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 ( fromJust, 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
177 -- Extend the envt right away with all
178 -- the Ids declared with type signatures
179 ; (binds', thing) <- tcExtendIdEnv poly_ids $
180 tc_val_binds top_lvl sig_fn prag_fn
183 ; return (ValBindsOut binds' sigs, thing) }
185 ------------------------
186 tc_val_binds :: TopLevelFlag -> TcSigFun -> TcPragFun
187 -> [(RecFlag, LHsBinds Name)] -> TcM thing
188 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
189 -- Typecheck a whole lot of value bindings,
190 -- one strongly-connected component at a time
192 tc_val_binds top_lvl sig_fn prag_fn [] thing_inside
193 = do { thing <- thing_inside
194 ; return ([], thing) }
196 tc_val_binds top_lvl sig_fn prag_fn (group : groups) thing_inside
197 = do { (group', (groups', thing))
198 <- tc_group top_lvl sig_fn prag_fn group $
199 tc_val_binds top_lvl sig_fn prag_fn groups thing_inside
200 ; return (group' ++ groups', thing) }
202 ------------------------
203 tc_group :: TopLevelFlag -> TcSigFun -> TcPragFun
204 -> (RecFlag, LHsBinds Name) -> TcM thing
205 -> TcM ([(RecFlag, LHsBinds TcId)], thing)
207 -- Typecheck one strongly-connected component of the original program.
208 -- We get a list of groups back, because there may
209 -- be specialisations etc as well
211 tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
212 = -- A single non-recursive binding
213 -- We want to keep non-recursive things non-recursive
214 -- so that we desugar unlifted bindings correctly
215 do { (binds, thing) <- tcPolyBinds top_lvl NonRecursive NonRecursive
216 sig_fn prag_fn binds thing_inside
217 ; return ([(NonRecursive, b) | b <- binds], thing) }
219 tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
220 = -- A recursive strongly-connected component
221 -- To maximise polymorphism (with -fglasgow-exts), we do a new
222 -- strongly-connected-component analysis, this time omitting
223 -- any references to variables with type signatures.
225 -- Then we bring into scope all the variables with type signatures
226 do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
227 ; gla_exts <- doptM Opt_GlasgowExts
228 ; (binds,thing) <- if gla_exts
230 else tc_binds Recursive binds thing_inside
231 ; return ([(Recursive, unionManyBags binds)], thing) }
232 -- Rec them all together
234 new_sccs :: [SCC (LHsBind Name)]
235 new_sccs = stronglyConnComp (mkEdges sig_fn binds)
237 -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], thing)
238 go (scc:sccs) = do { (binds1, (binds2, thing)) <- go1 scc (go sccs)
239 ; return (binds1 ++ binds2, thing) }
240 go [] = do { thing <- thing_inside; return ([], thing) }
242 go1 (AcyclicSCC bind) = tc_binds NonRecursive (unitBag bind)
243 go1 (CyclicSCC binds) = tc_binds Recursive (listToBag binds)
245 tc_binds rec_tc binds = tcPolyBinds top_lvl Recursive rec_tc sig_fn prag_fn binds
247 ------------------------
248 mkEdges :: TcSigFun -> LHsBinds Name
249 -> [(LHsBind Name, BKey, [BKey])]
251 type BKey = Int -- Just number off the bindings
254 = [ (bind, key, [fromJust mb_key | n <- nameSetToList (bind_fvs (unLoc bind)),
255 let mb_key = lookupNameEnv key_map n,
258 | (bind, key) <- keyd_binds
261 no_sig :: Name -> Bool
262 no_sig n = isNothing (sig_fn n)
264 keyd_binds = bagToList binds `zip` [0::BKey ..]
