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/Commentary/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
45 import Var ( TyVar, varType )
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_vars = map instToVar dicts -- May include equality constraints
348 ; exports <- mapM (mkExport top_lvl prag_fn tyvars_to_gen (map varType dict_vars))
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
381 -- poly_id has a zonked type
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 { poly_ty' <- zonkTcType poly_ty
391 ; missingSigWarn warn poly_name poly_ty'
392 ; return (inferred_tvs, mkLocalId poly_name poly_ty') }
393 mk_poly_id warn (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
394 ; return (tvs, sig_id sig) }
396 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
398 ------------------------
399 type TcPragFun = Name -> [LSig Name]
401 mkPragFun :: [LSig Name] -> TcPragFun
402 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
404 prs = [(expectJust "mkPragFun" (sigName sig), sig)
405 | sig <- sigs, isPragLSig sig]
406 env = foldl add emptyNameEnv prs
407 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
409 tcPrags :: Id -> [LSig Name] -> TcM [LPrag]
410 tcPrags poly_id prags = mapM (wrapLocM tc_prag) prags
412 tc_prag prag = addErrCtxt (pragSigCtxt prag) $
415 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
417 tcPrag :: TcId -> Sig Name -> TcM Prag
418 -- Pre-condition: the poly_id is zonked
419 -- Reason: required by tcSubExp
420 tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
421 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
422 tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
425 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
426 tcSpecPrag poly_id hs_ty inl
427 = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
428 ; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty)
430 ; let const_dicts = map instToId lie
431 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty const_dicts inl) }
432 -- Most of the work of specialisation is done by
433 -- the desugarer, guided by the SpecPrag
436 -- If typechecking the binds fails, then return with each
437 -- signature-less binder given type (forall a.a), to minimise
438 -- subsequent error messages
439 recoveryCode binder_names sig_fn
440 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
441 ; poly_ids <- mapM mk_dummy binder_names
442 ; return ([], poly_ids) }
445 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
446 | otherwise = return (mkLocalId name forall_a_a) -- No signature
449 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
452 -- Check that non-overloaded unlifted bindings are
455 -- c) not a multiple-binding group (more or less implied by (a))
457 checkStrictBinds :: TopLevelFlag -> RecFlag
458 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
460 checkStrictBinds top_lvl rec_group mbind mono_tys infos
461 | unlifted || bang_pat
462 = do { checkTc (isNotTopLevel top_lvl)
463 (strictBindErr "Top-level" unlifted mbind)
464 ; checkTc (isNonRec rec_group)
465 (strictBindErr "Recursive" unlifted mbind)
466 ; checkTc (isSingletonBag mbind)
467 (strictBindErr "Multiple" unlifted mbind)
468 ; mapM_ check_sig infos
473 unlifted = any isUnLiftedType mono_tys
474 bang_pat = anyBag (isBangHsBind . unLoc) mbind
475 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
476 (badStrictSig unlifted sig)
477 check_sig other = return ()
479 strictBindErr flavour unlifted mbind
480 = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:"))
481 4 (pprLHsBinds mbind)
483 msg | unlifted = ptext SLIT("bindings for unlifted types")
484 | otherwise = ptext SLIT("bang-pattern bindings")
486 badStrictSig unlifted sig
487 = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
490 msg | unlifted = ptext SLIT("an unlifted binding")
491 | otherwise = ptext SLIT("a bang-pattern binding")
495 %************************************************************************
497 \subsection{tcMonoBind}
499 %************************************************************************
501 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
502 The signatures have been dealt with already.
505 tcMonoBinds :: [LHsBind Name]
507 -> RecFlag -- Whether the binding is recursive for typechecking purposes
508 -- i.e. the binders are mentioned in their RHSs, and
509 -- we are not resuced by a type signature
510 -> TcM (LHsBinds TcId, [MonoBindInfo])
512 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
513 fun_matches = matches, bind_fvs = fvs })]
514 sig_fn -- Single function binding,
515 NonRecursive -- binder isn't mentioned in RHS,
516 | Nothing <- sig_fn name -- ...with no type signature
517 = -- In this very special case we infer the type of the
518 -- right hand side first (it may have a higher-rank type)
519 -- and *then* make the monomorphic Id for the LHS
520 -- e.g. f = \(x::forall a. a->a) -> <body>
521 -- We want to infer a higher-rank type for f
523 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
525 -- Check for an unboxed tuple type
526 -- f = (# True, False #)
527 -- Zonk first just in case it's hidden inside a meta type variable
528 -- (This shows up as a (more obscure) kind error
529 -- in the 'otherwise' case of tcMonoBinds.)
