2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcBinds]{TcBinds}
8 module TcBinds ( tcLocalBinds, tcTopBinds,
9 tcHsBootSigs, tcMonoBinds, tcPolyBinds,
10 TcPragFun, tcSpecPrag, tcPrags, mkPragFun,
11 TcSigInfo(..), TcSigFun, mkTcSigFun,
12 badBootDeclErr ) where
14 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
15 import {-# SOURCE #-} TcExpr ( tcMonoExpr )
29 import {- Kind parts of -} Type
54 %************************************************************************
56 \subsection{Type-checking bindings}
58 %************************************************************************
60 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
61 it needs to know something about the {\em usage} of the things bound,
62 so that it can create specialisations of them. So @tcBindsAndThen@
63 takes a function which, given an extended environment, E, typechecks
64 the scope of the bindings returning a typechecked thing and (most
65 important) an LIE. It is this LIE which is then used as the basis for
66 specialising the things bound.
68 @tcBindsAndThen@ also takes a "combiner" which glues together the
69 bindings and the "thing" to make a new "thing".
71 The real work is done by @tcBindWithSigsAndThen@.
73 Recursive and non-recursive binds are handled in essentially the same
74 way: because of uniques there are no scoping issues left. The only
75 difference is that non-recursive bindings can bind primitive values.
77 Even for non-recursive binding groups we add typings for each binder
78 to the LVE for the following reason. When each individual binding is
79 checked the type of its LHS is unified with that of its RHS; and
80 type-checking the LHS of course requires that the binder is in scope.
82 At the top-level the LIE is sure to contain nothing but constant
83 dictionaries, which we resolve at the module level.
86 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
87 -- Note: returning the TcLclEnv is more than we really
88 -- want. The bit we care about is the local bindings
89 -- and the free type variables thereof
91 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
92 ; return (foldr (unionBags . snd) emptyBag prs, env) }
93 -- The top level bindings are flattened into a giant
94 -- implicitly-mutually-recursive LHsBinds
96 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
97 -- A hs-boot file has only one BindGroup, and it only has type
98 -- signatures in it. The renamer checked all this
99 tcHsBootSigs (ValBindsOut binds sigs)
100 = do { checkTc (null binds) badBootDeclErr
101 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
103 tc_boot_sig (TypeSig (L _ name) ty)
104 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
105 ; return (mkVanillaGlobal name sigma_ty) }
106 -- Notice that we make GlobalIds, not LocalIds
107 tc_boot_sig s = pprPanic "tcHsBootSigs/tc_boot_sig" (ppr s)
108 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
110 badBootDeclErr :: Message
111 badBootDeclErr = ptext (sLit "Illegal declarations in an hs-boot file")
113 ------------------------
114 tcLocalBinds :: HsLocalBinds Name -> TcM thing
115 -> TcM (HsLocalBinds TcId, thing)
117 tcLocalBinds EmptyLocalBinds thing_inside
118 = do { thing <- thing_inside
119 ; return (EmptyLocalBinds, thing) }
121 tcLocalBinds (HsValBinds binds) thing_inside
122 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
123 ; return (HsValBinds binds', thing) }
125 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
126 = do { (thing, lie) <- getLIE thing_inside
127 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
129 -- If the binding binds ?x = E, we must now
130 -- discharge any ?x constraints in expr_lie
131 ; dict_binds <- tcSimplifyIPs avail_ips lie
132 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
134 -- I wonder if we should do these one at at time
137 tc_ip_bind (IPBind ip expr) = do
138 ty <- newFlexiTyVarTy argTypeKind
139 (ip', ip_inst) <- newIPDict (IPBindOrigin ip) ip ty
140 expr' <- tcMonoExpr expr ty
141 return (ip_inst, (IPBind ip' expr'))
143 ------------------------
144 tcValBinds :: TopLevelFlag
145 -> HsValBinds Name -> TcM thing
146 -> TcM (HsValBinds TcId, thing)
148 tcValBinds _ (ValBindsIn binds _) _
149 = pprPanic "tcValBinds" (ppr binds)
151 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
152 = do { -- Typecheck the signature
153 ; let { prag_fn = mkPragFun sigs
154 ; ty_sigs = filter isVanillaLSig sigs
155 ; sig_fn = mkTcSigFun ty_sigs }
157 ; poly_ids <- checkNoErrs (mapAndRecoverM tcTySig ty_sigs)
158 -- No recovery from bad signatures, because the type sigs
159 -- may bind type variables, so proceeding without them
160 -- can lead to a cascade of errors
161 -- ToDo: this means we fall over immediately if any type sig
162 -- is wrong, which is over-conservative, see Trac bug #745
164 -- Extend the envt right away with all
165 -- the Ids declared with type signatures
166 ; poly_rec <- doptM Opt_RelaxedPolyRec
167 ; (binds', thing) <- tcExtendIdEnv poly_ids $
168 tcBindGroups poly_rec top_lvl sig_fn prag_fn
171 ; return (ValBindsOut binds' sigs, thing) }
173 ------------------------
174 tcBindGroups :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
175 -> [(RecFlag, LHsBinds Name)] -> TcM thing
176 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
177 -- Typecheck a whole lot of value bindings,
178 -- one strongly-connected component at a time
179 -- Here a "strongly connected component" has the strightforward
180 -- meaning of a group of bindings that mention each other,
181 -- ignoring type signatures (that part comes later)
183 tcBindGroups _ _ _ _ [] thing_inside
184 = do { thing <- thing_inside
185 ; return ([], thing) }
187 tcBindGroups poly_rec top_lvl sig_fn prag_fn (group : groups) thing_inside
188 = do { (group', (groups', thing))
189 <- tc_group poly_rec top_lvl sig_fn prag_fn group $
190 tcBindGroups poly_rec top_lvl sig_fn prag_fn groups thing_inside
191 ; return (group' ++ groups', thing) }
193 ------------------------
194 tc_group :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
195 -> (RecFlag, LHsBinds Name) -> TcM thing
196 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
198 -- Typecheck one strongly-connected component of the original program.
