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
54 %************************************************************************
56 \subsection{Type-checking bindings}
58 %************************************************************************
60 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
61 it needs to know something about the {\em usage} of the things bound,
62 so that it can create specialisations of them. So @tcBindsAndThen@
63 takes a function which, given an extended environment, E, typechecks
64 the scope of the bindings returning a typechecked thing and (most
65 important) an LIE. It is this LIE which is then used as the basis for
66 specialising the things bound.
68 @tcBindsAndThen@ also takes a "combiner" which glues together the
69 bindings and the "thing" to make a new "thing".
71 The real work is done by @tcBindWithSigsAndThen@.
73 Recursive and non-recursive binds are handled in essentially the same
74 way: because of uniques there are no scoping issues left. The only
75 difference is that non-recursive bindings can bind primitive values.
77 Even for non-recursive binding groups we add typings for each binder
78 to the LVE for the following reason. When each individual binding is
79 checked the type of its LHS is unified with that of its RHS; and
80 type-checking the LHS of course requires that the binder is in scope.
82 At the top-level the LIE is sure to contain nothing but constant
83 dictionaries, which we resolve at the module level.
86 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
87 -- Note: returning the TcLclEnv is more than we really
88 -- want. The bit we care about is the local bindings
89 -- and the free type variables thereof
91 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
92 ; return (foldr (unionBags . snd) emptyBag prs, env) }
93 -- The top level bindings are flattened into a giant
94 -- implicitly-mutually-recursive LHsBinds
96 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
97 -- A hs-boot file has only one BindGroup, and it only has type
98 -- signatures in it. The renamer checked all this
99 tcHsBootSigs (ValBindsOut binds sigs)
100 = do { checkTc (null binds) badBootDeclErr
101 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
103 tc_boot_sig (TypeSig (L _ name) ty)
104 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
105 ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
106 -- Notice that we make GlobalIds, not LocalIds
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)
137 = newFlexiTyVarTy argTypeKind `thenM` \ ty ->
138 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
139 tcMonoExpr expr ty `thenM` \ expr' ->
140 returnM (ip_inst, (IPBind ip' expr'))
142 ------------------------
143 tcValBinds :: TopLevelFlag
144 -> HsValBinds Name -> TcM thing
145 -> TcM (HsValBinds TcId, thing)
147 tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
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 isVanillaLSig sigs
154 ; sig_fn = mkTcSigFun ty_sigs }
156 ; poly_ids <- mapM 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 ; gla_exts <- doptM Opt_GlasgowExts
166 ; (binds', thing) <- tcExtendIdEnv poly_ids $
167 tc_val_binds gla_exts top_lvl sig_fn prag_fn
170 ; return (ValBindsOut binds' sigs, thing) }
172 ------------------------
173 tc_val_binds :: 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
179 tc_val_binds gla_exts top_lvl sig_fn prag_fn [] thing_inside
180 = do { thing <- thing_inside
181 ; return ([], thing) }
183 tc_val_binds gla_exts top_lvl sig_fn prag_fn (group : groups) thing_inside
184 = do { (group', (groups', thing))
185 <- tc_group gla_exts top_lvl sig_fn prag_fn group $
186 tc_val_binds gla_exts top_lvl sig_fn prag_fn groups thing_inside
187 ; return (group' ++ groups', thing) }
189 ------------------------
190 tc_group :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
191 -> (RecFlag, LHsBinds Name) -> TcM thing
192 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
194 -- Typecheck one strongly-connected component of the original program.
195 -- We get a list of groups back, because there may
196 -- be specialisations etc as well
198 tc_group gla_exts top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
199 -- A single non-recursive binding
200 -- We want to keep non-recursive things non-recursive
201 -- so that we desugar unlifted bindings correctly
202 = do { (binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn NonRecursive binds thing_inside
203 ; return ([(NonRecursive, b) | b <- binds], thing) }
205 tc_group gla_exts top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
206 | not gla_exts -- Recursive group, normal Haskell 98 route
207 = do { (binds1, thing) <- tc_haskell98 top_lvl sig_fn prag_fn Recursive binds thing_inside
208 ; return ([(Recursive, unionManyBags binds1)], thing) }
210 | otherwise -- Recursive group, with gla-exts
211 = -- To maximise polymorphism (with -fglasgow-exts), we do a new
212 -- strongly-connected-component analysis, this time omitting
213 -- any references to variables with type signatures.