530 ; zonked_rhs_ty <- zonkTcType rhs_ty
531 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
532 (unboxedTupleErr name zonked_rhs_ty)
534 ; mono_name <- newLocalName name
535 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
536 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
537 fun_matches = matches', bind_fvs = fvs,
538 fun_co_fn = co_fn, fun_tick = Nothing })),
539 [(name, Nothing, mono_id)]) }
541 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
542 fun_matches = matches, bind_fvs = fvs })]
543 sig_fn -- Single function binding
545 | Just scoped_tvs <- sig_fn name -- ...with a type signature
546 = -- When we have a single function binding, with a type signature
547 -- we can (a) use genuine, rigid skolem constants for the type variables
548 -- (b) bring (rigid) scoped type variables into scope
550 do { tc_sig <- tcInstSig True name scoped_tvs
551 ; mono_name <- newLocalName name
552 ; let mono_ty = sig_tau tc_sig
553 mono_id = mkLocalId mono_name mono_ty
554 rhs_tvs = [ (name, mkTyVarTy tv)
555 | (name, tv) <- sig_scoped tc_sig `zip` sig_tvs tc_sig ]
557 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
558 tcMatchesFun mono_name inf matches mono_ty
560 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
561 fun_infix = inf, fun_matches = matches',
562 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
564 ; return (unitBag (L b_loc fun_bind'),
565 [(name, Just tc_sig, mono_id)]) }
567 tcMonoBinds binds sig_fn non_rec
568 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
570 -- Bring the monomorphic Ids, into scope for the RHSs
571 ; let mono_info = getMonoBindInfo tc_binds
572 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
573 -- A monomorphic binding for each term variable that lacks
574 -- a type sig. (Ones with a sig are already in scope.)
576 ; binds' <- tcExtendIdEnv2 rhs_id_env $
577 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
578 | (n,id) <- rhs_id_env]) `thenM_`
579 mapM (wrapLocM tcRhs) tc_binds
580 ; return (listToBag binds', mono_info) }
582 ------------------------
583 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
584 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
585 -- if there's a signature for it, use the instantiated signature type
586 -- otherwise invent a type variable
587 -- You see that quite directly in the FunBind case.
589 -- But there's a complication for pattern bindings:
590 -- data T = MkT (forall a. a->a)
592 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
593 -- but we want to get (f::forall a. a->a) as the RHS environment.
594 -- The simplest way to do this is to typecheck the pattern, and then look up the
595 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
596 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
598 data TcMonoBind -- Half completed; LHS done, RHS not done
599 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
600 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
602 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
603 -- Type signature (if any), and
604 -- the monomorphic bound things
606 bndrNames :: [MonoBindInfo] -> [Name]
607 bndrNames mbi = [n | (n,_,_) <- mbi]
609 getMonoType :: MonoBindInfo -> TcTauType
610 getMonoType (_,_,mono_id) = idType mono_id
612 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
613 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
614 = do { mb_sig <- tcInstSig_maybe sig_fn name
615 ; mono_name <- newLocalName name
616 ; mono_ty <- mk_mono_ty mb_sig
617 ; let mono_id = mkLocalId mono_name mono_ty
618 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
620 mk_mono_ty (Just sig) = return (sig_tau sig)
621 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
623 tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
624 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
625 ; mono_pat_binds <- doptM Opt_MonoPatBinds
626 -- With -fmono-pat-binds, we do no generalisation of pattern bindings
627 -- But the signature can still be polymoprhic!
