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,
26 newLocalName, tcLookupLocalIds, pprBinders )
27 import TcUnify ( Expected(..), tcInfer, checkSigTyVars, sigCtxt )
28 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted,
29 tcSimplifyToDicts, tcSimplifyIPs )
30 import TcHsType ( tcHsSigType, UserTypeCtxt(..), tcAddLetBoundTyVars,
31 TcSigInfo(..), TcSigFun, lookupSig
33 import TcPat ( tcPat, PatCtxt(..) )
34 import TcSimplify ( bindInstsOfLocalFuns )
35 import TcMType ( newTyFlexiVarTy, tcSkolType, zonkQuantifiedTyVar, zonkTcTypes )
36 import TcType ( TcTyVar, SkolemInfo(SigSkol),
37 TcTauType, TcSigmaType,
38 TvSubstEnv, mkOpenTvSubst, substTheta, substTy,
39 mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
40 mkForAllTy, isUnLiftedType, tcGetTyVar_maybe,
42 import Unify ( tcMatchPreds )
43 import Kind ( argTypeKind )
44 import VarEnv ( lookupVarEnv )
45 import TysPrim ( alphaTyVar )
46 import Id ( mkLocalId, mkSpecPragmaId, setInlinePragma )
47 import Var ( idType, idName )
51 import SrcLoc ( Located(..), unLoc, noLoc, getLoc )
54 import Maybes ( orElse )
55 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isRec,
56 isNotTopLevel, isAlwaysActive )
57 import FiniteMap ( listToFM, lookupFM )
62 %************************************************************************
64 \subsection{Type-checking bindings}
66 %************************************************************************
68 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
69 it needs to know something about the {\em usage} of the things bound,
70 so that it can create specialisations of them. So @tcBindsAndThen@
71 takes a function which, given an extended environment, E, typechecks
72 the scope of the bindings returning a typechecked thing and (most
73 important) an LIE. It is this LIE which is then used as the basis for
74 specialising the things bound.
76 @tcBindsAndThen@ also takes a "combiner" which glues together the
77 bindings and the "thing" to make a new "thing".
79 The real work is done by @tcBindWithSigsAndThen@.
81 Recursive and non-recursive binds are handled in essentially the same
82 way: because of uniques there are no scoping issues left. The only
83 difference is that non-recursive bindings can bind primitive values.
85 Even for non-recursive binding groups we add typings for each binder
86 to the LVE for the following reason. When each individual binding is
87 checked the type of its LHS is unified with that of its RHS; and
88 type-checking the LHS of course requires that the binder is in scope.
90 At the top-level the LIE is sure to contain nothing but constant
91 dictionaries, which we resolve at the module level.
94 tcTopBinds :: [HsBindGroup Name] -> TcM (LHsBinds TcId, TcLclEnv)
95 -- Note: returning the TcLclEnv is more than we really
96 -- want. The bit we care about is the local bindings
97 -- and the free type variables thereof
99 = tc_binds_and_then TopLevel glue binds $
100 do { env <- getLclEnv
101 ; return (emptyLHsBinds, env) }
103 -- The top level bindings are flattened into a giant
104 -- implicitly-mutually-recursive MonoBinds
105 glue (HsBindGroup binds1 _ _) (binds2, env) = (binds1 `unionBags` binds2, env)
106 glue (HsIPBinds _) _ = panic "Top-level HsIpBinds"
107 -- Can't have a HsIPBinds at top level
109 tcHsBootSigs :: [HsBindGroup Name] -> TcM (LHsBinds TcId, TcLclEnv)
110 -- A hs-boot file has only one BindGroup, and it only has type
111 -- signatures in it. The renamer checked all this
112 tcHsBootSigs [HsBindGroup _ sigs _]
113 = do { ids <- mapM (addLocM tc_sig) (filter isVanillaLSig sigs)
114 ; tcExtendIdEnv ids $ do
116 ; return (emptyLHsBinds, env) }}
118 tc_sig (Sig (L _ name) ty)
119 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
120 ; return (mkLocalId name sigma_ty) }
123 :: (HsBindGroup TcId -> thing -> thing) -- Combinator
124 -> [HsBindGroup Name]