215 -- Notice that the bindInsts thing covers *all* the bindings in the original
216 -- group at once; an earlier one may use a later one!
217 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
218 ; (binds1,thing) <- bindLocalInsts top_lvl $
219 go (stronglyConnComp (mkEdges sig_fn binds))
220 ; return ([(Recursive, unionManyBags binds1)], thing) }
221 -- Rec them all together
223 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], [TcId], thing)
224 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
225 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
226 ; return (binds1 ++ binds2, ids1 ++ ids2, thing) }
227 go [] = do { thing <- thing_inside; return ([], [], thing) }
229 tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive (unitBag bind)
230 tc_scc (CyclicSCC binds) = tc_sub_group Recursive (listToBag binds)
232 tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
234 tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside
235 = bindLocalInsts top_lvl $ do
236 { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds
237 ; thing <- tcExtendIdEnv ids thing_inside
238 ; return (binds1, ids, thing) }
240 ------------------------
241 bindLocalInsts :: TopLevelFlag -> TcM ([LHsBinds TcId], [TcId], a) -> TcM ([LHsBinds TcId], a)
242 bindLocalInsts top_lvl thing_inside
243 | isTopLevel top_lvl = do { (binds, ids, thing) <- thing_inside; return (binds, thing) }
244 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff.
245 -- All the top level things are rec'd together anyway, so it's fine to
246 -- leave them to the tcSimplifyTop, and quite a bit faster too
248 | otherwise -- Nested case
249 = do { ((binds, ids, thing), lie) <- getLIE thing_inside
250 ; lie_binds <- bindInstsOfLocalFuns lie ids
251 ; return (binds ++ [lie_binds], thing) }
253 ------------------------
254 mkEdges :: TcSigFun -> LHsBinds Name
255 -> [(LHsBind Name, BKey, [BKey])]
257 type BKey = Int -- Just number off the bindings
260 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
261 Just key <- [lookupNameEnv key_map n], no_sig n ])
262 | (bind, key) <- keyd_binds
265 no_sig :: Name -> Bool
266 no_sig n = isNothing (sig_fn n)
268 keyd_binds = bagToList binds `zip` [0::BKey ..]
270 key_map :: NameEnv BKey -- Which binding it comes from
271 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
272 , bndr <- bindersOfHsBind bind ]
274 bindersOfHsBind :: HsBind Name -> [Name]
275 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
276 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
278 ------------------------
279 tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragFun
280 -> RecFlag -- Whether the group is really recursive
281 -> RecFlag -- Whether it's recursive after breaking
282 -- dependencies based on type signatures
284 -> TcM ([LHsBinds TcId], [TcId])
286 -- Typechecks a single bunch of bindings all together,
287 -- and generalises them. The bunch may be only part of a recursive
288 -- group, because we use type signatures to maximise polymorphism
290 -- Returns a list because the input may be a single non-recursive binding,
291 -- in which case the dependency order of the resulting bindings is
294 -- Knows nothing about the scope of the bindings
296 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds
298 bind_list = bagToList binds
299 binder_names = collectHsBindBinders binds
300 loc = getLoc (head bind_list)
301 -- TODO: location a bit awkward, but the mbinds have been
302 -- dependency analysed and may no longer be adjacent
304 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
306 recoverM (recoveryCode binder_names sig_fn) $ do
308 { traceTc (ptext SLIT("------------------------------------------------"))
309 ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
311 -- TYPECHECK THE BINDINGS
312 ; ((binds', mono_bind_infos), lie_req)
313 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
314 ; traceTc (text "temp" <+> (ppr binds' $$ ppr lie_req))
316 -- CHECK FOR UNLIFTED BINDINGS
317 -- These must be non-recursive etc, and are not generalised
318 -- They desugar to a case expression in the end
319 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
320 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
321 zonked_mono_tys mono_bind_infos
323 do { extendLIEs lie_req
324 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
325 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
326 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
327 -- ToDo: prags for unlifted bindings
329 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
330 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
332 else do -- The normal lifted case: GENERALISE
334 ; (tyvars_to_gen, dicts, dict_binds)
335 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
336 generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
