2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcBinds]{TcBinds}
7 module TcBinds ( tcBindsAndThen, tcTopBinds, tcMonoBinds, tcSpecSigs ) where
9 #include "HsVersions.h"
11 import {-# SOURCE #-} TcMatches ( tcGRHSs, tcMatchesFun )
12 import {-# SOURCE #-} TcExpr ( tcExpr, tcMonoExpr )
14 import CmdLineOpts ( DynFlag(Opt_NoMonomorphismRestriction) )
15 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..),
16 Match(..), HsMatchContext(..), mkMonoBind,
17 collectMonoBinders, andMonoBinds,
18 collectSigTysFromMonoBinds
20 import RnHsSyn ( RenamedHsBinds, RenamedSig, RenamedMonoBinds )
21 import TcHsSyn ( TcHsBinds, TcMonoBinds, TcId, zonkId, mkHsLet )
24 import Inst ( InstOrigin(..), newDicts, newIPDict, instToId )
25 import TcEnv ( tcExtendLocalValEnv, tcExtendLocalValEnv2, newLocalName )
26 import TcUnify ( unifyTauTyLists, checkSigTyVarsWrt, sigCtxt )
27 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted,
28 tcSimplifyToDicts, tcSimplifyIPs )
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)
91 -- Note: returning the TcLclEnv is more than we really
92 -- want. The bit we care about is the local bindings
93 -- and the free type variables thereof
95 = tc_binds_and_then TopLevel glue binds $
96 getLclEnv `thenM` \ env ->
97 returnM (EmptyMonoBinds, env)
99 -- The top level bindings are flattened into a giant
100 -- implicitly-mutually-recursive MonoBinds
101 glue binds1 (binds2, env) = (flatten binds1 `AndMonoBinds` binds2, env)
102 flatten EmptyBinds = EmptyMonoBinds
103 flatten (b1 `ThenBinds` b2) = flatten b1 `AndMonoBinds` flatten b2
104 flatten (MonoBind b _ _) = b
105 -- Can't have a IPBinds at top level
109 :: (TcHsBinds -> thing -> thing) -- Combinator
114 tcBindsAndThen = tc_binds_and_then NotTopLevel
116 tc_binds_and_then top_lvl combiner EmptyBinds do_next
118 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
121 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
122 = tc_binds_and_then top_lvl combiner b1 $
123 tc_binds_and_then top_lvl combiner b2 $
126 tc_binds_and_then top_lvl combiner (IPBinds binds is_with) do_next
127 = getLIE do_next `thenM` \ (result, expr_lie) ->
128 mapAndUnzipM tc_ip_bind binds `thenM` \ (avail_ips, binds') ->
130 -- If the binding binds ?x = E, we must now
131 -- discharge any ?x constraints in expr_lie
132 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
134 returnM (combiner (IPBinds binds' is_with) $
135 combiner (mkMonoBind Recursive dict_binds) result)
137 -- I wonder if we should do these one at at time
140 tc_ip_bind (ip, expr)
141 = newTyVarTy openTypeKind `thenM` \ ty ->
142 getSrcLocM `thenM` \ loc ->
143 newIPDict (IPBind ip) ip ty `thenM` \ (ip', ip_inst) ->
144 tcMonoExpr expr ty `thenM` \ expr' ->
145 returnM (ip_inst, (ip', expr'))
147 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
148 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
149 -- Notice that they scope over
150 -- a) the type signatures in the binding group
151 -- b) the bindings in the group
152 -- c) the scope of the binding group (the "in" part)
153 tcAddScopedTyVars (collectSigTysFromMonoBinds bind) $
155 tcBindWithSigs top_lvl bind sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
158 TopLevel -- For the top level don't bother will all this
159 -- bindInstsOfLocalFuns stuff. All the top level
160 -- things are rec'd together anyway, so it's fine to
161 -- leave them to the tcSimplifyTop, and quite a bit faster too
163 -- Subtle (and ugly) point: furthermore at top level we
164 -- return the TcLclEnv, which contains the LIE var; we
165 -- don't want to return the wrong one!
