2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBinds, tcHsBootSigs, tcMonoBinds, tcSpecSigs ) where
9 #include "HsVersions.h"
11 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
12 import {-# SOURCE #-} TcExpr ( tcCheckSigma, tcCheckRho )
14 import CmdLineOpts ( DynFlag(Opt_MonomorphismRestriction) )
15 import HsSyn ( HsExpr(..), HsBind(..), LHsBinds, Sig(..),
16 LSig, Match(..), HsBindGroup(..), IPBind(..),
17 HsType(..), hsLTyVarNames, isVanillaLSig,
18 LPat, GRHSs, MatchGroup(..), emptyLHsBinds, isEmptyLHsBinds,
19 collectHsBindBinders, collectPatBinders, pprPatBind
21 import TcHsSyn ( TcId, TcDictBinds, zonkId, mkHsLet )
24 import Inst ( InstOrigin(..), newDictsAtLoc, newIPDict, instToId )
25 import TcEnv ( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2, newLocalName, tcLookupLocalIds )
26 import TcUnify ( Expected(..), tcInfer, checkSigTyVars, sigCtxt )
27 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted,
28 tcSimplifyToDicts, tcSimplifyIPs )
29 import TcHsType ( tcHsSigType, UserTypeCtxt(..), tcAddLetBoundTyVars,
30 TcSigInfo(..), TcSigFun, lookupSig
32 import TcPat ( tcPat, PatCtxt(..) )
33 import TcSimplify ( bindInstsOfLocalFuns )
34 import TcMType ( newTyFlexiVarTy, tcSkolType, zonkQuantifiedTyVar, zonkTcTypes )
35 import TcType ( TcTyVar, SkolemInfo(SigSkol),
36 TcTauType, TcSigmaType,
37 TvSubstEnv, mkOpenTvSubst, substTheta, substTy,
38 mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
39 mkForAllTy, isUnLiftedType, tcGetTyVar_maybe,
41 import Unify ( tcMatchPreds )
42 import Kind ( argTypeKind )
43 import VarEnv ( lookupVarEnv )
44 import TysPrim ( alphaTyVar )
45 import Id ( mkLocalId, mkSpecPragmaId, setInlinePragma )
46 import Var ( idType, idName )
50 import SrcLoc ( Located(..), unLoc, noLoc, getLoc )
53 import Maybes ( orElse )
54 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isRec,
55 isNotTopLevel, isAlwaysActive )
56 import FiniteMap ( listToFM, lookupFM )
61 %************************************************************************
63 \subsection{Type-checking bindings}
65 %************************************************************************
67 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
68 it needs to know something about the {\em usage} of the things bound,
69 so that it can create specialisations of them. So @tcBindsAndThen@
70 takes a function which, given an extended environment, E, typechecks
71 the scope of the bindings returning a typechecked thing and (most
72 important) an LIE. It is this LIE which is then used as the basis for
73 specialising the things bound.
75 @tcBindsAndThen@ also takes a "combiner" which glues together the
76 bindings and the "thing" to make a new "thing".
78 The real work is done by @tcBindWithSigsAndThen@.
80 Recursive and non-recursive binds are handled in essentially the same
81 way: because of uniques there are no scoping issues left. The only
82 difference is that non-recursive bindings can bind primitive values.
84 Even for non-recursive binding groups we add typings for each binder
85 to the LVE for the following reason. When each individual binding is
86 checked the type of its LHS is unified with that of its RHS; and
87 type-checking the LHS of course requires that the binder is in scope.
89 At the top-level the LIE is sure to contain nothing but constant
90 dictionaries, which we resolve at the module level.