628 -- data T = MkT (forall a. a->a)
629 -- x :: forall a. a->a
631 -- The function get_sig_ty decides whether the pattern-bound variables
632 -- should have exactly the type in the type signature (-fmono-pat-binds),
633 -- or the instantiated version (-fmono-pat-binds)
635 ; let nm_sig_prs = names `zip` mb_sigs
636 get_sig_ty | mono_pat_binds = idType . sig_id
637 | otherwise = sig_tau
638 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
639 | (name, Just sig) <- nm_sig_prs]
640 sig_tau_fn = lookupNameEnv tau_sig_env
642 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
643 mapM lookup_info nm_sig_prs
645 -- After typechecking the pattern, look up the binder
646 -- names, which the pattern has brought into scope.
647 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
648 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
649 ; return (name, mb_sig, mono_id) }
651 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
654 ; return (TcPatBind infos pat' grhss pat_ty) }
656 names = collectPatBinders pat
659 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
660 -- AbsBind, VarBind impossible
663 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
664 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
665 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
666 matches (idType mono_id)
667 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
668 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
669 fun_tick = Nothing }) }
671 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
672 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
673 tcGRHSsPat grhss pat_ty
674 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
675 bind_fvs = placeHolderNames }) }
678 ---------------------
679 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
680 getMonoBindInfo tc_binds
681 = foldr (get_info . unLoc) [] tc_binds
683 get_info (TcFunBind info _ _ _) rest = info : rest
684 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
688 %************************************************************************
692 %************************************************************************
695 generalise :: DynFlags -> TopLevelFlag
696 -> [LHsBind Name] -> TcSigFun
697 -> [MonoBindInfo] -> [Inst]
698 -> TcM ([TyVar], [Inst], TcDictBinds)
699 -- The returned [TyVar] are all ready to quantify
701 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
702 | isMonoGroup dflags bind_list
703 = do { extendLIEs lie_req
704 ; return ([], [], emptyBag) }
706 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
707 = -- Check signature contexts are empty
708 do { checkTc (all is_mono_sig sigs)
709 (restrictedBindCtxtErr bndrs)
711 -- Now simplify with exactly that set of tyvars
712 -- We have to squash those Methods
713 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
716 -- Check that signature type variables are OK
717 ; final_qtvs <- checkSigsTyVars qtvs sigs
719 ; return (final_qtvs, [], binds) }
721 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
722 = tcSimplifyInfer doc tau_tvs lie_req
724 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
725 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
726 ; let -- The "sig_avails" is the stuff available. We get that from
727 -- the context of the type signature, BUT ALSO the lie_avail
728 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
729 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
730 sig_avails = sig_lie ++ local_meths
731 loc = sig_loc (head sigs)
733 -- Check that the needed dicts can be
734 -- expressed in terms of the signature ones
735 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
737 -- Check that signature type variables are OK
738 ; final_qtvs <- checkSigsTyVars qtvs sigs
740 ; returnM (final_qtvs, sig_lie, binds) }
742 bndrs = bndrNames mono_infos
743 sigs = [sig | (_, Just sig, _) <- mono_infos]
744 get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
745 | otherwise = exactTyVarsOfType
746 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
747 is_mono_sig sig = null (sig_theta sig)
748 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
750 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
751 sig_theta = theta, sig_loc = loc }) mono_id
752 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
753 tci_theta = theta, tci_loc = loc}
756 unifyCtxts checks that all the signature contexts are the same
757 The type signatures on a mutually-recursive group of definitions
758 must all have the same context (or none).
760 The trick here is that all the signatures should have the same
761 context, and we want to share type variables for that context, so that
762 all the right hand sides agree a common vocabulary for their type
765 We unify them because, with polymorphic recursion, their types
766 might not otherwise be related. This is a rather subtle issue.
769 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
770 -- Post-condition: the returned Insts are full zonked
771 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
772 = do { mapM unify_ctxt sigs
773 ; theta <- zonkTcThetaType (sig_theta sig1)
774 ; newDictBndrs (sig_loc sig1) theta }
776 theta1 = sig_theta sig1
777 unify_ctxt :: TcSigInfo -> TcM ()
778 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
779 = setSrcSpan (instLocSpan (sig_loc sig)) $
780 addErrCtxt (sigContextsCtxt sig1 sig) $
781 do { cois <- unifyTheta theta1 theta
782 ; -- Check whether all coercions are identity coercions
783 -- That can happen if we have, say
785 -- g :: C (F a) => ...
