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, tcPrags, mkPragFun,
11 TcSigInfo(..), TcSigFun, mkTcSigFun,
12 badBootDeclErr ) where
14 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
15 import {-# SOURCE #-} TcExpr ( tcMonoExpr )
52 %************************************************************************
54 \subsection{Type-checking bindings}
56 %************************************************************************
58 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
59 it needs to know something about the {\em usage} of the things bound,
60 so that it can create specialisations of them. So @tcBindsAndThen@
61 takes a function which, given an extended environment, E, typechecks
62 the scope of the bindings returning a typechecked thing and (most
63 important) an LIE. It is this LIE which is then used as the basis for
64 specialising the things bound.
66 @tcBindsAndThen@ also takes a "combiner" which glues together the
67 bindings and the "thing" to make a new "thing".
69 The real work is done by @tcBindWithSigsAndThen@.
71 Recursive and non-recursive binds are handled in essentially the same
72 way: because of uniques there are no scoping issues left. The only
73 difference is that non-recursive bindings can bind primitive values.
75 Even for non-recursive binding groups we add typings for each binder
76 to the LVE for the following reason. When each individual binding is
77 checked the type of its LHS is unified with that of its RHS; and
78 type-checking the LHS of course requires that the binder is in scope.
80 At the top-level the LIE is sure to contain nothing but constant
81 dictionaries, which we resolve at the module level.
84 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
85 -- Note: returning the TcLclEnv is more than we really
86 -- want. The bit we care about is the local bindings
87 -- and the free type variables thereof
89 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
90 ; return (foldr (unionBags . snd) emptyBag prs, env) }
91 -- The top level bindings are flattened into a giant
92 -- implicitly-mutually-recursive LHsBinds
94 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
95 -- A hs-boot file has only one BindGroup, and it only has type
96 -- signatures in it. The renamer checked all this
97 tcHsBootSigs (ValBindsOut binds sigs)
98 = do { checkTc (null binds) badBootDeclErr
99 ; mapM (addLocM tc_boot_sig) (filter isTypeLSig sigs) }
101 tc_boot_sig (TypeSig (L _ name) ty)
102 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
103 ; return (mkVanillaGlobal name sigma_ty) }
104 -- Notice that we make GlobalIds, not LocalIds
105 tc_boot_sig s = pprPanic "tcHsBootSigs/tc_boot_sig" (ppr s)
106 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
108 badBootDeclErr :: Message
109 badBootDeclErr = ptext (sLit "Illegal declarations in an hs-boot file")
111 ------------------------
112 tcLocalBinds :: HsLocalBinds Name -> TcM thing
113 -> TcM (HsLocalBinds TcId, thing)
115 tcLocalBinds EmptyLocalBinds thing_inside
116 = do { thing <- thing_inside
117 ; return (EmptyLocalBinds, thing) }
119 tcLocalBinds (HsValBinds binds) thing_inside
120 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
121 ; return (HsValBinds binds', thing) }
123 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
124 = do { (thing, lie) <- getLIE thing_inside
125 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
127 -- If the binding binds ?x = E, we must now
128 -- discharge any ?x constraints in expr_lie
129 ; dict_binds <- tcSimplifyIPs avail_ips lie
130 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
132 -- I wonder if we should do these one at at time
135 tc_ip_bind (IPBind ip expr) = do
136 ty <- newFlexiTyVarTy argTypeKind
137 (ip', ip_inst) <- newIPDict (IPBindOrigin ip) ip ty
138 expr' <- tcMonoExpr expr ty
139 return (ip_inst, (IPBind ip' expr'))
141 ------------------------
142 tcValBinds :: TopLevelFlag
143 -> HsValBinds Name -> TcM thing
144 -> TcM (HsValBinds TcId, thing)
146 tcValBinds _ (ValBindsIn binds _) _
147 = pprPanic "tcValBinds" (ppr binds)
149 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
150 = do { -- Typecheck the signature
151 ; let { prag_fn = mkPragFun sigs
152 ; ty_sigs = filter isTypeLSig sigs
153 ; sig_fn = mkTcSigFun ty_sigs }
155 ; poly_ids <- checkNoErrs (mapAndRecoverM tcTySig ty_sigs)
156 -- No recovery from bad signatures, because the type sigs
157 -- may bind type variables, so proceeding without them
158 -- can lead to a cascade of errors
159 -- ToDo: this means we fall over immediately if any type sig
160 -- is wrong, which is over-conservative, see Trac bug #745
162 -- Extend the envt right away with all
163 -- the Ids declared with type signatures
164 ; poly_rec <- doptM Opt_RelaxedPolyRec
165 ; (binds', thing) <- tcExtendIdEnv poly_ids $
166 tcBindGroups poly_rec top_lvl sig_fn prag_fn
169 ; return (ValBindsOut binds' sigs, thing) }
171 ------------------------
172 tcBindGroups :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
173 -> [(RecFlag, LHsBinds Name)] -> TcM thing
174 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
175 -- Typecheck a whole lot of value bindings,
176 -- one strongly-connected component at a time
177 -- Here a "strongly connected component" has the strightforward
178 -- meaning of a group of bindings that mention each other,
179 -- ignoring type signatures (that part comes later)
181 tcBindGroups _ _ _ _ [] thing_inside
182 = do { thing <- thing_inside
183 ; return ([], thing) }
185 tcBindGroups poly_rec top_lvl sig_fn prag_fn (group : groups) thing_inside
186 = do { (group', (groups', thing))
187 <- tc_group poly_rec top_lvl sig_fn prag_fn group $
188 tcBindGroups poly_rec top_lvl sig_fn prag_fn groups thing_inside
189 ; return (group' ++ groups', thing) }
191 ------------------------
192 tc_group :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
193 -> (RecFlag, LHsBinds Name) -> TcM thing
194 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
196 -- Typecheck one strongly-connected component of the original program.
