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 )
48 import Data.List( partition )
53 %************************************************************************
55 \subsection{Type-checking bindings}
57 %************************************************************************
59 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
60 it needs to know something about the {\em usage} of the things bound,
61 so that it can create specialisations of them. So @tcBindsAndThen@
62 takes a function which, given an extended environment, E, typechecks
63 the scope of the bindings returning a typechecked thing and (most
64 important) an LIE. It is this LIE which is then used as the basis for
65 specialising the things bound.
67 @tcBindsAndThen@ also takes a "combiner" which glues together the
68 bindings and the "thing" to make a new "thing".
70 The real work is done by @tcBindWithSigsAndThen@.
72 Recursive and non-recursive binds are handled in essentially the same
73 way: because of uniques there are no scoping issues left. The only
74 difference is that non-recursive bindings can bind primitive values.
76 Even for non-recursive binding groups we add typings for each binder
77 to the LVE for the following reason. When each individual binding is
78 checked the type of its LHS is unified with that of its RHS; and
79 type-checking the LHS of course requires that the binder is in scope.
81 At the top-level the LIE is sure to contain nothing but constant
82 dictionaries, which we resolve at the module level.
85 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
86 -- Note: returning the TcLclEnv is more than we really
87 -- want. The bit we care about is the local bindings
88 -- and the free type variables thereof
90 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
91 ; return (foldr (unionBags . snd) emptyBag prs, env) }
92 -- The top level bindings are flattened into a giant
93 -- implicitly-mutually-recursive LHsBinds
95 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
96 -- A hs-boot file has only one BindGroup, and it only has type
97 -- signatures in it. The renamer checked all this
98 tcHsBootSigs (ValBindsOut binds sigs)
99 = do { checkTc (null binds) badBootDeclErr
100 ; mapM (addLocM tc_boot_sig) (filter isTypeLSig sigs) }
102 tc_boot_sig (TypeSig (L _ name) ty)
103 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
104 ; return (mkVanillaGlobal name sigma_ty) }
105 -- Notice that we make GlobalIds, not LocalIds
106 tc_boot_sig s = pprPanic "tcHsBootSigs/tc_boot_sig" (ppr s)
107 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
109 badBootDeclErr :: Message
110 badBootDeclErr = ptext (sLit "Illegal declarations in an hs-boot file")
112 ------------------------
113 tcLocalBinds :: HsLocalBinds Name -> TcM thing
114 -> TcM (HsLocalBinds TcId, thing)
116 tcLocalBinds EmptyLocalBinds thing_inside
117 = do { thing <- thing_inside
118 ; return (EmptyLocalBinds, thing) }
120 tcLocalBinds (HsValBinds binds) thing_inside
121 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
122 ; return (HsValBinds binds', thing) }
124 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
125 = do { (thing, lie) <- getLIE thing_inside
126 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
128 -- If the binding binds ?x = E, we must now
129 -- discharge any ?x constraints in expr_lie
130 ; dict_binds <- tcSimplifyIPs avail_ips lie
131 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
133 -- I wonder if we should do these one at at time
136 tc_ip_bind (IPBind ip expr) = do
137 ty <- newFlexiTyVarTy argTypeKind
138 (ip', ip_inst) <- newIPDict (IPBindOrigin ip) ip ty
139 expr' <- tcMonoExpr expr ty
140 return (ip_inst, (IPBind ip' expr'))
142 ------------------------
143 tcValBinds :: TopLevelFlag
144 -> HsValBinds Name -> TcM thing
145 -> TcM (HsValBinds TcId, thing)
147 tcValBinds _ (ValBindsIn binds _) _
148 = pprPanic "tcValBinds" (ppr binds)
150 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
151 = do { -- Typecheck the signature
152 ; let { prag_fn = mkPragFun sigs (foldr (unionBags . snd) emptyBag binds)
153 ; ty_sigs = filter isTypeLSig sigs
154 ; sig_fn = mkTcSigFun ty_sigs }
156 ; poly_ids <- checkNoErrs (mapAndRecoverM tcTySig ty_sigs)
157 -- No recovery from bad signatures, because the type sigs
158 -- may bind type variables, so proceeding without them
159 -- can lead to a cascade of errors
160 -- ToDo: this means we fall over immediately if any type sig
161 -- is wrong, which is over-conservative, see Trac bug #745
163 -- Extend the envt right away with all
164 -- the Ids declared with type signatures
165 ; poly_rec <- doptM Opt_RelaxedPolyRec
166 ; (binds', thing) <- tcExtendIdEnv poly_ids $
167 tcBindGroups poly_rec top_lvl sig_fn prag_fn
170 ; return (ValBindsOut binds' sigs, thing) }
172 ------------------------
173 tcBindGroups :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
174 -> [(RecFlag, LHsBinds Name)] -> TcM thing
175 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
176 -- Typecheck a whole lot of value bindings,
177 -- one strongly-connected component at a time
178 -- Here a "strongly connected component" has the strightforward
179 -- meaning of a group of bindings that mention each other,
180 -- ignoring type signatures (that part comes later)
182 tcBindGroups _ _ _ _ [] thing_inside
183 = do { thing <- thing_inside
184 ; return ([], thing) }
186 tcBindGroups poly_rec top_lvl sig_fn prag_fn (group : groups) thing_inside
187 = do { (group', (groups', thing))
188 <- tc_group poly_rec top_lvl sig_fn prag_fn group $
189 tcBindGroups poly_rec top_lvl sig_fn prag_fn groups thing_inside
190 ; return (group' ++ groups', thing) }
192 ------------------------
193 tc_group :: Bool -> TopLevelFlag -> TcSigFun -> TcPragFun
194 -> (RecFlag, LHsBinds Name) -> TcM thing
195 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
197 -- Typecheck one strongly-connected component of the original program.
