2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBinds, tcMonoBinds,
8 tcSpecSigs, tcBindWithSigs ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcMatches ( tcGRHSs, tcMatchesFun )
13 import {-# SOURCE #-} TcExpr ( tcExpr )
15 import CmdLineOpts ( DynFlag(Opt_NoMonomorphismRestriction) )
16 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..),
17 Match(..), HsMatchContext(..),
18 collectMonoBinders, andMonoBinds,
19 collectSigTysFromMonoBinds
21 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
22 import TcHsSyn ( TcMonoBinds, TcId, zonkId, mkHsLet )
25 import Inst ( InstOrigin(..), newDicts, instToId )
26 import TcEnv ( tcExtendLocalValEnv, tcExtendLocalValEnv2, newLocalName )
27 import TcUnify ( unifyTauTyLists, checkSigTyVarsWrt, sigCtxt )
28 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted, tcSimplifyToDicts )
29 import TcMonoType ( tcHsSigType, UserTypeCtxt(..), TcSigInfo(..),
30 tcTySig, maybeSig, tcSigPolyId, tcSigMonoId, tcAddScopedTyVars
32 import TcPat ( tcPat, tcSubPat, tcMonoPatBndr )
33 import TcSimplify ( bindInstsOfLocalFuns )
34 import TcMType ( newTyVar, newTyVarTy, newHoleTyVarTy,
35 zonkTcTyVarToTyVar, readHoleResult
37 import TcType ( TcTyVar, mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
38 mkPredTy, mkForAllTy, isUnLiftedType,
39 unliftedTypeKind, liftedTypeKind, openTypeKind, eqKind
42 import CoreFVs ( idFreeTyVars )
43 import Id ( mkLocalId, mkSpecPragmaId, setInlinePragma )
44 import Var ( idType, idName )
45 import Name ( Name, getSrcLoc )
47 import Var ( tyVarKind )
50 import Util ( isIn, equalLength )
51 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isRec,
52 isNotTopLevel, isAlwaysActive )
53 import FiniteMap ( listToFM, lookupFM )
58 %************************************************************************
60 \subsection{Type-checking bindings}
62 %************************************************************************
64 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
65 it needs to know something about the {\em usage} of the things bound,
66 so that it can create specialisations of them. So @tcBindsAndThen@
67 takes a function which, given an extended environment, E, typechecks
68 the scope of the bindings returning a typechecked thing and (most
69 important) an LIE. It is this LIE which is then used as the basis for
70 specialising the things bound.
72 @tcBindsAndThen@ also takes a "combiner" which glues together the
73 bindings and the "thing" to make a new "thing".
75 The real work is done by @tcBindWithSigsAndThen@.
77 Recursive and non-recursive binds are handled in essentially the same
78 way: because of uniques there are no scoping issues left. The only
79 difference is that non-recursive bindings can bind primitive values.
81 Even for non-recursive binding groups we add typings for each binder
82 to the LVE for the following reason. When each individual binding is
83 checked the type of its LHS is unified with that of its RHS; and
84 type-checking the LHS of course requires that the binder is in scope.
86 At the top-level the LIE is sure to contain nothing but constant
87 dictionaries, which we resolve at the module level.
