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 { let name = idName poly_id
428 ; spec_ty <- tcHsSigType (FunSigCtxt name) hs_ty
429 ; co_fn <- tcSubExp (SpecPragOrigin name) (idType poly_id) spec_ty
430 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty inl) }
431 -- Most of the work of specialisation is done by
432 -- the desugarer, guided by the SpecPrag
435 -- If typechecking the binds fails, then return with each
436 -- signature-less binder given type (forall a.a), to minimise
437 -- subsequent error messages
438 recoveryCode binder_names sig_fn
439 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
440 ; poly_ids <- mapM mk_dummy binder_names
441 ; return ([], poly_ids) }
444 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
445 | otherwise = return (mkLocalId name forall_a_a) -- No signature
448 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
451 -- Check that non-overloaded unlifted bindings are
454 -- c) not a multiple-binding group (more or less implied by (a))
456 checkStrictBinds :: TopLevelFlag -> RecFlag
457 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
459 checkStrictBinds top_lvl rec_group mbind mono_tys infos
460 | unlifted || bang_pat
461 = do { checkTc (isNotTopLevel top_lvl)
462 (strictBindErr "Top-level" unlifted mbind)
463 ; checkTc (isNonRec rec_group)
464 (strictBindErr "Recursive" unlifted mbind)
465 ; checkTc (isSingletonBag mbind)
466 (strictBindErr "Multiple" unlifted mbind)
467 ; mapM_ check_sig infos
472 unlifted = any isUnLiftedType mono_tys
473 bang_pat = anyBag (isBangHsBind . unLoc) mbind
474 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
475 (badStrictSig unlifted sig)
476 check_sig other = return ()
478 strictBindErr flavour unlifted mbind
479 = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:"))
480 4 (pprLHsBinds mbind)
482 msg | unlifted = ptext SLIT("bindings for unlifted types")
483 | otherwise = ptext SLIT("bang-pattern bindings")
485 badStrictSig unlifted sig
486 = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
489 msg | unlifted = ptext SLIT("an unlifted binding")
490 | otherwise = ptext SLIT("a bang-pattern binding")
494 %************************************************************************
496 \subsection{tcMonoBind}
498 %************************************************************************
500 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
501 The signatures have been dealt with already.
504 tcMonoBinds :: [LHsBind Name]
506 -> RecFlag -- Whether the binding is recursive for typechecking purposes
507 -- i.e. the binders are mentioned in their RHSs, and
508 -- we are not resuced by a type signature
509 -> TcM (LHsBinds TcId, [MonoBindInfo])
511 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
512 fun_matches = matches, bind_fvs = fvs })]
513 sig_fn -- Single function binding,
514 NonRecursive -- binder isn't mentioned in RHS,
515 | Nothing <- sig_fn name -- ...with no type signature
516 = -- In this very special case we infer the type of the
517 -- right hand side first (it may have a higher-rank type)
518 -- and *then* make the monomorphic Id for the LHS
519 -- e.g. f = \(x::forall a. a->a) -> <body>
520 -- We want to infer a higher-rank type for f
522 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
524 -- Check for an unboxed tuple type
525 -- f = (# True, False #)
526 -- Zonk first just in case it's hidden inside a meta type variable
527 -- (This shows up as a (more obscure) kind error
528 -- in the 'otherwise' case of tcMonoBinds.)
529 ; zonked_rhs_ty <- zonkTcType rhs_ty
530 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
531 (unboxedTupleErr name zonked_rhs_ty)
533 ; mono_name <- newLocalName name
534 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
535 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
536 fun_matches = matches', bind_fvs = fvs,
537 fun_co_fn = co_fn, fun_tick = Nothing })),
538 [(name, Nothing, mono_id)]) }
540 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
541 fun_matches = matches, bind_fvs = fvs })]
542 sig_fn -- Single function binding
544 | Just scoped_tvs <- sig_fn name -- ...with a type signature
545 = -- When we have a single function binding, with a type signature
546 -- we can (a) use genuine, rigid skolem constants for the type variables
547 -- (b) bring (rigid) scoped type variables into scope
549 do { tc_sig <- tcInstSig True name
550 ; mono_name <- newLocalName name
551 ; let mono_ty = sig_tau tc_sig
552 mono_id = mkLocalId mono_name mono_ty
553 rhs_tvs = [ (name, mkTyVarTy tv)
554 | (name, tv) <- scoped_tvs `zip` sig_tvs tc_sig ]
555 -- See Note [More instantiated than scoped]
556 -- Note that the scoped_tvs and the (sig_tvs sig)
557 -- may have different Names. That's quite ok.