198 -- We get a list of groups back, because there may
199 -- be specialisations etc as well
201 tc_group _ top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
202 -- A single non-recursive binding
203 -- We want to keep non-recursive things non-recursive
204 -- so that we desugar unlifted bindings correctly
205 = do { (binds1, lie_binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn
206 NonRecursive binds thing_inside
207 ; return ( [(NonRecursive, unitBag b) | b <- bagToList binds1]
208 ++ [(Recursive, lie_binds)] -- TcDictBinds have scrambled dependency order
211 tc_group poly_rec top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
212 | not poly_rec -- Recursive group, normal Haskell 98 route
213 = do { (binds1, lie_binds, thing) <- tc_haskell98 top_lvl sig_fn prag_fn
214 Recursive binds thing_inside
215 ; return ([(Recursive, binds1 `unionBags` lie_binds)], thing) }
217 | otherwise -- Recursive group, with -XRelaxedPolyRec
218 = -- To maximise polymorphism (with -XRelaxedPolyRec), we do a new
219 -- strongly-connected-component analysis, this time omitting
220 -- any references to variables with type signatures.
222 -- Notice that the bindInsts thing covers *all* the bindings in
223 -- the original group at once; an earlier one may use a later one!
224 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
225 ; (binds1,lie_binds,thing) <- bindLocalInsts top_lvl $
226 go (stronglyConnCompFromEdgedVertices (mkEdges sig_fn binds))
227 ; return ([(Recursive, binds1 `unionBags` lie_binds)], thing) }
228 -- Rec them all together
230 -- go :: SCC (LHsBind Name) -> TcM (LHsBinds TcId, [TcId], thing)
231 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
232 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
233 ; return (binds1 `unionBags` binds2, ids1 ++ ids2, thing) }
234 go [] = do { thing <- thing_inside; return (emptyBag, [], thing) }
236 tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive (unitBag bind)
237 tc_scc (CyclicSCC binds) = tc_sub_group Recursive (listToBag binds)
239 tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
241 tc_haskell98 :: TopLevelFlag -> TcSigFun -> TcPragFun -> RecFlag
242 -> LHsBinds Name -> TcM a -> TcM (LHsBinds TcId, TcDictBinds, a)
243 tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside
244 = bindLocalInsts top_lvl $
245 do { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds
246 ; thing <- tcExtendIdEnv ids thing_inside
247 ; return (binds1, ids, thing) }
249 ------------------------
250 bindLocalInsts :: TopLevelFlag
251 -> TcM (LHsBinds TcId, [TcId], a)
252 -> TcM (LHsBinds TcId, TcDictBinds, a)
253 bindLocalInsts top_lvl thing_inside
255 = do { (binds, _, thing) <- thing_inside; return (binds, emptyBag, thing) }
256 -- For the top level don't bother with all this bindInstsOfLocalFuns stuff.
257 -- All the top level things are rec'd together anyway, so it's fine to
258 -- leave them to the tcSimplifyTop, and quite a bit faster too
260 | otherwise -- Nested case
261 = do { ((binds, ids, thing), lie) <- getLIE thing_inside
262 ; lie_binds <- bindInstsOfLocalFuns lie ids
263 ; return (binds, lie_binds, thing) }
265 ------------------------
266 mkEdges :: TcSigFun -> LHsBinds Name
267 -> [(LHsBind Name, BKey, [BKey])]
269 type BKey = Int -- Just number off the bindings
272 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
273 Just key <- [lookupNameEnv key_map n], no_sig n ])
274 | (bind, key) <- keyd_binds
277 no_sig :: Name -> Bool
278 no_sig n = isNothing (sig_fn n)
280 keyd_binds = bagToList binds `zip` [0::BKey ..]
282 key_map :: NameEnv BKey -- Which binding it comes from
283 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
284 , bndr <- bindersOfHsBind bind ]
286 bindersOfHsBind :: HsBind Name -> [Name]
287 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
288 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
289 bindersOfHsBind (AbsBinds {}) = panic "bindersOfHsBind AbsBinds"
290 bindersOfHsBind (VarBind {}) = panic "bindersOfHsBind VarBind"
292 ------------------------
293 tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragFun
294 -> RecFlag -- Whether the group is really recursive
295 -> RecFlag -- Whether it's recursive after breaking
296 -- dependencies based on type signatures
298 -> TcM (LHsBinds TcId, [TcId])
300 -- Typechecks a single bunch of bindings all together,
301 -- and generalises them. The bunch may be only part of a recursive
302 -- group, because we use type signatures to maximise polymorphism
304 -- Returns a list because the input may be a single non-recursive binding,
305 -- in which case the dependency order of the resulting bindings is
308 -- Knows nothing about the scope of the bindings
310 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds
312 bind_list = bagToList binds
313 binder_names = collectHsBindsBinders binds
314 loc = getLoc (head bind_list)
315 -- TODO: location a bit awkward, but the mbinds have been
316 -- dependency analysed and may no longer be adjacent
318 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
320 recoverM (recoveryCode binder_names sig_fn) $ do
322 { traceTc (ptext (sLit "------------------------------------------------"))
323 ; traceTc (ptext (sLit "Bindings for") <+> ppr binder_names)
325 -- TYPECHECK THE BINDINGS
326 ; ((binds', mono_bind_infos), lie_req)
327 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
328 ; traceTc (text "temp" <+> (ppr binds' $$ ppr lie_req))
330 -- CHECK FOR UNLIFTED BINDINGS
331 -- These must be non-recursive etc, and are not generalised
332 -- They desugar to a case expression in the end
333 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
334 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
