2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcLocalBinds, tcTopBinds,
8 tcHsBootSigs, tcMonoBinds,
9 TcPragFun, tcSpecPrag, tcPrags, mkPragFun,
11 badBootDeclErr ) where
13 #include "HsVersions.h"
15 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
16 import {-# SOURCE #-} TcExpr ( tcMonoExpr )
18 import DynFlags ( DynFlag(Opt_MonomorphismRestriction, Opt_GlasgowExts) )
19 import HsSyn ( HsExpr(..), HsBind(..), LHsBinds, LHsBind, Sig(..),
20 HsLocalBinds(..), HsValBinds(..), HsIPBinds(..),
21 LSig, Match(..), IPBind(..), Prag(..),
22 HsType(..), LHsType, HsExplicitForAll(..), hsLTyVarNames,
23 isVanillaLSig, sigName, placeHolderNames, isPragLSig,
24 LPat, GRHSs, MatchGroup(..), pprLHsBinds, mkHsCoerce,
25 collectHsBindBinders, collectPatBinders, pprPatBind, isBangHsBind
27 import TcHsSyn ( zonkId )
30 import Inst ( newDictsAtLoc, newIPDict, instToId )
31 import TcEnv ( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2,
32 pprBinders, tcLookupLocalId_maybe, tcLookupId,
34 import TcUnify ( tcInfer, tcSubExp, unifyTheta,
35 bleatEscapedTvs, sigCtxt )
36 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck,
37 tcSimplifyRestricted, tcSimplifyIPs )
38 import TcHsType ( tcHsSigType, UserTypeCtxt(..) )
39 import TcPat ( tcPat, PatCtxt(..) )
40 import TcSimplify ( bindInstsOfLocalFuns )
41 import TcMType ( newFlexiTyVarTy, zonkQuantifiedTyVar, zonkSigTyVar,
42 tcInstSigTyVars, tcInstSkolTyVars, tcInstType,
43 zonkTcType, zonkTcTypes, zonkTcTyVars )
44 import TcType ( TcType, TcTyVar, TcThetaType,
45 SkolemInfo(SigSkol), UserTypeCtxt(FunSigCtxt),
46 TcTauType, TcSigmaType, isUnboxedTupleType,
47 mkTyVarTy, mkForAllTys, mkFunTys, exactTyVarsOfType,
48 mkForAllTy, isUnLiftedType, tcGetTyVar,
49 mkTyVarTys, tidyOpenTyVar )
50 import Kind ( argTypeKind )
51 import VarEnv ( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv )
52 import TysWiredIn ( unitTy )
53 import TysPrim ( alphaTyVar )
54 import Id ( Id, mkLocalId, mkVanillaGlobal )
55 import IdInfo ( vanillaIdInfo )
56 import Var ( TyVar, idType, idName )
61 import SrcLoc ( Located(..), unLoc, getLoc )
63 import ErrUtils ( Message )
64 import Digraph ( SCC(..), stronglyConnComp )
65 import Maybes ( expectJust, isJust, isNothing, orElse )
66 import Util ( singleton )
67 import BasicTypes ( TopLevelFlag(..), isTopLevel, isNotTopLevel,
68 RecFlag(..), isNonRec, InlineSpec, defaultInlineSpec )
73 %************************************************************************
75 \subsection{Type-checking bindings}
77 %************************************************************************
79 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
80 it needs to know something about the {\em usage} of the things bound,
81 so that it can create specialisations of them. So @tcBindsAndThen@
82 takes a function which, given an extended environment, E, typechecks
83 the scope of the bindings returning a typechecked thing and (most
84 important) an LIE. It is this LIE which is then used as the basis for
85 specialising the things bound.
87 @tcBindsAndThen@ also takes a "combiner" which glues together the
88 bindings and the "thing" to make a new "thing".
90 The real work is done by @tcBindWithSigsAndThen@.
92 Recursive and non-recursive binds are handled in essentially the same
93 way: because of uniques there are no scoping issues left. The only
94 difference is that non-recursive bindings can bind primitive values.
96 Even for non-recursive binding groups we add typings for each binder
97 to the LVE for the following reason. When each individual binding is
98 checked the type of its LHS is unified with that of its RHS; and
99 type-checking the LHS of course requires that the binder is in scope.
101 At the top-level the LIE is sure to contain nothing but constant
102 dictionaries, which we resolve at the module level.