128 tcBindsAndThen = tc_binds_and_then NotTopLevel
130 tc_binds_and_then top_lvl combiner [] do_next
132 tc_binds_and_then top_lvl combiner (group : groups) do_next
133 = tc_bind_and_then top_lvl combiner group $
134 tc_binds_and_then top_lvl combiner groups do_next
136 tc_bind_and_then top_lvl combiner (HsIPBinds binds) do_next
137 = getLIE do_next `thenM` \ (result, expr_lie) ->
138 mapAndUnzipM (wrapLocSndM tc_ip_bind) binds `thenM` \ (avail_ips, binds') ->
140 -- If the binding binds ?x = E, we must now
141 -- discharge any ?x constraints in expr_lie
142 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
144 returnM (combiner (HsIPBinds binds') $
145 combiner (HsBindGroup dict_binds [] Recursive) result)
147 -- I wonder if we should do these one at at time
150 tc_ip_bind (IPBind ip expr)
151 = newTyFlexiVarTy argTypeKind `thenM` \ ty ->
152 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
153 tcCheckRho expr ty `thenM` \ expr' ->
154 returnM (ip_inst, (IPBind ip' expr'))
156 tc_bind_and_then top_lvl combiner (HsBindGroup binds sigs is_rec) do_next
157 | isEmptyLHsBinds binds
160 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
161 -- Notice that they scope over
162 -- a) the type signatures in the binding group
163 -- b) the bindings in the group
164 -- c) the scope of the binding group (the "in" part)
165 tcAddLetBoundTyVars binds $
168 TopLevel -- For the top level don't bother will all this
169 -- bindInstsOfLocalFuns stuff. All the top level
170 -- things are rec'd together anyway, so it's fine to
171 -- leave them to the tcSimplifyTop, and quite a bit faster too
172 -> tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
173 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
174 returnM (combiner (HsBindGroup
175 (poly_binds `unionBags` prag_binds)
180 NotTopLevel -- For nested bindings we must do the bindInstsOfLocalFuns thing.
181 | not (isRec is_rec) -- Non-recursive group
182 -> -- We want to keep non-recursive things non-recursive
183 -- so that we desugar unlifted bindings correctly
184 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
185 getLIE (tc_body poly_ids) `thenM` \ ((prag_binds, thing), lie) ->
187 -- Create specialisations of functions bound here
188 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
191 combiner (HsBindGroup poly_binds [] NonRecursive) $
192 combiner (HsBindGroup prag_binds [] NonRecursive) $
193 combiner (HsBindGroup lie_binds [] Recursive) $
194 -- NB: the binds returned by tcSimplify and
195 -- bindInstsOfLocalFuns aren't guaranteed in
196 -- dependency order (though we could change that);
197 -- hence the Recursive marker.
201 -> -- NB: polymorphic recursion means that a function
202 -- may use an instance of itself, we must look at the LIE arising
203 -- from the function's own right hand side. Hence the getLIE
204 -- encloses the tcBindWithSigs.
207 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
208 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
209 returnM (poly_ids, poly_binds `unionBags` prag_binds, thing)
210 ) `thenM` \ ((poly_ids, extra_binds, thing), lie) ->
212 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
214 returnM (combiner (HsBindGroup
215 (extra_binds `unionBags` lie_binds)
219 tc_body poly_ids -- Type check the pragmas and "thing inside"
220 = -- Extend the environment to bind the new polymorphic Ids
221 tcExtendIdEnv poly_ids $
223 -- Build bindings and IdInfos corresponding to user pragmas
224 tcSpecSigs sigs `thenM` \ prag_binds ->
226 -- Now do whatever happens next, in the augmented envt
227 do_next `thenM` \ thing ->
229 returnM (prag_binds, thing)
233 %************************************************************************
235 \subsection{tcBindWithSigs}
237 %************************************************************************
239 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
240 so all the clever stuff is in here.
