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 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
22 import {-# SOURCE #-} TcExpr ( tcMonoExpr )
37 import {- Kind parts of -} Type
43 import Var ( TyVar, varType )
63 %************************************************************************
65 \subsection{Type-checking bindings}
67 %************************************************************************
69 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
70 it needs to know something about the {\em usage} of the things bound,
71 so that it can create specialisations of them. So @tcBindsAndThen@
72 takes a function which, given an extended environment, E, typechecks
73 the scope of the bindings returning a typechecked thing and (most
74 important) an LIE. It is this LIE which is then used as the basis for
75 specialising the things bound.
77 @tcBindsAndThen@ also takes a "combiner" which glues together the
78 bindings and the "thing" to make a new "thing".
80 The real work is done by @tcBindWithSigsAndThen@.
82 Recursive and non-recursive binds are handled in essentially the same
83 way: because of uniques there are no scoping issues left. The only
84 difference is that non-recursive bindings can bind primitive values.
86 Even for non-recursive binding groups we add typings for each binder
87 to the LVE for the following reason. When each individual binding is
88 checked the type of its LHS is unified with that of its RHS; and
89 type-checking the LHS of course requires that the binder is in scope.
91 At the top-level the LIE is sure to contain nothing but constant
92 dictionaries, which we resolve at the module level.
95 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
96 -- Note: returning the TcLclEnv is more than we really
97 -- want. The bit we care about is the local bindings
98 -- and the free type variables thereof
100 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
101 ; return (foldr (unionBags . snd) emptyBag prs, env) }
102 -- The top level bindings are flattened into a giant
103 -- implicitly-mutually-recursive LHsBinds
105 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
106 -- A hs-boot file has only one BindGroup, and it only has type
107 -- signatures in it. The renamer checked all this
108 tcHsBootSigs (ValBindsOut binds sigs)
109 = do { checkTc (null binds) badBootDeclErr
110 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
112 tc_boot_sig (TypeSig (L _ name) ty)
113 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
114 ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
115 -- Notice that we make GlobalIds, not LocalIds
116 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
118 badBootDeclErr :: Message
119 badBootDeclErr = ptext (sLit "Illegal declarations in an hs-boot file")
121 ------------------------
122 tcLocalBinds :: HsLocalBinds Name -> TcM thing
123 -> TcM (HsLocalBinds TcId, thing)
125 tcLocalBinds EmptyLocalBinds thing_inside
126 = do { thing <- thing_inside
127 ; return (EmptyLocalBinds, thing) }
129 tcLocalBinds (HsValBinds binds) thing_inside
130 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
131 ; return (HsValBinds binds', thing) }
133 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
134 = do { (thing, lie) <- getLIE thing_inside
135 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
137 -- If the binding binds ?x = E, we must now
138 -- discharge any ?x constraints in expr_lie
139 ; dict_binds <- tcSimplifyIPs avail_ips lie
140 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
142 -- I wonder if we should do these one at at time
145 tc_ip_bind (IPBind ip expr) = do
146 ty <- newFlexiTyVarTy argTypeKind
147 (ip', ip_inst) <- newIPDict (IPBindOrigin ip) ip ty
148 expr' <- tcMonoExpr expr ty
149 return (ip_inst, (IPBind ip' expr'))
151 ------------------------
152 tcValBinds :: TopLevelFlag
153 -> HsValBinds Name -> TcM thing
154 -> TcM (HsValBinds TcId, thing)
156 tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
157 = pprPanic "tcValBinds" (ppr binds)
159 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
160 = do { -- Typecheck the signature
161 ; let { prag_fn = mkPragFun sigs
162 ; ty_sigs = filter isVanillaLSig sigs
163 ; sig_fn = mkTcSigFun ty_sigs }
165 ; poly_ids <- mapM tcTySig ty_sigs
166 -- No recovery from bad signatures, because the type sigs
167 -- may bind type variables, so proceeding without them
168 -- can lead to a cascade of errors
169 -- ToDo: this means we fall over immediately if any type sig
170 -- is wrong, which is over-conservative, see Trac bug #745
172 -- Extend the envt right away with all
173 -- the Ids declared with type signatures
174 ; poly_rec <- doptM Opt_RelaxedPolyRec
175 ; (binds', thing) <- tcExtendIdEnv poly_ids $
176 tc_val_binds poly_rec top_lvl sig_fn prag_fn
179 ; return (ValBindsOut binds' sigs, thing) }
181 ------------------------
182 tc_val_binds :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
183 -> [(RecFlag, LHsBinds Name)] -> TcM thing
184 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
185 -- Typecheck a whole lot of value bindings,
186 -- one strongly-connected component at a time
188 tc_val_binds poly_rec top_lvl sig_fn prag_fn [] thing_inside
189 = do { thing <- thing_inside
190 ; return ([], thing) }
192 tc_val_binds poly_rec top_lvl sig_fn prag_fn (group : groups) thing_inside
193 = do { (group', (groups', thing))
194 <- tc_group poly_rec top_lvl sig_fn prag_fn group $
195 tc_val_binds poly_rec top_lvl sig_fn prag_fn groups thing_inside
196 ; return (group' ++ groups', thing) }
198 ------------------------
199 tc_group :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
200 -> (RecFlag, LHsBinds Name) -> TcM thing
201 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
203 -- Typecheck one strongly-connected component of the original program.
