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, tcPolyBinds,
10 PragFun, tcSpecPrags, mkPragFun,
11 TcSigInfo(..), SigFun, mkSigFun,
12 badBootDeclErr ) where
14 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
15 import {-# SOURCE #-} TcExpr ( tcMonoExpr )
28 import RnBinds( misplacedSigErr )
47 import Data.List( partition )
50 #include "HsVersions.h"
54 %************************************************************************
56 \subsection{Type-checking bindings}
58 %************************************************************************
60 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
61 it needs to know something about the {\em usage} of the things bound,
62 so that it can create specialisations of them. So @tcBindsAndThen@
63 takes a function which, given an extended environment, E, typechecks
64 the scope of the bindings returning a typechecked thing and (most
65 important) an LIE. It is this LIE which is then used as the basis for
66 specialising the things bound.
68 @tcBindsAndThen@ also takes a "combiner" which glues together the
69 bindings and the "thing" to make a new "thing".
71 The real work is done by @tcBindWithSigsAndThen@.
73 Recursive and non-recursive binds are handled in essentially the same
74 way: because of uniques there are no scoping issues left. The only
75 difference is that non-recursive bindings can bind primitive values.
77 Even for non-recursive binding groups we add typings for each binder
78 to the LVE for the following reason. When each individual binding is
79 checked the type of its LHS is unified with that of its RHS; and
80 type-checking the LHS of course requires that the binder is in scope.
82 At the top-level the LIE is sure to contain nothing but constant
83 dictionaries, which we resolve at the module level.
86 tcTopBinds :: HsValBinds Name
87 -> TcM ( LHsBinds TcId -- Typechecked bindings
88 , [LTcSpecPrag] -- SPECIALISE prags for imported Ids
89 , TcLclEnv) -- Augmented environment
91 -- Note: returning the TcLclEnv is more than we really
92 -- want. The bit we care about is the local bindings
93 -- and the free type variables thereof
95 = do { (ValBindsOut prs sigs, env) <- tcValBinds TopLevel binds getLclEnv
96 ; let binds = foldr (unionBags . snd) emptyBag prs
97 ; specs <- tcImpPrags sigs
98 ; return (binds, specs, env) }
99 -- The top level bindings are flattened into a giant
100 -- implicitly-mutually-recursive LHsBinds
102 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
103 -- A hs-boot file has only one BindGroup, and it only has type
104 -- signatures in it. The renamer checked all this
105 tcHsBootSigs (ValBindsOut binds sigs)
106 = do { checkTc (null binds) badBootDeclErr
107 ; mapM (addLocM tc_boot_sig) (filter isTypeLSig sigs) }
109 tc_boot_sig (TypeSig (L _ name) ty)
110 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
111 ; return (mkVanillaGlobal name sigma_ty) }
112 -- Notice that we make GlobalIds, not LocalIds
113 tc_boot_sig s = pprPanic "tcHsBootSigs/tc_boot_sig" (ppr s)
114 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
116 badBootDeclErr :: Message
117 badBootDeclErr = ptext (sLit "Illegal declarations in an hs-boot file")
119 ------------------------
120 tcLocalBinds :: HsLocalBinds Name -> TcM thing
121 -> TcM (HsLocalBinds TcId, thing)
123 tcLocalBinds EmptyLocalBinds thing_inside
124 = do { thing <- thing_inside
125 ; return (EmptyLocalBinds, thing) }
127 tcLocalBinds (HsValBinds binds) thing_inside
128 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
129 ; return (HsValBinds binds', thing) }
131 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
132 = do { (given_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
133 ; let ip_tvs = foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet given_ips
135 -- If the binding binds ?x = E, we must now
136 -- discharge any ?x constraints in expr_lie
137 ; (ev_binds, result) <- checkConstraints (IPSkol ips)
138 ip_tvs -- See Note [Implicit parameter untouchables]
142 ; return (HsIPBinds (IPBinds ip_binds' ev_binds), result) }
144 ips = [ip | L _ (IPBind ip _) <- ip_binds]
146 -- I wonder if we should do these one at at time
149 tc_ip_bind (IPBind ip expr)
150 = do { ty <- newFlexiTyVarTy argTypeKind
151 ; ip_id <- newIP ip ty
152 ; expr' <- tcMonoExpr expr ty
153 ; return (ip_id, (IPBind (IPName ip_id) expr')) }
156 Note [Implicit parameter untouchables]
157 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
158 We add the type variables in the types of the implicit parameters
159 as untouchables, not so much because we really must not unify them,
160 but rather because we otherwise end up with constraints like this
161 Num alpha, Implic { wanted = alpha ~ Int }
162 The constraint solver solves alpha~Int by unification, but then
163 doesn't float that solved constraint out (it's not an unsolved
164 wanted. Result disaster: the (Num alpha) is again solved, this
165 time by defaulting. No no no.
