2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBinds,
8 tcHsBootSigs, tcMonoBinds, tcSpecSigs,
11 #include "HsVersions.h"
13 import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
14 import {-# SOURCE #-} TcExpr ( tcCheckSigma, tcCheckRho )
16 import DynFlags ( DynFlag(Opt_MonomorphismRestriction) )
17 import HsSyn ( HsExpr(..), HsBind(..), LHsBinds, Sig(..),
18 LSig, Match(..), HsBindGroup(..), IPBind(..),
19 HsType(..), HsExplicitForAll(..), hsLTyVarNames, isVanillaLSig,
20 LPat, GRHSs, MatchGroup(..), emptyLHsBinds, isEmptyLHsBinds,
21 collectHsBindBinders, collectPatBinders, pprPatBind
23 import TcHsSyn ( zonkId, mkHsLet )
26 import Inst ( newDictsAtLoc, newIPDict, instToId )
27 import TcEnv ( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2,
28 newLocalName, tcLookupLocalIds, pprBinders,
30 import TcUnify ( Expected(..), tcInfer, unifyTheta,
31 bleatEscapedTvs, sigCtxt )
32 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted,
33 tcSimplifyToDicts, tcSimplifyIPs )
34 import TcHsType ( tcHsSigType, UserTypeCtxt(..), tcAddLetBoundTyVars,
35 TcSigInfo(..), TcSigFun, lookupSig
37 import TcPat ( tcPat, PatCtxt(..) )
38 import TcSimplify ( bindInstsOfLocalFuns )
39 import TcMType ( newTyFlexiVarTy, zonkQuantifiedTyVar,
40 tcInstSigType, zonkTcType, zonkTcTypes, zonkTcTyVar )
41 import TcType ( TcTyVar, SkolemInfo(SigSkol),
42 TcTauType, TcSigmaType, isUnboxedTupleType,
43 mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
44 mkForAllTy, isUnLiftedType, tcGetTyVar,
45 mkTyVarTys, tidyOpenTyVar )
46 import Kind ( argTypeKind )
47 import VarEnv ( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv, emptyTidyEnv )
48 import TysPrim ( alphaTyVar )
49 import Id ( Id, mkLocalId, mkVanillaGlobal, mkSpecPragmaId, setInlinePragma )
50 import IdInfo ( vanillaIdInfo )
51 import Var ( idType, idName )
55 import SrcLoc ( Located(..), unLoc, noLoc, getLoc )
57 import ErrUtils ( Message )
59 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isRec,
60 isNotTopLevel, isAlwaysActive )
61 import FiniteMap ( listToFM, lookupFM )
66 %************************************************************************
68 \subsection{Type-checking bindings}
70 %************************************************************************
72 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
73 it needs to know something about the {\em usage} of the things bound,
74 so that it can create specialisations of them. So @tcBindsAndThen@
75 takes a function which, given an extended environment, E, typechecks
76 the scope of the bindings returning a typechecked thing and (most
77 important) an LIE. It is this LIE which is then used as the basis for
78 specialising the things bound.
80 @tcBindsAndThen@ also takes a "combiner" which glues together the
81 bindings and the "thing" to make a new "thing".
83 The real work is done by @tcBindWithSigsAndThen@.
85 Recursive and non-recursive binds are handled in essentially the same
86 way: because of uniques there are no scoping issues left. The only
87 difference is that non-recursive bindings can bind primitive values.
89 Even for non-recursive binding groups we add typings for each binder
90 to the LVE for the following reason. When each individual binding is
91 checked the type of its LHS is unified with that of its RHS; and
92 type-checking the LHS of course requires that the binder is in scope.
94 At the top-level the LIE is sure to contain nothing but constant
95 dictionaries, which we resolve at the module level.