197 -- We get a list of groups back, because there may
198 -- be specialisations etc as well
200 tc_group _ top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
201 -- A single non-recursive binding
202 -- We want to keep non-recursive things non-recursive
203 -- so that we desugar unlifted bindings correctly
204 = do { (binds1, lie_binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn
205 NonRecursive binds thing_inside
206 ; return ( [(NonRecursive, unitBag b) | b <- bagToList binds1]
207 ++ [(Recursive, lie_binds)] -- TcDictBinds have scrambled dependency order
210 tc_group poly_rec top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
211 | not poly_rec -- Recursive group, normal Haskell 98 route
212 = do { (binds1, lie_binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn
213 Recursive binds thing_inside
214 ; return ([(Recursive, binds1 `unionBags` lie_binds)], thing) }
216 | otherwise -- Recursive group, with -XRelaxedPolyRec
217 = -- To maximise polymorphism (with -XRelaxedPolyRec), we do a new
218 -- strongly-connected-component analysis, this time omitting
219 -- any references to variables with type signatures.
221 -- Notice that the bindInsts thing covers *all* the bindings in
222 -- the original group at once; an earlier one may use a later one!
223 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
224 ; (binds1,lie_binds,thing) <- bindLocalInsts top_lvl $
225 go (stronglyConnCompFromEdgedVertices (mkEdges sig_fn binds))
226 ; return ([(Recursive, binds1 `unionBags` lie_binds)], thing) }
227 -- Rec them all together
229 -- go :: SCC (LHsBind Name) -> TcM (LHsBinds TcId, [TcId], thing)
230 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
231 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
232 ; return (binds1 `unionBags` binds2, ids1 ++ ids2, thing) }
233 go [] = do { thing <- thing_inside; return (emptyBag, [], thing) }
235 tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive (unitBag bind)
236 tc_scc (CyclicSCC binds) = tc_sub_group Recursive (listToBag binds)
238 tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
240 tc_haskell98 :: TopLevelFlag -> TcSigFun -> TcPragFun -> RecFlag
241 -> LHsBinds Name -> TcM a -> TcM (LHsBinds TcId, TcDictBinds, a)
242 tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside
243 = bindLocalInsts top_lvl $
244 do { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds
245 ; thing <- tcExtendIdEnv ids thing_inside
246 ; return (binds1, ids, thing) }
248 ------------------------
249 bindLocalInsts :: TopLevelFlag
250 -> TcM (LHsBinds TcId, [TcId], a)
251 -> TcM (LHsBinds TcId, TcDictBinds, a)
252 bindLocalInsts top_lvl thing_inside
254 = do { (binds, _, thing) <- thing_inside; return (binds, emptyBag, thing) }
255 -- For the top level don't bother with all this bindInstsOfLocalFuns stuff.
256 -- All the top level things are rec'd together anyway, so it's fine to
257 -- leave them to the tcSimplifyTop, and quite a bit faster too
259 | otherwise -- Nested case
260 = do { ((binds, ids, thing), lie) <- getLIE thing_inside
261 ; lie_binds <- bindInstsOfLocalFuns lie ids
262 ; return (binds, lie_binds, thing) }
264 ------------------------
265 mkEdges :: TcSigFun -> LHsBinds Name
266 -> [(LHsBind Name, BKey, [BKey])]
268 type BKey = Int -- Just number off the bindings
271 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
272 Just key <- [lookupNameEnv key_map n], no_sig n ])
273 | (bind, key) <- keyd_binds
276 no_sig :: Name -> Bool
277 no_sig n = isNothing (sig_fn n)
279 keyd_binds = bagToList binds `zip` [0::BKey ..]