168 tcValBinds :: TopLevelFlag
169 -> HsValBinds Name -> TcM thing
170 -> TcM (HsValBinds TcId, thing)
172 tcValBinds _ (ValBindsIn binds _) _
173 = pprPanic "tcValBinds" (ppr binds)
175 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
176 = do { -- Typecheck the signature
177 ; let { prag_fn = mkPragFun sigs (foldr (unionBags . snd) emptyBag binds)
178 ; ty_sigs = filter isTypeLSig sigs
179 ; sig_fn = mkSigFun ty_sigs }
181 ; poly_ids <- checkNoErrs (mapAndRecoverM tcTySig ty_sigs)
182 -- No recovery from bad signatures, because the type sigs
183 -- may bind type variables, so proceeding without them
184 -- can lead to a cascade of errors
185 -- ToDo: this means we fall over immediately if any type sig
186 -- is wrong, which is over-conservative, see Trac bug #745
188 -- Extend the envt right away with all
189 -- the Ids declared with type signatures
190 ; (binds', thing) <- tcExtendIdEnv poly_ids $
191 tcBindGroups top_lvl sig_fn prag_fn
194 ; return (ValBindsOut binds' sigs, thing) }
196 ------------------------
197 tcBindGroups :: TopLevelFlag -> SigFun -> PragFun
198 -> [(RecFlag, LHsBinds Name)] -> TcM thing
199 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
200 -- Typecheck a whole lot of value bindings,
201 -- one strongly-connected component at a time
202 -- Here a "strongly connected component" has the strightforward
203 -- meaning of a group of bindings that mention each other,
204 -- ignoring type signatures (that part comes later)
206 tcBindGroups _ _ _ [] thing_inside
207 = do { thing <- thing_inside
208 ; return ([], thing) }
210 tcBindGroups top_lvl sig_fn prag_fn (group : groups) thing_inside
211 = do { (group', (groups', thing))
212 <- tc_group top_lvl sig_fn prag_fn group $
213 tcBindGroups top_lvl sig_fn prag_fn groups thing_inside
214 ; return (group' ++ groups', thing) }
216 ------------------------
217 tc_group :: forall thing.
218 TopLevelFlag -> SigFun -> PragFun
219 -> (RecFlag, LHsBinds Name) -> TcM thing
220 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
222 -- Typecheck one strongly-connected component of the original program.
223 -- We get a list of groups back, because there may
224 -- be specialisations etc as well
226 tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
227 -- A single non-recursive binding
228 -- We want to keep non-recursive things non-recursive
229 -- so that we desugar unlifted bindings correctly
230 = do { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn NonRecursive NonRecursive
232 ; thing <- tcExtendIdEnv ids thing_inside
233 ; return ( [(NonRecursive, binds1)], thing) }
235 tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
236 = -- To maximise polymorphism (assumes -XRelaxedPolyRec), we do a new
237 -- strongly-connected-component analysis, this time omitting
238 -- any references to variables with type signatures.
239 do { traceTc "tc_group rec" (pprLHsBinds binds)
240 ; (binds1, _ids, thing) <- go sccs
241 -- Here is where we should do bindInstsOfLocalFuns
242 -- if we start having Methods again
243 ; return ([(Recursive, binds1)], thing) }
244 -- Rec them all together
246 sccs :: [SCC (LHsBind Name)]
247 sccs = stronglyConnCompFromEdgedVertices (mkEdges sig_fn binds)
249 go :: [SCC (LHsBind Name)] -> TcM (LHsBinds TcId, [TcId], thing)
250 go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
251 ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
252 ; return (binds1 `unionBags` binds2, ids1 ++ ids2, thing) }
253 go [] = do { thing <- thing_inside; return (emptyBag, [], thing) }
255 tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive [bind]
256 tc_scc (CyclicSCC binds) = tc_sub_group Recursive binds
258 tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
261 ------------------------
263 bindLocalInsts :: TopLevelFlag
264 -> TcM (LHsBinds TcId, [TcId], a)
265 -> TcM (LHsBinds TcId, TcEvBinds, a)
266 bindLocalInsts top_lvl thing_inside
268 = do { (binds, _, thing) <- thing_inside; return (binds, emptyBag, thing) }
269 -- For the top level don't bother with all this bindInstsOfLocalFuns stuff.
270 -- All the top level things are rec'd together anyway, so it's fine to
271 -- leave them to the tcSimplifyTop, and quite a bit faster too
273 | otherwise -- Nested case
274 = do { ((binds, ids, thing), lie) <- captureConstraints thing_inside
275 ; lie_binds <- bindLocalMethods lie ids
276 ; return (binds, lie_binds, thing) }
279 ------------------------
280 mkEdges :: SigFun -> LHsBinds Name
281 -> [(LHsBind Name, BKey, [BKey])]
283 type BKey = Int -- Just number off the bindings
286 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
287 Just key <- [lookupNameEnv key_map n], no_sig n ])
288 | (bind, key) <- keyd_binds
291 no_sig :: Name -> Bool
292 no_sig n = isNothing (sig_fn n)
294 keyd_binds = bagToList binds `zip` [0::BKey ..]