199 -- We get a list of groups back, because there may
200 -- be specialisations etc as well
202 tc_group _ top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
203 -- A single non-recursive binding
204 -- We want to keep non-recursive things non-recursive
205 -- so that we desugar unlifted bindings correctly
206 = do { (binds1, lie_binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn
207 NonRecursive binds thing_inside
208 ; return ( [(NonRecursive, unitBag b) | b <- bagToList binds1]
209 ++ [(Recursive, lie_binds)] -- TcDictBinds have scrambled dependency order
212 tc_group poly_rec top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
213 | not poly_rec -- Recursive group, normal Haskell 98 route
214 = do { (binds1, lie_binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn
215 Recursive binds thing_inside
216 ; return ([(Recursive, binds1 `unionBags` lie_binds)], thing) }
218 | otherwise -- Recursive group, with -XRelaxedPolyRec
219 = -- To maximise polymorphism (with -XRelaxedPolyRec), 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
224 -- the original group at once; an earlier one may use a later one!
225 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
226 ; (binds1,lie_binds,thing) <- bindLocalInsts top_lvl $
227 go (stronglyConnCompFromEdgedVertices (mkEdges sig_fn binds))
228 ; return ([(Recursive, binds1 `unionBags` lie_binds)], thing) }
229 -- Rec them all together
231 -- go :: SCC (LHsBind Name) -> TcM (LHsBinds TcId, [TcId], thing)
232 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
233 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
234 ; return (binds1 `unionBags` binds2, ids1 ++ ids2, thing) }
235 go [] = do { thing <- thing_inside; return (emptyBag, [], 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 :: TopLevelFlag -> TcSigFun -> TcPragFun -> RecFlag
243 -> LHsBinds Name -> TcM a -> TcM (LHsBinds TcId, TcDictBinds, a)
244 tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside
245 = bindLocalInsts top_lvl $
246 do { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds
247 ; thing <- tcExtendIdEnv ids thing_inside
248 ; return (binds1, ids, thing) }
250 ------------------------
251 bindLocalInsts :: TopLevelFlag
252 -> TcM (LHsBinds TcId, [TcId], a)
253 -> TcM (LHsBinds TcId, TcDictBinds, a)
254 bindLocalInsts top_lvl thing_inside
256 = do { (binds, _, thing) <- thing_inside; return (binds, emptyBag, thing) }
257 -- For the top level don't bother with all this bindInstsOfLocalFuns stuff.
258 -- All the top level things are rec'd together anyway, so it's fine to
259 -- leave them to the tcSimplifyTop, and quite a bit faster too
261 | otherwise -- Nested case
262 = do { ((binds, ids, thing), lie) <- getLIE thing_inside
263 ; lie_binds <- bindInstsOfLocalFuns lie ids
264 ; return (binds, lie_binds, thing) }
266 ------------------------
267 mkEdges :: TcSigFun -> LHsBinds Name
268 -> [(LHsBind Name, BKey, [BKey])]
270 type BKey = Int -- Just number off the bindings
273 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
274 Just key <- [lookupNameEnv key_map n], no_sig n ])
275 | (bind, key) <- keyd_binds
278 no_sig :: Name -> Bool
279 no_sig n = isNothing (sig_fn n)
281 keyd_binds = bagToList binds `zip` [0::BKey ..]
