their RHSs, and
501 -- we are not resuced by a type signature
502 -> TcM (LHsBinds TcId, [MonoBindInfo])
504 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
505 fun_matches = matches, bind_fvs = fvs })]
506 sig_fn -- Single function binding,
507 NonRecursive -- binder isn't mentioned in RHS,
508 | Nothing <- sig_fn name -- ...with no type signature
509 = -- In this very special case we infer the type of the
510 -- right hand side first (it may have a higher-rank type)
511 -- and *then* make the monomorphic Id for the LHS
512 -- e.g. f = \(x::forall a. a->a) -> <body>
513 -- We want to infer a higher-rank type for f
515 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
517 -- Check for an unboxed tuple type
518 -- f = (# True, False #)
519 -- Zonk first just in case it's hidden inside a meta type variable
520 -- (This shows up as a (more obscure) kind error
521 -- in the 'otherwise' case of tcMonoBinds.)
522 ; zonked_rhs_ty <- zonkTcType rhs_ty
523 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
524 (unboxedTupleErr name zonked_rhs_ty)
526 ; mono_name <- newLocalName name
527 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
528 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
529 fun_matches = matches', bind_fvs = fvs,
530 fun_co_fn = co_fn, fun_tick = Nothing })),
531 [(name, Nothing, mono_id)]) }
533 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
534 fun_matches = matches, bind_fvs = fvs })]
535 sig_fn -- Single function binding
537 | Just scoped_tvs <- sig_fn name -- ...with a type signature
538 = -- When we have a single function binding, with a type signature
539 -- we can (a) use genuine, rigid skolem constants for the type variables
540 -- (b) bring (rigid) scoped type variables into scope
542 do { tc_sig <- tcInstSig True name scoped_tvs
543 ; mono_name <- newLocalName name
544 ; let mono_ty = sig_tau tc_sig
545 mono_id = mkLocalId mono_name mono_ty
546 rhs_tvs = [ (name, mkTyVarTy tv)
547 | (name, tv) <- sig_scoped tc_sig `zip` sig_tvs tc_sig ]
549 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
550 tcMatchesFun mono_name inf matches mono_ty
552 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
553 fun_infix = inf, fun_matches = matches',
554 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
556 ; return (unitBag (L b_loc fun_bind'),
557 [(name, Just tc_sig, mono_id)]) }
559 tcMonoBinds binds sig_fn non_rec
560 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
562 -- Bring the monomorphic Ids, into scope for the RHSs
563 ; let mono_info = getMonoBindInfo tc_binds
564 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
565 -- A monomorphic binding for each term variable that lacks
566 -- a type sig. (Ones with a sig are already in scope.)
568 ; binds' <- tcExtendIdEnv2 rhs_id_env $
569 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
570 | (n,id) <- rhs_id_env]) `thenM_`
571 mapM (wrapLocM tcRhs) tc_binds
572 ; return (listToBag binds', mono_info) }
574 ------------------------
575 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
576 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
577 -- if there's a signature for it, use the instantiated signature type
578 -- otherwise invent a type variable
579 -- You see that quite directly in the FunBind case.
581 -- But there's a complication for pattern bindings:
582 -- data T = MkT (forall a. a->a)
584 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
585 -- but we want to get (f::forall a. a->a) as the RHS environment.
586 -- The simplest way to do this is to typecheck the pattern, and then look up the
587 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
588 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
590 data TcMonoBind -- Half completed; LHS done, RHS not done
591 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
592 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
594 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
595 -- Type signature (if any), and
596 -- the monomorphic bound things
598 bndrNames :: [MonoBindInfo] -> [Name]
599 bndrNames mbi = [n | (n,_,_) <- mbi]
601 getMonoType :: MonoBindInfo -> TcTauType
602 getMonoType (_,_,mono_id) = idType mono_id
604 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
605 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
606 = do { mb_sig <- tcInstSig_maybe sig_fn name
607 ; mono_name <- newLocalName name
608 ; mono_ty <- mk_mono_ty mb_sig
609 ; let mono_id = mkLocalId mono_name mono_ty
610 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
612 mk_mono_ty (Just sig) = return (sig_tau sig)
613 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
615 tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
616 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
617 ; mono_pat_binds <- doptM Opt_MonoPatBinds
618 -- With -fmono-pat-binds, we do no generalisation of pattern bindings
619 -- But the signature can still be polymoprhic!