296 key_map :: NameEnv BKey -- Which binding it comes from
297 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
298 , bndr <- bindersOfHsBind bind ]
300 bindersOfHsBind :: HsBind Name -> [Name]
301 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
302 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
303 bindersOfHsBind (AbsBinds {}) = panic "bindersOfHsBind AbsBinds"
304 bindersOfHsBind (VarBind {}) = panic "bindersOfHsBind VarBind"
306 ------------------------
307 tcPolyBinds :: TopLevelFlag -> SigFun -> PragFun
308 -> RecFlag -- Whether the group is really recursive
309 -> RecFlag -- Whether it's recursive after breaking
310 -- dependencies based on type signatures
312 -> TcM (LHsBinds TcId, [TcId])
314 -- Typechecks a single bunch of bindings all together,
315 -- and generalises them. The bunch may be only part of a recursive
316 -- group, because we use type signatures to maximise polymorphism
318 -- Returns a list because the input may be a single non-recursive binding,
319 -- in which case the dependency order of the resulting bindings is
322 -- Knows nothing about the scope of the bindings
324 tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc bind_list
326 recoverM (recoveryCode binder_names sig_fn) $ do
327 -- Set up main recoer; take advantage of any type sigs
329 { traceTc "------------------------------------------------" empty
330 ; traceTc "Bindings for" (ppr binder_names)
332 ; tc_sig_fn <- tcInstSigs sig_fn binder_names
335 ; let plan = decideGeneralisationPlan dflags top_lvl binder_names bind_list tc_sig_fn
336 ; traceTc "Generalisation plan" (ppr plan)
337 ; (binds, poly_ids) <- case plan of
338 NoGen -> tcPolyNoGen tc_sig_fn prag_fn rec_tc bind_list
339 InferGen mono -> tcPolyInfer top_lvl mono tc_sig_fn prag_fn rec_tc bind_list
340 CheckGen sig -> tcPolyCheck sig prag_fn rec_tc bind_list
342 -- Check whether strict bindings are ok
343 -- These must be non-recursive etc, and are not generalised
344 -- They desugar to a case expression in the end
345 ; checkStrictBinds top_lvl rec_group bind_list poly_ids
347 ; return (binds, poly_ids) }
349 binder_names = collectHsBindListBinders bind_list
350 loc = getLoc (head bind_list)
351 -- TODO: location a bit awkward, but the mbinds have been
352 -- dependency analysed and may no longer be adjacent
356 :: TcSigFun -> PragFun
357 -> RecFlag -- Whether it's recursive after breaking
358 -- dependencies based on type signatures
360 -> TcM (LHsBinds TcId, [TcId])
361 -- No generalisation whatsoever
363 tcPolyNoGen tc_sig_fn prag_fn rec_tc bind_list
364 = do { (binds', mono_infos) <- tcMonoBinds tc_sig_fn (LetGblBndr prag_fn)
366 ; mono_ids' <- mapM tc_mono_info mono_infos
367 ; return (binds', mono_ids') }
369 tc_mono_info (name, _, mono_id)
370 = do { mono_ty' <- zonkTcTypeCarefully (idType mono_id)
371 -- Zonk, mainly to expose unboxed types to checkStrictBinds
372 ; let mono_id' = setIdType mono_id mono_ty'
373 ; _specs <- tcSpecPrags mono_id' (prag_fn name)
375 -- NB: tcPrags generates error messages for
376 -- specialisation pragmas for non-overloaded sigs
377 -- Indeed that is why we call it here!
378 -- So we can safely ignore _specs
381 tcPolyCheck :: TcSigInfo -> PragFun
382 -> RecFlag -- Whether it's recursive after breaking
383 -- dependencies based on type signatures
385 -> TcM (LHsBinds TcId, [TcId])
386 -- There is just one binding,
387 -- it binds a single variable,
388 -- it has a signature,
389 tcPolyCheck sig@(TcSigInfo { sig_id = id, sig_tvs = tvs, sig_scoped = scoped
390 , sig_theta = theta, sig_loc = loc })
391 prag_fn rec_tc bind_list
392 = do { ev_vars <- newEvVars theta
394 ; let skol_info = SigSkol (FunSigCtxt (idName id))
395 ; (ev_binds, (binds', [mono_info]))
396 <- checkConstraints skol_info emptyVarSet tvs ev_vars $
397 tcExtendTyVarEnv2 (scoped `zip` mkTyVarTys tvs) $
398 tcMonoBinds (\_ -> Just sig) LetLclBndr rec_tc bind_list
400 ; export <- mkExport prag_fn tvs theta mono_info
402 ; let (_, poly_id, _, _) = export
403 abs_bind = L loc $ AbsBinds
405 , abs_ev_vars = ev_vars, abs_ev_binds = ev_binds
406 , abs_exports = [export], abs_binds = binds' }
407 ; return (unitBag abs_bind, [poly_id]) }
412 -> Bool -- True <=> apply the monomorphism restriction
413 -> TcSigFun -> PragFun
414 -> RecFlag -- Whether it's recursive after breaking
415 -- dependencies based on type signatures
417 -> TcM (LHsBinds TcId, [TcId])
418 tcPolyInfer top_lvl mono sig_fn prag_fn rec_tc bind_list
419 = do { ((binds', mono_infos), wanted)
420 <- captureConstraints $
421 tcMonoBinds sig_fn LetLclBndr rec_tc bind_list
423 ; unifyCtxts [sig | (_, Just sig, _) <- mono_infos]
425 ; let get_tvs | isTopLevel top_lvl = tyVarsOfType
426 | otherwise = exactTyVarsOfType
427 -- See Note [Silly type synonym] in TcType
428 tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
430 ; (qtvs, givens, ev_binds) <- simplifyInfer mono tau_tvs wanted
432 ; exports <- mapM (mkExport prag_fn qtvs (map evVarPred givens))
435 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
