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 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, 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 is_with) 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' is_with) $
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
227 -> [RenamedSig] -- Used solely to get INLINE, NOINLINE sigs
229 -> TcM (TcMonoBinds, [TcId])
231 tcBindWithSigs top_lvl mbind sigs is_rec
232 = -- TYPECHECK THE SIGNATURES
233 recoverM (returnM []) (
234 mappM tcTySig [sig | sig@(Sig name _ _) <- sigs]
235 ) `thenM` \ tc_ty_sigs ->
237 -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
239 -- If typechecking the binds fails, then return with each
240 -- signature-less binder given type (forall a.a), to minimise subsequent
242 newTyVar liftedTypeKind `thenM` \ alpha_tv ->
244 forall_a_a = mkForAllTy alpha_tv (mkTyVarTy alpha_tv)
245 binder_names = collectMonoBinders mbind
246 poly_ids = map mk_dummy binder_names
247 mk_dummy name = case maybeSig tc_ty_sigs name of
248 Just sig -> tcSigPolyId sig -- Signature
249 Nothing -> mkLocalId name forall_a_a -- No signature
251 traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names) `thenM_`
252 returnM (EmptyMonoBinds, poly_ids)
255 -- TYPECHECK THE BINDINGS
256 getLIE (tcMonoBinds mbind tc_ty_sigs is_rec) `thenM` \ ((mbind', bndr_names_w_ids), lie_req) ->
258 (binder_names, mono_ids) = unzip (bagToList bndr_names_w_ids)
259 tau_tvs = foldr (unionVarSet . tyVarsOfType . idType) emptyVarSet mono_ids
263 -- (it seems a bit crude to have to do getLIE twice,
264 -- but I can't see a better way just now)
265 addSrcLoc (minimum (map getSrcLoc binder_names)) $
266 addErrCtxt (genCtxt binder_names) $
267 getLIE (generalise binder_names mbind tau_tvs lie_req tc_ty_sigs)
268 `thenM` \ ((tc_tyvars_to_gen, dict_binds, dict_ids), lie_free) ->
271 -- ZONK THE GENERALISED TYPE VARIABLES TO REAL TyVars
272 -- This commits any unbound kind variables to boxed kind, by unification
273 -- It's important that the final quanfified type variables
274 -- are fully zonked, *including boxity*, because they'll be
275 -- included in the forall types of the polymorphic Ids.
276 -- At calls of these Ids we'll instantiate fresh type variables from
277 -- them, and we use their boxity then.
278 mappM zonkTcTyVarToTyVar tc_tyvars_to_gen `thenM` \ real_tyvars_to_gen ->
281 -- It's important that the dict Ids are zonked, including the boxity set
282 -- in the previous step, because they are later used to form the type of
283 -- the polymorphic thing, and forall-types must be zonked so far as
284 -- their bound variables are concerned
285 mappM zonkId dict_ids `thenM` \ zonked_dict_ids ->
286 mappM zonkId mono_ids `thenM` \ zonked_mono_ids ->
288 -- BUILD THE POLYMORPHIC RESULT IDs
290 exports = zipWith mk_export binder_names zonked_mono_ids
291 poly_ids = [poly_id | (_, poly_id, _) <- exports]
292 dict_tys = map idType zonked_dict_ids
294 inlines = mkNameSet [name | InlineSig True name _ loc <- sigs]
295 -- Any INLINE sig (regardless of phase control)
296 -- makes the RHS look small
297 inline_phases = listToFM [(name, phase) | InlineSig _ name phase _ <- sigs,
298 not (isAlwaysActive phase)]
299 -- Set the IdInfo field to control the inline phase
300 -- AlwaysActive is the default, so don't bother with them
302 mk_export binder_name zonked_mono_id
304 attachInlinePhase inline_phases poly_id,
308 case maybeSig tc_ty_sigs binder_name of
309 Just (TySigInfo sig_poly_id sig_tyvars _ _ _ _ _) ->
