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 isTypeLSig 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 isTypeLSig 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 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 -> 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 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 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 :: Id -> [LSig Name] -> TcM [LPrag]
417 tcPrags poly_id prags = mapM (wrapLocM tc_prag) prags
419 tc_prag prag = addErrCtxt (pragSigCtxt prag) $
422 pragSigCtxt :: Sig Name -> SDoc
423 pragSigCtxt prag = hang (ptext (sLit "In the pragma")) 2 (ppr prag)
425 tcPrag :: TcId -> Sig Name -> TcM Prag
426 -- Pre-condition: the poly_id is zonked
427 -- Reason: required by tcSubExp
428 tcPrag poly_id (SpecSig _ hs_ty inl) = tcSpecPrag poly_id hs_ty inl
429 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
430 tcPrag _ (InlineSig _ inl) = return (InlinePrag inl)
431 tcPrag _ sig = pprPanic "tcPrag" (ppr sig)
434 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
435 tcSpecPrag poly_id hs_ty inl
436 = do { let name = idName poly_id
437 ; spec_ty <- tcHsSigType (FunSigCtxt name) hs_ty
438 ; co_fn <- tcSubExp (SpecPragOrigin name) (idType poly_id) spec_ty
439 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty inl) }
440 -- Most of the work of specialisation is done by
441 -- the desugarer, guided by the SpecPrag
444 -- If typechecking the binds fails, then return with each
445 -- signature-less binder given type (forall a.a), to minimise
446 -- subsequent error messages
447 recoveryCode :: [Name] -> (Name -> Maybe [Name])
448 -> TcM (LHsBinds TcId, [Id])
449 recoveryCode binder_names sig_fn
450 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
451 ; poly_ids <- mapM mk_dummy binder_names
452 ; return (emptyBag, poly_ids) }
455 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
456 | otherwise = return (mkLocalId name forall_a_a) -- No signature
459 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
462 -- Check that non-overloaded unlifted bindings are
465 -- c) not a multiple-binding group (more or less implied by (a))
467 checkStrictBinds :: TopLevelFlag -> RecFlag
468 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
470 checkStrictBinds top_lvl rec_group mbind mono_tys infos
471 | unlifted || bang_pat
472 = do { checkTc (isNotTopLevel top_lvl)
473 (strictBindErr "Top-level" unlifted mbind)
474 ; checkTc (isNonRec rec_group)
475 (strictBindErr "Recursive" unlifted mbind)
476 ; checkTc (isSingletonBag mbind)
477 (strictBindErr "Multiple" unlifted mbind)
478 -- This should be a checkTc, not a warnTc, but as of GHC 6.11
479 -- the versions of alex and happy available have non-conforming
480 -- templates, so the GHC build fails if it's an error:
481 ; warnTc (not bang_pat)
482 (unliftedMustBeBang mbind)
483 ; mapM_ check_sig infos
488 unlifted = any isUnLiftedType mono_tys
489 bang_pat = anyBag (isBangHsBind . unLoc) mbind
490 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
491 (badStrictSig unlifted sig)
492 check_sig _ = return ()
494 unliftedMustBeBang :: LHsBindsLR Var Var -> SDoc
495 unliftedMustBeBang mbind
496 = hang (text "Bindings containing unlifted types must use an outermost bang pattern:")
497 4 (pprLHsBinds mbind)
499 strictBindErr :: String -> Bool -> LHsBindsLR Var Var -> SDoc
500 strictBindErr flavour unlifted mbind
501 = hang (text flavour <+> msg <+> ptext (sLit "aren't allowed:"))
502 4 (pprLHsBinds mbind)
504 msg | unlifted = ptext (sLit "bindings for unlifted types")
505 | otherwise = ptext (sLit "bang-pattern bindings")
507 badStrictSig :: Bool -> TcSigInfo -> SDoc
508 badStrictSig unlifted sig
509 = hang (ptext (sLit "Illegal polymorphic signature in") <+> msg)
512 msg | unlifted = ptext (sLit "an unlifted binding")
513 | otherwise = ptext (sLit "a bang-pattern binding")