242 * binder_names and mbind must define the same set of Names
244 * The Names in tc_ty_sigs must be a subset of binder_names
246 * The Ids in tc_ty_sigs don't necessarily have to have the same name
247 as the Name in the tc_ty_sig
250 tcBindWithSigs :: TopLevelFlag
254 -> TcM (LHsBinds TcId, [TcId])
255 -- The returned TcIds are guaranteed zonked
257 tcBindWithSigs top_lvl mbind sigs is_rec = do
258 { -- TYPECHECK THE SIGNATURES
259 tc_ty_sigs <- recoverM (returnM []) $
260 tcTySigs (filter isVanillaLSig sigs)
261 ; let lookup_sig = lookupSig tc_ty_sigs
263 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
264 ; recoverM (recoveryCode mbind lookup_sig) $ do
266 { traceTc (ptext SLIT("--------------------------------------------------------"))
267 ; traceTc (ptext SLIT("Bindings for") <+> ppr (collectHsBindBinders mbind))
269 -- TYPECHECK THE BINDINGS
270 ; ((mbind', mono_bind_infos), lie_req)
271 <- getLIE (tcMonoBinds mbind lookup_sig is_rec)
273 -- CHECK FOR UNLIFTED BINDINGS
274 -- These must be non-recursive etc, and are not generalised
275 -- They desugar to a case expression in the end
276 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
277 ; if any isUnLiftedType zonked_mono_tys then
278 do { -- Unlifted bindings
279 checkUnliftedBinds top_lvl is_rec mbind
281 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
282 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id)
283 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id)
285 ; return ( unitBag $ noLoc $ AbsBinds [] [] exports emptyNameSet mbind',
286 [poly_id | (_, poly_id, _) <- exports]) } -- Guaranteed zonked
288 else do -- The normal lifted case: GENERALISE
289 { is_unres <- isUnRestrictedGroup mbind tc_ty_sigs
290 ; (tyvars_to_gen, dict_binds, dict_ids)
291 <- setSrcSpan (getLoc (head (bagToList mbind))) $
292 -- TODO: location a bit awkward, but the mbinds have been
293 -- dependency analysed and may no longer be adjacent
294 addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
295 generalise top_lvl is_unres mono_bind_infos tc_ty_sigs lie_req
297 -- FINALISE THE QUANTIFIED TYPE VARIABLES
298 -- The quantified type variables often include meta type variables
299 -- we want to freeze them into ordinary type variables, and
300 -- default their kind (e.g. from OpenTypeKind to TypeKind)
301 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
303 -- BUILD THE POLYMORPHIC RESULT IDs
305 exports = map mk_export mono_bind_infos
306 poly_ids = [poly_id | (_, poly_id, _) <- exports]
307 dict_tys = map idType dict_ids
309 inlines = mkNameSet [ name
310 | L _ (InlineSig True (L _ name) _) <- sigs]
311 -- Any INLINE sig (regardless of phase control)
312 -- makes the RHS look small
313 inline_phases = listToFM [ (name, phase)
314 | L _ (InlineSig _ (L _ name) phase) <- sigs,
315 not (isAlwaysActive phase)]
316 -- Set the IdInfo field to control the inline phase
317 -- AlwaysActive is the default, so don't bother with them
318 add_inlines id = attachInlinePhase inline_phases id
320 mk_export (binder_name, mb_sig, mono_id)
322 Just sig -> (sig_tvs sig, add_inlines (sig_id sig), mono_id)
323 Nothing -> (tyvars_to_gen', add_inlines new_poly_id, mono_id)
325 new_poly_id = mkLocalId binder_name poly_ty
326 poly_ty = mkForAllTys tyvars_to_gen'
330 -- ZONK THE poly_ids, because they are used to extend the type
331 -- environment; see the invariant on TcEnv.tcExtendIdEnv
332 ; zonked_poly_ids <- mappM zonkId poly_ids
334 ; traceTc (text "binding:" <+> ppr ((dict_ids, dict_binds),
335 exports, map idType zonked_poly_ids))
339 AbsBinds tyvars_to_gen'
343 (dict_binds `unionBags` mbind'),
348 -- If typechecking the binds fails, then return with each
349 -- signature-less binder given type (forall a.a), to minimise
350 -- subsequent error messages
351 recoveryCode mbind lookup_sig
352 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
353 ; return (emptyLHsBinds, poly_ids) }
355 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
356 binder_names = collectHsBindBinders mbind
357 poly_ids = map mk_dummy binder_names
358 mk_dummy name = case lookup_sig name of
359 Just sig -> sig_id sig -- Signature
360 Nothing -> mkLocalId name forall_a_a -- No signature
362 attachInlinePhase inline_phases bndr
363 = case lookupFM inline_phases (idName bndr) of
364 Just prag -> bndr `setInlinePragma` prag
367 -- Check that non-overloaded unlifted bindings are
370 -- c) not a multiple-binding group (more or less implied by (a))
372 checkUnliftedBinds top_lvl is_rec mbind
373 = checkTc (isNotTopLevel top_lvl)
374 (unliftedBindErr "Top-level" mbind) `thenM_`
375 checkTc (isNonRec is_rec)
376 (unliftedBindErr "Recursive" mbind) `thenM_`
377 checkTc (isSingletonBag mbind)
378 (unliftedBindErr "Multiple" mbind)
382 Polymorphic recursion
383 ~~~~~~~~~~~~~~~~~~~~~
384 The game plan for polymorphic recursion in the code above is
386 * Bind any variable for which we have a type signature
387 to an Id with a polymorphic type. Then when type-checking
388 the RHSs we'll make a full polymorphic call.
