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 )
65 %************************************************************************
67 \subsection{Type-checking bindings}
69 %************************************************************************
71 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
72 it needs to know something about the {\em usage} of the things bound,
73 so that it can create specialisations of them. So @tcBindsAndThen@
74 takes a function which, given an extended environment, E, typechecks
75 the scope of the bindings returning a typechecked thing and (most
76 important) an LIE. It is this LIE which is then used as the basis for
77 specialising the things bound.
79 @tcBindsAndThen@ also takes a "combiner" which glues together the
80 bindings and the "thing" to make a new "thing".
82 The real work is done by @tcBindWithSigsAndThen@.
84 Recursive and non-recursive binds are handled in essentially the same
85 way: because of uniques there are no scoping issues left. The only
86 difference is that non-recursive bindings can bind primitive values.
88 Even for non-recursive binding groups we add typings for each binder
89 to the LVE for the following reason. When each individual binding is
90 checked the type of its LHS is unified with that of its RHS; and
91 type-checking the LHS of course requires that the binder is in scope.
93 At the top-level the LIE is sure to contain nothing but constant
94 dictionaries, which we resolve at the module level.
97 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
98 -- Note: returning the TcLclEnv is more than we really
99 -- want. The bit we care about is the local bindings
100 -- and the free type variables thereof
102 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
103 ; return (foldr (unionBags . snd) emptyBag prs, env) }
104 -- The top level bindings are flattened into a giant
105 -- implicitly-mutually-recursive LHsBinds
107 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
108 -- A hs-boot file has only one BindGroup, and it only has type
109 -- signatures in it. The renamer checked all this
110 tcHsBootSigs (ValBindsOut binds sigs)
111 = do { checkTc (null binds) badBootDeclErr
112 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
114 tc_boot_sig (TypeSig (L _ name) ty)
115 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
116 ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
117 -- Notice that we make GlobalIds, not LocalIds
118 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
120 badBootDeclErr :: Message
121 badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file")
123 ------------------------
124 tcLocalBinds :: HsLocalBinds Name -> TcM thing
125 -> TcM (HsLocalBinds TcId, thing)
127 tcLocalBinds EmptyLocalBinds thing_inside
128 = do { thing <- thing_inside
129 ; return (EmptyLocalBinds, thing) }
131 tcLocalBinds (HsValBinds binds) thing_inside
132 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
133 ; return (HsValBinds binds', thing) }
135 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
136 = do { (thing, lie) <- getLIE thing_inside
137 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
139 -- If the binding binds ?x = E, we must now
140 -- discharge any ?x constraints in expr_lie
141 ; dict_binds <- tcSimplifyIPs avail_ips lie
142 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
144 -- I wonder if we should do these one at at time
147 tc_ip_bind (IPBind ip expr) = do
148 ty <- newFlexiTyVarTy argTypeKind
149 (ip', ip_inst) <- newIPDict (IPBindOrigin ip) ip ty
150 expr' <- tcMonoExpr expr ty
151 return (ip_inst, (IPBind ip' expr'))
153 ------------------------
154 tcValBinds :: TopLevelFlag
155 -> HsValBinds Name -> TcM thing
156 -> TcM (HsValBinds TcId, thing)
158 tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
159 = pprPanic "tcValBinds" (ppr binds)
161 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
162 = do { -- Typecheck the signature
163 ; let { prag_fn = mkPragFun sigs
164 ; ty_sigs = filter isVanillaLSig sigs
165 ; sig_fn = mkTcSigFun ty_sigs }
167 ; poly_ids <- mapM tcTySig ty_sigs
168 -- No recovery from bad signatures, because the type sigs
169 -- may bind type variables, so proceeding without them
170 -- can lead to a cascade of errors
171 -- ToDo: this means we fall over immediately if any type sig
172 -- is wrong, which is over-conservative, see Trac bug #745
174 -- Extend the envt right away with all
175 -- the Ids declared with type signatures
176 ; poly_rec <- doptM Opt_RelaxedPolyRec
177 ; (binds', thing) <- tcExtendIdEnv poly_ids $
178 tc_val_binds poly_rec top_lvl sig_fn prag_fn
181 ; return (ValBindsOut binds' sigs, thing) }
183 ------------------------
184 tc_val_binds :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
185 -> [(RecFlag, LHsBinds Name)] -> TcM thing
186 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
187 -- Typecheck a whole lot of value bindings,
188 -- one strongly-connected component at a time
190 tc_val_binds poly_rec top_lvl sig_fn prag_fn [] thing_inside
191 = do { thing <- thing_inside
192 ; return ([], thing) }
194 tc_val_binds poly_rec top_lvl sig_fn prag_fn (group : groups) thing_inside
195 = do { (group', (groups', thing))
196 <- tc_group poly_rec top_lvl sig_fn prag_fn group $
197 tc_val_binds poly_rec top_lvl sig_fn prag_fn groups thing_inside
198 ; return (group' ++ groups', thing) }
200 ------------------------
201 tc_group :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
202 -> (RecFlag, LHsBinds Name) -> TcM thing
203 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
205 -- Typecheck one strongly-connected component of the original program.