310 (sig_tyvars, sig_poly_id)
311 Nothing -> (real_tyvars_to_gen, new_poly_id)
313 new_poly_id = mkLocalId binder_name poly_ty
314 poly_ty = mkForAllTys real_tyvars_to_gen
316 $ idType zonked_mono_id
317 -- It's important to build a fully-zonked poly_ty, because
318 -- we'll slurp out its free type variables when extending the
319 -- local environment (tcExtendLocalValEnv); if it's not zonked
320 -- it appears to have free tyvars that aren't actually free
324 traceTc (text "binding:" <+> ppr ((zonked_dict_ids, dict_binds),
325 exports, map idType poly_ids)) `thenM_`
327 -- Check for an unlifted, non-overloaded group
328 -- In that case we must make extra checks
329 if any (isUnLiftedType . idType) zonked_mono_ids && null zonked_dict_ids
330 then -- Some bindings are unlifted
331 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind `thenM_`
333 extendLIEs lie_req `thenM_`
335 AbsBinds [] [] exports inlines mbind',
336 -- Do not generate even any x=y bindings
340 else -- The normal case
341 extendLIEs lie_free `thenM_`
343 AbsBinds real_tyvars_to_gen
347 (dict_binds `andMonoBinds` mbind'),
351 attachInlinePhase inline_phases bndr
352 = case lookupFM inline_phases (idName bndr) of
353 Just prag -> bndr `setInlinePragma` prag
356 -- Check that non-overloaded unlifted bindings are
359 -- c) non-polymorphic
360 -- d) not a multiple-binding group (more or less implied by (a))
362 checkUnliftedBinds top_lvl is_rec real_tyvars_to_gen mbind
363 = ASSERT( not (any ((eqKind unliftedTypeKind) . tyVarKind) real_tyvars_to_gen) )
364 -- The instCantBeGeneralised stuff in tcSimplify should have
365 -- already raised an error if we're trying to generalise an
366 -- unboxed tyvar (NB: unboxed tyvars are always introduced
367 -- along with a class constraint) and it's better done there
368 -- because we have more precise origin information.
369 -- That's why we just use an ASSERT here.
371 checkTc (isNotTopLevel top_lvl)
372 (unliftedBindErr "Top-level" mbind) `thenM_`
373 checkTc (isNonRec is_rec)
374 (unliftedBindErr "Recursive" mbind) `thenM_`
375 checkTc (single_bind mbind)
376 (unliftedBindErr "Multiple" mbind) `thenM_`
377 checkTc (null real_tyvars_to_gen)
378 (unliftedBindErr "Polymorphic" mbind)
381 single_bind (PatMonoBind _ _ _) = True
382 single_bind (FunMonoBind _ _ _ _) = True
383 single_bind other = False
387 Polymorphic recursion
388 ~~~~~~~~~~~~~~~~~~~~~
389 The game plan for polymorphic recursion in the code above is
391 * Bind any variable for which we have a type signature
392 to an Id with a polymorphic type. Then when type-checking
393 the RHSs we'll make a full polymorphic call.
395 This fine, but if you aren't a bit careful you end up with a horrendous
396 amount of partial application and (worse) a huge space leak. For example:
398 f :: Eq a => [a] -> [a]
401 If we don't take care, after typechecking we get
403 f = /\a -> \d::Eq a -> let f' = f a d
407 Notice the the stupid construction of (f a d), which is of course
408 identical to the function we're executing. In this case, the
409 polymorphic recursion isn't being used (but that's a very common case).
412 f = /\a -> \d::Eq a -> letrec
413 fm = \ys:[a] -> ...fm...
417 This can lead to a massive space leak, from the following top-level defn
423 Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
424 f' is another thunk which evaluates to the same thing... and you end
425 up with a chain of identical values all hung onto by the CAF ff.
429 = let f' = f Int dEqInt in \ys. ...f'...