335 zonked_mono_tys mono_bind_infos
337 do { extendLIEs lie_req
338 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
339 mk_export (name, mb_sig, mono_id) mono_ty
340 = ([], the_id, mono_id, noSpecPrags)
341 -- ToDo: prags for unlifted bindings
343 the_id = case mb_sig of
344 Just sig -> sig_id sig
345 Nothing -> mkLocalId name mono_ty
347 ; return ( unitBag $ L loc $ AbsBinds [] [] exports binds',
348 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
350 else do -- The normal lifted case: GENERALISE
352 ; (tyvars_to_gen, dicts, dict_binds)
353 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
354 generalise dflags top_lvl bind_list sig_fn mono_bind_infos lie_req
356 -- BUILD THE POLYMORPHIC RESULT IDs
357 ; let dict_vars = map instToVar dicts -- May include equality constraints
358 ; exports <- mapM (mkExport top_lvl rec_group (length mono_bind_infos > 1)
359 prag_fn tyvars_to_gen (map varType dict_vars))
362 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
363 ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids))
365 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen
367 (dict_binds `unionBags` binds')
369 ; return (unitBag abs_bind, poly_ids) -- poly_ids are guaranteed zonked by mkExport
374 mkExport :: TopLevelFlag -> RecFlag
375 -> Bool -- More than one variable is bound, so we'll desugar to
376 -- a tuple, so INLINE pragmas won't work
377 -> TcPragFun -> [TyVar] -> [TcType]
379 -> TcM ([TyVar], Id, Id, TcSpecPrags)
380 -- mkExport generates exports with
381 -- zonked type variables,
383 -- The former is just because no further unifications will change
384 -- the quantified type variables, so we can fix their final form
386 -- The latter is needed because the poly_ids are used to extend the
387 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
389 -- Pre-condition: the inferred_tvs are already zonked
391 mkExport top_lvl rec_group multi_bind prag_fn inferred_tvs dict_tys
392 (poly_name, mb_sig, mono_id)
393 = do { warn_missing_sigs <- doptM Opt_WarnMissingSigs
394 ; let warn = isTopLevel top_lvl && warn_missing_sigs
395 ; (tvs, poly_id) <- mk_poly_id warn mb_sig
396 -- poly_id has a zonked type
398 ; (poly_id', spec_prags) <- tcPrags rec_group multi_bind (notNull dict_tys)
399 poly_id (prag_fn poly_name)
400 -- tcPrags requires a zonked poly_id
402 ; return (tvs, poly_id', mono_id, SpecPrags spec_prags) }
404 poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id))
406 mk_poly_id warn Nothing = do { poly_ty' <- zonkTcType poly_ty
407 ; missingSigWarn warn poly_name poly_ty'
408 ; return (inferred_tvs, mkLocalId poly_name poly_ty') }
409 mk_poly_id _ (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
410 ; return (tvs, sig_id sig) }
412 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
414 ------------------------
415 type TcPragFun = Name -> [LSig Name]
417 mkPragFun :: [LSig Name] -> LHsBinds Name -> TcPragFun
418 mkPragFun sigs binds = \n -> lookupNameEnv prag_env n `orElse` []
420 prs = mapCatMaybes get_sig sigs
422 get_sig :: LSig Name -> Maybe (Located Name, LSig Name)
423 get_sig (L l (SpecSig nm ty inl)) = Just (nm, L l $ SpecSig nm ty (add_arity nm inl))
424 get_sig (L l (InlineSig nm inl)) = Just (nm, L l $ InlineSig nm (add_arity nm inl))
427 add_arity (L _ n) inl_prag -- Adjust inl_sat field to match visible arity of function
428 | Just ar <- lookupNameEnv ar_env n = inl_prag { inl_sat = Just ar }
429 | otherwise = inl_prag
431 prag_env :: NameEnv [LSig Name]
432 prag_env = foldl add emptyNameEnv prs
433 add env (L _ n,p) = extendNameEnv_Acc (:) singleton env n p
435 -- ar_env maps a local to the arity of its definition
436 ar_env :: NameEnv Arity
437 ar_env = foldrBag lhsBindArity emptyNameEnv binds
439 lhsBindArity :: LHsBind Name -> NameEnv Arity -> NameEnv Arity
440 lhsBindArity (L _ (FunBind { fun_id = id, fun_matches = ms })) env
441 = extendNameEnv env (unLoc id) (matchGroupArity ms)
442 lhsBindArity _ env = env -- PatBind/VarBind
445 -> Bool -- True <=> AbsBinds binds more than one variable
446 -> Bool -- True <=> function is overloaded
448 -> TcM (Id, [Located TcSpecPrag])
449 -- Add INLINE and SPECLIASE pragmas
450 -- INLINE prags are added to the (polymorphic) Id directly
451 -- SPECIALISE prags are passed to the desugarer via TcSpecPrags
452 -- Pre-condition: the poly_id is zonked
453 -- Reason: required by tcSubExp
454 tcPrags _rec_group _multi_bind _is_overloaded_id poly_id prag_sigs
455 = do { poly_id' <- tc_inl inl_sigs
457 ; spec_prags <- mapM (wrapLocM (tcSpecPrag poly_id')) spec_sigs
459 -- Commented out until bytestring library removes redundant pragmas
460 -- for packWith and unpackWith
461 -- ; unless (null spec_sigs || is_overloaded_id) warn_discarded_spec
463 ; unless (null bad_sigs) warn_discarded_sigs
465 ; return (poly_id', spec_prags) }
467 (inl_sigs, other_sigs) = partition isInlineLSig prag_sigs
468 (spec_sigs, bad_sigs) = partition isSpecLSig other_sigs
470 -- warn_discarded_spec = warnPrags poly_id spec_sigs $
471 -- ptext (sLit "SPECIALISE pragmas for non-overloaded function")
472 warn_dup_inline = warnPrags poly_id inl_sigs $
473 ptext (sLit "Duplicate INLINE pragmas for")
474 warn_discarded_sigs = warnPrags poly_id bad_sigs $
475 ptext (sLit "Discarding unexpected pragmas for")
478 tc_inl [] = return poly_id
479 tc_inl (L loc (InlineSig _ prag) : other_inls)
480 = do { unless (null other_inls) (setSrcSpan loc warn_dup_inline)
481 ; return (poly_id `setInlinePragma` prag) }
482 tc_inl _ = panic "tc_inl"
484 {- Earlier we tried to warn about
485 (a) INLINE for recursive function
486 (b) INLINE for function that is part of a multi-binder group
487 Code fragments below. But we want to allow
491 even though they are mutually recursive.
