2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBinds,
8 tcHsBootSigs, tcMonoBinds, tcSpecSigs,
11 #include "HsVersions.h"
13 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
14 import {-# SOURCE #-} TcExpr ( tcCheckSigma, tcCheckRho )
16 import DynFlags ( DynFlag(Opt_MonomorphismRestriction) )
17 import HsSyn ( HsExpr(..), HsBind(..), LHsBinds, Sig(..),
18 LSig, Match(..), HsBindGroup(..), IPBind(..),
19 HsType(..), HsExplicitForAll(..), hsLTyVarNames, isVanillaLSig,
20 LPat, GRHSs, MatchGroup(..), emptyLHsBinds, isEmptyLHsBinds,
21 collectHsBindBinders, collectPatBinders, pprPatBind
23 import TcHsSyn ( TcId, TcDictBinds, zonkId, mkHsLet )
26 import Inst ( InstOrigin(..), newDictsAtLoc, newIPDict, instToId )
27 import TcEnv ( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2,
28 newLocalName, tcLookupLocalIds, pprBinders,
30 import TcUnify ( Expected(..), tcInfer, unifyTheta,
31 bleatEscapedTvs, sigCtxt )
32 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted,
33 tcSimplifyToDicts, tcSimplifyIPs )
34 import TcHsType ( tcHsSigType, UserTypeCtxt(..), tcAddLetBoundTyVars,
35 TcSigInfo(..), TcSigFun, lookupSig
37 import TcPat ( tcPat, PatCtxt(..) )
38 import TcSimplify ( bindInstsOfLocalFuns )
39 import TcMType ( newTyFlexiVarTy, zonkQuantifiedTyVar,
40 tcInstSigType, zonkTcTypes, zonkTcTyVar )
41 import TcType ( TcTyVar, SkolemInfo(SigSkol),
42 TcTauType, TcSigmaType,
43 mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
44 mkForAllTy, isUnLiftedType, tcGetTyVar,
45 mkTyVarTys, tidyOpenTyVar )
46 import Kind ( argTypeKind )
47 import VarEnv ( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv, emptyTidyEnv )
48 import TysPrim ( alphaTyVar )
49 import Id ( Id, mkLocalId, mkVanillaGlobal, mkSpecPragmaId, setInlinePragma )
50 import IdInfo ( vanillaIdInfo )
51 import Var ( idType, idName )
55 import SrcLoc ( Located(..), unLoc, noLoc, getLoc )
57 import ErrUtils ( Message )
59 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isRec,
60 isNotTopLevel, isAlwaysActive )
61 import FiniteMap ( listToFM, lookupFM )
66 %************************************************************************
68 \subsection{Type-checking bindings}
70 %************************************************************************
72 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
73 it needs to know something about the {\em usage} of the things bound,
74 so that it can create specialisations of them. So @tcBindsAndThen@
75 takes a function which, given an extended environment, E, typechecks
76 the scope of the bindings returning a typechecked thing and (most
77 important) an LIE. It is this LIE which is then used as the basis for
78 specialising the things bound.
80 @tcBindsAndThen@ also takes a "combiner" which glues together the
81 bindings and the "thing" to make a new "thing".
83 The real work is done by @tcBindWithSigsAndThen@.
85 Recursive and non-recursive binds are handled in essentially the same
86 way: because of uniques there are no scoping issues left. The only
87 difference is that non-recursive bindings can bind primitive values.
89 Even for non-recursive binding groups we add typings for each binder
90 to the LVE for the following reason. When each individual binding is
91 checked the type of its LHS is unified with that of its RHS; and
92 type-checking the LHS of course requires that the binder is in scope.
94 At the top-level the LIE is sure to contain nothing but constant
95 dictionaries, which we resolve at the module level.