431 = let f' = let f' = f Int dEqInt in \ys. ...f'...
435 Solution: when typechecking the RHSs we always have in hand the
436 *monomorphic* Ids for each binding. So we just need to make sure that
437 if (Method f a d) shows up in the constraints emerging from (...f...)
438 we just use the monomorphic Id. We achieve this by adding monomorphic Ids
439 to the "givens" when simplifying constraints. That's what the "lies_avail"
443 %************************************************************************
445 \subsection{getTyVarsToGen}
447 %************************************************************************
450 generalise binder_names mbind tau_tvs lie_req sigs =
452 -- check for -fno-monomorphism-restriction
453 doptM Opt_NoMonomorphismRestriction `thenM` \ no_MR ->
454 let is_unrestricted | no_MR = True
455 | otherwise = isUnRestrictedGroup tysig_names mbind
458 if not is_unrestricted then -- RESTRICTED CASE
459 -- Check signature contexts are empty
460 checkTc (all is_mono_sig sigs)
461 (restrictedBindCtxtErr binder_names) `thenM_`
463 -- Now simplify with exactly that set of tyvars
464 -- We have to squash those Methods
465 tcSimplifyRestricted doc tau_tvs lie_req `thenM` \ (qtvs, binds) ->
467 -- Check that signature type variables are OK
468 checkSigsTyVars qtvs sigs `thenM` \ final_qtvs ->
470 returnM (final_qtvs, binds, [])
472 else if null sigs then -- UNRESTRICTED CASE, NO TYPE SIGS
473 tcSimplifyInfer doc tau_tvs lie_req
475 else -- UNRESTRICTED CASE, WITH TYPE SIGS
476 -- CHECKING CASE: Unrestricted group, there are type signatures
477 -- Check signature contexts are identical
478 checkSigsCtxts sigs `thenM` \ (sig_avails, sig_dicts) ->
480 -- Check that the needed dicts can be
481 -- expressed in terms of the signature ones
482 tcSimplifyInferCheck doc tau_tvs sig_avails lie_req `thenM` \ (forall_tvs, dict_binds) ->
484 -- Check that signature type variables are OK
485 checkSigsTyVars forall_tvs sigs `thenM` \ final_qtvs ->
487 returnM (final_qtvs, dict_binds, sig_dicts)
490 tysig_names = map (idName . tcSigPolyId) sigs
491 is_mono_sig (TySigInfo _ _ theta _ _ _ _) = null theta
493 doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
495 -----------------------
496 -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
497 -- The type signatures on a mutually-recursive group of definitions
498 -- must all have the same context (or none).
500 -- We unify them because, with polymorphic recursion, their types
501 -- might not otherwise be related. This is a rather subtle issue.
503 checkSigsCtxts sigs@(TySigInfo id1 sig_tvs theta1 _ _ _ src_loc : other_sigs)
504 = addSrcLoc src_loc $
505 mappM_ check_one other_sigs `thenM_`
507 returnM ([], []) -- Non-overloaded type signatures
509 newDicts SignatureOrigin theta1 `thenM` \ sig_dicts ->
511 -- The "sig_avails" is the stuff available. We get that from
512 -- the context of the type signature, BUT ALSO the lie_avail
513 -- so that polymorphic recursion works right (see comments at end of fn)
514 sig_avails = sig_dicts ++ sig_meths
516 returnM (sig_avails, map instToId sig_dicts)
518 sig1_dict_tys = map mkPredTy theta1
519 sig_meths = concat [insts | TySigInfo _ _ _ _ _ insts _ <- sigs]
521 check_one sig@(TySigInfo id _ theta _ _ _ _)
522 = addErrCtxt (sigContextsCtxt id1 id) $
523 checkTc (equalLength theta theta1) sigContextsErr `thenM_`
524 unifyTauTyLists sig1_dict_tys (map mkPredTy theta)
526 checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
527 checkSigsTyVars qtvs sigs
528 = mappM check_one sigs `thenM` \ sig_tvs_s ->
530 -- Sigh. Make sure that all the tyvars in the type sigs
531 -- appear in the returned ty var list, which is what we are
532 -- going to generalise over. Reason: we occasionally get
534 -- type T a = () -> ()
537 -- Here, 'a' won't appear in qtvs, so we have to add it
539 sig_tvs = foldr (unionVarSet . mkVarSet) emptyVarSet sig_tvs_s
540 all_tvs = mkVarSet qtvs `unionVarSet` sig_tvs
542 returnM (varSetElems all_tvs)
544 check_one (TySigInfo id sig_tyvars sig_theta sig_tau _ _ src_loc)
545 = addSrcLoc src_loc $
546 addErrCtxt (ptext SLIT("When checking the type signature for")
547 <+> quotes (ppr id)) $
548 addErrCtxtM (sigCtxt id sig_tyvars sig_theta sig_tau) $
549 checkSigTyVarsWrt (idFreeTyVars id) sig_tyvars
552 @getTyVarsToGen@ decides what type variables to generalise over.
