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 ( LIE, emptyLIE, mkLIE, plusLIE, InstOrigin(..),
28 import TcEnv ( tcExtendLocalValEnv, tcExtendLocalValEnv2, newLocalName )
29 import TcUnify ( unifyTauTyLists, checkSigTyVarsWrt, sigCtxt )
30 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted, tcSimplifyToDicts )
31 import TcMonoType ( tcHsSigType, UserTypeCtxt(..), TcSigInfo(..),
32 tcTySig, maybeSig, tcSigPolyId, tcSigMonoId, tcAddScopedTyVars
34 import TcPat ( tcPat, tcSubPat, tcMonoPatBndr )
35 import TcSimplify ( bindInstsOfLocalFuns )
36 import TcMType ( newTyVar, newTyVarTy, newHoleTyVarTy,
37 zonkTcTyVarToTyVar, readHoleResult
39 import TcType ( TcTyVar, mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
40 mkPredTy, mkForAllTy, isUnLiftedType,
41 unliftedTypeKind, liftedTypeKind, openTypeKind, eqKind
44 import CoreFVs ( idFreeTyVars )
45 import Id ( mkLocalId, mkSpecPragmaId, setInlinePragma )
46 import Var ( idType, idName )
47 import Name ( Name, getSrcLoc )
49 import Var ( tyVarKind )
52 import Util ( isIn, equalLength )
53 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isNotTopLevel,
55 import FiniteMap ( listToFM, lookupFM )
60 %************************************************************************
62 \subsection{Type-checking bindings}
64 %************************************************************************
66 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
67 it needs to know something about the {\em usage} of the things bound,
68 so that it can create specialisations of them. So @tcBindsAndThen@
69 takes a function which, given an extended environment, E, typechecks
70 the scope of the bindings returning a typechecked thing and (most
71 important) an LIE. It is this LIE which is then used as the basis for
72 specialising the things bound.
74 @tcBindsAndThen@ also takes a "combiner" which glues together the
75 bindings and the "thing" to make a new "thing".
77 The real work is done by @tcBindWithSigsAndThen@.
79 Recursive and non-recursive binds are handled in essentially the same
80 way: because of uniques there are no scoping issues left. The only
81 difference is that non-recursive bindings can bind primitive values.
83 Even for non-recursive binding groups we add typings for each binder
84 to the LVE for the following reason. When each individual binding is
85 checked the type of its LHS is unified with that of its RHS; and
86 type-checking the LHS of course requires that the binder is in scope.
88 At the top-level the LIE is sure to contain nothing but constant
89 dictionaries, which we resolve at the module level.
92 tcTopBinds :: RenamedHsBinds -> TcM ((TcMonoBinds, TcEnv), LIE)
94 = tc_binds_and_then TopLevel glue binds $
95 tcGetEnv `thenNF_Tc` \ env ->
96 returnTc ((EmptyMonoBinds, env), emptyLIE)
98 glue is_rec binds1 (binds2, thing) = (binds1 `AndMonoBinds` binds2, thing)
102 :: (RecFlag -> TcMonoBinds -> thing -> thing) -- Combinator
107 tcBindsAndThen = tc_binds_and_then NotTopLevel
109 tc_binds_and_then top_lvl combiner EmptyBinds do_next
111 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
114 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
115 = tc_binds_and_then top_lvl combiner b1 $
116 tc_binds_and_then top_lvl combiner b2 $
119 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
120 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
121 -- Notice that they scope over
122 -- a) the type signatures in the binding group
123 -- b) the bindings in the group
124 -- c) the scope of the binding group (the "in" part)
125 tcAddScopedTyVars (collectSigTysFromMonoBinds bind) $
127 -- TYPECHECK THE SIGNATURES
128 mapTc tcTySig [sig | sig@(Sig name _ _) <- sigs] `thenTc` \ tc_ty_sigs ->
130 tcBindWithSigs top_lvl bind tc_ty_sigs
131 sigs is_rec `thenTc` \ (poly_binds, poly_lie, 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 `thenTc` \ (prag_binds, prag_lie) ->
139 -- Now do whatever happens next, in the augmented envt
140 do_next `thenTc` \ (thing, thing_lie) ->
142 -- Create specialisations of functions bound here
143 -- We want to keep non-recursive things non-recursive
144 -- so that we desugar unlifted bindings correctly
145 case (top_lvl, is_rec) of
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 -> returnTc (combiner Recursive (poly_binds `andMonoBinds` prag_binds) thing,
152 thing_lie `plusLIE` prag_lie `plusLIE` poly_lie)
154 (NotTopLevel, NonRecursive)
155 -> bindInstsOfLocalFuns
156 (thing_lie `plusLIE` prag_lie)
157 poly_ids `thenTc` \ (thing_lie', lie_binds) ->
160 combiner NonRecursive poly_binds $
161 combiner NonRecursive prag_binds $
162 combiner Recursive lie_binds $
163 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
164 -- aren't guaranteed in dependency order (though we could change
165 -- that); hence the Recursive marker.
