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,
28 import TcUnify ( Expected(..), tcInfer, unifyTheta,
29 bleatEscapedTvs, sigCtxt )
30 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted,
31 tcSimplifyToDicts, tcSimplifyIPs )
32 import TcHsType ( tcHsSigType, UserTypeCtxt(..), tcAddLetBoundTyVars,
33 TcSigInfo(..), TcSigFun, lookupSig
35 import TcPat ( tcPat, PatCtxt(..) )
36 import TcSimplify ( bindInstsOfLocalFuns )
37 import TcMType ( newTyFlexiVarTy, zonkQuantifiedTyVar,
38 tcInstSigType, zonkTcTypes, zonkTcTyVar )
39 import TcType ( TcTyVar, SkolemInfo(SigSkol),
40 TcTauType, TcSigmaType,
41 mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
42 mkForAllTy, isUnLiftedType, tcGetTyVar,
43 mkTyVarTys, tidyOpenTyVar, tidyOpenType )
44 import Kind ( argTypeKind )
45 import VarEnv ( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv, emptyTidyEnv )
46 import TysPrim ( alphaTyVar )
47 import Id ( mkLocalId, mkSpecPragmaId, setInlinePragma )
48 import Var ( idType, idName )
52 import SrcLoc ( Located(..), unLoc, noLoc, getLoc )
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 traceTc (text "tcMonoBinds" <+> vcat [ppr n <+> ppr id <+> ppr (idType id) | (n,id) <- rhs_id_env]) `thenM_`
468 mapBagM (wrapLocM tcRhs) tc_binds
469 ; return (binds', mono_info) }
471 mk (name, Just sig, _) = (name, sig_id sig) -- Use the type sig if there is one
472 mk (name, Nothing, mono_id) = (name, mono_id) -- otherwise use a monomorphic version
474 ------------------------
475 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
476 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
477 -- if there's a signature for it, use the instantiated signature type
478 -- otherwise invent a type variable
479 -- You see that quite directly in the FunBind case.
481 -- But there's a complication for pattern bindings:
482 -- data T = MkT (forall a. a->a)
484 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
485 -- but we want to get (f::forall a. a->a) as the RHS environment.
486 -- The simplest way to do this is to typecheck the pattern, and then look up the
487 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
488 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
490 data TcMonoBind -- Half completed; LHS done, RHS not done
491 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
492 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
494 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
495 -- Type signature (if any), and
496 -- the monomorphic bound things
498 bndrNames :: [MonoBindInfo] -> [Name]
499 bndrNames mbi = [n | (n,_,_) <- mbi]
501 getMonoType :: MonoBindInfo -> TcTauType
502 getMonoType (_,_,mono_id) = idType mono_id
504 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
505 tcLhs lookup_sig (FunBind (L nm_loc name) inf matches)
506 = do { let mb_sig = lookup_sig name
507 ; mono_name <- newLocalName name
508 ; mono_ty <- mk_mono_ty mb_sig
509 ; let mono_id = mkLocalId mono_name mono_ty
510 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
512 mk_mono_ty (Just sig) = return (sig_tau sig)
513 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
515 tcLhs lookup_sig bind@(PatBind pat grhss _)
516 = do { let tc_pat exp_ty = tcPat (LetPat lookup_sig) pat exp_ty lookup_infos
517 ; ((pat', ex_tvs, infos), pat_ty)
518 <- addErrCtxt (patMonoBindsCtxt pat grhss)
521 -- Don't know how to deal with pattern-bound existentials yet
522 ; checkTc (null ex_tvs) (existentialExplode bind)
524 ; return (TcPatBind infos pat' grhss pat_ty) }
526 names = collectPatBinders pat
528 -- After typechecking the pattern, look up the binder
529 -- names, which the pattern has brought into scope.