492 So I'm just omitting the warnings for now
494 | multi_bind && isInlinePragma prag
495 = do { setSrcSpan loc $ addWarnTc multi_bind_warn
498 ; when (isInlinePragma prag && isRec rec_group)
499 (setSrcSpan loc (addWarnTc rec_inline_warn))
501 rec_inline_warn = ptext (sLit "INLINE pragma for recursive binder")
502 <+> quotes (ppr poly_id) <+> ptext (sLit "may be discarded")
504 multi_bind_warn = hang (ptext (sLit "Discarding INLINE pragma for") <+> quotes (ppr poly_id))
505 2 (ptext (sLit "because it is bound by a pattern, or mutual recursion") )
509 warnPrags :: Id -> [LSig Name] -> SDoc -> TcM ()
510 warnPrags id bad_sigs herald
511 = addWarnTc (hang (herald <+> quotes (ppr id))
512 2 (ppr_sigs bad_sigs))
514 ppr_sigs sigs = vcat (map (ppr . getLoc) sigs)
517 tcSpecPrag :: TcId -> Sig Name -> TcM TcSpecPrag
518 tcSpecPrag poly_id prag@(SpecSig _ hs_ty inl)
519 = addErrCtxt (spec_ctxt prag) $
520 do { let name = idName poly_id
521 ; spec_ty <- tcHsSigType (FunSigCtxt name) hs_ty
522 ; co_fn <- tcSubExp (SpecPragOrigin name) (idType poly_id) spec_ty
523 ; return (SpecPrag co_fn inl) }
525 spec_ctxt prag = hang (ptext (sLit "In the SPECIALISE pragma")) 2 (ppr prag)
526 tcSpecPrag _ sig = pprPanic "tcSpecPrag" (ppr sig)
530 -- If typechecking the binds fails, then return with each
531 -- signature-less binder given type (forall a.a), to minimise
532 -- subsequent error messages
533 recoveryCode :: [Name] -> (Name -> Maybe [Name])
534 -> TcM (LHsBinds TcId, [Id])
535 recoveryCode binder_names sig_fn
536 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
537 ; poly_ids <- mapM mk_dummy binder_names
538 ; return (emptyBag, poly_ids) }
541 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
542 | otherwise = return (mkLocalId name forall_a_a) -- No signature
545 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
548 -- Check that non-overloaded unlifted bindings are
551 -- c) not a multiple-binding group (more or less implied by (a))
553 checkStrictBinds :: TopLevelFlag -> RecFlag
554 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
556 checkStrictBinds top_lvl rec_group mbind mono_tys infos
557 | unlifted || bang_pat
558 = do { checkTc (isNotTopLevel top_lvl)
559 (strictBindErr "Top-level" unlifted mbind)
560 ; checkTc (isNonRec rec_group)
561 (strictBindErr "Recursive" unlifted mbind)
562 ; checkTc (isSingletonBag mbind)
563 (strictBindErr "Multiple" unlifted mbind)
564 -- This should be a checkTc, not a warnTc, but as of GHC 6.11
565 -- the versions of alex and happy available have non-conforming
566 -- templates, so the GHC build fails if it's an error:
567 ; warnUnlifted <- doptM Opt_WarnLazyUnliftedBindings
568 ; warnTc (warnUnlifted && not bang_pat)
569 (unliftedMustBeBang mbind)
570 ; mapM_ check_sig infos
575 unlifted = any isUnLiftedType mono_tys
576 bang_pat = anyBag (isBangHsBind . unLoc) mbind
577 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
578 (badStrictSig unlifted sig)
579 check_sig _ = return ()
581 unliftedMustBeBang :: LHsBindsLR Var Var -> SDoc
582 unliftedMustBeBang mbind
583 = hang (text "Bindings containing unlifted types must use an outermost bang pattern:")
584 4 (pprLHsBinds mbind)
585 $$ text "*** This will be an error in GHC 6.14! Fix your code now!"
587 strictBindErr :: String -> Bool -> LHsBindsLR Var Var -> SDoc
588 strictBindErr flavour unlifted mbind
589 = hang (text flavour <+> msg <+> ptext (sLit "aren't allowed:"))
590 4 (pprLHsBinds mbind)
592 msg | unlifted = ptext (sLit "bindings for unlifted types")
593 | otherwise = ptext (sLit "bang-pattern bindings")
595 badStrictSig :: Bool -> TcSigInfo -> SDoc
596 badStrictSig unlifted sig
597 = hang (ptext (sLit "Illegal polymorphic signature in") <+> msg)
600 msg | unlifted = ptext (sLit "an unlifted binding")
601 | otherwise = ptext (sLit "a bang-pattern binding")
605 %************************************************************************
607 \subsection{tcMonoBind}
609 %************************************************************************
611 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
612 The signatures have been dealt with already.
615 tcMonoBinds :: [LHsBind Name]
617 -> RecFlag -- Whether the binding is recursive for typechecking purposes
618 -- i.e. the binders are mentioned in their RHSs, and
619 -- we are not resuced by a type signature
620 -> TcM (LHsBinds TcId, [MonoBindInfo])
622 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
623 fun_matches = matches, bind_fvs = fvs })]
624 sig_fn -- Single function binding,
625 NonRecursive -- binder isn't mentioned in RHS,
626 | Nothing <- sig_fn name -- ...with no type signature
627 = -- In this very special case we infer the type of the
628 -- right hand side first (it may have a higher-rank type)
629 -- and *then* make the monomorphic Id for the LHS
630 -- e.g. f = \(x::forall a. a->a) -> <body>
631 -- We want to infer a higher-rank type for f
633 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
635 -- Check for an unboxed tuple type
636 -- f = (# True, False #)
637 -- Zonk first just in case it's hidden inside a meta type variable
638 -- (This shows up as a (more obscure) kind error
639 -- in the 'otherwise' case of tcMonoBinds.)
640 ; zonked_rhs_ty <- zonkTcType rhs_ty
641 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
642 (unboxedTupleErr name zonked_rhs_ty)
644 ; mono_name <- newLocalName name
645 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
646 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
647 fun_matches = matches', bind_fvs = fvs,
648 fun_co_fn = co_fn, fun_tick = Nothing })),
649 [(name, Nothing, mono_id)]) }
651 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
652 fun_matches = matches })]
653 sig_fn -- Single function binding
655 | Just scoped_tvs <- sig_fn name -- ...with a type signature
656 = -- When we have a single function binding, with a type signature
657 -- we can (a) use genuine, rigid skolem constants for the type variables
658 -- (b) bring (rigid) scoped type variables into scope
660 do { tc_sig <- tcInstSig True name
661 ; mono_name <- newLocalName name
662 ; let mono_ty = sig_tau tc_sig
663 mono_id = mkLocalId mono_name mono_ty
664 rhs_tvs = [ (name, mkTyVarTy tv)
665 | (name, tv) <- scoped_tvs `zip` sig_tvs tc_sig ]
666 -- See Note [More instantiated than scoped]
667 -- Note that the scoped_tvs and the (sig_tvs sig)
668 -- may have different Names. That's quite ok.