266 key_map :: NameEnv BKey -- Which binding it comes from
267 key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
268 , bndr <- bindersOfHsBind bind ]
270 bindersOfHsBind :: HsBind Name -> [Name]
271 bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
272 bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
274 ------------------------
275 tcPolyBinds :: TopLevelFlag
276 -> RecFlag -- Whether the group is really recursive
277 -> RecFlag -- Whether it's recursive for typechecking purposes
278 -> TcSigFun -> TcPragFun
281 -> TcM ([LHsBinds TcId], thing)
283 -- Typechecks a single bunch of bindings all together,
284 -- and generalises them. The bunch may be only part of a recursive
285 -- group, because we use type signatures to maximise polymorphism
287 -- Deals with the bindInstsOfLocalFuns thing too
289 -- Returns a list because the input may be a single non-recursive binding,
290 -- in which case the dependency order of the resulting bindings is
293 tcPolyBinds top_lvl rec_group rec_tc sig_fn prag_fn scc thing_inside
294 = -- NB: polymorphic recursion means that a function
295 -- may use an instance of itself, we must look at the LIE arising
296 -- from the function's own right hand side. Hence the getLIE
297 -- encloses the tc_poly_binds.
298 do { traceTc (text "tcPolyBinds" <+> ppr scc)
299 ; ((binds1, poly_ids, thing), lie) <- getLIE $
300 do { (binds1, poly_ids) <- tc_poly_binds top_lvl rec_group rec_tc
302 ; thing <- tcExtendIdEnv poly_ids thing_inside
303 ; return (binds1, poly_ids, thing) }
305 ; if isTopLevel top_lvl
306 then -- For the top level don't bother will all this
307 -- bindInstsOfLocalFuns stuff. All the top level
308 -- things are rec'd together anyway, so it's fine to
309 -- leave them to the tcSimplifyTop,
310 -- and quite a bit faster too
311 do { extendLIEs lie; return (binds1, thing) }
313 else do -- Nested case
314 { lie_binds <- bindInstsOfLocalFuns lie poly_ids
315 ; return (binds1 ++ [lie_binds], thing) }}
317 ------------------------
318 tc_poly_binds :: TopLevelFlag -- See comments on tcPolyBinds
319 -> RecFlag -> RecFlag
320 -> TcSigFun -> TcPragFun
322 -> TcM ([LHsBinds TcId], [TcId])
323 -- Typechecks the bindings themselves
324 -- Knows nothing about the scope of the bindings
326 tc_poly_binds top_lvl rec_group rec_tc sig_fn prag_fn binds
328 binder_names = collectHsBindBinders binds
329 bind_list = bagToList binds
331 loc = getLoc (head bind_list)
332 -- TODO: location a bit awkward, but the mbinds have been
333 -- dependency analysed and may no longer be adjacent
335 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
337 recoverM (recoveryCode binder_names) $ do
339 { traceTc (ptext SLIT("------------------------------------------------"))
340 ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
342 -- TYPECHECK THE BINDINGS
343 ; ((binds', mono_bind_infos), lie_req)
344 <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
346 -- CHECK FOR UNLIFTED BINDINGS
347 -- These must be non-recursive etc, and are not generalised
348 -- They desugar to a case expression in the end
349 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
350 ; is_strict <- checkStrictBinds top_lvl rec_group binds'
351 zonked_mono_tys mono_bind_infos
353 do { extendLIEs lie_req
354 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
355 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
356 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
357 -- ToDo: prags for unlifted bindings
359 ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
360 [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
362 else do -- The normal lifted case: GENERALISE
363 { is_unres <- isUnRestrictedGroup bind_list sig_fn
364 ; (tyvars_to_gen, dict_binds, dict_ids)
365 <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
366 generalise top_lvl is_unres mono_bind_infos lie_req
368 -- FINALISE THE QUANTIFIED TYPE VARIABLES
369 -- The quantified type variables often include meta type variables
370 -- we want to freeze them into ordinary type variables, and
371 -- default their kind (e.g. from OpenTypeKind to TypeKind)
372 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
374 -- BUILD THE POLYMORPHIC RESULT IDs