559 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
560 tcMatchesFun mono_name inf matches mono_ty
562 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
563 fun_infix = inf, fun_matches = matches',
564 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
566 ; return (unitBag (L b_loc fun_bind'),
567 [(name, Just tc_sig, mono_id)]) }
569 tcMonoBinds binds sig_fn non_rec
570 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
572 -- Bring the monomorphic Ids, into scope for the RHSs
573 ; let mono_info = getMonoBindInfo tc_binds
574 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
575 -- A monomorphic binding for each term variable that lacks
576 -- a type sig. (Ones with a sig are already in scope.)
578 ; binds' <- tcExtendIdEnv2 rhs_id_env $
579 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
580 | (n,id) <- rhs_id_env]) `thenM_`
581 mapM (wrapLocM tcRhs) tc_binds
582 ; return (listToBag binds', mono_info) }
584 ------------------------
585 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
586 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
587 -- if there's a signature for it, use the instantiated signature type
588 -- otherwise invent a type variable
589 -- You see that quite directly in the FunBind case.
591 -- But there's a complication for pattern bindings:
592 -- data T = MkT (forall a. a->a)
594 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
595 -- but we want to get (f::forall a. a->a) as the RHS environment.
596 -- The simplest way to do this is to typecheck the pattern, and then look up the
597 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
598 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
600 data TcMonoBind -- Half completed; LHS done, RHS not done
601 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
602 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
604 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
605 -- Type signature (if any), and
606 -- the monomorphic bound things
608 bndrNames :: [MonoBindInfo] -> [Name]
609 bndrNames mbi = [n | (n,_,_) <- mbi]
611 getMonoType :: MonoBindInfo -> TcTauType
612 getMonoType (_,_,mono_id) = idType mono_id
614 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
615 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
616 = do { mb_sig <- tcInstSig_maybe sig_fn name
617 ; mono_name <- newLocalName name
618 ; mono_ty <- mk_mono_ty mb_sig
619 ; let mono_id = mkLocalId mono_name mono_ty
620 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
622 mk_mono_ty (Just sig) = return (sig_tau sig)
623 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
625 tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
626 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
627 ; mono_pat_binds <- doptM Opt_MonoPatBinds
628 -- With -fmono-pat-binds, we do no generalisation of pattern bindings
629 -- But the signature can still be polymoprhic!
630 -- data T = MkT (forall a. a->a)
631 -- x :: forall a. a->a
633 -- The function get_sig_ty decides whether the pattern-bound variables
634 -- should have exactly the type in the type signature (-fmono-pat-binds),
635 -- or the instantiated version (-fmono-pat-binds)
637 ; let nm_sig_prs = names `zip` mb_sigs
638 get_sig_ty | mono_pat_binds = idType . sig_id
639 | otherwise = sig_tau
640 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
641 | (name, Just sig) <- nm_sig_prs]
642 sig_tau_fn = lookupNameEnv tau_sig_env
644 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
645 mapM lookup_info nm_sig_prs
647 -- After typechecking the pattern, look up the binder
648 -- names, which the pattern has brought into scope.
649 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
650 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
651 ; return (name, mb_sig, mono_id) }
653 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
656 ; return (TcPatBind infos pat' grhss pat_ty) }
658 names = collectPatBinders pat
661 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
662 -- AbsBind, VarBind impossible
665 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
666 -- When we are doing pattern bindings, or multiple function bindings at a time
667 -- we *don't* bring any scoped type variables into scope
668 -- Wny not? They are not completely rigid.