93 tcTopBinds :: [HsBindGroup Name] -> TcM (LHsBinds TcId, TcLclEnv)
94 -- Note: returning the TcLclEnv is more than we really
95 -- want. The bit we care about is the local bindings
96 -- and the free type variables thereof
98 = tc_binds_and_then TopLevel glue binds $
100 ; return (emptyLHsBinds, env) }
102 -- The top level bindings are flattened into a giant
103 -- implicitly-mutually-recursive MonoBinds
104 glue (HsBindGroup binds1 _ _) (binds2, env) = (binds1 `unionBags` binds2, env)
105 glue (HsIPBinds _) _ = panic "Top-level HsIpBinds"
106 -- Can't have a HsIPBinds at top level
108 tcHsBootSigs :: [HsBindGroup Name] -> TcM (LHsBinds TcId, TcLclEnv)
109 -- A hs-boot file has only one BindGroup, and it only has type
110 -- signatures in it. The renamer checked all this
111 tcHsBootSigs [HsBindGroup _ sigs _]
112 = do { ids <- mapM (addLocM tc_sig) (filter isVanillaLSig sigs)
113 ; tcExtendIdEnv ids $ do
115 ; return (emptyLHsBinds, env) }}
117 tc_sig (Sig (L _ name) ty)
118 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
119 ; return (mkLocalId name sigma_ty) }
122 :: (HsBindGroup TcId -> thing -> thing) -- Combinator
123 -> [HsBindGroup Name]
127 tcBindsAndThen = tc_binds_and_then NotTopLevel
129 tc_binds_and_then top_lvl combiner [] do_next
131 tc_binds_and_then top_lvl combiner (group : groups) do_next
132 = tc_bind_and_then top_lvl combiner group $
133 tc_binds_and_then top_lvl combiner groups do_next
135 tc_bind_and_then top_lvl combiner (HsIPBinds binds) do_next
136 = getLIE do_next `thenM` \ (result, expr_lie) ->
137 mapAndUnzipM (wrapLocSndM tc_ip_bind) binds `thenM` \ (avail_ips, binds') ->
139 -- If the binding binds ?x = E, we must now
140 -- discharge any ?x constraints in expr_lie
141 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
143 returnM (combiner (HsIPBinds binds') $
144 combiner (HsBindGroup dict_binds [] Recursive) result)
146 -- I wonder if we should do these one at at time
149 tc_ip_bind (IPBind ip expr)
150 = newTyFlexiVarTy argTypeKind `thenM` \ ty ->
151 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
152 tcCheckRho expr ty `thenM` \ expr' ->
153 returnM (ip_inst, (IPBind ip' expr'))
155 tc_bind_and_then top_lvl combiner (HsBindGroup binds sigs is_rec) do_next
156 | isEmptyLHsBinds binds
159 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
160 -- Notice that they scope over
161 -- a) the type signatures in the binding group
162 -- b) the bindings in the group
163 -- c) the scope of the binding group (the "in" part)
164 tcAddLetBoundTyVars binds $
167 TopLevel -- For the top level don't bother will all this
168 -- bindInstsOfLocalFuns stuff. All the top level
169 -- things are rec'd together anyway, so it's fine to
170 -- leave them to the tcSimplifyTop, and quite a bit faster too
171 -> tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
172 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
173 returnM (combiner (HsBindGroup
174 (poly_binds `unionBags` prag_binds)
179 NotTopLevel -- For nested bindings we must do the bindInstsOfLocalFuns thing.
180 | not (isRec is_rec) -- Non-recursive group
181 -> -- We want to keep non-recursive things non-recursive
182 -- so that we desugar unlifted bindings correctly
183 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
184 getLIE (tc_body poly_ids) `thenM` \ ((prag_binds, thing), lie) ->
186 -- Create specialisations of functions bound here
187 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
190 combiner (HsBindGroup poly_binds [] NonRecursive) $
191 combiner (HsBindGroup prag_binds [] NonRecursive) $
192 combiner (HsBindGroup lie_binds [] Recursive) $
193 -- NB: the binds returned by tcSimplify and
194 -- bindInstsOfLocalFuns aren't guaranteed in
195 -- dependency order (though we could change that);
196 -- hence the Recursive marker.