390 This fine, but if you aren't a bit careful you end up with a horrendous
391 amount of partial application and (worse) a huge space leak. For example:
393 f :: Eq a => [a] -> [a]
396 If we don't take care, after typechecking we get
398 f = /\a -> \d::Eq a -> let f' = f a d
402 Notice the the stupid construction of (f a d), which is of course
403 identical to the function we're executing. In this case, the
404 polymorphic recursion isn't being used (but that's a very common case).
407 f = /\a -> \d::Eq a -> letrec
408 fm = \ys:[a] -> ...fm...
412 This can lead to a massive space leak, from the following top-level defn
418 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
419 f' is another thunk which evaluates to the same thing... and you end
420 up with a chain of identical values all hung onto by the CAF ff.
424 = let f' = f Int dEqInt in \ys. ...f'...
426 = let f' = let f' = f Int dEqInt in \ys. ...f'...
430 Solution: when typechecking the RHSs we always have in hand the
431 *monomorphic* Ids for each binding. So we just need to make sure that
432 if (Method f a d) shows up in the constraints emerging from (...f...)
433 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
434 to the "givens" when simplifying constraints. That's what the "lies_avail"
438 %************************************************************************
440 \subsection{tcMonoBind}
442 %************************************************************************
444 @tcMonoBinds@ deals with a single @MonoBind@.
445 The signatures have been dealt with already.
448 tcMonoBinds :: LHsBinds Name
449 -> TcSigFun -> RecFlag
450 -> TcM (LHsBinds TcId, [MonoBindInfo])
452 tcMonoBinds binds lookup_sig is_rec
453 = do { tc_binds <- mapBagM (wrapLocM (tcLhs lookup_sig)) binds
455 -- Bring (a) the scoped type variables, and (b) the Ids, into scope for the RHSs
456 -- For (a) it's ok to bring them all into scope at once, even
457 -- though each type sig should scope only over its own RHS,
458 -- because the renamer has sorted all that out.
459 ; let mono_info = getMonoBindInfo tc_binds
460 rhs_tvs = [ (name, mkTyVarTy tv)
461 | (_, Just sig, _) <- mono_info,
462 (name, tv) <- sig_scoped sig `zip` sig_tvs sig ]
463 rhs_id_env = map mk mono_info -- A binding for each term variable
465 ; binds' <- tcExtendTyVarEnv2 rhs_tvs $
466 tcExtendIdEnv2 rhs_id_env $
467 mapBagM (wrapLocM tcRhs) tc_binds
468 ; return (binds', mono_info) }
470 mk (name, Just sig, _) = (name, sig_id sig) -- Use the type sig if there is one
471 mk (name, Nothing, mono_id) = (name, mono_id) -- otherwise use a monomorphic version
473 ------------------------
474 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
475 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
476 -- if there's a signature for it, use the instantiated signature type
477 -- otherwise invent a type variable
478 -- You see that quite directly in the FunBind case.
480 -- But there's a complication for pattern bindings:
481 -- data T = MkT (forall a. a->a)
483 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
484 -- but we want to get (f::forall a. a->a) as the RHS environment.