98 tcTopBinds :: [HsBindGroup Name] -> TcM (LHsBinds TcId, TcLclEnv)
99 -- Note: returning the TcLclEnv is more than we really
100 -- want. The bit we care about is the local bindings
101 -- and the free type variables thereof
103 = tc_binds_and_then TopLevel glue binds $
104 do { env <- getLclEnv
105 ; return (emptyLHsBinds, env) }
107 -- The top level bindings are flattened into a giant
108 -- implicitly-mutually-recursive MonoBinds
109 glue (HsBindGroup binds1 _ _) (binds2, env) = (binds1 `unionBags` binds2, env)
110 glue (HsIPBinds _) _ = panic "Top-level HsIpBinds"
111 -- Can't have a HsIPBinds at top level
113 tcHsBootSigs :: [HsBindGroup Name] -> TcM [Id]
114 -- A hs-boot file has only one BindGroup, and it only has type
115 -- signatures in it. The renamer checked all this
116 tcHsBootSigs [HsBindGroup binds sigs _]
117 = do { checkTc (isEmptyLHsBinds binds) badBootDeclErr
118 ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
120 tc_boot_sig (Sig (L _ name) ty)
121 = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
122 ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
123 -- Notice that we make GlobalIds, not LocalIds
124 tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
126 badBootDeclErr :: Message
127 badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file")
130 :: (HsBindGroup TcId -> thing -> thing) -- Combinator
131 -> [HsBindGroup Name]
135 tcBindsAndThen = tc_binds_and_then NotTopLevel
137 tc_binds_and_then top_lvl combiner [] do_next
139 tc_binds_and_then top_lvl combiner (group : groups) do_next
140 = tc_bind_and_then top_lvl combiner group $
141 tc_binds_and_then top_lvl combiner groups do_next
143 tc_bind_and_then top_lvl combiner (HsIPBinds binds) do_next
144 = getLIE do_next `thenM` \ (result, expr_lie) ->
145 mapAndUnzipM (wrapLocSndM tc_ip_bind) binds `thenM` \ (avail_ips, binds') ->
147 -- If the binding binds ?x = E, we must now
148 -- discharge any ?x constraints in expr_lie
149 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
151 returnM (combiner (HsIPBinds binds') $
152 combiner (HsBindGroup dict_binds [] Recursive) result)
154 -- I wonder if we should do these one at at time
157 tc_ip_bind (IPBind ip expr)
158 = newTyFlexiVarTy argTypeKind `thenM` \ ty ->
159 newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
160 tcCheckRho expr ty `thenM` \ expr' ->
161 returnM (ip_inst, (IPBind ip' expr'))
163 tc_bind_and_then top_lvl combiner (HsBindGroup binds sigs is_rec) do_next
164 | isEmptyLHsBinds binds
167 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
168 -- Notice that they scope over
169 -- a) the type signatures in the binding group
170 -- b) the bindings in the group
171 -- c) the scope of the binding group (the "in" part)
172 tcAddLetBoundTyVars binds $
175 TopLevel -- For the top level don't bother will all this
176 -- bindInstsOfLocalFuns stuff. All the top level
177 -- things are rec'd together anyway, so it's fine to
178 -- leave them to the tcSimplifyTop, and quite a bit faster too
179 -> tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
180 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
181 returnM (combiner (HsBindGroup
182 (poly_binds `unionBags` prag_binds)
187 NotTopLevel -- For nested bindings we must do the bindInstsOfLocalFuns thing.
188 | not (isRec is_rec) -- Non-recursive group
189 -> -- We want to keep non-recursive things non-recursive
190 -- so that we desugar unlifted bindings correctly
191 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
192 getLIE (tc_body poly_ids) `thenM` \ ((prag_binds, thing), lie) ->
194 -- Create specialisations of functions bound here
195 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
198 combiner (HsBindGroup poly_binds [] NonRecursive) $
199 combiner (HsBindGroup prag_binds [] NonRecursive) $
200 combiner (HsBindGroup lie_binds [] Recursive) $
201 -- NB: the binds returned by tcSimplify and
202 -- bindInstsOfLocalFuns aren't guaranteed in
203 -- dependency order (though we could change that);
204 -- hence the Recursive marker.
208 -> -- NB: polymorphic recursion means that a function
209 -- may use an instance of itself, we must look at the LIE arising
210 -- from the function's own right hand side. Hence the getLIE
211 -- encloses the tcBindWithSigs.
214 tcBindWithSigs top_lvl binds sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
215 tc_body poly_ids `thenM` \ (prag_binds, thing) ->
216 returnM (poly_ids, poly_binds `unionBags` prag_binds, thing)
217 ) `thenM` \ ((poly_ids, extra_binds, thing), lie) ->
219 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
221 returnM (combiner (HsBindGroup
222 (extra_binds `unionBags` lie_binds)
226 tc_body poly_ids -- Type check the pragmas and "thing inside"
227 = -- Extend the environment to bind the new polymorphic Ids
228 tcExtendIdEnv poly_ids $
230 -- Build bindings and IdInfos corresponding to user pragmas
231 tcSpecSigs sigs `thenM` \ prag_binds ->
233 -- Now do whatever happens next, in the augmented envt
234 do_next `thenM` \ thing ->
236 returnM (prag_binds, thing)
240 %************************************************************************
242 \subsection{tcBindWithSigs}
244 %************************************************************************
246 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
247 so all the clever stuff is in here.