554 For a "restricted group" -- see the monomorphism restriction
555 for a definition -- we bind no dictionaries, and
556 remove from tyvars_to_gen any constrained type variables
558 *Don't* simplify dicts at this point, because we aren't going
559 to generalise over these dicts. By the time we do simplify them
560 we may well know more. For example (this actually came up)
562 f x = array ... xs where xs = [1,2,3,4,5]
563 We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
564 stuff. If we simplify only at the f-binding (not the xs-binding)
565 we'll know that the literals are all Ints, and we can just produce
568 Find all the type variables involved in overloading, the
569 "constrained_tyvars". These are the ones we *aren't* going to
570 generalise. We must be careful about doing this:
572 (a) If we fail to generalise a tyvar which is not actually
573 constrained, then it will never, ever get bound, and lands
574 up printed out in interface files! Notorious example:
575 instance Eq a => Eq (Foo a b) where ..
576 Here, b is not constrained, even though it looks as if it is.
577 Another, more common, example is when there's a Method inst in
578 the LIE, whose type might very well involve non-overloaded
580 [NOTE: Jan 2001: I don't understand the problem here so I'm doing
581 the simple thing instead]
583 (b) On the other hand, we mustn't generalise tyvars which are constrained,
584 because we are going to pass on out the unmodified LIE, with those
585 tyvars in it. They won't be in scope if we've generalised them.
587 So we are careful, and do a complete simplification just to find the
588 constrained tyvars. We don't use any of the results, except to
589 find which tyvars are constrained.
592 isUnRestrictedGroup :: [Name] -- Signatures given for these
596 is_elem v vs = isIn "isUnResMono" v vs
598 isUnRestrictedGroup sigs (PatMonoBind other _ _) = False
599 isUnRestrictedGroup sigs (VarMonoBind v _) = v `is_elem` sigs
600 isUnRestrictedGroup sigs (FunMonoBind v _ matches _) = isUnRestrictedMatch matches ||
602 isUnRestrictedGroup sigs (AndMonoBinds mb1 mb2) = isUnRestrictedGroup sigs mb1 &&
603 isUnRestrictedGroup sigs mb2
604 isUnRestrictedGroup sigs EmptyMonoBinds = True
606 isUnRestrictedMatch (Match [] _ _ : _) = False -- No args => like a pattern binding
607 isUnRestrictedMatch other = True -- Some args => a function binding
611 %************************************************************************
613 \subsection{tcMonoBind}
615 %************************************************************************
617 @tcMonoBinds@ deals with a single @MonoBind@.