620 -- data T = MkT (forall a. a->a)
621 -- x :: forall a. a->a
623 -- The function get_sig_ty decides whether the pattern-bound variables
624 -- should have exactly the type in the type signature (-fmono-pat-binds),
625 -- or the instantiated version (-fmono-pat-binds)
627 ; let nm_sig_prs = names `zip` mb_sigs
628 get_sig_ty | mono_pat_binds = idType . sig_id
629 | otherwise = sig_tau
630 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
631 | (name, Just sig) <- nm_sig_prs]
632 sig_tau_fn = lookupNameEnv tau_sig_env
634 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
635 mapM lookup_info nm_sig_prs
637 -- After typechecking the pattern, look up the binder
638 -- names, which the pattern has brought into scope.
639 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
640 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
641 ; return (name, mb_sig, mono_id) }
643 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
646 ; return (TcPatBind infos pat' grhss pat_ty) }
648 names = collectPatBinders pat
651 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
652 -- AbsBind, VarBind impossible
655 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
656 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
657 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
658 matches (idType mono_id)
659 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
660 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
661 fun_tick = Nothing }) }
663 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
664 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
665 tcGRHSsPat grhss pat_ty
666 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
667 bind_fvs = placeHolderNames }) }
670 ---------------------
671 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
672 getMonoBindInfo tc_binds
673 = foldr (get_info . unLoc) [] tc_binds
675 get_info (TcFunBind info _ _ _) rest = info : rest
676 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
680 %************************************************************************
684 %************************************************************************
687 generalise :: DynFlags -> TopLevelFlag
688 -> [LHsBind Name] -> TcSigFun
689 -> [MonoBindInfo] -> [Inst]
690 -> TcM ([TyVar], [Inst], TcDictBinds)
691 -- The returned [TyVar] are all ready to quantify
693 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
694 | isMonoGroup dflags bind_list
695 = do { extendLIEs lie_req
696 ; return ([], [], emptyBag) }
698 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
699 = -- Check signature contexts are empty
700 do { checkTc (all is_mono_sig sigs)
701 (restrictedBindCtxtErr bndrs)
703 -- Now simplify with exactly that set of tyvars
704 -- We have to squash those Methods
705 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
708 -- Check that signature type variables are OK
709 ; final_qtvs <- checkSigsTyVars qtvs sigs
711 ; return (final_qtvs, [], binds) }
713 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
714 = tcSimplifyInfer doc tau_tvs lie_req
716 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
717 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
718 ; let -- The "sig_avails" is the stuff available. We get that from
719 -- the context of the type signature, BUT ALSO the lie_avail
720 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
721 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
722 sig_avails = sig_lie ++ local_meths
723 loc = sig_loc (head sigs)
725 -- Check that the needed dicts can be
726 -- expressed in terms of the signature ones
727 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
729 -- Check that signature type variables are OK
730 ; final_qtvs <- checkSigsTyVars qtvs sigs
732 ; returnM (final_qtvs, sig_lie, binds) }
734 bndrs = bndrNames mono_infos
735 sigs = [sig | (_, Just sig, _) <- mono_infos]
736 tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos
737 -- NB: exactTyVarsOfType; see Note [Silly type synonym]
738 -- near defn of TcType.exactTyVarsOfType
739 is_mono_sig sig = null (sig_theta sig)
740 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
742 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
743 sig_theta = theta, sig_loc = loc }) mono_id
744 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
745 tci_theta = theta, tci_loc = loc}
748 unifyCtxts checks that all the signature contexts are the same
749 The type signatures on a mutually-recursive group of definitions
750 must all have the same context (or none).
752 The trick here is that all the signatures should have the same
753 context, and we want to share type variables for that context, so that
754 all the right hand sides agree a common vocabulary for their type
757 We unify them because, with polymorphic recursion, their types
758 might not otherwise be related. This is a rather subtle issue.
761 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
762 -- Post-condition: the returned Insts are full zonked
763 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
764 = do { mapM unify_ctxt sigs
765 ; theta <- zonkTcThetaType (sig_theta sig1)
766 ; newDictBndrs (sig_loc sig1) theta }
768 theta1 = sig_theta sig1
769 unify_ctxt :: TcSigInfo -> TcM ()
770 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
771 = setSrcSpan (instLocSpan (sig_loc sig)) $
772 addErrCtxt (sigContextsCtxt sig1 sig) $
773 do { cois <- unifyTheta theta1 theta
774 ; -- Check whether all coercions are identity coercions
775 -- That can happen if we have, say
777 -- g :: C (F a) => ...