669 -- That's why we have the special case for a single FunBind in tcMonoBinds
670 tcRhs (TcFunBind (_,_,mono_id) fun' inf matches)
671 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
672 matches (idType mono_id)
673 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
674 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
675 fun_tick = Nothing }) }
677 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
678 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
679 tcGRHSsPat grhss pat_ty
680 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
681 bind_fvs = placeHolderNames }) }
684 ---------------------
685 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
686 getMonoBindInfo tc_binds
687 = foldr (get_info . unLoc) [] tc_binds
689 get_info (TcFunBind info _ _ _) rest = info : rest
690 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
694 %************************************************************************
698 %************************************************************************
701 generalise :: DynFlags -> TopLevelFlag
702 -> [LHsBind Name] -> TcSigFun
703 -> [MonoBindInfo] -> [Inst]
704 -> TcM ([TyVar], [Inst], TcDictBinds)
705 -- The returned [TyVar] are all ready to quantify
707 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
708 | isMonoGroup dflags bind_list
709 = do { extendLIEs lie_req
710 ; return ([], [], emptyBag) }
712 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
713 = -- Check signature contexts are empty
714 do { checkTc (all is_mono_sig sigs)
715 (restrictedBindCtxtErr bndrs)
717 -- Now simplify with exactly that set of tyvars
718 -- We have to squash those Methods
719 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
722 -- Check that signature type variables are OK
723 ; final_qtvs <- checkSigsTyVars qtvs sigs
725 ; return (final_qtvs, [], binds) }
727 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
728 = tcSimplifyInfer doc tau_tvs lie_req
730 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
731 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
732 ; let -- The "sig_avails" is the stuff available. We get that from
733 -- the context of the type signature, BUT ALSO the lie_avail
734 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
735 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
736 sig_avails = sig_lie ++ local_meths
737 loc = sig_loc (head sigs)
739 -- Check that the needed dicts can be
740 -- expressed in terms of the signature ones
741 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
743 -- Check that signature type variables are OK
744 ; final_qtvs <- checkSigsTyVars qtvs sigs
746 ; returnM (final_qtvs, sig_lie, binds) }
748 bndrs = bndrNames mono_infos
749 sigs = [sig | (_, Just sig, _) <- mono_infos]
750 get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
751 | otherwise = exactTyVarsOfType
752 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
753 is_mono_sig sig = null (sig_theta sig)
754 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
756 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
757 sig_theta = theta, sig_loc = loc }) mono_id
758 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
759 tci_theta = theta, tci_loc = loc}
762 unifyCtxts checks that all the signature contexts are the same
763 The type signatures on a mutually-recursive group of definitions
764 must all have the same context (or none).
766 The trick here is that all the signatures should have the same
767 context, and we want to share type variables for that context, so that
768 all the right hand sides agree a common vocabulary for their type
771 We unify them because, with polymorphic recursion, their types
772 might not otherwise be related. This is a rather subtle issue.
775 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
776 -- Post-condition: the returned Insts are full zonked
777 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
778 = do { mapM unify_ctxt sigs
779 ; theta <- zonkTcThetaType (sig_theta sig1)
780 ; newDictBndrs (sig_loc sig1) theta }
782 theta1 = sig_theta sig1
783 unify_ctxt :: TcSigInfo -> TcM ()
784 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
785 = setSrcSpan (instLocSpan (sig_loc sig)) $
786 addErrCtxt (sigContextsCtxt sig1 sig) $
787 do { cois <- unifyTheta theta1 theta
788 ; -- Check whether all coercions are identity coercions
789 -- That can happen if we have, say
791 -- g :: C (F a) => ...