517 %************************************************************************
519 \subsection{tcMonoBind}
521 %************************************************************************
523 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
524 The signatures have been dealt with already.
527 tcMonoBinds :: [LHsBind Name]
529 -> RecFlag -- Whether the binding is recursive for typechecking purposes
530 -- i.e. the binders are mentioned in their RHSs, and
531 -- we are not resuced by a type signature
532 -> TcM (LHsBinds TcId, [MonoBindInfo])
534 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
535 fun_matches = matches, bind_fvs = fvs })]
536 sig_fn -- Single function binding,
537 NonRecursive -- binder isn't mentioned in RHS,
538 | Nothing <- sig_fn name -- ...with no type signature
539 = -- In this very special case we infer the type of the
540 -- right hand side first (it may have a higher-rank type)
541 -- and *then* make the monomorphic Id for the LHS
542 -- e.g. f = \(x::forall a. a->a) -> <body>
543 -- We want to infer a higher-rank type for f
545 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
547 -- Check for an unboxed tuple type
548 -- f = (# True, False #)
549 -- Zonk first just in case it's hidden inside a meta type variable
550 -- (This shows up as a (more obscure) kind error
551 -- in the 'otherwise' case of tcMonoBinds.)
552 ; zonked_rhs_ty <- zonkTcType rhs_ty
553 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
554 (unboxedTupleErr name zonked_rhs_ty)
556 ; mono_name <- newLocalName name
557 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
558 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
559 fun_matches = matches', bind_fvs = fvs,
560 fun_co_fn = co_fn, fun_tick = Nothing })),
561 [(name, Nothing, mono_id)]) }
563 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
564 fun_matches = matches })]
565 sig_fn -- Single function binding
567 | Just scoped_tvs <- sig_fn name -- ...with a type signature
568 = -- When we have a single function binding, with a type signature
569 -- we can (a) use genuine, rigid skolem constants for the type variables
570 -- (b) bring (rigid) scoped type variables into scope
572 do { tc_sig <- tcInstSig True name
573 ; mono_name <- newLocalName name
574 ; let mono_ty = sig_tau tc_sig
575 mono_id = mkLocalId mono_name mono_ty
576 rhs_tvs = [ (name, mkTyVarTy tv)
577 | (name, tv) <- scoped_tvs `zip` sig_tvs tc_sig ]
578 -- See Note [More instantiated than scoped]
579 -- Note that the scoped_tvs and the (sig_tvs sig)
580 -- may have different Names. That's quite ok.
582 ; traceTc (text "tcMoonBinds" <+> ppr scoped_tvs $$ ppr tc_sig)
583 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
584 tcMatchesFun mono_name inf matches mono_ty
585 -- Note that "mono_ty" might actually be a polymorphic type,
586 -- if the original function had a signature like
587 -- forall a. Eq a => forall b. Ord b => ....
588 -- But that's ok: tcMatchesFun can deal with that
589 -- It happens, too! See Note [Polymorphic methods] in TcClassDcl.
591 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
592 fun_infix = inf, fun_matches = matches',
593 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
595 ; return (unitBag (L b_loc fun_bind'),
596 [(name, Just tc_sig, mono_id)]) }
598 tcMonoBinds binds sig_fn _
599 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
601 -- Bring the monomorphic Ids, into scope for the RHSs
602 ; let mono_info = getMonoBindInfo tc_binds
603 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
604 -- A monomorphic binding for each term variable that lacks
605 -- a type sig. (Ones with a sig are already in scope.)
607 ; binds' <- tcExtendIdEnv2 rhs_id_env $ do
608 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
609 | (n,id) <- rhs_id_env])
610 mapM (wrapLocM tcRhs) tc_binds
611 ; return (listToBag binds', mono_info) }
613 ------------------------
614 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
615 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
616 -- if there's a signature for it, use the instantiated signature type
617 -- otherwise invent a type variable
618 -- You see that quite directly in the FunBind case.
620 -- But there's a complication for pattern bindings:
621 -- data T = MkT (forall a. a->a)
623 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
624 -- but we want to get (f::forall a. a->a) as the RHS environment.