168 thing_lie' `plusLIE` poly_lie
171 (NotTopLevel, Recursive)
172 -> bindInstsOfLocalFuns
173 (thing_lie `plusLIE` poly_lie `plusLIE` prag_lie)
174 poly_ids `thenTc` \ (final_lie, lie_binds) ->
178 poly_binds `andMonoBinds`
179 lie_binds `andMonoBinds`
186 %************************************************************************
188 \subsection{tcBindWithSigs}
190 %************************************************************************
192 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
193 so all the clever stuff is in here.
195 * binder_names and mbind must define the same set of Names
197 * The Names in tc_ty_sigs must be a subset of binder_names
199 * The Ids in tc_ty_sigs don't necessarily have to have the same name
200 as the Name in the tc_ty_sig
207 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
209 -> TcM (TcMonoBinds, LIE, [TcId])
211 tcBindWithSigs top_lvl mbind tc_ty_sigs inline_sigs is_rec
213 -- If typechecking the binds fails, then return with each
214 -- signature-less binder given type (forall a.a), to minimise subsequent
216 newTyVar liftedTypeKind `thenNF_Tc` \ alpha_tv ->
218 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
219 binder_names = collectMonoBinders mbind
220 poly_ids = map mk_dummy binder_names
221 mk_dummy name = case maybeSig tc_ty_sigs name of
222 Just sig -> tcSigPolyId sig -- Signature
223 Nothing -> mkLocalId name forall_a_a -- No signature
225 returnTc (EmptyMonoBinds, emptyLIE, poly_ids)
228 -- TYPECHECK THE BINDINGS
229 tcMonoBinds mbind tc_ty_sigs is_rec `thenTc` \ (mbind', lie_req, binder_names, mono_ids) ->
231 tau_tvs = foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet mono_ids
235 tcAddSrcLoc (minimum (map getSrcLoc binder_names)) $
236 tcAddErrCtxt (genCtxt binder_names) $
237 generalise binder_names mbind tau_tvs lie_req tc_ty_sigs
238 `thenTc` \ (tc_tyvars_to_gen, lie_free, dict_binds, dict_ids) ->
241 -- ZONK THE GENERALISED TYPE VARIABLES TO REAL TyVars
242 -- This commits any unbound kind variables to boxed kind, by unification
243 -- It's important that the final quanfified type variables
244 -- are fully zonked, *including boxity*, because they'll be
245 -- included in the forall types of the polymorphic Ids.
246 -- At calls of these Ids we'll instantiate fresh type variables from
247 -- them, and we use their boxity then.