105 tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
106 -- Note: returning the TcLclEnv is more than we really
107 -- want. The bit we care about is the local bindings
108 -- and the free type variables thereof
110 = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
111 ; return (foldr (unionBags . snd) emptyBag prs, env) }
112 -- The top level bindings are flattened into a giant
113 -- implicitly-mutually-recursive LHsBinds
115 tcHsBootSigs :: HsValBinds Name -> TcM [Id]
116 -- A hs-boot file has only one BindGroup, and it only has type
117 -- signatures in it. The renamer checked all this
118 tcHsBootSigs (ValBindsOut binds sigs)
119 = do { checkTc (null binds) badBootDeclErr
120 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
122 tc_boot_sig (TypeSig (L _ name) ty)
123 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
124 ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
125 -- Notice that we make GlobalIds, not LocalIds
126 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
128 badBootDeclErr :: Message
129 badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file")
131 ------------------------
132 tcLocalBinds :: HsLocalBinds Name -> TcM thing
133 -> TcM (HsLocalBinds TcId, thing)
135 tcLocalBinds EmptyLocalBinds thing_inside
136 = do { thing <- thing_inside
137 ; return (EmptyLocalBinds, thing) }
139 tcLocalBinds (HsValBinds binds) thing_inside
140 = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
141 ; return (HsValBinds binds', thing) }
143 tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
144 = do { (thing, lie) <- getLIE thing_inside
145 ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
147 -- If the binding binds ?x = E, we must now
148 -- discharge any ?x constraints in expr_lie
149 ; dict_binds <- tcSimplifyIPs avail_ips lie
150 ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
152 -- I wonder if we should do these one at at time
155 tc_ip_bind (IPBind ip expr)
156 = newFlexiTyVarTy argTypeKind `thenM` \ ty ->
157 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
158 tcMonoExpr expr ty `thenM` \ expr' ->
159 returnM (ip_inst, (IPBind ip' expr'))
161 ------------------------
162 tcValBinds :: TopLevelFlag
163 -> HsValBinds Name -> TcM thing
164 -> TcM (HsValBinds TcId, thing)
166 tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
167 = pprPanic "tcValBinds" (ppr binds)
169 tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
170 = do { -- Typecheck the signature
171 ; let { prag_fn = mkPragFun sigs
172 ; ty_sigs = filter isVanillaLSig sigs
173 ; sig_fn = mkSigFun ty_sigs }
175 ; poly_ids <- mapM tcTySig ty_sigs
176 -- No recovery from bad signatures, because the type sigs
177 -- may bind type variables, so proceeding without them
178 -- can lead to a cascade of errors
179 -- ToDo: this means we fall over immediately if any type sig
180 -- is wrong, which is over-conservative, see Trac bug #745
182 -- Extend the envt right away with all
183 -- the Ids declared with type signatures
184 ; (binds', thing) <- tcExtendIdEnv poly_ids $
185 tc_val_binds top_lvl sig_fn prag_fn
188 ; return (ValBindsOut binds' sigs, thing) }
190 ------------------------
191 tc_val_binds :: TopLevelFlag -> TcSigFun -> TcPragFun
192 -> [(RecFlag, LHsBinds Name)] -> TcM thing
193 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
194 -- Typecheck a whole lot of value bindings,
195 -- one strongly-connected component at a time
197 tc_val_binds top_lvl sig_fn prag_fn [] thing_inside
198 = do { thing <- thing_inside
199 ; return ([], thing) }
201 tc_val_binds top_lvl sig_fn prag_fn (group : groups) thing_inside
202 = do { (group', (groups', thing))
203 <- tc_group top_lvl sig_fn prag_fn group $
204 tc_val_binds top_lvl sig_fn prag_fn groups thing_inside
205 ; return (group' ++ groups', thing) }
207 ------------------------
208 tc_group :: TopLevelFlag -> TcSigFun -> TcPragFun
209 -> (RecFlag, LHsBinds Name) -> TcM thing
210 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
212 -- Typecheck one strongly-connected component of the original program.
213 -- We get a list of groups back, because there may
214 -- be specialisations etc as well
216 tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
217 = -- A single non-recursive binding
218 -- We want to keep non-recursive things non-recursive
219 -- so that we desugar unlifted bindings correctly
220 do { (binds, thing) <- tcPolyBinds top_lvl NonRecursive NonRecursive
221 sig_fn prag_fn binds thing_inside
222 ; return ([(NonRecursive, b) | b <- binds], thing) }
224 tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
225 = -- A recursive strongly-connected component
226 -- To maximise polymorphism (with -fglasgow-exts), we do a new
227 -- strongly-connected-component analysis, this time omitting
228 -- any references to variables with type signatures.