283 key_map :: NameEnv BKey -- Which binding it comes from
284 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
285 , bndr <- bindersOfHsBind bind ]
287 bindersOfHsBind :: HsBind Name -> [Name]
288 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
289 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
290 bindersOfHsBind (AbsBinds {}) = panic "bindersOfHsBind AbsBinds"
291 bindersOfHsBind (VarBind {}) = panic "bindersOfHsBind VarBind"
293 ------------------------
294 tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragFun
295 -> RecFlag -- Whether the group is really recursive
296 -> RecFlag -- Whether it's recursive after breaking
297 -- dependencies based on type signatures
299 -> TcM (LHsBinds TcId, [TcId])
301 -- Typechecks a single bunch of bindings all together,
302 -- and generalises them. The bunch may be only part of a recursive
303 -- group, because we use type signatures to maximise polymorphism
305 -- Returns a list because the input may be a single non-recursive binding,
306 -- in which case the dependency order of the resulting bindings is
309 -- Knows nothing about the scope of the bindings
311 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds
313 bind_list = bagToList binds
314 binder_names = collectHsBindBinders binds
315 loc = getLoc (head bind_list)
316 -- TODO: location a bit awkward, but the mbinds have been
317 -- dependency analysed and may no longer be adjacent
319 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
321 recoverM (recoveryCode binder_names sig_fn) $ do
323 { traceTc (ptext (sLit "------------------------------------------------"))
324 ; traceTc (ptext (sLit "Bindings for") <+> ppr binder_names)
326 -- TYPECHECK THE BINDINGS
327 ; ((binds', mono_bind_infos), lie_req)
328 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
329 ; traceTc (text "temp" <+> (ppr binds' $$ ppr lie_req))
331 -- CHECK FOR UNLIFTED BINDINGS
332 -- These must be non-recursive etc, and are not generalised
333 -- They desugar to a case expression in the end
334 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
335 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
336 zonked_mono_tys mono_bind_infos
338 do { extendLIEs lie_req
339 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
340 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
341 mk_export (_, Just sig, mono_id) _ = ([], sig_id sig, mono_id, [])
342 -- ToDo: prags for unlifted bindings
344 ; return ( unitBag $ L loc $ AbsBinds [] [] exports binds',
345 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
347 else do -- The normal lifted case: GENERALISE
349 ; (tyvars_to_gen, dicts, dict_binds)
350 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
351 generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
353 -- BUILD THE POLYMORPHIC RESULT IDs
354 ; let dict_vars = map instToVar dicts -- May include equality constraints
355 ; exports <- mapM (mkExport top_lvl rec_group prag_fn tyvars_to_gen (map varType dict_vars))
358 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
359 ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids))
361 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen
363 (dict_binds `unionBags` binds')
365 ; return (unitBag abs_bind, poly_ids) -- poly_ids are guaranteed zonked by mkExport
370 mkExport :: TopLevelFlag -> RecFlag -> TcPragFun -> [TyVar] -> [TcType]
372 -> TcM ([TyVar], Id, Id, [LPrag])
373 -- mkExport generates exports with
374 -- zonked type variables,
376 -- The former is just because no further unifications will change
377 -- the quantified type variables, so we can fix their final form
379 -- The latter is needed because the poly_ids are used to extend the
380 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
382 -- Pre-condition: the inferred_tvs are already zonked
384 mkExport top_lvl rec_group prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
385 = do { warn_missing_sigs <- doptM Opt_WarnMissingSigs
386 ; let warn = isTopLevel top_lvl && warn_missing_sigs
387 ; (tvs, poly_id) <- mk_poly_id warn mb_sig
388 -- poly_id has a zonked type
390 ; prags <- tcPrags rec_group poly_id (prag_fn poly_name)
391 -- tcPrags requires a zonked poly_id
393 ; return (tvs, poly_id, mono_id, prags) }
395 poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id))
397 mk_poly_id warn Nothing = do { poly_ty' <- zonkTcType poly_ty
398 ; missingSigWarn warn poly_name poly_ty'
399 ; return (inferred_tvs, mkLocalId poly_name poly_ty') }
400 mk_poly_id _ (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
401 ; return (tvs, sig_id sig) }
403 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
405 ------------------------
406 type TcPragFun = Name -> [LSig Name]
408 mkPragFun :: [LSig Name] -> TcPragFun
409 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
411 prs = [(expectJust "mkPragFun" (sigName sig), sig)
412 | sig <- sigs, isPragLSig sig]
413 env = foldl add emptyNameEnv prs
414 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
416 tcPrags :: RecFlag -> Id -> [LSig Name] -> TcM [LPrag]
417 -- Pre-condition: the poly_id is zonked
418 -- Reason: required by tcSubExp
419 tcPrags rec_group poly_id prags = mapM tc_lprag prags
421 tc_lprag :: LSig Name -> TcM LPrag
422 tc_lprag (L loc prag) = setSrcSpan loc $
423 addErrCtxt (pragSigCtxt prag) $
424 do { prag' <- tc_prag prag
425 ; return (L loc prag') }
427 tc_prag (SpecSig _ hs_ty inl) = tcSpecPrag poly_id hs_ty inl
428 tc_prag (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
429 tc_prag (InlineSig _ inl) = do { warnIfRecInline rec_group inl poly_id
430 ; return (InlinePrag inl) }
431 tc_prag (FixSig {}) = panic "tcPrag FixSig"
432 tc_prag (TypeSig {}) = panic "tcPrag TypeSig"
434 pragSigCtxt :: Sig Name -> SDoc
435 pragSigCtxt prag = hang (ptext (sLit "In the pragma")) 2 (ppr prag)
437 warnIfRecInline :: RecFlag -> InlineSpec -> TcId -> TcM ()
438 warnIfRecInline rec_group (Inline _ is_inline) poly_id
439 | is_inline && isRec rec_group = addWarnTc warn
440 | otherwise = return ()
442 warn = ptext (sLit "INLINE pragma for recursive binder") <+> quotes (ppr poly_id)