485 -- The simplest way to do this is to typecheck the pattern, and then look up the
486 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
487 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
489 data TcMonoBind -- Half completed; LHS done, RHS not done
490 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
491 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
493 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
494 -- Type signature (if any), and
495 -- the monomorphic bound things
497 bndrNames :: [MonoBindInfo] -> [Name]
498 bndrNames mbi = [n | (n,_,_) <- mbi]
500 getMonoType :: MonoBindInfo -> TcTauType
501 getMonoType (_,_,mono_id) = idType mono_id
503 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
504 tcLhs lookup_sig (FunBind (L nm_loc name) inf matches)
505 = do { let mb_sig = lookup_sig name
506 ; mono_name <- newLocalName name
507 ; mono_ty <- mk_mono_ty mb_sig
508 ; let mono_id = mkLocalId mono_name mono_ty
509 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
511 mk_mono_ty (Just sig) = return (sig_tau sig)
512 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
514 tcLhs lookup_sig bind@(PatBind pat grhss _)
515 = do { let tc_pat exp_ty = tcPat (LetPat lookup_sig) pat exp_ty lookup_infos
516 ; ((pat', ex_tvs, infos), pat_ty)
517 <- addErrCtxt (patMonoBindsCtxt pat grhss)
520 -- Don't know how to deal with pattern-bound existentials yet
521 ; checkTc (null ex_tvs) (existentialExplode bind)
523 ; return (TcPatBind infos pat' grhss pat_ty) }
525 names = collectPatBinders pat
527 -- After typechecking the pattern, look up the binder
528 -- names, which the pattern has brought into scope.
529 lookup_infos :: TcM [MonoBindInfo]
530 lookup_infos = do { mono_ids <- tcLookupLocalIds names
531 ; return [ (name, lookup_sig name, mono_id)
532 | (name, mono_id) <- names `zip` mono_ids] }
535 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
536 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
537 = do { matches' <- tcMatchesFun (idName mono_id) matches
538 (Check (idType mono_id))
539 ; return (FunBind fun' inf matches') }
541 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
542 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
543 tcGRHSsPat grhss (Check pat_ty)
544 ; return (PatBind pat' grhss' pat_ty) }
547 ---------------------
548 getMonoBindInfo :: Bag (Located TcMonoBind) -> [MonoBindInfo]
549 getMonoBindInfo tc_binds
550 = foldrBag (get_info . unLoc) [] tc_binds
552 get_info (TcFunBind info _ _ _) rest = info : rest
553 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
557 %************************************************************************
559 \subsection{getTyVarsToGen}
561 %************************************************************************
564 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
565 -- The trick here is that all the signatures should have the same
566 -- context, and we want to share type variables for that context, so that
567 -- all the right hand sides agree a common vocabulary for their type
569 tcTySigs [] = return []
572 = do { (tc_sig1 : tc_sigs) <- mappM tcTySig sigs
573 ; tc_sigs' <- mapM (checkSigCtxt tc_sig1) tc_sigs
574 ; return (tc_sig1 : tc_sigs') }
576 tcTySig :: LSig Name -> TcM TcSigInfo
577 tcTySig (L span (Sig (L _ name) ty))
579 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
580 ; let rigid_info = SigSkol name
581 poly_id = mkLocalId name sigma_ty
583 -- The scoped names are the ones explicitly mentioned
584 -- in the HsForAll. (There may be more in sigma_ty, because
585 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
586 scoped_names = case ty of
587 L _ (HsForAllTy _ tvs _ _) -> hsLTyVarNames tvs
590 ; (tvs, theta, tau) <- tcSkolType rigid_info sigma_ty
591 ; loc <- getInstLoc (SigOrigin rigid_info)
592 ; return (TcSigInfo { sig_id = poly_id, sig_scoped = scoped_names,
593 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
596 checkSigCtxt :: TcSigInfo -> TcSigInfo -> TcM TcSigInfo
597 checkSigCtxt sig1 sig@(TcSigInfo { sig_tvs = tvs, sig_theta = theta, sig_tau = tau })
598 = -- Try to match the context of this signature with
599 -- that of the first signature
600 case tcMatchPreds (sig_tvs sig) (sig_theta sig) (sig_theta sig1) of {
601 Nothing -> bale_out ;
604 case check_tvs tenv tvs of {
605 Nothing -> bale_out ;
609 subst = mkOpenTvSubst tenv
611 return (sig { sig_tvs = tvs',
612 sig_theta = substTheta subst theta,
613 sig_tau = substTy subst tau }) }}
616 bale_out = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
618 sigContextsErr (sig_id sig1) (sig_id sig)
620 -- Rather tedious check that the type variables
621 -- have been matched only with another type variable,