338 -- BUILD THE POLYMORPHIC RESULT IDs
339 ; let dict_ids = map instToId dicts
340 ; exports <- mapM (mkExport top_lvl prag_fn tyvars_to_gen (map idType dict_ids))
343 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
344 ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids))
346 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen
348 (dict_binds `unionBags` binds')
350 ; return ([unitBag abs_bind], poly_ids) -- poly_ids are guaranteed zonked by mkExport
355 mkExport :: TopLevelFlag -> TcPragFun -> [TyVar] -> [TcType]
357 -> TcM ([TyVar], Id, Id, [LPrag])
358 -- mkExport generates exports with
359 -- zonked type variables,
361 -- The former is just because no further unifications will change
362 -- the quantified type variables, so we can fix their final form
364 -- The latter is needed because the poly_ids are used to extend the
365 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
367 -- Pre-condition: the inferred_tvs are already zonked
369 mkExport top_lvl prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
370 = do { warn_missing_sigs <- doptM Opt_WarnMissingSigs
371 ; let warn = isTopLevel top_lvl && warn_missing_sigs
372 ; (tvs, poly_id) <- mk_poly_id warn mb_sig
374 ; poly_id' <- zonkId poly_id
375 ; prags <- tcPrags poly_id' (prag_fn poly_name)
376 -- tcPrags requires a zonked poly_id
378 ; return (tvs, poly_id', mono_id, prags) }
380 poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id))
382 mk_poly_id warn Nothing = do { missingSigWarn warn poly_name poly_ty
383 ; return (inferred_tvs, mkLocalId poly_name poly_ty) }
384 mk_poly_id warn (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
385 ; return (tvs, sig_id sig) }
387 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
389 ------------------------
390 type TcPragFun = Name -> [LSig Name]
392 mkPragFun :: [LSig Name] -> TcPragFun
393 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
395 prs = [(expectJust "mkPragFun" (sigName sig), sig)
396 | sig <- sigs, isPragLSig sig]
397 env = foldl add emptyNameEnv prs
398 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
400 tcPrags :: Id -> [LSig Name] -> TcM [LPrag]
401 tcPrags poly_id prags = mapM (wrapLocM tc_prag) prags
403 tc_prag prag = addErrCtxt (pragSigCtxt prag) $
406 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
408 tcPrag :: TcId -> Sig Name -> TcM Prag
409 -- Pre-condition: the poly_id is zonked
410 -- Reason: required by tcSubExp
411 tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
412 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
413 tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
416 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
417 tcSpecPrag poly_id hs_ty inl
418 = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
419 ; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty)
421 ; let const_dicts = map instToId lie
422 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty const_dicts inl) }
423 -- Most of the work of specialisation is done by
424 -- the desugarer, guided by the SpecPrag
427 -- If typechecking the binds fails, then return with each
428 -- signature-less binder given type (forall a.a), to minimise
429 -- subsequent error messages
430 recoveryCode binder_names sig_fn
431 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
432 ; poly_ids <- mapM mk_dummy binder_names
433 ; return ([], poly_ids) }
436 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
437 | otherwise = return (mkLocalId name forall_a_a) -- No signature
440 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
443 -- Check that non-overloaded unlifted bindings are
446 -- c) not a multiple-binding group (more or less implied by (a))
448 checkStrictBinds :: TopLevelFlag -> RecFlag
449 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
451 checkStrictBinds top_lvl rec_group mbind mono_tys infos
452 | unlifted || bang_pat
453 = do { checkTc (isNotTopLevel top_lvl)
454 (strictBindErr "Top-level" unlifted mbind)
455 ; checkTc (isNonRec rec_group)
456 (strictBindErr "Recursive" unlifted mbind)
457 ; checkTc (isSingletonBag mbind)
458 (strictBindErr "Multiple" unlifted mbind)
459 ; mapM_ check_sig infos
464 unlifted = any isUnLiftedType mono_tys
465 bang_pat = anyBag (isBangHsBind . unLoc) mbind
466 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
467 (badStrictSig unlifted sig)
468 check_sig other = return ()
470 strictBindErr flavour unlifted mbind
471 = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:"))
472 4 (pprLHsBinds mbind)
474 msg | unlifted = ptext SLIT("bindings for unlifted types")
475 | otherwise = ptext SLIT("bang-pattern bindings")
477 badStrictSig unlifted sig
478 = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
481 msg | unlifted = ptext SLIT("an unlifted binding")
482 | otherwise = ptext SLIT("a bang-pattern binding")