230 -- Then we bring into scope all the variables with type signatures
231 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
232 ; gla_exts <- doptM Opt_GlasgowExts
233 ; (binds,thing) <- if gla_exts
235 else tc_binds Recursive binds thing_inside
236 ; return ([(Recursive, unionManyBags binds)], thing) }
237 -- Rec them all together
239 new_sccs :: [SCC (LHsBind Name)]
240 new_sccs = stronglyConnComp (mkEdges sig_fn binds)
242 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], thing)
243 go (scc:sccs) = do { (binds1, (binds2, thing)) <- go1 scc (go sccs)
244 ; return (binds1 ++ binds2, thing) }
245 go [] = do { thing <- thing_inside; return ([], thing) }
247 go1 (AcyclicSCC bind) = tc_binds NonRecursive (unitBag bind)
248 go1 (CyclicSCC binds) = tc_binds Recursive (listToBag binds)
250 tc_binds rec_tc binds = tcPolyBinds top_lvl Recursive rec_tc sig_fn prag_fn binds
252 ------------------------
253 mkEdges :: TcSigFun -> LHsBinds Name
254 -> [(LHsBind Name, BKey, [BKey])]
256 type BKey = Int -- Just number off the bindings
259 = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
260 Just key <- [lookupNameEnv key_map n], no_sig n ])
261 | (bind, key) <- keyd_binds
264 no_sig :: Name -> Bool
265 no_sig n = isNothing (sig_fn n)
267 keyd_binds = bagToList binds `zip` [0::BKey ..]
269 key_map :: NameEnv BKey -- Which binding it comes from
270 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
271 , bndr <- bindersOfHsBind bind ]
273 bindersOfHsBind :: HsBind Name -> [Name]
274 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
275 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
277 ------------------------
278 tcPolyBinds :: TopLevelFlag
279 -> RecFlag -- Whether the group is really recursive
280 -> RecFlag -- Whether it's recursive for typechecking purposes
281 -> TcSigFun -> TcPragFun
284 -> TcM ([LHsBinds TcId], thing)
286 -- Typechecks a single bunch of bindings all together,
287 -- and generalises them. The bunch may be only part of a recursive
288 -- group, because we use type signatures to maximise polymorphism
290 -- Deals with the bindInstsOfLocalFuns thing too
292 -- Returns a list because the input may be a single non-recursive binding,
293 -- in which case the dependency order of the resulting bindings is
296 tcPolyBinds top_lvl rec_group rec_tc sig_fn prag_fn scc thing_inside
297 = -- NB: polymorphic recursion means that a function
298 -- may use an instance of itself, we must look at the LIE arising
299 -- from the function's own right hand side. Hence the getLIE
300 -- encloses the tc_poly_binds.
301 do { traceTc (text "tcPolyBinds" <+> ppr scc)
302 ; ((binds1, poly_ids, thing), lie) <- getLIE $
303 do { (binds1, poly_ids) <- tc_poly_binds top_lvl rec_group rec_tc
305 ; thing <- tcExtendIdEnv poly_ids thing_inside
306 ; return (binds1, poly_ids, thing) }
308 ; if isTopLevel top_lvl
309 then -- For the top level don't bother will all this
310 -- bindInstsOfLocalFuns stuff. All the top level
311 -- things are rec'd together anyway, so it's fine to
312 -- leave them to the tcSimplifyTop,
313 -- and quite a bit faster too
314 do { extendLIEs lie; return (binds1, thing) }
316 else do -- Nested case
317 { lie_binds <- bindInstsOfLocalFuns lie poly_ids
318 ; return (binds1 ++ [lie_binds], thing) }}
320 ------------------------
321 tc_poly_binds :: TopLevelFlag -- See comments on tcPolyBinds
322 -> RecFlag -> RecFlag
323 -> TcSigFun -> TcPragFun
325 -> TcM ([LHsBinds TcId], [TcId])
326 -- Typechecks the bindings themselves
327 -- Knows nothing about the scope of the bindings
329 tc_poly_binds top_lvl rec_group rec_tc sig_fn prag_fn binds
331 binder_names = collectHsBindBinders binds
332 bind_list = bagToList binds
334 loc = getLoc (head bind_list)
335 -- TODO: location a bit awkward, but the mbinds have been
336 -- dependency analysed and may no longer be adjacent
338 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
340 recoverM (recoveryCode binder_names) $ do
342 { traceTc (ptext SLIT("------------------------------------------------"))
343 ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
345 -- TYPECHECK THE BINDINGS
346 ; ((binds', mono_bind_infos), lie_req)
347 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
349 -- CHECK FOR UNLIFTED BINDINGS
350 -- These must be non-recursive etc, and are not generalised
351 -- They desugar to a case expression in the end
352 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
353 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
354 zonked_mono_tys mono_bind_infos
356 do { extendLIEs lie_req
357 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
358 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
359 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
360 -- ToDo: prags for unlifted bindings
362 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
363 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