204 -- We get a list of groups back, because there may
205 -- be specialisations etc as well
207 tc_group poly_rec top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
208 -- A single non-recursive binding
209 -- We want to keep non-recursive things non-recursive
210 -- so that we desugar unlifted bindings correctly
211 = do { (binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn NonRecursive binds thing_inside
212 ; return ([(NonRecursive, b) | b <- binds], thing) }
214 tc_group poly_rec top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
215 | not poly_rec -- Recursive group, normal Haskell 98 route
216 = do { (binds1, thing) <- tc_haskell98 top_lvl sig_fn prag_fn Recursive binds thing_inside
217 ; return ([(Recursive, unionManyBags binds1)], thing) }
219 | otherwise -- Recursive group, with gla-exts
220 = -- To maximise polymorphism (with -fglasgow-exts), we do a new
221 -- strongly-connected-component analysis, this time omitting
222 -- any references to variables with type signatures.
224 -- Notice that the bindInsts thing covers *all* the bindings in the original
225 -- group at once; an earlier one may use a later one!
226 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
227 ; (binds1,thing) <- bindLocalInsts top_lvl $
228 go (stronglyConnComp (mkEdges sig_fn binds))
229 ; return ([(Recursive, unionManyBags binds1)], thing) }
230 -- Rec them all together
232 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], [TcId], thing)
233 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
234 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
235 ; return (binds1 ++ binds2, ids1 ++ ids2, thing) }
236 go [] = do { thing <- thing_inside; return ([], [], thing) }
238 tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive (unitBag bind)
239 tc_scc (CyclicSCC binds) = tc_sub_group Recursive (listToBag binds)
241 tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
243 tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside
244 = bindLocalInsts top_lvl $ do
245 { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds
246 ; thing <- tcExtendIdEnv ids thing_inside
247 ; return (binds1, ids, thing) }
249 ------------------------
250 bindLocalInsts :: TopLevelFlag -> TcM ([LHsBinds TcId], [TcId], a) -> TcM ([LHsBinds TcId], a)
251 bindLocalInsts top_lvl thing_inside
252 | isTopLevel top_lvl = do { (binds, ids, thing) <- thing_inside; return (binds, thing) }
253 -- For the top level don't bother with all this bindInstsOfLocalFuns stuff.
254 -- All the top level things are rec'd together anyway, so it's fine to
255 -- leave them to the tcSimplifyTop, and quite a bit faster too
257 | otherwise -- Nested case
258 = do { ((binds, ids, thing), lie) <- getLIE thing_inside
259 ; lie_binds <- bindInstsOfLocalFuns lie ids
260 ; return (binds ++ [lie_binds], thing) }
262 ------------------------
263 mkEdges :: TcSigFun -> LHsBinds Name
264 -> [(LHsBind Name, BKey, [BKey])]
266 type BKey = Int -- Just number off the bindings
269 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
270 Just key <- [lookupNameEnv key_map n], no_sig n ])
271 | (bind, key) <- keyd_binds
274 no_sig :: Name -> Bool
275 no_sig n = isNothing (sig_fn n)
277 keyd_binds = bagToList binds `zip` [0::BKey ..]