443 <+> ptext (sLit "may be discarded")
445 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
446 tcSpecPrag poly_id hs_ty inl
447 = do { let name = idName poly_id
448 ; spec_ty <- tcHsSigType (FunSigCtxt name) hs_ty
449 ; co_fn <- tcSubExp (SpecPragOrigin name) (idType poly_id) spec_ty
450 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty inl) }
451 -- Most of the work of specialisation is done by
452 -- the desugarer, guided by the SpecPrag
455 -- If typechecking the binds fails, then return with each
456 -- signature-less binder given type (forall a.a), to minimise
457 -- subsequent error messages
458 recoveryCode :: [Name] -> (Name -> Maybe [Name])
459 -> TcM (LHsBinds TcId, [Id])
460 recoveryCode binder_names sig_fn
461 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
462 ; poly_ids <- mapM mk_dummy binder_names
463 ; return (emptyBag, poly_ids) }
466 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
467 | otherwise = return (mkLocalId name forall_a_a) -- No signature
470 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
473 -- Check that non-overloaded unlifted bindings are
476 -- c) not a multiple-binding group (more or less implied by (a))
478 checkStrictBinds :: TopLevelFlag -> RecFlag
479 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
481 checkStrictBinds top_lvl rec_group mbind mono_tys infos
482 | unlifted || bang_pat
483 = do { checkTc (isNotTopLevel top_lvl)
484 (strictBindErr "Top-level" unlifted mbind)
485 ; checkTc (isNonRec rec_group)
486 (strictBindErr "Recursive" unlifted mbind)
487 ; checkTc (isSingletonBag mbind)
488 (strictBindErr "Multiple" unlifted mbind)
489 ; mapM_ check_sig infos
494 unlifted = any isUnLiftedType mono_tys
495 bang_pat = anyBag (isBangHsBind . unLoc) mbind
496 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
497 (badStrictSig unlifted sig)
498 check_sig _ = return ()
500 strictBindErr :: String -> Bool -> LHsBindsLR Var Var -> SDoc
501 strictBindErr flavour unlifted mbind
502 = hang (text flavour <+> msg <+> ptext (sLit "aren't allowed:"))
503 4 (pprLHsBinds mbind)
505 msg | unlifted = ptext (sLit "bindings for unlifted types")
506 | otherwise = ptext (sLit "bang-pattern bindings")
508 badStrictSig :: Bool -> TcSigInfo -> SDoc
509 badStrictSig unlifted sig
510 = hang (ptext (sLit "Illegal polymorphic signature in") <+> msg)
513 msg | unlifted = ptext (sLit "an unlifted binding")
514 | otherwise = ptext (sLit "a bang-pattern binding")
518 %************************************************************************
520 \subsection{tcMonoBind}
522 %************************************************************************
524 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
525 The signatures have been dealt with already.
528 tcMonoBinds :: [LHsBind Name]
530 -> RecFlag -- Whether the binding is recursive for typechecking purposes
531 -- i.e. the binders are mentioned in their RHSs, and
532 -- we are not resuced by a type signature
533 -> TcM (LHsBinds TcId, [MonoBindInfo])
535 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
536 fun_matches = matches, bind_fvs = fvs })]
537 sig_fn -- Single function binding,
538 NonRecursive -- binder isn't mentioned in RHS,
539 | Nothing <- sig_fn name -- ...with no type signature
540 = -- In this very special case we infer the type of the
541 -- right hand side first (it may have a higher-rank type)
542 -- and *then* make the monomorphic Id for the LHS
543 -- e.g. f = \(x::forall a. a->a) -> <body>
544 -- We want to infer a higher-rank type for f
546 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
548 -- Check for an unboxed tuple type
549 -- f = (# True, False #)
550 -- Zonk first just in case it's hidden inside a meta type variable
551 -- (This shows up as a (more obscure) kind error
552 -- in the 'otherwise' case of tcMonoBinds.)
553 ; zonked_rhs_ty <- zonkTcType rhs_ty
554 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
555 (unboxedTupleErr name zonked_rhs_ty)
557 ; mono_name <- newLocalName name
558 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
559 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
560 fun_matches = matches', bind_fvs = fvs,
561 fun_co_fn = co_fn, fun_tick = Nothing })),
562 [(name, Nothing, mono_id)]) }
564 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
565 fun_matches = matches })]
566 sig_fn -- Single function binding
568 | Just scoped_tvs <- sig_fn name -- ...with a type signature
569 = -- When we have a single function binding, with a type signature
570 -- we can (a) use genuine, rigid skolem constants for the type variables
571 -- (b) bring (rigid) scoped type variables into scope
573 do { tc_sig <- tcInstSig True name
574 ; mono_name <- newLocalName name
575 ; let mono_ty = sig_tau tc_sig
576 mono_id = mkLocalId mono_name mono_ty
577 rhs_tvs = [ (name, mkTyVarTy tv)
578 | (name, tv) <- scoped_tvs `zip` sig_tvs tc_sig ]
579 -- See Note [More instantiated than scoped]
580 -- Note that the scoped_tvs and the (sig_tvs sig)
581 -- may have different Names. That's quite ok.
583 ; traceTc (text "tcMoonBinds" <+> ppr scoped_tvs $$ ppr tc_sig)
584 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
585 tcMatchesFun mono_name inf matches mono_ty
586 -- Note that "mono_ty" might actually be a polymorphic type,
587 -- if the original function had a signature like
588 -- forall a. Eq a => forall b. Ord b => ....
589 -- But that's ok: tcMatchesFun can deal with that
590 -- It happens, too! See Note [Polymorphic methods] in TcClassDcl.
592 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
593 fun_infix = inf, fun_matches = matches',
594 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
596 ; return (unitBag (L b_loc fun_bind'),
597 [(name, Just tc_sig, mono_id)]) }
599 tcMonoBinds binds sig_fn _
600 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
602 -- Bring the monomorphic Ids, into scope for the RHSs
603 ; let mono_info = getMonoBindInfo tc_binds
604 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
605 -- A monomorphic binding for each term variable that lacks
606 -- a type sig. (Ones with a sig are already in scope.)