248 mapNF_Tc zonkTcTyVarToTyVar tc_tyvars_to_gen `thenNF_Tc` \ real_tyvars_to_gen ->
251 -- It's important that the dict Ids are zonked, including the boxity set
252 -- in the previous step, because they are later used to form the type of
253 -- the polymorphic thing, and forall-types must be zonked so far as
254 -- their bound variables are concerned
255 mapNF_Tc zonkId dict_ids `thenNF_Tc` \ zonked_dict_ids ->
256 mapNF_Tc zonkId mono_ids `thenNF_Tc` \ zonked_mono_ids ->
258 -- BUILD THE POLYMORPHIC RESULT IDs
260 exports = zipWith mk_export binder_names zonked_mono_ids
261 poly_ids = [poly_id | (_, poly_id, _) <- exports]
262 dict_tys = map idType zonked_dict_ids
264 inlines = mkNameSet [name | InlineSig True name _ loc <- inline_sigs]
265 -- Any INLINE sig (regardless of phase control)
266 -- makes the RHS look small
267 inline_phases = listToFM [(name, phase) | InlineSig _ name phase _ <- inline_sigs,
268 not (isAlwaysActive phase)]
269 -- Set the IdInfo field to control the inline phase
270 -- AlwaysActive is the default, so don't bother with them
272 mk_export binder_name zonked_mono_id
274 attachInlinePhase inline_phases poly_id,
278 case maybeSig tc_ty_sigs binder_name of
279 Just (TySigInfo sig_poly_id sig_tyvars _ _ _ _ _) ->
280 (sig_tyvars, sig_poly_id)
281 Nothing -> (real_tyvars_to_gen, new_poly_id)
283 new_poly_id = mkLocalId binder_name poly_ty
284 poly_ty = mkForAllTys real_tyvars_to_gen
286 $ idType zonked_mono_id
287 -- It's important to build a fully-zonked poly_ty, because
288 -- we'll slurp out its free type variables when extending the
289 -- local environment (tcExtendLocalValEnv); if it's not zonked
290 -- it appears to have free tyvars that aren't actually free
294 traceTc (text "binding:" <+> ppr ((zonked_dict_ids, dict_binds),
295 exports, map idType poly_ids)) `thenTc_`
297 -- Check for an unlifted, non-overloaded group
298 -- In that case we must make extra checks
299 if any (isUnLiftedType . idType) zonked_mono_ids && null zonked_dict_ids
300 then -- Some bindings are unlifted
301 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind `thenTc_`
304 AbsBinds [] [] exports inlines mbind',
305 lie_req, -- Do not generate even any x=y bindings
309 else -- The normal case
311 AbsBinds real_tyvars_to_gen
315 (dict_binds `andMonoBinds` mbind'),
319 attachInlinePhase inline_phases bndr
320 = case lookupFM inline_phases (idName bndr) of
321 Just prag -> bndr `setInlinePragma` prag
324 -- Check that non-overloaded unlifted bindings are
327 -- c) non-polymorphic
328 -- d) not a multiple-binding group (more or less implied by (a))
330 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind
331 = ASSERT( not (any ((eqKind unliftedTypeKind) . tyVarKind) real_tyvars_to_gen) )
332 -- The instCantBeGeneralised stuff in tcSimplify should have
333 -- already raised an error if we're trying to generalise an
334 -- unboxed tyvar (NB: unboxed tyvars are always introduced
335 -- along with a class constraint) and it's better done there
336 -- because we have more precise origin information.
337 -- That's why we just use an ASSERT here.
339 checkTc (isNotTopLevel top_lvl)
340 (unliftedBindErr "Top-level" mbind) `thenTc_`
341 checkTc (isNonRec is_rec)
342 (unliftedBindErr "Recursive" mbind) `thenTc_`
343 checkTc (single_bind mbind)
344 (unliftedBindErr "Multiple" mbind) `thenTc_`
345 checkTc (null real_tyvars_to_gen)
346 (unliftedBindErr "Polymorphic" mbind)
349 single_bind (PatMonoBind _ _ _) = True
350 single_bind (FunMonoBind _ _ _ _) = True
351 single_bind other = False
355 Polymorphic recursion
356 ~~~~~~~~~~~~~~~~~~~~~
357 The game plan for polymorphic recursion in the code above is
359 * Bind any variable for which we have a type signature
360 to an Id with a polymorphic type. Then when type-checking
361 the RHSs we'll make a full polymorphic call.
363 This fine, but if you aren't a bit careful you end up with a horrendous
364 amount of partial application and (worse) a huge space leak. For example:
366 f :: Eq a => [a] -> [a]
369 If we don't take care, after typechecking we get
371 f = /\a -> \d::Eq a -> let f' = f a d
375 Notice the the stupid construction of (f a d), which is of course
376 identical to the function we're executing. In this case, the
377 polymorphic recursion isn't being used (but that's a very common case).
380 f = /\a -> \d::Eq a -> letrec
381 fm = \ys:[a] -> ...fm...
385 This can lead to a massive space leak, from the following top-level defn
391 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
392 f' is another thunk which evaluates to the same thing... and you end
393 up with a chain of identical values all hung onto by the CAF ff.