365 else do -- The normal lifted case: GENERALISE
366 { is_unres <- isUnRestrictedGroup bind_list sig_fn
367 ; (tyvars_to_gen, dict_binds, dict_ids)
368 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
369 generalise top_lvl is_unres mono_bind_infos lie_req
371 -- FINALISE THE QUANTIFIED TYPE VARIABLES
372 -- The quantified type variables often include meta type variables
373 -- we want to freeze them into ordinary type variables, and
374 -- default their kind (e.g. from OpenTypeKind to TypeKind)
375 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
377 -- BUILD THE POLYMORPHIC RESULT IDs
378 ; exports <- mapM (mkExport prag_fn tyvars_to_gen' (map idType dict_ids))
381 -- ZONK THE poly_ids, because they are used to extend the type
382 -- environment; see the invariant on TcEnv.tcExtendIdEnv
383 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
384 ; zonked_poly_ids <- mappM zonkId poly_ids
386 ; traceTc (text "binding:" <+> ppr (zonked_poly_ids `zip` map idType zonked_poly_ids))
388 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen'
390 (dict_binds `unionBags` binds')
392 ; return ([unitBag abs_bind], zonked_poly_ids)
397 mkExport :: TcPragFun -> [TyVar] -> [TcType] -> MonoBindInfo
398 -> TcM ([TyVar], Id, Id, [Prag])
399 mkExport prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
401 Nothing -> do { prags <- tcPrags poly_id (prag_fn poly_name)
402 ; return (inferred_tvs, poly_id, mono_id, prags) }
404 poly_id = mkLocalId poly_name poly_ty
405 poly_ty = mkForAllTys inferred_tvs
409 Just sig -> do { let poly_id = sig_id sig
410 ; prags <- tcPrags poly_id (prag_fn poly_name)
411 ; sig_tys <- zonkTcTyVars (sig_tvs sig)
412 ; let sig_tvs' = map (tcGetTyVar "mkExport") sig_tys
413 ; return (sig_tvs', poly_id, mono_id, prags) }
414 -- We zonk the sig_tvs here so that the export triple
415 -- always has zonked type variables;
416 -- a convenient invariant
419 ------------------------
420 type TcPragFun = Name -> [LSig Name]
422 mkPragFun :: [LSig Name] -> TcPragFun
423 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
425 prs = [(expectJust "mkPragFun" (sigName sig), sig)
426 | sig <- sigs, isPragLSig sig]
427 env = foldl add emptyNameEnv prs
428 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
430 tcPrags :: Id -> [LSig Name] -> TcM [Prag]
431 tcPrags poly_id prags = mapM tc_prag prags
433 tc_prag (L loc prag) = setSrcSpan loc $
434 addErrCtxt (pragSigCtxt prag) $
437 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
439 tcPrag :: TcId -> Sig Name -> TcM Prag
440 tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
441 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
442 tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
445 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
446 tcSpecPrag poly_id hs_ty inl
447 = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
448 ; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty)
450 ; let const_dicts = map instToId lie
451 ; return (SpecPrag (mkHsCoerce co_fn (HsVar poly_id)) spec_ty const_dicts inl) }
454 -- If typechecking the binds fails, then return with each
455 -- signature-less binder given type (forall a.a), to minimise
456 -- subsequent error messages
457 recoveryCode binder_names
458 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
459 ; poly_ids <- mapM mk_dummy binder_names
460 ; return ([], poly_ids) }
462 mk_dummy name = do { mb_id <- tcLookupLocalId_maybe name
464 Just id -> return id -- Had signature, was in envt
465 Nothing -> return (mkLocalId name forall_a_a) } -- No signature
468 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
471 -- Check that non-overloaded unlifted bindings are
474 -- c) not a multiple-binding group (more or less implied by (a))
476 checkStrictBinds :: TopLevelFlag -> RecFlag
477 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
479 checkStrictBinds top_lvl rec_group mbind mono_tys infos
480 | unlifted || bang_pat
481 = do { checkTc (isNotTopLevel top_lvl)
482 (strictBindErr "Top-level" unlifted mbind)
483 ; checkTc (isNonRec rec_group)
484 (strictBindErr "Recursive" unlifted mbind)
485 ; checkTc (isSingletonBag mbind)
486 (strictBindErr "Multiple" unlifted mbind)
487 ; mapM_ check_sig infos
492 unlifted = any isUnLiftedType mono_tys
493 bang_pat = anyBag (isBangHsBind . unLoc) mbind
494 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
495 (badStrictSig unlifted sig)
496 check_sig other = return ()
498 strictBindErr flavour unlifted mbind
499 = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:")) 4 (ppr mbind)
501 msg | unlifted = ptext SLIT("bindings for unlifted types")
502 | otherwise = ptext SLIT("bang-pattern bindings")
504 badStrictSig unlifted sig
505 = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
508 msg | unlifted = ptext SLIT("an unlifted binding")
509 | otherwise = ptext SLIT("a bang-pattern binding")