206 -- We get a list of groups back, because there may
207 -- be specialisations etc as well
209 tc_group poly_rec top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
210 -- A single non-recursive binding
211 -- We want to keep non-recursive things non-recursive
212 -- so that we desugar unlifted bindings correctly
213 = do { (binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn NonRecursive binds thing_inside
214 ; return ([(NonRecursive, b) | b <- binds], thing) }
216 tc_group poly_rec top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
217 | not poly_rec -- Recursive group, normal Haskell 98 route
218 = do { (binds1, thing) <- tc_haskell98 top_lvl sig_fn prag_fn Recursive binds thing_inside
219 ; return ([(Recursive, unionManyBags binds1)], thing) }
221 | otherwise -- Recursive group, with gla-exts
222 = -- To maximise polymorphism (with -fglasgow-exts), we do a new
223 -- strongly-connected-component analysis, this time omitting
224 -- any references to variables with type signatures.
226 -- Notice that the bindInsts thing covers *all* the bindings in the original
227 -- group at once; an earlier one may use a later one!
228 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
229 ; (binds1,thing) <- bindLocalInsts top_lvl $
230 go (stronglyConnComp (mkEdges sig_fn binds))
231 ; return ([(Recursive, unionManyBags binds1)], thing) }
232 -- Rec them all together
234 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], [TcId], thing)
235 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
236 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
237 ; return (binds1 ++ binds2, ids1 ++ ids2, thing) }
238 go [] = do { thing <- thing_inside; return ([], [], thing) }
240 tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive (unitBag bind)
241 tc_scc (CyclicSCC binds) = tc_sub_group Recursive (listToBag binds)
243 tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
245 tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside
246 = bindLocalInsts top_lvl $ do
247 { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds
248 ; thing <- tcExtendIdEnv ids thing_inside
249 ; return (binds1, ids, thing) }
251 ------------------------
252 bindLocalInsts :: TopLevelFlag -> TcM ([LHsBinds TcId], [TcId], a) -> TcM ([LHsBinds TcId], a)
253 bindLocalInsts top_lvl thing_inside
254 | isTopLevel top_lvl = do { (binds, ids, thing) <- thing_inside; return (binds, thing) }
255 -- For the top level don't bother with all this bindInstsOfLocalFuns stuff.
256 -- All the top level things are rec'd together anyway, so it's fine to
257 -- leave them to the tcSimplifyTop, and quite a bit faster too
259 | otherwise -- Nested case
260 = do { ((binds, ids, thing), lie) <- getLIE thing_inside
261 ; lie_binds <- bindInstsOfLocalFuns lie ids
262 ; return (binds ++ [lie_binds], thing) }
264 ------------------------
265 mkEdges :: TcSigFun -> LHsBinds Name
266 -> [(LHsBind Name, BKey, [BKey])]
268 type BKey = Int -- Just number off the bindings
271 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
272 Just key <- [lookupNameEnv key_map n], no_sig n ])
273 | (bind, key) <- keyd_binds
276 no_sig :: Name -> Bool
277 no_sig n = isNothing (sig_fn n)
279 keyd_binds = bagToList binds `zip` [0::BKey ..]