98 tcTopBinds :: [HsBindGroup Name] -> TcM (LHsBinds TcId, TcLclEnv)
99 -- Note: returning the TcLclEnv is more than we really
100 -- want. The bit we care about is the local bindings
101 -- and the free type variables thereof
103 = tc_binds_and_then TopLevel glue binds $
104 do { env <- getLclEnv
105 ; return (emptyLHsBinds, env) }
107 -- The top level bindings are flattened into a giant
108 -- implicitly-mutually-recursive MonoBinds
109 glue (HsBindGroup binds1 _ _) (binds2, env) = (binds1 `unionBags` binds2, env)
110 glue (HsIPBinds _) _ = panic "Top-level HsIpBinds"
111 -- Can't have a HsIPBinds at top level
113 tcHsBootSigs :: [HsBindGroup Name] -> TcM [Id]
114 -- A hs-boot file has only one BindGroup, and it only has type
115 -- signatures in it. The renamer checked all this
116 tcHsBootSigs [HsBindGroup binds sigs _]
117 = do { checkTc (isEmptyLHsBinds binds) badBootDeclErr
118 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
120 tc_boot_sig (Sig (L _ name) ty)
121 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
122 ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
123 -- Notice that we make GlobalIds, not LocalIds
124 tcHsBootSits groups = pprPanic "tcHsBootSigs" (ppr groups)
126 badBootDeclErr :: Message
127 badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file")
130 :: (HsBindGroup TcId -> thing -> thing) -- Combinator
131 -> [HsBindGroup Name]
135 tcBindsAndThen = tc_binds_and_then NotTopLevel
137 tc_binds_and_then top_lvl combiner [] do_next
139 tc_binds_and_then top_lvl combiner (group : groups) do_next
140 = tc_bind_and_then top_lvl combiner group $
141 tc_binds_and_then top_lvl combiner groups do_next
143 tc_bind_and_then top_lvl combiner (HsIPBinds binds) do_next
144 = getLIE do_next `thenM` \ (result, expr_lie) ->
145 mapAndUnzipM (wrapLocSndM tc_ip_bind) binds `thenM` \ (avail_ips, binds') ->
147 -- If the binding binds ?x = E, we must now
148 -- discharge any ?x constraints in expr_lie
149 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
151 returnM (combiner (HsIPBinds binds') $
152 combiner (HsBindGroup dict_binds [] Recursive) result)
154 -- I wonder if we should do these one at at time
157 tc_ip_bind (IPBind ip expr)
158 = newTyFlexiVarTy argTypeKind `thenM` \ ty ->
159 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
160 tcCheckRho expr ty `thenM` \ expr' ->
161 returnM (ip_inst, (IPBind ip' expr'))
163 tc_bind_and_then top_lvl combiner (HsBindGroup binds sigs is_rec) do_next
164 | isEmptyLHsBinds binds
167 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
168 -- Notice that they scope over
169 -- a) the type signatures in the binding group
170 -- b) the bindings in the group
171 -- c) the scope of the binding group (the "in" part)
172 tcAddLetBoundTyVars binds $
175 TopLevel -- For the top level don't bother will all this
176 -- bindInstsOfLocalFuns stuff. All the top level
177 -- things are rec'd together anyway, so it's fine to
178 -- leave them to the tcSimplifyTop, and quite a bit faster too
179 -> tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
180 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
181 returnM (combiner (HsBindGroup
182 (poly_binds `unionBags` prag_binds)
187 NotTopLevel -- For nested bindings we must do the bindInstsOfLocalFuns thing.
188 | not (isRec is_rec) -- Non-recursive group
189 -> -- We want to keep non-recursive things non-recursive
190 -- so that we desugar unlifted bindings correctly
191 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
192 getLIE (tc_body poly_ids) `thenM` \ ((prag_binds, thing), lie) ->
194 -- Create specialisations of functions bound here
195 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
198 combiner (HsBindGroup poly_binds [] NonRecursive) $
199 combiner (HsBindGroup prag_binds [] NonRecursive) $
200 combiner (HsBindGroup lie_binds [] Recursive) $
201 -- NB: the binds returned by tcSimplify and
202 -- bindInstsOfLocalFuns aren't guaranteed in
203 -- dependency order (though we could change that);
204 -- hence the Recursive marker.
208 -> -- NB: polymorphic recursion means that a function
209 -- may use an instance of itself, we must look at the LIE arising
210 -- from the function's own right hand side. Hence the getLIE
211 -- encloses the tcBindWithSigs.