279 key_map :: NameEnv BKey -- Which binding it comes from
280 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
281 , bndr <- bindersOfHsBind bind ]
283 bindersOfHsBind :: HsBind Name -> [Name]
284 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
285 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
287 ------------------------
288 tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragFun
289 -> RecFlag -- Whether the group is really recursive
290 -> RecFlag -- Whether it's recursive after breaking
291 -- dependencies based on type signatures
293 -> TcM ([LHsBinds TcId], [TcId])
295 -- Typechecks a single bunch of bindings all together,
296 -- and generalises them. The bunch may be only part of a recursive
297 -- group, because we use type signatures to maximise polymorphism
299 -- Returns a list because the input may be a single non-recursive binding,
300 -- in which case the dependency order of the resulting bindings is
303 -- Knows nothing about the scope of the bindings
305 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds
307 bind_list = bagToList binds
308 binder_names = collectHsBindBinders binds
309 loc = getLoc (head bind_list)
310 -- TODO: location a bit awkward, but the mbinds have been
311 -- dependency analysed and may no longer be adjacent
313 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
315 recoverM (recoveryCode binder_names sig_fn) $ do
317 { traceTc (ptext (sLit "------------------------------------------------"))
318 ; traceTc (ptext (sLit "Bindings for") <+> ppr binder_names)
320 -- TYPECHECK THE BINDINGS
321 ; ((binds', mono_bind_infos), lie_req)
322 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
323 ; traceTc (text "temp" <+> (ppr binds' $$ ppr lie_req))
325 -- CHECK FOR UNLIFTED BINDINGS
326 -- These must be non-recursive etc, and are not generalised
327 -- They desugar to a case expression in the end
328 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
329 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
330 zonked_mono_tys mono_bind_infos
332 do { extendLIEs lie_req
333 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
334 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
335 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
336 -- ToDo: prags for unlifted bindings
338 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
339 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
341 else do -- The normal lifted case: GENERALISE
343 ; (tyvars_to_gen, dicts, dict_binds)
344 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
345 generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
347 -- BUILD THE POLYMORPHIC RESULT IDs
348 ; let dict_vars = map instToVar dicts -- May include equality constraints
349 ; exports <- mapM (mkExport top_lvl prag_fn tyvars_to_gen (map varType dict_vars))
352 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
353 ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids))
355 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen
357 (dict_binds `unionBags` binds')
359 ; return ([unitBag abs_bind], poly_ids) -- poly_ids are guaranteed zonked by mkExport
364 mkExport :: TopLevelFlag -> TcPragFun -> [TyVar] -> [TcType]
366 -> TcM ([TyVar], Id, Id, [LPrag])
367 -- mkExport generates exports with
368 -- zonked type variables,
370 -- The former is just because no further unifications will change
371 -- the quantified type variables, so we can fix their final form
373 -- The latter is needed because the poly_ids are used to extend the
374 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
376 -- Pre-condition: the inferred_tvs are already zonked
378 mkExport top_lvl prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
379 = do { warn_missing_sigs <- doptM Opt_WarnMissingSigs
380 ; let warn = isTopLevel top_lvl && warn_missing_sigs
381 ; (tvs, poly_id) <- mk_poly_id warn mb_sig
382 -- poly_id has a zonked type
384 ; prags <- tcPrags poly_id (prag_fn poly_name)
385 -- tcPrags requires a zonked poly_id
387 ; return (tvs, poly_id, mono_id, prags) }
389 poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id))
391 mk_poly_id warn Nothing = do { poly_ty' <- zonkTcType poly_ty
392 ; missingSigWarn warn poly_name poly_ty'
393 ; return (inferred_tvs, mkLocalId poly_name poly_ty') }
394 mk_poly_id warn (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
395 ; return (tvs, sig_id sig) }
397 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
399 ------------------------
400 type TcPragFun = Name -> [LSig Name]
402 mkPragFun :: [LSig Name] -> TcPragFun
403 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
405 prs = [(expectJust "mkPragFun" (sigName sig), sig)
406 | sig <- sigs, isPragLSig sig]
407 env = foldl add emptyNameEnv prs
408 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
410 tcPrags :: Id -> [LSig Name] -> TcM [LPrag]
411 tcPrags poly_id prags = mapM (wrapLocM tc_prag) prags
413 tc_prag prag = addErrCtxt (pragSigCtxt prag) $
416 pragSigCtxt prag = hang (ptext (sLit "In the pragma")) 2 (ppr prag)
418 tcPrag :: TcId -> Sig Name -> TcM Prag
419 -- Pre-condition: the poly_id is zonked
420 -- Reason: required by tcSubExp
421 tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
422 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
423 tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
426 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
427 tcSpecPrag poly_id hs_ty inl
428 = do { let name = idName poly_id
429 ; spec_ty <- tcHsSigType (FunSigCtxt name) hs_ty
430 ; co_fn <- tcSubExp (SpecPragOrigin name) (idType poly_id) spec_ty
431 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty 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
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) <- scoped_tvs `zip` sig_tvs tc_sig ]
556 -- See Note [More instantiated than scoped]
557 -- Note that the scoped_tvs and the (sig_tvs sig)
558 -- may have different Names. That's quite ok.