375 ; exports <- mapM (mkExport prag_fn tyvars_to_gen' (map idType dict_ids))
378 -- ZONK THE poly_ids, because they are used to extend the type
379 -- environment; see the invariant on TcEnv.tcExtendIdEnv
380 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
381 ; zonked_poly_ids <- mappM zonkId poly_ids
383 ; traceTc (text "binding:" <+> ppr (zonked_poly_ids `zip` map idType zonked_poly_ids))
385 ; let abs_bind = L loc $ AbsBinds tyvars_to_gen'
387 (dict_binds `unionBags` binds')
389 ; return ([unitBag abs_bind], zonked_poly_ids)
394 mkExport :: TcPragFun -> [TyVar] -> [TcType] -> MonoBindInfo
395 -> TcM ([TyVar], Id, Id, [Prag])
396 mkExport prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
398 Nothing -> do { prags <- tcPrags poly_id (prag_fn poly_name)
399 ; return (inferred_tvs, poly_id, mono_id, prags) }
401 poly_id = mkLocalId poly_name poly_ty
402 poly_ty = mkForAllTys inferred_tvs
406 Just sig -> do { let poly_id = sig_id sig
407 ; prags <- tcPrags poly_id (prag_fn poly_name)
408 ; sig_tys <- zonkTcTyVars (sig_tvs sig)
409 ; let sig_tvs' = map (tcGetTyVar "mkExport") sig_tys
410 ; return (sig_tvs', poly_id, mono_id, prags) }
411 -- We zonk the sig_tvs here so that the export triple
412 -- always has zonked type variables;
413 -- a convenient invariant
416 ------------------------
417 type TcPragFun = Name -> [LSig Name]
419 mkPragFun :: [LSig Name] -> TcPragFun
420 mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
422 prs = [(fromJust (sigName sig), sig) | sig <- sigs, isPragLSig sig]
423 env = foldl add emptyNameEnv prs
424 add env (n,p) = extendNameEnv_Acc (:) singleton env n p
426 tcPrags :: Id -> [LSig Name] -> TcM [Prag]
427 tcPrags poly_id prags = mapM tc_prag prags
429 tc_prag (L loc prag) = setSrcSpan loc $
430 addErrCtxt (pragSigCtxt prag) $
433 pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
435 tcPrag :: TcId -> Sig Name -> TcM Prag
436 tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
437 tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
438 tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
441 tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
442 tcSpecPrag poly_id hs_ty inl
443 = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
444 ; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty)
446 ; let const_dicts = map instToId lie
447 ; return (SpecPrag (mkHsCoerce co_fn (HsVar poly_id)) spec_ty const_dicts inl) }
450 -- If typechecking the binds fails, then return with each
451 -- signature-less binder given type (forall a.a), to minimise
452 -- subsequent error messages
453 recoveryCode binder_names
454 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
455 ; poly_ids <- mapM mk_dummy binder_names
456 ; return ([], poly_ids) }
458 mk_dummy name = do { mb_id <- tcLookupLocalId_maybe name
460 Just id -> return id -- Had signature, was in envt
461 Nothing -> return (mkLocalId name forall_a_a) } -- No signature
464 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
467 -- Check that non-overloaded unlifted bindings are
470 -- c) not a multiple-binding group (more or less implied by (a))
472 checkStrictBinds :: TopLevelFlag -> RecFlag
473 -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
475 checkStrictBinds top_lvl rec_group mbind mono_tys infos
476 | unlifted || bang_pat
477 = do { checkTc (isNotTopLevel top_lvl)
478 (strictBindErr "Top-level" unlifted mbind)
479 ; checkTc (isNonRec rec_group)
480 (strictBindErr "Recursive" unlifted mbind)
481 ; checkTc (isSingletonBag mbind)
482 (strictBindErr "Multiple" unlifted mbind)
483 ; mapM_ check_sig infos
488 unlifted = any isUnLiftedType mono_tys
489 bang_pat = anyBag (isBangHsBind . unLoc) mbind
490 check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
491 (badStrictSig unlifted sig)
492 check_sig other = return ()
494 strictBindErr flavour unlifted mbind
495 = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:")) 4 (ppr mbind)
497 msg | unlifted = ptext SLIT("bindings for unlifted types")
498 | otherwise = ptext SLIT("bang-pattern bindings")
500 badStrictSig unlifted sig
501 = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
504 msg | unlifted = ptext SLIT("an unlifted binding")
505 | otherwise = ptext SLIT("a bang-pattern binding")