397 = let f' = f Int dEqInt in \ys. ...f'...
399 = let f' = let f' = f Int dEqInt in \ys. ...f'...
403 Solution: when typechecking the RHSs we always have in hand the
404 *monomorphic* Ids for each binding. So we just need to make sure that
405 if (Method f a d) shows up in the constraints emerging from (...f...)
406 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
407 to the "givens" when simplifying constraints. That's what the "lies_avail"
411 %************************************************************************
413 \subsection{getTyVarsToGen}
415 %************************************************************************
418 generalise binder_names mbind tau_tvs lie_req sigs =
420 -- check for -fno-monomorphism-restriction
421 doptsTc Opt_NoMonomorphismRestriction `thenTc` \ no_MR ->
422 let is_unrestricted | no_MR = True
423 | otherwise = isUnRestrictedGroup tysig_names mbind
426 if not is_unrestricted then -- RESTRICTED CASE
427 -- Check signature contexts are empty
428 checkTc (all is_mono_sig sigs)
429 (restrictedBindCtxtErr binder_names) `thenTc_`
431 -- Now simplify with exactly that set of tyvars
432 -- We have to squash those Methods
433 tcSimplifyRestricted doc tau_tvs lie_req `thenTc` \ (qtvs, lie_free, binds) ->
435 -- Check that signature type variables are OK
436 checkSigsTyVars qtvs sigs `thenTc` \ final_qtvs ->
438 returnTc (final_qtvs, lie_free, binds, [])
440 else if null sigs then -- UNRESTRICTED CASE, NO TYPE SIGS
441 tcSimplifyInfer doc tau_tvs lie_req
443 else -- UNRESTRICTED CASE, WITH TYPE SIGS
444 -- CHECKING CASE: Unrestricted group, there are type signatures
445 -- Check signature contexts are identical
446 checkSigsCtxts sigs `thenTc` \ (sig_avails, sig_dicts) ->
448 -- Check that the needed dicts can be
449 -- expressed in terms of the signature ones
450 tcSimplifyInferCheck doc tau_tvs sig_avails lie_req `thenTc` \ (forall_tvs, lie_free, dict_binds) ->
452 -- Check that signature type variables are OK
453 checkSigsTyVars forall_tvs sigs `thenTc` \ final_qtvs ->
455 returnTc (final_qtvs, lie_free, dict_binds, sig_dicts)
458 tysig_names = map (idName . tcSigPolyId) sigs
459 is_mono_sig (TySigInfo _ _ theta _ _ _ _) = null theta
461 doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
463 -----------------------
464 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
465 -- The type signatures on a mutually-recursive group of definitions
466 -- must all have the same context (or none).
468 -- We unify them because, with polymorphic recursion, their types
469 -- might not otherwise be related. This is a rather subtle issue.
471 checkSigsCtxts sigs@(TySigInfo id1 sig_tvs theta1 _ _ _ src_loc : other_sigs)
472 = tcAddSrcLoc src_loc $
473 mapTc_ check_one other_sigs `thenTc_`
475 returnTc ([], []) -- Non-overloaded type signatures
477 newDicts SignatureOrigin theta1 `thenNF_Tc` \ sig_dicts ->
479 -- The "sig_avails" is the stuff available. We get that from
480 -- the context of the type signature, BUT ALSO the lie_avail
481 -- so that polymorphic recursion works right (see comments at end of fn)
482 sig_avails = sig_dicts ++ sig_meths
484 returnTc (sig_avails, map instToId sig_dicts)
486 sig1_dict_tys = map mkPredTy theta1
487 sig_meths = concat [insts | TySigInfo _ _ _ _ _ insts _ <- sigs]
489 check_one sig@(TySigInfo id _ theta _ _ _ _)
490 = tcAddErrCtxt (sigContextsCtxt id1 id) $
491 checkTc (equalLength theta theta1) sigContextsErr `thenTc_`
492 unifyTauTyLists sig1_dict_tys (map mkPredTy theta)
494 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
495 checkSigsTyVars qtvs sigs
496 = mapTc check_one sigs `thenTc` \ sig_tvs_s ->
498 -- Sigh. Make sure that all the tyvars in the type sigs
499 -- appear in the returned ty var list, which is what we are
500 -- going to generalise over. Reason: we occasionally get
502 -- type T a = () -> ()
505 -- Here, 'a' won't appear in qtvs, so we have to add it
507 sig_tvs = foldr (unionVarSet . mkVarSet) emptyVarSet sig_tvs_s
508 all_tvs = mkVarSet qtvs `unionVarSet` sig_tvs
510 returnTc (varSetElems all_tvs)
512 check_one (TySigInfo id sig_tyvars sig_theta sig_tau _ _ src_loc)
513 = tcAddSrcLoc src_loc $
514 tcAddErrCtxt (ptext SLIT("When checking the type signature for")
515 <+> quotes (ppr id)) $
516 tcAddErrCtxtM (sigCtxt id sig_tyvars sig_theta sig_tau) $
517 checkSigTyVarsWrt (idFreeTyVars id) sig_tyvars
520 @getTyVarsToGen@ decides what type variables to generalise over.