166 -> tc_body poly_ids `thenM` \ (prag_binds, thing) ->
167 returnM (combiner (mkMonoBind Recursive (poly_binds `andMonoBinds` prag_binds))
170 NotTopLevel -- For nested bindings we must
171 -> getLIE (tc_body poly_ids) `thenM` \ ((prag_binds, thing), lie) ->
173 -- Create specialisations of functions bound here
174 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
176 -- We want to keep non-recursive things non-recursive
177 -- so that we desugar unlifted bindings correctly
180 combiner (mkMonoBind Recursive (
181 poly_binds `andMonoBinds`
182 lie_binds `andMonoBinds`
187 combiner (mkMonoBind NonRecursive poly_binds) $
188 combiner (mkMonoBind NonRecursive prag_binds) $
189 combiner (mkMonoBind Recursive lie_binds) $
190 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
191 -- aren't guaranteed in dependency order (though we could change
192 -- that); hence the Recursive marker.
195 tc_body poly_ids -- Type check the pragmas and "thing inside"
196 = -- Extend the environment to bind the new polymorphic Ids
197 tcExtendLocalValEnv poly_ids $
199 -- Build bindings and IdInfos corresponding to user pragmas
200 tcSpecSigs sigs `thenM` \ prag_binds ->
202 -- Now do whatever happens next, in the augmented envt
203 do_next `thenM` \ thing ->
205 returnM (prag_binds, thing)
209 %************************************************************************
211 \subsection{tcBindWithSigs}
213 %************************************************************************
215 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
216 so all the clever stuff is in here.
218 * binder_names and mbind must define the same set of Names
220 * The Names in tc_ty_sigs must be a subset of binder_names
222 * The Ids in tc_ty_sigs don't necessarily have to have the same name
223 as the Name in the tc_ty_sig
229 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
231 -> TcM (TcMonoBinds, [TcId])
233 tcBindWithSigs top_lvl mbind sigs is_rec
234 = -- TYPECHECK THE SIGNATURES
235 recoverM (returnM []) (
236 mappM tcTySig [sig | sig@(Sig name _ _) <- sigs]
237 ) `thenM` \ tc_ty_sigs ->
239 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
241 -- If typechecking the binds fails, then return with each
242 -- signature-less binder given type (forall a.a), to minimise subsequent
244 newTyVar liftedTypeKind `thenM` \ alpha_tv ->
246 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
247 binder_names = collectMonoBinders mbind
248 poly_ids = map mk_dummy binder_names
249 mk_dummy name = case maybeSig tc_ty_sigs name of
250 Just sig -> tcSigPolyId sig -- Signature
251 Nothing -> mkLocalId name forall_a_a -- No signature
253 traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names) `thenM_`
254 returnM (EmptyMonoBinds, poly_ids)
257 -- TYPECHECK THE BINDINGS
258 getLIE (tcMonoBinds mbind tc_ty_sigs is_rec) `thenM` \ ((mbind', binder_names, mono_ids), lie_req) ->
260 tau_tvs = foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet mono_ids
264 -- (it seems a bit crude to have to do getLIE twice,
265 -- but I can't see a better way just now)
266 addSrcLoc (minimum (map getSrcLoc binder_names)) $
267 addErrCtxt (genCtxt binder_names) $
268 getLIE (generalise binder_names mbind tau_tvs lie_req tc_ty_sigs)
269 `thenM` \ ((tc_tyvars_to_gen, dict_binds, dict_ids), lie_free) ->
272 -- ZONK THE GENERALISED TYPE VARIABLES TO REAL TyVars
273 -- This commits any unbound kind variables to boxed kind, by unification
274 -- It's important that the final quanfified type variables
275 -- are fully zonked, *including boxity*, because they'll be
276 -- included in the forall types of the polymorphic Ids.
277 -- At calls of these Ids we'll instantiate fresh type variables from
278 -- them, and we use their boxity then.