281 key_map :: NameEnv BKey -- Which binding it comes from
282 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
283 , bndr <- bindersOfHsBind bind ]
285 bindersOfHsBind :: HsBind Name -> [Name]
286 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
287 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
288 bindersOfHsBind (AbsBinds {}) = panic "bindersOfHsBind AbsBinds"
289 bindersOfHsBind (VarBind {}) = panic "bindersOfHsBind VarBind"
291 ------------------------
292 tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragFun
293 -> RecFlag -- Whether the group is really recursive
294 -> RecFlag -- Whether it's recursive after breaking
295 -- dependencies based on type signatures
297 -> TcM (LHsBinds TcId, [TcId])
299 -- Typechecks a single bunch of bindings all together,
300 -- and generalises them. The bunch may be only part of a recursive
301 -- group, because we use type signatures to maximise polymorphism
303 -- Returns a list because the input may be a single non-recursive binding,
304 -- in which case the dependency order of the resulting bindings is
307 -- Knows nothing about the scope of the bindings
309 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds
311 bind_list = bagToList binds
312 binder_names = collectHsBindBinders binds
313 loc = getLoc (head bind_list)
314 -- TODO: location a bit awkward, but the mbinds have been
315 -- dependency analysed and may no longer be adjacent
317 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
319 recoverM (recoveryCode binder_names sig_fn) $ do
321 { traceTc (ptext (sLit "------------------------------------------------"))
322 ; traceTc (ptext (sLit "Bindings for") <+> ppr binder_names)
324 -- TYPECHECK THE BINDINGS
325 ; ((binds', mono_bind_infos), lie_req)
326 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
327 ; traceTc (text "temp" <+> (ppr binds' $$ ppr lie_req))
329 -- CHECK FOR UNLIFTED BINDINGS
330 -- These must be non-recursive etc, and are not generalised
331 -- They desugar to a case expression in the end
332 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
333 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
334 zonked_mono_tys mono_bind_infos
336 do { extendLIEs lie_req
337 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
338 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
339 mk_export (_, Just sig, mono_id) _ = ([], sig_id sig, mono_id, [])
340 -- ToDo: prags for unlifted bindings
342 ; return ( unitBag $ L loc $ AbsBinds [] [] exports binds',
343 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
345 else do -- The normal lifted case: GENERALISE
347 ; (tyvars_to_gen, dicts, dict_binds)
348 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
349 generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
351 -- BUILD THE POLYMORPHIC RESULT IDs
352 ; let dict_vars = map instToVar dicts -- May include equality constraints
353 ; exports <- mapM (mkExport top_lvl prag_fn tyvars_to_gen (map varType dict_vars))
356 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
357 ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids))
359 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen
361 (dict_binds `unionBags` binds')
363 ; return (unitBag abs_bind, poly_ids) -- poly_ids are guaranteed zonked by mkExport
368 mkExport :: TopLevelFlag -> TcPragFun -> [TyVar] -> [TcType]
370 -> TcM ([TyVar], Id, Id, [LPrag])
371 -- mkExport generates exports with
372 -- zonked type variables,
374 -- The former is just because no further unifications will change
375 -- the quantified type variables, so we can fix their final form
377 -- The latter is needed because the poly_ids are used to extend the
378 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
380 -- Pre-condition: the inferred_tvs are already zonked
382 mkExport top_lvl prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
383 = do { warn_missing_sigs <- doptM Opt_WarnMissingSigs
384 ; let warn = isTopLevel top_lvl && warn_missing_sigs
385 ; (tvs, poly_id) <- mk_poly_id warn mb_sig
386 -- poly_id has a zonked type
388 ; prags <- tcPrags poly_id (prag_fn poly_name)
389 -- tcPrags requires a zonked poly_id
391 ; return (tvs, poly_id, mono_id, prags) }
393 poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id))
395 mk_poly_id warn Nothing = do { poly_ty' <- zonkTcType poly_ty
396 ; missingSigWarn warn poly_name poly_ty'
397 ; return (inferred_tvs, mkLocalId poly_name poly_ty') }
398 mk_poly_id _ (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
399 ; return (tvs, sig_id sig) }
401 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
403 ------------------------
404 type TcPragFun = Name -> [LSig Name]
406 mkPragFun :: [LSig Name] -> TcPragFun
407 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
409 prs = [(expectJust "mkPragFun" (sigName sig), sig)
410 | sig <- sigs, isPragLSig sig]
411 env = foldl add emptyNameEnv prs
412 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
414 tcPrags :: Id -> [LSig Name] -> TcM [LPrag]
415 tcPrags poly_id prags = mapM (wrapLocM tc_prag) prags
417 tc_prag prag = addErrCtxt (pragSigCtxt prag) $
420 pragSigCtxt :: Sig Name -> SDoc
421 pragSigCtxt prag = hang (ptext (sLit "In the pragma")) 2 (ppr prag)
423 tcPrag :: TcId -> Sig Name -> TcM Prag
424 -- Pre-condition: the poly_id is zonked
425 -- Reason: required by tcSubExp
426 -- Most of the work of specialisation is done by
427 -- the desugarer, guided by the SpecPrag
428 tcPrag poly_id (SpecSig _ hs_ty inl)
429 = do { let name = idName poly_id
430 ; spec_ty <- tcHsSigType (FunSigCtxt name) hs_ty
431 ; co_fn <- tcSubExp (SpecPragOrigin name) (idType poly_id) spec_ty
432 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty inl) }
433 tcPrag poly_id (SpecInstSig hs_ty)
434 = do { let name = idName poly_id
435 ; (tyvars, theta, tau) <- tcHsInstHead hs_ty
436 ; let spec_ty = mkSigmaTy tyvars theta tau
437 ; co_fn <- tcSubExp (SpecPragOrigin name) (idType poly_id) spec_ty
438 ; return (SpecPrag (mkHsWrap co_fn (HsVar poly_id)) spec_ty defaultInlineSpec) }
440 tcPrag _ (InlineSig _ inl) = return (InlinePrag inl)
441 tcPrag _ sig = pprPanic "tcPrag" (ppr sig)
445 -- If typechecking the binds fails, then return with each
446 -- signature-less binder given type (forall a.a), to minimise
447 -- subsequent error messages
448 recoveryCode :: [Name] -> (Name -> Maybe [Name])
449 -> TcM (LHsBinds TcId, [Id])
450 recoveryCode binder_names sig_fn
451 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
452 ; poly_ids <- mapM mk_dummy binder_names
453 ; return (emptyBag, poly_ids) }
456 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
457 | otherwise = return (mkLocalId name forall_a_a) -- No signature
460 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
463 -- Check that non-overloaded unlifted bindings are
466 -- c) not a multiple-binding group (more or less implied by (a))
468 checkStrictBinds :: TopLevelFlag -> RecFlag
469 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
471 checkStrictBinds top_lvl rec_group mbind mono_tys infos
472 | unlifted || bang_pat
473 = do { checkTc (isNotTopLevel top_lvl)
474 (strictBindErr "Top-level" unlifted mbind)
475 ; checkTc (isNonRec rec_group)
476 (strictBindErr "Recursive" unlifted mbind)
477 ; checkTc (isSingletonBag mbind)
478 (strictBindErr "Multiple" unlifted mbind)
479 -- This should be a checkTc, not a warnTc, but as of GHC 6.11
480 -- the versions of alex and happy available have non-conforming
481 -- templates, so the GHC build fails if it's an error:
482 ; warnUnlifted <- doptM Opt_WarnLazyUnliftedBindings
483 ; warnTc (warnUnlifted && not bang_pat)
484 (unliftedMustBeBang mbind)
485 ; mapM_ check_sig infos
490 unlifted = any isUnLiftedType mono_tys
491 bang_pat = anyBag (isBangHsBind . unLoc) mbind
492 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
493 (badStrictSig unlifted sig)
494 check_sig _ = return ()
496 unliftedMustBeBang :: LHsBindsLR Var Var -> SDoc
497 unliftedMustBeBang mbind
498 = hang (text "Bindings containing unlifted types must use an outermost bang pattern:")
499 4 (pprLHsBinds mbind)
500 $$ text "*** This will be an error in GHC 6.14! Fix your code now!"