622 -- and that two type variables have not been matched
624 -- A return of Nothing indicates that one of the bad
625 -- things has happened
626 check_tvs :: TvSubstEnv -> [TcTyVar] -> Maybe [TcTyVar]
627 check_tvs tenv [] = Just []
628 check_tvs tenv (tv:tvs)
629 = do { let ty = lookupVarEnv tenv tv `orElse` mkTyVarTy tv
630 ; tv' <- tcGetTyVar_maybe ty
631 ; tvs' <- check_tvs tenv tvs
634 else Just (tv':tvs') }
638 generalise :: TopLevelFlag -> Bool -> [MonoBindInfo] -> [TcSigInfo] -> [Inst]
639 -> TcM ([TcTyVar], TcDictBinds, [TcId])
640 generalise top_lvl is_unrestricted mono_infos sigs lie_req
641 | not is_unrestricted -- RESTRICTED CASE
642 = -- Check signature contexts are empty
643 do { checkTc (all is_mono_sig sigs)
644 (restrictedBindCtxtErr bndr_names)
646 -- Now simplify with exactly that set of tyvars
647 -- We have to squash those Methods
648 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndr_names
651 -- Check that signature type variables are OK
652 ; final_qtvs <- checkSigsTyVars qtvs sigs
654 ; return (final_qtvs, binds, []) }
656 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
657 = tcSimplifyInfer doc tau_tvs lie_req
659 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
660 = do { let sig1 = head sigs
661 ; sig_lie <- newDictsAtLoc (sig_loc sig1) (sig_theta sig1)
662 ; let -- The "sig_avails" is the stuff available. We get that from
663 -- the context of the type signature, BUT ALSO the lie_avail
664 -- so that polymorphic recursion works right (see comments at end of fn)
665 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
666 sig_avails = sig_lie ++ local_meths
668 -- Check that the needed dicts can be
669 -- expressed in terms of the signature ones
670 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
672 -- Check that signature type variables are OK
673 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
675 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
678 bndr_names = bndrNames mono_infos
679 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
680 is_mono_sig sig = null (sig_theta sig)
681 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndr_names
683 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
684 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
685 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
687 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
688 checkSigsTyVars qtvs sigs
689 = mappM check_one sigs `thenM` \ sig_tvs_s ->
691 -- 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
700 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
701 all_tvs = extendVarSetList sig_tvs qtvs
703 returnM (varSetElems all_tvs)
705 check_one (TcSigInfo {sig_id = id, sig_tvs = tvs, sig_theta = theta, sig_tau = tau})
706 = addErrCtxt (ptext SLIT("In the type signature for")
707 <+> quotes (ppr id)) $
708 addErrCtxtM (sigCtxt id tvs theta tau) $
709 do { checkSigTyVars tvs; return tvs }
712 @getTyVarsToGen@ decides what type variables to generalise over.
714 For a "restricted group" -- see the monomorphism restriction
715 for a definition -- we bind no dictionaries, and
716 remove from tyvars_to_gen any constrained type variables
718 *Don't* simplify dicts at this point, because we aren't going
719 to generalise over these dicts. By the time we do simplify them
720 we may well know more. For example (this actually came up)
722 f x = array ... xs where xs = [1,2,3,4,5]
723 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
724 stuff. If we simplify only at the f-binding (not the xs-binding)
725 we'll know that the literals are all Ints, and we can just produce
728 Find all the type variables involved in overloading, the
729 "constrained_tyvars". These are the ones we *aren't* going to
730 generalise. We must be careful about doing this:
732 (a) If we fail to generalise a tyvar which is not actually
733 constrained, then it will never, ever get bound, and lands
734 up printed out in interface files! Notorious example:
735 instance Eq a => Eq (Foo a b) where ..
736 Here, b is not constrained, even though it looks as if it is.
737 Another, more common, example is when there's a Method inst in
738 the LIE, whose type might very well involve non-overloaded
740 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
741 the simple thing instead]
743 (b) On the other hand, we mustn't generalise tyvars which are constrained,
744 because we are going to pass on out the unmodified LIE, with those
745 tyvars in it. They won't be in scope if we've generalised them.
747 So we are careful, and do a complete simplification just to find the
748 constrained tyvars. We don't use any of the results, except to
749 find which tyvars are constrained.