786 -- where F is a type function and (F a ~ [a])
787 -- Then unification might succeed with a coercion. But it's much
788 -- much simpler to require that such signatures have identical contexts
789 checkTc (all isIdentityCoercion cois)
790 (ptext SLIT("Mutually dependent functions have syntactically distinct contexts"))
793 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
794 checkSigsTyVars qtvs sigs
795 = do { gbl_tvs <- tcGetGlobalTyVars
796 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
798 ; let -- Sigh. Make sure that all the tyvars in the type sigs
799 -- appear in the returned ty var list, which is what we are
800 -- going to generalise over. Reason: we occasionally get
802 -- type T a = () -> ()
805 -- Here, 'a' won't appear in qtvs, so we have to add it
806 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
807 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
810 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
811 sig_theta = theta, sig_tau = tau})
812 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
813 addErrCtxtM (sigCtxt id tvs theta tau) $
814 do { tvs' <- checkDistinctTyVars tvs
815 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
816 (bleatEscapedTvs gbl_tvs tvs tvs')
819 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
820 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
821 -- are still all type variables, and all distinct from each other.
822 -- It returns a zonked set of type variables.
823 -- For example, if the type sig is
824 -- f :: forall a b. a -> b -> b
825 -- we want to check that 'a' and 'b' haven't
826 -- (a) been unified with a non-tyvar type
827 -- (b) been unified with each other (all distinct)
829 checkDistinctTyVars sig_tvs
830 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
831 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
832 ; return zonked_tvs }
834 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
835 -- The TyVarEnv maps each zonked type variable back to its
836 -- corresponding user-written signature type variable
837 check_dup acc (sig_tv, zonked_tv)
838 = case lookupVarEnv acc zonked_tv of
839 Just sig_tv' -> bomb_out sig_tv sig_tv'
841 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
843 bomb_out sig_tv1 sig_tv2
844 = do { env0 <- tcInitTidyEnv
845 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
846 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
847 msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
848 <+> ptext SLIT("is unified with another quantified type variable")
849 <+> quotes (ppr tidy_tv2)
850 ; failWithTcM (env2, msg) }
855 @getTyVarsToGen@ decides what type variables to generalise over.
857 For a "restricted group" -- see the monomorphism restriction
858 for a definition -- we bind no dictionaries, and
859 remove from tyvars_to_gen any constrained type variables
861 *Don't* simplify dicts at this point, because we aren't going
862 to generalise over these dicts. By the time we do simplify them
863 we may well know more. For example (this actually came up)
865 f x = array ... xs where xs = [1,2,3,4,5]
866 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
867 stuff. If we simplify only at the f-binding (not the xs-binding)
868 we'll know that the literals are all Ints, and we can just produce
871 Find all the type variables involved in overloading, the
872 "constrained_tyvars". These are the ones we *aren't* going to
873 generalise. We must be careful about doing this:
875 (a) If we fail to generalise a tyvar which is not actually
876 constrained, then it will never, ever get bound, and lands
877 up printed out in interface files! Notorious example:
878 instance Eq a => Eq (Foo a b) where ..
879 Here, b is not constrained, even though it looks as if it is.
880 Another, more common, example is when there's a Method inst in
881 the LIE, whose type might very well involve non-overloaded
883 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
884 the simple thing instead]
886 (b) On the other hand, we mustn't generalise tyvars which are constrained,
887 because we are going to pass on out the unmodified LIE, with those
888 tyvars in it. They won't be in scope if we've generalised them.
890 So we are careful, and do a complete simplification just to find the
891 constrained tyvars. We don't use any of the results, except to
892 find which tyvars are constrained.
894 Note [Polymorphic recursion]
895 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
896 The game plan for polymorphic recursion in the code above is
898 * Bind any variable for which we have a type signature
899 to an Id with a polymorphic type. Then when type-checking
900 the RHSs we'll make a full polymorphic call.
902 This fine, but if you aren't a bit careful you end up with a horrendous
903 amount of partial application and (worse) a huge space leak. For example:
905 f :: Eq a => [a] -> [a]
908 If we don't take care, after typechecking we get
910 f = /\a -> \d::Eq a -> let f' = f a d
914 Notice the the stupid construction of (f a d), which is of course
915 identical to the function we're executing. In this case, the
916 polymorphic recursion isn't being used (but that's a very common case).