90 tcTopBinds :: RenamedHsBinds -> TcM (TcMonoBinds, TcLclEnv)
92 = tc_binds_and_then TopLevel glue binds $
93 getLclEnv `thenM` \ env ->
94 returnM (EmptyMonoBinds, env)
96 glue is_rec binds1 (binds2, thing) = (binds1 `AndMonoBinds` binds2, thing)
100 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
105 tcBindsAndThen = tc_binds_and_then NotTopLevel
107 tc_binds_and_then top_lvl combiner EmptyBinds do_next
109 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
112 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
113 = tc_binds_and_then top_lvl combiner b1 $
114 tc_binds_and_then top_lvl combiner b2 $
117 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
118 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
119 -- Notice that they scope over
120 -- a) the type signatures in the binding group
121 -- b) the bindings in the group
122 -- c) the scope of the binding group (the "in" part)
123 tcAddScopedTyVars (collectSigTysFromMonoBinds bind) $
125 -- TYPECHECK THE SIGNATURES
126 mappM tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenM` \ tc_ty_sigs ->
129 tcBindWithSigs top_lvl bind
130 tc_ty_sigs sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
133 -- Extend the environment to bind the new polymorphic Ids
134 tcExtendLocalValEnv poly_ids $
136 -- Build bindings and IdInfos corresponding to user pragmas
137 tcSpecSigs sigs `thenM` \ prag_binds ->
139 -- Now do whatever happens next, in the augmented envt
140 do_next `thenM` \ thing ->
142 returnM (prag_binds, thing)
143 ) `thenM` \ ((prag_binds, thing), lie) ->
147 -- For the top level don't bother will all this bindInstsOfLocalFuns stuff
148 -- All the top level things are rec'd together anyway, so it's fine to
149 -- leave them to the tcSimplifyTop, and quite a bit faster too
151 -> extendLIEs lie `thenM_`
152 returnM (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing)
155 -> bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
156 -- Create specialisations of functions bound here
158 -- We want to keep non-recursive things non-recursive
159 -- so that we desugar unlifted bindings correctly
163 poly_binds `andMonoBinds`
164 lie_binds `andMonoBinds`
169 combiner NonRecursive poly_binds $
170 combiner NonRecursive prag_binds $
171 combiner Recursive lie_binds $
172 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
173 -- aren't guaranteed in dependency order (though we could change
174 -- that); hence the Recursive marker.
179 %************************************************************************
181 \subsection{tcBindWithSigs}
183 %************************************************************************
185 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
186 so all the clever stuff is in here.
188 * binder_names and mbind must define the same set of Names
190 * The Names in tc_ty_sigs must be a subset of binder_names
192 * The Ids in tc_ty_sigs don't necessarily have to have the same name
193 as the Name in the tc_ty_sig
200 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
202 -> TcM (TcMonoBinds, [TcId])
204 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
206 -- If typechecking the binds fails, then return with each
207 -- signature-less binder given type (forall a.a), to minimise subsequent
209 newTyVar liftedTypeKind `thenM` \ alpha_tv ->
211 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
212 binder_names = collectMonoBinders mbind
213 poly_ids = map mk_dummy binder_names
214 mk_dummy name = case maybeSig tc_ty_sigs name of
215 Just sig -> tcSigPolyId sig -- Signature
216 Nothing -> mkLocalId name forall_a_a -- No signature
218 returnM (EmptyMonoBinds, poly_ids)
221 -- TYPECHECK THE BINDINGS
222 getLIE (tcMonoBinds mbind tc_ty_sigs is_rec) `thenM` \ ((mbind', binder_names, mono_ids), lie_req) ->
224 tau_tvs = foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet mono_ids
228 -- (it seems a bit crude to have to do getLIE twice,
229 -- but I can't see a better way just now)
230 addSrcLoc (minimum (map getSrcLoc binder_names)) $
231 addErrCtxt (genCtxt binder_names) $
232 getLIE (generalise binder_names mbind tau_tvs lie_req tc_ty_sigs)
233 `thenM` \ ((tc_tyvars_to_gen, dict_binds, dict_ids), lie_free) ->
236 -- ZONK THE GENERALISED TYPE VARIABLES TO REAL TyVars
237 -- This commits any unbound kind variables to boxed kind, by unification
238 -- It's important that the final quanfified type variables
239 -- are fully zonked, *including boxity*, because they'll be
240 -- included in the forall types of the polymorphic Ids.
241 -- At calls of these Ids we'll instantiate fresh type variables from
242 -- them, and we use their boxity then.