509 %************************************************************************
511 \subsection{tcMonoBind}
513 %************************************************************************
515 @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
516 The signatures have been dealt with already.
519 tcMonoBinds :: [LHsBind Name]
521 -> RecFlag -- Whether the binding is recursive for typechecking purposes
522 -- i.e. the binders are mentioned in their RHSs, and
523 -- we are not resuced by a type signature
524 -> TcM (LHsBinds TcId, [MonoBindInfo])
526 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
527 fun_matches = matches, bind_fvs = fvs })]
528 sig_fn -- Single function binding,
529 NonRecursive -- binder isn't mentioned in RHS,
530 | Nothing <- sig_fn name -- ...with no type signature
531 = -- In this very special case we infer the type of the
532 -- right hand side first (it may have a higher-rank type)
533 -- and *then* make the monomorphic Id for the LHS
534 -- e.g. f = \(x::forall a. a->a) -> <body>
535 -- We want to infer a higher-rank type for f
537 do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name matches)
539 -- Check for an unboxed tuple type
540 -- f = (# True, False #)
541 -- Zonk first just in case it's hidden inside a meta type variable
542 -- (This shows up as a (more obscure) kind error
543 -- in the 'otherwise' case of tcMonoBinds.)
544 ; zonked_rhs_ty <- zonkTcType rhs_ty
545 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
546 (unboxedTupleErr name zonked_rhs_ty)
548 ; mono_name <- newLocalName name
549 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
550 ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
551 fun_matches = matches', bind_fvs = fvs,
552 fun_co_fn = co_fn })),
553 [(name, Nothing, mono_id)]) }
555 tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
556 fun_matches = matches, bind_fvs = fvs })]
557 sig_fn -- Single function binding
559 | Just sig <- sig_fn name -- ...with a type signature
560 = -- When we have a single function binding, with a type signature
561 -- we can (a) use genuine, rigid skolem constants for the type variables
562 -- (b) bring (rigid) scoped type variables into scope
564 do { tc_sig <- tcInstSig True sig
565 ; mono_name <- newLocalName name
566 ; let mono_ty = sig_tau tc_sig
567 mono_id = mkLocalId mono_name mono_ty
568 rhs_tvs = [ (name, mkTyVarTy tv)
569 | (name, tv) <- sig_scoped tc_sig `zip` sig_tvs tc_sig ]
571 ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
572 tcMatchesFun mono_name matches mono_ty
574 ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
575 fun_infix = inf, fun_matches = matches',
576 bind_fvs = placeHolderNames, fun_co_fn = co_fn }
577 ; return (unitBag (L b_loc fun_bind'),
578 [(name, Just tc_sig, mono_id)]) }
580 tcMonoBinds binds sig_fn non_rec
581 = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
583 -- Bring the monomorphic Ids, into scope for the RHSs
584 ; let mono_info = getMonoBindInfo tc_binds
585 rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
586 -- A monomorphic binding for each term variable that lacks
587 -- a type sig. (Ones with a sig are already in scope.)
589 ; binds' <- tcExtendIdEnv2 rhs_id_env $
590 traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
591 | (n,id) <- rhs_id_env]) `thenM_`
592 mapM (wrapLocM tcRhs) tc_binds
593 ; return (listToBag binds', mono_info) }
595 ------------------------
596 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
597 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
598 -- if there's a signature for it, use the instantiated signature type
599 -- otherwise invent a type variable
600 -- You see that quite directly in the FunBind case.
602 -- But there's a complication for pattern bindings:
603 -- data T = MkT (forall a. a->a)
605 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
606 -- but we want to get (f::forall a. a->a) as the RHS environment.