618 The signatures have been dealt with already.
621 tcMonoBinds :: RenamedMonoBinds
622 -> [TcSigInfo] -> RecFlag
624 Bag (Name, -- Bound names
625 TcId)) -- Corresponding monomorphic bound things
627 tcMonoBinds mbinds tc_ty_sigs is_rec
629 -- 1. Check the patterns, building up an environment binding
630 -- the variables in this group (in the recursive case)
631 -- 2. Extend the environment
633 = tc_mb_pats mbinds `thenM` \ (complete_it, xve) ->
634 tcExtendLocalValEnv2 (bagToList xve) complete_it
636 tc_mb_pats EmptyMonoBinds
637 = returnM (returnM (EmptyMonoBinds, emptyBag), emptyBag)
639 tc_mb_pats (AndMonoBinds mb1 mb2)
640 = tc_mb_pats mb1 `thenM` \ (complete_it1, xve1) ->
641 tc_mb_pats mb2 `thenM` \ (complete_it2, xve2) ->
643 complete_it = complete_it1 `thenM` \ (mb1', bs1) ->
644 complete_it2 `thenM` \ (mb2', bs2) ->
645 returnM (AndMonoBinds mb1' mb2', bs1 `unionBags` bs2)
647 returnM (complete_it, xve1 `unionBags` xve2)
649 tc_mb_pats (FunMonoBind name inf matches locn)
651 -- a) Type sig supplied
652 -- b) No type sig and recursive
653 -- c) No type sig and non-recursive
655 | Just sig <- maybeSig tc_ty_sigs name
656 = let -- (a) There is a type signature
657 -- Use it for the environment extension, and check
658 -- the RHS has the appropriate type (with outer for-alls stripped off)
659 mono_id = tcSigMonoId sig
660 mono_ty = idType mono_id
661 complete_it = addSrcLoc locn $
662 tcMatchesFun name matches (Check mono_ty) `thenM` \ matches' ->
663 returnM (FunMonoBind mono_id inf matches' locn,
664 unitBag (name, mono_id))
666 returnM (complete_it, if isRec is_rec then unitBag (name,tcSigPolyId sig)
670 = -- (b) No type signature, and recursive
671 -- So we must use an ordinary H-M type variable
672 -- which means the variable gets an inferred tau-type
673 newLocalName name `thenM` \ mono_name ->
674 newTyVarTy openTypeKind `thenM` \ mono_ty ->
676 mono_id = mkLocalId mono_name mono_ty
677 complete_it = addSrcLoc locn $
678 tcMatchesFun name matches (Check mono_ty) `thenM` \ matches' ->
679 returnM (FunMonoBind mono_id inf matches' locn,
680 unitBag (name, mono_id))
682 returnM (complete_it, unitBag (name, mono_id))
684 | otherwise -- (c) No type signature, and non-recursive
685 = let -- So we can use a 'hole' type to infer a higher-rank type
688 newHole `thenM` \ hole ->
689 tcMatchesFun name matches (Infer hole) `thenM` \ matches' ->
690 readMutVar hole `thenM` \ fun_ty ->
691 newLocalName name `thenM` \ mono_name ->
693 mono_id = mkLocalId mono_name fun_ty
695 returnM (FunMonoBind mono_id inf matches' locn,
696 unitBag (name, mono_id))
698 returnM (complete_it, emptyBag)
700 tc_mb_pats bind@(PatMonoBind pat grhss locn)
703 -- Now typecheck the pattern
704 -- We do now support binding fresh (not-already-in-scope) scoped
705 -- type variables in the pattern of a pattern binding.
706 -- For example, this is now legal:
708 -- The type variables are brought into scope in tc_binds_and_then,
709 -- so we don't have to do anything here.
711 newHole `thenM` \ hole ->
712 tcPat tc_pat_bndr pat (Infer hole) `thenM` \ (pat', tvs, ids, lie_avail) ->
713 readMutVar hole `thenM` \ pat_ty ->
715 -- Don't know how to deal with pattern-bound existentials yet
716 checkTc (isEmptyBag tvs && null lie_avail)
717 (existentialExplode bind) `thenM_`
720 complete_it = addSrcLoc locn $
721 addErrCtxt (patMonoBindsCtxt bind) $
722 tcGRHSsPat grhss (Check pat_ty) `thenM` \ grhss' ->
723 returnM (PatMonoBind pat' grhss' locn, ids)
725 returnM (complete_it, if isRec is_rec then ids else emptyBag)
727 -- tc_pat_bndr is used when dealing with a LHS binder in a pattern.