243 mappM zonkTcTyVarToTyVar tc_tyvars_to_gen `thenM` \ real_tyvars_to_gen ->
246 -- It's important that the dict Ids are zonked, including the boxity set
247 -- in the previous step, because they are later used to form the type of
248 -- the polymorphic thing, and forall-types must be zonked so far as
249 -- their bound variables are concerned
250 mappM zonkId dict_ids `thenM` \ zonked_dict_ids ->
251 mappM zonkId mono_ids `thenM` \ zonked_mono_ids ->
253 -- BUILD THE POLYMORPHIC RESULT IDs
255 exports = zipWith mk_export binder_names zonked_mono_ids
256 poly_ids = [poly_id | (_, poly_id, _) <- exports]
257 dict_tys = map idType zonked_dict_ids
259 inlines = mkNameSet [name | InlineSig True name _ loc <- inline_sigs]
260 -- Any INLINE sig (regardless of phase control)
261 -- makes the RHS look small
262 inline_phases = listToFM [(name, phase) | InlineSig _ name phase _ <- inline_sigs,
263 not (isAlwaysActive phase)]
264 -- Set the IdInfo field to control the inline phase
265 -- AlwaysActive is the default, so don't bother with them
267 mk_export binder_name zonked_mono_id
269 attachInlinePhase inline_phases poly_id,
273 case maybeSig tc_ty_sigs binder_name of
274 Just (TySigInfo sig_poly_id sig_tyvars _ _ _ _ _) ->
275 (sig_tyvars, sig_poly_id)
276 Nothing -> (real_tyvars_to_gen, new_poly_id)
278 new_poly_id = mkLocalId binder_name poly_ty
279 poly_ty = mkForAllTys real_tyvars_to_gen
281 $ idType zonked_mono_id
282 -- It's important to build a fully-zonked poly_ty, because
283 -- we'll slurp out its free type variables when extending the
284 -- local environment (tcExtendLocalValEnv); if it's not zonked
285 -- it appears to have free tyvars that aren't actually free
289 traceTc (text "binding:" <+> ppr ((zonked_dict_ids, dict_binds),
290 exports, map idType poly_ids)) `thenM_`
292 -- Check for an unlifted, non-overloaded group
293 -- In that case we must make extra checks
294 if any (isUnLiftedType . idType) zonked_mono_ids && null zonked_dict_ids
295 then -- Some bindings are unlifted
296 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind `thenM_`
298 extendLIEs lie_req `thenM_`
300 AbsBinds [] [] exports inlines mbind',
301 -- Do not generate even any x=y bindings
305 else -- The normal case
306 extendLIEs lie_free `thenM_`
308 AbsBinds real_tyvars_to_gen
312 (dict_binds `andMonoBinds` mbind'),
316 attachInlinePhase inline_phases bndr
317 = case lookupFM inline_phases (idName bndr) of
318 Just prag -> bndr `setInlinePragma` prag
321 -- Check that non-overloaded unlifted bindings are
324 -- c) non-polymorphic
325 -- d) not a multiple-binding group (more or less implied by (a))
327 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind
328 = ASSERT( not (any ((eqKind unliftedTypeKind) . tyVarKind) real_tyvars_to_gen) )
329 -- The instCantBeGeneralised stuff in tcSimplify should have
330 -- already raised an error if we're trying to generalise an
331 -- unboxed tyvar (NB: unboxed tyvars are always introduced
332 -- along with a class constraint) and it's better done there
333 -- because we have more precise origin information.
334 -- That's why we just use an ASSERT here.
336 checkTc (isNotTopLevel top_lvl)
337 (unliftedBindErr "Top-level" mbind) `thenM_`
338 checkTc (isNonRec is_rec)
339 (unliftedBindErr "Recursive" mbind) `thenM_`
340 checkTc (single_bind mbind)
341 (unliftedBindErr "Multiple" mbind) `thenM_`
342 checkTc (null real_tyvars_to_gen)
343 (unliftedBindErr "Polymorphic" mbind)
346 single_bind (PatMonoBind _ _ _) = True
347 single_bind (FunMonoBind _ _ _ _) = True
348 single_bind other = False
352 Polymorphic recursion
353 ~~~~~~~~~~~~~~~~~~~~~
354 The game plan for polymorphic recursion in the code above is
356 * Bind any variable for which we have a type signature
357 to an Id with a polymorphic type. Then when type-checking
358 the RHSs we'll make a full polymorphic call.
360 This fine, but if you aren't a bit careful you end up with a horrendous
361 amount of partial application and (worse) a huge space leak. For example:
363 f :: Eq a => [a] -> [a]
366 If we don't take care, after typechecking we get
368 f = /\a -> \d::Eq a -> let f' = f a d
372 Notice the the stupid construction of (f a d), which is of course
373 identical to the function we're executing. In this case, the
374 polymorphic recursion isn't being used (but that's a very common case).