607 -- The simplest way to do this is to typecheck the pattern, and then look up the
608 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
609 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
611 data TcMonoBind -- Half completed; LHS done, RHS not done
612 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
613 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
615 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
616 -- Type signature (if any), and
617 -- the monomorphic bound things
619 bndrNames :: [MonoBindInfo] -> [Name]
620 bndrNames mbi = [n | (n,_,_) <- mbi]
622 getMonoType :: MonoBindInfo -> TcTauType
623 getMonoType (_,_,mono_id) = idType mono_id
625 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
626 tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
627 = do { mb_sig <- tcInstSig_maybe (sig_fn name)
628 ; mono_name <- newLocalName name
629 ; mono_ty <- mk_mono_ty mb_sig
630 ; let mono_id = mkLocalId mono_name mono_ty
631 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
633 mk_mono_ty (Just sig) = return (sig_tau sig)
634 mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
636 tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
637 = do { mb_sigs <- mapM (tcInstSig_maybe . sig_fn) names
639 ; let nm_sig_prs = names `zip` mb_sigs
640 tau_sig_env = mkNameEnv [ (name, sig_tau sig) | (name, Just sig) <- nm_sig_prs]
641 sig_tau_fn = lookupNameEnv tau_sig_env
643 tc_pat exp_ty = tcPat (LetPat sig_tau_fn) pat exp_ty unitTy $ \ _ ->
644 mapM lookup_info nm_sig_prs
645 -- The unitTy is a bit bogus; it's the "result type" for lookup_info.
647 -- After typechecking the pattern, look up the binder
648 -- names, which the pattern has brought into scope.
649 lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
650 lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
651 ; return (name, mb_sig, mono_id) }
653 ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
656 ; return (TcPatBind infos pat' grhss pat_ty) }
658 names = collectPatBinders pat
661 tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
662 -- AbsBind, VarBind impossible
665 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
666 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
667 = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) matches
669 ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
670 bind_fvs = placeHolderNames, fun_co_fn = co_fn }) }
672 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
673 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
674 tcGRHSsPat grhss pat_ty
675 ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty,
676 bind_fvs = placeHolderNames }) }
679 ---------------------
680 getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
681 getMonoBindInfo tc_binds
682 = foldr (get_info . unLoc) [] tc_binds
684 get_info (TcFunBind info _ _ _) rest = info : rest
685 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
689 %************************************************************************
693 %************************************************************************
696 generalise :: TopLevelFlag -> Bool
697 -> [MonoBindInfo] -> [Inst]
698 -> TcM ([TcTyVar], TcDictBinds, [TcId])
699 generalise top_lvl is_unrestricted mono_infos lie_req
700 | not is_unrestricted -- RESTRICTED CASE
701 = -- Check signature contexts are empty
702 do { checkTc (all is_mono_sig sigs)
703 (restrictedBindCtxtErr bndrs)
705 -- Now simplify with exactly that set of tyvars
706 -- We have to squash those Methods
707 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
710 -- Check that signature type variables are OK
711 ; final_qtvs <- checkSigsTyVars qtvs sigs
713 ; return (final_qtvs, binds, []) }
715 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
716 = tcSimplifyInfer doc tau_tvs lie_req
718 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
719 = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty
720 ; let -- The "sig_avails" is the stuff available. We get that from
721 -- the context of the type signature, BUT ALSO the lie_avail
722 -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
723 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
724 sig_avails = sig_lie ++ local_meths
726 -- Check that the needed dicts can be
727 -- expressed in terms of the signature ones
728 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
730 -- Check that signature type variables are OK
731 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
733 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
735 bndrs = bndrNames mono_infos
736 sigs = [sig | (_, Just sig, _) <- mono_infos]
737 tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos
738 -- NB: exactTyVarsOfType; see Note [Silly type synonym]
739 -- near defn of TcType.exactTyVarsOfType
740 is_mono_sig sig = null (sig_theta sig)
741 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
743 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
744 sig_theta = theta, sig_loc = loc }) mono_id
745 = Method mono_id poly_id (mkTyVarTys tvs) theta loc
748 unifyCtxts checks that all the signature contexts are the same
749 The type signatures on a mutually-recursive group of definitions
750 must all have the same context (or none).