728 -- If there was a type sig for that Id, we want to make it much
729 -- as if that type signature had been on the binder as a SigPatIn.
730 -- We check for a type signature; if there is one, we use the mono_id
731 -- from the signature. This is how we make sure the tau part of the
732 -- signature actually matches the type of the LHS; then tc_mb_pats
733 -- ensures the LHS and RHS have the same type
735 tc_pat_bndr name pat_ty
736 = case maybeSig tc_ty_sigs name of
737 Nothing -> newLocalName name `thenM` \ bndr_name ->
738 tcMonoPatBndr bndr_name pat_ty
740 Just sig -> addSrcLoc (getSrcLoc name) $
741 tcSubPat (idType mono_id) pat_ty `thenM` \ co_fn ->
742 returnM (co_fn, mono_id)
744 mono_id = tcSigMonoId sig
748 %************************************************************************
750 \subsection{SPECIALIZE pragmas}
752 %************************************************************************
754 @tcSpecSigs@ munches up the specialisation "signatures" that arise through *user*
755 pragmas. It is convenient for them to appear in the @[RenamedSig]@
756 part of a binding because then the same machinery can be used for
757 moving them into place as is done for type signatures.
762 f :: Ord a => [a] -> b -> b
763 {-# SPECIALIZE f :: [Int] -> b -> b #-}
766 For this we generate:
768 f* = /\ b -> let d1 = ...
772 where f* is a SpecPragmaId. The **sole** purpose of SpecPragmaIds is to
773 retain a right-hand-side that the simplifier will otherwise discard as
774 dead code... the simplifier has a flag that tells it not to discard
775 SpecPragmaId bindings.
777 In this case the f* retains a call-instance of the overloaded
778 function, f, (including appropriate dictionaries) so that the
779 specialiser will subsequently discover that there's a call of @f@ at
780 Int, and will create a specialisation for @f@. After that, the
781 binding for @f*@ can be discarded.
783 We used to have a form
784 {-# SPECIALISE f :: <type> = g #-}
785 which promised that g implemented f at <type>, but we do that with
787 {-# SPECIALISE (f::<type) = g #-}
790 tcSpecSigs :: [RenamedSig] -> TcM TcMonoBinds
791 tcSpecSigs (SpecSig name poly_ty src_loc : sigs)
792 = -- SPECIALISE f :: forall b. theta => tau = g
794 addErrCtxt (valSpecSigCtxt name poly_ty) $
796 -- Get and instantiate its alleged specialised type
797 tcHsSigType (FunSigCtxt name) poly_ty `thenM` \ sig_ty ->
799 -- Check that f has a more general type, and build a RHS for
800 -- the spec-pragma-id at the same time
801 getLIE (tcCheckSigma (HsVar name) sig_ty) `thenM` \ (spec_expr, spec_lie) ->
803 -- Squeeze out any Methods (see comments with tcSimplifyToDicts)
804 tcSimplifyToDicts spec_lie `thenM` \ spec_binds ->
806 -- Just specialise "f" by building a SpecPragmaId binding
807 -- It is the thing that makes sure we don't prematurely
808 -- dead-code-eliminate the binding we are really interested in.
809 newLocalName name `thenM` \ spec_name ->
811 spec_bind = VarMonoBind (mkSpecPragmaId spec_name sig_ty)
812 (mkHsLet spec_binds spec_expr)
815 -- Do the rest and combine
816 tcSpecSigs sigs `thenM` \ binds_rest ->
817 returnM (binds_rest `andMonoBinds` spec_bind)
819 tcSpecSigs (other_sig : sigs) = tcSpecSigs sigs
820 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