486 %************************************************************************
488 \subsection{tcMonoBind}
490 %************************************************************************
492 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
493 The signatures have been dealt with already.
496 tcMonoBinds :: [LHsBind Name]
498 -> RecFlag -- Whether the binding is recursive for typechecking purposes
499 -- i.e. the binders are mentioned in their RHSs, and
500 -- we are not resuced by a type signature
501 -> TcM (LHsBinds TcId, [MonoBindInfo])
503 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
504 fun_matches = matches, bind_fvs = fvs })]
505 sig_fn -- Single function binding,
506 NonRecursive -- binder isn't mentioned in RHS,
507 | Nothing <- sig_fn name -- ...with no type signature
508 = -- In this very special case we infer the type of the
509 -- right hand side first (it may have a higher-rank type)
510 -- and *then* make the monomorphic Id for the LHS
511 -- e.g. f = \(x::forall a. a->a) -> <body>
512 -- We want to infer a higher-rank type for f
514 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name matches)
516 -- Check for an unboxed tuple type
517 -- f = (# True, False #)
518 -- Zonk first just in case it's hidden inside a meta type variable
519 -- (This shows up as a (more obscure) kind error
520 -- in the 'otherwise' case of tcMonoBinds.)
521 ; zonked_rhs_ty <- zonkTcType rhs_ty
522 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
523 (unboxedTupleErr name zonked_rhs_ty)
525 ; mono_name <- newLocalName name
526 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
527 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
528 fun_matches = matches', bind_fvs = fvs,
529 fun_co_fn = co_fn, fun_tick = Nothing })),
530 [(name, Nothing, mono_id)]) }
532 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
533 fun_matches = matches, bind_fvs = fvs })]
534 sig_fn -- Single function binding
536 | Just scoped_tvs <- sig_fn name -- ...with a type signature
537 = -- When we have a single function binding, with a type signature
538 -- we can (a) use genuine, rigid skolem constants for the type variables
539 -- (b) bring (rigid) scoped type variables into scope
541 do { tc_sig <- tcInstSig True name scoped_tvs
542 ; mono_name <- newLocalName name
543 ; let mono_ty = sig_tau tc_sig
544 mono_id = mkLocalId mono_name mono_ty
545 rhs_tvs = [ (name, mkTyVarTy tv)
546 | (name, tv) <- sig_scoped tc_sig `zip` sig_tvs tc_sig ]
548 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
549 tcMatchesFun mono_name matches mono_ty
551 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
552 fun_infix = inf, fun_matches = matches',
553 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
555 ; return (unitBag (L b_loc fun_bind'),
556 [(name, Just tc_sig, mono_id)]) }
558 tcMonoBinds binds sig_fn non_rec
559 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
561 -- Bring the monomorphic Ids, into scope for the RHSs
562 ; let mono_info = getMonoBindInfo tc_binds
563 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
564 -- A monomorphic binding for each term variable that lacks
565 -- a type sig. (Ones with a sig are already in scope.)
567 ; binds' <- tcExtendIdEnv2 rhs_id_env $
568 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
569 | (n,id) <- rhs_id_env]) `thenM_`
570 mapM (wrapLocM tcRhs) tc_binds
571 ; return (listToBag binds', mono_info) }
573 ------------------------
574 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
575 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
576 -- if there's a signature for it, use the instantiated signature type
577 -- otherwise invent a type variable
578 -- You see that quite directly in the FunBind case.
580 -- But there's a complication for pattern bindings:
581 -- data T = MkT (forall a. a->a)
583 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
584 -- but we want to get (f::forall a. a->a) as the RHS environment.