792 -- where F is a type function and (F a ~ [a])
793 -- Then unification might succeed with a coercion. But it's much
794 -- much simpler to require that such signatures have identical contexts
795 checkTc (all isIdentityCoercion cois)
796 (ptext SLIT("Mutually dependent functions have syntactically distinct contexts"))
799 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
800 checkSigsTyVars qtvs sigs
801 = do { gbl_tvs <- tcGetGlobalTyVars
802 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
804 ; let -- Sigh. Make sure that all the tyvars in the type sigs
805 -- appear in the returned ty var list, which is what we are
806 -- going to generalise over. Reason: we occasionally get
808 -- type T a = () -> ()
811 -- Here, 'a' won't appear in qtvs, so we have to add it
812 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
813 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
816 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
817 sig_theta = theta, sig_tau = tau})
818 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
819 addErrCtxtM (sigCtxt id tvs theta tau) $
820 do { tvs' <- checkDistinctTyVars tvs
821 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
822 (bleatEscapedTvs gbl_tvs tvs tvs')
825 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
826 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
827 -- are still all type variables, and all distinct from each other.
828 -- It returns a zonked set of type variables.
829 -- For example, if the type sig is
830 -- f :: forall a b. a -> b -> b
831 -- we want to check that 'a' and 'b' haven't
832 -- (a) been unified with a non-tyvar type
833 -- (b) been unified with each other (all distinct)
835 checkDistinctTyVars sig_tvs
836 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
837 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
838 ; return zonked_tvs }
840 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
841 -- The TyVarEnv maps each zonked type variable back to its
842 -- corresponding user-written signature type variable
843 check_dup acc (sig_tv, zonked_tv)
844 = case lookupVarEnv acc zonked_tv of
845 Just sig_tv' -> bomb_out sig_tv sig_tv'
847 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
849 bomb_out sig_tv1 sig_tv2
850 = do { env0 <- tcInitTidyEnv
851 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
852 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
853 msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
854 <+> ptext SLIT("is unified with another quantified type variable")
855 <+> quotes (ppr tidy_tv2)
856 ; failWithTcM (env2, msg) }
861 @getTyVarsToGen@ decides what type variables to generalise over.
863 For a "restricted group" -- see the monomorphism restriction
864 for a definition -- we bind no dictionaries, and
865 remove from tyvars_to_gen any constrained type variables
867 *Don't* simplify dicts at this point, because we aren't going
868 to generalise over these dicts. By the time we do simplify them
869 we may well know more. For example (this actually came up)
871 f x = array ... xs where xs = [1,2,3,4,5]
872 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
873 stuff. If we simplify only at the f-binding (not the xs-binding)
874 we'll know that the literals are all Ints, and we can just produce
877 Find all the type variables involved in overloading, the
878 "constrained_tyvars". These are the ones we *aren't* going to
879 generalise. We must be careful about doing this:
881 (a) If we fail to generalise a tyvar which is not actually
882 constrained, then it will never, ever get bound, and lands
883 up printed out in interface files! Notorious example:
884 instance Eq a => Eq (Foo a b) where ..
885 Here, b is not constrained, even though it looks as if it is.
886 Another, more common, example is when there's a Method inst in
887 the LIE, whose type might very well involve non-overloaded
889 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
890 the simple thing instead]
892 (b) On the other hand, we mustn't generalise tyvars which are constrained,
893 because we are going to pass on out the unmodified LIE, with those
894 tyvars in it. They won't be in scope if we've generalised them.
896 So we are careful, and do a complete simplification just to find the
897 constrained tyvars. We don't use any of the results, except to
898 find which tyvars are constrained.
900 Note [Polymorphic recursion]
901 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
902 The game plan for polymorphic recursion in the code above is
904 * Bind any variable for which we have a type signature
905 to an Id with a polymorphic type. Then when type-checking
906 the RHSs we'll make a full polymorphic call.
908 This fine, but if you aren't a bit careful you end up with a horrendous
909 amount of partial application and (worse) a huge space leak. For example:
911 f :: Eq a => [a] -> [a]
914 If we don't take care, after typechecking we get
916 f = /\a -> \d::Eq a -> let f' = f a d
920 Notice the the stupid construction of (f a d), which is of course
921 identical to the function we're executing. In this case, the
922 polymorphic recursion isn't being used (but that's a very common case).
923 This can lead to a massive space leak, from the following top-level defn
929 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
930 f' is another thunk which evaluates to the same thing... and you end
931 up with a chain of identical values all hung onto by the CAF ff.
935 = let f' = f Int dEqInt in \ys. ...f'...