279 mappM zonkTcTyVarToTyVar tc_tyvars_to_gen `thenM` \ real_tyvars_to_gen ->
282 -- It's important that the dict Ids are zonked, including the boxity set
283 -- in the previous step, because they are later used to form the type of
284 -- the polymorphic thing, and forall-types must be zonked so far as
285 -- their bound variables are concerned
286 mappM zonkId dict_ids `thenM` \ zonked_dict_ids ->
287 mappM zonkId mono_ids `thenM` \ zonked_mono_ids ->
289 -- BUILD THE POLYMORPHIC RESULT IDs
291 exports = zipWith mk_export binder_names zonked_mono_ids
292 poly_ids = [poly_id | (_, poly_id, _) <- exports]
293 dict_tys = map idType zonked_dict_ids
295 inlines = mkNameSet [name | InlineSig True name _ loc <- sigs]
296 -- Any INLINE sig (regardless of phase control)
297 -- makes the RHS look small
298 inline_phases = listToFM [(name, phase) | InlineSig _ name phase _ <- sigs,
299 not (isAlwaysActive phase)]
300 -- Set the IdInfo field to control the inline phase
301 -- AlwaysActive is the default, so don't bother with them
303 mk_export binder_name zonked_mono_id
305 attachInlinePhase inline_phases poly_id,
309 case maybeSig tc_ty_sigs binder_name of
310 Just (TySigInfo sig_poly_id sig_tyvars _ _ _ _ _) ->
311 (sig_tyvars, sig_poly_id)
312 Nothing -> (real_tyvars_to_gen, new_poly_id)
314 new_poly_id = mkLocalId binder_name poly_ty
315 poly_ty = mkForAllTys real_tyvars_to_gen
317 $ idType zonked_mono_id
318 -- It's important to build a fully-zonked poly_ty, because
319 -- we'll slurp out its free type variables when extending the
320 -- local environment (tcExtendLocalValEnv); if it's not zonked
321 -- it appears to have free tyvars that aren't actually free
325 traceTc (text "binding:" <+> ppr ((zonked_dict_ids, dict_binds),
326 exports, map idType poly_ids)) `thenM_`
328 -- Check for an unlifted, non-overloaded group
329 -- In that case we must make extra checks
330 if any (isUnLiftedType . idType) zonked_mono_ids && null zonked_dict_ids
331 then -- Some bindings are unlifted
332 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind `thenM_`
334 extendLIEs lie_req `thenM_`
336 AbsBinds [] [] exports inlines mbind',
337 -- Do not generate even any x=y bindings
341 else -- The normal case
342 extendLIEs lie_free `thenM_`
344 AbsBinds real_tyvars_to_gen
348 (dict_binds `andMonoBinds` mbind'),
352 attachInlinePhase inline_phases bndr
353 = case lookupFM inline_phases (idName bndr) of
354 Just prag -> bndr `setInlinePragma` prag
357 -- Check that non-overloaded unlifted bindings are
360 -- c) non-polymorphic
361 -- d) not a multiple-binding group (more or less implied by (a))
363 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind
364 = ASSERT( not (any ((eqKind unliftedTypeKind) . tyVarKind) real_tyvars_to_gen) )
365 -- The instCantBeGeneralised stuff in tcSimplify should have
366 -- already raised an error if we're trying to generalise an
367 -- unboxed tyvar (NB: unboxed tyvars are always introduced
368 -- along with a class constraint) and it's better done there
369 -- because we have more precise origin information.
370 -- That's why we just use an ASSERT here.
372 checkTc (isNotTopLevel top_lvl)
373 (unliftedBindErr "Top-level" mbind) `thenM_`
374 checkTc (isNonRec is_rec)
375 (unliftedBindErr "Recursive" mbind) `thenM_`
376 checkTc (single_bind mbind)
377 (unliftedBindErr "Multiple" mbind) `thenM_`
378 checkTc (null real_tyvars_to_gen)
379 (unliftedBindErr "Polymorphic" mbind)
382 single_bind (PatMonoBind _ _ _) = True
383 single_bind (FunMonoBind _ _ _ _) = True
384 single_bind other = False
388 Polymorphic recursion
389 ~~~~~~~~~~~~~~~~~~~~~
390 The game plan for polymorphic recursion in the code above is
392 * Bind any variable for which we have a type signature
393 to an Id with a polymorphic type. Then when type-checking
394 the RHSs we'll make a full polymorphic call.