502 strictBindErr :: String -> Bool -> LHsBindsLR Var Var -> SDoc
503 strictBindErr flavour unlifted mbind
504 = hang (text flavour <+> msg <+> ptext (sLit "aren't allowed:"))
505 4 (pprLHsBinds mbind)
507 msg | unlifted = ptext (sLit "bindings for unlifted types")
508 | otherwise = ptext (sLit "bang-pattern bindings")
510 badStrictSig :: Bool -> TcSigInfo -> SDoc
511 badStrictSig unlifted sig
512 = hang (ptext (sLit "Illegal polymorphic signature in") <+> msg)
515 msg | unlifted = ptext (sLit "an unlifted binding")
516 | otherwise = ptext (sLit "a bang-pattern binding")
520 %************************************************************************
522 \subsection{tcMonoBind}
524 %************************************************************************
526 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
527 The signatures have been dealt with already.
530 tcMonoBinds :: [LHsBind Name]
532 -> RecFlag -- Whether the binding is recursive for typechecking purposes
533 -- i.e. the binders are mentioned in their RHSs, and
534 -- we are not resuced by a type signature
535 -> TcM (LHsBinds TcId, [MonoBindInfo])
537 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
538 fun_matches = matches, bind_fvs = fvs })]
539 sig_fn -- Single function binding,
540 NonRecursive -- binder isn't mentioned in RHS,
541 | Nothing <- sig_fn name -- ...with no type signature
542 = -- In this very special case we infer the type of the
543 -- right hand side first (it may have a higher-rank type)
544 -- and *then* make the monomorphic Id for the LHS
545 -- e.g. f = \(x::forall a. a->a) -> <body>
546 -- We want to infer a higher-rank type for f
548 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
550 -- Check for an unboxed tuple type
551 -- f = (# True, False #)
552 -- Zonk first just in case it's hidden inside a meta type variable
553 -- (This shows up as a (more obscure) kind error
554 -- in the 'otherwise' case of tcMonoBinds.)
555 ; zonked_rhs_ty <- zonkTcType rhs_ty
556 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
557 (unboxedTupleErr name zonked_rhs_ty)
559 ; mono_name <- newLocalName name
560 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
561 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
562 fun_matches = matches', bind_fvs = fvs,
563 fun_co_fn = co_fn, fun_tick = Nothing })),
564 [(name, Nothing, mono_id)]) }
566 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
567 fun_matches = matches })]
568 sig_fn -- Single function binding
570 | Just scoped_tvs <- sig_fn name -- ...with a type signature
571 = -- When we have a single function binding, with a type signature
572 -- we can (a) use genuine, rigid skolem constants for the type variables
573 -- (b) bring (rigid) scoped type variables into scope
575 do { tc_sig <- tcInstSig True name
576 ; mono_name <- newLocalName name
577 ; let mono_ty = sig_tau tc_sig
578 mono_id = mkLocalId mono_name mono_ty
579 rhs_tvs = [ (name, mkTyVarTy tv)
580 | (name, tv) <- scoped_tvs `zip` sig_tvs tc_sig ]
581 -- See Note [More instantiated than scoped]
582 -- Note that the scoped_tvs and the (sig_tvs sig)
583 -- may have different Names. That's quite ok.
585 ; traceTc (text "tcMoonBinds" <+> ppr scoped_tvs $$ ppr tc_sig)
586 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
587 tcMatchesFun mono_name inf matches mono_ty
588 -- Note that "mono_ty" might actually be a polymorphic type,
589 -- if the original function had a signature like
590 -- forall a. Eq a => forall b. Ord b => ....
591 -- But that's ok: tcMatchesFun can deal with that
592 -- It happens, too! See Note [Polymorphic methods] in TcClassDcl.
594 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
595 fun_infix = inf, fun_matches = matches',
596 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
598 ; return (unitBag (L b_loc fun_bind'),
599 [(name, Just tc_sig, mono_id)]) }
601 tcMonoBinds binds sig_fn _
602 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
604 -- Bring the monomorphic Ids, into scope for the RHSs
605 ; let mono_info = getMonoBindInfo tc_binds
606 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
607 -- A monomorphic binding for each term variable that lacks
608 -- a type sig. (Ones with a sig are already in scope.)