937 = let f' = let f' = f Int dEqInt in \ys. ...f'...
942 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
943 which would make the space leak go away in this case
945 Solution: when typechecking the RHSs we always have in hand the
946 *monomorphic* Ids for each binding. So we just need to make sure that
947 if (Method f a d) shows up in the constraints emerging from (...f...)
948 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
949 to the "givens" when simplifying constraints. That's what the "lies_avail"
954 f = /\a -> \d::Eq a -> letrec
955 fm = \ys:[a] -> ...fm...
961 %************************************************************************
965 %************************************************************************
967 Type signatures are tricky. See Note [Signature skolems] in TcType
969 @tcSigs@ checks the signatures for validity, and returns a list of
970 {\em freshly-instantiated} signatures. That is, the types are already
971 split up, and have fresh type variables installed. All non-type-signature
972 "RenamedSigs" are ignored.
974 The @TcSigInfo@ contains @TcTypes@ because they are unified with
975 the variable's type, and after that checked to see whether they've
980 The -XScopedTypeVariables flag brings lexically-scoped type variables
981 into scope for any explicitly forall-quantified type variables:
982 f :: forall a. a -> a
984 Then 'a' is in scope inside 'e'.
986 However, we do *not* support this
987 - For pattern bindings e.g
991 - For multiple function bindings, unless Opt_RelaxedPolyRec is on
992 f :: forall a. a -> a
994 g :: forall b. b -> b
996 Reason: we use mutable variables for 'a' and 'b', since they may
997 unify to each other, and that means the scoped type variable would
998 not stand for a completely rigid variable.
1000 Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
1003 Note [More instantiated than scoped]
1004 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1005 There may be more instantiated type variables than lexically-scoped
1007 type T a = forall b. b -> (a,b)
1009 Here, the signature for f will have one scoped type variable, c,
1010 but two instantiated type variables, c' and b'.
1012 We assume that the scoped ones are at the *front* of sig_tvs,
1013 and remember the names from the original HsForAllTy in the TcSigFun.
1017 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
1018 -- type variables brought into scope
1019 -- by its type signature.
1020 -- Nothing => no type signature
1022 mkTcSigFun :: [LSig Name] -> TcSigFun
1023 -- Search for a particular type signature
1024 -- Precondition: the sigs are all type sigs
1025 -- Precondition: no duplicates
1026 mkTcSigFun sigs = lookupNameEnv env
1028 env = mkNameEnv [(name, hsExplicitTvs lhs_ty)
1029 | L span (TypeSig (L _ name) lhs_ty) <- sigs]
1030 -- The scoped names are the ones explicitly mentioned
1031 -- in the HsForAll. (There may be more in sigma_ty, because
1032 -- of nested type synonyms. See Note [More instantiated than scoped].)
1033 -- See Note [Only scoped tyvars are in the TyVarEnv]
1038 sig_id :: TcId, -- *Polymorphic* binder for this value...
1040 sig_tvs :: [TcTyVar], -- Instantiated type variables
1041 -- See Note [Instantiate sig]
1043 sig_theta :: TcThetaType, -- Instantiated theta
1044 sig_tau :: TcTauType, -- Instantiated tau
1045 sig_loc :: InstLoc -- The location of the signature
1049 -- Note [Only scoped tyvars are in the TyVarEnv]
1050 -- We are careful to keep only the *lexically scoped* type variables in
1051 -- the type environment. Why? After all, the renamer has ensured
1052 -- that only legal occurrences occur, so we could put all type variables
1053 -- into the type env.
1055 -- But we want to check that two distinct lexically scoped type variables
1056 -- do not map to the same internal type variable. So we need to know which
1057 -- the lexically-scoped ones are... and at the moment we do that by putting
1058 -- only the lexically scoped ones into the environment.
1061 -- Note [Instantiate sig]
1062 -- It's vital to instantiate a type signature with fresh variables.
1064 -- type S = forall a. a->a
1068 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1069 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1070 -- it's all cool; each signature has distinct type variables from the renamer.)