522 For a "restricted group" -- see the monomorphism restriction
523 for a definition -- we bind no dictionaries, and
524 remove from tyvars_to_gen any constrained type variables
526 *Don't* simplify dicts at this point, because we aren't going
527 to generalise over these dicts. By the time we do simplify them
528 we may well know more. For example (this actually came up)
530 f x = array ... xs where xs = [1,2,3,4,5]
531 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
532 stuff. If we simplify only at the f-binding (not the xs-binding)
533 we'll know that the literals are all Ints, and we can just produce
536 Find all the type variables involved in overloading, the
537 "constrained_tyvars". These are the ones we *aren't* going to
538 generalise. We must be careful about doing this:
540 (a) If we fail to generalise a tyvar which is not actually
541 constrained, then it will never, ever get bound, and lands
542 up printed out in interface files! Notorious example:
543 instance Eq a => Eq (Foo a b) where ..
544 Here, b is not constrained, even though it looks as if it is.
545 Another, more common, example is when there's a Method inst in
546 the LIE, whose type might very well involve non-overloaded
548 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
549 the simple thing instead]
551 (b) On the other hand, we mustn't generalise tyvars which are constrained,
552 because we are going to pass on out the unmodified LIE, with those
553 tyvars in it. They won't be in scope if we've generalised them.
555 So we are careful, and do a complete simplification just to find the
556 constrained tyvars. We don't use any of the results, except to
557 find which tyvars are constrained.
560 isUnRestrictedGroup :: [Name] -- Signatures given for these
564 is_elem v vs = isIn "isUnResMono" v vs
566 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
567 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
568 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = isUnRestrictedMatch matches ||
570 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
571 isUnRestrictedGroup sigs mb2
572 isUnRestrictedGroup sigs EmptyMonoBinds = True
574 isUnRestrictedMatch (Match [] _ _ : _) = False -- No args => like a pattern binding
575 isUnRestrictedMatch other = True -- Some args => a function binding
579 %************************************************************************
581 \subsection{tcMonoBind}
583 %************************************************************************
585 @tcMonoBinds@ deals with a single @MonoBind@.
586 The signatures have been dealt with already.
589 tcMonoBinds :: RenamedMonoBinds
594 [Name], -- Bound names
595 [TcId]) -- Corresponding monomorphic bound things
597 tcMonoBinds mbinds tc_ty_sigs is_rec
598 = tc_mb_pats mbinds `thenTc` \ (complete_it, lie_req_pat, tvs, ids, lie_avail) ->
600 id_list = bagToList ids
601 (names, mono_ids) = unzip id_list
603 -- This last defn is the key one:
604 -- extend the val envt with bindings for the
605 -- things bound in this group, overriding the monomorphic
606 -- ids with the polymorphic ones from the pattern
607 extra_val_env = case is_rec of
608 Recursive -> map mk_bind id_list
611 -- Don't know how to deal with pattern-bound existentials yet
612 checkTc (isEmptyBag tvs && isEmptyBag lie_avail)
613 (existentialExplode mbinds) `thenTc_`
615 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
616 -- extend the envt with bindings for all the bound ids;
617 -- and *then* override with the polymorphic Ids from the signatures
618 -- That is the whole point of the "complete_it" stuff.
620 -- There's a further wrinkle: we have to delay extending the environment
621 -- until after we've dealt with any pattern-bound signature type variables
622 -- Consider f (x::a) = ...f...