608 ; binds' <- tcExtendIdEnv2 rhs_id_env $ do
609 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
610 | (n,id) <- rhs_id_env])
611 mapM (wrapLocM tcRhs) tc_binds
612 ; return (listToBag binds', mono_info) }
614 ------------------------
615 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
616 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
617 -- if there's a signature for it, use the instantiated signature type
618 -- otherwise invent a type variable
619 -- You see that quite directly in the FunBind case.
621 -- But there's a complication for pattern bindings:
622 -- data T = MkT (forall a. a->a)
624 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
625 -- but we want to get (f::forall a. a->a) as the RHS environment.
626 -- The simplest way to do this is to typecheck the pattern, and then look up the
627 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
628 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
630 data TcMonoBind -- Half completed; LHS done, RHS not done
631 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
632 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
634 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
635 -- Type signature (if any), and
636 -- the monomorphic bound things
638 bndrNames :: [MonoBindInfo] -> [Name]
639 bndrNames mbi = [n | (n,_,_) <- mbi]
641 getMonoType :: MonoBindInfo -> TcTauType
642 getMonoType (_,_,mono_id) = idType mono_id
644 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
645 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
646 = do { mb_sig <- tcInstSig_maybe sig_fn name
647 ; mono_name <- newLocalName name
648 ; mono_ty <- mk_mono_ty mb_sig
649 ; let mono_id = mkLocalId mono_name mono_ty
650 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
652 mk_mono_ty (Just sig) = return (sig_tau sig)
653 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
655 tcLhs sig_fn (PatBind { pat_lhs = pat, pat_rhs = grhss })
656 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
657 ; mono_pat_binds <- doptM Opt_MonoPatBinds
658 -- With -XMonoPatBinds, we do no generalisation of pattern bindings
659 -- But the signature can still be polymoprhic!
660 -- data T = MkT (forall a. a->a)
661 -- x :: forall a. a->a
663 -- The function get_sig_ty decides whether the pattern-bound variables
664 -- should have exactly the type in the type signature (-XMonoPatBinds),
665 -- or the instantiated version (-XMonoPatBinds)
667 ; let nm_sig_prs = names `zip` mb_sigs
668 get_sig_ty | mono_pat_binds = idType . sig_id
669 | otherwise = sig_tau
670 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
671 | (name, Just sig) <- nm_sig_prs]
672 sig_tau_fn = lookupNameEnv tau_sig_env
674 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
675 mapM lookup_info nm_sig_prs
677 -- After typechecking the pattern, look up the binder
678 -- names, which the pattern has brought into scope.
679 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
680 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
681 ; return (name, mb_sig, mono_id) }
683 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
686 ; return (TcPatBind infos pat' grhss pat_ty) }
688 names = collectPatBinders pat
691 tcLhs _ other_bind = pprPanic "tcLhs" (ppr other_bind)
692 -- AbsBind, VarBind impossible
695 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
696 -- When we are doing pattern bindings, or multiple function bindings at a time
697 -- we *don't* bring any scoped type variables into scope
698 -- Wny not? They are not completely rigid.
699 -- That's why we have the special case for a single FunBind in tcMonoBinds
700 tcRhs (TcFunBind (_,_,mono_id) fun' inf matches)
701 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
702 matches (idType mono_id)
703 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
704 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
705 fun_tick = Nothing }) }
707 tcRhs (TcPatBind _ pat' grhss pat_ty)
708 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
709 tcGRHSsPat grhss pat_ty
710 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
711 bind_fvs = placeHolderNames }) }
714 ---------------------
715 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
716 getMonoBindInfo tc_binds
717 = foldr (get_info . unLoc) [] tc_binds
719 get_info (TcFunBind info _ _ _) rest = info : rest
720 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
724 %************************************************************************
728 %************************************************************************
731 generalise :: DynFlags -> TopLevelFlag
732 -> [LHsBind Name] -> TcSigFun
733 -> [MonoBindInfo] -> [Inst]
734 -> TcM ([TyVar], [Inst], TcDictBinds)
735 -- The returned [TyVar] are all ready to quantify
737 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
738 | isMonoGroup dflags bind_list
739 = do { extendLIEs lie_req
740 ; return ([], [], emptyBag) }
742 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
743 = -- Check signature contexts are empty
744 do { checkTc (all is_mono_sig sigs)
745 (restrictedBindCtxtErr bndrs)
747 -- Now simplify with exactly that set of tyvars
748 -- We have to squash those Methods
749 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
752 -- Check that signature type variables are OK
753 ; final_qtvs <- checkSigsTyVars qtvs sigs
755 ; return (final_qtvs, [], binds) }
757 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
758 = tcSimplifyInfer doc tau_tvs lie_req
760 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
761 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
762 ; let -- The "sig_avails" is the stuff available. We get that from
763 -- the context of the type signature, BUT ALSO the lie_avail
764 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
765 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
766 sig_avails = sig_lie ++ local_meths
767 loc = sig_loc (head sigs)
769 -- Check that the needed dicts can be
770 -- expressed in terms of the signature ones
771 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
773 -- Check that signature type variables are OK
774 ; final_qtvs <- checkSigsTyVars qtvs sigs
776 ; return (final_qtvs, sig_lie, binds) }
778 bndrs = bndrNames mono_infos
779 sigs = [sig | (_, Just sig, _) <- mono_infos]
780 get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
781 | otherwise = exactTyVarsOfType
782 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
783 is_mono_sig sig = null (sig_theta sig)
784 doc = ptext (sLit "type signature(s) for") <+> pprBinders bndrs
786 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
787 sig_theta = theta, sig_loc = loc }) mono_id
788 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
789 tci_theta = theta, tci_loc = loc}
792 unifyCtxts checks that all the signature contexts are the same
793 The type signatures on a mutually-recursive group of definitions
794 must all have the same context (or none).