778 -- where F is a type function and (F a ~ [a])
779 -- Then unification might succeed with a coercion. But it's much
780 -- much simpler to require that such signatures have identical contexts
781 checkTc (all isIdentityCoercion cois)
782 (ptext SLIT("Mutually dependent functions have syntactically distinct contexts"))
785 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
786 checkSigsTyVars qtvs sigs
787 = do { gbl_tvs <- tcGetGlobalTyVars
788 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
790 ; let -- Sigh. Make sure that all the tyvars in the type sigs
791 -- appear in the returned ty var list, which is what we are
792 -- going to generalise over. Reason: we occasionally get
794 -- type T a = () -> ()
797 -- Here, 'a' won't appear in qtvs, so we have to add it
798 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
799 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
802 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
803 sig_theta = theta, sig_tau = tau})
804 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
805 addErrCtxtM (sigCtxt id tvs theta tau) $
806 do { tvs' <- checkDistinctTyVars tvs
807 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
808 (bleatEscapedTvs gbl_tvs tvs tvs')
811 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
812 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
813 -- are still all type variables, and all distinct from each other.
814 -- It returns a zonked set of type variables.
815 -- For example, if the type sig is
816 -- f :: forall a b. a -> b -> b
817 -- we want to check that 'a' and 'b' haven't
818 -- (a) been unified with a non-tyvar type
819 -- (b) been unified with each other (all distinct)
821 checkDistinctTyVars sig_tvs
822 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
823 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
824 ; return zonked_tvs }
826 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
827 -- The TyVarEnv maps each zonked type variable back to its
828 -- corresponding user-written signature type variable
829 check_dup acc (sig_tv, zonked_tv)
830 = case lookupVarEnv acc zonked_tv of
831 Just sig_tv' -> bomb_out sig_tv sig_tv'
833 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
835 bomb_out sig_tv1 sig_tv2
836 = do { env0 <- tcInitTidyEnv
837 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
838 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
839 msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
840 <+> ptext SLIT("is unified with another quantified type variable")
841 <+> quotes (ppr tidy_tv2)
842 ; failWithTcM (env2, msg) }
847 @getTyVarsToGen@ decides what type variables to generalise over.
849 For a "restricted group" -- see the monomorphism restriction
850 for a definition -- we bind no dictionaries, and
851 remove from tyvars_to_gen any constrained type variables
853 *Don't* simplify dicts at this point, because we aren't going
854 to generalise over these dicts. By the time we do simplify them
855 we may well know more. For example (this actually came up)
857 f x = array ... xs where xs = [1,2,3,4,5]
858 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
859 stuff. If we simplify only at the f-binding (not the xs-binding)
860 we'll know that the literals are all Ints, and we can just produce
863 Find all the type variables involved in overloading, the
864 "constrained_tyvars". These are the ones we *aren't* going to
865 generalise. We must be careful about doing this:
867 (a) If we fail to generalise a tyvar which is not actually
868 constrained, then it will never, ever get bound, and lands
869 up printed out in interface files! Notorious example:
870 instance Eq a => Eq (Foo a b) where ..
871 Here, b is not constrained, even though it looks as if it is.
872 Another, more common, example is when there's a Method inst in
873 the LIE, whose type might very well involve non-overloaded
875 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
876 the simple thing instead]
878 (b) On the other hand, we mustn't generalise tyvars which are constrained,
879 because we are going to pass on out the unmodified LIE, with those
880 tyvars in it. They won't be in scope if we've generalised them.
882 So we are careful, and do a complete simplification just to find the
883 constrained tyvars. We don't use any of the results, except to
884 find which tyvars are constrained.
886 Note [Polymorphic recursion]
887 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
888 The game plan for polymorphic recursion in the code above is
890 * Bind any variable for which we have a type signature
891 to an Id with a polymorphic type. Then when type-checking
892 the RHSs we'll make a full polymorphic call.