281 key_map :: NameEnv BKey -- Which binding it comes from
282 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
283 , bndr <- bindersOfHsBind bind ]
285 bindersOfHsBind :: HsBind Name -> [Name]
286 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
287 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
289 ------------------------
290 tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragFun
291 -> RecFlag -- Whether the group is really recursive
292 -> RecFlag -- Whether it's recursive after breaking
293 -- dependencies based on type signatures
295 -> TcM ([LHsBinds TcId], [TcId])
297 -- Typechecks a single bunch of bindings all together,
298 -- and generalises them. The bunch may be only part of a recursive
299 -- group, because we use type signatures to maximise polymorphism
301 -- Returns a list because the input may be a single non-recursive binding,
302 -- in which case the dependency order of the resulting bindings is
305 -- Knows nothing about the scope of the bindings
307 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds
309 bind_list = bagToList binds
310 binder_names = collectHsBindBinders binds
311 loc = getLoc (head bind_list)
312 -- TODO: location a bit awkward, but the mbinds have been
313 -- dependency analysed and may no longer be adjacent
315 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
317 recoverM (recoveryCode binder_names sig_fn) $ do
319 { traceTc (ptext SLIT("------------------------------------------------"))
320 ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
322 -- TYPECHECK THE BINDINGS
323 ; ((binds', mono_bind_infos), lie_req)
324 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
325 ; traceTc (text "temp" <+> (ppr binds' $$ ppr lie_req))
327 -- CHECK FOR UNLIFTED BINDINGS
328 -- These must be non-recursive etc, and are not generalised
329 -- They desugar to a case expression in the end
330 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
331 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
332 zonked_mono_tys mono_bind_infos
334 do { extendLIEs lie_req
335 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
336 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
337 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
338 -- ToDo: prags for unlifted bindings
340 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
341 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
343 else do -- The normal lifted case: GENERALISE
345 ; (tyvars_to_gen, dicts, dict_binds)
346 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
347 generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
349 -- BUILD THE POLYMORPHIC RESULT IDs
350 ; let dict_vars = map instToVar dicts -- May include equality constraints
351 ; exports <- mapM (mkExport top_lvl prag_fn tyvars_to_gen (map varType dict_vars))
354 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
355 ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids))
357 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen
359 (dict_binds `unionBags` binds')
361 ; return ([unitBag abs_bind], poly_ids) -- poly_ids are guaranteed zonked by mkExport
366 mkExport :: TopLevelFlag -> TcPragFun -> [TyVar] -> [TcType]
368 -> TcM ([TyVar], Id, Id, [LPrag])
369 -- mkExport generates exports with
370 -- zonked type variables,
372 -- The former is just because no further unifications will change
373 -- the quantified type variables, so we can fix their final form
375 -- The latter is needed because the poly_ids are used to extend the
376 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
378 -- Pre-condition: the inferred_tvs are already zonked
380 mkExport top_lvl prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
381 = do { warn_missing_sigs <- doptM Opt_WarnMissingSigs
382 ; let warn = isTopLevel top_lvl && warn_missing_sigs
383 ; (tvs, poly_id) <- mk_poly_id warn mb_sig
384 -- poly_id has a zonked type
386 ; prags <- tcPrags poly_id (prag_fn poly_name)
387 -- tcPrags requires a zonked poly_id
389 ; return (tvs, poly_id, mono_id, prags) }
391 poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id))
393 mk_poly_id warn Nothing = do { poly_ty' <- zonkTcType poly_ty
394 ; missingSigWarn warn poly_name poly_ty'
395 ; return (inferred_tvs, mkLocalId poly_name poly_ty') }
396 mk_poly_id warn (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
397 ; return (tvs, sig_id sig) }
399 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
401 ------------------------
402 type TcPragFun = Name -> [LSig Name]
404 mkPragFun :: [LSig Name] -> TcPragFun
405 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
407 prs = [(expectJust "mkPragFun" (sigName sig), sig)
408 | sig <- sigs, isPragLSig sig]
409 env = foldl add emptyNameEnv prs
410 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
412 tcPrags :: Id -> [LSig Name] -> TcM [LPrag]
413 tcPrags poly_id prags = mapM (wrapLocM tc_prag) prags
415 tc_prag prag = addErrCtxt (pragSigCtxt prag) $
418 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
420 tcPrag :: TcId -> Sig Name -> TcM Prag
421 -- Pre-condition: the poly_id is zonked
422 -- Reason: required by tcSubExp
423 tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
424 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
425 tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
428 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
429 tcSpecPrag poly_id hs_ty inl
430 = do { let name = idName poly_id
431 ; spec_ty <- tcHsSigType (FunSigCtxt name) hs_ty
432 ; co_fn <- tcSubExp (SpecPragOrigin name) (idType poly_id) spec_ty
433 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty inl) }
434 -- Most of the work of specialisation is done by
435 -- the desugarer, guided by the SpecPrag
438 -- If typechecking the binds fails, then return with each
439 -- signature-less binder given type (forall a.a), to minimise
440 -- subsequent error messages
441 recoveryCode binder_names sig_fn
442 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
443 ; poly_ids <- mapM mk_dummy binder_names
444 ; return ([], poly_ids) }
447 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
448 | otherwise = return (mkLocalId name forall_a_a) -- No signature
451 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
454 -- Check that non-overloaded unlifted bindings are
457 -- c) not a multiple-binding group (more or less implied by (a))
459 checkStrictBinds :: TopLevelFlag -> RecFlag
460 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
462 checkStrictBinds top_lvl rec_group mbind mono_tys infos
463 | unlifted || bang_pat
464 = do { checkTc (isNotTopLevel top_lvl)
465 (strictBindErr "Top-level" unlifted mbind)
466 ; checkTc (isNonRec rec_group)
467 (strictBindErr "Recursive" unlifted mbind)
468 ; checkTc (isSingletonBag mbind)
469 (strictBindErr "Multiple" unlifted mbind)
470 ; mapM_ check_sig infos
475 unlifted = any isUnLiftedType mono_tys
476 bang_pat = anyBag (isBangHsBind . unLoc) mbind
477 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
478 (badStrictSig unlifted sig)
479 check_sig other = return ()
481 strictBindErr flavour unlifted mbind
482 = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:"))
483 4 (pprLHsBinds mbind)
485 msg | unlifted = ptext SLIT("bindings for unlifted types")
486 | otherwise = ptext SLIT("bang-pattern bindings")
488 badStrictSig unlifted sig
489 = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
492 msg | unlifted = ptext SLIT("an unlifted binding")
493 | otherwise = ptext SLIT("a bang-pattern binding")