377 f = /\a -> \d::Eq a -> letrec
378 fm = \ys:[a] -> ...fm...
382 This can lead to a massive space leak, from the following top-level defn
388 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
389 f' is another thunk which evaluates to the same thing... and you end
390 up with a chain of identical values all hung onto by the CAF ff.
394 = let f' = f Int dEqInt in \ys. ...f'...
396 = let f' = let f' = f Int dEqInt in \ys. ...f'...
400 Solution: when typechecking the RHSs we always have in hand the
401 *monomorphic* Ids for each binding. So we just need to make sure that
402 if (Method f a d) shows up in the constraints emerging from (...f...)
403 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
404 to the "givens" when simplifying constraints. That's what the "lies_avail"
408 %************************************************************************
410 \subsection{getTyVarsToGen}
412 %************************************************************************
415 generalise binder_names mbind tau_tvs lie_req sigs =
417 -- check for -fno-monomorphism-restriction
418 doptM Opt_NoMonomorphismRestriction `thenM` \ no_MR ->
419 let is_unrestricted | no_MR = True
420 | otherwise = isUnRestrictedGroup tysig_names mbind
423 if not is_unrestricted then -- RESTRICTED CASE
424 -- Check signature contexts are empty
425 checkTc (all is_mono_sig sigs)
426 (restrictedBindCtxtErr binder_names) `thenM_`
428 -- Now simplify with exactly that set of tyvars
429 -- We have to squash those Methods
430 tcSimplifyRestricted doc tau_tvs lie_req `thenM` \ (qtvs, binds) ->
432 -- Check that signature type variables are OK
433 checkSigsTyVars qtvs sigs `thenM` \ final_qtvs ->
435 returnM (final_qtvs, binds, [])
437 else if null sigs then -- UNRESTRICTED CASE, NO TYPE SIGS
438 tcSimplifyInfer doc tau_tvs lie_req
440 else -- UNRESTRICTED CASE, WITH TYPE SIGS
441 -- CHECKING CASE: Unrestricted group, there are type signatures
442 -- Check signature contexts are identical
443 checkSigsCtxts sigs `thenM` \ (sig_avails, sig_dicts) ->
445 -- Check that the needed dicts can be
446 -- expressed in terms of the signature ones
447 tcSimplifyInferCheck doc tau_tvs sig_avails lie_req `thenM` \ (forall_tvs, dict_binds) ->
449 -- Check that signature type variables are OK
450 checkSigsTyVars forall_tvs sigs `thenM` \ final_qtvs ->
452 returnM (final_qtvs, dict_binds, sig_dicts)
455 tysig_names = map (idName . tcSigPolyId) sigs
456 is_mono_sig (TySigInfo _ _ theta _ _ _ _) = null theta
458 doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
460 -----------------------
461 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
462 -- The type signatures on a mutually-recursive group of definitions
463 -- must all have the same context (or none).
465 -- We unify them because, with polymorphic recursion, their types
466 -- might not otherwise be related. This is a rather subtle issue.