396 This fine, but if you aren't a bit careful you end up with a horrendous
397 amount of partial application and (worse) a huge space leak. For example:
399 f :: Eq a => [a] -> [a]
402 If we don't take care, after typechecking we get
404 f = /\a -> \d::Eq a -> let f' = f a d
408 Notice the the stupid construction of (f a d), which is of course
409 identical to the function we're executing. In this case, the
410 polymorphic recursion isn't being used (but that's a very common case).
413 f = /\a -> \d::Eq a -> letrec
414 fm = \ys:[a] -> ...fm...
418 This can lead to a massive space leak, from the following top-level defn
424 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
425 f' is another thunk which evaluates to the same thing... and you end
426 up with a chain of identical values all hung onto by the CAF ff.
430 = let f' = f Int dEqInt in \ys. ...f'...
432 = let f' = let f' = f Int dEqInt in \ys. ...f'...
436 Solution: when typechecking the RHSs we always have in hand the
437 *monomorphic* Ids for each binding. So we just need to make sure that
438 if (Method f a d) shows up in the constraints emerging from (...f...)
439 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
440 to the "givens" when simplifying constraints. That's what the "lies_avail"
444 %************************************************************************
446 \subsection{getTyVarsToGen}
448 %************************************************************************
451 generalise binder_names mbind tau_tvs lie_req sigs =
453 -- check for -fno-monomorphism-restriction
454 doptM Opt_NoMonomorphismRestriction `thenM` \ no_MR ->
455 let is_unrestricted | no_MR = True
456 | otherwise = isUnRestrictedGroup tysig_names mbind
459 if not is_unrestricted then -- RESTRICTED CASE
460 -- Check signature contexts are empty
461 checkTc (all is_mono_sig sigs)
462 (restrictedBindCtxtErr binder_names) `thenM_`
464 -- Now simplify with exactly that set of tyvars
465 -- We have to squash those Methods
466 tcSimplifyRestricted doc tau_tvs lie_req `thenM` \ (qtvs, binds) ->
468 -- Check that signature type variables are OK
469 checkSigsTyVars qtvs sigs `thenM` \ final_qtvs ->
471 returnM (final_qtvs, binds, [])
473 else if null sigs then -- UNRESTRICTED CASE, NO TYPE SIGS
474 tcSimplifyInfer doc tau_tvs lie_req
476 else -- UNRESTRICTED CASE, WITH TYPE SIGS
477 -- CHECKING CASE: Unrestricted group, there are type signatures
478 -- Check signature contexts are identical
479 checkSigsCtxts sigs `thenM` \ (sig_avails, sig_dicts) ->
481 -- Check that the needed dicts can be
482 -- expressed in terms of the signature ones
483 tcSimplifyInferCheck doc tau_tvs sig_avails lie_req `thenM` \ (forall_tvs, dict_binds) ->
485 -- Check that signature type variables are OK
486 checkSigsTyVars forall_tvs sigs `thenM` \ final_qtvs ->
488 returnM (final_qtvs, dict_binds, sig_dicts)
491 tysig_names = map (idName . tcSigPolyId) sigs
492 is_mono_sig (TySigInfo _ _ theta _ _ _ _) = null theta
494 doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
496 -----------------------
497 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
498 -- The type signatures on a mutually-recursive group of definitions
499 -- must all have the same context (or none).
501 -- We unify them because, with polymorphic recursion, their types
502 -- might not otherwise be related. This is a rather subtle issue.