497 %************************************************************************
499 \subsection{tcMonoBind}
501 %************************************************************************
503 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
504 The signatures have been dealt with already.
507 tcMonoBinds :: [LHsBind Name]
509 -> RecFlag -- Whether the binding is recursive for typechecking purposes
510 -- i.e. the binders are mentioned in their RHSs, and
511 -- we are not resuced by a type signature
512 -> TcM (LHsBinds TcId, [MonoBindInfo])
514 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
515 fun_matches = matches, bind_fvs = fvs })]
516 sig_fn -- Single function binding,
517 NonRecursive -- binder isn't mentioned in RHS,
518 | Nothing <- sig_fn name -- ...with no type signature
519 = -- In this very special case we infer the type of the
520 -- right hand side first (it may have a higher-rank type)
521 -- and *then* make the monomorphic Id for the LHS
522 -- e.g. f = \(x::forall a. a->a) -> <body>
523 -- We want to infer a higher-rank type for f
525 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
527 -- Check for an unboxed tuple type
528 -- f = (# True, False #)
529 -- Zonk first just in case it's hidden inside a meta type variable
530 -- (This shows up as a (more obscure) kind error
531 -- in the 'otherwise' case of tcMonoBinds.)
532 ; zonked_rhs_ty <- zonkTcType rhs_ty
533 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
534 (unboxedTupleErr name zonked_rhs_ty)
536 ; mono_name <- newLocalName name
537 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
538 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
539 fun_matches = matches', bind_fvs = fvs,
540 fun_co_fn = co_fn, fun_tick = Nothing })),
541 [(name, Nothing, mono_id)]) }
543 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
544 fun_matches = matches, bind_fvs = fvs })]
545 sig_fn -- Single function binding
547 | Just scoped_tvs <- sig_fn name -- ...with a type signature
548 = -- When we have a single function binding, with a type signature
549 -- we can (a) use genuine, rigid skolem constants for the type variables
550 -- (b) bring (rigid) scoped type variables into scope
552 do { tc_sig <- tcInstSig True name
553 ; mono_name <- newLocalName name
554 ; let mono_ty = sig_tau tc_sig
555 mono_id = mkLocalId mono_name mono_ty
556 rhs_tvs = [ (name, mkTyVarTy tv)
557 | (name, tv) <- scoped_tvs `zip` sig_tvs tc_sig ]
558 -- See Note [More instantiated than scoped]
559 -- Note that the scoped_tvs and the (sig_tvs sig)
560 -- may have different Names. That's quite ok.
562 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
563 tcMatchesFun mono_name inf matches mono_ty
565 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
566 fun_infix = inf, fun_matches = matches',
567 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
569 ; return (unitBag (L b_loc fun_bind'),
570 [(name, Just tc_sig, mono_id)]) }
572 tcMonoBinds binds sig_fn non_rec
573 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
575 -- Bring the monomorphic Ids, into scope for the RHSs
576 ; let mono_info = getMonoBindInfo tc_binds
577 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
578 -- A monomorphic binding for each term variable that lacks
579 -- a type sig. (Ones with a sig are already in scope.)
581 ; binds' <- tcExtendIdEnv2 rhs_id_env $ do
582 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
583 | (n,id) <- rhs_id_env])
584 mapM (wrapLocM tcRhs) tc_binds
585 ; return (listToBag binds', mono_info) }
587 ------------------------
588 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
589 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
590 -- if there's a signature for it, use the instantiated signature type
591 -- otherwise invent a type variable
592 -- You see that quite directly in the FunBind case.
594 -- But there's a complication for pattern bindings:
595 -- data T = MkT (forall a. a->a)
597 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
598 -- but we want to get (f::forall a. a->a) as the RHS environment.