468 checkSigsCtxts sigs@(TySigInfo id1 sig_tvs theta1 _ _ _ src_loc : other_sigs)
469 = addSrcLoc src_loc $
470 mappM_ check_one other_sigs `thenM_`
472 returnM ([], []) -- Non-overloaded type signatures
474 newDicts SignatureOrigin theta1 `thenM` \ sig_dicts ->
476 -- The "sig_avails" is the stuff available. We get that from
477 -- the context of the type signature, BUT ALSO the lie_avail
478 -- so that polymorphic recursion works right (see comments at end of fn)
479 sig_avails = sig_dicts ++ sig_meths
481 returnM (sig_avails, map instToId sig_dicts)
483 sig1_dict_tys = map mkPredTy theta1
484 sig_meths = concat [insts | TySigInfo _ _ _ _ _ insts _ <- sigs]
486 check_one sig@(TySigInfo id _ theta _ _ _ _)
487 = addErrCtxt (sigContextsCtxt id1 id) $
488 checkTc (equalLength theta theta1) sigContextsErr `thenM_`
489 unifyTauTyLists sig1_dict_tys (map mkPredTy theta)
491 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
492 checkSigsTyVars qtvs sigs
493 = mappM check_one sigs `thenM` \ sig_tvs_s ->
495 -- Sigh. Make sure that all the tyvars in the type sigs
496 -- appear in the returned ty var list, which is what we are
497 -- going to generalise over. Reason: we occasionally get
499 -- type T a = () -> ()
502 -- Here, 'a' won't appear in qtvs, so we have to add it
504 sig_tvs = foldr (unionVarSet . mkVarSet) emptyVarSet sig_tvs_s
505 all_tvs = mkVarSet qtvs `unionVarSet` sig_tvs
507 returnM (varSetElems all_tvs)
509 check_one (TySigInfo id sig_tyvars sig_theta sig_tau _ _ src_loc)
510 = addSrcLoc src_loc $
511 addErrCtxt (ptext SLIT("When checking the type signature for")
512 <+> quotes (ppr id)) $
513 addErrCtxtM (sigCtxt id sig_tyvars sig_theta sig_tau) $
514 checkSigTyVarsWrt (idFreeTyVars id) sig_tyvars
517 @getTyVarsToGen@ decides what type variables to generalise over.
519 For a "restricted group" -- see the monomorphism restriction
520 for a definition -- we bind no dictionaries, and
521 remove from tyvars_to_gen any constrained type variables
523 *Don't* simplify dicts at this point, because we aren't going
524 to generalise over these dicts. By the time we do simplify them
525 we may well know more. For example (this actually came up)
527 f x = array ... xs where xs = [1,2,3,4,5]
528 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
529 stuff. If we simplify only at the f-binding (not the xs-binding)
530 we'll know that the literals are all Ints, and we can just produce
533 Find all the type variables involved in overloading, the
534 "constrained_tyvars". These are the ones we *aren't* going to
535 generalise. We must be careful about doing this:
537 (a) If we fail to generalise a tyvar which is not actually
538 constrained, then it will never, ever get bound, and lands
539 up printed out in interface files! Notorious example:
540 instance Eq a => Eq (Foo a b) where ..
541 Here, b is not constrained, even though it looks as if it is.
542 Another, more common, example is when there's a Method inst in
543 the LIE, whose type might very well involve non-overloaded
545 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
546 the simple thing instead]
548 (b) On the other hand, we mustn't generalise tyvars which are constrained,
549 because we are going to pass on out the unmodified LIE, with those
550 tyvars in it. They won't be in scope if we've generalised them.
552 So we are careful, and do a complete simplification just to find the
553 constrained tyvars. We don't use any of the results, except to
554 find which tyvars are constrained.
557 isUnRestrictedGroup :: [Name] -- Signatures given for these
561 is_elem v vs = isIn "isUnResMono" v vs
563 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
564 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
565 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = isUnRestrictedMatch matches ||
567 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
568 isUnRestrictedGroup sigs mb2
569 isUnRestrictedGroup sigs EmptyMonoBinds = True
571 isUnRestrictedMatch (Match [] _ _ : _) = False -- No args => like a pattern binding
572 isUnRestrictedMatch other = True -- Some args => a function binding
576 %************************************************************************
578 \subsection{tcMonoBind}
580 %************************************************************************
582 @tcMonoBinds@ deals with a single @MonoBind@.
583 The signatures have been dealt with already.
586 tcMonoBinds :: RenamedMonoBinds
590 [Name], -- Bound names
591 [TcId]) -- Corresponding monomorphic bound things
593 tcMonoBinds mbinds tc_ty_sigs is_rec
594 = tc_mb_pats mbinds `thenM` \ (complete_it, tvs, ids, lie_avail) ->
596 id_list = bagToList ids
597 (names, mono_ids) = unzip id_list
599 -- This last defn is the key one:
600 -- extend the val envt with bindings for the
601 -- things bound in this group, overriding the monomorphic
602 -- ids with the polymorphic ones from the pattern
603 extra_val_env = case is_rec of
604 Recursive -> map mk_bind id_list
607 -- Don't know how to deal with pattern-bound existentials yet
608 checkTc (isEmptyBag tvs && null lie_avail)
609 (existentialExplode mbinds) `thenM_`
611 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
612 -- extend the envt with bindings for all the bound ids;
613 -- and *then* override with the polymorphic Ids from the signatures
614 -- That is the whole point of the "complete_it" stuff.