436 ; traceTc "Binding:" (ppr (poly_ids `zip` map idType poly_ids))
439 ; let abs_bind = L loc $ AbsBinds { abs_tvs = qtvs
440 , abs_ev_vars = givens, abs_ev_binds = ev_binds
441 , abs_exports = exports, abs_binds = binds' }
443 ; return (unitBag abs_bind, poly_ids) -- poly_ids are guaranteed zonked by mkExport
448 mkExport :: PragFun -> [TyVar] -> TcThetaType
450 -> TcM ([TyVar], Id, Id, TcSpecPrags)
451 -- mkExport generates exports with
452 -- zonked type variables,
454 -- The former is just because no further unifications will change
455 -- the quantified type variables, so we can fix their final form
457 -- The latter is needed because the poly_ids are used to extend the
458 -- type environment; see the invariant on TcEnv.tcExtendIdEnv
460 -- Pre-condition: the inferred_tvs are already zonked
462 mkExport prag_fn inferred_tvs theta
463 (poly_name, mb_sig, mono_id)
464 = do { (tvs, poly_id) <- mk_poly_id mb_sig
465 -- poly_id has a zonked type
467 ; poly_id' <- addInlinePrags poly_id prag_sigs
469 ; spec_prags <- tcSpecPrags poly_id prag_sigs
470 -- tcPrags requires a zonked poly_id
472 ; return (tvs, poly_id', mono_id, SpecPrags spec_prags) }
474 prag_sigs = prag_fn poly_name
475 poly_ty = mkSigmaTy inferred_tvs theta (idType mono_id)
477 mk_poly_id Nothing = do { poly_ty' <- zonkTcTypeCarefully poly_ty
478 ; return (inferred_tvs, mkLocalId poly_name poly_ty') }
479 mk_poly_id (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
480 ; return (tvs, sig_id sig) }
482 zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
484 ------------------------
485 type PragFun = Name -> [LSig Name]
487 mkPragFun :: [LSig Name] -> LHsBinds Name -> PragFun
488 mkPragFun sigs binds = \n -> lookupNameEnv prag_env n `orElse` []
490 prs = mapCatMaybes get_sig sigs
492 get_sig :: LSig Name -> Maybe (Located Name, LSig Name)
493 get_sig (L l (SpecSig nm ty inl)) = Just (nm, L l $ SpecSig nm ty (add_arity nm inl))
494 get_sig (L l (InlineSig nm inl)) = Just (nm, L l $ InlineSig nm (add_arity nm inl))
497 add_arity (L _ n) inl_prag -- Adjust inl_sat field to match visible arity of function
498 | Just ar <- lookupNameEnv ar_env n,
499 Inline <- inl_inline inl_prag = inl_prag { inl_sat = Just ar }
500 -- add arity only for real INLINE pragmas, not INLINABLE
501 | otherwise = inl_prag
503 prag_env :: NameEnv [LSig Name]
504 prag_env = foldl add emptyNameEnv prs
505 add env (L _ n,p) = extendNameEnv_Acc (:) singleton env n p
507 -- ar_env maps a local to the arity of its definition
508 ar_env :: NameEnv Arity
509 ar_env = foldrBag lhsBindArity emptyNameEnv binds
511 lhsBindArity :: LHsBind Name -> NameEnv Arity -> NameEnv Arity
512 lhsBindArity (L _ (FunBind { fun_id = id, fun_matches = ms })) env
513 = extendNameEnv env (unLoc id) (matchGroupArity ms)
514 lhsBindArity _ env = env -- PatBind/VarBind
517 tcSpecPrags :: Id -> [LSig Name]
519 -- Add INLINE and SPECIALSE pragmas
520 -- INLINE prags are added to the (polymorphic) Id directly
521 -- SPECIALISE prags are passed to the desugarer via TcSpecPrags
522 -- Pre-condition: the poly_id is zonked
523 -- Reason: required by tcSubExp
524 tcSpecPrags poly_id prag_sigs
525 = do { unless (null bad_sigs) warn_discarded_sigs
526 ; mapAndRecoverM (wrapLocM (tcSpec poly_id)) spec_sigs }
528 spec_sigs = filter isSpecLSig prag_sigs
529 bad_sigs = filter is_bad_sig prag_sigs
530 is_bad_sig s = not (isSpecLSig s || isInlineLSig s)
532 warn_discarded_sigs = warnPrags poly_id bad_sigs $
533 ptext (sLit "Discarding unexpected pragmas for")
537 tcSpec :: TcId -> Sig Name -> TcM TcSpecPrag
538 tcSpec poly_id prag@(SpecSig _ hs_ty inl)
539 -- The Name in the SpecSig may not be the same as that of the poly_id
540 -- Example: SPECIALISE for a class method: the Name in the SpecSig is
541 -- for the selector Id, but the poly_id is something like $cop
542 = addErrCtxt (spec_ctxt prag) $
543 do { spec_ty <- tcHsSigType sig_ctxt hs_ty
544 ; checkTc (isOverloadedTy poly_ty)
545 (ptext (sLit "Discarding pragma for non-overloaded function") <+> quotes (ppr poly_id))
546 ; wrap <- tcSubType origin skol_info (idType poly_id) spec_ty
547 ; return (SpecPrag poly_id wrap inl) }
549 name = idName poly_id
550 poly_ty = idType poly_id
551 origin = SpecPragOrigin name
552 sig_ctxt = FunSigCtxt name
553 skol_info = SigSkol sig_ctxt
554 spec_ctxt prag = hang (ptext (sLit "In the SPECIALISE pragma")) 2 (ppr prag)
556 tcSpec _ prag = pprPanic "tcSpec" (ppr prag)
559 tcImpPrags :: [LSig Name] -> TcM [LTcSpecPrag]
561 = do { this_mod <- getModule
563 = case sigName prag of
565 Just name -> not (nameIsLocalOrFrom this_mod name)
566 (spec_prags, others) = partition isSpecLSig $
568 ; mapM_ misplacedSigErr others
569 -- Messy that this misplaced-sig error comes here
570 -- but the others come from the renamer
571 ; mapAndRecoverM (wrapLocM tcImpSpec) spec_prags }
573 tcImpSpec :: Sig Name -> TcM TcSpecPrag
574 tcImpSpec prag@(SpecSig (L _ name) _ _)
575 = do { id <- tcLookupId name
576 ; checkTc (isInlinePragma (idInlinePragma id))
579 tcImpSpec p = pprPanic "tcImpSpec" (ppr p)
581 impSpecErr :: Name -> SDoc