752 The trick here is that all the signatures should have the same
753 context, and we want to share type variables for that context, so that
754 all the right hand sides agree a common vocabulary for their type
757 We unify them because, with polymorphic recursion, their types
758 might not otherwise be related. This is a rather subtle issue.
761 unifyCtxts :: [TcSigInfo] -> TcM [Inst]
762 unifyCtxts (sig1 : sigs) -- Argument is always non-empty
763 = do { mapM unify_ctxt sigs
764 ; newDictsAtLoc (sig_loc sig1) (sig_theta sig1) }
766 theta1 = sig_theta sig1
767 unify_ctxt :: TcSigInfo -> TcM ()
768 unify_ctxt sig@(TcSigInfo { sig_theta = theta })
769 = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
770 addErrCtxt (sigContextsCtxt sig1 sig) $
771 unifyTheta theta1 theta
773 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
774 checkSigsTyVars qtvs sigs
775 = do { gbl_tvs <- tcGetGlobalTyVars
776 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
778 ; let -- Sigh. Make sure that all the tyvars in the type sigs
779 -- appear in the returned ty var list, which is what we are
780 -- going to generalise over. Reason: we occasionally get
782 -- type T a = () -> ()
785 -- Here, 'a' won't appear in qtvs, so we have to add it
786 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
787 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
790 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
791 sig_theta = theta, sig_tau = tau})
792 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
793 addErrCtxtM (sigCtxt id tvs theta tau) $
794 do { tvs' <- checkDistinctTyVars tvs
795 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
796 (bleatEscapedTvs gbl_tvs tvs tvs')
799 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
800 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
801 -- are still all type variables, and all distinct from each other.
802 -- It returns a zonked set of type variables.
803 -- For example, if the type sig is
804 -- f :: forall a b. a -> b -> b
805 -- we want to check that 'a' and 'b' haven't
806 -- (a) been unified with a non-tyvar type
807 -- (b) been unified with each other (all distinct)
809 checkDistinctTyVars sig_tvs
810 = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
811 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
812 ; return zonked_tvs }
814 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
815 -- The TyVarEnv maps each zonked type variable back to its
816 -- corresponding user-written signature type variable
817 check_dup acc (sig_tv, zonked_tv)
818 = case lookupVarEnv acc zonked_tv of
819 Just sig_tv' -> bomb_out sig_tv sig_tv'
821 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
823 bomb_out sig_tv1 sig_tv2
824 = do { env0 <- tcInitTidyEnv
825 ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
826 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
827 msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
828 <+> ptext SLIT("is unified with another quantified type variable")
829 <+> quotes (ppr tidy_tv2)
830 ; failWithTcM (env2, msg) }
835 @getTyVarsToGen@ decides what type variables to generalise over.
837 For a "restricted group" -- see the monomorphism restriction
838 for a definition -- we bind no dictionaries, and
839 remove from tyvars_to_gen any constrained type variables
841 *Don't* simplify dicts at this point, because we aren't going
842 to generalise over these dicts. By the time we do simplify them
843 we may well know more. For example (this actually came up)
845 f x = array ... xs where xs = [1,2,3,4,5]
846 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
847 stuff. If we simplify only at the f-binding (not the xs-binding)
848 we'll know that the literals are all Ints, and we can just produce
851 Find all the type variables involved in overloading, the
852 "constrained_tyvars". These are the ones we *aren't* going to
853 generalise. We must be careful about doing this:
855 (a) If we fail to generalise a tyvar which is not actually
856 constrained, then it will never, ever get bound, and lands
857 up printed out in interface files! Notorious example:
858 instance Eq a => Eq (Foo a b) where ..