249 * binder_names and mbind must define the same set of Names
251 * The Names in tc_ty_sigs must be a subset of binder_names
253 * The Ids in tc_ty_sigs don't necessarily have to have the same name
254 as the Name in the tc_ty_sig
257 tcBindWithSigs :: TopLevelFlag
261 -> TcM (LHsBinds TcId, [TcId])
262 -- The returned TcIds are guaranteed zonked
264 tcBindWithSigs top_lvl mbind sigs is_rec = do
265 { -- TYPECHECK THE SIGNATURES
266 tc_ty_sigs <- recoverM (returnM []) $
267 tcTySigs (filter isVanillaLSig sigs)
268 ; let lookup_sig = lookupSig tc_ty_sigs
270 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
271 ; recoverM (recoveryCode mbind lookup_sig) $ do
273 { traceTc (ptext SLIT("--------------------------------------------------------"))
274 ; traceTc (ptext SLIT("Bindings for") <+> ppr (collectHsBindBinders mbind))
276 -- TYPECHECK THE BINDINGS
277 ; ((mbind', mono_bind_infos), lie_req)
278 <- getLIE (tcMonoBinds mbind lookup_sig is_rec)
280 -- CHECK FOR UNLIFTED BINDINGS
281 -- These must be non-recursive etc, and are not generalised
282 -- They desugar to a case expression in the end
283 ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
284 ; if any isUnLiftedType zonked_mono_tys then
285 do { -- Unlifted bindings
286 checkUnliftedBinds top_lvl is_rec mbind
288 ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
289 mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id)
290 mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id)
292 ; return ( unitBag $ noLoc $ AbsBinds [] [] exports emptyNameSet mbind',
293 [poly_id | (_, poly_id, _) <- exports]) } -- Guaranteed zonked
295 else do -- The normal lifted case: GENERALISE
296 { is_unres <- isUnRestrictedGroup mbind tc_ty_sigs
297 ; (tyvars_to_gen, dict_binds, dict_ids)
298 <- setSrcSpan (getLoc (head (bagToList mbind))) $
299 -- TODO: location a bit awkward, but the mbinds have been
300 -- dependency analysed and may no longer be adjacent
301 addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
302 generalise top_lvl is_unres mono_bind_infos tc_ty_sigs lie_req
304 -- FINALISE THE QUANTIFIED TYPE VARIABLES
305 -- The quantified type variables often include meta type variables
306 -- we want to freeze them into ordinary type variables, and
307 -- default their kind (e.g. from OpenTypeKind to TypeKind)
308 ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
310 -- BUILD THE POLYMORPHIC RESULT IDs
312 exports = map mk_export mono_bind_infos
313 poly_ids = [poly_id | (_, poly_id, _) <- exports]
314 dict_tys = map idType dict_ids
316 inlines = mkNameSet [ name
317 | L _ (InlineSig True (L _ name) _) <- sigs]
318 -- Any INLINE sig (regardless of phase control)
319 -- makes the RHS look small
320 inline_phases = listToFM [ (name, phase)
321 | L _ (InlineSig _ (L _ name) phase) <- sigs,
322 not (isAlwaysActive phase)]
323 -- Set the IdInfo field to control the inline phase
324 -- AlwaysActive is the default, so don't bother with them
325 add_inlines id = attachInlinePhase inline_phases id
327 mk_export (binder_name, mb_sig, mono_id)
329 Just sig -> (sig_tvs sig, add_inlines (sig_id sig), mono_id)
330 Nothing -> (tyvars_to_gen', add_inlines new_poly_id, mono_id)
332 new_poly_id = mkLocalId binder_name poly_ty
333 poly_ty = mkForAllTys tyvars_to_gen'
337 -- ZONK THE poly_ids, because they are used to extend the type
338 -- environment; see the invariant on TcEnv.tcExtendIdEnv
339 ; zonked_poly_ids <- mappM zonkId poly_ids
341 ; traceTc (text "binding:" <+> ppr ((dict_ids, dict_binds),
342 exports, map idType zonked_poly_ids))
346 AbsBinds tyvars_to_gen'
350 (dict_binds `unionBags` mbind'),
355 -- If typechecking the binds fails, then return with each
356 -- signature-less binder given type (forall a.a), to minimise