670 ; traceTc (text "tcMoonBinds" <+> ppr scoped_tvs $$ ppr tc_sig)
671 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
672 tcMatchesFun mono_name inf matches mono_ty
673 -- Note that "mono_ty" might actually be a polymorphic type,
674 -- if the original function had a signature like
675 -- forall a. Eq a => forall b. Ord b => ....
676 -- But that's ok: tcMatchesFun can deal with that
677 -- It happens, too! See Note [Polymorphic methods] in TcClassDcl.
679 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
680 fun_infix = inf, fun_matches = matches',
681 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
683 ; return (unitBag (L b_loc fun_bind'),
684 [(name, Just tc_sig, mono_id)]) }
686 tcMonoBinds binds sig_fn _
687 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
689 -- Bring the monomorphic Ids, into scope for the RHSs
690 ; let mono_info = getMonoBindInfo tc_binds
691 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
692 -- A monomorphic binding for each term variable that lacks
693 -- a type sig. (Ones with a sig are already in scope.)
695 ; binds' <- tcExtendIdEnv2 rhs_id_env $ do
696 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
697 | (n,id) <- rhs_id_env])
698 mapM (wrapLocM tcRhs) tc_binds
699 ; return (listToBag binds', mono_info) }
701 ------------------------
702 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
703 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
704 -- if there's a signature for it, use the instantiated signature type
705 -- otherwise invent a type variable
706 -- You see that quite directly in the FunBind case.
708 -- But there's a complication for pattern bindings:
709 -- data T = MkT (forall a. a->a)
711 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
712 -- but we want to get (f::forall a. a->a) as the RHS environment.
713 -- The simplest way to do this is to typecheck the pattern, and then look up the
714 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
715 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
717 data TcMonoBind -- Half completed; LHS done, RHS not done
718 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
719 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
721 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
722 -- Type signature (if any), and
723 -- the monomorphic bound things
725 bndrNames :: [MonoBindInfo] -> [Name]
726 bndrNames mbi = [n | (n,_,_) <- mbi]
728 getMonoType :: MonoBindInfo -> TcTauType
729 getMonoType (_,_,mono_id) = idType mono_id
731 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
732 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
733 = do { mb_sig <- tcInstSig_maybe sig_fn name
734 ; mono_name <- newLocalName name
735 ; mono_ty <- mk_mono_ty mb_sig
736 ; let mono_id = mkLocalId mono_name mono_ty
737 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
739 mk_mono_ty (Just sig) = return (sig_tau sig)
740 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
742 tcLhs sig_fn (PatBind { pat_lhs = pat, pat_rhs = grhss })
743 = do { mb_sigs <- mapM (tcInstSig_maybe sig_fn) names
744 ; mono_pat_binds <- doptM Opt_MonoPatBinds
745 -- With -XMonoPatBinds, we do no generalisation of pattern bindings
746 -- But the signature can still be polymoprhic!
747 -- data T = MkT (forall a. a->a)
748 -- x :: forall a. a->a
750 -- The function get_sig_ty decides whether the pattern-bound variables
751 -- should have exactly the type in the type signature (-XMonoPatBinds),
752 -- or the instantiated version (-XMonoPatBinds)
754 ; let nm_sig_prs = names `zip` mb_sigs
755 get_sig_ty | mono_pat_binds = idType . sig_id
756 | otherwise = sig_tau
757 tau_sig_env = mkNameEnv [ (name, get_sig_ty sig)
758 | (name, Just sig) <- nm_sig_prs]
759 sig_tau_fn = lookupNameEnv tau_sig_env
761 tc_pat exp_ty = tcLetPat sig_tau_fn pat exp_ty $
762 mapM lookup_info nm_sig_prs
764 -- After typechecking the pattern, look up the binder
765 -- names, which the pattern has brought into scope.
766 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
767 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
768 ; return (name, mb_sig, mono_id) }
770 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
773 ; return (TcPatBind infos pat' grhss pat_ty) }
775 names = collectPatBinders pat
778 tcLhs _ other_bind = pprPanic "tcLhs" (ppr other_bind)
779 -- AbsBind, VarBind impossible
782 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
783 -- When we are doing pattern bindings, or multiple function bindings at a time
784 -- we *don't* bring any scoped type variables into scope
785 -- Wny not? They are not completely rigid.