796 The trick here is that all the signatures should have the same
797 context, and we want to share type variables for that context, so that
798 all the right hand sides agree a common vocabulary for their type
801 We unify them because, with polymorphic recursion, their types
802 might not otherwise be related. This is a rather subtle issue.
805 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
806 -- Post-condition: the returned Insts are full zonked
807 unifyCtxts [] = panic "unifyCtxts []"
808 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
809 = do { mapM unify_ctxt sigs
810 ; theta <- zonkTcThetaType (sig_theta sig1)
811 ; newDictBndrs (sig_loc sig1) theta }
813 theta1 = sig_theta sig1
814 unify_ctxt :: TcSigInfo -> TcM ()
815 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
816 = setSrcSpan (instLocSpan (sig_loc sig)) $
817 addErrCtxt (sigContextsCtxt sig1 sig) $
818 do { cois <- unifyTheta theta1 theta
819 ; -- Check whether all coercions are identity coercions
820 -- That can happen if we have, say
822 -- g :: C (F a) => ...
823 -- where F is a type function and (F a ~ [a])
824 -- Then unification might succeed with a coercion. But it's much
825 -- much simpler to require that such signatures have identical contexts
826 checkTc (all isIdentityCoercion cois)
827 (ptext (sLit "Mutually dependent functions have syntactically distinct contexts"))
830 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
831 checkSigsTyVars qtvs sigs
832 = do { gbl_tvs <- tcGetGlobalTyVars
833 ; sig_tvs_s <- mapM (check_sig gbl_tvs) sigs
835 ; let -- Sigh. Make sure that all the tyvars in the type sigs
836 -- appear in the returned ty var list, which is what we are
837 -- going to generalise over. Reason: we occasionally get
839 -- type T a = () -> ()
842 -- Here, 'a' won't appear in qtvs, so we have to add it
843 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
844 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
847 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
848 sig_theta = theta, sig_tau = tau})
849 = addErrCtxt (ptext (sLit "In the type signature for") <+> quotes (ppr id)) $
850 addErrCtxtM (sigCtxt id tvs theta tau) $
851 do { tvs' <- checkDistinctTyVars tvs
852 ; when (any (`elemVarSet` gbl_tvs) tvs')
853 (bleatEscapedTvs gbl_tvs tvs tvs')
856 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
857 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
858 -- are still all type variables, and all distinct from each other.
859 -- It returns a zonked set of type variables.
860 -- For example, if the type sig is
861 -- f :: forall a b. a -> b -> b
862 -- we want to check that 'a' and 'b' haven't
863 -- (a) been unified with a non-tyvar type
864 -- (b) been unified with each other (all distinct)
866 checkDistinctTyVars sig_tvs
867 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
868 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
869 ; return zonked_tvs }
871 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
872 -- The TyVarEnv maps each zonked type variable back to its
873 -- corresponding user-written signature type variable
874 check_dup acc (sig_tv, zonked_tv)
875 = case lookupVarEnv acc zonked_tv of
876 Just sig_tv' -> bomb_out sig_tv sig_tv'
878 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
880 bomb_out sig_tv1 sig_tv2
881 = do { env0 <- tcInitTidyEnv
882 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
883 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
884 msg = ptext (sLit "Quantified type variable") <+> quotes (ppr tidy_tv1)
885 <+> ptext (sLit "is unified with another quantified type variable")
886 <+> quotes (ppr tidy_tv2)
887 ; failWithTcM (env2, msg) }
891 @getTyVarsToGen@ decides what type variables to generalise over.
893 For a "restricted group" -- see the monomorphism restriction
894 for a definition -- we bind no dictionaries, and
895 remove from tyvars_to_gen any constrained type variables
897 *Don't* simplify dicts at this point, because we aren't going
898 to generalise over these dicts. By the time we do simplify them
899 we may well know more. For example (this actually came up)
901 f x = array ... xs where xs = [1,2,3,4,5]
902 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
903 stuff. If we simplify only at the f-binding (not the xs-binding)
904 we'll know that the literals are all Ints, and we can just produce
907 Find all the type variables involved in overloading, the
908 "constrained_tyvars". These are the ones we *aren't* going to
909 generalise. We must be careful about doing this:
911 (a) If we fail to generalise a tyvar which is not actually
912 constrained, then it will never, ever get bound, and lands
913 up printed out in interface files! Notorious example:
914 instance Eq a => Eq (Foo a b) where ..
915 Here, b is not constrained, even though it looks as if it is.
916 Another, more common, example is when there's a Method inst in
917 the LIE, whose type might very well involve non-overloaded
919 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
920 the simple thing instead]
922 (b) On the other hand, we mustn't generalise tyvars which are constrained,
923 because we are going to pass on out the unmodified LIE, with those
924 tyvars in it. They won't be in scope if we've generalised them.