513 %************************************************************************
515 \subsection{tcMonoBind}
517 %************************************************************************
519 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
520 The signatures have been dealt with already.
523 tcMonoBinds :: [LHsBind Name]
525 -> RecFlag -- Whether the binding is recursive for typechecking purposes
526 -- i.e. the binders are mentioned in their RHSs, and
527 -- we are not resuced by a type signature
528 -> TcM (LHsBinds TcId, [MonoBindInfo])
530 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
531 fun_matches = matches, bind_fvs = fvs })]
532 sig_fn -- Single function binding,
533 NonRecursive -- binder isn't mentioned in RHS,
534 | Nothing <- sig_fn name -- ...with no type signature
535 = -- In this very special case we infer the type of the
536 -- right hand side first (it may have a higher-rank type)
537 -- and *then* make the monomorphic Id for the LHS
538 -- e.g. f = \(x::forall a. a->a) -> <body>
539 -- We want to infer a higher-rank type for f
541 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name matches)
543 -- Check for an unboxed tuple type
544 -- f = (# True, False #)
545 -- Zonk first just in case it's hidden inside a meta type variable
546 -- (This shows up as a (more obscure) kind error
547 -- in the 'otherwise' case of tcMonoBinds.)
548 ; zonked_rhs_ty <- zonkTcType rhs_ty
549 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
550 (unboxedTupleErr name zonked_rhs_ty)
552 ; mono_name <- newLocalName name
553 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
554 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
555 fun_matches = matches', bind_fvs = fvs,
556 fun_co_fn = co_fn })),
557 [(name, Nothing, mono_id)]) }
559 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
560 fun_matches = matches, bind_fvs = fvs })]
561 sig_fn -- Single function binding
563 | Just sig <- sig_fn name -- ...with a type signature
564 = -- When we have a single function binding, with a type signature
565 -- we can (a) use genuine, rigid skolem constants for the type variables
566 -- (b) bring (rigid) scoped type variables into scope
568 do { tc_sig <- tcInstSig True sig
569 ; mono_name <- newLocalName name
570 ; let mono_ty = sig_tau tc_sig
571 mono_id = mkLocalId mono_name mono_ty
572 rhs_tvs = [ (name, mkTyVarTy tv)
573 | (name, tv) <- sig_scoped tc_sig `zip` sig_tvs tc_sig ]
575 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
576 tcMatchesFun mono_name matches mono_ty
578 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
579 fun_infix = inf, fun_matches = matches',
580 bind_fvs = placeHolderNames, fun_co_fn = co_fn }
581 ; return (unitBag (L b_loc fun_bind'),
582 [(name, Just tc_sig, mono_id)]) }
584 tcMonoBinds binds sig_fn non_rec
585 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
587 -- Bring the monomorphic Ids, into scope for the RHSs
588 ; let mono_info = getMonoBindInfo tc_binds
589 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
590 -- A monomorphic binding for each term variable that lacks
591 -- a type sig. (Ones with a sig are already in scope.)
593 ; binds' <- tcExtendIdEnv2 rhs_id_env $
594 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
595 | (n,id) <- rhs_id_env]) `thenM_`
596 mapM (wrapLocM tcRhs) tc_binds
597 ; return (listToBag binds', mono_info) }
599 ------------------------
600 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
601 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
602 -- if there's a signature for it, use the instantiated signature type
603 -- otherwise invent a type variable
604 -- You see that quite directly in the FunBind case.
606 -- But there's a complication for pattern bindings:
607 -- data T = MkT (forall a. a->a)
609 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
610 -- but we want to get (f::forall a. a->a) as the RHS environment.
611 -- The simplest way to do this is to typecheck the pattern, and then look up the
612 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
613 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
615 data TcMonoBind -- Half completed; LHS done, RHS not done
616 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
617 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
619 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
620 -- Type signature (if any), and
621 -- the monomorphic bound things
623 bndrNames :: [MonoBindInfo] -> [Name]
624 bndrNames mbi = [n | (n,_,_) <- mbi]
626 getMonoType :: MonoBindInfo -> TcTauType
627 getMonoType (_,_,mono_id) = idType mono_id
629 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
630 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
631 = do { mb_sig <- tcInstSig_maybe (sig_fn name)
632 ; mono_name <- newLocalName name
633 ; mono_ty <- mk_mono_ty mb_sig
634 ; let mono_id = mkLocalId mono_name mono_ty
635 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
637 mk_mono_ty (Just sig) = return (sig_tau sig)
638 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
640 tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
641 = do { mb_sigs <- mapM (tcInstSig_maybe . sig_fn) names
643 ; let nm_sig_prs = names `zip` mb_sigs
644 tau_sig_env = mkNameEnv [ (name, sig_tau sig) | (name, Just sig) <- nm_sig_prs]
645 sig_tau_fn = lookupNameEnv tau_sig_env
647 tc_pat exp_ty = tcPat (LetPat sig_tau_fn) pat exp_ty unitTy $ \ _ ->
648 mapM lookup_info nm_sig_prs
649 -- The unitTy is a bit bogus; it's the "result type" for lookup_info.