585 -- The simplest way to do this is to typecheck the pattern, and then look up the
586 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
587 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
589 data TcMonoBind -- Half completed; LHS done, RHS not done
590 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
591 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
593 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
594 -- Type signature (if any), and
595 -- the monomorphic bound things
597 bndrNames :: [MonoBindInfo] -> [Name]
598 bndrNames mbi = [n | (n,_,_) <- mbi]
600 getMonoType :: MonoBindInfo -> TcTauType
601 getMonoType (_,_,mono_id) = idType mono_id
603 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
604 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
605 = do { mb_sig <- tcInstSig_maybe sig_fn name
606 ; mono_name <- newLocalName name
607 ; mono_ty <- mk_mono_ty mb_sig
608 ; let mono_id = mkLocalId mono_name mono_ty
609 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
611 mk_mono_ty (Just sig) = return (sig_tau sig)
612 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
614 tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
615 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
616 ; mono_pat_binds <- doptM Opt_MonoPatBinds
617 -- With -fmono-pat-binds, we do no generalisation of pattern bindings
618 -- But the signature can still be polymoprhic!
619 -- data T = MkT (forall a. a->a)
620 -- x :: forall a. a->a
622 -- The function get_sig_ty decides whether the pattern-bound variables
623 -- should have exactly the type in the type signature (-fmono-pat-binds),
624 -- or the instantiated version (-fmono-pat-binds)
626 ; let nm_sig_prs = names `zip` mb_sigs
627 get_sig_ty | mono_pat_binds = idType . sig_id
628 | otherwise = sig_tau
629 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
630 | (name, Just sig) <- nm_sig_prs]
631 sig_tau_fn = lookupNameEnv tau_sig_env
633 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
634 mapM lookup_info nm_sig_prs
636 -- After typechecking the pattern, look up the binder
637 -- names, which the pattern has brought into scope.
638 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
639 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
640 ; return (name, mb_sig, mono_id) }
642 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
645 ; return (TcPatBind infos pat' grhss pat_ty) }
647 names = collectPatBinders pat
650 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
651 -- AbsBind, VarBind impossible
654 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
655 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
656 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) matches
658 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
659 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
660 fun_tick = Nothing }) }
662 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
663 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
664 tcGRHSsPat grhss pat_ty
665 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
666 bind_fvs = placeHolderNames }) }
669 ---------------------
670 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
671 getMonoBindInfo tc_binds
672 = foldr (get_info . unLoc) [] tc_binds
674 get_info (TcFunBind info _ _ _) rest = info : rest
675 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
679 %************************************************************************
683 %************************************************************************
686 generalise :: DynFlags -> TopLevelFlag
687 -> [LHsBind Name] -> TcSigFun
688 -> [MonoBindInfo] -> [Inst]
689 -> TcM ([TyVar], [Inst], TcDictBinds)
690 -- The returned [TyVar] are all ready to quantify
692 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
693 | isMonoGroup dflags bind_list
694 = do { extendLIEs lie_req
695 ; return ([], [], emptyBag) }
697 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
698 = -- Check signature contexts are empty
699 do { checkTc (all is_mono_sig sigs)
700 (restrictedBindCtxtErr bndrs)
702 -- Now simplify with exactly that set of tyvars
703 -- We have to squash those Methods
704 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
707 -- Check that signature type variables are OK
708 ; final_qtvs <- checkSigsTyVars qtvs sigs
710 ; return (final_qtvs, [], binds) }
712 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
713 = tcSimplifyInfer doc tau_tvs lie_req
715 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
716 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
717 ; let -- The "sig_avails" is the stuff available. We get that from
718 -- the context of the type signature, BUT ALSO the lie_avail
719 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
720 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
721 sig_avails = sig_lie ++ local_meths
722 loc = sig_loc (head sigs)
724 -- Check that the needed dicts can be
725 -- expressed in terms of the signature ones
726 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
728 -- Check that signature type variables are OK
729 ; final_qtvs <- checkSigsTyVars qtvs sigs
731 ; returnM (final_qtvs, sig_lie, binds) }
733 bndrs = bndrNames mono_infos
734 sigs = [sig | (_, Just sig, _) <- mono_infos]
735 tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos
736 -- NB: exactTyVarsOfType; see Note [Silly type synonym]
737 -- near defn of TcType.exactTyVarsOfType
738 is_mono_sig sig = null (sig_theta sig)
739 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
741 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
742 sig_theta = theta, sig_loc = loc }) mono_id
743 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
744 tci_theta = theta, tci_loc = loc}
747 unifyCtxts checks that all the signature contexts are the same
748 The type signatures on a mutually-recursive group of definitions
749 must all have the same context (or none).
751 The trick here is that all the signatures should have the same
752 context, and we want to share type variables for that context, so that
753 all the right hand sides agree a common vocabulary for their type
756 We unify them because, with polymorphic recursion, their types
757 might not otherwise be related. This is a rather subtle issue.