583 = hang (ptext (sLit "You cannot SPECIALISE") <+> quotes (ppr name))
584 2 (ptext (sLit "because its definition has no INLINE/INLINABLE pragma"))
587 -- If typechecking the binds fails, then return with each
588 -- signature-less binder given type (forall a.a), to minimise
589 -- subsequent error messages
590 recoveryCode :: [Name] -> SigFun -> TcM (LHsBinds TcId, [Id])
591 recoveryCode binder_names sig_fn
592 = do { traceTc "tcBindsWithSigs: error recovery" (ppr binder_names)
593 ; poly_ids <- mapM mk_dummy binder_names
594 ; return (emptyBag, poly_ids) }
597 | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up
598 | otherwise = return (mkLocalId name forall_a_a) -- No signature
601 forall_a_a = mkForAllTy openAlphaTyVar (mkTyVarTy openAlphaTyVar)
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 :: TcSigFun -> LetBndrSpec
616 -> RecFlag -- Whether the binding is recursive for typechecking purposes
617 -- i.e. the binders are mentioned in their RHSs, and
618 -- we are not resuced by a type signature
620 -> TcM (LHsBinds TcId, [MonoBindInfo])
622 tcMonoBinds sig_fn no_gen is_rec
623 [ L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
624 fun_matches = matches, bind_fvs = fvs })]
625 -- Single function binding,
626 | NonRecursive <- is_rec -- ...binder isn't mentioned in RHS
627 , Nothing <- sig_fn name -- ...with no type signature
628 = -- In this very special case we infer the type of the
629 -- right hand side first (it may have a higher-rank type)
630 -- and *then* make the monomorphic Id for the LHS
631 -- e.g. f = \(x::forall a. a->a) -> <body>
632 -- We want to infer a higher-rank type for f
634 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
636 ; mono_id <- newNoSigLetBndr no_gen name rhs_ty
637 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
638 fun_matches = matches', bind_fvs = fvs,
639 fun_co_fn = co_fn, fun_tick = Nothing })),
640 [(name, Nothing, mono_id)]) }
642 tcMonoBinds sig_fn no_gen _ binds
643 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn no_gen)) binds
645 -- Bring the monomorphic Ids, into scope for the RHSs
646 ; let mono_info = getMonoBindInfo tc_binds
647 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
648 -- A monomorphic binding for each term variable that lacks
649 -- a type sig. (Ones with a sig are already in scope.)
651 ; binds' <- tcExtendIdEnv2 rhs_id_env $ do
652 traceTc "tcMonoBinds" $ vcat [ ppr n <+> ppr id <+> ppr (idType id)
653 | (n,id) <- rhs_id_env]
654 mapM (wrapLocM tcRhs) tc_binds
655 ; return (listToBag binds', mono_info) }
657 ------------------------
658 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
659 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
660 -- if there's a signature for it, use the instantiated signature type
661 -- otherwise invent a type variable
662 -- You see that quite directly in the FunBind case.
664 -- But there's a complication for pattern bindings:
665 -- data T = MkT (forall a. a->a)
667 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
668 -- but we want to get (f::forall a. a->a) as the RHS environment.
669 -- The simplest way to do this is to typecheck the pattern, and then look up the
670 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
671 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
673 data TcMonoBind -- Half completed; LHS done, RHS not done
674 = TcFunBind MonoBindInfo SrcSpan Bool (MatchGroup Name)
675 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
677 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
678 -- Type signature (if any), and
679 -- the monomorphic bound things
681 getMonoType :: MonoBindInfo -> TcTauType
682 getMonoType (_,_,mono_id) = idType mono_id
684 tcLhs :: TcSigFun -> LetBndrSpec -> HsBind Name -> TcM TcMonoBind
685 tcLhs sig_fn no_gen (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
686 | Just sig <- sig_fn name
687 = do { mono_id <- newSigLetBndr no_gen name sig
688 ; return (TcFunBind (name, Just sig, mono_id) nm_loc inf matches) }
690 = do { mono_ty <- newFlexiTyVarTy argTypeKind
691 ; mono_id <- newNoSigLetBndr no_gen name mono_ty
692 ; return (TcFunBind (name, Nothing, mono_id) nm_loc inf matches) }
694 tcLhs sig_fn no_gen (PatBind { pat_lhs = pat, pat_rhs = grhss })
695 = do { let tc_pat exp_ty = tcLetPat sig_fn no_gen pat exp_ty $
696 mapM lookup_info (collectPatBinders pat)
698 -- After typechecking the pattern, look up the binder
699 -- names, which the pattern has brought into scope.
700 lookup_info :: Name -> TcM MonoBindInfo
701 lookup_info name = do { mono_id <- tcLookupId name
702 ; return (name, sig_fn name, mono_id) }
704 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
707 ; return (TcPatBind infos pat' grhss pat_ty) }
709 tcLhs _ _ other_bind = pprPanic "tcLhs" (ppr other_bind)
710 -- AbsBind, VarBind impossible
713 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
714 -- When we are doing pattern bindings, or multiple function bindings at a time
715 -- we *don't* bring any scoped type variables into scope
716 -- Wny not? They are not completely rigid.