651 -- After typechecking the pattern, look up the binder
652 -- names, which the pattern has brought into scope.
653 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
654 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
655 ; return (name, mb_sig, mono_id) }
657 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
660 ; return (TcPatBind infos pat' grhss pat_ty) }
662 names = collectPatBinders pat
665 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
666 -- AbsBind, VarBind impossible
669 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
670 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
671 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) matches
673 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
674 bind_fvs = placeHolderNames, fun_co_fn = co_fn }) }
676 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
677 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
678 tcGRHSsPat grhss pat_ty
679 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
680 bind_fvs = placeHolderNames }) }
683 ---------------------
684 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
685 getMonoBindInfo tc_binds
686 = foldr (get_info . unLoc) [] tc_binds
688 get_info (TcFunBind info _ _ _) rest = info : rest
689 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
693 %************************************************************************
697 %************************************************************************
700 generalise :: TopLevelFlag -> Bool
701 -> [MonoBindInfo] -> [Inst]
702 -> TcM ([TcTyVar], TcDictBinds, [TcId])
703 generalise top_lvl is_unrestricted mono_infos lie_req
704 | not is_unrestricted -- RESTRICTED CASE
705 = -- Check signature contexts are empty
706 do { checkTc (all is_mono_sig sigs)
707 (restrictedBindCtxtErr bndrs)
709 -- Now simplify with exactly that set of tyvars
710 -- We have to squash those Methods
711 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
714 -- Check that signature type variables are OK
715 ; final_qtvs <- checkSigsTyVars qtvs sigs
717 ; return (final_qtvs, binds, []) }
719 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
720 = tcSimplifyInfer doc tau_tvs lie_req
722 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
723 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty
724 ; let -- The "sig_avails" is the stuff available. We get that from
725 -- the context of the type signature, BUT ALSO the lie_avail
726 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
727 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
728 sig_avails = sig_lie ++ local_meths
730 -- Check that the needed dicts can be
731 -- expressed in terms of the signature ones
732 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
734 -- Check that signature type variables are OK
735 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
737 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
739 bndrs = bndrNames mono_infos
740 sigs = [sig | (_, Just sig, _) <- mono_infos]
741 tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos
742 -- NB: exactTyVarsOfType; see Note [Silly type synonym]
743 -- near defn of TcType.exactTyVarsOfType
744 is_mono_sig sig = null (sig_theta sig)
745 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
747 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
748 sig_theta = theta, sig_loc = loc }) mono_id
749 = Method mono_id poly_id (mkTyVarTys tvs) theta loc
752 unifyCtxts checks that all the signature contexts are the same
753 The type signatures on a mutually-recursive group of definitions
754 must all have the same context (or none).
756 The trick here is that all the signatures should have the same
757 context, and we want to share type variables for that context, so that
758 all the right hand sides agree a common vocabulary for their type
761 We unify them because, with polymorphic recursion, their types
762 might not otherwise be related. This is a rather subtle issue.
765 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
766 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
767 = do { mapM unify_ctxt sigs
768 ; newDictsAtLoc (sig_loc sig1) (sig_theta sig1) }
770 theta1 = sig_theta sig1
771 unify_ctxt :: TcSigInfo -> TcM ()
772 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
773 = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
774 addErrCtxt (sigContextsCtxt sig1 sig) $
775 unifyTheta theta1 theta
777 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
778 checkSigsTyVars qtvs sigs
779 = do { gbl_tvs <- tcGetGlobalTyVars
780 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
782 ; let -- Sigh. Make sure that all the tyvars in the type sigs
783 -- appear in the returned ty var list, which is what we are
784 -- going to generalise over. Reason: we occasionally get
786 -- type T a = () -> ()
789 -- Here, 'a' won't appear in qtvs, so we have to add it
790 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
791 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
794 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
795 sig_theta = theta, sig_tau = tau})
796 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
797 addErrCtxtM (sigCtxt id tvs theta tau) $
798 do { tvs' <- checkDistinctTyVars tvs
799 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
800 (bleatEscapedTvs gbl_tvs tvs tvs')
803 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
804 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
805 -- are still all type variables, and all distinct from each other.
806 -- It returns a zonked set of type variables.