504 checkSigsCtxts sigs@(TySigInfo id1 sig_tvs theta1 _ _ _ src_loc : other_sigs)
505 = addSrcLoc src_loc $
506 mappM_ check_one other_sigs `thenM_`
508 returnM ([], []) -- Non-overloaded type signatures
510 newDicts SignatureOrigin theta1 `thenM` \ sig_dicts ->
512 -- The "sig_avails" is the stuff available. We get that from
513 -- the context of the type signature, BUT ALSO the lie_avail
514 -- so that polymorphic recursion works right (see comments at end of fn)
515 sig_avails = sig_dicts ++ sig_meths
517 returnM (sig_avails, map instToId sig_dicts)
519 sig1_dict_tys = map mkPredTy theta1
520 sig_meths = concat [insts | TySigInfo _ _ _ _ _ insts _ <- sigs]
522 check_one sig@(TySigInfo id _ theta _ _ _ _)
523 = addErrCtxt (sigContextsCtxt id1 id) $
524 checkTc (equalLength theta theta1) sigContextsErr `thenM_`
525 unifyTauTyLists sig1_dict_tys (map mkPredTy theta)
527 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
528 checkSigsTyVars qtvs sigs
529 = mappM check_one sigs `thenM` \ sig_tvs_s ->
531 -- Sigh. Make sure that all the tyvars in the type sigs
532 -- appear in the returned ty var list, which is what we are
533 -- going to generalise over. Reason: we occasionally get
535 -- type T a = () -> ()
538 -- Here, 'a' won't appear in qtvs, so we have to add it
540 sig_tvs = foldr (unionVarSet . mkVarSet) emptyVarSet sig_tvs_s
541 all_tvs = mkVarSet qtvs `unionVarSet` sig_tvs
543 returnM (varSetElems all_tvs)
545 check_one (TySigInfo id sig_tyvars sig_theta sig_tau _ _ src_loc)
546 = addSrcLoc src_loc $
547 addErrCtxt (ptext SLIT("When checking the type signature for")
548 <+> quotes (ppr id)) $
549 addErrCtxtM (sigCtxt id sig_tyvars sig_theta sig_tau) $
550 checkSigTyVarsWrt (idFreeTyVars id) sig_tyvars
553 @getTyVarsToGen@ decides what type variables to generalise over.
555 For a "restricted group" -- see the monomorphism restriction
556 for a definition -- we bind no dictionaries, and
557 remove from tyvars_to_gen any constrained type variables
559 *Don't* simplify dicts at this point, because we aren't going
560 to generalise over these dicts. By the time we do simplify them
561 we may well know more. For example (this actually came up)
563 f x = array ... xs where xs = [1,2,3,4,5]
564 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
565 stuff. If we simplify only at the f-binding (not the xs-binding)
566 we'll know that the literals are all Ints, and we can just produce
569 Find all the type variables involved in overloading, the
570 "constrained_tyvars". These are the ones we *aren't* going to
571 generalise. We must be careful about doing this:
573 (a) If we fail to generalise a tyvar which is not actually
574 constrained, then it will never, ever get bound, and lands
575 up printed out in interface files! Notorious example:
576 instance Eq a => Eq (Foo a b) where ..
577 Here, b is not constrained, even though it looks as if it is.
578 Another, more common, example is when there's a Method inst in
579 the LIE, whose type might very well involve non-overloaded
581 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
582 the simple thing instead]
584 (b) On the other hand, we mustn't generalise tyvars which are constrained,
585 because we are going to pass on out the unmodified LIE, with those
586 tyvars in it. They won't be in scope if we've generalised them.
588 So we are careful, and do a complete simplification just to find the
589 constrained tyvars. We don't use any of the results, except to
590 find which tyvars are constrained.
593 isUnRestrictedGroup :: [Name] -- Signatures given for these
597 is_elem v vs = isIn "isUnResMono" v vs
599 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
600 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
601 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = isUnRestrictedMatch matches ||
603 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
604 isUnRestrictedGroup sigs mb2
605 isUnRestrictedGroup sigs EmptyMonoBinds = True
607 isUnRestrictedMatch (Match [] _ _ : _) = False -- No args => like a pattern binding
608 isUnRestrictedMatch other = True -- Some args => a function binding
612 %************************************************************************
614 \subsection{tcMonoBind}
616 %************************************************************************
618 @tcMonoBinds@ deals with a single @MonoBind@.
619 The signatures have been dealt with already.
622 tcMonoBinds :: RenamedMonoBinds
626 [Name], -- Bound names
627 [TcId]) -- Corresponding monomorphic bound things
629 tcMonoBinds mbinds tc_ty_sigs is_rec
630 = tc_mb_pats mbinds `thenM` \ (complete_it, tvs, ids, lie_avail) ->
632 id_list = bagToList ids
633 (names, mono_ids) = unzip id_list
635 -- This last defn is the key one:
636 -- extend the val envt with bindings for the
637 -- things bound in this group, overriding the monomorphic
638 -- ids with the polymorphic ones from the pattern
639 extra_val_env = case is_rec of
640 Recursive -> map mk_bind id_list
643 -- Don't know how to deal with pattern-bound existentials yet
644 checkTc (isEmptyBag tvs && null lie_avail)
645 (existentialExplode mbinds) `thenM_`
647 -- *Before* checking the RHSs, but *after* checking *all* the patterns,
648 -- extend the envt with bindings for all the bound ids;
649 -- and *then* override with the polymorphic Ids from the signatures
650 -- That is the whole point of the "complete_it" stuff.