599 -- The simplest way to do this is to typecheck the pattern, and then look up the
600 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
601 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
603 data TcMonoBind -- Half completed; LHS done, RHS not done
604 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
605 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
607 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
608 -- Type signature (if any), and
609 -- the monomorphic bound things
611 bndrNames :: [MonoBindInfo] -> [Name]
612 bndrNames mbi = [n | (n,_,_) <- mbi]
614 getMonoType :: MonoBindInfo -> TcTauType
615 getMonoType (_,_,mono_id) = idType mono_id
617 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
618 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
619 = do { mb_sig <- tcInstSig_maybe sig_fn name
620 ; mono_name <- newLocalName name
621 ; mono_ty <- mk_mono_ty mb_sig
622 ; let mono_id = mkLocalId mono_name mono_ty
623 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
625 mk_mono_ty (Just sig) = return (sig_tau sig)
626 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
628 tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
629 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
630 ; mono_pat_binds <- doptM Opt_MonoPatBinds
631 -- With -fmono-pat-binds, we do no generalisation of pattern bindings
632 -- But the signature can still be polymoprhic!
633 -- data T = MkT (forall a. a->a)
634 -- x :: forall a. a->a
636 -- The function get_sig_ty decides whether the pattern-bound variables
637 -- should have exactly the type in the type signature (-fmono-pat-binds),
638 -- or the instantiated version (-fmono-pat-binds)
640 ; let nm_sig_prs = names `zip` mb_sigs
641 get_sig_ty | mono_pat_binds = idType . sig_id
642 | otherwise = sig_tau
643 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
644 | (name, Just sig) <- nm_sig_prs]
645 sig_tau_fn = lookupNameEnv tau_sig_env
647 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
648 mapM lookup_info nm_sig_prs
650 -- After typechecking the pattern, look up the binder
651 -- names, which the pattern has brought into scope.
652 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
653 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
654 ; return (name, mb_sig, mono_id) }
656 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
659 ; return (TcPatBind infos pat' grhss pat_ty) }
661 names = collectPatBinders pat
664 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
665 -- AbsBind, VarBind impossible
668 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
669 -- When we are doing pattern bindings, or multiple function bindings at a time
670 -- we *don't* bring any scoped type variables into scope
671 -- Wny not? They are not completely rigid.
672 -- That's why we have the special case for a single FunBind in tcMonoBinds
673 tcRhs (TcFunBind (_,_,mono_id) fun' inf matches)
674 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
675 matches (idType mono_id)
676 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
677 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
678 fun_tick = Nothing }) }
680 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
681 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
682 tcGRHSsPat grhss pat_ty
683 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
684 bind_fvs = placeHolderNames }) }
687 ---------------------
688 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
689 getMonoBindInfo tc_binds
690 = foldr (get_info . unLoc) [] tc_binds
692 get_info (TcFunBind info _ _ _) rest = info : rest
693 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
697 %************************************************************************
701 %************************************************************************
704 generalise :: DynFlags -> TopLevelFlag
705 -> [LHsBind Name] -> TcSigFun
706 -> [MonoBindInfo] -> [Inst]
707 -> TcM ([TyVar], [Inst], TcDictBinds)
708 -- The returned [TyVar] are all ready to quantify
710 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
711 | isMonoGroup dflags bind_list
712 = do { extendLIEs lie_req
713 ; return ([], [], emptyBag) }
715 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
716 = -- Check signature contexts are empty
717 do { checkTc (all is_mono_sig sigs)
718 (restrictedBindCtxtErr bndrs)
720 -- Now simplify with exactly that set of tyvars
721 -- We have to squash those Methods
722 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
725 -- Check that signature type variables are OK
726 ; final_qtvs <- checkSigsTyVars qtvs sigs
728 ; return (final_qtvs, [], binds) }
730 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
731 = tcSimplifyInfer doc tau_tvs lie_req
733 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
734 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
735 ; let -- The "sig_avails" is the stuff available. We get that from
736 -- the context of the type signature, BUT ALSO the lie_avail
737 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
738 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
739 sig_avails = sig_lie ++ local_meths
740 loc = sig_loc (head sigs)
742 -- Check that the needed dicts can be
743 -- expressed in terms of the signature ones
744 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
746 -- Check that signature type variables are OK
747 ; final_qtvs <- checkSigsTyVars qtvs sigs
749 ; return (final_qtvs, sig_lie, binds) }
751 bndrs = bndrNames mono_infos
752 sigs = [sig | (_, Just sig, _) <- mono_infos]
753 get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
754 | otherwise = exactTyVarsOfType
755 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
756 is_mono_sig sig = null (sig_theta sig)
757 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
759 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
760 sig_theta = theta, sig_loc = loc }) mono_id
761 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
762 tci_theta = theta, tci_loc = loc}
765 unifyCtxts checks that all the signature contexts are the same
766 The type signatures on a mutually-recursive group of definitions
767 must all have the same context (or none).