530 lookup_infos :: TcM [MonoBindInfo]
531 lookup_infos = do { mono_ids <- tcLookupLocalIds names
532 ; return [ (name, lookup_sig name, mono_id)
533 | (name, mono_id) <- names `zip` mono_ids] }
536 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
537 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
538 = do { matches' <- tcMatchesFun (idName mono_id) matches
539 (Check (idType mono_id))
540 ; return (FunBind fun' inf matches') }
542 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
543 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
544 tcGRHSsPat grhss (Check pat_ty)
545 ; return (PatBind pat' grhss' pat_ty) }
548 ---------------------
549 getMonoBindInfo :: Bag (Located TcMonoBind) -> [MonoBindInfo]
550 getMonoBindInfo tc_binds
551 = foldrBag (get_info . unLoc) [] tc_binds
553 get_info (TcFunBind info _ _ _) rest = info : rest
554 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
558 %************************************************************************
560 \subsection{getTyVarsToGen}
562 %************************************************************************
564 Type signatures are tricky. See Note [Signature skolems] in TcType
567 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
568 -- The trick here is that all the signatures should have the same
569 -- context, and we want to share type variables for that context, so that
570 -- all the right hand sides agree a common vocabulary for their type
572 tcTySigs [] = return []
575 = do { (tc_sig1 : tc_sigs) <- mappM tcTySig sigs
576 ; mapM (check_ctxt tc_sig1) tc_sigs
577 ; return (tc_sig1 : tc_sigs) }
579 -- Check tha all the signature contexts are the same
580 -- The type signatures on a mutually-recursive group of definitions
581 -- must all have the same context (or none).
583 -- We unify them because, with polymorphic recursion, their types
584 -- might not otherwise be related. This is a rather subtle issue.
585 check_ctxt :: TcSigInfo -> TcSigInfo -> TcM ()
586 check_ctxt sig1@(TcSigInfo { sig_theta = theta1 }) sig@(TcSigInfo { sig_theta = theta })
587 = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
588 addErrCtxt (sigContextsCtxt sig1 sig) $
589 unifyTheta theta1 theta
592 tcTySig :: LSig Name -> TcM TcSigInfo
593 tcTySig (L span (Sig (L _ name) ty))
595 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
596 ; (tvs, theta, tau) <- tcInstSigType name sigma_ty
597 ; loc <- getInstLoc (SigOrigin (SigSkol name))
599 ; let poly_id = mkLocalId name sigma_ty
601 -- The scoped names are the ones explicitly mentioned
602 -- in the HsForAll. (There may be more in sigma_ty, because
603 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
604 scoped_names = case ty of
605 L _ (HsForAllTy _ tvs _ _) -> hsLTyVarNames tvs
608 ; return (TcSigInfo { sig_id = poly_id, sig_scoped = scoped_names,
609 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
614 generalise :: TopLevelFlag -> Bool -> [MonoBindInfo] -> [TcSigInfo] -> [Inst]
615 -> TcM ([TcTyVar], TcDictBinds, [TcId])
616 generalise top_lvl is_unrestricted mono_infos sigs lie_req
617 | not is_unrestricted -- RESTRICTED CASE
618 = -- Check signature contexts are empty
619 do { checkTc (all is_mono_sig sigs)
620 (restrictedBindCtxtErr bndr_names)
622 -- Now simplify with exactly that set of tyvars
623 -- We have to squash those Methods
624 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndr_names
627 -- Check that signature type variables are OK
628 ; final_qtvs <- checkSigsTyVars qtvs sigs
630 ; return (final_qtvs, binds, []) }
632 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
633 = tcSimplifyInfer doc tau_tvs lie_req
635 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
636 = do { let sig1 = head sigs
637 ; sig_lie <- newDictsAtLoc (sig_loc sig1) (sig_theta sig1)
638 ; let -- The "sig_avails" is the stuff available. We get that from
639 -- the context of the type signature, BUT ALSO the lie_avail
640 -- so that polymorphic recursion works right (see comments at end of fn)
641 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
642 sig_avails = sig_lie ++ local_meths
644 -- Check that the needed dicts can be
645 -- expressed in terms of the signature ones
646 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
648 -- Check that signature type variables are OK
649 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
651 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
654 bndr_names = bndrNames mono_infos
655 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
656 is_mono_sig sig = null (sig_theta sig)
657 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndr_names
659 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
660 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
661 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
663 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
664 checkSigsTyVars qtvs sigs
665 = do { gbl_tvs <- tcGetGlobalTyVars
666 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
668 ; let -- Sigh. Make sure that all the tyvars in the type sigs
669 -- appear in the returned ty var list, which is what we are
670 -- going to generalise over. Reason: we occasionally get
672 -- type T a = () -> ()
675 -- Here, 'a' won't appear in qtvs, so we have to add it
676 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
677 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
680 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
681 sig_theta = theta, sig_tau = tau})
682 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
683 addErrCtxtM (sigCtxt id tvs theta tau) $
684 do { tvs' <- checkDistinctTyVars tvs
685 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
686 (bleatEscapedTvs gbl_tvs tvs tvs')
689 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
690 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
691 -- are still all type variables, and all distinct from each other.