760 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
761 -- Post-condition: the returned Insts are full zonked
762 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
763 = do { mapM unify_ctxt sigs
764 ; theta <- zonkTcThetaType (sig_theta sig1)
765 ; newDictBndrs (sig_loc sig1) theta }
767 theta1 = sig_theta sig1
768 unify_ctxt :: TcSigInfo -> TcM ()
769 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
770 = setSrcSpan (instLocSpan (sig_loc sig)) $
771 addErrCtxt (sigContextsCtxt sig1 sig) $
772 unifyTheta theta1 theta
774 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
775 checkSigsTyVars qtvs sigs
776 = do { gbl_tvs <- tcGetGlobalTyVars
777 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
779 ; let -- Sigh. Make sure that all the tyvars in the type sigs
780 -- appear in the returned ty var list, which is what we are
781 -- going to generalise over. Reason: we occasionally get
783 -- type T a = () -> ()
786 -- Here, 'a' won't appear in qtvs, so we have to add it
787 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
788 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
791 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
792 sig_theta = theta, sig_tau = tau})
793 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
794 addErrCtxtM (sigCtxt id tvs theta tau) $
795 do { tvs' <- checkDistinctTyVars tvs
796 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
797 (bleatEscapedTvs gbl_tvs tvs tvs')
800 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
801 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
802 -- are still all type variables, and all distinct from each other.
803 -- It returns a zonked set of type variables.
804 -- For example, if the type sig is
805 -- f :: forall a b. a -> b -> b
806 -- we want to check that 'a' and 'b' haven't
807 -- (a) been unified with a non-tyvar type
808 -- (b) been unified with each other (all distinct)
810 checkDistinctTyVars sig_tvs
811 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
812 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
813 ; return zonked_tvs }
815 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
816 -- The TyVarEnv maps each zonked type variable back to its
817 -- corresponding user-written signature type variable
818 check_dup acc (sig_tv, zonked_tv)
819 = case lookupVarEnv acc zonked_tv of
820 Just sig_tv' -> bomb_out sig_tv sig_tv'
822 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
824 bomb_out sig_tv1 sig_tv2
825 = do { env0 <- tcInitTidyEnv
826 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
827 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
828 msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
829 <+> ptext SLIT("is unified with another quantified type variable")
830 <+> quotes (ppr tidy_tv2)
831 ; failWithTcM (env2, msg) }
836 @getTyVarsToGen@ decides what type variables to generalise over.
838 For a "restricted group" -- see the monomorphism restriction
839 for a definition -- we bind no dictionaries, and
840 remove from tyvars_to_gen any constrained type variables
842 *Don't* simplify dicts at this point, because we aren't going
843 to generalise over these dicts. By the time we do simplify them
844 we may well know more. For example (this actually came up)
846 f x = array ... xs where xs = [1,2,3,4,5]
847 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
848 stuff. If we simplify only at the f-binding (not the xs-binding)
849 we'll know that the literals are all Ints, and we can just produce
852 Find all the type variables involved in overloading, the
853 "constrained_tyvars". These are the ones we *aren't* going to
854 generalise. We must be careful about doing this:
856 (a) If we fail to generalise a tyvar which is not actually
857 constrained, then it will never, ever get bound, and lands
858 up printed out in interface files! Notorious example:
859 instance Eq a => Eq (Foo a b) where ..
860 Here, b is not constrained, even though it looks as if it is.
861 Another, more common, example is when there's a Method inst in
862 the LIE, whose type might very well involve non-overloaded
864 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
865 the simple thing instead]
867 (b) On the other hand, we mustn't generalise tyvars which are constrained,
868 because we are going to pass on out the unmodified LIE, with those
869 tyvars in it. They won't be in scope if we've generalised them.
871 So we are careful, and do a complete simplification just to find the
872 constrained tyvars. We don't use any of the results, except to
873 find which tyvars are constrained.
875 Note [Polymorphic recursion]
876 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
877 The game plan for polymorphic recursion in the code above is
879 * Bind any variable for which we have a type signature
880 to an Id with a polymorphic type. Then when type-checking
881 the RHSs we'll make a full polymorphic call.