926 So we are careful, and do a complete simplification just to find the
927 constrained tyvars. We don't use any of the results, except to
928 find which tyvars are constrained.
930 Note [Polymorphic recursion]
931 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
932 The game plan for polymorphic recursion in the code above is
934 * Bind any variable for which we have a type signature
935 to an Id with a polymorphic type. Then when type-checking
936 the RHSs we'll make a full polymorphic call.
938 This fine, but if you aren't a bit careful you end up with a horrendous
939 amount of partial application and (worse) a huge space leak. For example:
941 f :: Eq a => [a] -> [a]
944 If we don't take care, after typechecking we get
946 f = /\a -> \d::Eq a -> let f' = f a d
950 Notice the the stupid construction of (f a d), which is of course
951 identical to the function we're executing. In this case, the
952 polymorphic recursion isn't being used (but that's a very common case).
953 This can lead to a massive space leak, from the following top-level defn
959 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
960 f' is another thunk which evaluates to the same thing... and you end
961 up with a chain of identical values all hung onto by the CAF ff.
965 = let f' = f Int dEqInt in \ys. ...f'...
967 = let f' = let f' = f Int dEqInt in \ys. ...f'...
972 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
973 which would make the space leak go away in this case
975 Solution: when typechecking the RHSs we always have in hand the
976 *monomorphic* Ids for each binding. So we just need to make sure that
977 if (Method f a d) shows up in the constraints emerging from (...f...)
978 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
979 to the "givens" when simplifying constraints. That's what the "lies_avail"
984 f = /\a -> \d::Eq a -> letrec
985 fm = \ys:[a] -> ...fm...
991 %************************************************************************
995 %************************************************************************
997 Type signatures are tricky. See Note [Signature skolems] in TcType
999 @tcSigs@ checks the signatures for validity, and returns a list of
1000 {\em freshly-instantiated} signatures. That is, the types are already
1001 split up, and have fresh type variables installed. All non-type-signature
1002 "RenamedSigs" are ignored.
1004 The @TcSigInfo@ contains @TcTypes@ because they are unified with
1005 the variable's type, and after that checked to see whether they've
1008 Note [Scoped tyvars]
1009 ~~~~~~~~~~~~~~~~~~~~
1010 The -XScopedTypeVariables flag brings lexically-scoped type variables
1011 into scope for any explicitly forall-quantified type variables:
1012 f :: forall a. a -> a
1014 Then 'a' is in scope inside 'e'.
1016 However, we do *not* support this
1017 - For pattern bindings e.g
1021 - For multiple function bindings, unless Opt_RelaxedPolyRec is on
1022 f :: forall a. a -> a
1024 g :: forall b. b -> b
1026 Reason: we use mutable variables for 'a' and 'b', since they may
1027 unify to each other, and that means the scoped type variable would
1028 not stand for a completely rigid variable.
1030 Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
1033 Note [More instantiated than scoped]
1034 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1035 There may be more instantiated type variables than lexically-scoped
1037 type T a = forall b. b -> (a,b)
1039 Here, the signature for f will have one scoped type variable, c,
1040 but two instantiated type variables, c' and b'.
1042 We assume that the scoped ones are at the *front* of sig_tvs,
1043 and remember the names from the original HsForAllTy in the TcSigFun.
1047 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
1048 -- type variables brought into scope
1049 -- by its type signature.
1050 -- Nothing => no type signature
1052 mkTcSigFun :: [LSig Name] -> TcSigFun
1053 -- Search for a particular type signature
1054 -- Precondition: the sigs are all type sigs
1055 -- Precondition: no duplicates
1056 mkTcSigFun sigs = lookupNameEnv env
1058 env = mkNameEnv [(name, hsExplicitTvs lhs_ty)
1059 | L _ (TypeSig (L _ name) lhs_ty) <- sigs]
1060 -- The scoped names are the ones explicitly mentioned
1061 -- in the HsForAll. (There may be more in sigma_ty, because
1062 -- of nested type synonyms. See Note [More instantiated than scoped].)
1063 -- See Note [Only scoped tyvars are in the TyVarEnv]
1068 sig_id :: TcId, -- *Polymorphic* binder for this value...
1070 sig_tvs :: [TcTyVar], -- Instantiated type variables
1071 -- See Note [Instantiate sig]
1073 sig_theta :: TcThetaType, -- Instantiated theta
1074 sig_tau :: TcTauType, -- Instantiated tau
1075 sig_loc :: InstLoc -- The location of the signature
1079 -- Note [Only scoped tyvars are in the TyVarEnv]
1080 -- We are careful to keep only the *lexically scoped* type variables in
1081 -- the type environment. Why? After all, the renamer has ensured
1082 -- that only legal occurrences occur, so we could put all type variables
1083 -- into the type env.
1085 -- But we want to check that two distinct lexically scoped type variables
1086 -- do not map to the same internal type variable. So we need to know which
1087 -- the lexically-scoped ones are... and at the moment we do that by putting
1088 -- only the lexically scoped ones into the environment.
1091 -- Note [Instantiate sig]
1092 -- It's vital to instantiate a type signature with fresh variables.
1094 -- type S = forall a. a->a
1098 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1099 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1100 -- it's all cool; each signature has distinct type variables from the renamer.)