560 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
561 tcMatchesFun mono_name inf matches mono_ty
563 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
564 fun_infix = inf, fun_matches = matches',
565 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
567 ; return (unitBag (L b_loc fun_bind'),
568 [(name, Just tc_sig, mono_id)]) }
570 tcMonoBinds binds sig_fn non_rec
571 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
573 -- Bring the monomorphic Ids, into scope for the RHSs
574 ; let mono_info = getMonoBindInfo tc_binds
575 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
576 -- A monomorphic binding for each term variable that lacks
577 -- a type sig. (Ones with a sig are already in scope.)
579 ; binds' <- tcExtendIdEnv2 rhs_id_env $ do
580 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
581 | (n,id) <- rhs_id_env])
582 mapM (wrapLocM tcRhs) tc_binds
583 ; return (listToBag binds', mono_info) }
585 ------------------------
586 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
587 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
588 -- if there's a signature for it, use the instantiated signature type
589 -- otherwise invent a type variable
590 -- You see that quite directly in the FunBind case.
592 -- But there's a complication for pattern bindings:
593 -- data T = MkT (forall a. a->a)
595 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
596 -- but we want to get (f::forall a. a->a) as the RHS environment.
597 -- The simplest way to do this is to typecheck the pattern, and then look up the
598 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
599 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
601 data TcMonoBind -- Half completed; LHS done, RHS not done
602 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
603 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
605 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
606 -- Type signature (if any), and
607 -- the monomorphic bound things
609 bndrNames :: [MonoBindInfo] -> [Name]
610 bndrNames mbi = [n | (n,_,_) <- mbi]
612 getMonoType :: MonoBindInfo -> TcTauType
613 getMonoType (_,_,mono_id) = idType mono_id
615 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
616 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
617 = do { mb_sig <- tcInstSig_maybe sig_fn name
618 ; mono_name <- newLocalName name
619 ; mono_ty <- mk_mono_ty mb_sig
620 ; let mono_id = mkLocalId mono_name mono_ty
621 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
623 mk_mono_ty (Just sig) = return (sig_tau sig)
624 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
626 tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
627 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
628 ; mono_pat_binds <- doptM Opt_MonoPatBinds
629 -- With -fmono-pat-binds, we do no generalisation of pattern bindings
630 -- But the signature can still be polymoprhic!
631 -- data T = MkT (forall a. a->a)
632 -- x :: forall a. a->a
634 -- The function get_sig_ty decides whether the pattern-bound variables
635 -- should have exactly the type in the type signature (-fmono-pat-binds),
636 -- or the instantiated version (-fmono-pat-binds)
638 ; let nm_sig_prs = names `zip` mb_sigs
639 get_sig_ty | mono_pat_binds = idType . sig_id
640 | otherwise = sig_tau
641 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
642 | (name, Just sig) <- nm_sig_prs]
643 sig_tau_fn = lookupNameEnv tau_sig_env
645 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
646 mapM lookup_info nm_sig_prs
648 -- After typechecking the pattern, look up the binder
649 -- names, which the pattern has brought into scope.
650 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
651 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
652 ; return (name, mb_sig, mono_id) }
654 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
657 ; return (TcPatBind infos pat' grhss pat_ty) }
659 names = collectPatBinders pat
662 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
663 -- AbsBind, VarBind impossible
666 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
667 -- When we are doing pattern bindings, or multiple function bindings at a time
668 -- we *don't* bring any scoped type variables into scope
669 -- Wny not? They are not completely rigid.
