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 ( tcGRHSsPat, tcMatchesFun )
12 import {-# SOURCE #-} TcExpr ( tcCheckSigma, tcCheckRho )
14 import CmdLineOpts ( DynFlag(Opt_NoMonomorphismRestriction) )
15 import HsSyn ( HsExpr(..), HsBinds(..), MonoBinds(..), Sig(..),
16 Match(..), 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 ( Expected(..), newHole, unifyTauTyLists, checkSigTyVarsWrt, sigCtxt )
27 import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted,
28 tcSimplifyToDicts, tcSimplifyIPs )
29 import TcHsType ( tcHsSigType, UserTypeCtxt(..), TcSigInfo(..),
30 tcTySig, maybeSig, tcSigPolyId, tcSigMonoId, tcAddScopedTyVars
32 import TcPat ( tcPat, tcSubPat, tcMonoPatBndr )
33 import TcSimplify ( bindInstsOfLocalFuns )
34 import TcMType ( newTyVar, newTyVarTy, zonkTcTyVarToTyVar )
35 import TcType ( TcTyVar, mkTyVarTy, mkForAllTys, mkFunTys, tyVarsOfType,
36 mkPredTy, mkForAllTy, isUnLiftedType,
37 unliftedTypeKind, liftedTypeKind, openTypeKind, eqKind
40 import CoreFVs ( idFreeTyVars )
41 import Id ( mkLocalId, mkSpecPragmaId, setInlinePragma )
42 import Var ( idType, idName )
43 import Name ( Name, getSrcLoc )
45 import Var ( tyVarKind )
48 import Util ( isIn, equalLength )
49 import BasicTypes ( TopLevelFlag(..), RecFlag(..), isNonRec, isRec,
50 isNotTopLevel, isAlwaysActive )
51 import FiniteMap ( listToFM, lookupFM )
56 %************************************************************************
58 \subsection{Type-checking bindings}
60 %************************************************************************
62 @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
63 it needs to know something about the {\em usage} of the things bound,
64 so that it can create specialisations of them. So @tcBindsAndThen@
65 takes a function which, given an extended environment, E, typechecks
66 the scope of the bindings returning a typechecked thing and (most
67 important) an LIE. It is this LIE which is then used as the basis for
68 specialising the things bound.
70 @tcBindsAndThen@ also takes a "combiner" which glues together the
71 bindings and the "thing" to make a new "thing".
73 The real work is done by @tcBindWithSigsAndThen@.
75 Recursive and non-recursive binds are handled in essentially the same
76 way: because of uniques there are no scoping issues left. The only
77 difference is that non-recursive bindings can bind primitive values.
79 Even for non-recursive binding groups we add typings for each binder
80 to the LVE for the following reason. When each individual binding is
81 checked the type of its LHS is unified with that of its RHS; and
82 type-checking the LHS of course requires that the binder is in scope.
84 At the top-level the LIE is sure to contain nothing but constant
85 dictionaries, which we resolve at the module level.
88 tcTopBinds :: RenamedHsBinds -> TcM (TcMonoBinds, TcLclEnv)
89 -- Note: returning the TcLclEnv is more than we really
90 -- want. The bit we care about is the local bindings
91 -- and the free type variables thereof
93 = tc_binds_and_then TopLevel glue binds $
94 getLclEnv `thenM` \ env ->
95 returnM (EmptyMonoBinds, env)
97 -- The top level bindings are flattened into a giant
98 -- implicitly-mutually-recursive MonoBinds
99 glue binds1 (binds2, env) = (flatten binds1 `AndMonoBinds` binds2, env)
100 flatten EmptyBinds = EmptyMonoBinds
101 flatten (b1 `ThenBinds` b2) = flatten b1 `AndMonoBinds` flatten b2
102 flatten (MonoBind b _ _) = b
103 -- Can't have a IPBinds at top level
107 :: (TcHsBinds -> thing -> thing) -- Combinator