610 ; binds' <- tcExtendIdEnv2 rhs_id_env $ do
611 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
612 | (n,id) <- rhs_id_env])
613 mapM (wrapLocM tcRhs) tc_binds
614 ; return (listToBag binds', mono_info) }
616 ------------------------
617 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
618 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
619 -- if there's a signature for it, use the instantiated signature type
620 -- otherwise invent a type variable
621 -- You see that quite directly in the FunBind case.
623 -- But there's a complication for pattern bindings:
624 -- data T = MkT (forall a. a->a)
626 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
627 -- but we want to get (f::forall a. a->a) as the RHS environment.
628 -- The simplest way to do this is to typecheck the pattern, and then look up the
629 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
630 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
632 data TcMonoBind -- Half completed; LHS done, RHS not done
633 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
634 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
636 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
637 -- Type signature (if any), and
638 -- the monomorphic bound things
640 bndrNames :: [MonoBindInfo] -> [Name]
641 bndrNames mbi = [n | (n,_,_) <- mbi]
643 getMonoType :: MonoBindInfo -> TcTauType
644 getMonoType (_,_,mono_id) = idType mono_id
646 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
647 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
648 = do { mb_sig <- tcInstSig_maybe sig_fn name
649 ; mono_name <- newLocalName name
650 ; mono_ty <- mk_mono_ty mb_sig
651 ; let mono_id = mkLocalId mono_name mono_ty
652 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
654 mk_mono_ty (Just sig) = return (sig_tau sig)
655 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
657 tcLhs sig_fn (PatBind { pat_lhs = pat, pat_rhs = grhss })
658 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
659 ; mono_pat_binds <- doptM Opt_MonoPatBinds
660 -- With -XMonoPatBinds, we do no generalisation of pattern bindings
661 -- But the signature can still be polymoprhic!
662 -- data T = MkT (forall a. a->a)
663 -- x :: forall a. a->a
665 -- The function get_sig_ty decides whether the pattern-bound variables
666 -- should have exactly the type in the type signature (-XMonoPatBinds),
667 -- or the instantiated version (-XMonoPatBinds)
669 ; let nm_sig_prs = names `zip` mb_sigs
670 get_sig_ty | mono_pat_binds = idType . sig_id
671 | otherwise = sig_tau
672 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
673 | (name, Just sig) <- nm_sig_prs]
674 sig_tau_fn = lookupNameEnv tau_sig_env
676 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
677 mapM lookup_info nm_sig_prs
679 -- After typechecking the pattern, look up the binder
680 -- names, which the pattern has brought into scope.
681 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
682 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
683 ; return (name, mb_sig, mono_id) }
685 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
688 ; return (TcPatBind infos pat' grhss pat_ty) }
690 names = collectPatBinders pat
693 tcLhs _ other_bind = pprPanic "tcLhs" (ppr other_bind)
694 -- AbsBind, VarBind impossible
697 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
698 -- When we are doing pattern bindings, or multiple function bindings at a time
699 -- we *don't* bring any scoped type variables into scope
700 -- Wny not? They are not completely rigid.
701 -- That's why we have the special case for a single FunBind in tcMonoBinds
702 tcRhs (TcFunBind (_,_,mono_id) fun' inf matches)
703 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
704 matches (idType mono_id)
705 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
706 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
707 fun_tick = Nothing }) }
709 tcRhs (TcPatBind _ pat' grhss pat_ty)
710 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
711 tcGRHSsPat grhss pat_ty
712 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
713 bind_fvs = placeHolderNames }) }
716 ---------------------
717 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
718 getMonoBindInfo tc_binds
719 = foldr (get_info . unLoc) [] tc_binds
721 get_info (TcFunBind info _ _ _) rest = info : rest
722 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
726 %************************************************************************
730 %************************************************************************
733 generalise :: DynFlags -> TopLevelFlag
734 -> [LHsBind Name] -> TcSigFun
735 -> [MonoBindInfo] -> [Inst]
736 -> TcM ([TyVar], [Inst], TcDictBinds)
737 -- The returned [TyVar] are all ready to quantify
739 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
740 | isMonoGroup dflags top_lvl bind_list sigs
741 = do { extendLIEs lie_req
742 ; return ([], [], emptyBag) }
744 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
745 = -- Check signature contexts are empty
746 do { checkTc (all is_mono_sig sigs)
747 (restrictedBindCtxtErr bndrs)
749 -- Now simplify with exactly that set of tyvars
750 -- We have to squash those Methods
751 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
754 -- Check that signature type variables are OK
755 ; final_qtvs <- checkSigsTyVars qtvs sigs
757 ; return (final_qtvs, [], binds) }
759 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
760 = tcSimplifyInfer doc tau_tvs lie_req
762 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
763 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
764 ; let -- The "sig_avails" is the stuff available. We get that from
765 -- the context of the type signature, BUT ALSO the lie_avail
766 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
767 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
768 sig_avails = sig_lie ++ local_meths
769 loc = sig_loc (head sigs)
771 -- Check that the needed dicts can be
772 -- expressed in terms of the signature ones
773 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
775 -- Check that signature type variables are OK
776 ; final_qtvs <- checkSigsTyVars qtvs sigs
778 ; return (final_qtvs, sig_lie, binds) }
780 bndrs = bndrNames mono_infos
781 sigs = [sig | (_, Just sig, _) <- mono_infos]
782 get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
783 | otherwise = exactTyVarsOfType
784 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
785 is_mono_sig sig = null (sig_theta sig)
786 doc = ptext (sLit "type signature(s) for") <+> pprBinders bndrs
788 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
789 sig_theta = theta, sig_loc = loc }) mono_id
790 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
791 tci_theta = theta, tci_loc = loc}
794 unifyCtxts checks that all the signature contexts are the same
795 The type signatures on a mutually-recursive group of definitions
796 must all have the same context (or none).