670 -- That's why we have the special case for a single FunBind in tcMonoBinds
671 tcRhs (TcFunBind (_,_,mono_id) fun' inf matches)
672 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
673 matches (idType mono_id)
674 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
675 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
676 fun_tick = Nothing }) }
678 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
679 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
680 tcGRHSsPat grhss pat_ty
681 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
682 bind_fvs = placeHolderNames }) }
685 ---------------------
686 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
687 getMonoBindInfo tc_binds
688 = foldr (get_info . unLoc) [] tc_binds
690 get_info (TcFunBind info _ _ _) rest = info : rest
691 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
695 %************************************************************************
699 %************************************************************************
702 generalise :: DynFlags -> TopLevelFlag
703 -> [LHsBind Name] -> TcSigFun
704 -> [MonoBindInfo] -> [Inst]
705 -> TcM ([TyVar], [Inst], TcDictBinds)
706 -- The returned [TyVar] are all ready to quantify
708 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
709 | isMonoGroup dflags bind_list
710 = do { extendLIEs lie_req
711 ; return ([], [], emptyBag) }
713 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
714 = -- Check signature contexts are empty
715 do { checkTc (all is_mono_sig sigs)
716 (restrictedBindCtxtErr bndrs)
718 -- Now simplify with exactly that set of tyvars
719 -- We have to squash those Methods
720 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
723 -- Check that signature type variables are OK
724 ; final_qtvs <- checkSigsTyVars qtvs sigs
726 ; return (final_qtvs, [], binds) }
728 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
729 = tcSimplifyInfer doc tau_tvs lie_req
731 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
732 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
733 ; let -- The "sig_avails" is the stuff available. We get that from
734 -- the context of the type signature, BUT ALSO the lie_avail
735 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
736 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
737 sig_avails = sig_lie ++ local_meths
738 loc = sig_loc (head sigs)
740 -- Check that the needed dicts can be
741 -- expressed in terms of the signature ones
742 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
744 -- Check that signature type variables are OK
745 ; final_qtvs <- checkSigsTyVars qtvs sigs
747 ; return (final_qtvs, sig_lie, binds) }
749 bndrs = bndrNames mono_infos
750 sigs = [sig | (_, Just sig, _) <- mono_infos]
751 get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
752 | otherwise = exactTyVarsOfType
753 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
754 is_mono_sig sig = null (sig_theta sig)
755 doc = ptext (sLit "type signature(s) for") <+> pprBinders bndrs
757 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
758 sig_theta = theta, sig_loc = loc }) mono_id
759 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
760 tci_theta = theta, tci_loc = loc}
763 unifyCtxts checks that all the signature contexts are the same
764 The type signatures on a mutually-recursive group of definitions
765 must all have the same context (or none).
767 The trick here is that all the signatures should have the same
768 context, and we want to share type variables for that context, so that
769 all the right hand sides agree a common vocabulary for their type
772 We unify them because, with polymorphic recursion, their types
773 might not otherwise be related. This is a rather subtle issue.
776 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
777 -- Post-condition: the returned Insts are full zonked
778 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
779 = do { mapM unify_ctxt sigs
780 ; theta <- zonkTcThetaType (sig_theta sig1)
781 ; newDictBndrs (sig_loc sig1) theta }
783 theta1 = sig_theta sig1
784 unify_ctxt :: TcSigInfo -> TcM ()
785 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
786 = setSrcSpan (instLocSpan (sig_loc sig)) $
787 addErrCtxt (sigContextsCtxt sig1 sig) $
788 do { cois <- unifyTheta theta1 theta
789 ; -- Check whether all coercions are identity coercions
790 -- That can happen if we have, say
792 -- g :: C (F a) => ...
793 -- where F is a type function and (F a ~ [a])
794 -- Then unification might succeed with a coercion. But it's much
795 -- much simpler to require that such signatures have identical contexts
796 checkTc (all isIdentityCoercion cois)
797 (ptext (sLit "Mutually dependent functions have syntactically distinct contexts"))
800 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
801 checkSigsTyVars qtvs sigs
802 = do { gbl_tvs <- tcGetGlobalTyVars
803 ; sig_tvs_s <- mapM (check_sig gbl_tvs) sigs
805 ; let -- Sigh. Make sure that all the tyvars in the type sigs
806 -- appear in the returned ty var list, which is what we are
807 -- going to generalise over. Reason: we occasionally get
809 -- type T a = () -> ()
812 -- Here, 'a' won't appear in qtvs, so we have to add it
813 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
814 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
817 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
818 sig_theta = theta, sig_tau = tau})
819 = addErrCtxt (ptext (sLit "In the type signature for") <+> quotes (ppr id)) $
820 addErrCtxtM (sigCtxt id tvs theta tau) $
821 do { tvs' <- checkDistinctTyVars tvs
822 ; when (any (`elemVarSet` gbl_tvs) tvs')
823 (bleatEscapedTvs gbl_tvs tvs tvs')
826 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
827 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
828 -- are still all type variables, and all distinct from each other.