112 tcBindsAndThen = tc_binds_and_then NotTopLevel
114 tc_binds_and_then top_lvl combiner EmptyBinds do_next
116 tc_binds_and_then top_lvl combiner (MonoBind EmptyMonoBinds sigs is_rec) do_next
119 tc_binds_and_then top_lvl combiner (ThenBinds b1 b2) do_next
120 = tc_binds_and_then top_lvl combiner b1 $
121 tc_binds_and_then top_lvl combiner b2 $
124 tc_binds_and_then top_lvl combiner (IPBinds binds) do_next
125 = getLIE do_next `thenM` \ (result, expr_lie) ->
126 mapAndUnzipM tc_ip_bind binds `thenM` \ (avail_ips, binds') ->
128 -- If the binding binds ?x = E, we must now
129 -- discharge any ?x constraints in expr_lie
130 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
132 returnM (combiner (IPBinds binds') $
133 combiner (mkMonoBind Recursive dict_binds) result)
135 -- I wonder if we should do these one at at time
138 tc_ip_bind (ip, expr)
139 = newTyVarTy openTypeKind `thenM` \ ty ->
140 getSrcLocM `thenM` \ loc ->
141 newIPDict (IPBind ip) ip ty `thenM` \ (ip', ip_inst) ->
142 tcCheckRho expr ty `thenM` \ expr' ->
143 returnM (ip_inst, (ip', expr'))
145 tc_binds_and_then top_lvl combiner (MonoBind bind sigs is_rec) do_next
146 = -- BRING ANY SCOPED TYPE VARIABLES INTO SCOPE
147 -- Notice that they scope over
148 -- a) the type signatures in the binding group
149 -- b) the bindings in the group
150 -- c) the scope of the binding group (the "in" part)
151 tcAddScopedTyVars (collectSigTysFromMonoBinds bind) $
153 tcBindWithSigs top_lvl bind sigs is_rec `thenM` \ (poly_binds, poly_ids) ->
156 TopLevel -- For the top level don't bother will all this
157 -- bindInstsOfLocalFuns stuff. All the top level
158 -- things are rec'd together anyway, so it's fine to
159 -- leave them to the tcSimplifyTop, and quite a bit faster too
161 -- Subtle (and ugly) point: furthermore at top level we
162 -- return the TcLclEnv, which contains the LIE var; we
163 -- don't want to return the wrong one!
164 -> tc_body poly_ids `thenM` \ (prag_binds, thing) ->
165 returnM (combiner (mkMonoBind Recursive (poly_binds `andMonoBinds` prag_binds))
168 NotTopLevel -- For nested bindings we must do teh bindInstsOfLocalFuns thing
169 -> getLIE (tc_body poly_ids) `thenM` \ ((prag_binds, thing), lie) ->
171 -- Create specialisations of functions bound here
172 bindInstsOfLocalFuns lie poly_ids `thenM` \ lie_binds ->
174 -- We want to keep non-recursive things non-recursive
175 -- so that we desugar unlifted bindings correctly
178 combiner (mkMonoBind Recursive (
179 poly_binds `andMonoBinds`
180 lie_binds `andMonoBinds`
185 combiner (mkMonoBind NonRecursive poly_binds) $
186 combiner (mkMonoBind NonRecursive prag_binds) $
187 combiner (mkMonoBind Recursive lie_binds) $
188 -- NB: the binds returned by tcSimplify and bindInstsOfLocalFuns
189 -- aren't guaranteed in dependency order (though we could change
190 -- that); hence the Recursive marker.
193 tc_body poly_ids -- Type check the pragmas and "thing inside"
194 = -- Extend the environment to bind the new polymorphic Ids
195 tcExtendLocalValEnv poly_ids $
197 -- Build bindings and IdInfos corresponding to user pragmas
198 tcSpecSigs sigs `thenM` \ prag_binds ->
200 -- Now do whatever happens next, in the augmented envt
201 do_next `thenM` \ thing ->
203 returnM (prag_binds, thing)
207 %************************************************************************
209 \subsection{tcBindWithSigs}
211 %************************************************************************
213 @tcBindWithSigs@ deals with a single binding group. It does generalisation,
214 so all the clever stuff is in here.