214 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
215 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
216 returnM (poly_ids, poly_binds `unionBags` prag_binds, thing)
217 ) `thenM` \ ((poly_ids, extra_binds, thing), lie) ->
219 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
221 returnM (combiner (HsBindGroup
222 (extra_binds `unionBags` lie_binds)
226 tc_body poly_ids -- Type check the pragmas and "thing inside"
227 = -- Extend the environment to bind the new polymorphic Ids
228 tcExtendIdEnv poly_ids $
230 -- Build bindings and IdInfos corresponding to user pragmas
231 tcSpecSigs sigs `thenM` \ prag_binds ->
233 -- Now do whatever happens next, in the augmented envt
234 do_next `thenM` \ thing ->
236 returnM (prag_binds, thing)
240 %************************************************************************
242 \subsection{tcBindWithSigs}
244 %************************************************************************
246 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
247 so all the clever stuff is in here.
249 * binder_names and mbind must define the same set of Names
251 * The Names in tc_ty_sigs must be a subset of binder_names
253 * The Ids in tc_ty_sigs don't necessarily have to have the same name
254 as the Name in the tc_ty_sig
257 tcBindWithSigs :: TopLevelFlag
261 -> TcM (LHsBinds TcId, [TcId])
262 -- The returned TcIds are guaranteed zonked
264 tcBindWithSigs top_lvl mbind sigs is_rec = do
265 { -- TYPECHECK THE SIGNATURES
266 tc_ty_sigs <- recoverM (returnM []) $
267 tcTySigs (filter isVanillaLSig sigs)
268 ; let lookup_sig = lookupSig tc_ty_sigs
270 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
271 ; recoverM (recoveryCode mbind lookup_sig) $ do
273 { traceTc (ptext SLIT("--------------------------------------------------------"))
274 ; traceTc (ptext SLIT("Bindings for") <+> ppr (collectHsBindBinders mbind))
276 -- TYPECHECK THE BINDINGS
277 ; ((mbind', mono_bind_infos), lie_req)
278 <- getLIE (tcMonoBinds mbind lookup_sig is_rec)
280 -- CHECK FOR UNLIFTED BINDINGS
281 -- These must be non-recursive etc, and are not generalised
282 -- They desugar to a case expression in the end
283 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
284 ; if any isUnLiftedType zonked_mono_tys then
285 do { -- Unlifted bindings
286 checkUnliftedBinds top_lvl is_rec mbind
288 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
289 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id)
290 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id)
292 ; return ( unitBag $ noLoc $ AbsBinds [] [] exports emptyNameSet mbind',
293 [poly_id | (_, poly_id, _) <- exports]) } -- Guaranteed zonked
295 else do -- The normal lifted case: GENERALISE
296 { is_unres <- isUnRestrictedGroup mbind tc_ty_sigs
297 ; (tyvars_to_gen, dict_binds, dict_ids)
298 <- setSrcSpan (getLoc (head (bagToList mbind))) $
299 -- TODO: location a bit awkward, but the mbinds have been
300 -- dependency analysed and may no longer be adjacent
301 addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
302 generalise top_lvl is_unres mono_bind_infos tc_ty_sigs lie_req
304 -- FINALISE THE QUANTIFIED TYPE VARIABLES
305 -- The quantified type variables often include meta type variables
306 -- we want to freeze them into ordinary type variables, and
307 -- default their kind (e.g. from OpenTypeKind to TypeKind)
308 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
310 -- BUILD THE POLYMORPHIC RESULT IDs
312 exports = map mk_export mono_bind_infos
313 poly_ids = [poly_id | (_, poly_id, _) <- exports]
314 dict_tys = map idType dict_ids
316 inlines = mkNameSet [ name
317 | L _ (InlineSig True (L _ name) _) <- sigs]
318 -- Any INLINE sig (regardless of phase control)
319 -- makes the RHS look small
320 inline_phases = listToFM [ (name, phase)