859 Here, b is not constrained, even though it looks as if it is.
860 Another, more common, example is when there's a Method inst in
861 the LIE, whose type might very well involve non-overloaded
863 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
864 the simple thing instead]
866 (b) On the other hand, we mustn't generalise tyvars which are constrained,
867 because we are going to pass on out the unmodified LIE, with those
868 tyvars in it. They won't be in scope if we've generalised them.
870 So we are careful, and do a complete simplification just to find the
871 constrained tyvars. We don't use any of the results, except to
872 find which tyvars are constrained.
874 Note [Polymorphic recursion]
875 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
876 The game plan for polymorphic recursion in the code above is
878 * Bind any variable for which we have a type signature
879 to an Id with a polymorphic type. Then when type-checking
880 the RHSs we'll make a full polymorphic call.
882 This fine, but if you aren't a bit careful you end up with a horrendous
883 amount of partial application and (worse) a huge space leak. For example:
885 f :: Eq a => [a] -> [a]
888 If we don't take care, after typechecking we get
890 f = /\a -> \d::Eq a -> let f' = f a d
894 Notice the the stupid construction of (f a d), which is of course
895 identical to the function we're executing. In this case, the
896 polymorphic recursion isn't being used (but that's a very common case).
897 This can lead to a massive space leak, from the following top-level defn
903 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
904 f' is another thunk which evaluates to the same thing... and you end
905 up with a chain of identical values all hung onto by the CAF ff.
909 = let f' = f Int dEqInt in \ys. ...f'...
911 = let f' = let f' = f Int dEqInt in \ys. ...f'...
916 NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
917 which would make the space leak go away in this case
919 Solution: when typechecking the RHSs we always have in hand the
920 *monomorphic* Ids for each binding. So we just need to make sure that
921 if (Method f a d) shows up in the constraints emerging from (...f...)
922 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
923 to the "givens" when simplifying constraints. That's what the "lies_avail"
928 f = /\a -> \d::Eq a -> letrec
929 fm = \ys:[a] -> ...fm...
935 %************************************************************************
939 %************************************************************************
941 Type signatures are tricky. See Note [Signature skolems] in TcType
943 @tcSigs@ checks the signatures for validity, and returns a list of
944 {\em freshly-instantiated} signatures. That is, the types are already
945 split up, and have fresh type variables installed. All non-type-signature
946 "RenamedSigs" are ignored.
948 The @TcSigInfo@ contains @TcTypes@ because they are unified with
949 the variable's type, and after that checked to see whether they've
953 type TcSigFun = Name -> Maybe (LSig Name)
955 mkSigFun :: [LSig Name] -> TcSigFun
956 -- Search for a particular type signature
957 -- Precondition: the sigs are all type sigs
958 -- Precondition: no duplicates
959 mkSigFun sigs = lookupNameEnv env
961 env = mkNameEnv [(fromJust (sigName sig), sig) | sig <- sigs]
966 sig_id :: TcId, -- *Polymorphic* binder for this value...
968 sig_scoped :: [Name], -- Names for any scoped type variables
969 -- Invariant: correspond 1-1 with an initial
970 -- segment of sig_tvs (see Note [Scoped])
972 sig_tvs :: [TcTyVar], -- Instantiated type variables
973 -- See Note [Instantiate sig]
975 sig_theta :: TcThetaType, -- Instantiated theta
976 sig_tau :: TcTauType, -- Instantiated tau
977 sig_loc :: InstLoc -- The location of the signature
981 -- There may be more instantiated type variables than scoped
982 -- ones. For example:
983 -- type T a = forall b. b -> (a,b)
984 -- f :: forall c. T c
985 -- Here, the signature for f will have one scoped type variable, c,
986 -- but two instantiated type variables, c' and b'.
988 -- We assume that the scoped ones are at the *front* of sig_tvs,
989 -- and remember the names from the original HsForAllTy in sig_scoped
991 -- Note [Instantiate sig]
992 -- It's vital to instantiate a type signature with fresh variable.
994 -- type S = forall a. a->a
998 -- Here, we must use distinct type variables when checking f,g's right hand sides.