717 -- That's why we have the special case for a single FunBind in tcMonoBinds
718 tcRhs (TcFunBind (_,_,mono_id) loc inf matches)
719 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
720 matches (idType mono_id)
721 ; return (FunBind { fun_id = L loc mono_id, fun_infix = inf
722 , fun_matches = matches'
724 , bind_fvs = placeHolderNames, fun_tick = Nothing }) }
726 tcRhs (TcPatBind _ pat' grhss pat_ty)
727 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
728 tcGRHSsPat grhss pat_ty
729 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty
730 , bind_fvs = placeHolderNames }) }
733 ---------------------
734 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
735 getMonoBindInfo tc_binds
736 = foldr (get_info . unLoc) [] tc_binds
738 get_info (TcFunBind info _ _ _) rest = info : rest
739 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
743 %************************************************************************
747 %************************************************************************
749 unifyCtxts checks that all the signature contexts are the same
750 The type signatures on a mutually-recursive group of definitions
751 must all have the same context (or none).
753 The trick here is that all the signatures should have the same
754 context, and we want to share type variables for that context, so that
755 all the right hand sides agree a common vocabulary for their type
758 We unify them because, with polymorphic recursion, their types
759 might not otherwise be related. This is a rather subtle issue.
762 unifyCtxts :: [TcSigInfo] -> TcM ()
763 -- Post-condition: the returned Insts are full zonked
764 unifyCtxts [] = return ()
765 unifyCtxts (sig1 : sigs)
766 = do { traceTc "unifyCtxts" (ppr (sig1 : sigs))
767 ; mapM_ unify_ctxt sigs }
769 theta1 = sig_theta sig1
770 unify_ctxt :: TcSigInfo -> TcM ()
771 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
772 = setSrcSpan (sig_loc sig) $
773 addErrCtxt (sigContextsCtxt sig1 sig) $
774 do { cois <- unifyTheta theta1 theta
775 ; -- Check whether all coercions are identity coercions
776 -- That can happen if we have, say
778 -- g :: C (F a) => ...
779 -- where F is a type function and (F a ~ [a])
780 -- Then unification might succeed with a coercion. But it's much
781 -- much simpler to require that such signatures have identical contexts
782 checkTc (all isIdentityCoI cois)
783 (ptext (sLit "Mutually dependent functions have syntactically distinct contexts"))
788 @getTyVarsToGen@ decides what type variables to generalise over.
790 For a "restricted group" -- see the monomorphism restriction
791 for a definition -- we bind no dictionaries, and
792 remove from tyvars_to_gen any constrained type variables
794 *Don't* simplify dicts at this point, because we aren't going
795 to generalise over these dicts. By the time we do simplify them
796 we may well know more. For example (this actually came up)
798 f x = array ... xs where xs = [1,2,3,4,5]
799 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
800 stuff. If we simplify only at the f-binding (not the xs-binding)
801 we'll know that the literals are all Ints, and we can just produce
804 Find all the type variables involved in overloading, the
805 "constrained_tyvars". These are the ones we *aren't* going to
806 generalise. We must be careful about doing this:
808 (a) If we fail to generalise a tyvar which is not actually
809 constrained, then it will never, ever get bound, and lands
810 up printed out in interface files! Notorious example:
811 instance Eq a => Eq (Foo a b) where ..
812 Here, b is not constrained, even though it looks as if it is.
813 Another, more common, example is when there's a Method inst in
814 the LIE, whose type might very well involve non-overloaded
816 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
817 the simple thing instead]
819 (b) On the other hand, we mustn't generalise tyvars which are constrained,
820 because we are going to pass on out the unmodified LIE, with those
821 tyvars in it. They won't be in scope if we've generalised them.
823 So we are careful, and do a complete simplification just to find the
824 constrained tyvars. We don't use any of the results, except to
825 find which tyvars are constrained.
827 Note [Polymorphic recursion]
828 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
829 The game plan for polymorphic recursion in the code above is
831 * Bind any variable for which we have a type signature
832 to an Id with a polymorphic type. Then when type-checking
833 the RHSs we'll make a full polymorphic call.
835 This fine, but if you aren't a bit careful you end up with a horrendous
836 amount of partial application and (worse) a huge space leak. For example:
838 f :: Eq a => [a] -> [a]
841 If we don't take care, after typechecking we get
843 f = /\a -> \d::Eq a -> let f' = f a d
847 Notice the the stupid construction of (f a d), which is of course
848 identical to the function we're executing. In this case, the
849 polymorphic recursion isn't being used (but that's a very common case).
850 This can lead to a massive space leak, from the following top-level defn
856 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
857 f' is another thunk which evaluates to the same thing... and you end
858 up with a chain of identical values all hung onto by the CAF ff.
862 = let f' = f Int dEqInt in \ys. ...f'...
864 = let f' = let f' = f Int dEqInt in \ys. ...f'...
869 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
870 which would make the space leak go away in this case
872 Solution: when typechecking the RHSs we always have in hand the
873 *monomorphic* Ids for each binding. So we just need to make sure that
874 if (Method f a d) shows up in the constraints emerging from (...f...)
875 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
876 to the "givens" when simplifying constraints. That's what the "lies_avail"
881 f = /\a -> \d::Eq a -> letrec
882 fm = \ys:[a] -> ...fm...