200 -> -- NB: polymorphic recursion means that a function
201 -- may use an instance of itself, we must look at the LIE arising
202 -- from the function's own right hand side. Hence the getLIE
203 -- encloses the tcBindWithSigs.
206 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
207 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
208 returnM (poly_ids, poly_binds `unionBags` prag_binds, thing)
209 ) `thenM` \ ((poly_ids, extra_binds, thing), lie) ->
211 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
213 returnM (combiner (HsBindGroup
214 (extra_binds `unionBags` lie_binds)
218 tc_body poly_ids -- Type check the pragmas and "thing inside"
219 = -- Extend the environment to bind the new polymorphic Ids
220 tcExtendIdEnv poly_ids $
222 -- Build bindings and IdInfos corresponding to user pragmas
223 tcSpecSigs sigs `thenM` \ prag_binds ->
225 -- Now do whatever happens next, in the augmented envt
226 do_next `thenM` \ thing ->
228 returnM (prag_binds, thing)
232 %************************************************************************
234 \subsection{tcBindWithSigs}
236 %************************************************************************
238 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
239 so all the clever stuff is in here.
241 * binder_names and mbind must define the same set of Names
243 * The Names in tc_ty_sigs must be a subset of binder_names
245 * The Ids in tc_ty_sigs don't necessarily have to have the same name
246 as the Name in the tc_ty_sig
249 tcBindWithSigs :: TopLevelFlag
253 -> TcM (LHsBinds TcId, [TcId])
254 -- The returned TcIds are guaranteed zonked
256 tcBindWithSigs top_lvl mbind sigs is_rec = do
257 { -- TYPECHECK THE SIGNATURES
258 tc_ty_sigs <- recoverM (returnM []) $
259 tcTySigs (filter isVanillaLSig sigs)
260 ; let lookup_sig = lookupSig tc_ty_sigs
262 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
263 ; recoverM (recoveryCode mbind lookup_sig) $ do
265 { traceTc (ptext SLIT("--------------------------------------------------------"))
266 ; traceTc (ptext SLIT("Bindings for") <+> ppr (collectHsBindBinders mbind))
268 -- TYPECHECK THE BINDINGS
269 ; ((mbind', mono_bind_infos), lie_req)
270 <- getLIE (tcMonoBinds mbind lookup_sig is_rec)
272 -- CHECK FOR UNLIFTED BINDINGS
273 -- These must be non-recursive etc, and are not generalised
274 -- They desugar to a case expression in the end
275 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
276 ; if any isUnLiftedType zonked_mono_tys then
277 do { -- Unlifted bindings
278 checkUnliftedBinds top_lvl is_rec mbind
280 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
281 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id)
282 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id)
284 ; return ( unitBag $ noLoc $ AbsBinds [] [] exports emptyNameSet mbind',
285 [poly_id | (_, poly_id, _) <- exports]) } -- Guaranteed zonked
287 else do -- The normal lifted case: GENERALISE
288 { is_unres <- isUnRestrictedGroup mbind tc_ty_sigs
289 ; (tyvars_to_gen, dict_binds, dict_ids)
290 <- setSrcSpan (getLoc (head (bagToList mbind))) $
291 -- TODO: location a bit awkward, but the mbinds have been
292 -- dependency analysed and may no longer be adjacent
293 addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
294 generalise is_unres mono_bind_infos tc_ty_sigs lie_req
296 -- FINALISE THE QUANTIFIED TYPE VARIABLES
297 -- The quantified type variables often include meta type variables
298 -- we want to freeze them into ordinary type variables, and
299 -- default their kind (e.g. from OpenTypeKind to TypeKind)
300 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