917 This can lead to a massive space leak, from the following top-level defn
923 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
924 f' is another thunk which evaluates to the same thing... and you end
925 up with a chain of identical values all hung onto by the CAF ff.
929 = let f' = f Int dEqInt in \ys. ...f'...
931 = let f' = let f' = f Int dEqInt in \ys. ...f'...
936 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
937 which would make the space leak go away in this case
939 Solution: when typechecking the RHSs we always have in hand the
940 *monomorphic* Ids for each binding. So we just need to make sure that
941 if (Method f a d) shows up in the constraints emerging from (...f...)
942 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
943 to the "givens" when simplifying constraints. That's what the "lies_avail"
948 f = /\a -> \d::Eq a -> letrec
949 fm = \ys:[a] -> ...fm...
955 %************************************************************************
959 %************************************************************************
961 Type signatures are tricky. See Note [Signature skolems] in TcType
963 @tcSigs@ checks the signatures for validity, and returns a list of
964 {\em freshly-instantiated} signatures. That is, the types are already
965 split up, and have fresh type variables installed. All non-type-signature
966 "RenamedSigs" are ignored.
968 The @TcSigInfo@ contains @TcTypes@ because they are unified with
969 the variable's type, and after that checked to see whether they've
973 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
974 -- type variables brought into scope
975 -- by its type signature.
976 -- Nothing => no type signature
978 mkTcSigFun :: [LSig Name] -> TcSigFun
979 -- Search for a particular type signature
980 -- Precondition: the sigs are all type sigs
981 -- Precondition: no duplicates
982 mkTcSigFun sigs = lookupNameEnv env
984 env = mkNameEnv [(name, hsExplicitTvs lhs_ty)
985 | L span (TypeSig (L _ name) lhs_ty) <- sigs]
986 -- The scoped names are the ones explicitly mentioned
987 -- in the HsForAll. (There may be more in sigma_ty, because
988 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
989 -- See Note [Only scoped tyvars are in the TyVarEnv]
994 sig_id :: TcId, -- *Polymorphic* binder for this value...
996 sig_scoped :: [Name], -- Names for any scoped type variables
997 -- Invariant: correspond 1-1 with an initial
998 -- segment of sig_tvs (see Note [Scoped])
1000 sig_tvs :: [TcTyVar], -- Instantiated type variables
1001 -- See Note [Instantiate sig]
1003 sig_theta :: TcThetaType, -- Instantiated theta
1004 sig_tau :: TcTauType, -- Instantiated tau
1005 sig_loc :: InstLoc -- The location of the signature
1009 -- Note [Only scoped tyvars are in the TyVarEnv]
1010 -- We are careful to keep only the *lexically scoped* type variables in
1011 -- the type environment. Why? After all, the renamer has ensured
1012 -- that only legal occurrences occur, so we could put all type variables
1013 -- into the type env.
1015 -- But we want to check that two distinct lexically scoped type variables
1016 -- do not map to the same internal type variable. So we need to know which
1017 -- the lexically-scoped ones are... and at the moment we do that by putting
1018 -- only the lexically scoped ones into the environment.
1022 -- There may be more instantiated type variables than scoped
1023 -- ones. For example:
1024 -- type T a = forall b. b -> (a,b)
1025 -- f :: forall c. T c
1026 -- Here, the signature for f will have one scoped type variable, c,
1027 -- but two instantiated type variables, c' and b'.
1029 -- We assume that the scoped ones are at the *front* of sig_tvs,
1030 -- and remember the names from the original HsForAllTy in sig_scoped
1032 -- Note [Instantiate sig]
1033 -- It's vital to instantiate a type signature with fresh variables.
1035 -- type S = forall a. a->a
1039 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1040 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1041 -- it's all cool; each signature has distinct type variables from the renamer.)