1102 instance Outputable TcSigInfo where
1103 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1104 = ppr id <+> ptext (sLit "::") <+> ppr tyvars <+> ppr theta <+> ptext (sLit "=>") <+> ppr tau
1108 tcTySig :: LSig Name -> TcM TcId
1109 tcTySig (L span (TypeSig (L _ name) ty))
1111 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1112 ; return (mkLocalId name sigma_ty) }
1113 tcTySig s = pprPanic "tcTySig" (ppr s)
1116 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1117 -- Instantiate with *meta* type variables;
1118 -- this signature is part of a multi-signature group
1119 tcInstSig_maybe sig_fn name
1120 = case sig_fn name of
1121 Nothing -> return Nothing
1122 Just _scoped_tvs -> do { tc_sig <- tcInstSig False name
1123 ; return (Just tc_sig) }
1124 -- NB: the _scoped_tvs may be non-empty, but we can
1125 -- just ignore them. See Note [Scoped tyvars].
1127 tcInstSig :: Bool -> Name -> TcM TcSigInfo
1128 -- Instantiate the signature, with either skolems or meta-type variables
1129 -- depending on the use_skols boolean. This variable is set True
1130 -- when we are typechecking a single function binding; and False for
1131 -- pattern bindings and a group of several function bindings.
1132 -- Reason: in the latter cases, the "skolems" can be unified together,
1133 -- so they aren't properly rigid in the type-refinement sense.
1134 -- NB: unless we are doing H98, each function with a sig will be done
1135 -- separately, even if it's mutually recursive, so use_skols will be True
1137 -- We always instantiate with fresh uniques,
1138 -- although we keep the same print-name
1140 -- type T = forall a. [a] -> [a]
1142 -- f = g where { g :: T; g = <rhs> }
1144 -- We must not use the same 'a' from the defn of T at both places!!
1146 tcInstSig use_skols name
1147 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1148 -- scope when starting the binding group
1149 ; let skol_info = SigSkol (FunSigCtxt name)
1150 ; (tvs, theta, tau) <- tcInstSigType use_skols skol_info (idType poly_id)
1151 ; loc <- getInstLoc (SigOrigin skol_info)
1152 ; return (TcSigInfo { sig_id = poly_id,
1153 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1157 isMonoGroup :: DynFlags -> [LHsBind Name] -> Bool
1158 -- No generalisation at all
1159 isMonoGroup dflags binds
1160 = dopt Opt_MonoPatBinds dflags && any is_pat_bind binds
1162 is_pat_bind (L _ (PatBind {})) = True
1163 is_pat_bind _ = False
1166 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1167 isRestrictedGroup dflags binds sig_fn
1168 = mono_restriction && not all_unrestricted
1170 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1171 all_unrestricted = all (unrestricted . unLoc) binds
1172 has_sig n = isJust (sig_fn n)
1174 unrestricted (PatBind {}) = False
1175 unrestricted (VarBind { var_id = v }) = has_sig v
1176 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1177 || has_sig (unLoc v)
1178 unrestricted (AbsBinds {})
1179 = panic "isRestrictedGroup/unrestricted AbsBinds"
1181 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1182 -- No args => like a pattern binding
1183 unrestricted_match _ = True
1184 -- Some args => a function binding
1188 %************************************************************************
1190 \subsection[TcBinds-errors]{Error contexts and messages}
1192 %************************************************************************
1196 -- This one is called on LHS, when pat and grhss are both Name
1197 -- and on RHS, when pat is TcId and grhss is still Name
1198 patMonoBindsCtxt :: OutputableBndr id => LPat id -> GRHSs Name -> SDoc
1199 patMonoBindsCtxt pat grhss
1200 = hang (ptext (sLit "In a pattern binding:")) 4 (pprPatBind pat grhss)
1202 -----------------------------------------------
1203 sigContextsCtxt :: TcSigInfo -> TcSigInfo -> SDoc
1204 sigContextsCtxt sig1 sig2
1205 = vcat [ptext (sLit "When matching the contexts of the signatures for"),
1206 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1207 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1208 ptext (sLit "The signature contexts in a mutually recursive group should all be identical")]
1214 -----------------------------------------------
1215 unboxedTupleErr :: Name -> Type -> SDoc
1216 unboxedTupleErr name ty
1217 = hang (ptext (sLit "Illegal binding of unboxed tuple"))
1218 4 (ppr name <+> dcolon <+> ppr ty)
1220 -----------------------------------------------
1221 restrictedBindCtxtErr :: [Name] -> SDoc
1222 restrictedBindCtxtErr binder_names
1223 = hang (ptext (sLit "Illegal overloaded type signature(s)"))
1224 4 (vcat [ptext (sLit "in a binding group for") <+> pprBinders binder_names,
1225 ptext (sLit "that falls under the monomorphism restriction")])
1227 genCtxt :: [Name] -> SDoc
1228 genCtxt binder_names
1229 = ptext (sLit "When generalising the type(s) for") <+> pprBinders binder_names
1231 missingSigWarn :: Bool -> Name -> Type -> TcM ()
1232 missingSigWarn False _ _ = return ()
1233 missingSigWarn True name ty
1234 = do { env0 <- tcInitTidyEnv
1235 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1236 ; addWarnTcM (env1, mk_msg tidy_ty) }
1238 mk_msg ty = vcat [ptext (sLit "Definition but no type signature for") <+> quotes (ppr name),
1239 sep [ptext (sLit "Inferred type:") <+> pprHsVar name <+> dcolon <+> ppr ty]]