302 -- BUILD THE POLYMORPHIC RESULT IDs
304 exports = map mk_export mono_bind_infos
305 poly_ids = [poly_id | (_, poly_id, _) <- exports]
306 dict_tys = map idType dict_ids
308 inlines = mkNameSet [ name
309 | L _ (InlineSig True (L _ name) _) <- sigs]
310 -- Any INLINE sig (regardless of phase control)
311 -- makes the RHS look small
312 inline_phases = listToFM [ (name, phase)
313 | L _ (InlineSig _ (L _ name) phase) <- sigs,
314 not (isAlwaysActive phase)]
315 -- Set the IdInfo field to control the inline phase
316 -- AlwaysActive is the default, so don't bother with them
317 add_inlines id = attachInlinePhase inline_phases id
319 mk_export (binder_name, mb_sig, mono_id)
321 Just sig -> (sig_tvs sig, add_inlines (sig_id sig), mono_id)
322 Nothing -> (tyvars_to_gen', add_inlines new_poly_id, mono_id)
324 new_poly_id = mkLocalId binder_name poly_ty
325 poly_ty = mkForAllTys tyvars_to_gen'
329 -- ZONK THE poly_ids, because they are used to extend the type
330 -- environment; see the invariant on TcEnv.tcExtendIdEnv
331 ; zonked_poly_ids <- mappM zonkId poly_ids
333 ; traceTc (text "binding:" <+> ppr ((dict_ids, dict_binds),
334 exports, map idType zonked_poly_ids))
338 AbsBinds tyvars_to_gen'
342 (dict_binds `unionBags` mbind'),
347 -- If typechecking the binds fails, then return with each
348 -- signature-less binder given type (forall a.a), to minimise
349 -- subsequent error messages
350 recoveryCode mbind lookup_sig
351 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
352 ; return (emptyLHsBinds, poly_ids) }
354 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
355 binder_names = collectHsBindBinders mbind
356 poly_ids = map mk_dummy binder_names
357 mk_dummy name = case lookup_sig name of
358 Just sig -> sig_id sig -- Signature
359 Nothing -> mkLocalId name forall_a_a -- No signature
361 attachInlinePhase inline_phases bndr
362 = case lookupFM inline_phases (idName bndr) of
363 Just prag -> bndr `setInlinePragma` prag
366 -- Check that non-overloaded unlifted bindings are
369 -- c) not a multiple-binding group (more or less implied by (a))
371 checkUnliftedBinds top_lvl is_rec mbind
372 = checkTc (isNotTopLevel top_lvl)
373 (unliftedBindErr "Top-level" mbind) `thenM_`
374 checkTc (isNonRec is_rec)
375 (unliftedBindErr "Recursive" mbind) `thenM_`
376 checkTc (isSingletonBag mbind)
377 (unliftedBindErr "Multiple" mbind)
381 Polymorphic recursion
382 ~~~~~~~~~~~~~~~~~~~~~
383 The game plan for polymorphic recursion in the code above is
385 * Bind any variable for which we have a type signature
386 to an Id with a polymorphic type. Then when type-checking
387 the RHSs we'll make a full polymorphic call.
389 This fine, but if you aren't a bit careful you end up with a horrendous
390 amount of partial application and (worse) a huge space leak. For example:
392 f :: Eq a => [a] -> [a]
395 If we don't take care, after typechecking we get
397 f = /\a -> \d::Eq a -> let f' = f a d
401 Notice the the stupid construction of (f a d), which is of course
402 identical to the function we're executing. In this case, the
403 polymorphic recursion isn't being used (but that's a very common case).
406 f = /\a -> \d::Eq a -> letrec
407 fm = \ys:[a] -> ...fm...
411 This can lead to a massive space leak, from the following top-level defn
417 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
418 f' is another thunk which evaluates to the same thing... and you end
419 up with a chain of identical values all hung onto by the CAF ff.
423 = let f' = f Int dEqInt in \ys. ...f'...
425 = let f' = let f' = f Int dEqInt in \ys. ...f'...