692 -- It returns a zonked set of type variables.
693 -- For example, if the type sig is
694 -- f :: forall a b. a -> b -> b
695 -- we want to check that 'a' and 'b' haven't
696 -- (a) been unified with a non-tyvar type
697 -- (b) been unified with each other (all distinct)
699 checkDistinctTyVars sig_tvs
700 = do { zonked_tvs <- mapM zonk_one sig_tvs
701 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
702 ; return zonked_tvs }
704 zonk_one sig_tv = do { ty <- zonkTcTyVar sig_tv
705 ; return (tcGetTyVar "checkDistinctTyVars" ty) }
706 -- 'ty' is bound to be a type variable, because SigSkolTvs
707 -- can only be unified with type variables
709 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
710 -- The TyVarEnv maps each zonked type variable back to its
711 -- corresponding user-written signature type variable
712 check_dup acc (sig_tv, zonked_tv)
713 = case lookupVarEnv acc zonked_tv of
714 Just sig_tv' -> bomb_out sig_tv sig_tv'
716 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
718 bomb_out sig_tv1 sig_tv2
719 = failWithTc (ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
720 <+> ptext SLIT("is unified with another quantified type variable")
723 (env1, tidy_tv1) = tidyOpenTyVar emptyTidyEnv sig_tv1
724 (_env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
728 @getTyVarsToGen@ decides what type variables to generalise over.
730 For a "restricted group" -- see the monomorphism restriction
731 for a definition -- we bind no dictionaries, and
732 remove from tyvars_to_gen any constrained type variables
734 *Don't* simplify dicts at this point, because we aren't going
735 to generalise over these dicts. By the time we do simplify them
736 we may well know more. For example (this actually came up)
738 f x = array ... xs where xs = [1,2,3,4,5]
739 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
740 stuff. If we simplify only at the f-binding (not the xs-binding)
741 we'll know that the literals are all Ints, and we can just produce
744 Find all the type variables involved in overloading, the
745 "constrained_tyvars". These are the ones we *aren't* going to
746 generalise. We must be careful about doing this:
748 (a) If we fail to generalise a tyvar which is not actually
749 constrained, then it will never, ever get bound, and lands
750 up printed out in interface files! Notorious example:
751 instance Eq a => Eq (Foo a b) where ..
752 Here, b is not constrained, even though it looks as if it is.
753 Another, more common, example is when there's a Method inst in
754 the LIE, whose type might very well involve non-overloaded
756 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
757 the simple thing instead]
759 (b) On the other hand, we mustn't generalise tyvars which are constrained,
760 because we are going to pass on out the unmodified LIE, with those
761 tyvars in it. They won't be in scope if we've generalised them.
763 So we are careful, and do a complete simplification just to find the
764 constrained tyvars. We don't use any of the results, except to
765 find which tyvars are constrained.