829 -- It returns a zonked set of type variables.
830 -- For example, if the type sig is
831 -- f :: forall a b. a -> b -> b
832 -- we want to check that 'a' and 'b' haven't
833 -- (a) been unified with a non-tyvar type
834 -- (b) been unified with each other (all distinct)
836 checkDistinctTyVars sig_tvs
837 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
838 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
839 ; return zonked_tvs }
841 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
842 -- The TyVarEnv maps each zonked type variable back to its
843 -- corresponding user-written signature type variable
844 check_dup acc (sig_tv, zonked_tv)
845 = case lookupVarEnv acc zonked_tv of
846 Just sig_tv' -> bomb_out sig_tv sig_tv'
848 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
850 bomb_out sig_tv1 sig_tv2
851 = do { env0 <- tcInitTidyEnv
852 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
853 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
854 msg = ptext (sLit "Quantified type variable") <+> quotes (ppr tidy_tv1)
855 <+> ptext (sLit "is unified with another quantified type variable")
856 <+> quotes (ppr tidy_tv2)
857 ; failWithTcM (env2, msg) }
862 @getTyVarsToGen@ decides what type variables to generalise over.
864 For a "restricted group" -- see the monomorphism restriction
865 for a definition -- we bind no dictionaries, and
866 remove from tyvars_to_gen any constrained type variables
868 *Don't* simplify dicts at this point, because we aren't going
869 to generalise over these dicts. By the time we do simplify them
870 we may well know more. For example (this actually came up)
872 f x = array ... xs where xs = [1,2,3,4,5]
873 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
874 stuff. If we simplify only at the f-binding (not the xs-binding)
875 we'll know that the literals are all Ints, and we can just produce
878 Find all the type variables involved in overloading, the
879 "constrained_tyvars". These are the ones we *aren't* going to
880 generalise. We must be careful about doing this:
882 (a) If we fail to generalise a tyvar which is not actually
883 constrained, then it will never, ever get bound, and lands
884 up printed out in interface files! Notorious example:
885 instance Eq a => Eq (Foo a b) where ..
886 Here, b is not constrained, even though it looks as if it is.
887 Another, more common, example is when there's a Method inst in
888 the LIE, whose type might very well involve non-overloaded
890 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
891 the simple thing instead]
893 (b) On the other hand, we mustn't generalise tyvars which are constrained,
894 because we are going to pass on out the unmodified LIE, with those
895 tyvars in it. They won't be in scope if we've generalised them.
897 So we are careful, and do a complete simplification just to find the
898 constrained tyvars. We don't use any of the results, except to
899 find which tyvars are constrained.
901 Note [Polymorphic recursion]
902 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
903 The game plan for polymorphic recursion in the code above is
905 * Bind any variable for which we have a type signature
906 to an Id with a polymorphic type. Then when type-checking
907 the RHSs we'll make a full polymorphic call.
909 This fine, but if you aren't a bit careful you end up with a horrendous
910 amount of partial application and (worse) a huge space leak. For example:
912 f :: Eq a => [a] -> [a]
915 If we don't take care, after typechecking we get
917 f = /\a -> \d::Eq a -> let f' = f a d
921 Notice the the stupid construction of (f a d), which is of course
922 identical to the function we're executing. In this case, the
923 polymorphic recursion isn't being used (but that's a very common case).
924 This can lead to a massive space leak, from the following top-level defn
930 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
931 f' is another thunk which evaluates to the same thing... and you end
932 up with a chain of identical values all hung onto by the CAF ff.
936 = let f' = f Int dEqInt in \ys. ...f'...
938 = let f' = let f' = f Int dEqInt in \ys. ...f'...