894 This fine, but if you aren't a bit careful you end up with a horrendous
895 amount of partial application and (worse) a huge space leak. For example:
897 f :: Eq a => [a] -> [a]
900 If we don't take care, after typechecking we get
902 f = /\a -> \d::Eq a -> let f' = f a d
906 Notice the the stupid construction of (f a d), which is of course
907 identical to the function we're executing. In this case, the
908 polymorphic recursion isn't being used (but that's a very common case).
909 This can lead to a massive space leak, from the following top-level defn
915 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
916 f' is another thunk which evaluates to the same thing... and you end
917 up with a chain of identical values all hung onto by the CAF ff.
921 = let f' = f Int dEqInt in \ys. ...f'...
923 = let f' = let f' = f Int dEqInt in \ys. ...f'...
928 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
929 which would make the space leak go away in this case
931 Solution: when typechecking the RHSs we always have in hand the
932 *monomorphic* Ids for each binding. So we just need to make sure that
933 if (Method f a d) shows up in the constraints emerging from (...f...)
934 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
935 to the "givens" when simplifying constraints. That's what the "lies_avail"
940 f = /\a -> \d::Eq a -> letrec
941 fm = \ys:[a] -> ...fm...
947 %************************************************************************
951 %************************************************************************
953 Type signatures are tricky. See Note [Signature skolems] in TcType
955 @tcSigs@ checks the signatures for validity, and returns a list of
956 {\em freshly-instantiated} signatures. That is, the types are already
957 split up, and have fresh type variables installed. All non-type-signature
958 "RenamedSigs" are ignored.
960 The @TcSigInfo@ contains @TcTypes@ because they are unified with
961 the variable's type, and after that checked to see whether they've
965 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
966 -- type variables brought into scope
967 -- by its type signature.
968 -- Nothing => no type signature
970 mkTcSigFun :: [LSig Name] -> TcSigFun
971 -- Search for a particular type signature
972 -- Precondition: the sigs are all type sigs
973 -- Precondition: no duplicates
974 mkTcSigFun sigs = lookupNameEnv env
976 env = mkNameEnv [(name, hsExplicitTvs lhs_ty)
977 | L span (TypeSig (L _ name) lhs_ty) <- sigs]
978 -- The scoped names are the ones explicitly mentioned
979 -- in the HsForAll. (There may be more in sigma_ty, because
980 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
981 -- See Note [Only scoped tyvars are in the TyVarEnv]
986 sig_id :: TcId, -- *Polymorphic* binder for this value...
988 sig_scoped :: [Name], -- Names for any scoped type variables
989 -- Invariant: correspond 1-1 with an initial
990 -- segment of sig_tvs (see Note [Scoped])
992 sig_tvs :: [TcTyVar], -- Instantiated type variables
993 -- See Note [Instantiate sig]
995 sig_theta :: TcThetaType, -- Instantiated theta
996 sig_tau :: TcTauType, -- Instantiated tau
997 sig_loc :: InstLoc -- The location of the signature
1001 -- Note [Only scoped tyvars are in the TyVarEnv]
1002 -- We are careful to keep only the *lexically scoped* type variables in
1003 -- the type environment. Why? After all, the renamer has ensured
1004 -- that only legal occurrences occur, so we could put all type variables
1005 -- into the type env.
1007 -- But we want to check that two distinct lexically scoped type variables
1008 -- do not map to the same internal type variable. So we need to know which
1009 -- the lexically-scoped ones are... and at the moment we do that by putting
1010 -- only the lexically scoped ones into the environment.
1014 -- There may be more instantiated type variables than scoped
1015 -- ones. For example:
1016 -- type T a = forall b. b -> (a,b)
1017 -- f :: forall c. T c
1018 -- Here, the signature for f will have one scoped type variable, c,
1019 -- but two instantiated type variables, c' and b'.
1021 -- We assume that the scoped ones are at the *front* of sig_tvs,
1022 -- and remember the names from the original HsForAllTy in sig_scoped
1024 -- Note [Instantiate sig]
1025 -- It's vital to instantiate a type signature with fresh variables.
1027 -- type S = forall a. a->a
1031 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1032 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1033 -- it's all cool; each signature has distinct type variables from the renamer.)