652 -- There's a further wrinkle: we have to delay extending the environment
653 -- until after we've dealt with any pattern-bound signature type variables
654 -- Consider f (x::a) = ...f...
655 -- We're going to check that a isn't unified with anything in the envt,
656 -- so f itself had better not be! So we pass the envt binding f into
657 -- complete_it, which extends the actual envt in TcMatches.tcMatch, after
658 -- dealing with the signature tyvars
660 complete_it extra_val_env `thenM` \ mbinds' ->
662 returnM (mbinds', names, mono_ids)
665 mk_bind (name, mono_id) = case maybeSig tc_ty_sigs name of
666 Nothing -> (name, mono_id)
667 Just sig -> (idName poly_id, poly_id)
669 poly_id = tcSigPolyId sig
671 tc_mb_pats EmptyMonoBinds
672 = returnM (\ xve -> returnM EmptyMonoBinds, emptyBag, emptyBag, [])
674 tc_mb_pats (AndMonoBinds mb1 mb2)
675 = tc_mb_pats mb1 `thenM` \ (complete_it1, tvs1, ids1, lie_avail1) ->
676 tc_mb_pats mb2 `thenM` \ (complete_it2, tvs2, ids2, lie_avail2) ->
678 complete_it xve = complete_it1 xve `thenM` \ mb1' ->
679 complete_it2 xve `thenM` \ mb2' ->
680 returnM (AndMonoBinds mb1' mb2')
682 returnM (complete_it,
683 tvs1 `unionBags` tvs2,
684 ids1 `unionBags` ids2,
685 lie_avail1 ++ lie_avail2)
687 tc_mb_pats (FunMonoBind name inf matches locn)
688 = (case maybeSig tc_ty_sigs name of
689 Just sig -> returnM (tcSigMonoId sig)
690 Nothing -> newLocalName name `thenM` \ bndr_name ->
691 newTyVarTy openTypeKind `thenM` \ bndr_ty ->
692 -- NB: not a 'hole' tyvar; since there is no type
693 -- signature, we revert to ordinary H-M typechecking
694 -- which means the variable gets an inferred tau-type
695 returnM (mkLocalId bndr_name bndr_ty)
696 ) `thenM` \ bndr_id ->
698 bndr_ty = idType bndr_id
699 complete_it xve = addSrcLoc locn $
700 tcMatchesFun xve name bndr_ty matches `thenM` \ matches' ->
701 returnM (FunMonoBind bndr_id inf matches' locn)
703 returnM (complete_it, emptyBag, unitBag (name, bndr_id), [])
705 tc_mb_pats bind@(PatMonoBind pat grhss locn)
707 newHoleTyVarTy `thenM` \ pat_ty ->
709 -- Now typecheck the pattern
710 -- We do now support binding fresh (not-already-in-scope) scoped
711 -- type variables in the pattern of a pattern binding.
712 -- For example, this is now legal:
714 -- The type variables are brought into scope in tc_binds_and_then,
715 -- so we don't have to do anything here.
717 tcPat tc_pat_bndr pat pat_ty `thenM` \ (pat', tvs, ids, lie_avail) ->
718 readHoleResult pat_ty `thenM` \ pat_ty' ->
720 complete_it xve = addSrcLoc locn $
721 addErrCtxt (patMonoBindsCtxt bind) $
722 tcExtendLocalValEnv2 xve $
723 tcGRHSs PatBindRhs grhss pat_ty' `thenM` \ grhss' ->
724 returnM (PatMonoBind pat' grhss' locn)
726 returnM (complete_it, tvs, ids, lie_avail)
728 -- tc_pat_bndr is used when dealing with a LHS binder in a pattern.
729 -- If there was a type sig for that Id, we want to make it much
730 -- as if that type signature had been on the binder as a SigPatIn.