625 -- The simplest way to do this is to typecheck the pattern, and then look up the
626 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
627 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
629 data TcMonoBind -- Half completed; LHS done, RHS not done
630 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
631 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
633 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
634 -- Type signature (if any), and
635 -- the monomorphic bound things
637 bndrNames :: [MonoBindInfo] -> [Name]
638 bndrNames mbi = [n | (n,_,_) <- mbi]
640 getMonoType :: MonoBindInfo -> TcTauType
641 getMonoType (_,_,mono_id) = idType mono_id
643 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
644 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
645 = do { mb_sig <- tcInstSig_maybe sig_fn name
646 ; mono_name <- newLocalName name
647 ; mono_ty <- mk_mono_ty mb_sig
648 ; let mono_id = mkLocalId mono_name mono_ty
649 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
651 mk_mono_ty (Just sig) = return (sig_tau sig)
652 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
654 tcLhs sig_fn (PatBind { pat_lhs = pat, pat_rhs = grhss })
655 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
656 ; mono_pat_binds <- doptM Opt_MonoPatBinds
657 -- With -XMonoPatBinds, we do no generalisation of pattern bindings
658 -- But the signature can still be polymoprhic!
659 -- data T = MkT (forall a. a->a)
660 -- x :: forall a. a->a
662 -- The function get_sig_ty decides whether the pattern-bound variables
663 -- should have exactly the type in the type signature (-XMonoPatBinds),
664 -- or the instantiated version (-XMonoPatBinds)
666 ; let nm_sig_prs = names `zip` mb_sigs
667 get_sig_ty | mono_pat_binds = idType . sig_id
668 | otherwise = sig_tau
669 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
670 | (name, Just sig) <- nm_sig_prs]
671 sig_tau_fn = lookupNameEnv tau_sig_env
673 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
674 mapM lookup_info nm_sig_prs
676 -- After typechecking the pattern, look up the binder
677 -- names, which the pattern has brought into scope.
678 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
679 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
680 ; return (name, mb_sig, mono_id) }
682 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
685 ; return (TcPatBind infos pat' grhss pat_ty) }
687 names = collectPatBinders pat
690 tcLhs _ other_bind = pprPanic "tcLhs" (ppr other_bind)
691 -- AbsBind, VarBind impossible
694 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
695 -- When we are doing pattern bindings, or multiple function bindings at a time
696 -- we *don't* bring any scoped type variables into scope
697 -- Wny not? They are not completely rigid.
698 -- That's why we have the special case for a single FunBind in tcMonoBinds
699 tcRhs (TcFunBind (_,_,mono_id) fun' inf matches)
700 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
701 matches (idType mono_id)
702 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
703 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
704 fun_tick = Nothing }) }
706 tcRhs (TcPatBind _ pat' grhss pat_ty)
707 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
708 tcGRHSsPat grhss pat_ty
709 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
710 bind_fvs = placeHolderNames }) }
713 ---------------------
714 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
715 getMonoBindInfo tc_binds
716 = foldr (get_info . unLoc) [] tc_binds
718 get_info (TcFunBind info _ _ _) rest = info : rest
719 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
723 %************************************************************************
727 %************************************************************************
730 generalise :: DynFlags -> TopLevelFlag
731 -> [LHsBind Name] -> TcSigFun
732 -> [MonoBindInfo] -> [Inst]
733 -> TcM ([TyVar], [Inst], TcDictBinds)
734 -- The returned [TyVar] are all ready to quantify
736 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
737 | isMonoGroup dflags bind_list
738 = do { extendLIEs lie_req
739 ; return ([], [], emptyBag) }
741 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
742 = -- Check signature contexts are empty
743 do { checkTc (all is_mono_sig sigs)
744 (restrictedBindCtxtErr bndrs)
746 -- Now simplify with exactly that set of tyvars
747 -- We have to squash those Methods
748 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
751 -- Check that signature type variables are OK
752 ; final_qtvs <- checkSigsTyVars qtvs sigs
754 ; return (final_qtvs, [], binds) }
756 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
757 = tcSimplifyInfer doc tau_tvs lie_req
759 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
760 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
761 ; let -- The "sig_avails" is the stuff available. We get that from
762 -- the context of the type signature, BUT ALSO the lie_avail
763 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
764 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
765 sig_avails = sig_lie ++ local_meths
766 loc = sig_loc (head sigs)
768 -- Check that the needed dicts can be
769 -- expressed in terms of the signature ones
770 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
772 -- Check that signature type variables are OK
773 ; final_qtvs <- checkSigsTyVars qtvs sigs
775 ; return (final_qtvs, sig_lie, binds) }
777 bndrs = bndrNames mono_infos
778 sigs = [sig | (_, Just sig, _) <- mono_infos]
779 get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
780 | otherwise = exactTyVarsOfType
781 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
782 is_mono_sig sig = null (sig_theta sig)
783 doc = ptext (sLit "type signature(s) for") <+> pprBinders bndrs
785 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
786 sig_theta = theta, sig_loc = loc }) mono_id
787 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
788 tci_theta = theta, tci_loc = loc}
791 unifyCtxts checks that all the signature contexts are the same
792 The type signatures on a mutually-recursive group of definitions
793 must all have the same context (or none).