1072 instance Outputable TcSigInfo where
1073 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1074 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
1078 tcTySig :: LSig Name -> TcM TcId
1079 tcTySig (L span (TypeSig (L _ name) ty))
1081 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1082 ; return (mkLocalId name sigma_ty) }
1085 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1086 -- Instantiate with *meta* type variables;
1087 -- this signature is part of a multi-signature group
1088 tcInstSig_maybe sig_fn name
1089 = case sig_fn name of
1090 Nothing -> return Nothing
1091 Just scoped_tvs -> do { tc_sig <- tcInstSig False name
1092 ; return (Just tc_sig) }
1093 -- NB: the scoped_tvs may be non-empty, but we can
1094 -- just ignore them. See Note [Scoped tyvars].
1096 tcInstSig :: Bool -> Name -> TcM TcSigInfo
1097 -- Instantiate the signature, with either skolems or meta-type variables
1098 -- depending on the use_skols boolean. This variable is set True
1099 -- when we are typechecking a single function binding; and False for
1100 -- pattern bindings and a group of several function bindings.
1101 -- Reason: in the latter cases, the "skolems" can be unified together,
1102 -- so they aren't properly rigid in the type-refinement sense.
1103 -- NB: unless we are doing H98, each function with a sig will be done
1104 -- separately, even if it's mutually recursive, so use_skols will be True
1106 -- We always instantiate with fresh uniques,
1107 -- although we keep the same print-name
1109 -- type T = forall a. [a] -> [a]
1111 -- f = g where { g :: T; g = <rhs> }
1113 -- We must not use the same 'a' from the defn of T at both places!!
1115 tcInstSig use_skols name
1116 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1117 -- scope when starting the binding group
1118 ; let skol_info = SigSkol (FunSigCtxt name)
1119 inst_tyvars = tcInstSigTyVars use_skols skol_info
1120 ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
1121 ; loc <- getInstLoc (SigOrigin skol_info)
1122 ; return (TcSigInfo { sig_id = poly_id,
1123 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1127 isMonoGroup :: DynFlags -> [LHsBind Name] -> Bool
1128 -- No generalisation at all
1129 isMonoGroup dflags binds
1130 = dopt Opt_MonoPatBinds dflags && any is_pat_bind binds
1132 is_pat_bind (L _ (PatBind {})) = True
1133 is_pat_bind other = False
1136 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1137 isRestrictedGroup dflags binds sig_fn
1138 = mono_restriction && not all_unrestricted
1140 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1141 all_unrestricted = all (unrestricted . unLoc) binds
1142 has_sig n = isJust (sig_fn n)
1144 unrestricted (PatBind {}) = False
1145 unrestricted (VarBind { var_id = v }) = has_sig v
1146 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1147 || has_sig (unLoc v)
1149 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1150 -- No args => like a pattern binding
1151 unrestricted_match other = True
1152 -- Some args => a function binding
1156 %************************************************************************
1158 \subsection[TcBinds-errors]{Error contexts and messages}
1160 %************************************************************************
1164 -- This one is called on LHS, when pat and grhss are both Name
1165 -- and on RHS, when pat is TcId and grhss is still Name
1166 patMonoBindsCtxt pat grhss
1167 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
1169 -----------------------------------------------
1170 sigContextsCtxt sig1 sig2
1171 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
1172 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1173 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1174 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
1180 -----------------------------------------------
1181 unboxedTupleErr name ty
1182 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
1183 4 (ppr name <+> dcolon <+> ppr ty)
1185 -----------------------------------------------
1186 restrictedBindCtxtErr binder_names
1187 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
1188 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
1189 ptext SLIT("that falls under the monomorphism restriction")])
1191 genCtxt binder_names
1192 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
1194 missingSigWarn False name ty = return ()
1195 missingSigWarn True name ty
1196 = do { env0 <- tcInitTidyEnv
1197 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1198 ; addWarnTcM (env1, mk_msg tidy_ty) }
1200 mk_msg ty = vcat [ptext SLIT("Definition but no type signature for") <+> quotes (ppr name),
1201 sep [ptext SLIT("Inferred type:") <+> ppr name <+> dcolon <+> ppr ty]]