616 -- There's a further wrinkle: we have to delay extending the environment
617 -- until after we've dealt with any pattern-bound signature type variables
618 -- Consider f (x::a) = ...f...
619 -- We're going to check that a isn't unified with anything in the envt,
620 -- so f itself had better not be! So we pass the envt binding f into
621 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
622 -- dealing with the signature tyvars
624 complete_it extra_val_env `thenM` \ mbinds' ->
626 returnM (mbinds', names, mono_ids)
629 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
630 Nothing -> (name, mono_id)
631 Just sig -> (idName poly_id, poly_id)
633 poly_id = tcSigPolyId sig
635 tc_mb_pats EmptyMonoBinds
636 = returnM (\ xve -> returnM EmptyMonoBinds, emptyBag, emptyBag, [])
638 tc_mb_pats (AndMonoBinds mb1 mb2)
639 = tc_mb_pats mb1 `thenM` \ (complete_it1, tvs1, ids1, lie_avail1) ->
640 tc_mb_pats mb2 `thenM` \ (complete_it2, tvs2, ids2, lie_avail2) ->
642 complete_it xve = complete_it1 xve `thenM` \ mb1' ->
643 complete_it2 xve `thenM` \ mb2' ->
644 returnM (AndMonoBinds mb1' mb2')
646 returnM (complete_it,
647 tvs1 `unionBags` tvs2,
648 ids1 `unionBags` ids2,
649 lie_avail1 ++ lie_avail2)
651 tc_mb_pats (FunMonoBind name inf matches locn)
652 = (case maybeSig tc_ty_sigs name of
653 Just sig -> returnM (tcSigMonoId sig)
654 Nothing -> newLocalName name `thenM` \ bndr_name ->
655 newTyVarTy openTypeKind `thenM` \ bndr_ty ->
656 -- NB: not a 'hole' tyvar; since there is no type
657 -- signature, we revert to ordinary H-M typechecking
658 -- which means the variable gets an inferred tau-type
659 returnM (mkLocalId bndr_name bndr_ty)
660 ) `thenM` \ bndr_id ->
662 bndr_ty = idType bndr_id
663 complete_it xve = addSrcLoc locn $
664 tcMatchesFun xve name bndr_ty matches `thenM` \ matches' ->
665 returnM (FunMonoBind bndr_id inf matches' locn)
667 returnM (complete_it, emptyBag, unitBag (name, bndr_id), [])
669 tc_mb_pats bind@(PatMonoBind pat grhss locn)
671 newHoleTyVarTy `thenM` \ pat_ty ->
673 -- Now typecheck the pattern
674 -- We do now support binding fresh (not-already-in-scope) scoped
675 -- type variables in the pattern of a pattern binding.
676 -- For example, this is now legal:
678 -- The type variables are brought into scope in tc_binds_and_then,
679 -- so we don't have to do anything here.
681 tcPat tc_pat_bndr pat pat_ty `thenM` \ (pat', tvs, ids, lie_avail) ->
682 readHoleResult pat_ty `thenM` \ pat_ty' ->
684 complete_it xve = addSrcLoc locn $
685 addErrCtxt (patMonoBindsCtxt bind) $
686 tcExtendLocalValEnv2 xve $
687 tcGRHSs PatBindRhs grhss pat_ty' `thenM` \ grhss' ->
688 returnM (PatMonoBind pat' grhss' locn)
690 returnM (complete_it, tvs, ids, lie_avail)
692 -- tc_pat_bndr is used when dealing with a LHS binder in a pattern.
693 -- If there was a type sig for that Id, we want to make it much
694 -- as if that type signature had been on the binder as a SigPatIn.