1035 instance Outputable TcSigInfo where
1036 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1037 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
1041 tcTySig :: LSig Name -> TcM TcId
1042 tcTySig (L span (TypeSig (L _ name) ty))
1044 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1045 ; return (mkLocalId name sigma_ty) }
1048 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1049 -- Instantiate with *meta* type variables;
1050 -- this signature is part of a multi-signature group
1051 tcInstSig_maybe sig_fn name
1052 = case sig_fn name of
1053 Nothing -> return Nothing
1054 Just tvs -> do { tc_sig <- tcInstSig False name tvs
1055 ; return (Just tc_sig) }
1057 tcInstSig :: Bool -> Name -> [Name] -> TcM TcSigInfo
1058 -- Instantiate the signature, with either skolems or meta-type variables
1059 -- depending on the use_skols boolean. This variable is set True
1060 -- when we are typechecking a single function binding; and False for
1061 -- pattern bindings and a group of several function bindings.
1062 -- Reason: in the latter cases, the "skolems" can be unified together,
1063 -- so they aren't properly rigid in the type-refinement sense.
1064 -- NB: unless we are doing H98, each function with a sig will be done
1065 -- separately, even if it's mutually recursive, so use_skols will be True
1067 -- We always instantiate with fresh uniques,
1068 -- although we keep the same print-name
1070 -- type T = forall a. [a] -> [a]
1072 -- f = g where { g :: T; g = <rhs> }
1074 -- We must not use the same 'a' from the defn of T at both places!!
1076 tcInstSig use_skols name scoped_names
1077 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1078 -- scope when starting the binding group
1079 ; let skol_info = SigSkol (FunSigCtxt name)
1080 inst_tyvars = tcInstSigTyVars use_skols skol_info
1081 ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
1082 ; loc <- getInstLoc (SigOrigin skol_info)
1083 ; return (TcSigInfo { sig_id = poly_id,
1084 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1085 sig_scoped = final_scoped_names, sig_loc = loc }) }
1086 -- Note that the scoped_names and the sig_tvs will have
1087 -- different Names. That's quite ok; when we bring the
1088 -- scoped_names into scope, we just bind them to the sig_tvs
1090 -- We also only have scoped type variables when we are instantiating
1091 -- with true skolems
1092 final_scoped_names | use_skols = scoped_names
1096 isMonoGroup :: DynFlags -> [LHsBind Name] -> Bool
1097 -- No generalisation at all
1098 isMonoGroup dflags binds
1099 = dopt Opt_MonoPatBinds dflags && any is_pat_bind binds
1101 is_pat_bind (L _ (PatBind {})) = True
1102 is_pat_bind other = False
1105 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1106 isRestrictedGroup dflags binds sig_fn
1107 = mono_restriction && not all_unrestricted
1109 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1110 all_unrestricted = all (unrestricted . unLoc) binds
1111 has_sig n = isJust (sig_fn n)
1113 unrestricted (PatBind {}) = False
1114 unrestricted (VarBind { var_id = v }) = has_sig v
1115 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1116 || has_sig (unLoc v)
1118 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1119 -- No args => like a pattern binding
1120 unrestricted_match other = True
1121 -- Some args => a function binding
1125 %************************************************************************
1127 \subsection[TcBinds-errors]{Error contexts and messages}
1129 %************************************************************************
1133 -- This one is called on LHS, when pat and grhss are both Name
1134 -- and on RHS, when pat is TcId and grhss is still Name
1135 patMonoBindsCtxt pat grhss
1136 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
1138 -----------------------------------------------
1139 sigContextsCtxt sig1 sig2
1140 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
1141 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1142 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1143 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
1149 -----------------------------------------------
1150 unboxedTupleErr name ty
1151 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
1152 4 (ppr name <+> dcolon <+> ppr ty)
1154 -----------------------------------------------
1155 restrictedBindCtxtErr binder_names
1156 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
1157 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
1158 ptext SLIT("that falls under the monomorphism restriction")])
1160 genCtxt binder_names
1161 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
1163 missingSigWarn False name ty = return ()
1164 missingSigWarn True name ty
1165 = do { env0 <- tcInitTidyEnv
1166 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1167 ; addWarnTcM (env1, mk_msg tidy_ty) }
1169 mk_msg ty = vcat [ptext SLIT("Definition but no type signature for") <+> quotes (ppr name),
1170 sep [ptext SLIT("Inferred type:") <+> ppr name <+> dcolon <+> ppr ty]]