786 -- That's why we have the special case for a single FunBind in tcMonoBinds
787 tcRhs (TcFunBind (_,_,mono_id) fun' inf matches)
788 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
789 matches (idType mono_id)
790 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
791 bind_fvs = placeHolderNames, fun_co_fn = co_fn,
792 fun_tick = Nothing }) }
794 tcRhs (TcPatBind _ pat' grhss pat_ty)
795 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
796 tcGRHSsPat grhss pat_ty
797 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
798 bind_fvs = placeHolderNames }) }
801 ---------------------
802 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
803 getMonoBindInfo tc_binds
804 = foldr (get_info . unLoc) [] tc_binds
806 get_info (TcFunBind info _ _ _) rest = info : rest
807 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
811 %************************************************************************
815 %************************************************************************
818 generalise :: DynFlags -> TopLevelFlag
819 -> [LHsBind Name] -> TcSigFun
820 -> [MonoBindInfo] -> [Inst]
821 -> TcM ([TyVar], [Inst], TcDictBinds)
822 -- The returned [TyVar] are all ready to quantify
824 generalise dflags top_lvl bind_list sig_fn mono_infos lie_req
825 | isMonoGroup dflags top_lvl bind_list sigs
826 = do { extendLIEs lie_req
827 ; return ([], [], emptyBag) }
829 | isRestrictedGroup dflags bind_list sig_fn -- RESTRICTED CASE
830 = -- Check signature contexts are empty
831 do { checkTc (all is_mono_sig sigs)
832 (restrictedBindCtxtErr bndrs)
834 -- Now simplify with exactly that set of tyvars
835 -- We have to squash those Methods
836 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
839 -- Check that signature type variables are OK
840 ; final_qtvs <- checkSigsTyVars qtvs sigs
842 ; return (final_qtvs, [], binds) }
844 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
845 = tcSimplifyInfer doc tau_tvs lie_req
847 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
848 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty; sig_lie is zonked
849 ; let -- The "sig_avails" is the stuff available. We get that from
850 -- the context of the type signature, BUT ALSO the lie_avail
851 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
852 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
853 sig_avails = sig_lie ++ local_meths
854 loc = sig_loc (head sigs)
856 -- Check that the needed dicts can be
857 -- expressed in terms of the signature ones
858 ; (qtvs, binds) <- tcSimplifyInferCheck loc tau_tvs sig_avails lie_req
860 -- Check that signature type variables are OK
861 ; final_qtvs <- checkSigsTyVars qtvs sigs
863 ; return (final_qtvs, sig_lie, binds) }
865 bndrs = bndrNames mono_infos
866 sigs = [sig | (_, Just sig, _) <- mono_infos]
867 get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
868 | otherwise = exactTyVarsOfType
869 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
870 is_mono_sig sig = null (sig_theta sig)
871 doc = ptext (sLit "type signature(s) for") <+> pprBinders bndrs
873 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
874 sig_theta = theta, sig_loc = loc }) mono_id
875 = Method {tci_id = mono_id, tci_oid = poly_id, tci_tys = mkTyVarTys tvs,
876 tci_theta = theta, tci_loc = loc}
879 unifyCtxts checks that all the signature contexts are the same
880 The type signatures on a mutually-recursive group of definitions
881 must all have the same context (or none).
883 The trick here is that all the signatures should have the same
884 context, and we want to share type variables for that context, so that
885 all the right hand sides agree a common vocabulary for their type
888 We unify them because, with polymorphic recursion, their types
889 might not otherwise be related. This is a rather subtle issue.
892 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
893 -- Post-condition: the returned Insts are full zonked
894 unifyCtxts [] = panic "unifyCtxts []"
895 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
896 = do { traceTc $ text "unifyCtxts" <+> ppr (sig1 : sigs)
897 ; mapM_ unify_ctxt sigs
898 ; theta <- zonkTcThetaType (sig_theta sig1)
899 ; newDictBndrs (sig_loc sig1) theta }
901 theta1 = sig_theta sig1
902 unify_ctxt :: TcSigInfo -> TcM ()
903 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
904 = setSrcSpan (instLocSpan (sig_loc sig)) $
905 addErrCtxt (sigContextsCtxt sig1 sig) $
906 do { cois <- unifyTheta theta1 theta
907 ; -- Check whether all coercions are identity coercions
908 -- That can happen if we have, say
910 -- g :: C (F a) => ...
911 -- where F is a type function and (F a ~ [a])
912 -- Then unification might succeed with a coercion. But it's much
913 -- much simpler to require that such signatures have identical contexts
914 checkTc (all isIdentityCoI cois)
915 (ptext (sLit "Mutually dependent functions have syntactically distinct contexts"))
918 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
919 checkSigsTyVars qtvs sigs
920 = do { gbl_tvs <- tcGetGlobalTyVars
921 ; sig_tvs_s <- mapM (check_sig gbl_tvs) sigs
923 ; let -- Sigh. Make sure that all the tyvars in the type sigs
924 -- appear in the returned ty var list, which is what we are
925 -- going to generalise over. Reason: we occasionally get
927 -- type T a = () -> ()
930 -- Here, 'a' won't appear in qtvs, so we have to add it
931 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
932 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
935 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
936 sig_theta = theta, sig_tau = tau})
937 = addErrCtxt (ptext (sLit "In the type signature for") <+> quotes (ppr id)) $
938 addErrCtxtM (sigCtxt id tvs theta tau) $
939 do { tvs' <- checkDistinctTyVars tvs
940 ; when (any (`elemVarSet` gbl_tvs) tvs')
941 (bleatEscapedTvs gbl_tvs tvs tvs')
944 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
945 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
946 -- are still all type variables, and all distinct from each other.
947 -- It returns a zonked set of type variables.
948 -- For example, if the type sig is
949 -- f :: forall a b. a -> b -> b
950 -- we want to check that 'a' and 'b' haven't
951 -- (a) been unified with a non-tyvar type
952 -- (b) been unified with each other (all distinct)
954 checkDistinctTyVars sig_tvs
955 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
956 ; foldlM_ check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
957 ; return zonked_tvs }
959 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
960 -- The TyVarEnv maps each zonked type variable back to its
961 -- corresponding user-written signature type variable
962 check_dup acc (sig_tv, zonked_tv)
963 = case lookupVarEnv acc zonked_tv of
964 Just sig_tv' -> bomb_out sig_tv sig_tv'
966 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
968 bomb_out sig_tv1 sig_tv2
969 = do { env0 <- tcInitTidyEnv
970 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
971 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
972 msg = ptext (sLit "Quantified type variable") <+> quotes (ppr tidy_tv1)
973 <+> ptext (sLit "is unified with another quantified type variable")
974 <+> quotes (ppr tidy_tv2)
975 ; failWithTcM (env2, msg) }
979 @getTyVarsToGen@ decides what type variables to generalise over.
981 For a "restricted group" -- see the monomorphism restriction
982 for a definition -- we bind no dictionaries, and
983 remove from tyvars_to_gen any constrained type variables
985 *Don't* simplify dicts at this point, because we aren't going
986 to generalise over these dicts. By the time we do simplify them
987 we may well know more. For example (this actually came up)
989 f x = array ... xs where xs = [1,2,3,4,5]
990 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
991 stuff. If we simplify only at the f-binding (not the xs-binding)
992 we'll know that the literals are all Ints, and we can just produce
995 Find all the type variables involved in overloading, the
996 "constrained_tyvars". These are the ones we *aren't* going to
997 generalise. We must be careful about doing this:
999 (a) If we fail to generalise a tyvar which is not actually
1000 constrained, then it will never, ever get bound, and lands
1001 up printed out in interface files! Notorious example:
1002 instance Eq a => Eq (Foo a b) where ..