357 -- subsequent error messages
358 recoveryCode mbind lookup_sig
359 = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
360 ; return (emptyLHsBinds, poly_ids) }
362 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
363 binder_names = collectHsBindBinders mbind
364 poly_ids = map mk_dummy binder_names
365 mk_dummy name = case lookup_sig name of
366 Just sig -> sig_id sig -- Signature
367 Nothing -> mkLocalId name forall_a_a -- No signature
369 attachInlinePhase inline_phases bndr
370 = case lookupFM inline_phases (idName bndr) of
371 Just prag -> bndr `setInlinePragma` prag
374 -- Check that non-overloaded unlifted bindings are
377 -- c) not a multiple-binding group (more or less implied by (a))
379 checkUnliftedBinds top_lvl is_rec mbind
380 = checkTc (isNotTopLevel top_lvl)
381 (unliftedBindErr "Top-level" mbind) `thenM_`
382 checkTc (isNonRec is_rec)
383 (unliftedBindErr "Recursive" mbind) `thenM_`
384 checkTc (isSingletonBag mbind)
385 (unliftedBindErr "Multiple" mbind)
389 Polymorphic recursion
390 ~~~~~~~~~~~~~~~~~~~~~
391 The game plan for polymorphic recursion in the code above is
393 * Bind any variable for which we have a type signature
394 to an Id with a polymorphic type. Then when type-checking
395 the RHSs we'll make a full polymorphic call.
397 This fine, but if you aren't a bit careful you end up with a horrendous
398 amount of partial application and (worse) a huge space leak. For example:
400 f :: Eq a => [a] -> [a]
403 If we don't take care, after typechecking we get
405 f = /\a -> \d::Eq a -> let f' = f a d
409 Notice the the stupid construction of (f a d), which is of course
410 identical to the function we're executing. In this case, the
411 polymorphic recursion isn't being used (but that's a very common case).
414 f = /\a -> \d::Eq a -> letrec
415 fm = \ys:[a] -> ...fm...
419 This can lead to a massive space leak, from the following top-level defn
425 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
426 f' is another thunk which evaluates to the same thing... and you end
427 up with a chain of identical values all hung onto by the CAF ff.
431 = let f' = f Int dEqInt in \ys. ...f'...
433 = let f' = let f' = f Int dEqInt in \ys. ...f'...
437 Solution: when typechecking the RHSs we always have in hand the
438 *monomorphic* Ids for each binding. So we just need to make sure that
439 if (Method f a d) shows up in the constraints emerging from (...f...)
440 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
441 to the "givens" when simplifying constraints. That's what the "lies_avail"
445 %************************************************************************
447 \subsection{tcMonoBind}
449 %************************************************************************
451 @tcMonoBinds@ deals with a single @MonoBind@.
452 The signatures have been dealt with already.
455 tcMonoBinds :: LHsBinds Name
456 -> TcSigFun -> RecFlag
457 -> TcM (LHsBinds TcId, [MonoBindInfo])
459 tcMonoBinds binds lookup_sig is_rec
460 | isNonRec is_rec, -- Non-recursive, single function binding
461 [L b_loc (FunBind (L nm_loc name) inf matches)] <- bagToList binds,
462 Nothing <- lookup_sig name -- ...with no type signature
463 = -- In this very special case we infer the type of the
464 -- right hand side first (it may have a higher-rank type)
465 -- and *then* make the monomorphic Id for the LHS
466 -- e.g. f = \(x::forall a. a->a) -> <body>
467 -- We want to infer a higher-rank type for f
469 do { (matches', rhs_ty) <- tcInfer (tcMatchesFun name matches)
470 -- Check for an unboxed tuple type
471 -- f = (# True, False #)
472 -- Zonk first just in case it's hidden inside a meta type variable
473 -- (This shows up as a (more obscure) kind error
474 -- in the 'otherwise' case of tcMonoBinds.)