321 | L _ (InlineSig _ (L _ name) phase) <- sigs,
322 not (isAlwaysActive phase)]
323 -- Set the IdInfo field to control the inline phase
324 -- AlwaysActive is the default, so don't bother with them
325 add_inlines id = attachInlinePhase inline_phases id
327 mk_export (binder_name, mb_sig, mono_id)
329 Just sig -> (sig_tvs sig, add_inlines (sig_id sig), mono_id)
330 Nothing -> (tyvars_to_gen', add_inlines new_poly_id, mono_id)
332 new_poly_id = mkLocalId binder_name poly_ty
333 poly_ty = mkForAllTys tyvars_to_gen'
337 -- ZONK THE poly_ids, because they are used to extend the type
338 -- environment; see the invariant on TcEnv.tcExtendIdEnv
339 ; zonked_poly_ids <- mappM zonkId poly_ids
341 ; traceTc (text "binding:" <+> ppr ((dict_ids, dict_binds),
342 exports, map idType zonked_poly_ids))
346 AbsBinds tyvars_to_gen'
350 (dict_binds `unionBags` mbind'),
355 -- If typechecking the binds fails, then return with each
356 -- signature-less binder given type (forall a.a), to minimise
357 -- subsequent error messages
358 recoveryCode mbind lookup_sig
359 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
360 ; return (emptyLHsBinds, poly_ids) }
362 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
363 binder_names = collectHsBindBinders mbind
364 poly_ids = map mk_dummy binder_names
365 mk_dummy name = case lookup_sig name of
366 Just sig -> sig_id sig -- Signature
367 Nothing -> mkLocalId name forall_a_a -- No signature
369 attachInlinePhase inline_phases bndr
370 = case lookupFM inline_phases (idName bndr) of
371 Just prag -> bndr `setInlinePragma` prag
374 -- Check that non-overloaded unlifted bindings are
377 -- c) not a multiple-binding group (more or less implied by (a))
379 checkUnliftedBinds top_lvl is_rec mbind
380 = checkTc (isNotTopLevel top_lvl)
381 (unliftedBindErr "Top-level" mbind) `thenM_`
382 checkTc (isNonRec is_rec)
383 (unliftedBindErr "Recursive" mbind) `thenM_`
384 checkTc (isSingletonBag mbind)
385 (unliftedBindErr "Multiple" mbind)
389 Polymorphic recursion
390 ~~~~~~~~~~~~~~~~~~~~~
391 The game plan for polymorphic recursion in the code above is
393 * Bind any variable for which we have a type signature
394 to an Id with a polymorphic type. Then when type-checking
395 the RHSs we'll make a full polymorphic call.
397 This fine, but if you aren't a bit careful you end up with a horrendous
398 amount of partial application and (worse) a huge space leak. For example:
400 f :: Eq a => [a] -> [a]
403 If we don't take care, after typechecking we get
405 f = /\a -> \d::Eq a -> let f' = f a d
409 Notice the the stupid construction of (f a d), which is of course
410 identical to the function we're executing. In this case, the
411 polymorphic recursion isn't being used (but that's a very common case).
414 f = /\a -> \d::Eq a -> letrec
415 fm = \ys:[a] -> ...fm...
419 This can lead to a massive space leak, from the following top-level defn
425 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
426 f' is another thunk which evaluates to the same thing... and you end
427 up with a chain of identical values all hung onto by the CAF ff.
431 = let f' = f Int dEqInt in \ys. ...f'...
433 = let f' = let f' = f Int dEqInt in \ys. ...f'...
437 Solution: when typechecking the RHSs we always have in hand the
438 *monomorphic* Ids for each binding. So we just need to make sure that
439 if (Method f a d) shows up in the constraints emerging from (...f...)
440 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
441 to the "givens" when simplifying constraints. That's what the "lies_avail"
445 %************************************************************************
447 \subsection{tcMonoBind}
449 %************************************************************************
451 @tcMonoBinds@ deals with a single @MonoBind@.