795 The trick here is that all the signatures should have the same
796 context, and we want to share type variables for that context, so that
797 all the right hand sides agree a common vocabulary for their type
800 We unify them because, with polymorphic recursion, their types
801 might not otherwise be related. This is a rather subtle issue.
804 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
805 -- Post-condition: the returned Insts are full zonked
806 unifyCtxts [] = panic "unifyCtxts []"
807 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
808 = do { mapM unify_ctxt sigs
809 ; theta <- zonkTcThetaType (sig_theta sig1)
810 ; newDictBndrs (sig_loc sig1) theta }
812 theta1 = sig_theta sig1
813 unify_ctxt :: TcSigInfo -> TcM ()
814 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
815 = setSrcSpan (instLocSpan (sig_loc sig)) $
816 addErrCtxt (sigContextsCtxt sig1 sig) $
817 do { cois <- unifyTheta theta1 theta
818 ; -- Check whether all coercions are identity coercions
819 -- That can happen if we have, say
821 -- g :: C (F a) => ...
822 -- where F is a type function and (F a ~ [a])
823 -- Then unification might succeed with a coercion. But it's much
824 -- much simpler to require that such signatures have identical contexts
825 checkTc (all isIdentityCoI cois)
826 (ptext (sLit "Mutually dependent functions have syntactically distinct contexts"))
829 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
830 checkSigsTyVars qtvs sigs
831 = do { gbl_tvs <- tcGetGlobalTyVars
832 ; sig_tvs_s <- mapM (check_sig gbl_tvs) sigs
834 ; let -- Sigh. Make sure that all the tyvars in the type sigs
835 -- appear in the returned ty var list, which is what we are
836 -- going to generalise over. Reason: we occasionally get
838 -- type T a = () -> ()
841 -- Here, 'a' won't appear in qtvs, so we have to add it
842 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
843 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
846 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
847 sig_theta = theta, sig_tau = tau})
848 = addErrCtxt (ptext (sLit "In the type signature for") <+> quotes (ppr id)) $
849 addErrCtxtM (sigCtxt id tvs theta tau) $
850 do { tvs' <- checkDistinctTyVars tvs
851 ; when (any (`elemVarSet` gbl_tvs) tvs')
852 (bleatEscapedTvs gbl_tvs tvs tvs')
855 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
856 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
857 -- are still all type variables, and all distinct from each other.
858 -- It returns a zonked set of type variables.
859 -- For example, if the type sig is
860 -- f :: forall a b. a -> b -> b
861 -- we want to check that 'a' and 'b' haven't
862 -- (a) been unified with a non-tyvar type
863 -- (b) been unified with each other (all distinct)
865 checkDistinctTyVars sig_tvs
866 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
867 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
868 ; return zonked_tvs }
870 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
871 -- The TyVarEnv maps each zonked type variable back to its
872 -- corresponding user-written signature type variable
873 check_dup acc (sig_tv, zonked_tv)
874 = case lookupVarEnv acc zonked_tv of
875 Just sig_tv' -> bomb_out sig_tv sig_tv'
877 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
879 bomb_out sig_tv1 sig_tv2
880 = do { env0 <- tcInitTidyEnv
881 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
882 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
883 msg = ptext (sLit "Quantified type variable") <+> quotes (ppr tidy_tv1)
884 <+> ptext (sLit "is unified with another quantified type variable")
885 <+> quotes (ppr tidy_tv2)
886 ; failWithTcM (env2, msg) }
890 @getTyVarsToGen@ decides what type variables to generalise over.