731 -- We check for a type signature; if there is one, we use the mono_id
732 -- from the signature. This is how we make sure the tau part of the
733 -- signature actually matches the type of the LHS; then tc_mb_pats
734 -- ensures the LHS and RHS have the same type
736 tc_pat_bndr name pat_ty
737 = case maybeSig tc_ty_sigs name of
739 -> newLocalName name `thenM` \ bndr_name ->
740 tcMonoPatBndr bndr_name pat_ty
742 Just sig -> addSrcLoc (getSrcLoc name) $
743 tcSubPat (idType mono_id) pat_ty `thenM` \ co_fn ->
744 returnM (co_fn, mono_id)
746 mono_id = tcSigMonoId sig
750 %************************************************************************
752 \subsection{SPECIALIZE pragmas}
754 %************************************************************************
756 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
757 pragmas. It is convenient for them to appear in the @[RenamedSig]@
758 part of a binding because then the same machinery can be used for
759 moving them into place as is done for type signatures.
764 f :: Ord a => [a] -> b -> b
765 {-# SPECIALIZE f :: [Int] -> b -> b #-}
768 For this we generate:
770 f* = /\ b -> let d1 = ...
774 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
775 retain a right-hand-side that the simplifier will otherwise discard as
776 dead code... the simplifier has a flag that tells it not to discard
777 SpecPragmaId bindings.
779 In this case the f* retains a call-instance of the overloaded
780 function, f, (including appropriate dictionaries) so that the
781 specialiser will subsequently discover that there's a call of @f@ at
782 Int, and will create a specialisation for @f@. After that, the
783 binding for @f*@ can be discarded.
785 We used to have a form
786 {-# SPECIALISE f :: <type> = g #-}
787 which promised that g implemented f at <type>, but we do that with
789 {-# SPECIALISE (f::<type) = g #-}
792 tcSpecSigs :: [RenamedSig] -> TcM TcMonoBinds
793 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
794 = -- SPECIALISE f :: forall b. theta => tau = g
796 addErrCtxt (valSpecSigCtxt name poly_ty) $
798 -- Get and instantiate its alleged specialised type
799 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
801 -- Check that f has a more general type, and build a RHS for
802 -- the spec-pragma-id at the same time
803 getLIE (tcExpr (HsVar name) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
805 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
806 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
808 -- Just specialise "f" by building a SpecPragmaId binding
809 -- It is the thing that makes sure we don't prematurely
810 -- dead-code-eliminate the binding we are really interested in.
811 newLocalName name `thenM` \ spec_name ->
813 spec_bind = VarMonoBind (mkSpecPragmaId spec_name sig_ty)
814 (mkHsLet spec_binds spec_expr)
817 -- Do the rest and combine
818 tcSpecSigs sigs `thenM` \ binds_rest ->
819 returnM (binds_rest `andMonoBinds` spec_bind)
821 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
822 tcSpecSigs [] = returnM EmptyMonoBinds
826 %************************************************************************
828 \subsection[TcBinds-errors]{Error contexts and messages}
830 %************************************************************************
834 patMonoBindsCtxt bind
835 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
837 -----------------------------------------------
839 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
840 nest 4 (ppr v <+> dcolon <+> ppr ty)]
842 -----------------------------------------------
843 sigContextsErr = ptext SLIT("Mismatched contexts")
845 sigContextsCtxt s1 s2
846 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
847 nest 2 (vcat [ppr s1 <+> dcolon <+> ppr (idType s1),
848 ppr s2 <+> dcolon <+> ppr (idType s2)]),
849 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
851 -----------------------------------------------
852 unliftedBindErr flavour mbind
853 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
856 -----------------------------------------------
857 existentialExplode mbinds
858 = hang (vcat [text "My brain just exploded.",
859 text "I can't handle pattern bindings for existentially-quantified constructors.",
860 text "In the binding group"])
863 -----------------------------------------------
864 restrictedBindCtxtErr binder_names
865 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
866 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
867 ptext SLIT("that falls under the monomorphism restriction")])
870 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
872 -- Used in error messages
873 -- Use quotes for a single one; they look a bit "busy" for several
874 pprBinders [bndr] = quotes (ppr bndr)
875 pprBinders bndrs = pprWithCommas ppr bndrs