452 The signatures have been dealt with already.
455 tcMonoBinds :: LHsBinds Name
456 -> TcSigFun -> RecFlag
457 -> TcM (LHsBinds TcId, [MonoBindInfo])
459 tcMonoBinds binds lookup_sig is_rec
460 | isNonRec is_rec, -- Non-recursive, single function binding
461 [L b_loc (FunBind (L nm_loc name) inf matches)] <- bagToList binds,
462 Nothing <- lookup_sig name -- ...with no type signature
463 = -- In this very special case we infer the type of the
464 -- right hand side first (it may have a higher-rank type)
465 -- and *then* make the monomorphic Id for the LHS
466 -- e.g. f = \(x::forall a. a->a) -> <body>
467 -- We want to infer a higher-rank type for f
469 do { (matches', rhs_ty) <- tcInfer (tcMatchesFun name matches)
470 ; mono_name <- newLocalName name
471 ; let mono_id = mkLocalId mono_name rhs_ty
472 ; return (unitBag (L b_loc (FunBind (L nm_loc mono_id) inf matches')),
473 [(name, Nothing, mono_id)]) }
476 = do { tc_binds <- mapBagM (wrapLocM (tcLhs lookup_sig)) binds
478 -- Bring (a) the scoped type variables, and (b) the Ids, into scope for the RHSs
479 -- For (a) it's ok to bring them all into scope at once, even
480 -- though each type sig should scope only over its own RHS,
481 -- because the renamer has sorted all that out.
482 ; let mono_info = getMonoBindInfo tc_binds
483 rhs_tvs = [ (name, mkTyVarTy tv)
484 | (_, Just sig, _) <- mono_info,
485 (name, tv) <- sig_scoped sig `zip` sig_tvs sig ]
486 rhs_id_env = map mk mono_info -- A binding for each term variable
488 ; binds' <- tcExtendTyVarEnv2 rhs_tvs $
489 tcExtendIdEnv2 rhs_id_env $
490 traceTc (text "tcMonoBinds" <+> vcat [ppr n <+> ppr id <+> ppr (idType id) | (n,id) <- rhs_id_env]) `thenM_`
491 mapBagM (wrapLocM tcRhs) tc_binds
492 ; return (binds', mono_info) }
494 mk (name, Just sig, _) = (name, sig_id sig) -- Use the type sig if there is one
495 mk (name, Nothing, mono_id) = (name, mono_id) -- otherwise use a monomorphic version
497 ------------------------
498 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
499 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
500 -- if there's a signature for it, use the instantiated signature type
501 -- otherwise invent a type variable
502 -- You see that quite directly in the FunBind case.
504 -- But there's a complication for pattern bindings:
505 -- data T = MkT (forall a. a->a)
507 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
508 -- but we want to get (f::forall a. a->a) as the RHS environment.
509 -- The simplest way to do this is to typecheck the pattern, and then look up the
510 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
511 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
513 data TcMonoBind -- Half completed; LHS done, RHS not done
514 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
515 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
517 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
518 -- Type signature (if any), and
519 -- the monomorphic bound things
521 bndrNames :: [MonoBindInfo] -> [Name]
522 bndrNames mbi = [n | (n,_,_) <- mbi]
524 getMonoType :: MonoBindInfo -> TcTauType
525 getMonoType (_,_,mono_id) = idType mono_id
527 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
528 tcLhs lookup_sig (FunBind (L nm_loc name) inf matches)
529 = do { let mb_sig = lookup_sig name
530 ; mono_name <- newLocalName name
531 ; mono_ty <- mk_mono_ty mb_sig
532 ; let mono_id = mkLocalId mono_name mono_ty
533 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
535 mk_mono_ty (Just sig) = return (sig_tau sig)
536 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
538 tcLhs lookup_sig bind@(PatBind pat grhss _)
539 = do { let tc_pat exp_ty = tcPat (LetPat lookup_sig) pat exp_ty lookup_infos
540 ; ((pat', ex_tvs, infos), pat_ty)
541 <- addErrCtxt (patMonoBindsCtxt pat grhss)
544 -- Don't know how to deal with pattern-bound existentials yet
545 ; checkTc (null ex_tvs) (existentialExplode bind)
547 ; return (TcPatBind infos pat' grhss pat_ty) }
549 names = collectPatBinders pat
551 -- After typechecking the pattern, look up the binder
552 -- names, which the pattern has brought into scope.