886 %************************************************************************
890 %************************************************************************
892 Type signatures are tricky. See Note [Signature skolems] in TcType
894 @tcSigs@ checks the signatures for validity, and returns a list of
895 {\em freshly-instantiated} signatures. That is, the types are already
896 split up, and have fresh type variables installed. All non-type-signature
897 "RenamedSigs" are ignored.
899 The @TcSigInfo@ contains @TcTypes@ because they are unified with
900 the variable's type, and after that checked to see whether they've
905 The -XScopedTypeVariables flag brings lexically-scoped type variables
906 into scope for any explicitly forall-quantified type variables:
907 f :: forall a. a -> a
909 Then 'a' is in scope inside 'e'.
911 However, we do *not* support this
912 - For pattern bindings e.g
916 - For multiple function bindings, unless Opt_RelaxedPolyRec is on
917 f :: forall a. a -> a
919 g :: forall b. b -> b
921 Reason: we use mutable variables for 'a' and 'b', since they may
922 unify to each other, and that means the scoped type variable would
923 not stand for a completely rigid variable.
925 Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
928 Note [More instantiated than scoped]
929 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
930 There may be more instantiated type variables than lexically-scoped
932 type T a = forall b. b -> (a,b)
934 Here, the signature for f will have one scoped type variable, c,
935 but two instantiated type variables, c' and b'.
937 We assume that the scoped ones are at the *front* of sig_tvs,
938 and remember the names from the original HsForAllTy in the TcSigFun.
940 Note [Signature skolems]
941 ~~~~~~~~~~~~~~~~~~~~~~~~
942 When instantiating a type signature, we do so with either skolems or
943 SigTv meta-type variables depending on the use_skols boolean. This
944 variable is set True when we are typechecking a single function
945 binding; and False for pattern bindings and a group of several
948 Reason: in the latter cases, the "skolems" can be unified together,
949 so they aren't properly rigid in the type-refinement sense.
950 NB: unless we are doing H98, each function with a sig will be done
951 separately, even if it's mutually recursive, so use_skols will be True
954 Note [Only scoped tyvars are in the TyVarEnv]
955 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
956 We are careful to keep only the *lexically scoped* type variables in
957 the type environment. Why? After all, the renamer has ensured
958 that only legal occurrences occur, so we could put all type variables
961 But we want to check that two distinct lexically scoped type variables
962 do not map to the same internal type variable. So we need to know which
963 the lexically-scoped ones are... and at the moment we do that by putting
964 only the lexically scoped ones into the environment.
966 Note [Instantiate sig with fresh variables]
967 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
968 It's vital to instantiate a type signature with fresh variables.
970 type T = forall a. [a] -> [a]
972 f = g where { g :: T; g = <rhs> }
974 We must not use the same 'a' from the defn of T at both places!!
975 (Instantiation is only necessary because of type synonyms. Otherwise,
976 it's all cool; each signature has distinct type variables from the renamer.)
979 type SigFun = Name -> Maybe ([Name], SrcSpan)
980 -- Maps a let-binder to the list of
981 -- type variables brought into scope
982 -- by its type signature, plus location
983 -- Nothing => no type signature
985 mkSigFun :: [LSig Name] -> SigFun
986 -- Search for a particular type signature
987 -- Precondition: the sigs are all type sigs
988 -- Precondition: no duplicates
989 mkSigFun sigs = lookupNameEnv env
991 env = mkNameEnv (mapCatMaybes mk_pair sigs)
992 mk_pair (L loc (TypeSig (L _ name) lhs_ty)) = Just (name, (hsExplicitTvs lhs_ty, loc))
993 mk_pair (L loc (IdSig id)) = Just (idName id, ([], loc))
995 -- The scoped names are the ones explicitly mentioned
996 -- in the HsForAll. (There may be more in sigma_ty, because
997 -- of nested type synonyms. See Note [More instantiated than scoped].)
998 -- See Note [Only scoped tyvars are in the TyVarEnv]
1002 tcTySig :: LSig Name -> TcM TcId
1003 tcTySig (L span (TypeSig (L _ name) ty))
1005 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1006 ; return (mkLocalId name sigma_ty) }
1007 tcTySig (L _ (IdSig id))
1009 tcTySig s = pprPanic "tcTySig" (ppr s)
1012 tcInstSigs :: SigFun -> [Name] -> TcM TcSigFun
1013 tcInstSigs sig_fn bndrs
1014 = do { prs <- mapMaybeM (tcInstSig sig_fn use_skols) bndrs
1015 ; return (lookupNameEnv (mkNameEnv prs)) }
1017 use_skols = isSingleton bndrs -- See Note [Signature skolems]
1019 tcInstSig :: SigFun -> Bool -> Name -> TcM (Maybe (Name, TcSigInfo))
1020 -- For use_skols :: Bool see Note [Signature skolems]
1022 -- We must instantiate with fresh uniques,
1023 -- (see Note [Instantiate sig with fresh variables])
1024 -- although we keep the same print-name.