892 For a "restricted group" -- see the monomorphism restriction
893 for a definition -- we bind no dictionaries, and
894 remove from tyvars_to_gen any constrained type variables
896 *Don't* simplify dicts at this point, because we aren't going
897 to generalise over these dicts. By the time we do simplify them
898 we may well know more. For example (this actually came up)
900 f x = array ... xs where xs = [1,2,3,4,5]
901 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
902 stuff. If we simplify only at the f-binding (not the xs-binding)
903 we'll know that the literals are all Ints, and we can just produce
906 Find all the type variables involved in overloading, the
907 "constrained_tyvars". These are the ones we *aren't* going to
908 generalise. We must be careful about doing this:
910 (a) If we fail to generalise a tyvar which is not actually
911 constrained, then it will never, ever get bound, and lands
912 up printed out in interface files! Notorious example:
913 instance Eq a => Eq (Foo a b) where ..
914 Here, b is not constrained, even though it looks as if it is.
915 Another, more common, example is when there's a Method inst in
916 the LIE, whose type might very well involve non-overloaded
918 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
919 the simple thing instead]
921 (b) On the other hand, we mustn't generalise tyvars which are constrained,
922 because we are going to pass on out the unmodified LIE, with those
923 tyvars in it. They won't be in scope if we've generalised them.
925 So we are careful, and do a complete simplification just to find the
926 constrained tyvars. We don't use any of the results, except to
927 find which tyvars are constrained.
929 Note [Polymorphic recursion]
930 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
931 The game plan for polymorphic recursion in the code above is
933 * Bind any variable for which we have a type signature
934 to an Id with a polymorphic type. Then when type-checking
935 the RHSs we'll make a full polymorphic call.
937 This fine, but if you aren't a bit careful you end up with a horrendous
938 amount of partial application and (worse) a huge space leak. For example:
940 f :: Eq a => [a] -> [a]
943 If we don't take care, after typechecking we get
945 f = /\a -> \d::Eq a -> let f' = f a d
949 Notice the the stupid construction of (f a d), which is of course
950 identical to the function we're executing. In this case, the
951 polymorphic recursion isn't being used (but that's a very common case).
952 This can lead to a massive space leak, from the following top-level defn
958 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
959 f' is another thunk which evaluates to the same thing... and you end
960 up with a chain of identical values all hung onto by the CAF ff.
964 = let f' = f Int dEqInt in \ys. ...f'...
966 = let f' = let f' = f Int dEqInt in \ys. ...f'...
971 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
972 which would make the space leak go away in this case
974 Solution: when typechecking the RHSs we always have in hand the
975 *monomorphic* Ids for each binding. So we just need to make sure that
976 if (Method f a d) shows up in the constraints emerging from (...f...)
977 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
978 to the "givens" when simplifying constraints. That's what the "lies_avail"
983 f = /\a -> \d::Eq a -> letrec
984 fm = \ys:[a] -> ...fm...
990 %************************************************************************
994 %************************************************************************
996 Type signatures are tricky. See Note [Signature skolems] in TcType
998 @tcSigs@ checks the signatures for validity, and returns a list of
999 {\em freshly-instantiated} signatures. That is, the types are already
1000 split up, and have fresh type variables installed. All non-type-signature
1001 "RenamedSigs" are ignored.
1003 The @TcSigInfo@ contains @TcTypes@ because they are unified with
1004 the variable's type, and after that checked to see whether they've
1007 Note [Scoped tyvars]
1008 ~~~~~~~~~~~~~~~~~~~~
1009 The -XScopedTypeVariables flag brings lexically-scoped type variables
1010 into scope for any explicitly forall-quantified type variables:
1011 f :: forall a. a -> a
1013 Then 'a' is in scope inside 'e'.
1015 However, we do *not* support this
1016 - For pattern bindings e.g
1020 - For multiple function bindings, unless Opt_RelaxedPolyRec is on
1021 f :: forall a. a -> a
1023 g :: forall b. b -> b
1025 Reason: we use mutable variables for 'a' and 'b', since they may
1026 unify to each other, and that means the scoped type variable would
1027 not stand for a completely rigid variable.