553 lookup_infos :: TcM [MonoBindInfo]
554 lookup_infos = do { mono_ids <- tcLookupLocalIds names
555 ; return [ (name, lookup_sig name, mono_id)
556 | (name, mono_id) <- names `zip` mono_ids] }
558 tcLhs lookup_sig other_bind = pprPanic "tcLhs" (ppr other_bind)
559 -- AbsBind, VarBind impossible
562 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
563 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
564 = do { matches' <- tcMatchesFun (idName mono_id) matches
565 (Check (idType mono_id))
566 ; return (FunBind fun' inf matches') }
568 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
569 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
570 tcGRHSsPat grhss (Check pat_ty)
571 ; return (PatBind pat' grhss' pat_ty) }
574 ---------------------
575 getMonoBindInfo :: Bag (Located TcMonoBind) -> [MonoBindInfo]
576 getMonoBindInfo tc_binds
577 = foldrBag (get_info . unLoc) [] tc_binds
579 get_info (TcFunBind info _ _ _) rest = info : rest
580 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
584 %************************************************************************
586 \subsection{getTyVarsToGen}
588 %************************************************************************
590 Type signatures are tricky. See Note [Signature skolems] in TcType
593 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
594 -- The trick here is that all the signatures should have the same
595 -- context, and we want to share type variables for that context, so that
596 -- all the right hand sides agree a common vocabulary for their type
598 tcTySigs [] = return []
601 = do { (tc_sig1 : tc_sigs) <- mappM tcTySig sigs
602 ; mapM (check_ctxt tc_sig1) tc_sigs
603 ; return (tc_sig1 : tc_sigs) }
605 -- Check tha all the signature contexts are the same
606 -- The type signatures on a mutually-recursive group of definitions
607 -- must all have the same context (or none).
609 -- We unify them because, with polymorphic recursion, their types
610 -- might not otherwise be related. This is a rather subtle issue.
611 check_ctxt :: TcSigInfo -> TcSigInfo -> TcM ()
612 check_ctxt sig1@(TcSigInfo { sig_theta = theta1 }) sig@(TcSigInfo { sig_theta = theta })
613 = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
614 addErrCtxt (sigContextsCtxt sig1 sig) $
615 unifyTheta theta1 theta
618 tcTySig :: LSig Name -> TcM TcSigInfo
619 tcTySig (L span (Sig (L _ name) ty))
621 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
622 ; (tvs, theta, tau) <- tcInstSigType name scoped_names sigma_ty
623 ; loc <- getInstLoc (SigOrigin (SigSkol name))
624 ; return (TcSigInfo { sig_id = mkLocalId name sigma_ty,
625 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
626 sig_scoped = scoped_names, sig_loc = loc }) }
628 -- The scoped names are the ones explicitly mentioned
629 -- in the HsForAll. (There may be more in sigma_ty, because
630 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
631 scoped_names = case ty of
632 L _ (HsForAllTy Explicit tvs _ _) -> hsLTyVarNames tvs
637 generalise :: TopLevelFlag -> Bool -> [MonoBindInfo] -> [TcSigInfo] -> [Inst]
638 -> TcM ([TcTyVar], TcDictBinds, [TcId])
639 generalise top_lvl is_unrestricted mono_infos sigs lie_req
640 | not is_unrestricted -- RESTRICTED CASE
641 = -- Check signature contexts are empty
642 do { checkTc (all is_mono_sig sigs)
643 (restrictedBindCtxtErr bndr_names)
645 -- Now simplify with exactly that set of tyvars
646 -- We have to squash those Methods
647 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndr_names
650 -- Check that signature type variables are OK
651 ; final_qtvs <- checkSigsTyVars qtvs sigs
653 ; return (final_qtvs, binds, []) }
655 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
656 = tcSimplifyInfer doc tau_tvs lie_req
658 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
659 = do { let sig1 = head sigs
660 ; sig_lie <- newDictsAtLoc (sig_loc sig1) (sig_theta sig1)
661 ; let -- The "sig_avails" is the stuff available. We get that from
662 -- the context of the type signature, BUT ALSO the lie_avail
663 -- so that polymorphic recursion works right (see comments at end of fn)
664 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
665 sig_avails = sig_lie ++ local_meths
667 -- Check that the needed dicts can be
668 -- expressed in terms of the signature ones
669 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
671 -- Check that signature type variables are OK
672 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
674 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
677 bndr_names = bndrNames mono_infos
678 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
679 is_mono_sig sig = null (sig_theta sig)
680 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndr_names
682 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
683 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
684 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
686 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
687 checkSigsTyVars qtvs sigs
688 = do { gbl_tvs <- tcGetGlobalTyVars
689 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
691 ; let -- Sigh. Make sure that all the tyvars in the type sigs
692 -- appear in the returned ty var list, which is what we are
693 -- going to generalise over. Reason: we occasionally get
695 -- type T a = () -> ()
698 -- Here, 'a' won't appear in qtvs, so we have to add it
699 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
700 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
703 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
704 sig_theta = theta, sig_tau = tau})
705 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
706 addErrCtxtM (sigCtxt id tvs theta tau) $
707 do { tvs' <- checkDistinctTyVars tvs
708 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
709 (bleatEscapedTvs gbl_tvs tvs tvs')
712 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
713 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
714 -- are still all type variables, and all distinct from each other.