1026 tcInstSig sig_fn use_skols name
1027 | Just (scoped_tvs, loc) <- sig_fn name
1028 = do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1029 -- scope when starting the binding group
1030 ; (tvs, theta, tau) <- tcInstSigType use_skols name (idType poly_id)
1031 ; let sig = TcSigInfo { sig_id = poly_id
1032 , sig_scoped = scoped_tvs
1033 , sig_tvs = tvs, sig_theta = theta, sig_tau = tau
1035 ; return (Just (name, sig)) }
1039 -------------------------------
1040 data GeneralisationPlan
1041 = NoGen -- No generalisation, no AbsBinds
1042 | InferGen Bool -- Implicit generalisation; there is an AbsBinds
1043 -- True <=> apply the MR; generalise only unconstrained type vars
1044 | CheckGen TcSigInfo -- Explicit generalisation; there is an AbsBinds
1046 -- A consequence of the no-AbsBinds choice (NoGen) is that there is
1047 -- no "polymorphic Id" and "monmomorphic Id"; there is just the one
1049 instance Outputable GeneralisationPlan where
1050 ppr NoGen = ptext (sLit "NoGen")
1051 ppr (InferGen b) = ptext (sLit "InferGen") <+> ppr b
1052 ppr (CheckGen s) = ptext (sLit "CheckGen") <+> ppr s
1054 decideGeneralisationPlan
1055 :: DynFlags -> TopLevelFlag -> [Name] -> [LHsBind Name] -> TcSigFun -> GeneralisationPlan
1056 decideGeneralisationPlan dflags top_lvl _bndrs binds sig_fn
1057 | mono_pat_binds = NoGen
1058 | Just sig <- one_funbind_with_sig binds = if null (sig_tvs sig) && null (sig_theta sig)
1059 then NoGen -- Optimise common case
1061 | (xopt Opt_MonoLocalBinds dflags
1062 && isNotTopLevel top_lvl) = NoGen
1063 | otherwise = InferGen mono_restriction
1066 mono_pat_binds = xopt Opt_MonoPatBinds dflags
1067 && any (is_pat_bind . unLoc) binds
1069 mono_restriction = xopt Opt_MonomorphismRestriction dflags
1070 && any (restricted . unLoc) binds
1072 no_sig n = isNothing (sig_fn n)
1074 -- With OutsideIn, all nested bindings are monomorphic
1075 -- except a single function binding with a signature
1076 one_funbind_with_sig [L _ FunBind { fun_id = v }] = sig_fn (unLoc v)
1077 one_funbind_with_sig _ = Nothing
1079 -- The Haskell 98 monomorphism resetriction
1080 restricted (PatBind {}) = True
1081 restricted (VarBind { var_id = v }) = no_sig v
1082 restricted (FunBind { fun_id = v, fun_matches = m }) = restricted_match m
1084 restricted (AbsBinds {}) = panic "isRestrictedGroup/unrestricted AbsBinds"
1086 restricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = True
1087 restricted_match _ = False
1088 -- No args => like a pattern binding
1089 -- Some args => a function binding
1091 is_pat_bind (PatBind {}) = True
1092 is_pat_bind _ = False
1095 checkStrictBinds :: TopLevelFlag -> RecFlag
1096 -> [LHsBind Name] -> [Id]
1098 -- Check that non-overloaded unlifted bindings are
1099 -- a) non-recursive,
1100 -- b) not top level,
1101 -- c) not a multiple-binding group (more or less implied by (a))
1103 checkStrictBinds top_lvl rec_group binds poly_ids
1104 | unlifted || bang_pat
1105 = do { checkTc (isNotTopLevel top_lvl)
1106 (strictBindErr "Top-level" unlifted binds)
1107 ; checkTc (isNonRec rec_group)
1108 (strictBindErr "Recursive" unlifted binds)
1109 ; checkTc (isSingleton binds)
1110 (strictBindErr "Multiple" unlifted binds)
1111 -- This should be a checkTc, not a warnTc, but as of GHC 6.11
1112 -- the versions of alex and happy available have non-conforming
1113 -- templates, so the GHC build fails if it's an error:
1114 ; warnUnlifted <- doptM Opt_WarnLazyUnliftedBindings
1115 ; warnTc (warnUnlifted && not bang_pat)
1116 (unliftedMustBeBang binds) }
1120 unlifted = any is_unlifted poly_ids
1121 bang_pat = any (isBangHsBind . unLoc) binds
1122 is_unlifted id = case tcSplitForAllTys (idType id) of
1123 (_, rho) -> isUnLiftedType rho
1125 unliftedMustBeBang :: [LHsBind Name] -> SDoc
1126 unliftedMustBeBang binds
1127 = hang (text "Bindings containing unlifted types should use an outermost bang pattern:")
1128 2 (pprBindList binds)
1130 strictBindErr :: String -> Bool -> [LHsBind Name] -> SDoc
1131 strictBindErr flavour unlifted binds
1132 = hang (text flavour <+> msg <+> ptext (sLit "aren't allowed:"))
1133 2 (pprBindList binds)
1135 msg | unlifted = ptext (sLit "bindings for unlifted types")
1136 | otherwise = ptext (sLit "bang-pattern bindings")
1138 pprBindList :: [LHsBind Name] -> SDoc
1139 pprBindList binds = vcat (map ppr binds)
1143 %************************************************************************
1145 \subsection[TcBinds-errors]{Error contexts and messages}
1147 %************************************************************************
1151 -- This one is called on LHS, when pat and grhss are both Name
1152 -- and on RHS, when pat is TcId and grhss is still Name
1153 patMonoBindsCtxt :: OutputableBndr id => LPat id -> GRHSs Name -> SDoc
1154 patMonoBindsCtxt pat grhss
1155 = hang (ptext (sLit "In a pattern binding:")) 2 (pprPatBind pat grhss)
1157 -----------------------------------------------
1158 sigContextsCtxt :: TcSigInfo -> TcSigInfo -> SDoc
1159 sigContextsCtxt sig1 sig2
1160 = vcat [ptext (sLit "When matching the contexts of the signatures for"),
1161 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1162 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1163 ptext (sLit "The signature contexts in a mutually recursive group should all be identical")]