216 * binder_names and mbind must define the same set of Names
218 * The Names in tc_ty_sigs must be a subset of binder_names
220 * The Ids in tc_ty_sigs don't necessarily have to have the same name
221 as the Name in the tc_ty_sig
224 tcBindWithSigs :: TopLevelFlag
228 -> TcM (TcMonoBinds, [TcId])
230 tcBindWithSigs top_lvl mbind sigs is_rec
231 = -- TYPECHECK THE SIGNATURES
232 recoverM (returnM []) (
233 mappM tcTySig [sig | sig@(Sig name _ _) <- sigs]
234 ) `thenM` \ tc_ty_sigs ->
236 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
238 -- If typechecking the binds fails, then return with each
239 -- signature-less binder given type (forall a.a), to minimise subsequent
241 newTyVar liftedTypeKind `thenM` \ alpha_tv ->
243 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
244 binder_names = collectMonoBinders mbind
245 poly_ids = map mk_dummy binder_names
246 mk_dummy name = case maybeSig tc_ty_sigs name of
247 Just sig -> tcSigPolyId sig -- Signature
248 Nothing -> mkLocalId name forall_a_a -- No signature
250 traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names) `thenM_`
251 returnM (EmptyMonoBinds, poly_ids)
254 -- TYPECHECK THE BINDINGS
255 traceTc (ptext SLIT("--------------------------------------------------------")) `thenM_`
256 traceTc (ptext SLIT("Bindings for") <+> ppr (collectMonoBinders mbind)) `thenM_`
257 getLIE (tcMonoBinds mbind tc_ty_sigs is_rec) `thenM` \ ((mbind', bndr_names_w_ids), lie_req) ->
259 (binder_names, mono_ids) = unzip (bagToList bndr_names_w_ids)
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("In 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
623 -> [TcSigInfo] -> RecFlag
625 Bag (Name, -- Bound names
626 TcId)) -- Corresponding monomorphic bound things
628 tcMonoBinds mbinds tc_ty_sigs is_rec
630 -- 1. Check the patterns, building up an environment binding
631 -- the variables in this group (in the recursive case)
632 -- 2. Extend the environment
634 = tc_mb_pats mbinds `thenM` \ (complete_it, xve) ->
635 tcExtendLocalValEnv2 (bagToList xve) complete_it
637 tc_mb_pats EmptyMonoBinds
638 = returnM (returnM (EmptyMonoBinds, emptyBag), emptyBag)
640 tc_mb_pats (AndMonoBinds mb1 mb2)
641 = tc_mb_pats mb1 `thenM` \ (complete_it1, xve1) ->
642 tc_mb_pats mb2 `thenM` \ (complete_it2, xve2) ->
644 complete_it = complete_it1 `thenM` \ (mb1', bs1) ->
645 complete_it2 `thenM` \ (mb2', bs2) ->
646 returnM (AndMonoBinds mb1' mb2', bs1 `unionBags` bs2)
648 returnM (complete_it, xve1 `unionBags` xve2)
650 tc_mb_pats (FunMonoBind name inf matches locn)
652 -- a) Type sig supplied
653 -- b) No type sig and recursive
654 -- c) No type sig and non-recursive
656 | Just sig <- maybeSig tc_ty_sigs name
657 = let -- (a) There is a type signature
658 -- Use it for the environment extension, and check
659 -- the RHS has the appropriate type (with outer for-alls stripped off)
660 mono_id = tcSigMonoId sig
661 mono_ty = idType mono_id
662 complete_it = addSrcLoc locn $
663 tcMatchesFun name matches (Check mono_ty) `thenM` \ matches' ->
664 returnM (FunMonoBind mono_id inf matches' locn,
665 unitBag (name, mono_id))
667 returnM (complete_it, if isRec is_rec then unitBag (name,tcSigPolyId sig)
671 = -- (b) No type signature, and recursive
672 -- So we must use an ordinary H-M type variable
673 -- which means the variable gets an inferred tau-type
674 newLocalName name `thenM` \ mono_name ->
675 newTyVarTy openTypeKind `thenM` \ mono_ty ->
677 mono_id = mkLocalId mono_name mono_ty
678 complete_it = addSrcLoc locn $
679 tcMatchesFun name matches (Check mono_ty) `thenM` \ matches' ->
680 returnM (FunMonoBind mono_id inf matches' locn,
681 unitBag (name, mono_id))
683 returnM (complete_it, unitBag (name, mono_id))
685 | otherwise -- (c) No type signature, and non-recursive
686 = let -- So we can use a 'hole' type to infer a higher-rank type
689 newHole `thenM` \ hole ->
690 tcMatchesFun name matches (Infer hole) `thenM` \ matches' ->
691 readMutVar hole `thenM` \ fun_ty ->
692 newLocalName name `thenM` \ mono_name ->
694 mono_id = mkLocalId mono_name fun_ty
696 returnM (FunMonoBind mono_id inf matches' locn,
697 unitBag (name, mono_id))
699 returnM (complete_it, emptyBag)
701 tc_mb_pats bind@(PatMonoBind pat grhss locn)
704 -- Now typecheck the pattern
705 -- We do now support binding fresh (not-already-in-scope) scoped
706 -- type variables in the pattern of a pattern binding.
707 -- For example, this is now legal:
709 -- The type variables are brought into scope in tc_binds_and_then,
710 -- so we don't have to do anything here.