1003 Here, b is not constrained, even though it looks as if it is.
1004 Another, more common, example is when there's a Method inst in
1005 the LIE, whose type might very well involve non-overloaded
1007 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
1008 the simple thing instead]
1010 (b) On the other hand, we mustn't generalise tyvars which are constrained,
1011 because we are going to pass on out the unmodified LIE, with those
1012 tyvars in it. They won't be in scope if we've generalised them.
1014 So we are careful, and do a complete simplification just to find the
1015 constrained tyvars. We don't use any of the results, except to
1016 find which tyvars are constrained.
1018 Note [Polymorphic recursion]
1019 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1020 The game plan for polymorphic recursion in the code above is
1022 * Bind any variable for which we have a type signature
1023 to an Id with a polymorphic type. Then when type-checking
1024 the RHSs we'll make a full polymorphic call.
1026 This fine, but if you aren't a bit careful you end up with a horrendous
1027 amount of partial application and (worse) a huge space leak. For example:
1029 f :: Eq a => [a] -> [a]
1032 If we don't take care, after typechecking we get
1034 f = /\a -> \d::Eq a -> let f' = f a d
1038 Notice the the stupid construction of (f a d), which is of course
1039 identical to the function we're executing. In this case, the
1040 polymorphic recursion isn't being used (but that's a very common case).
1041 This can lead to a massive space leak, from the following top-level defn
1044 ff :: [Int] -> [Int]
1047 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
1048 f' is another thunk which evaluates to the same thing... and you end
1049 up with a chain of identical values all hung onto by the CAF ff.
1053 = let f' = f Int dEqInt in \ys. ...f'...
1055 = let f' = let f' = f Int dEqInt in \ys. ...f'...
1060 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
1061 which would make the space leak go away in this case
1063 Solution: when typechecking the RHSs we always have in hand the
1064 *monomorphic* Ids for each binding. So we just need to make sure that
1065 if (Method f a d) shows up in the constraints emerging from (...f...)
1066 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
1067 to the "givens" when simplifying constraints. That's what the "lies_avail"
1072 f = /\a -> \d::Eq a -> letrec
1073 fm = \ys:[a] -> ...fm...
1079 %************************************************************************
1083 %************************************************************************
1085 Type signatures are tricky. See Note [Signature skolems] in TcType
1087 @tcSigs@ checks the signatures for validity, and returns a list of
1088 {\em freshly-instantiated} signatures. That is, the types are already
1089 split up, and have fresh type variables installed. All non-type-signature
1090 "RenamedSigs" are ignored.
1092 The @TcSigInfo@ contains @TcTypes@ because they are unified with
1093 the variable's type, and after that checked to see whether they've
1096 Note [Scoped tyvars]
1097 ~~~~~~~~~~~~~~~~~~~~
1098 The -XScopedTypeVariables flag brings lexically-scoped type variables
1099 into scope for any explicitly forall-quantified type variables:
1100 f :: forall a. a -> a
1102 Then 'a' is in scope inside 'e'.
1104 However, we do *not* support this
1105 - For pattern bindings e.g
1109 - For multiple function bindings, unless Opt_RelaxedPolyRec is on
1110 f :: forall a. a -> a
1112 g :: forall b. b -> b
1114 Reason: we use mutable variables for 'a' and 'b', since they may
1115 unify to each other, and that means the scoped type variable would
1116 not stand for a completely rigid variable.
1118 Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
1121 Note [More instantiated than scoped]
1122 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1123 There may be more instantiated type variables than lexically-scoped
1125 type T a = forall b. b -> (a,b)
1127 Here, the signature for f will have one scoped type variable, c,
1128 but two instantiated type variables, c' and b'.
1130 We assume that the scoped ones are at the *front* of sig_tvs,
1131 and remember the names from the original HsForAllTy in the TcSigFun.
1135 type TcSigFun = Name -> Maybe [Name] -- Maps a let-binder to the list of
1136 -- type variables brought into scope
1137 -- by its type signature.
1138 -- Nothing => no type signature
1140 mkTcSigFun :: [LSig Name] -> TcSigFun
1141 -- Search for a particular type signature
1142 -- Precondition: the sigs are all type sigs
1143 -- Precondition: no duplicates
1144 mkTcSigFun sigs = lookupNameEnv env
1146 env = mkNameEnv (mapCatMaybes mk_pair sigs)
1147 mk_pair (L _ (TypeSig (L _ name) lhs_ty)) = Just (name, hsExplicitTvs lhs_ty)
1148 mk_pair (L _ (IdSig id)) = Just (idName id, [])
1150 -- The scoped names are the ones explicitly mentioned
1151 -- in the HsForAll. (There may be more in sigma_ty, because
1152 -- of nested type synonyms. See Note [More instantiated than scoped].)
1153 -- See Note [Only scoped tyvars are in the TyVarEnv]
1158 sig_id :: TcId, -- *Polymorphic* binder for this value...
1160 sig_tvs :: [TcTyVar], -- Instantiated type variables
1161 -- See Note [Instantiate sig]
1163 sig_theta :: TcThetaType, -- Instantiated theta
1164 sig_tau :: TcTauType, -- Instantiated tau
1165 sig_loc :: InstLoc -- The location of the signature
1169 -- Note [Only scoped tyvars are in the TyVarEnv]
1170 -- We are careful to keep only the *lexically scoped* type variables in
1171 -- the type environment. Why? After all, the renamer has ensured
1172 -- that only legal occurrences occur, so we could put all type variables
1173 -- into the type env.
1175 -- But we want to check that two distinct lexically scoped type variables
1176 -- do not map to the same internal type variable. So we need to know which
1177 -- the lexically-scoped ones are... and at the moment we do that by putting
1178 -- only the lexically scoped ones into the environment.
1181 -- Note [Instantiate sig]
1182 -- It's vital to instantiate a type signature with fresh variables.
1184 -- type S = forall a. a->a
1188 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1189 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1190 -- it's all cool; each signature has distinct type variables from the renamer.)