883 This fine, but if you aren't a bit careful you end up with a horrendous
884 amount of partial application and (worse) a huge space leak. For example:
886 f :: Eq a => [a] -> [a]
889 If we don't take care, after typechecking we get
891 f = /\a -> \d::Eq a -> let f' = f a d
895 Notice the the stupid construction of (f a d), which is of course
896 identical to the function we're executing. In this case, the
897 polymorphic recursion isn't being used (but that's a very common case).
898 This can lead to a massive space leak, from the following top-level defn
904 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
905 f' is another thunk which evaluates to the same thing... and you end
906 up with a chain of identical values all hung onto by the CAF ff.
910 = let f' = f Int dEqInt in \ys. ...f'...
912 = let f' = let f' = f Int dEqInt in \ys. ...f'...
917 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
918 which would make the space leak go away in this case
920 Solution: when typechecking the RHSs we always have in hand the
921 *monomorphic* Ids for each binding. So we just need to make sure that
922 if (Method f a d) shows up in the constraints emerging from (...f...)
923 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
924 to the "givens" when simplifying constraints. That's what the "lies_avail"
929 f = /\a -> \d::Eq a -> letrec
930 fm = \ys:[a] -> ...fm...
936 %************************************************************************
940 %************************************************************************
942 Type signatures are tricky. See Note [Signature skolems] in TcType
944 @tcSigs@ checks the signatures for validity, and returns a list of
945 {\em freshly-instantiated} signatures. That is, the types are already
946 split up, and have fresh type variables installed. All non-type-signature
947 "RenamedSigs" are ignored.
949 The @TcSigInfo@ contains @TcTypes@ because they are unified with
950 the variable's type, and after that checked to see whether they've
954 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
955 -- type variables brought into scope
956 -- by its type signature.
957 -- Nothing => no type signature
959 mkTcSigFun :: [LSig Name] -> TcSigFun
960 -- Search for a particular type signature
961 -- Precondition: the sigs are all type sigs
962 -- Precondition: no duplicates
963 mkTcSigFun sigs = lookupNameEnv env
965 env = mkNameEnv [(name, hsExplicitTvs lhs_ty)
966 | L span (TypeSig (L _ name) lhs_ty) <- sigs]
967 -- The scoped names are the ones explicitly mentioned
968 -- in the HsForAll. (There may be more in sigma_ty, because
969 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
970 -- See Note [Only scoped tyvars are in the TyVarEnv]
975 sig_id :: TcId, -- *Polymorphic* binder for this value...
977 sig_scoped :: [Name], -- Names for any scoped type variables
978 -- Invariant: correspond 1-1 with an initial
979 -- segment of sig_tvs (see Note [Scoped])
981 sig_tvs :: [TcTyVar], -- Instantiated type variables
982 -- See Note [Instantiate sig]
984 sig_theta :: TcThetaType, -- Instantiated theta
985 sig_tau :: TcTauType, -- Instantiated tau
986 sig_loc :: InstLoc -- The location of the signature
990 -- Note [Only scoped tyvars are in the TyVarEnv]
991 -- We are careful to keep only the *lexically scoped* type variables in
992 -- the type environment. Why? After all, the renamer has ensured
993 -- that only legal occurrences occur, so we could put all type variables
994 -- into the type env.
996 -- But we want to check that two distinct lexically scoped type variables
997 -- do not map to the same internal type variable. So we need to know which
998 -- the lexically-scoped ones are... and at the moment we do that by putting
999 -- only the lexically scoped ones into the environment.
1003 -- There may be more instantiated type variables than scoped
1004 -- ones. For example:
1005 -- type T a = forall b. b -> (a,b)
1006 -- f :: forall c. T c
1007 -- Here, the signature for f will have one scoped type variable, c,
1008 -- but two instantiated type variables, c' and b'.
1010 -- We assume that the scoped ones are at the *front* of sig_tvs,
1011 -- and remember the names from the original HsForAllTy in sig_scoped
1013 -- Note [Instantiate sig]
1014 -- It's vital to instantiate a type signature with fresh variables.
1016 -- type S = forall a. a->a
1020 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1021 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1022 -- it's all cool; each signature has distinct type variables from the renamer.)