715 -- It returns a zonked set of type variables.
716 -- For example, if the type sig is
717 -- f :: forall a b. a -> b -> b
718 -- we want to check that 'a' and 'b' haven't
719 -- (a) been unified with a non-tyvar type
720 -- (b) been unified with each other (all distinct)
722 checkDistinctTyVars sig_tvs
723 = do { zonked_tvs <- mapM zonk_one sig_tvs
724 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
725 ; return zonked_tvs }
727 zonk_one sig_tv = do { ty <- zonkTcTyVar sig_tv
728 ; return (tcGetTyVar "checkDistinctTyVars" ty) }
729 -- 'ty' is bound to be a type variable, because SigSkolTvs
730 -- can only be unified with type variables
732 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
733 -- The TyVarEnv maps each zonked type variable back to its
734 -- corresponding user-written signature type variable
735 check_dup acc (sig_tv, zonked_tv)
736 = case lookupVarEnv acc zonked_tv of
737 Just sig_tv' -> bomb_out sig_tv sig_tv'
739 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
741 bomb_out sig_tv1 sig_tv2
742 = failWithTc (ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
743 <+> ptext SLIT("is unified with another quantified type variable")
744 <+> quotes (ppr tidy_tv2))
746 (env1, tidy_tv1) = tidyOpenTyVar emptyTidyEnv sig_tv1
747 (_env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
751 @getTyVarsToGen@ decides what type variables to generalise over.
753 For a "restricted group" -- see the monomorphism restriction
754 for a definition -- we bind no dictionaries, and
755 remove from tyvars_to_gen any constrained type variables
757 *Don't* simplify dicts at this point, because we aren't going
758 to generalise over these dicts. By the time we do simplify them
759 we may well know more. For example (this actually came up)
761 f x = array ... xs where xs = [1,2,3,4,5]
762 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
763 stuff. If we simplify only at the f-binding (not the xs-binding)
764 we'll know that the literals are all Ints, and we can just produce
767 Find all the type variables involved in overloading, the
768 "constrained_tyvars". These are the ones we *aren't* going to
769 generalise. We must be careful about doing this:
771 (a) If we fail to generalise a tyvar which is not actually
772 constrained, then it will never, ever get bound, and lands
773 up printed out in interface files! Notorious example:
774 instance Eq a => Eq (Foo a b) where ..
775 Here, b is not constrained, even though it looks as if it is.
776 Another, more common, example is when there's a Method inst in
777 the LIE, whose type might very well involve non-overloaded
779 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
780 the simple thing instead]
782 (b) On the other hand, we mustn't generalise tyvars which are constrained,
783 because we are going to pass on out the unmodified LIE, with those
784 tyvars in it. They won't be in scope if we've generalised them.
786 So we are careful, and do a complete simplification just to find the
787 constrained tyvars. We don't use any of the results, except to
788 find which tyvars are constrained.