475 ; zonked_rhs_ty <- zonkTcType rhs_ty
476 ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
477 (unboxedTupleErr name zonked_rhs_ty)
478 ; mono_name <- newLocalName name
479 ; let mono_id = mkLocalId mono_name zonked_rhs_ty
480 ; return (unitBag (L b_loc (FunBind (L nm_loc mono_id) inf matches')),
481 [(name, Nothing, mono_id)]) }
484 = do { tc_binds <- mapBagM (wrapLocM (tcLhs lookup_sig)) binds
486 -- Bring (a) the scoped type variables, and (b) the Ids, into scope for the RHSs
487 -- For (a) it's ok to bring them all into scope at once, even
488 -- though each type sig should scope only over its own RHS,
489 -- because the renamer has sorted all that out.
490 ; let mono_info = getMonoBindInfo tc_binds
491 rhs_tvs = [ (name, mkTyVarTy tv)
492 | (_, Just sig, _) <- mono_info,
493 (name, tv) <- sig_scoped sig `zip` sig_tvs sig ]
494 rhs_id_env = map mk mono_info -- A binding for each term variable
496 ; binds' <- tcExtendTyVarEnv2 rhs_tvs $
497 tcExtendIdEnv2 rhs_id_env $
498 traceTc (text "tcMonoBinds" <+> vcat [ppr n <+> ppr id <+> ppr (idType id) | (n,id) <- rhs_id_env]) `thenM_`
499 mapBagM (wrapLocM tcRhs) tc_binds
500 ; return (binds', mono_info) }
502 mk (name, Just sig, _) = (name, sig_id sig) -- Use the type sig if there is one
503 mk (name, Nothing, mono_id) = (name, mono_id) -- otherwise use a monomorphic version
505 ------------------------
506 -- tcLhs typechecks the LHS of the bindings, to construct the environment in which
507 -- we typecheck the RHSs. Basically what we are doing is this: for each binder:
508 -- if there's a signature for it, use the instantiated signature type
509 -- otherwise invent a type variable
510 -- You see that quite directly in the FunBind case.
512 -- But there's a complication for pattern bindings:
513 -- data T = MkT (forall a. a->a)
515 -- Here we can guess a type variable for the entire LHS (which will be refined to T)
516 -- but we want to get (f::forall a. a->a) as the RHS environment.
517 -- The simplest way to do this is to typecheck the pattern, and then look up the
518 -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
519 -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
521 data TcMonoBind -- Half completed; LHS done, RHS not done
522 = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
523 | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
525 type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
526 -- Type signature (if any), and
527 -- the monomorphic bound things
529 bndrNames :: [MonoBindInfo] -> [Name]
530 bndrNames mbi = [n | (n,_,_) <- mbi]
532 getMonoType :: MonoBindInfo -> TcTauType
533 getMonoType (_,_,mono_id) = idType mono_id
535 tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
536 tcLhs lookup_sig (FunBind (L nm_loc name) inf matches)
537 = do { let mb_sig = lookup_sig name
538 ; mono_name <- newLocalName name
539 ; mono_ty <- mk_mono_ty mb_sig
540 ; let mono_id = mkLocalId mono_name mono_ty
541 ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
543 mk_mono_ty (Just sig) = return (sig_tau sig)
544 mk_mono_ty Nothing = newTyFlexiVarTy argTypeKind
546 tcLhs lookup_sig bind@(PatBind pat grhss _)
547 = do { let tc_pat exp_ty = tcPat (LetPat lookup_sig) pat exp_ty lookup_infos
548 ; ((pat', ex_tvs, infos), pat_ty)
549 <- addErrCtxt (patMonoBindsCtxt pat grhss)
552 -- Don't know how to deal with pattern-bound existentials yet
553 ; checkTc (null ex_tvs) (existentialExplode bind)
555 ; return (TcPatBind infos pat' grhss pat_ty) }
557 names = collectPatBinders pat
559 -- After typechecking the pattern, look up the binder
560 -- names, which the pattern has brought into scope.