1192 instance Outputable TcSigInfo where
1193 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1194 = ppr id <+> ptext (sLit "::") <+> ppr tyvars <+> ppr theta <+> ptext (sLit "=>") <+> ppr tau
1198 tcTySig :: LSig Name -> TcM TcId
1199 tcTySig (L span (TypeSig (L _ name) ty))
1201 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1202 ; return (mkLocalId name sigma_ty) }
1203 tcTySig (L _ (IdSig id))
1205 tcTySig s = pprPanic "tcTySig" (ppr s)
1208 tcInstSig_maybe :: TcSigFun -> Name -> TcM (Maybe TcSigInfo)
1209 -- Instantiate with *meta* type variables;
1210 -- this signature is part of a multi-signature group
1211 tcInstSig_maybe sig_fn name
1212 = case sig_fn name of
1213 Nothing -> return Nothing
1214 Just _scoped_tvs -> do { tc_sig <- tcInstSig False name
1215 ; return (Just tc_sig) }
1216 -- NB: the _scoped_tvs may be non-empty, but we can
1217 -- just ignore them. See Note [Scoped tyvars].
1219 tcInstSig :: Bool -> Name -> TcM TcSigInfo
1220 -- Instantiate the signature, with either skolems or meta-type variables
1221 -- depending on the use_skols boolean. This variable is set True
1222 -- when we are typechecking a single function binding; and False for
1223 -- pattern bindings and a group of several function bindings.
1224 -- Reason: in the latter cases, the "skolems" can be unified together,
1225 -- so they aren't properly rigid in the type-refinement sense.
1226 -- NB: unless we are doing H98, each function with a sig will be done
1227 -- separately, even if it's mutually recursive, so use_skols will be True
1229 -- We always instantiate with fresh uniques,
1230 -- although we keep the same print-name
1232 -- type T = forall a. [a] -> [a]
1234 -- f = g where { g :: T; g = <rhs> }
1236 -- We must not use the same 'a' from the defn of T at both places!!
1238 tcInstSig use_skols name
1239 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1240 -- scope when starting the binding group
1241 ; let skol_info = SigSkol (FunSigCtxt name)
1242 ; (tvs, theta, tau) <- tcInstSigType use_skols skol_info (idType poly_id)
1243 ; loc <- getInstLoc (SigOrigin skol_info)
1244 ; return (TcSigInfo { sig_id = poly_id,
1245 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1249 isMonoGroup :: DynFlags -> TopLevelFlag -> [LHsBind Name]
1250 -> [TcSigInfo] -> Bool
1251 -- No generalisation at all
1252 isMonoGroup dflags top_lvl binds sigs
1253 = (dopt Opt_MonoPatBinds dflags && any is_pat_bind binds)
1254 || (dopt Opt_MonoLocalBinds dflags && null sigs && not (isTopLevel top_lvl))
1256 is_pat_bind (L _ (PatBind {})) = True
1257 is_pat_bind _ = False
1260 isRestrictedGroup :: DynFlags -> [LHsBind Name] -> TcSigFun -> Bool
1261 isRestrictedGroup dflags binds sig_fn
1262 = mono_restriction && not all_unrestricted
1264 mono_restriction = dopt Opt_MonomorphismRestriction dflags
1265 all_unrestricted = all (unrestricted . unLoc) binds
1266 has_sig n = isJust (sig_fn n)
1268 unrestricted (PatBind {}) = False
1269 unrestricted (VarBind { var_id = v }) = has_sig v
1270 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1271 || has_sig (unLoc v)
1272 unrestricted (AbsBinds {})
1273 = panic "isRestrictedGroup/unrestricted AbsBinds"
1275 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1276 -- No args => like a pattern binding
1277 unrestricted_match _ = True
1278 -- Some args => a function binding
1282 %************************************************************************
1284 \subsection[TcBinds-errors]{Error contexts and messages}
1286 %************************************************************************
1290 -- This one is called on LHS, when pat and grhss are both Name
1291 -- and on RHS, when pat is TcId and grhss is still Name
1292 patMonoBindsCtxt :: OutputableBndr id => LPat id -> GRHSs Name -> SDoc
1293 patMonoBindsCtxt pat grhss
1294 = hang (ptext (sLit "In a pattern binding:")) 4 (pprPatBind pat grhss)
1296 -----------------------------------------------
1297 sigContextsCtxt :: TcSigInfo -> TcSigInfo -> SDoc
1298 sigContextsCtxt sig1 sig2
1299 = vcat [ptext (sLit "When matching the contexts of the signatures for"),
1300 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1301 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1302 ptext (sLit "The signature contexts in a mutually recursive group should all be identical")]
1308 -----------------------------------------------
1309 unboxedTupleErr :: Name -> Type -> SDoc
1310 unboxedTupleErr name ty
1311 = hang (ptext (sLit "Illegal binding of unboxed tuple"))
1312 4 (ppr name <+> dcolon <+> ppr ty)
1314 -----------------------------------------------
1315 restrictedBindCtxtErr :: [Name] -> SDoc
1316 restrictedBindCtxtErr binder_names
1317 = hang (ptext (sLit "Illegal overloaded type signature(s)"))
1318 4 (vcat [ptext (sLit "in a binding group for") <+> pprBinders binder_names,
1319 ptext (sLit "that falls under the monomorphism restriction")])
1321 genCtxt :: [Name] -> SDoc
1322 genCtxt binder_names
1323 = ptext (sLit "When generalising the type(s) for") <+> pprBinders binder_names
1325 missingSigWarn :: Bool -> Name -> Type -> TcM ()
1326 missingSigWarn False _ _ = return ()
1327 missingSigWarn True name ty
1328 = do { env0 <- tcInitTidyEnv
1329 ; let (env1, tidy_ty) = tidyOpenType env0 ty
1330 ; addWarnTcM (env1, mk_msg tidy_ty) }
1332 mk_msg ty = vcat [ptext (sLit "Definition but no type signature for") <+> quotes (ppr name),
1333 sep [ptext (sLit "Inferred type:") <+> pprHsVar name <+> dcolon <+> ppr ty]]