1043 instance Outputable TcSigInfo where
1044 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1045 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
1049 tcTySig :: LSig Name -> TcM TcId
1050 tcTySig (L span (TypeSig (L _ name) ty))
1052 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1053 ; return (mkLocalId name sigma_ty) }
1056 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1057 -- Instantiate with *meta* type variables;
1058 -- this signature is part of a multi-signature group
1059 tcInstSig_maybe sig_fn name
1060 = case sig_fn name of
1061 Nothing -> return Nothing
1062 Just tvs -> do { tc_sig <- tcInstSig False name tvs
1063 ; return (Just tc_sig) }
1065 tcInstSig :: Bool -> Name -> [Name] -> TcM TcSigInfo
1066 -- Instantiate the signature, with either skolems or meta-type variables
1067 -- depending on the use_skols boolean. This variable is set True
1068 -- when we are typechecking a single function binding; and False for
1069 -- pattern bindings and a group of several function bindings.
1070 -- Reason: in the latter cases, the "skolems" can be unified together,
1071 -- so they aren't properly rigid in the type-refinement sense.
1072 -- NB: unless we are doing H98, each function with a sig will be done
1073 -- separately, even if it's mutually recursive, so use_skols will be True
1075 -- We always instantiate with fresh uniques,
1076 -- although we keep the same print-name
1078 -- type T = forall a. [a] -> [a]
1080 -- f = g where { g :: T; g = <rhs> }
1082 -- We must not use the same 'a' from the defn of T at both places!!
1084 tcInstSig use_skols name scoped_names
1085 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1086 -- scope when starting the binding group
1087 ; let skol_info = SigSkol (FunSigCtxt name)
1088 inst_tyvars = tcInstSigTyVars use_skols skol_info
1089 ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
1090 ; loc <- getInstLoc (SigOrigin skol_info)
1091 ; return (TcSigInfo { sig_id = poly_id,
1092 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1093 sig_scoped = final_scoped_names, sig_loc = loc }) }
1094 -- Note that the scoped_names and the sig_tvs will have
1095 -- different Names. That's quite ok; when we bring the
1096 -- scoped_names into scope, we just bind them to the sig_tvs
1098 -- We also only have scoped type variables when we are instantiating
1099 -- with true skolems
1100 final_scoped_names | use_skols = scoped_names
1104 isMonoGroup :: DynFlags -> [LHsBind Name] -> Bool
1105 -- No generalisation at all
1106 isMonoGroup dflags binds
1107 = dopt Opt_MonoPatBinds dflags && any is_pat_bind binds
1109 is_pat_bind (L _ (PatBind {})) = True
1110 is_pat_bind other = False
1113 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1114 isRestrictedGroup dflags binds sig_fn
1115 = mono_restriction && not all_unrestricted
1117 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1118 all_unrestricted = all (unrestricted . unLoc) binds
1119 has_sig n = isJust (sig_fn n)
1121 unrestricted (PatBind {}) = False
1122 unrestricted (VarBind { var_id = v }) = has_sig v
1123 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1124 || has_sig (unLoc v)
1126 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1127 -- No args => like a pattern binding
1128 unrestricted_match other = True
1129 -- Some args => a function binding
1133 %************************************************************************
1135 \subsection[TcBinds-errors]{Error contexts and messages}
1137 %************************************************************************
1141 -- This one is called on LHS, when pat and grhss are both Name
1142 -- and on RHS, when pat is TcId and grhss is still Name
1143 patMonoBindsCtxt pat grhss
1144 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
1146 -----------------------------------------------
1147 sigContextsCtxt sig1 sig2
1148 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
1149 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1150 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1151 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
1157 -----------------------------------------------
1158 unboxedTupleErr name ty
1159 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
1160 4 (ppr name <+> dcolon <+> ppr ty)
1162 -----------------------------------------------
1163 restrictedBindCtxtErr binder_names
1164 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
1165 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
1166 ptext SLIT("that falls under the monomorphism restriction")])
1168 genCtxt binder_names
1169 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
1171 missingSigWarn False name ty = return ()
1172 missingSigWarn True name ty
1173 = do { env0 <- tcInitTidyEnv
1174 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1175 ; addWarnTcM (env1, mk_msg tidy_ty) }
1177 mk_msg ty = vcat [ptext SLIT("Definition but no type signature for") <+> quotes (ppr name),
1178 sep [ptext SLIT("Inferred type:") <+> ppr name <+> dcolon <+> ppr ty]]