943 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
944 which would make the space leak go away in this case
946 Solution: when typechecking the RHSs we always have in hand the
947 *monomorphic* Ids for each binding. So we just need to make sure that
948 if (Method f a d) shows up in the constraints emerging from (...f...)
949 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
950 to the "givens" when simplifying constraints. That's what the "lies_avail"
955 f = /\a -> \d::Eq a -> letrec
956 fm = \ys:[a] -> ...fm...
962 %************************************************************************
966 %************************************************************************
968 Type signatures are tricky. See Note [Signature skolems] in TcType
970 @tcSigs@ checks the signatures for validity, and returns a list of
971 {\em freshly-instantiated} signatures. That is, the types are already
972 split up, and have fresh type variables installed. All non-type-signature
973 "RenamedSigs" are ignored.
975 The @TcSigInfo@ contains @TcTypes@ because they are unified with
976 the variable's type, and after that checked to see whether they've
981 The -XScopedTypeVariables flag brings lexically-scoped type variables
982 into scope for any explicitly forall-quantified type variables:
983 f :: forall a. a -> a
985 Then 'a' is in scope inside 'e'.
987 However, we do *not* support this
988 - For pattern bindings e.g
992 - For multiple function bindings, unless Opt_RelaxedPolyRec is on
993 f :: forall a. a -> a
995 g :: forall b. b -> b
997 Reason: we use mutable variables for 'a' and 'b', since they may
998 unify to each other, and that means the scoped type variable would
999 not stand for a completely rigid variable.
1001 Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
1004 Note [More instantiated than scoped]
1005 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1006 There may be more instantiated type variables than lexically-scoped
1008 type T a = forall b. b -> (a,b)
1010 Here, the signature for f will have one scoped type variable, c,
1011 but two instantiated type variables, c' and b'.
1013 We assume that the scoped ones are at the *front* of sig_tvs,
1014 and remember the names from the original HsForAllTy in the TcSigFun.
1018 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
1019 -- type variables brought into scope
1020 -- by its type signature.
1021 -- Nothing => no type signature
1023 mkTcSigFun :: [LSig Name] -> TcSigFun
1024 -- Search for a particular type signature
1025 -- Precondition: the sigs are all type sigs
1026 -- Precondition: no duplicates
1027 mkTcSigFun sigs = lookupNameEnv env
1029 env = mkNameEnv [(name, hsExplicitTvs lhs_ty)
1030 | L span (TypeSig (L _ name) lhs_ty) <- sigs]
1031 -- The scoped names are the ones explicitly mentioned
1032 -- in the HsForAll. (There may be more in sigma_ty, because
1033 -- of nested type synonyms. See Note [More instantiated than scoped].)
1034 -- See Note [Only scoped tyvars are in the TyVarEnv]
1039 sig_id :: TcId, -- *Polymorphic* binder for this value...
1041 sig_tvs :: [TcTyVar], -- Instantiated type variables
1042 -- See Note [Instantiate sig]
1044 sig_theta :: TcThetaType, -- Instantiated theta
1045 sig_tau :: TcTauType, -- Instantiated tau
1046 sig_loc :: InstLoc -- The location of the signature
1050 -- Note [Only scoped tyvars are in the TyVarEnv]
1051 -- We are careful to keep only the *lexically scoped* type variables in
1052 -- the type environment. Why? After all, the renamer has ensured
1053 -- that only legal occurrences occur, so we could put all type variables
1054 -- into the type env.
1056 -- But we want to check that two distinct lexically scoped type variables
1057 -- do not map to the same internal type variable. So we need to know which
1058 -- the lexically-scoped ones are... and at the moment we do that by putting
1059 -- only the lexically scoped ones into the environment.
1062 -- Note [Instantiate sig]
1063 -- It's vital to instantiate a type signature with fresh variables.
1065 -- type S = forall a. a->a
1069 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1070 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1071 -- it's all cool; each signature has distinct type variables from the renamer.)
1073 instance Outputable TcSigInfo where
1074 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1075 = ppr id <+> ptext (sLit "::") <+> ppr tyvars <+> ppr theta <+> ptext (sLit "=>") <+> ppr tau
1079 tcTySig :: LSig Name -> TcM TcId
1080 tcTySig (L span (TypeSig (L _ name) ty))
1082 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1083 ; return (mkLocalId name sigma_ty) }
1086 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1087 -- Instantiate with *meta* type variables;
1088 -- this signature is part of a multi-signature group
1089 tcInstSig_maybe sig_fn name
1090 = case sig_fn name of
1091 Nothing -> return Nothing
1092 Just scoped_tvs -> do { tc_sig <- tcInstSig False name
1093 ; return (Just tc_sig) }
1094 -- NB: the scoped_tvs may be non-empty, but we can
1095 -- just ignore them. See Note [Scoped tyvars].