623 -- We're going to check that a isn't unified with anything in the envt,
624 -- so f itself had better not be! So we pass the envt binding f into
625 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
626 -- dealing with the signature tyvars
628 complete_it extra_val_env `thenTc` \ (mbinds', lie_req_rhss) ->
630 returnTc (mbinds', lie_req_pat `plusLIE` lie_req_rhss, names, mono_ids)
633 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
634 Nothing -> (name, mono_id)
635 Just sig -> (idName poly_id, poly_id)
637 poly_id = tcSigPolyId sig
639 tc_mb_pats EmptyMonoBinds
640 = returnTc (\ xve -> returnTc (EmptyMonoBinds, emptyLIE), emptyLIE, emptyBag, emptyBag, emptyLIE)
642 tc_mb_pats (AndMonoBinds mb1 mb2)
643 = tc_mb_pats mb1 `thenTc` \ (complete_it1, lie_req1, tvs1, ids1, lie_avail1) ->
644 tc_mb_pats mb2 `thenTc` \ (complete_it2, lie_req2, tvs2, ids2, lie_avail2) ->
646 complete_it xve = complete_it1 xve `thenTc` \ (mb1', lie1) ->
647 complete_it2 xve `thenTc` \ (mb2', lie2) ->
648 returnTc (AndMonoBinds mb1' mb2', lie1 `plusLIE` lie2)
650 returnTc (complete_it,
651 lie_req1 `plusLIE` lie_req2,
652 tvs1 `unionBags` tvs2,
653 ids1 `unionBags` ids2,
654 lie_avail1 `plusLIE` lie_avail2)
656 tc_mb_pats (FunMonoBind name inf matches locn)
657 = (case maybeSig tc_ty_sigs name of
658 Just sig -> returnNF_Tc (tcSigMonoId sig)
659 Nothing -> newLocalName name `thenNF_Tc` \ bndr_name ->
660 newTyVarTy openTypeKind `thenNF_Tc` \ bndr_ty ->
661 -- NB: not a 'hole' tyvar; since there is no type
662 -- signature, we revert to ordinary H-M typechecking
663 -- which means the variable gets an inferred tau-type
664 returnNF_Tc (mkLocalId bndr_name bndr_ty)
665 ) `thenNF_Tc` \ bndr_id ->
667 bndr_ty = idType bndr_id
668 complete_it xve = tcAddSrcLoc locn $
669 tcMatchesFun xve name bndr_ty matches `thenTc` \ (matches', lie) ->
670 returnTc (FunMonoBind bndr_id inf matches' locn, lie)
672 returnTc (complete_it, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
674 tc_mb_pats bind@(PatMonoBind pat grhss locn)
676 newHoleTyVarTy `thenNF_Tc` \ pat_ty ->
678 -- Now typecheck the pattern
679 -- We do now support binding fresh (not-already-in-scope) scoped
680 -- type variables in the pattern of a pattern binding.
681 -- For example, this is now legal:
683 -- The type variables are brought into scope in tc_binds_and_then,
684 -- so we don't have to do anything here.
686 tcPat tc_pat_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
687 readHoleResult pat_ty `thenTc` \ pat_ty' ->
689 complete_it xve = tcAddSrcLoc locn $
690 tcAddErrCtxt (patMonoBindsCtxt bind) $
691 tcExtendLocalValEnv2 xve $
692 tcGRHSs PatBindRhs grhss pat_ty' `thenTc` \ (grhss', lie) ->
693 returnTc (PatMonoBind pat' grhss' locn, lie)
695 returnTc (complete_it, lie_req, tvs, ids, lie_avail)
697 -- tc_pat_bndr is used when dealing with a LHS binder in a pattern.
698 -- If there was a type sig for that Id, we want to make it much
699 -- as if that type signature had been on the binder as a SigPatIn.