798 The trick here is that all the signatures should have the same
799 context, and we want to share type variables for that context, so that
800 all the right hand sides agree a common vocabulary for their type
803 We unify them because, with polymorphic recursion, their types
804 might not otherwise be related. This is a rather subtle issue.
807 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
808 -- Post-condition: the returned Insts are full zonked
809 unifyCtxts [] = panic "unifyCtxts []"
810 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
811 = do { traceTc $ text "unifyCtxts" <+> ppr (sig1 : sigs)
812 ; mapM_ unify_ctxt sigs
813 ; theta <- zonkTcThetaType (sig_theta sig1)
814 ; newDictBndrs (sig_loc sig1) theta }
816 theta1 = sig_theta sig1
817 unify_ctxt :: TcSigInfo -> TcM ()
818 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
819 = setSrcSpan (instLocSpan (sig_loc sig)) $
820 addErrCtxt (sigContextsCtxt sig1 sig) $
821 do { cois <- unifyTheta theta1 theta
822 ; -- Check whether all coercions are identity coercions
823 -- That can happen if we have, say
825 -- g :: C (F a) => ...
826 -- where F is a type function and (F a ~ [a])
827 -- Then unification might succeed with a coercion. But it's much
828 -- much simpler to require that such signatures have identical contexts
829 checkTc (all isIdentityCoI cois)
830 (ptext (sLit "Mutually dependent functions have syntactically distinct contexts"))
833 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
834 checkSigsTyVars qtvs sigs
835 = do { gbl_tvs <- tcGetGlobalTyVars
836 ; sig_tvs_s <- mapM (check_sig gbl_tvs) sigs
838 ; let -- Sigh. Make sure that all the tyvars in the type sigs
839 -- appear in the returned ty var list, which is what we are
840 -- going to generalise over. Reason: we occasionally get
842 -- type T a = () -> ()
845 -- Here, 'a' won't appear in qtvs, so we have to add it
846 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
847 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
850 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
851 sig_theta = theta, sig_tau = tau})
852 = addErrCtxt (ptext (sLit "In the type signature for") <+> quotes (ppr id)) $
853 addErrCtxtM (sigCtxt id tvs theta tau) $
854 do { tvs' <- checkDistinctTyVars tvs
855 ; when (any (`elemVarSet` gbl_tvs) tvs')
856 (bleatEscapedTvs gbl_tvs tvs tvs')
859 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
860 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
861 -- are still all type variables, and all distinct from each other.
862 -- It returns a zonked set of type variables.
863 -- For example, if the type sig is
864 -- f :: forall a b. a -> b -> b
865 -- we want to check that 'a' and 'b' haven't
866 -- (a) been unified with a non-tyvar type
867 -- (b) been unified with each other (all distinct)
869 checkDistinctTyVars sig_tvs
870 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
871 ; foldlM_ check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
872 ; return zonked_tvs }
874 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
875 -- The TyVarEnv maps each zonked type variable back to its
876 -- corresponding user-written signature type variable
877 check_dup acc (sig_tv, zonked_tv)
878 = case lookupVarEnv acc zonked_tv of
879 Just sig_tv' -> bomb_out sig_tv sig_tv'
881 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
883 bomb_out sig_tv1 sig_tv2
884 = do { env0 <- tcInitTidyEnv
885 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
886 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
887 msg = ptext (sLit "Quantified type variable") <+> quotes (ppr tidy_tv1)
888 <+> ptext (sLit "is unified with another quantified type variable")
889 <+> quotes (ppr tidy_tv2)
890 ; failWithTcM (env2, msg) }
894 @getTyVarsToGen@ decides what type variables to generalise over.
896 For a "restricted group" -- see the monomorphism restriction
897 for a definition -- we bind no dictionaries, and
898 remove from tyvars_to_gen any constrained type variables
900 *Don't* simplify dicts at this point, because we aren't going
901 to generalise over these dicts. By the time we do simplify them
902 we may well know more. For example (this actually came up)
904 f x = array ... xs where xs = [1,2,3,4,5]
905 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
906 stuff. If we simplify only at the f-binding (not the xs-binding)
907 we'll know that the literals are all Ints, and we can just produce
910 Find all the type variables involved in overloading, the
911 "constrained_tyvars". These are the ones we *aren't* going to
912 generalise. We must be careful about doing this:
914 (a) If we fail to generalise a tyvar which is not actually
915 constrained, then it will never, ever get bound, and lands
916 up printed out in interface files! Notorious example:
917 instance Eq a => Eq (Foo a b) where ..
918 Here, b is not constrained, even though it looks as if it is.
919 Another, more common, example is when there's a Method inst in
920 the LIE, whose type might very well involve non-overloaded
922 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
923 the simple thing instead]
925 (b) On the other hand, we mustn't generalise tyvars which are constrained,
926 because we are going to pass on out the unmodified LIE, with those
927 tyvars in it. They won't be in scope if we've generalised them.
929 So we are careful, and do a complete simplification just to find the
930 constrained tyvars. We don't use any of the results, except to
931 find which tyvars are constrained.