769 The trick here is that all the signatures should have the same
770 context, and we want to share type variables for that context, so that
771 all the right hand sides agree a common vocabulary for their type
774 We unify them because, with polymorphic recursion, their types
775 might not otherwise be related. This is a rather subtle issue.
778 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
779 -- Post-condition: the returned Insts are full zonked
780 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
781 = do { mapM unify_ctxt sigs
782 ; theta <- zonkTcThetaType (sig_theta sig1)
783 ; newDictBndrs (sig_loc sig1) theta }
785 theta1 = sig_theta sig1
786 unify_ctxt :: TcSigInfo -> TcM ()
787 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
788 = setSrcSpan (instLocSpan (sig_loc sig)) $
789 addErrCtxt (sigContextsCtxt sig1 sig) $
790 do { cois <- unifyTheta theta1 theta
791 ; -- Check whether all coercions are identity coercions
792 -- That can happen if we have, say
794 -- g :: C (F a) => ...
795 -- where F is a type function and (F a ~ [a])
796 -- Then unification might succeed with a coercion. But it's much
797 -- much simpler to require that such signatures have identical contexts
798 checkTc (all isIdentityCoercion cois)
799 (ptext SLIT("Mutually dependent functions have syntactically distinct contexts"))
802 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
803 checkSigsTyVars qtvs sigs
804 = do { gbl_tvs <- tcGetGlobalTyVars
805 ; sig_tvs_s <- mapM (check_sig gbl_tvs) sigs
807 ; let -- Sigh. Make sure that all the tyvars in the type sigs
808 -- appear in the returned ty var list, which is what we are
809 -- going to generalise over. Reason: we occasionally get
811 -- type T a = () -> ()
814 -- Here, 'a' won't appear in qtvs, so we have to add it
815 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
816 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
819 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
820 sig_theta = theta, sig_tau = tau})
821 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
822 addErrCtxtM (sigCtxt id tvs theta tau) $
823 do { tvs' <- checkDistinctTyVars tvs
824 ; when (any (`elemVarSet` gbl_tvs) tvs')
825 (bleatEscapedTvs gbl_tvs tvs tvs')
828 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
829 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
830 -- are still all type variables, and all distinct from each other.
831 -- It returns a zonked set of type variables.
832 -- For example, if the type sig is
833 -- f :: forall a b. a -> b -> b
834 -- we want to check that 'a' and 'b' haven't
835 -- (a) been unified with a non-tyvar type
836 -- (b) been unified with each other (all distinct)
838 checkDistinctTyVars sig_tvs
839 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
840 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
841 ; return zonked_tvs }
843 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
844 -- The TyVarEnv maps each zonked type variable back to its
845 -- corresponding user-written signature type variable
846 check_dup acc (sig_tv, zonked_tv)
847 = case lookupVarEnv acc zonked_tv of
848 Just sig_tv' -> bomb_out sig_tv sig_tv'
850 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
852 bomb_out sig_tv1 sig_tv2
853 = do { env0 <- tcInitTidyEnv
854 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
855 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
856 msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
857 <+> ptext SLIT("is unified with another quantified type variable")
858 <+> quotes (ppr tidy_tv2)
859 ; failWithTcM (env2, msg) }
864 @getTyVarsToGen@ decides what type variables to generalise over.
866 For a "restricted group" -- see the monomorphism restriction
867 for a definition -- we bind no dictionaries, and
868 remove from tyvars_to_gen any constrained type variables
870 *Don't* simplify dicts at this point, because we aren't going
871 to generalise over these dicts. By the time we do simplify them
872 we may well know more. For example (this actually came up)
874 f x = array ... xs where xs = [1,2,3,4,5]
875 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
876 stuff. If we simplify only at the f-binding (not the xs-binding)
877 we'll know that the literals are all Ints, and we can just produce
880 Find all the type variables involved in overloading, the
881 "constrained_tyvars". These are the ones we *aren't* going to
882 generalise. We must be careful about doing this:
884 (a) If we fail to generalise a tyvar which is not actually
885 constrained, then it will never, ever get bound, and lands
886 up printed out in interface files! Notorious example:
887 instance Eq a => Eq (Foo a b) where ..
888 Here, b is not constrained, even though it looks as if it is.
889 Another, more common, example is when there's a Method inst in
890 the LIE, whose type might very well involve non-overloaded
892 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
893 the simple thing instead]
895 (b) On the other hand, we mustn't generalise tyvars which are constrained,
896 because we are going to pass on out the unmodified LIE, with those
897 tyvars in it. They won't be in scope if we've generalised them.