807 -- For example, if the type sig is
808 -- f :: forall a b. a -> b -> b
809 -- we want to check that 'a' and 'b' haven't
810 -- (a) been unified with a non-tyvar type
811 -- (b) been unified with each other (all distinct)
813 checkDistinctTyVars sig_tvs
814 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
815 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
816 ; return zonked_tvs }
818 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
819 -- The TyVarEnv maps each zonked type variable back to its
820 -- corresponding user-written signature type variable
821 check_dup acc (sig_tv, zonked_tv)
822 = case lookupVarEnv acc zonked_tv of
823 Just sig_tv' -> bomb_out sig_tv sig_tv'
825 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
827 bomb_out sig_tv1 sig_tv2
828 = do { env0 <- tcInitTidyEnv
829 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
830 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
831 msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
832 <+> ptext SLIT("is unified with another quantified type variable")
833 <+> quotes (ppr tidy_tv2)
834 ; failWithTcM (env2, msg) }
839 @getTyVarsToGen@ decides what type variables to generalise over.
841 For a "restricted group" -- see the monomorphism restriction
842 for a definition -- we bind no dictionaries, and
843 remove from tyvars_to_gen any constrained type variables
845 *Don't* simplify dicts at this point, because we aren't going
846 to generalise over these dicts. By the time we do simplify them
847 we may well know more. For example (this actually came up)
849 f x = array ... xs where xs = [1,2,3,4,5]
850 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
851 stuff. If we simplify only at the f-binding (not the xs-binding)
852 we'll know that the literals are all Ints, and we can just produce
855 Find all the type variables involved in overloading, the
856 "constrained_tyvars". These are the ones we *aren't* going to
857 generalise. We must be careful about doing this:
859 (a) If we fail to generalise a tyvar which is not actually
860 constrained, then it will never, ever get bound, and lands
861 up printed out in interface files! Notorious example:
862 instance Eq a => Eq (Foo a b) where ..
863 Here, b is not constrained, even though it looks as if it is.
864 Another, more common, example is when there's a Method inst in
865 the LIE, whose type might very well involve non-overloaded
867 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
868 the simple thing instead]
870 (b) On the other hand, we mustn't generalise tyvars which are constrained,
871 because we are going to pass on out the unmodified LIE, with those
872 tyvars in it. They won't be in scope if we've generalised them.
874 So we are careful, and do a complete simplification just to find the
875 constrained tyvars. We don't use any of the results, except to
876 find which tyvars are constrained.
878 Note [Polymorphic recursion]
879 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
880 The game plan for polymorphic recursion in the code above is
882 * Bind any variable for which we have a type signature
883 to an Id with a polymorphic type. Then when type-checking
884 the RHSs we'll make a full polymorphic call.
886 This fine, but if you aren't a bit careful you end up with a horrendous
887 amount of partial application and (worse) a huge space leak. For example:
889 f :: Eq a => [a] -> [a]
892 If we don't take care, after typechecking we get
894 f = /\a -> \d::Eq a -> let f' = f a d
898 Notice the the stupid construction of (f a d), which is of course
899 identical to the function we're executing. In this case, the
900 polymorphic recursion isn't being used (but that's a very common case).
901 This can lead to a massive space leak, from the following top-level defn
907 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
908 f' is another thunk which evaluates to the same thing... and you end
909 up with a chain of identical values all hung onto by the CAF ff.
913 = let f' = f Int dEqInt in \ys. ...f'...
915 = let f' = let f' = f Int dEqInt in \ys. ...f'...
920 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
921 which would make the space leak go away in this case
923 Solution: when typechecking the RHSs we always have in hand the
924 *monomorphic* Ids for each binding. So we just need to make sure that
925 if (Method f a d) shows up in the constraints emerging from (...f...)
926 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
927 to the "givens" when simplifying constraints. That's what the "lies_avail"
932 f = /\a -> \d::Eq a -> letrec
933 fm = \ys:[a] -> ...fm...
939 %************************************************************************
943 %************************************************************************
945 Type signatures are tricky. See Note [Signature skolems] in TcType
947 @tcSigs@ checks the signatures for validity, and returns a list of
948 {\em freshly-instantiated} signatures. That is, the types are already
949 split up, and have fresh type variables installed. All non-type-signature
950 "RenamedSigs" are ignored.
952 The @TcSigInfo@ contains @TcTypes@ because they are unified with
953 the variable's type, and after that checked to see whether they've
957 type TcSigFun = Name -> Maybe (LSig Name)
959 mkSigFun :: [LSig Name] -> TcSigFun
960 -- Search for a particular type signature
961 -- Precondition: the sigs are all type sigs
962 -- Precondition: no duplicates
963 mkSigFun sigs = lookupNameEnv env
965 env = mkNameEnv [(expectJust "mkSigFun" (sigName sig), sig) | sig <- sigs]
970 sig_id :: TcId, -- *Polymorphic* binder for this value...