933 Note [Polymorphic recursion]
934 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
935 The game plan for polymorphic recursion in the code above is
937 * Bind any variable for which we have a type signature
938 to an Id with a polymorphic type. Then when type-checking
939 the RHSs we'll make a full polymorphic call.
941 This fine, but if you aren't a bit careful you end up with a horrendous
942 amount of partial application and (worse) a huge space leak. For example:
944 f :: Eq a => [a] -> [a]
947 If we don't take care, after typechecking we get
949 f = /\a -> \d::Eq a -> let f' = f a d
953 Notice the the stupid construction of (f a d), which is of course
954 identical to the function we're executing. In this case, the
955 polymorphic recursion isn't being used (but that's a very common case).
956 This can lead to a massive space leak, from the following top-level defn
962 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
963 f' is another thunk which evaluates to the same thing... and you end
964 up with a chain of identical values all hung onto by the CAF ff.
968 = let f' = f Int dEqInt in \ys. ...f'...
970 = let f' = let f' = f Int dEqInt in \ys. ...f'...
975 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
976 which would make the space leak go away in this case
978 Solution: when typechecking the RHSs we always have in hand the
979 *monomorphic* Ids for each binding. So we just need to make sure that
980 if (Method f a d) shows up in the constraints emerging from (...f...)
981 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
982 to the "givens" when simplifying constraints. That's what the "lies_avail"
987 f = /\a -> \d::Eq a -> letrec
988 fm = \ys:[a] -> ...fm...
994 %************************************************************************
998 %************************************************************************
1000 Type signatures are tricky. See Note [Signature skolems] in TcType
1002 @tcSigs@ checks the signatures for validity, and returns a list of
1003 {\em freshly-instantiated} signatures. That is, the types are already
1004 split up, and have fresh type variables installed. All non-type-signature
1005 "RenamedSigs" are ignored.
1007 The @TcSigInfo@ contains @TcTypes@ because they are unified with
1008 the variable's type, and after that checked to see whether they've
1011 Note [Scoped tyvars]
1012 ~~~~~~~~~~~~~~~~~~~~
1013 The -XScopedTypeVariables flag brings lexically-scoped type variables
1014 into scope for any explicitly forall-quantified type variables:
1015 f :: forall a. a -> a
1017 Then 'a' is in scope inside 'e'.
1019 However, we do *not* support this
1020 - For pattern bindings e.g
1024 - For multiple function bindings, unless Opt_RelaxedPolyRec is on
1025 f :: forall a. a -> a
1027 g :: forall b. b -> b
1029 Reason: we use mutable variables for 'a' and 'b', since they may
1030 unify to each other, and that means the scoped type variable would
1031 not stand for a completely rigid variable.
1033 Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
1036 Note [More instantiated than scoped]
1037 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1038 There may be more instantiated type variables than lexically-scoped
1040 type T a = forall b. b -> (a,b)
1042 Here, the signature for f will have one scoped type variable, c,
1043 but two instantiated type variables, c' and b'.
1045 We assume that the scoped ones are at the *front* of sig_tvs,
1046 and remember the names from the original HsForAllTy in the TcSigFun.
1050 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
1051 -- type variables brought into scope
1052 -- by its type signature.
1053 -- Nothing => no type signature
1055 mkTcSigFun :: [LSig Name] -> TcSigFun
1056 -- Search for a particular type signature
1057 -- Precondition: the sigs are all type sigs
1058 -- Precondition: no duplicates
1059 mkTcSigFun sigs = lookupNameEnv env
1061 env = mkNameEnv (mapCatMaybes mk_pair sigs)
1062 mk_pair (L _ (TypeSig (L _ name) lhs_ty)) = Just (name, hsExplicitTvs lhs_ty)
1063 mk_pair (L _ (IdSig id)) = Just (idName id, [])
1065 -- The scoped names are the ones explicitly mentioned
1066 -- in the HsForAll. (There may be more in sigma_ty, because
1067 -- of nested type synonyms. See Note [More instantiated than scoped].)
1068 -- See Note [Only scoped tyvars are in the TyVarEnv]
1073 sig_id :: TcId, -- *Polymorphic* binder for this value...
1075 sig_tvs :: [TcTyVar], -- Instantiated type variables
1076 -- See Note [Instantiate sig]
1078 sig_theta :: TcThetaType, -- Instantiated theta
1079 sig_tau :: TcTauType, -- Instantiated tau
1080 sig_loc :: InstLoc -- The location of the signature
1084 -- Note [Only scoped tyvars are in the TyVarEnv]
1085 -- We are careful to keep only the *lexically scoped* type variables in
1086 -- the type environment. Why? After all, the renamer has ensured
1087 -- that only legal occurrences occur, so we could put all type variables
1088 -- into the type env.
1090 -- But we want to check that two distinct lexically scoped type variables
1091 -- do not map to the same internal type variable. So we need to know which
1092 -- the lexically-scoped ones are... and at the moment we do that by putting
1093 -- only the lexically scoped ones into the environment.
1096 -- Note [Instantiate sig]
1097 -- It's vital to instantiate a type signature with fresh variables.
1099 -- type S = forall a. a->a
1103 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1104 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1105 -- it's all cool; each signature has distinct type variables from the renamer.)