561 lookup_infos :: TcM [MonoBindInfo]
562 lookup_infos = do { mono_ids <- tcLookupLocalIds names
563 ; return [ (name, lookup_sig name, mono_id)
564 | (name, mono_id) <- names `zip` mono_ids] }
566 tcLhs lookup_sig other_bind = pprPanic "tcLhs" (ppr other_bind)
567 -- AbsBind, VarBind impossible
570 tcRhs :: TcMonoBind -> TcM (HsBind TcId)
571 tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
572 = do { matches' <- tcMatchesFun (idName mono_id) matches
573 (Check (idType mono_id))
574 ; return (FunBind fun' inf matches') }
576 tcRhs bind@(TcPatBind _ pat' grhss pat_ty)
577 = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
578 tcGRHSsPat grhss (Check pat_ty)
579 ; return (PatBind pat' grhss' pat_ty) }
582 ---------------------
583 getMonoBindInfo :: Bag (Located TcMonoBind) -> [MonoBindInfo]
584 getMonoBindInfo tc_binds
585 = foldrBag (get_info . unLoc) [] tc_binds
587 get_info (TcFunBind info _ _ _) rest = info : rest
588 get_info (TcPatBind infos _ _ _) rest = infos ++ rest
592 %************************************************************************
594 \subsection{getTyVarsToGen}
596 %************************************************************************
598 Type signatures are tricky. See Note [Signature skolems] in TcType
601 tcTySigs :: [LSig Name] -> TcM [TcSigInfo]
602 -- The trick here is that all the signatures should have the same
603 -- context, and we want to share type variables for that context, so that
604 -- all the right hand sides agree a common vocabulary for their type
606 tcTySigs [] = return []
609 = do { (tc_sig1 : tc_sigs) <- mappM tcTySig sigs
610 ; mapM (check_ctxt tc_sig1) tc_sigs
611 ; return (tc_sig1 : tc_sigs) }
613 -- Check tha all the signature contexts are the same
614 -- The type signatures on a mutually-recursive group of definitions
615 -- must all have the same context (or none).
617 -- We unify them because, with polymorphic recursion, their types
618 -- might not otherwise be related. This is a rather subtle issue.
619 check_ctxt :: TcSigInfo -> TcSigInfo -> TcM ()
620 check_ctxt sig1@(TcSigInfo { sig_theta = theta1 }) sig@(TcSigInfo { sig_theta = theta })
621 = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
622 addErrCtxt (sigContextsCtxt sig1 sig) $
623 unifyTheta theta1 theta
626 tcTySig :: LSig Name -> TcM TcSigInfo
627 tcTySig (L span (Sig (L _ name) ty))
629 do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
630 ; (tvs, theta, tau) <- tcInstSigType name scoped_names sigma_ty
631 ; loc <- getInstLoc (SigOrigin (SigSkol name))
632 ; return (TcSigInfo { sig_id = mkLocalId name sigma_ty,
633 sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
634 sig_scoped = scoped_names, sig_loc = loc }) }
636 -- The scoped names are the ones explicitly mentioned
637 -- in the HsForAll. (There may be more in sigma_ty, because
638 -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
639 scoped_names = case ty of
640 L _ (HsForAllTy Explicit tvs _ _) -> hsLTyVarNames tvs
645 generalise :: TopLevelFlag -> Bool -> [MonoBindInfo] -> [TcSigInfo] -> [Inst]
646 -> TcM ([TcTyVar], TcDictBinds, [TcId])
647 generalise top_lvl is_unrestricted mono_infos sigs lie_req
648 | not is_unrestricted -- RESTRICTED CASE
649 = -- Check signature contexts are empty
650 do { checkTc (all is_mono_sig sigs)
651 (restrictedBindCtxtErr bndr_names)
653 -- Now simplify with exactly that set of tyvars
654 -- We have to squash those Methods
655 ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndr_names
658 -- Check that signature type variables are OK
659 ; final_qtvs <- checkSigsTyVars qtvs sigs
661 ; return (final_qtvs, binds, []) }
663 | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
664 = tcSimplifyInfer doc tau_tvs lie_req
666 | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
667 = do { let sig1 = head sigs
668 ; sig_lie <- newDictsAtLoc (sig_loc sig1) (sig_theta sig1)
669 ; let -- The "sig_avails" is the stuff available. We get that from
670 -- the context of the type signature, BUT ALSO the lie_avail
671 -- so that polymorphic recursion works right (see comments at end of fn)
672 local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
673 sig_avails = sig_lie ++ local_meths
675 -- Check that the needed dicts can be
676 -- expressed in terms of the signature ones
677 ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
679 -- Check that signature type variables are OK
680 ; final_qtvs <- checkSigsTyVars forall_tvs sigs
682 ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
685 bndr_names = bndrNames mono_infos