1029 Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
1032 Note [More instantiated than scoped]
1033 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1034 There may be more instantiated type variables than lexically-scoped
1036 type T a = forall b. b -> (a,b)
1038 Here, the signature for f will have one scoped type variable, c,
1039 but two instantiated type variables, c' and b'.
1041 We assume that the scoped ones are at the *front* of sig_tvs,
1042 and remember the names from the original HsForAllTy in the TcSigFun.
1046 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
1047 -- type variables brought into scope
1048 -- by its type signature.
1049 -- Nothing => no type signature
1051 mkTcSigFun :: [LSig Name] -> TcSigFun
1052 -- Search for a particular type signature
1053 -- Precondition: the sigs are all type sigs
1054 -- Precondition: no duplicates
1055 mkTcSigFun sigs = lookupNameEnv env
1057 env = mkNameEnv (mapCatMaybes mk_pair sigs)
1058 mk_pair (L _ (TypeSig (L _ name) lhs_ty)) = Just (name, hsExplicitTvs lhs_ty)
1059 mk_pair (L _ (IdSig id)) = Just (idName id, [])
1061 -- The scoped names are the ones explicitly mentioned
1062 -- in the HsForAll. (There may be more in sigma_ty, because
1063 -- of nested type synonyms. See Note [More instantiated than scoped].)
1064 -- See Note [Only scoped tyvars are in the TyVarEnv]
1069 sig_id :: TcId, -- *Polymorphic* binder for this value...
1071 sig_tvs :: [TcTyVar], -- Instantiated type variables
1072 -- See Note [Instantiate sig]
1074 sig_theta :: TcThetaType, -- Instantiated theta
1075 sig_tau :: TcTauType, -- Instantiated tau
1076 sig_loc :: InstLoc -- The location of the signature
1080 -- Note [Only scoped tyvars are in the TyVarEnv]
1081 -- We are careful to keep only the *lexically scoped* type variables in
1082 -- the type environment. Why? After all, the renamer has ensured
1083 -- that only legal occurrences occur, so we could put all type variables
1084 -- into the type env.
1086 -- But we want to check that two distinct lexically scoped type variables
1087 -- do not map to the same internal type variable. So we need to know which
1088 -- the lexically-scoped ones are... and at the moment we do that by putting
1089 -- only the lexically scoped ones into the environment.
1092 -- Note [Instantiate sig]
1093 -- It's vital to instantiate a type signature with fresh variables.
1095 -- type S = forall a. a->a
1099 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1100 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1101 -- it's all cool; each signature has distinct type variables from the renamer.)
1103 instance Outputable TcSigInfo where
1104 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1105 = ppr id <+> ptext (sLit "::") <+> ppr tyvars <+> ppr theta <+> ptext (sLit "=>") <+> ppr tau
1109 tcTySig :: LSig Name -> TcM TcId
1110 tcTySig (L span (TypeSig (L _ name) ty))
1112 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1113 ; return (mkLocalId name sigma_ty) }
1114 tcTySig (L _ (IdSig id))
1116 tcTySig s = pprPanic "tcTySig" (ppr s)
1119 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1120 -- Instantiate with *meta* type variables;
1121 -- this signature is part of a multi-signature group
1122 tcInstSig_maybe sig_fn name
1123 = case sig_fn name of
1124 Nothing -> return Nothing
1125 Just _scoped_tvs -> do { tc_sig <- tcInstSig False name
1126 ; return (Just tc_sig) }
1127 -- NB: the _scoped_tvs may be non-empty, but we can
1128 -- just ignore them. See Note [Scoped tyvars].
1130 tcInstSig :: Bool -> Name -> TcM TcSigInfo
1131 -- Instantiate the signature, with either skolems or meta-type variables
1132 -- depending on the use_skols boolean. This variable is set True
1133 -- when we are typechecking a single function binding; and False for
1134 -- pattern bindings and a group of several function bindings.
1135 -- Reason: in the latter cases, the "skolems" can be unified together,
1136 -- so they aren't properly rigid in the type-refinement sense.