700 -- We check for a type signature; if there is one, we use the mono_id
701 -- from the signature. This is how we make sure the tau part of the
702 -- signature actually matches the type of the LHS; then tc_mb_pats
703 -- ensures the LHS and RHS have the same type
705 tc_pat_bndr name pat_ty
706 = case maybeSig tc_ty_sigs name of
708 -> newLocalName name `thenNF_Tc` \ bndr_name ->
709 tcMonoPatBndr bndr_name pat_ty
711 Just sig -> tcAddSrcLoc (getSrcLoc name) $
712 tcSubPat (idType mono_id) pat_ty `thenTc` \ (co_fn, lie) ->
713 returnTc (co_fn, lie, mono_id)
715 mono_id = tcSigMonoId sig
719 %************************************************************************
721 \subsection{SPECIALIZE pragmas}
723 %************************************************************************
725 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
726 pragmas. It is convenient for them to appear in the @[RenamedSig]@
727 part of a binding because then the same machinery can be used for
728 moving them into place as is done for type signatures.
733 f :: Ord a => [a] -> b -> b
734 {-# SPECIALIZE f :: [Int] -> b -> b #-}
737 For this we generate:
739 f* = /\ b -> let d1 = ...
743 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
744 retain a right-hand-side that the simplifier will otherwise discard as
745 dead code... the simplifier has a flag that tells it not to discard
746 SpecPragmaId bindings.
748 In this case the f* retains a call-instance of the overloaded
749 function, f, (including appropriate dictionaries) so that the
750 specialiser will subsequently discover that there's a call of @f@ at
751 Int, and will create a specialisation for @f@. After that, the
752 binding for @f*@ can be discarded.
754 We used to have a form
755 {-# SPECIALISE f :: <type> = g #-}
756 which promised that g implemented f at <type>, but we do that with
758 {-# SPECIALISE (f::<type) = g #-}
761 tcSpecSigs :: [RenamedSig] -> TcM (TcMonoBinds, LIE)
762 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
763 = -- SPECIALISE f :: forall b. theta => tau = g
764 tcAddSrcLoc src_loc $
765 tcAddErrCtxt (valSpecSigCtxt name poly_ty) $
767 -- Get and instantiate its alleged specialised type
768 tcHsSigType (FunSigCtxt name) poly_ty `thenTc` \ sig_ty ->
770 -- Check that f has a more general type, and build a RHS for
771 -- the spec-pragma-id at the same time
772 tcExpr (HsVar name) sig_ty `thenTc` \ (spec_expr, spec_lie) ->
774 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
775 tcSimplifyToDicts spec_lie `thenTc` \ (spec_dicts, spec_binds) ->
777 -- Just specialise "f" by building a SpecPragmaId binding
778 -- It is the thing that makes sure we don't prematurely
779 -- dead-code-eliminate the binding we are really interested in.
780 newLocalName name `thenNF_Tc` \ spec_name ->
782 spec_bind = VarMonoBind (mkSpecPragmaId spec_name sig_ty)
783 (mkHsLet spec_binds spec_expr)
786 -- Do the rest and combine
787 tcSpecSigs sigs `thenTc` \ (binds_rest, lie_rest) ->
788 returnTc (binds_rest `andMonoBinds` spec_bind,
789 lie_rest `plusLIE` mkLIE spec_dicts)
791 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
792 tcSpecSigs [] = returnTc (EmptyMonoBinds, emptyLIE)
796 %************************************************************************
798 \subsection[TcBinds-errors]{Error contexts and messages}
800 %************************************************************************
804 patMonoBindsCtxt bind
805 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
807 -----------------------------------------------
809 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
810 nest 4 (ppr v <+> dcolon <+> ppr ty)]
812 -----------------------------------------------
813 sigContextsErr = ptext SLIT("Mismatched contexts")
815 sigContextsCtxt s1 s2
816 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
817 nest 2 (vcat [ppr s1 <+> dcolon <+> ppr (idType s1),
818 ppr s2 <+> dcolon <+> ppr (idType s2)]),
819 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
821 -----------------------------------------------
822 unliftedBindErr flavour mbind
823 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
826 -----------------------------------------------
827 existentialExplode mbinds
828 = hang (vcat [text "My brain just exploded.",
829 text "I can't handle pattern bindings for existentially-quantified constructors.",
830 text "In the binding group"])
833 -----------------------------------------------
834 restrictedBindCtxtErr binder_names
835 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
836 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
837 ptext SLIT("that falls under the monomorphism restriction")])
840 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
842 -- Used in error messages
843 -- Use quotes for a single one; they look a bit "busy" for several
844 pprBinders [bndr] = quotes (ppr bndr)
845 pprBinders bndrs = pprWithCommas ppr bndrs