972 sig_scoped :: [Name], -- Names for any scoped type variables
973 -- Invariant: correspond 1-1 with an initial
974 -- segment of sig_tvs (see Note [Scoped])
976 sig_tvs :: [TcTyVar], -- Instantiated type variables
977 -- See Note [Instantiate sig]
979 sig_theta :: TcThetaType, -- Instantiated theta
980 sig_tau :: TcTauType, -- Instantiated tau
981 sig_loc :: InstLoc -- The location of the signature
985 -- There may be more instantiated type variables than scoped
986 -- ones. For example:
987 -- type T a = forall b. b -> (a,b)
988 -- f :: forall c. T c
989 -- Here, the signature for f will have one scoped type variable, c,
990 -- but two instantiated type variables, c' and b'.
992 -- We assume that the scoped ones are at the *front* of sig_tvs,
993 -- and remember the names from the original HsForAllTy in sig_scoped
995 -- Note [Instantiate sig]
996 -- It's vital to instantiate a type signature with fresh variable.
998 -- type S = forall a. a->a
1002 -- Here, we must use distinct type variables when checking f,g's right hand sides.
1003 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1004 -- it's all cool; each signature has distinct type variables from the renamer.)
1006 instance Outputable TcSigInfo where
1007 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1008 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
1012 tcTySig :: LSig Name -> TcM TcId
1013 tcTySig (L span (TypeSig (L _ name) ty))
1015 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1016 ; return (mkLocalId name sigma_ty) }
1019 tcInstSig_maybe :: Maybe (LSig Name) -> TcM (Maybe TcSigInfo)
1020 -- Instantiate with *meta* type variables;
1021 -- this signature is part of a multi-signature group
1022 tcInstSig_maybe Nothing = return Nothing
1023 tcInstSig_maybe (Just sig) = do { tc_sig <- tcInstSig False sig
1024 ; return (Just tc_sig) }
1026 tcInstSig :: Bool -> LSig Name -> TcM TcSigInfo
1027 -- Instantiate the signature, with either skolems or meta-type variables
1028 -- depending on the use_skols boolean
1030 -- We always instantiate with freshs uniques,
1031 -- although we keep the same print-name
1033 -- type T = forall a. [a] -> [a]
1035 -- f = g where { g :: T; g = <rhs> }
1037 -- We must not use the same 'a' from the defn of T at both places!!
1039 tcInstSig use_skols (L loc (TypeSig (L _ name) hs_ty))
1041 do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1042 -- scope when starting the binding group
1043 ; let skol_info = SigSkol (FunSigCtxt name)
1044 inst_tyvars | use_skols = tcInstSkolTyVars skol_info
1045 | otherwise = tcInstSigTyVars skol_info
1046 ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
1047 ; loc <- getInstLoc (SigOrigin skol_info)
1048 ; return (TcSigInfo { sig_id = poly_id,
1049 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1050 sig_scoped = scoped_names, sig_loc = loc }) }
1051 -- Note that the scoped_names and the sig_tvs will have
1052 -- different Names. That's quite ok; when we bring the
1053 -- scoped_names into scope, we just bind them to the sig_tvs
1055 -- The scoped names are the ones explicitly mentioned
1056 -- in the HsForAll. (There may be more in sigma_ty, because
1057 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
1058 -- We also only have scoped type variables when we are instantiating
1059 -- with true skolems
1060 scoped_names = case (use_skols, hs_ty) of
1061 (True, L _ (HsForAllTy Explicit tvs _ _)) -> hsLTyVarNames tvs
1065 isUnRestrictedGroup :: [LHsBind Name] -> TcSigFun -> TcM Bool
1066 isUnRestrictedGroup binds sig_fn
1067 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
1068 ; return (not mono_restriction || all_unrestricted) }
1070 all_unrestricted = all (unrestricted . unLoc) binds
1071 has_sig n = isJust (sig_fn n)
1073 unrestricted (PatBind {}) = False
1074 unrestricted (VarBind { var_id = v }) = has_sig v
1075 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1076 || has_sig (unLoc v)
1078 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1079 -- No args => like a pattern binding
1080 unrestricted_match other = True
1081 -- Some args => a function binding
1085 %************************************************************************
1087 \subsection[TcBinds-errors]{Error contexts and messages}
1089 %************************************************************************
1093 -- This one is called on LHS, when pat and grhss are both Name
1094 -- and on RHS, when pat is TcId and grhss is still Name
1095 patMonoBindsCtxt pat grhss
1096 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
1098 -----------------------------------------------
1099 sigContextsCtxt sig1 sig2
1100 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
1101 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1102 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1103 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
1109 -----------------------------------------------
1110 unboxedTupleErr name ty
1111 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
1112 4 (ppr name <+> dcolon <+> ppr ty)
1114 -----------------------------------------------
1115 restrictedBindCtxtErr binder_names
1116 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
1117 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
1118 ptext SLIT("that falls under the monomorphism restriction")])
1120 genCtxt binder_names
1121 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names