768 isUnRestrictedGroup :: LHsBinds Name -> [TcSigInfo] -> TcM Bool
769 isUnRestrictedGroup binds sigs
770 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
771 ; return (not mono_restriction || all_unrestricted) }
773 all_unrestricted = all (unrestricted . unLoc) (bagToList binds)
774 tysig_names = map (idName . sig_id) sigs
776 unrestricted (PatBind other _ _) = False
777 unrestricted (VarBind v _) = v `is_elem` tysig_names
778 unrestricted (FunBind v _ matches) = unrestricted_match matches
779 || unLoc v `is_elem` tysig_names
781 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
782 -- No args => like a pattern binding
783 unrestricted_match other = True
784 -- Some args => a function binding
786 is_elem v vs = isIn "isUnResMono" v vs
790 %************************************************************************
792 \subsection{SPECIALIZE pragmas}
794 %************************************************************************
796 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
797 pragmas. It is convenient for them to appear in the @[RenamedSig]@
798 part of a binding because then the same machinery can be used for
799 moving them into place as is done for type signatures.
804 f :: Ord a => [a] -> b -> b
805 {-# SPECIALIZE f :: [Int] -> b -> b #-}
808 For this we generate:
810 f* = /\ b -> let d1 = ...
814 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
815 retain a right-hand-side that the simplifier will otherwise discard as
816 dead code... the simplifier has a flag that tells it not to discard
817 SpecPragmaId bindings.
819 In this case the f* retains a call-instance of the overloaded
820 function, f, (including appropriate dictionaries) so that the
821 specialiser will subsequently discover that there's a call of @f@ at
822 Int, and will create a specialisation for @f@. After that, the
823 binding for @f*@ can be discarded.
825 We used to have a form
826 {-# SPECIALISE f :: <type> = g #-}
827 which promised that g implemented f at <type>, but we do that with
829 {-# RULES (f::<type>) = g #-}
832 tcSpecSigs :: [LSig Name] -> TcM (LHsBinds TcId)
833 tcSpecSigs (L loc (SpecSig (L nm_loc name) poly_ty) : sigs)
834 = -- SPECIALISE f :: forall b. theta => tau = g
836 addErrCtxt (valSpecSigCtxt name poly_ty) $
838 -- Get and instantiate its alleged specialised type
839 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
841 -- Check that f has a more general type, and build a RHS for
842 -- the spec-pragma-id at the same time
843 getLIE (tcCheckSigma (L nm_loc (HsVar name)) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
845 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
846 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
848 -- Just specialise "f" by building a SpecPragmaId binding
849 -- It is the thing that makes sure we don't prematurely
850 -- dead-code-eliminate the binding we are really interested in.
851 newLocalName name `thenM` \ spec_name ->
853 spec_bind = VarBind (mkSpecPragmaId spec_name sig_ty)
854 (mkHsLet spec_binds spec_expr)
857 -- Do the rest and combine
858 tcSpecSigs sigs `thenM` \ binds_rest ->
859 returnM (binds_rest `snocBag` L loc spec_bind)
861 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
862 tcSpecSigs [] = returnM emptyLHsBinds
865 %************************************************************************
867 \subsection[TcBinds-errors]{Error contexts and messages}
869 %************************************************************************
873 -- This one is called on LHS, when pat and grhss are both Name
874 -- and on RHS, when pat is TcId and grhss is still Name
875 patMonoBindsCtxt pat grhss
876 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
878 -----------------------------------------------
880 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
881 nest 4 (ppr v <+> dcolon <+> ppr ty)]
883 -----------------------------------------------
884 sigContextsCtxt sig1 sig2
885 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
886 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
887 ppr id2 <+> dcolon <+> ppr (idType id2)]),
888 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
894 -----------------------------------------------
895 unliftedBindErr flavour mbind
896 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
899 -----------------------------------------------
900 existentialExplode mbinds
901 = hang (vcat [text "My brain just exploded.",
902 text "I can't handle pattern bindings for existentially-quantified constructors.",
903 text "In the binding group"])
906 -----------------------------------------------
907 restrictedBindCtxtErr binder_names
908 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
909 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
910 ptext SLIT("that falls under the monomorphism restriction")])
913 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names