429 Solution: when typechecking the RHSs we always have in hand the
430 *monomorphic* Ids for each binding. So we just need to make sure that
431 if (Method f a d) shows up in the constraints emerging from (...f...)
432 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
433 to the "givens" when simplifying constraints. That's what the "lies_avail"
437 %************************************************************************
439 \subsection{tcMonoBind}
441 %************************************************************************
443 @tcMonoBinds@ deals with a single @MonoBind@.
444 The signatures have been dealt with already.
447 tcMonoBinds :: LHsBinds Name
448 -> TcSigFun -> RecFlag
449 -> TcM (LHsBinds TcId, [MonoBindInfo])
451 tcMonoBinds binds lookup_sig is_rec
452 = do { tc_binds <- mapBagM (wrapLocM (tcLhs lookup_sig)) binds
454 -- Bring (a) the scoped type variables, and (b) the Ids, into scope for the RHSs
455 -- For (a) it's ok to bring them all into scope at once, even
456 -- though each type sig should scope only over its own RHS,
457 -- because the renamer has sorted all that out.
458 ; let mono_info = getMonoBindInfo tc_binds
459 rhs_tvs = [ (name, mkTyVarTy tv)
460 | (_, Just sig, _) <- mono_info,
461 (name, tv) <- sig_scoped sig `zip` sig_tvs sig ]
462 rhs_id_env = map mk mono_info -- A binding for each term variable
464 ; binds' <- tcExtendTyVarEnv2 rhs_tvs $
465 tcExtendIdEnv2 rhs_id_env $
466 mapBagM (wrapLocM tcRhs) tc_binds
467 ; return (binds', mono_info) }
469 mk (name, Just sig, _) = (name, sig_id sig) -- Use the type sig if there is one
470 mk (name, Nothing, mono_id) = (name, mono_id) -- otherwise use a monomorphic version
472 ------------------------
473 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
474 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
475 -- if there's a signature for it, use the instantiated signature type
476 -- otherwise invent a type variable
477 -- You see that quite directly in the FunBind case.
479 -- But there's a complication for pattern bindings:
480 -- data T = MkT (forall a. a->a)
482 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
483 -- but we want to get (f::forall a. a->a) as the RHS environment.
484 -- The simplest way to do this is to typecheck the pattern, and then look up the
485 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
486 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
488 data TcMonoBind -- Half completed; LHS done, RHS not done
489 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
490 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
492 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
493 -- Type signature (if any), and
494 -- the monomorphic bound things
496 bndrNames :: [MonoBindInfo] -> [Name]
497 bndrNames mbi = [n | (n,_,_) <- mbi]
499 getMonoType :: MonoBindInfo -> TcTauType
500 getMonoType (_,_,mono_id) = idType mono_id
502 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
503 tcLhs lookup_sig (FunBind (L nm_loc name) inf matches)
504 = do { let mb_sig = lookup_sig name
505 ; mono_name <- newLocalName name
506 ; mono_ty <- mk_mono_ty mb_sig
507 ; let mono_id = mkLocalId mono_name mono_ty
508 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
510 mk_mono_ty (Just sig) = return (sig_tau sig)
511 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
513 tcLhs lookup_sig bind@(PatBind pat grhss _)
514 = do { let tc_pat exp_ty = tcPat (LetPat lookup_sig) pat exp_ty lookup_infos
515 ; ((pat', ex_tvs, infos), pat_ty)
516 <- addErrCtxt (patMonoBindsCtxt pat grhss)
519 -- Don't know how to deal with pattern-bound existentials yet
520 ; checkTc (null ex_tvs) (existentialExplode bind)
522 ; return (TcPatBind infos pat' grhss pat_ty) }
524 names = collectPatBinders pat
526 -- After typechecking the pattern, look up the binder
527 -- names, which the pattern has brought into scope.