752 isUnRestrictedGroup :: LHsBinds Name -> [TcSigInfo] -> TcM Bool
753 isUnRestrictedGroup binds sigs
754 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
755 ; return (not mono_restriction || all_unrestricted) }
757 all_unrestricted = all (unrestricted . unLoc) (bagToList binds)
758 tysig_names = map (idName . sig_id) sigs
760 unrestricted (PatBind other _ _) = False
761 unrestricted (VarBind v _) = v `is_elem` tysig_names
762 unrestricted (FunBind v _ matches) = unrestricted_match matches
763 || unLoc v `is_elem` tysig_names
765 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
766 -- No args => like a pattern binding
767 unrestricted_match other = True
768 -- Some args => a function binding
770 is_elem v vs = isIn "isUnResMono" v vs
774 %************************************************************************
776 \subsection{SPECIALIZE pragmas}
778 %************************************************************************
780 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
781 pragmas. It is convenient for them to appear in the @[RenamedSig]@
782 part of a binding because then the same machinery can be used for
783 moving them into place as is done for type signatures.
788 f :: Ord a => [a] -> b -> b
789 {-# SPECIALIZE f :: [Int] -> b -> b #-}
792 For this we generate:
794 f* = /\ b -> let d1 = ...
798 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
799 retain a right-hand-side that the simplifier will otherwise discard as
800 dead code... the simplifier has a flag that tells it not to discard
801 SpecPragmaId bindings.
803 In this case the f* retains a call-instance of the overloaded
804 function, f, (including appropriate dictionaries) so that the
805 specialiser will subsequently discover that there's a call of @f@ at
806 Int, and will create a specialisation for @f@. After that, the
807 binding for @f*@ can be discarded.
809 We used to have a form
810 {-# SPECIALISE f :: <type> = g #-}
811 which promised that g implemented f at <type>, but we do that with
813 {-# RULES (f::<type>) = g #-}
816 tcSpecSigs :: [LSig Name] -> TcM (LHsBinds TcId)
817 tcSpecSigs (L loc (SpecSig (L nm_loc name) poly_ty) : sigs)
818 = -- SPECIALISE f :: forall b. theta => tau = g
820 addErrCtxt (valSpecSigCtxt name poly_ty) $
822 -- Get and instantiate its alleged specialised type
823 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
825 -- Check that f has a more general type, and build a RHS for
826 -- the spec-pragma-id at the same time
827 getLIE (tcCheckSigma (L nm_loc (HsVar name)) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
829 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
830 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
832 -- Just specialise "f" by building a SpecPragmaId binding
833 -- It is the thing that makes sure we don't prematurely
834 -- dead-code-eliminate the binding we are really interested in.
835 newLocalName name `thenM` \ spec_name ->
837 spec_bind = VarBind (mkSpecPragmaId spec_name sig_ty)
838 (mkHsLet spec_binds spec_expr)
841 -- Do the rest and combine
842 tcSpecSigs sigs `thenM` \ binds_rest ->
843 returnM (binds_rest `snocBag` L loc spec_bind)
845 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
846 tcSpecSigs [] = returnM emptyLHsBinds
849 %************************************************************************
851 \subsection[TcBinds-errors]{Error contexts and messages}
853 %************************************************************************
857 -- This one is called on LHS, when pat and grhss are both Name
858 -- and on RHS, when pat is TcId and grhss is still Name
859 patMonoBindsCtxt pat grhss
860 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
862 -----------------------------------------------
864 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
865 nest 4 (ppr v <+> dcolon <+> ppr ty)]
867 -----------------------------------------------
868 sigContextsErr id1 id2
869 = vcat [ptext SLIT("Mis-match between the contexts of the signatures for"),
870 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
871 ppr id2 <+> dcolon <+> ppr (idType id2)]),
872 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
875 -----------------------------------------------
876 unliftedBindErr flavour mbind
877 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
880 -----------------------------------------------
881 existentialExplode mbinds
882 = hang (vcat [text "My brain just exploded.",
883 text "I can't handle pattern bindings for existentially-quantified constructors.",
884 text "In the binding group"])
887 -----------------------------------------------
888 restrictedBindCtxtErr binder_names
889 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
890 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
891 ptext SLIT("that falls under the monomorphism restriction")])
894 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names