686 tau_tvs = foldr (unionVarSet . tyVarsOfType . getMonoType) emptyVarSet mono_infos
687 is_mono_sig sig = null (sig_theta sig)
688 doc = ptext SLIT("type signature(s) for") <+> pprBinders bndr_names
690 mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
691 sig_theta = theta, sig_tau = tau, sig_loc = loc }) mono_id
692 = Method mono_id poly_id (mkTyVarTys tvs) theta tau loc
694 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
695 checkSigsTyVars qtvs sigs
696 = do { gbl_tvs <- tcGetGlobalTyVars
697 ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
699 ; let -- Sigh. Make sure that all the tyvars in the type sigs
700 -- appear in the returned ty var list, which is what we are
701 -- going to generalise over. Reason: we occasionally get
703 -- type T a = () -> ()
706 -- Here, 'a' won't appear in qtvs, so we have to add it
707 sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
708 all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
711 check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
712 sig_theta = theta, sig_tau = tau})
713 = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
714 addErrCtxtM (sigCtxt id tvs theta tau) $
715 do { tvs' <- checkDistinctTyVars tvs
716 ; ifM (any (`elemVarSet` gbl_tvs) tvs')
717 (bleatEscapedTvs gbl_tvs tvs tvs')
720 checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
721 -- (checkDistinctTyVars tvs) checks that the tvs from one type signature
722 -- are still all type variables, and all distinct from each other.
723 -- It returns a zonked set of type variables.
724 -- For example, if the type sig is
725 -- f :: forall a b. a -> b -> b
726 -- we want to check that 'a' and 'b' haven't
727 -- (a) been unified with a non-tyvar type
728 -- (b) been unified with each other (all distinct)
730 checkDistinctTyVars sig_tvs
731 = do { zonked_tvs <- mapM zonk_one sig_tvs
732 ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
733 ; return zonked_tvs }
735 zonk_one sig_tv = do { ty <- zonkTcTyVar sig_tv
736 ; return (tcGetTyVar "checkDistinctTyVars" ty) }
737 -- 'ty' is bound to be a type variable, because SigSkolTvs
738 -- can only be unified with type variables
740 check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
741 -- The TyVarEnv maps each zonked type variable back to its
742 -- corresponding user-written signature type variable
743 check_dup acc (sig_tv, zonked_tv)
744 = case lookupVarEnv acc zonked_tv of
745 Just sig_tv' -> bomb_out sig_tv sig_tv'
747 Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
749 bomb_out sig_tv1 sig_tv2
750 = failWithTc (ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
751 <+> ptext SLIT("is unified with another quantified type variable")
752 <+> quotes (ppr tidy_tv2))
754 (env1, tidy_tv1) = tidyOpenTyVar emptyTidyEnv sig_tv1
755 (_env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
759 @getTyVarsToGen@ decides what type variables to generalise over.
761 For a "restricted group" -- see the monomorphism restriction
762 for a definition -- we bind no dictionaries, and
763 remove from tyvars_to_gen any constrained type variables
765 *Don't* simplify dicts at this point, because we aren't going
766 to generalise over these dicts. By the time we do simplify them
767 we may well know more. For example (this actually came up)
769 f x = array ... xs where xs = [1,2,3,4,5]
770 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
771 stuff. If we simplify only at the f-binding (not the xs-binding)
772 we'll know that the literals are all Ints, and we can just produce
775 Find all the type variables involved in overloading, the
776 "constrained_tyvars". These are the ones we *aren't* going to
777 generalise. We must be careful about doing this:
779 (a) If we fail to generalise a tyvar which is not actually
780 constrained, then it will never, ever get bound, and lands
781 up printed out in interface files! Notorious example:
782 instance Eq a => Eq (Foo a b) where ..
783 Here, b is not constrained, even though it looks as if it is.
784 Another, more common, example is when there's a Method inst in
785 the LIE, whose type might very well involve non-overloaded
787 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
788 the simple thing instead]
790 (b) On the other hand, we mustn't generalise tyvars which are constrained,
791 because we are going to pass on out the unmodified LIE, with those
792 tyvars in it. They won't be in scope if we've generalised them.
794 So we are careful, and do a complete simplification just to find the
795 constrained tyvars. We don't use any of the results, except to
796 find which tyvars are constrained.