528 lookup_infos :: TcM [MonoBindInfo]
529 lookup_infos = do { mono_ids <- tcLookupLocalIds names
530 ; return [ (name, lookup_sig name, mono_id)
531 | (name, mono_id) <- names `zip` mono_ids] }
534 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
535 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
536 = do { matches' <- tcMatchesFun (idName mono_id) matches
537 (Check (idType mono_id))
538 ; return (FunBind fun' inf matches') }
540 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
541 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
542 tcGRHSsPat grhss (Check pat_ty)
543 ; return (PatBind pat' grhss' pat_ty) }
546 ---------------------
547 getMonoBindInfo :: Bag (Located TcMonoBind) -> [MonoBindInfo]
548 getMonoBindInfo tc_binds
549 = foldrBag (get_info . unLoc) [] tc_binds
551 get_info (TcFunBind info _ _ _) rest = info : rest
552 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
556 %************************************************************************
558 \subsection{getTyVarsToGen}
560 %************************************************************************
563 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
564 -- The trick here is that all the signatures should have the same
565 -- context, and we want to share type variables for that context, so that
566 -- all the right hand sides agree a common vocabulary for their type
568 tcTySigs [] = return []
571 = do { (tc_sig1 : tc_sigs) <- mappM tcTySig sigs
572 ; tc_sigs' <- mapM (checkSigCtxt tc_sig1) tc_sigs
573 ; return (tc_sig1 : tc_sigs') }
575 tcTySig :: LSig Name -> TcM TcSigInfo
576 tcTySig (L span (Sig (L _ name) ty))
578 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
579 ; let rigid_info = SigSkol name
580 poly_id = mkLocalId name sigma_ty
582 -- The scoped names are the ones explicitly mentioned
583 -- in the HsForAll. (There may be more in sigma_ty, because
584 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
585 scoped_names = case ty of
586 L _ (HsForAllTy _ tvs _ _) -> hsLTyVarNames tvs
589 ; (tvs, theta, tau) <- tcSkolType rigid_info sigma_ty
590 ; loc <- getInstLoc (SigOrigin rigid_info)
591 ; return (TcSigInfo { sig_id = poly_id, sig_scoped = scoped_names,
592 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
595 checkSigCtxt :: TcSigInfo -> TcSigInfo -> TcM TcSigInfo
596 checkSigCtxt sig1 sig@(TcSigInfo { sig_tvs = tvs, sig_theta = theta, sig_tau = tau })
597 = -- Try to match the context of this signature with
598 -- that of the first signature
599 case tcMatchPreds (sig_tvs sig) (sig_theta sig) (sig_theta sig1) of {
600 Nothing -> bale_out ;
603 case check_tvs tenv tvs of {
604 Nothing -> bale_out ;
608 subst = mkOpenTvSubst tenv
610 return (sig { sig_tvs = tvs',
611 sig_theta = substTheta subst theta,
612 sig_tau = substTy subst tau }) }}
615 bale_out = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
617 sigContextsErr (sig_id sig1) (sig_id sig)
619 -- Rather tedious check that the type variables
620 -- have been matched only with another type variable,
621 -- and that two type variables have not been matched
623 -- A return of Nothing indicates that one of the bad
624 -- things has happened
625 check_tvs :: TvSubstEnv -> [TcTyVar] -> Maybe [TcTyVar]
626 check_tvs tenv [] = Just []
627 check_tvs tenv (tv:tvs)
628 = do { let ty = lookupVarEnv tenv tv `orElse` mkTyVarTy tv
629 ; tv' <- tcGetTyVar_maybe ty
630 ; tvs' <- check_tvs tenv tvs
633 else Just (tv':tvs') }
637 generalise :: Bool -> [MonoBindInfo] -> [TcSigInfo] -> [Inst]
638 -> TcM ([TcTyVar], TcDictBinds, [TcId])
639 generalise 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 tau_tvs lie_req
649 -- Check that signature type variables are OK
650 ; final_qtvs <- checkSigsTyVars qtvs sigs
652 ; return (final_qtvs, binds, []) }
654 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
655 = tcSimplifyInfer doc tau_tvs lie_req
657 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
658 = do { let sig1 = head sigs
659 ; sig_lie <- newDictsAtLoc (sig_loc sig1) (sig_theta sig1)
660 ; let -- The "sig_avails" is the stuff available. We get that from
661 -- the context of the type signature, BUT ALSO the lie_avail
662 -- so that polymorphic recursion works right (see comments at end of fn)
663 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
664 sig_avails = sig_lie ++ local_meths
666 -- Check that the needed dicts can be
667 -- expressed in terms of the signature ones