791 isUnRestrictedGroup :: LHsBinds Name -> [TcSigInfo] -> TcM Bool
792 isUnRestrictedGroup binds sigs
793 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
794 ; return (not mono_restriction || all_unrestricted) }
796 all_unrestricted = all (unrestricted . unLoc) (bagToList binds)
797 tysig_names = map (idName . sig_id) sigs
799 unrestricted (PatBind other _ _) = False
800 unrestricted (VarBind v _) = v `is_elem` tysig_names
801 unrestricted (FunBind v _ matches) = unrestricted_match matches
802 || unLoc v `is_elem` tysig_names
804 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
805 -- No args => like a pattern binding
806 unrestricted_match other = True
807 -- Some args => a function binding
809 is_elem v vs = isIn "isUnResMono" v vs
813 %************************************************************************
815 \subsection{SPECIALIZE pragmas}
817 %************************************************************************
819 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
820 pragmas. It is convenient for them to appear in the @[RenamedSig]@
821 part of a binding because then the same machinery can be used for
822 moving them into place as is done for type signatures.
827 f :: Ord a => [a] -> b -> b
828 {-# SPECIALIZE f :: [Int] -> b -> b #-}
831 For this we generate:
833 f* = /\ b -> let d1 = ...
837 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
838 retain a right-hand-side that the simplifier will otherwise discard as
839 dead code... the simplifier has a flag that tells it not to discard
840 SpecPragmaId bindings.
842 In this case the f* retains a call-instance of the overloaded
843 function, f, (including appropriate dictionaries) so that the
844 specialiser will subsequently discover that there's a call of @f@ at
845 Int, and will create a specialisation for @f@. After that, the
846 binding for @f*@ can be discarded.
848 We used to have a form
849 {-# SPECIALISE f :: <type> = g #-}
850 which promised that g implemented f at <type>, but we do that with
852 {-# RULES (f::<type>) = g #-}
855 tcSpecSigs :: [LSig Name] -> TcM (LHsBinds TcId)
856 tcSpecSigs (L loc (SpecSig (L nm_loc name) poly_ty) : sigs)
857 = -- SPECIALISE f :: forall b. theta => tau = g
859 addErrCtxt (valSpecSigCtxt name poly_ty) $
861 -- Get and instantiate its alleged specialised type
862 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
864 -- Check that f has a more general type, and build a RHS for
865 -- the spec-pragma-id at the same time
866 getLIE (tcCheckSigma (L nm_loc (HsVar name)) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
868 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
869 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
871 -- Just specialise "f" by building a SpecPragmaId binding
872 -- It is the thing that makes sure we don't prematurely
873 -- dead-code-eliminate the binding we are really interested in.
874 newLocalName name `thenM` \ spec_name ->
876 spec_bind = VarBind (mkSpecPragmaId spec_name sig_ty)
877 (mkHsLet spec_binds spec_expr)
880 -- Do the rest and combine
881 tcSpecSigs sigs `thenM` \ binds_rest ->
882 returnM (binds_rest `snocBag` L loc spec_bind)
884 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
885 tcSpecSigs [] = returnM emptyLHsBinds
888 %************************************************************************
890 \subsection[TcBinds-errors]{Error contexts and messages}
892 %************************************************************************
896 -- This one is called on LHS, when pat and grhss are both Name
897 -- and on RHS, when pat is TcId and grhss is still Name
898 patMonoBindsCtxt pat grhss
899 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
901 -----------------------------------------------
903 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
904 nest 4 (ppr v <+> dcolon <+> ppr ty)]
906 -----------------------------------------------
907 sigContextsCtxt sig1 sig2
908 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
909 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
910 ppr id2 <+> dcolon <+> ppr (idType id2)]),
911 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
917 -----------------------------------------------
918 unliftedBindErr flavour mbind
919 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
922 -----------------------------------------------
923 existentialExplode mbinds
924 = hang (vcat [text "My brain just exploded.",
925 text "I can't handle pattern bindings for existentially-quantified constructors.",
926 text "In the binding group"])
929 -----------------------------------------------
930 restrictedBindCtxtErr binder_names
931 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
932 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
933 ptext SLIT("that falls under the monomorphism restriction")])
936 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names