1024 instance Outputable TcSigInfo where
1025 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1026 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
1030 tcTySig :: LSig Name -> TcM TcId
1031 tcTySig (L span (TypeSig (L _ name) ty))
1033 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1034 ; return (mkLocalId name sigma_ty) }
1037 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1038 -- Instantiate with *meta* type variables;
1039 -- this signature is part of a multi-signature group
1040 tcInstSig_maybe sig_fn name
1041 = case sig_fn name of
1042 Nothing -> return Nothing
1043 Just tvs -> do { tc_sig <- tcInstSig False name tvs
1044 ; return (Just tc_sig) }
1046 tcInstSig :: Bool -> Name -> [Name] -> TcM TcSigInfo
1047 -- Instantiate the signature, with either skolems or meta-type variables
1048 -- depending on the use_skols boolean. This variable is set True
1049 -- when we are typechecking a single function binding; and False for
1050 -- pattern bindings and a group of several function bindings.
1051 -- Reason: in the latter cases, the "skolems" can be unified together,
1052 -- so they aren't properly rigid in the type-refinement sense.
1053 -- NB: unless we are doing H98, each function with a sig will be done
1054 -- separately, even if it's mutually recursive, so use_skols will be True
1056 -- We always instantiate with fresh uniques,
1057 -- although we keep the same print-name
1059 -- type T = forall a. [a] -> [a]
1061 -- f = g where { g :: T; g = <rhs> }
1063 -- We must not use the same 'a' from the defn of T at both places!!
1065 tcInstSig use_skols name scoped_names
1066 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1067 -- scope when starting the binding group
1068 ; let skol_info = SigSkol (FunSigCtxt name)
1069 inst_tyvars = tcInstSigTyVars use_skols skol_info
1070 ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
1071 ; loc <- getInstLoc (SigOrigin skol_info)
1072 ; return (TcSigInfo { sig_id = poly_id,
1073 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1074 sig_scoped = final_scoped_names, sig_loc = loc }) }
1075 -- Note that the scoped_names and the sig_tvs will have
1076 -- different Names. That's quite ok; when we bring the
1077 -- scoped_names into scope, we just bind them to the sig_tvs
1079 -- We also only have scoped type variables when we are instantiating
1080 -- with true skolems
1081 final_scoped_names | use_skols = scoped_names
1085 isMonoGroup :: DynFlags -> [LHsBind Name] -> Bool
1086 -- No generalisation at all
1087 isMonoGroup dflags binds
1088 = dopt Opt_MonoPatBinds dflags && any is_pat_bind binds
1090 is_pat_bind (L _ (PatBind {})) = True
1091 is_pat_bind other = False
1094 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1095 isRestrictedGroup dflags binds sig_fn
1096 = mono_restriction && not all_unrestricted
1098 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1099 all_unrestricted = all (unrestricted . unLoc) binds
1100 has_sig n = isJust (sig_fn n)
1102 unrestricted (PatBind {}) = False
1103 unrestricted (VarBind { var_id = v }) = has_sig v
1104 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1105 || has_sig (unLoc v)
1107 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1108 -- No args => like a pattern binding
1109 unrestricted_match other = True
1110 -- Some args => a function binding
1114 %************************************************************************
1116 \subsection[TcBinds-errors]{Error contexts and messages}
1118 %************************************************************************
1122 -- This one is called on LHS, when pat and grhss are both Name
1123 -- and on RHS, when pat is TcId and grhss is still Name
1124 patMonoBindsCtxt pat grhss
1125 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
1127 -----------------------------------------------
1128 sigContextsCtxt sig1 sig2
1129 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
1130 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1131 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1132 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
1138 -----------------------------------------------
1139 unboxedTupleErr name ty
1140 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
1141 4 (ppr name <+> dcolon <+> ppr ty)
1143 -----------------------------------------------
1144 restrictedBindCtxtErr binder_names
1145 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
1146 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
1147 ptext SLIT("that falls under the monomorphism restriction")])
1149 genCtxt binder_names
1150 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
1152 missingSigWarn False name ty = return ()
1153 missingSigWarn True name ty
1154 = do { env0 <- tcInitTidyEnv
1155 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1156 ; addWarnTcM (env1, mk_msg tidy_ty) }
1158 mk_msg ty = vcat [ptext SLIT("Definition but no type signature for") <+> quotes (ppr name),
1159 sep [ptext SLIT("Inferred type:") <+> ppr name <+> dcolon <+> ppr ty]]