1137 -- NB: unless we are doing H98, each function with a sig will be done
1138 -- separately, even if it's mutually recursive, so use_skols will be True
1140 -- We always instantiate with fresh uniques,
1141 -- although we keep the same print-name
1143 -- type T = forall a. [a] -> [a]
1145 -- f = g where { g :: T; g = <rhs> }
1147 -- We must not use the same 'a' from the defn of T at both places!!
1149 tcInstSig use_skols name
1150 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1151 -- scope when starting the binding group
1152 ; let skol_info = SigSkol (FunSigCtxt name)
1153 ; (tvs, theta, tau) <- tcInstSigType use_skols skol_info (idType poly_id)
1154 ; loc <- getInstLoc (SigOrigin skol_info)
1155 ; return (TcSigInfo { sig_id = poly_id,
1156 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1160 isMonoGroup :: DynFlags -> [LHsBind Name] -> Bool
1161 -- No generalisation at all
1162 isMonoGroup dflags binds
1163 = dopt Opt_MonoPatBinds dflags && any is_pat_bind binds
1165 is_pat_bind (L _ (PatBind {})) = True
1166 is_pat_bind _ = False
1169 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1170 isRestrictedGroup dflags binds sig_fn
1171 = mono_restriction && not all_unrestricted
1173 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1174 all_unrestricted = all (unrestricted . unLoc) binds
1175 has_sig n = isJust (sig_fn n)
1177 unrestricted (PatBind {}) = False
1178 unrestricted (VarBind { var_id = v }) = has_sig v
1179 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1180 || has_sig (unLoc v)
1181 unrestricted (AbsBinds {})
1182 = panic "isRestrictedGroup/unrestricted AbsBinds"
1184 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1185 -- No args => like a pattern binding
1186 unrestricted_match _ = True
1187 -- Some args => a function binding
1191 %************************************************************************
1193 \subsection[TcBinds-errors]{Error contexts and messages}
1195 %************************************************************************
1199 -- This one is called on LHS, when pat and grhss are both Name
1200 -- and on RHS, when pat is TcId and grhss is still Name
1201 patMonoBindsCtxt :: OutputableBndr id => LPat id -> GRHSs Name -> SDoc
1202 patMonoBindsCtxt pat grhss
1203 = hang (ptext (sLit "In a pattern binding:")) 4 (pprPatBind pat grhss)
1205 -----------------------------------------------
1206 sigContextsCtxt :: TcSigInfo -> TcSigInfo -> SDoc
1207 sigContextsCtxt sig1 sig2
1208 = vcat [ptext (sLit "When matching the contexts of the signatures for"),
1209 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1210 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1211 ptext (sLit "The signature contexts in a mutually recursive group should all be identical")]
1217 -----------------------------------------------
1218 unboxedTupleErr :: Name -> Type -> SDoc
1219 unboxedTupleErr name ty
1220 = hang (ptext (sLit "Illegal binding of unboxed tuple"))
1221 4 (ppr name <+> dcolon <+> ppr ty)
1223 -----------------------------------------------
1224 restrictedBindCtxtErr :: [Name] -> SDoc
1225 restrictedBindCtxtErr binder_names
1226 = hang (ptext (sLit "Illegal overloaded type signature(s)"))
1227 4 (vcat [ptext (sLit "in a binding group for") <+> pprBinders binder_names,
1228 ptext (sLit "that falls under the monomorphism restriction")])
1230 genCtxt :: [Name] -> SDoc
1231 genCtxt binder_names
1232 = ptext (sLit "When generalising the type(s) for") <+> pprBinders binder_names
1234 missingSigWarn :: Bool -> Name -> Type -> TcM ()
1235 missingSigWarn False _ _ = return ()
1236 missingSigWarn True name ty
1237 = do { env0 <- tcInitTidyEnv
1238 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1239 ; addWarnTcM (env1, mk_msg tidy_ty) }
1241 mk_msg ty = vcat [ptext (sLit "Definition but no type signature for") <+> quotes (ppr name),
1242 sep [ptext (sLit "Inferred type:") <+> pprHsVar name <+> dcolon <+> ppr ty]]