1097 tcInstSig :: Bool -> Name -> TcM TcSigInfo
1098 -- Instantiate the signature, with either skolems or meta-type variables
1099 -- depending on the use_skols boolean. This variable is set True
1100 -- when we are typechecking a single function binding; and False for
1101 -- pattern bindings and a group of several function bindings.
1102 -- Reason: in the latter cases, the "skolems" can be unified together,
1103 -- so they aren't properly rigid in the type-refinement sense.
1104 -- NB: unless we are doing H98, each function with a sig will be done
1105 -- separately, even if it's mutually recursive, so use_skols will be True
1107 -- We always instantiate with fresh uniques,
1108 -- although we keep the same print-name
1110 -- type T = forall a. [a] -> [a]
1112 -- f = g where { g :: T; g = <rhs> }
1114 -- We must not use the same 'a' from the defn of T at both places!!
1116 tcInstSig use_skols name
1117 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1118 -- scope when starting the binding group
1119 ; let skol_info = SigSkol (FunSigCtxt name)
1120 inst_tyvars = tcInstSigTyVars use_skols skol_info
1121 ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
1122 ; loc <- getInstLoc (SigOrigin skol_info)
1123 ; return (TcSigInfo { sig_id = poly_id,
1124 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1128 isMonoGroup :: DynFlags -> [LHsBind Name] -> Bool
1129 -- No generalisation at all
1130 isMonoGroup dflags binds
1131 = dopt Opt_MonoPatBinds dflags && any is_pat_bind binds
1133 is_pat_bind (L _ (PatBind {})) = True
1134 is_pat_bind other = False
1137 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1138 isRestrictedGroup dflags binds sig_fn
1139 = mono_restriction && not all_unrestricted
1141 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1142 all_unrestricted = all (unrestricted . unLoc) binds
1143 has_sig n = isJust (sig_fn n)
1145 unrestricted (PatBind {}) = False
1146 unrestricted (VarBind { var_id = v }) = has_sig v
1147 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1148 || has_sig (unLoc v)
1150 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1151 -- No args => like a pattern binding
1152 unrestricted_match other = True
1153 -- Some args => a function binding
1157 %************************************************************************
1159 \subsection[TcBinds-errors]{Error contexts and messages}
1161 %************************************************************************
1165 -- This one is called on LHS, when pat and grhss are both Name
1166 -- and on RHS, when pat is TcId and grhss is still Name
1167 patMonoBindsCtxt pat grhss
1168 = hang (ptext (sLit "In a pattern binding:")) 4 (pprPatBind pat grhss)
1170 -----------------------------------------------
1171 sigContextsCtxt sig1 sig2
1172 = vcat [ptext (sLit "When matching the contexts of the signatures for"),
1173 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1174 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1175 ptext (sLit "The signature contexts in a mutually recursive group should all be identical")]
1181 -----------------------------------------------
1182 unboxedTupleErr name ty
1183 = hang (ptext (sLit "Illegal binding of unboxed tuple"))
1184 4 (ppr name <+> dcolon <+> ppr ty)
1186 -----------------------------------------------
1187 restrictedBindCtxtErr binder_names
1188 = hang (ptext (sLit "Illegal overloaded type signature(s)"))
1189 4 (vcat [ptext (sLit "in a binding group for") <+> pprBinders binder_names,
1190 ptext (sLit "that falls under the monomorphism restriction")])
1192 genCtxt binder_names
1193 = ptext (sLit "When generalising the type(s) for") <+> pprBinders binder_names
1195 missingSigWarn False name ty = return ()
1196 missingSigWarn True name ty
1197 = do { env0 <- tcInitTidyEnv
1198 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1199 ; addWarnTcM (env1, mk_msg tidy_ty) }
1201 mk_msg ty = vcat [ptext (sLit "Definition but no type signature for") <+> quotes (ppr name),
1202 sep [ptext (sLit "Inferred type:") <+> pprHsVar name <+> dcolon <+> ppr ty]]