668 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
670 -- Check that signature type variables are OK
671 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
673 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
676 bndr_names = bndrNames mono_infos
677 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
678 is_mono_sig sig = null (sig_theta sig)
679 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndr_names
681 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
682 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
683 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
685 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
686 checkSigsTyVars qtvs sigs
687 = mappM check_one sigs `thenM` \ sig_tvs_s ->
689 -- Sigh. Make sure that all the tyvars in the type sigs
690 -- appear in the returned ty var list, which is what we are
691 -- going to generalise over. Reason: we occasionally get
693 -- type T a = () -> ()
696 -- Here, 'a' won't appear in qtvs, so we have to add it
698 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
699 all_tvs = extendVarSetList sig_tvs qtvs
701 returnM (varSetElems all_tvs)
703 check_one (TcSigInfo {sig_id = id, sig_tvs = tvs, sig_theta = theta, sig_tau = tau})
704 = addErrCtxt (ptext SLIT("In the type signature for")
705 <+> quotes (ppr id)) $
706 addErrCtxtM (sigCtxt id tvs theta tau) $
707 do { checkSigTyVars tvs; return tvs }
710 @getTyVarsToGen@ decides what type variables to generalise over.
712 For a "restricted group" -- see the monomorphism restriction
713 for a definition -- we bind no dictionaries, and
714 remove from tyvars_to_gen any constrained type variables
716 *Don't* simplify dicts at this point, because we aren't going
717 to generalise over these dicts. By the time we do simplify them
718 we may well know more. For example (this actually came up)
720 f x = array ... xs where xs = [1,2,3,4,5]
721 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
722 stuff. If we simplify only at the f-binding (not the xs-binding)
723 we'll know that the literals are all Ints, and we can just produce
726 Find all the type variables involved in overloading, the
727 "constrained_tyvars". These are the ones we *aren't* going to
728 generalise. We must be careful about doing this:
730 (a) If we fail to generalise a tyvar which is not actually
731 constrained, then it will never, ever get bound, and lands
732 up printed out in interface files! Notorious example:
733 instance Eq a => Eq (Foo a b) where ..
734 Here, b is not constrained, even though it looks as if it is.
735 Another, more common, example is when there's a Method inst in
736 the LIE, whose type might very well involve non-overloaded
738 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
739 the simple thing instead]
741 (b) On the other hand, we mustn't generalise tyvars which are constrained,
742 because we are going to pass on out the unmodified LIE, with those
743 tyvars in it. They won't be in scope if we've generalised them.
745 So we are careful, and do a complete simplification just to find the
746 constrained tyvars. We don't use any of the results, except to
747 find which tyvars are constrained.
750 isUnRestrictedGroup :: LHsBinds Name -> [TcSigInfo] -> TcM Bool
751 isUnRestrictedGroup binds sigs
752 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
753 ; return (not mono_restriction || all_unrestricted) }
755 all_unrestricted = all (unrestricted . unLoc) (bagToList binds)
756 tysig_names = map (idName . sig_id) sigs
758 unrestricted (PatBind other _ _) = False
759 unrestricted (VarBind v _) = v `is_elem` tysig_names
760 unrestricted (FunBind v _ matches) = unrestricted_match matches
761 || unLoc v `is_elem` tysig_names
763 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
764 -- No args => like a pattern binding
765 unrestricted_match other = True
766 -- Some args => a function binding
768 is_elem v vs = isIn "isUnResMono" v vs
772 %************************************************************************
774 \subsection{SPECIALIZE pragmas}
776 %************************************************************************
778 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
779 pragmas. It is convenient for them to appear in the @[RenamedSig]@
780 part of a binding because then the same machinery can be used for
781 moving them into place as is done for type signatures.