899 So we are careful, and do a complete simplification just to find the
900 constrained tyvars. We don't use any of the results, except to
901 find which tyvars are constrained.
903 Note [Polymorphic recursion]
904 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
905 The game plan for polymorphic recursion in the code above is
907 * Bind any variable for which we have a type signature
908 to an Id with a polymorphic type. Then when type-checking
909 the RHSs we'll make a full polymorphic call.
911 This fine, but if you aren't a bit careful you end up with a horrendous
912 amount of partial application and (worse) a huge space leak. For example:
914 f :: Eq a => [a] -> [a]
917 If we don't take care, after typechecking we get
919 f = /\a -> \d::Eq a -> let f' = f a d
923 Notice the the stupid construction of (f a d), which is of course
924 identical to the function we're executing. In this case, the
925 polymorphic recursion isn't being used (but that's a very common case).
926 This can lead to a massive space leak, from the following top-level defn
932 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
933 f' is another thunk which evaluates to the same thing... and you end
934 up with a chain of identical values all hung onto by the CAF ff.
938 = let f' = f Int dEqInt in \ys. ...f'...
940 = let f' = let f' = f Int dEqInt in \ys. ...f'...
945 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
946 which would make the space leak go away in this case
948 Solution: when typechecking the RHSs we always have in hand the
949 *monomorphic* Ids for each binding. So we just need to make sure that
950 if (Method f a d) shows up in the constraints emerging from (...f...)
951 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
952 to the "givens" when simplifying constraints. That's what the "lies_avail"
957 f = /\a -> \d::Eq a -> letrec
958 fm = \ys:[a] -> ...fm...
964 %************************************************************************
968 %************************************************************************
970 Type signatures are tricky. See Note [Signature skolems] in TcType
972 @tcSigs@ checks the signatures for validity, and returns a list of
973 {\em freshly-instantiated} signatures. That is, the types are already
974 split up, and have fresh type variables installed. All non-type-signature
975 "RenamedSigs" are ignored.
977 The @TcSigInfo@ contains @TcTypes@ because they are unified with
978 the variable's type, and after that checked to see whether they've
983 The -XScopedTypeVariables flag brings lexically-scoped type variables
984 into scope for any explicitly forall-quantified type variables:
985 f :: forall a. a -> a
987 Then 'a' is in scope inside 'e'.
989 However, we do *not* support this
990 - For pattern bindings e.g
994 - For multiple function bindings, unless Opt_RelaxedPolyRec is on
995 f :: forall a. a -> a
997 g :: forall b. b -> b
999 Reason: we use mutable variables for 'a' and 'b', since they may
1000 unify to each other, and that means the scoped type variable would
1001 not stand for a completely rigid variable.
1003 Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
1006 Note [More instantiated than scoped]
1007 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1008 There may be more instantiated type variables than lexically-scoped
1010 type T a = forall b. b -> (a,b)
1012 Here, the signature for f will have one scoped type variable, c,
1013 but two instantiated type variables, c' and b'.
1015 We assume that the scoped ones are at the *front* of sig_tvs,
1016 and remember the names from the original HsForAllTy in the TcSigFun.
1020 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
1021 -- type variables brought into scope
1022 -- by its type signature.
1023 -- Nothing => no type signature
1025 mkTcSigFun :: [LSig Name] -> TcSigFun
1026 -- Search for a particular type signature
1027 -- Precondition: the sigs are all type sigs
1028 -- Precondition: no duplicates
1029 mkTcSigFun sigs = lookupNameEnv env
1031 env = mkNameEnv [(name, hsExplicitTvs lhs_ty)
1032 | L span (TypeSig (L _ name) lhs_ty) <- sigs]
1033 -- The scoped names are the ones explicitly mentioned
1034 -- in the HsForAll. (There may be more in sigma_ty, because
1035 -- of nested type synonyms. See Note [More instantiated than scoped].)
1036 -- See Note [Only scoped tyvars are in the TyVarEnv]
1041 sig_id :: TcId, -- *Polymorphic* binder for this value...
1043 sig_tvs :: [TcTyVar], -- Instantiated type variables
1044 -- See Note [Instantiate sig]
1046 sig_theta :: TcThetaType, -- Instantiated theta
1047 sig_tau :: TcTauType, -- Instantiated tau
1048 sig_loc :: InstLoc -- The location of the signature
1052 -- Note [Only scoped tyvars are in the TyVarEnv]
1053 -- We are careful to keep only the *lexically scoped* type variables in
1054 -- the type environment. Why? After all, the renamer has ensured
1055 -- that only legal occurrences occur, so we could put all type variables
1056 -- into the type env.