999 -- (Instantiation is only necessary because of type synonyms. Otherwise,
1000 -- it's all cool; each signature has distinct type variables from the renamer.)
1002 instance Outputable TcSigInfo where
1003 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
1004 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
1008 tcTySig :: LSig Name -> TcM TcId
1009 tcTySig (L span (TypeSig (L _ name) ty))
1011 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
1012 ; return (mkLocalId name sigma_ty) }
1015 tcInstSig_maybe :: Maybe (LSig Name) -> TcM (Maybe TcSigInfo)
1016 -- Instantiate with *meta* type variables;
1017 -- this signature is part of a multi-signature group
1018 tcInstSig_maybe Nothing = return Nothing
1019 tcInstSig_maybe (Just sig) = do { tc_sig <- tcInstSig False sig
1020 ; return (Just tc_sig) }
1022 tcInstSig :: Bool -> LSig Name -> TcM TcSigInfo
1023 -- Instantiate the signature, with either skolems or meta-type variables
1024 -- depending on the use_skols boolean
1026 -- We always instantiate with freshs uniques,
1027 -- although we keep the same print-name
1029 -- type T = forall a. [a] -> [a]
1031 -- f = g where { g :: T; g = <rhs> }
1033 -- We must not use the same 'a' from the defn of T at both places!!
1035 tcInstSig use_skols (L loc (TypeSig (L _ name) hs_ty))
1037 do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
1038 -- scope when starting the binding group
1039 ; let skol_info = SigSkol (FunSigCtxt name)
1040 inst_tyvars | use_skols = tcInstSkolTyVars skol_info
1041 | otherwise = tcInstSigTyVars skol_info
1042 ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
1043 ; loc <- getInstLoc (SigOrigin skol_info)
1044 ; return (TcSigInfo { sig_id = poly_id,
1045 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
1046 sig_scoped = scoped_names, sig_loc = loc }) }
1047 -- Note that the scoped_names and the sig_tvs will have
1048 -- different Names. That's quite ok; when we bring the
1049 -- scoped_names into scope, we just bind them to the sig_tvs
1051 -- The scoped names are the ones explicitly mentioned
1052 -- in the HsForAll. (There may be more in sigma_ty, because
1053 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
1054 -- We also only have scoped type variables when we are instantiating
1055 -- with true skolems
1056 scoped_names = case (use_skols, hs_ty) of
1057 (True, L _ (HsForAllTy Explicit tvs _ _)) -> hsLTyVarNames tvs
1061 isUnRestrictedGroup :: [LHsBind Name] -> TcSigFun -> TcM Bool
1062 isUnRestrictedGroup binds sig_fn
1063 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
1064 ; return (not mono_restriction || all_unrestricted) }
1066 all_unrestricted = all (unrestricted . unLoc) binds
1067 has_sig n = isJust (sig_fn n)
1069 unrestricted (PatBind {}) = False
1070 unrestricted (VarBind { var_id = v }) = has_sig v
1071 unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
1072 || has_sig (unLoc v)
1074 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
1075 -- No args => like a pattern binding
1076 unrestricted_match other = True
1077 -- Some args => a function binding
1081 %************************************************************************
1083 \subsection[TcBinds-errors]{Error contexts and messages}
1085 %************************************************************************
1089 -- This one is called on LHS, when pat and grhss are both Name
1090 -- and on RHS, when pat is TcId and grhss is still Name
1091 patMonoBindsCtxt pat grhss
1092 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
1094 -----------------------------------------------
1095 sigContextsCtxt sig1 sig2
1096 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
1097 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
1098 ppr id2 <+> dcolon <+> ppr (idType id2)]),
1099 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
1105 -----------------------------------------------
1106 unboxedTupleErr name ty
1107 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
1108 4 (ppr name <+> dcolon <+> ppr ty)
1110 -----------------------------------------------
1111 restrictedBindCtxtErr binder_names
1112 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
1113 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
1114 ptext SLIT("that falls under the monomorphism restriction")])
1116 genCtxt binder_names
1117 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names