799 isUnRestrictedGroup :: LHsBinds Name -> [TcSigInfo] -> TcM Bool
800 isUnRestrictedGroup binds sigs
801 = do { mono_restriction <- doptM Opt_MonomorphismRestriction
802 ; return (not mono_restriction || all_unrestricted) }
804 all_unrestricted = all (unrestricted . unLoc) (bagToList binds)
805 tysig_names = map (idName . sig_id) sigs
807 unrestricted (PatBind other _ _) = False
808 unrestricted (VarBind v _) = v `is_elem` tysig_names
809 unrestricted (FunBind v _ matches) = unrestricted_match matches
810 || unLoc v `is_elem` tysig_names
812 unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
813 -- No args => like a pattern binding
814 unrestricted_match other = True
815 -- Some args => a function binding
817 is_elem v vs = isIn "isUnResMono" v vs
821 %************************************************************************
823 \subsection{SPECIALIZE pragmas}
825 %************************************************************************
827 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
828 pragmas. It is convenient for them to appear in the @[RenamedSig]@
829 part of a binding because then the same machinery can be used for
830 moving them into place as is done for type signatures.
835 f :: Ord a => [a] -> b -> b
836 {-# SPECIALIZE f :: [Int] -> b -> b #-}
839 For this we generate:
841 f* = /\ b -> let d1 = ...
845 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
846 retain a right-hand-side that the simplifier will otherwise discard as
847 dead code... the simplifier has a flag that tells it not to discard
848 SpecPragmaId bindings.
850 In this case the f* retains a call-instance of the overloaded
851 function, f, (including appropriate dictionaries) so that the
852 specialiser will subsequently discover that there's a call of @f@ at
853 Int, and will create a specialisation for @f@. After that, the
854 binding for @f*@ can be discarded.
856 We used to have a form
857 {-# SPECIALISE f :: <type> = g #-}
858 which promised that g implemented f at <type>, but we do that with
860 {-# RULES (f::<type>) = g #-}
863 tcSpecSigs :: [LSig Name] -> TcM (LHsBinds TcId)
864 tcSpecSigs (L loc (SpecSig (L nm_loc name) poly_ty) : sigs)
865 = -- SPECIALISE f :: forall b. theta => tau = g
867 addErrCtxt (valSpecSigCtxt name poly_ty) $
869 -- Get and instantiate its alleged specialised type
870 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
872 -- Check that f has a more general type, and build a RHS for
873 -- the spec-pragma-id at the same time
874 getLIE (tcCheckSigma (L nm_loc (HsVar name)) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
876 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
877 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
879 -- Just specialise "f" by building a SpecPragmaId binding
880 -- It is the thing that makes sure we don't prematurely
881 -- dead-code-eliminate the binding we are really interested in.
882 newLocalName name `thenM` \ spec_name ->
884 spec_bind = VarBind (mkSpecPragmaId spec_name sig_ty)
885 (mkHsLet spec_binds spec_expr)
888 -- Do the rest and combine
889 tcSpecSigs sigs `thenM` \ binds_rest ->
890 returnM (binds_rest `snocBag` L loc spec_bind)
892 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
893 tcSpecSigs [] = returnM emptyLHsBinds
896 %************************************************************************
898 \subsection[TcBinds-errors]{Error contexts and messages}
900 %************************************************************************
904 -- This one is called on LHS, when pat and grhss are both Name
905 -- and on RHS, when pat is TcId and grhss is still Name
906 patMonoBindsCtxt pat grhss
907 = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
909 -----------------------------------------------
911 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
912 nest 4 (ppr v <+> dcolon <+> ppr ty)]
914 -----------------------------------------------
915 sigContextsCtxt sig1 sig2
916 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
917 nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
918 ppr id2 <+> dcolon <+> ppr (idType id2)]),
919 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
925 -----------------------------------------------
926 unliftedBindErr flavour mbind
927 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
930 -----------------------------------------------
931 unboxedTupleErr name ty
932 = hang (ptext SLIT("Illegal binding of unboxed tuple"))
933 4 (ppr name <+> dcolon <+> ppr ty)
935 -----------------------------------------------
936 existentialExplode mbinds
937 = hang (vcat [text "My brain just exploded.",
938 text "I can't handle pattern bindings for existentially-quantified constructors.",
939 text "In the binding group"])
942 -----------------------------------------------
943 restrictedBindCtxtErr binder_names
944 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
945 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
946 ptext SLIT("that falls under the monomorphism restriction")])
949 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names