695 -- We check for a type signature; if there is one, we use the mono_id
696 -- from the signature. This is how we make sure the tau part of the
697 -- signature actually matches the type of the LHS; then tc_mb_pats
698 -- ensures the LHS and RHS have the same type
700 tc_pat_bndr name pat_ty
701 = case maybeSig tc_ty_sigs name of
703 -> newLocalName name `thenM` \ bndr_name ->
704 tcMonoPatBndr bndr_name pat_ty
706 Just sig -> addSrcLoc (getSrcLoc name) $
707 tcSubPat (idType mono_id) pat_ty `thenM` \ co_fn ->
708 returnM (co_fn, mono_id)
710 mono_id = tcSigMonoId sig
714 %************************************************************************
716 \subsection{SPECIALIZE pragmas}
718 %************************************************************************
720 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
721 pragmas. It is convenient for them to appear in the @[RenamedSig]@
722 part of a binding because then the same machinery can be used for
723 moving them into place as is done for type signatures.
728 f :: Ord a => [a] -> b -> b
729 {-# SPECIALIZE f :: [Int] -> b -> b #-}
732 For this we generate:
734 f* = /\ b -> let d1 = ...
738 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
739 retain a right-hand-side that the simplifier will otherwise discard as
740 dead code... the simplifier has a flag that tells it not to discard
741 SpecPragmaId bindings.
743 In this case the f* retains a call-instance of the overloaded
744 function, f, (including appropriate dictionaries) so that the
745 specialiser will subsequently discover that there's a call of @f@ at
746 Int, and will create a specialisation for @f@. After that, the
747 binding for @f*@ can be discarded.
749 We used to have a form
750 {-# SPECIALISE f :: <type> = g #-}
751 which promised that g implemented f at <type>, but we do that with
753 {-# SPECIALISE (f::<type) = g #-}
756 tcSpecSigs :: [RenamedSig] -> TcM TcMonoBinds
757 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
758 = -- SPECIALISE f :: forall b. theta => tau = g
760 addErrCtxt (valSpecSigCtxt name poly_ty) $
762 -- Get and instantiate its alleged specialised type
763 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
765 -- Check that f has a more general type, and build a RHS for
766 -- the spec-pragma-id at the same time
767 getLIE (tcExpr (HsVar name) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
769 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
770 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
772 -- Just specialise "f" by building a SpecPragmaId binding
773 -- It is the thing that makes sure we don't prematurely
774 -- dead-code-eliminate the binding we are really interested in.
775 newLocalName name `thenM` \ spec_name ->
777 spec_bind = VarMonoBind (mkSpecPragmaId spec_name sig_ty)
778 (mkHsLet spec_binds spec_expr)
781 -- Do the rest and combine
782 tcSpecSigs sigs `thenM` \ binds_rest ->
783 returnM (binds_rest `andMonoBinds` spec_bind)
785 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
786 tcSpecSigs [] = returnM EmptyMonoBinds
790 %************************************************************************
792 \subsection[TcBinds-errors]{Error contexts and messages}
794 %************************************************************************
798 patMonoBindsCtxt bind
799 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
801 -----------------------------------------------
803 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
804 nest 4 (ppr v <+> dcolon <+> ppr ty)]
806 -----------------------------------------------
807 sigContextsErr = ptext SLIT("Mismatched contexts")
809 sigContextsCtxt s1 s2
810 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
811 nest 2 (vcat [ppr s1 <+> dcolon <+> ppr (idType s1),
812 ppr s2 <+> dcolon <+> ppr (idType s2)]),
813 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
815 -----------------------------------------------
816 unliftedBindErr flavour mbind
817 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
820 -----------------------------------------------
821 existentialExplode mbinds
822 = hang (vcat [text "My brain just exploded.",
823 text "I can't handle pattern bindings for existentially-quantified constructors.",
824 text "In the binding group"])
827 -----------------------------------------------
828 restrictedBindCtxtErr binder_names
829 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
830 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
831 ptext SLIT("that falls under the monomorphism restriction")])
834 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
836 -- Used in error messages
837 -- Use quotes for a single one; they look a bit "busy" for several
838 pprBinders [bndr] = quotes (ppr bndr)
839 pprBinders bndrs = pprWithCommas ppr bndrs