1107 instance Outputable TcSigInfo where
1108 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1109 = ppr id <+> ptext (sLit "::") <+> ppr tyvars <+> ppr theta <+> ptext (sLit "=>") <+> ppr tau
1113 tcTySig :: LSig Name -> TcM TcId
1114 tcTySig (L span (TypeSig (L _ name) ty))
1116 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1117 ; return (mkLocalId name sigma_ty) }
1118 tcTySig (L _ (IdSig id))
1120 tcTySig s = pprPanic "tcTySig" (ppr s)
1123 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1124 -- Instantiate with *meta* type variables;
1125 -- this signature is part of a multi-signature group
1126 tcInstSig_maybe sig_fn name
1127 = case sig_fn name of
1128 Nothing -> return Nothing
1129 Just _scoped_tvs -> do { tc_sig <- tcInstSig False name
1130 ; return (Just tc_sig) }
1131 -- NB: the _scoped_tvs may be non-empty, but we can
1132 -- just ignore them. See Note [Scoped tyvars].
1134 tcInstSig :: Bool -> Name -> TcM TcSigInfo
1135 -- Instantiate the signature, with either skolems or meta-type variables
1136 -- depending on the use_skols boolean. This variable is set True
1137 -- when we are typechecking a single function binding; and False for
1138 -- pattern bindings and a group of several function bindings.
1139 -- Reason: in the latter cases, the "skolems" can be unified together,
1140 -- so they aren't properly rigid in the type-refinement sense.
1141 -- NB: unless we are doing H98, each function with a sig will be done
1142 -- separately, even if it's mutually recursive, so use_skols will be True
1144 -- We always instantiate with fresh uniques,
1145 -- although we keep the same print-name
1147 -- type T = forall a. [a] -> [a]
1149 -- f = g where { g :: T; g = <rhs> }
1151 -- We must not use the same 'a' from the defn of T at both places!!
1153 tcInstSig use_skols name
1154 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1155 -- scope when starting the binding group
1156 ; let skol_info = SigSkol (FunSigCtxt name)
1157 ; (tvs, theta, tau) <- tcInstSigType use_skols skol_info (idType poly_id)
1158 ; loc <- getInstLoc (SigOrigin skol_info)
1159 ; return (TcSigInfo { sig_id = poly_id,
1160 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1164 isMonoGroup :: DynFlags -> TopLevelFlag -> [LHsBind Name]
1165 -> [TcSigInfo] -> Bool
1166 -- No generalisation at all
1167 isMonoGroup dflags top_lvl binds sigs
1168 = (dopt Opt_MonoPatBinds dflags && any is_pat_bind binds)
1169 || (dopt Opt_MonoLocalBinds dflags && null sigs && not (isTopLevel top_lvl))
1171 is_pat_bind (L _ (PatBind {})) = True
1172 is_pat_bind _ = False
1175 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1176 isRestrictedGroup dflags binds sig_fn
1177 = mono_restriction && not all_unrestricted
1179 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1180 all_unrestricted = all (unrestricted . unLoc) binds
1181 has_sig n = isJust (sig_fn n)
1183 unrestricted (PatBind {}) = False
1184 unrestricted (VarBind { var_id = v }) = has_sig v
1185 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1186 || has_sig (unLoc v)
1187 unrestricted (AbsBinds {})
1188 = panic "isRestrictedGroup/unrestricted AbsBinds"
1190 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1191 -- No args => like a pattern binding
1192 unrestricted_match _ = True
1193 -- Some args => a function binding
1197 %************************************************************************
1199 \subsection[TcBinds-errors]{Error contexts and messages}
1201 %************************************************************************
1205 -- This one is called on LHS, when pat and grhss are both Name
1206 -- and on RHS, when pat is TcId and grhss is still Name
1207 patMonoBindsCtxt :: OutputableBndr id => LPat id -> GRHSs Name -> SDoc
1208 patMonoBindsCtxt pat grhss
1209 = hang (ptext (sLit "In a pattern binding:")) 4 (pprPatBind pat grhss)
1211 -----------------------------------------------
1212 sigContextsCtxt :: TcSigInfo -> TcSigInfo -> SDoc
1213 sigContextsCtxt sig1 sig2
1214 = vcat [ptext (sLit "When matching the contexts of the signatures for"),
1215 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1216 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1217 ptext (sLit "The signature contexts in a mutually recursive group should all be identical")]
1223 -----------------------------------------------
1224 unboxedTupleErr :: Name -> Type -> SDoc
1225 unboxedTupleErr name ty
1226 = hang (ptext (sLit "Illegal binding of unboxed tuple"))
1227 4 (ppr name <+> dcolon <+> ppr ty)
1229 -----------------------------------------------
1230 restrictedBindCtxtErr :: [Name] -> SDoc
1231 restrictedBindCtxtErr binder_names
1232 = hang (ptext (sLit "Illegal overloaded type signature(s)"))
1233 4 (vcat [ptext (sLit "in a binding group for") <+> pprBinders binder_names,
1234 ptext (sLit "that falls under the monomorphism restriction")])
1236 genCtxt :: [Name] -> SDoc
1237 genCtxt binder_names
1238 = ptext (sLit "When generalising the type(s) for") <+> pprBinders binder_names
1240 missingSigWarn :: Bool -> Name -> Type -> TcM ()
1241 missingSigWarn False _ _ = return ()
1242 missingSigWarn True name ty
1243 = do { env0 <- tcInitTidyEnv
1244 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1245 ; addWarnTcM (env1, mk_msg tidy_ty) }
1247 mk_msg ty = vcat [ptext (sLit "Definition but no type signature for") <+> quotes (ppr name),
1248 sep [ptext (sLit "Inferred type:") <+> pprHsVar name <+> dcolon <+> ppr ty]]