712 newHole `thenM` \ hole ->
713 tcPat tc_pat_bndr pat (Infer hole) `thenM` \ (pat', tvs, ids, lie_avail) ->
714 readMutVar hole `thenM` \ pat_ty ->
716 -- Don't know how to deal with pattern-bound existentials yet
717 checkTc (isEmptyBag tvs && null lie_avail)
718 (existentialExplode bind) `thenM_`
721 complete_it = addSrcLoc locn $
722 addErrCtxt (patMonoBindsCtxt bind) $
723 tcGRHSsPat grhss (Check pat_ty) `thenM` \ grhss' ->
724 returnM (PatMonoBind pat' grhss' locn, ids)
726 returnM (complete_it, if isRec is_rec then ids else emptyBag)
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
738 Nothing -> newLocalName name `thenM` \ bndr_name ->
739 tcMonoPatBndr bndr_name pat_ty
741 Just sig -> addSrcLoc (getSrcLoc name) $
742 tcSubPat (idType mono_id) pat_ty `thenM` \ co_fn ->
743 returnM (co_fn, mono_id)
745 mono_id = tcSigMonoId sig
749 %************************************************************************
751 \subsection{SPECIALIZE pragmas}
753 %************************************************************************
755 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
756 pragmas. It is convenient for them to appear in the @[RenamedSig]@
757 part of a binding because then the same machinery can be used for
758 moving them into place as is done for type signatures.
763 f :: Ord a => [a] -> b -> b
764 {-# SPECIALIZE f :: [Int] -> b -> b #-}
767 For this we generate:
769 f* = /\ b -> let d1 = ...
773 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
774 retain a right-hand-side that the simplifier will otherwise discard as
775 dead code... the simplifier has a flag that tells it not to discard
776 SpecPragmaId bindings.
778 In this case the f* retains a call-instance of the overloaded
779 function, f, (including appropriate dictionaries) so that the
780 specialiser will subsequently discover that there's a call of @f@ at
781 Int, and will create a specialisation for @f@. After that, the
782 binding for @f*@ can be discarded.
784 We used to have a form
785 {-# SPECIALISE f :: <type> = g #-}
786 which promised that g implemented f at <type>, but we do that with
788 {-# SPECIALISE (f::<type) = g #-}
791 tcSpecSigs :: [RenamedSig] -> TcM TcMonoBinds
792 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
793 = -- SPECIALISE f :: forall b. theta => tau = g
795 addErrCtxt (valSpecSigCtxt name poly_ty) $
797 -- Get and instantiate its alleged specialised type
798 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
800 -- Check that f has a more general type, and build a RHS for
801 -- the spec-pragma-id at the same time
802 getLIE (tcCheckSigma (HsVar name) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
804 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
805 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
807 -- Just specialise "f" by building a SpecPragmaId binding
808 -- It is the thing that makes sure we don't prematurely
809 -- dead-code-eliminate the binding we are really interested in.
810 newLocalName name `thenM` \ spec_name ->
812 spec_bind = VarMonoBind (mkSpecPragmaId spec_name sig_ty)
813 (mkHsLet spec_binds spec_expr)
816 -- Do the rest and combine
817 tcSpecSigs sigs `thenM` \ binds_rest ->
818 returnM (binds_rest `andMonoBinds` spec_bind)
820 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
821 tcSpecSigs [] = returnM EmptyMonoBinds
824 %************************************************************************
826 \subsection[TcBinds-errors]{Error contexts and messages}
828 %************************************************************************
832 patMonoBindsCtxt bind
833 = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
835 -----------------------------------------------
837 = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
838 nest 4 (ppr v <+> dcolon <+> ppr ty)]
840 -----------------------------------------------
841 sigContextsErr = ptext SLIT("Mismatched contexts")
843 sigContextsCtxt s1 s2
844 = vcat [ptext SLIT("When matching the contexts of the signatures for"),
845 nest 2 (vcat [ppr s1 <+> dcolon <+> ppr (idType s1),
846 ppr s2 <+> dcolon <+> ppr (idType s2)]),
847 ptext SLIT("The signature contexts in a mutually recursive group should all be identical")]
849 -----------------------------------------------
850 unliftedBindErr flavour mbind
851 = hang (text flavour <+> ptext SLIT("bindings for unlifted types aren't allowed:"))
854 -----------------------------------------------
855 existentialExplode mbinds
856 = hang (vcat [text "My brain just exploded.",
857 text "I can't handle pattern bindings for existentially-quantified constructors.",
858 text "In the binding group"])
861 -----------------------------------------------
862 restrictedBindCtxtErr binder_names
863 = hang (ptext SLIT("Illegal overloaded type signature(s)"))
864 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
865 ptext SLIT("that falls under the monomorphism restriction")])
868 = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
870 -- Used in error messages
871 -- Use quotes for a single one; they look a bit "busy" for several
872 pprBinders [bndr] = quotes (ppr bndr)
873 pprBinders bndrs = pprWithCommas ppr bndrs