786 f :: Ord a => [a] -> b -> b
787 {-# SPECIALIZE f :: [Int] -> b -> b #-}
790 For this we generate:
792 f* = /\ b -> let d1 = ...
796 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
797 retain a right-hand-side that the simplifier will otherwise discard as
798 dead code... the simplifier has a flag that tells it not to discard
799 SpecPragmaId bindings.
801 In this case the f* retains a call-instance of the overloaded
802 function, f, (including appropriate dictionaries) so that the
803 specialiser will subsequently discover that there's a call of @f@ at
804 Int, and will create a specialisation for @f@. After that, the
805 binding for @f*@ can be discarded.
807 We used to have a form
808 {-# SPECIALISE f :: <type> = g #-}
809 which promised that g implemented f at <type>, but we do that with
811 {-# RULES (f::<type>) = g #-}
814 tcSpecSigs :: [LSig Name] -> TcM (LHsBinds TcId)
815 tcSpecSigs (L loc (SpecSig (L nm_loc name) poly_ty) : sigs)
816 = -- SPECIALISE f :: forall b. theta => tau = g
818 addErrCtxt (valSpecSigCtxt name poly_ty) $
820 -- Get and instantiate its alleged specialised type
821 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
823 -- Check that f has a more general type, and build a RHS for
824 -- the spec-pragma-id at the same time
825 getLIE (tcCheckSigma (L nm_loc (HsVar name)) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
827 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
828 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
830 -- Just specialise "f" by building a SpecPragmaId binding
831 -- It is the thing that makes sure we don't prematurely
832 -- dead-code-eliminate the binding we are really interested in.
833 newLocalName name `thenM` \ spec_name ->
835 spec_bind = VarBind (mkSpecPragmaId spec_name sig_ty)
836 (mkHsLet spec_binds spec_expr)
839 -- Do the rest and combine
840 tcSpecSigs sigs `thenM` \ binds_rest ->
841 returnM (binds_rest `snocBag` L loc spec_bind)
843 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
844 tcSpecSigs [] = returnM emptyLHsBinds
847 %************************************************************************
849 \subsection[TcBinds-errors]{Error contexts and messages}
851 %************************************************************************
855 -- This one is called on LHS, when pat and grhss are both Name
856 -- and on RHS, when pat is TcId and grhss is still Name
857 patMonoBindsCtxt pat grhss
858 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
860 -----------------------------------------------
862 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
863 nest 4 (ppr v <+> dcolon <+> ppr ty)]
865 -----------------------------------------------
866 sigContextsErr id1 id2
867 = vcat [ptext SLIT("Mis-match between the contexts of the signatures for"),
868 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
869 ppr id2 <+> dcolon <+> ppr (idType id2)]),
870 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
873 -----------------------------------------------
874 unliftedBindErr flavour mbind
875 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
878 -----------------------------------------------
879 existentialExplode mbinds
880 = hang (vcat [text "My brain just exploded.",
881 text "I can't handle pattern bindings for existentially-quantified constructors.",
882 text "In the binding group"])
885 -----------------------------------------------
886 restrictedBindCtxtErr binder_names
887 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
888 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
889 ptext SLIT("that falls under the monomorphism restriction")])
892 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
894 -- Used in error messages
895 -- Use quotes for a single one; they look a bit "busy" for several
896 pprBinders [bndr] = quotes (ppr bndr)
897 pprBinders bndrs = pprWithCommas ppr bndrs