1058 -- But we want to check that two distinct lexically scoped type variables
1059 -- do not map to the same internal type variable. So we need to know which
1060 -- the lexically-scoped ones are... and at the moment we do that by putting
1061 -- only the lexically scoped ones into the environment.
1064 -- Note [Instantiate sig]
1065 -- It's vital to instantiate a type signature with fresh variables.
1067 -- type S = forall a. a->a
1071 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1072 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1073 -- it's all cool; each signature has distinct type variables from the renamer.)
1075 instance Outputable TcSigInfo where
1076 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1077 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
1081 tcTySig :: LSig Name -> TcM TcId
1082 tcTySig (L span (TypeSig (L _ name) ty))
1084 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1085 ; return (mkLocalId name sigma_ty) }
1088 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1089 -- Instantiate with *meta* type variables;
1090 -- this signature is part of a multi-signature group
1091 tcInstSig_maybe sig_fn name
1092 = case sig_fn name of
1093 Nothing -> return Nothing
1094 Just scoped_tvs -> do { tc_sig <- tcInstSig False name
1095 ; return (Just tc_sig) }
1096 -- NB: the scoped_tvs may be non-empty, but we can
1097 -- just ignore them. See Note [Scoped tyvars].
1099 tcInstSig :: Bool -> Name -> TcM TcSigInfo
1100 -- Instantiate the signature, with either skolems or meta-type variables
1101 -- depending on the use_skols boolean. This variable is set True
1102 -- when we are typechecking a single function binding; and False for
1103 -- pattern bindings and a group of several function bindings.
1104 -- Reason: in the latter cases, the "skolems" can be unified together,
1105 -- so they aren't properly rigid in the type-refinement sense.
1106 -- NB: unless we are doing H98, each function with a sig will be done
1107 -- separately, even if it's mutually recursive, so use_skols will be True
1109 -- We always instantiate with fresh uniques,
1110 -- although we keep the same print-name
1112 -- type T = forall a. [a] -> [a]
1114 -- f = g where { g :: T; g = <rhs> }
1116 -- We must not use the same 'a' from the defn of T at both places!!
1118 tcInstSig use_skols name
1119 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1120 -- scope when starting the binding group
1121 ; let skol_info = SigSkol (FunSigCtxt name)
1122 inst_tyvars = tcInstSigTyVars use_skols skol_info
1123 ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
1124 ; loc <- getInstLoc (SigOrigin skol_info)
1125 ; return (TcSigInfo { sig_id = poly_id,
1126 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1130 isMonoGroup :: DynFlags -> [LHsBind Name] -> Bool
1131 -- No generalisation at all
1132 isMonoGroup dflags binds
1133 = dopt Opt_MonoPatBinds dflags && any is_pat_bind binds
1135 is_pat_bind (L _ (PatBind {})) = True
1136 is_pat_bind other = False
1139 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1140 isRestrictedGroup dflags binds sig_fn
1141 = mono_restriction && not all_unrestricted
1143 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1144 all_unrestricted = all (unrestricted . unLoc) binds
1145 has_sig n = isJust (sig_fn n)
1147 unrestricted (PatBind {}) = False
1148 unrestricted (VarBind { var_id = v }) = has_sig v
1149 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1150 || has_sig (unLoc v)
1152 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1153 -- No args => like a pattern binding
1154 unrestricted_match other = True
1155 -- Some args => a function binding
1159 %************************************************************************
1161 \subsection[TcBinds-errors]{Error contexts and messages}
1163 %************************************************************************
1167 -- This one is called on LHS, when pat and grhss are both Name
1168 -- and on RHS, when pat is TcId and grhss is still Name
1169 patMonoBindsCtxt pat grhss
1170 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
1172 -----------------------------------------------
1173 sigContextsCtxt sig1 sig2
1174 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
1175 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1176 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1177 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
1183 -----------------------------------------------
1184 unboxedTupleErr name ty
1185 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
1186 4 (ppr name <+> dcolon <+> ppr ty)
1188 -----------------------------------------------
1189 restrictedBindCtxtErr binder_names
1190 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
1191 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
1192 ptext SLIT("that falls under the monomorphism restriction")])
1194 genCtxt binder_names
1195 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
1197 missingSigWarn False name ty = return ()
1198 missingSigWarn True name ty
1199 = do { env0 <- tcInitTidyEnv
1200 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1201 ; addWarnTcM (env1, mk_msg tidy_ty) }
1203 mk_msg ty = vcat [ptext SLIT("Definition but no type signature for") <+> quotes (ppr name),
1204 sep [ptext SLIT("Inferred type:") <+> pprHsVar name <+> dcolon <+> ppr ty]]