2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcDeriv]{Deriving}
6 Handles @deriving@ clauses on @data@ declarations.
9 module TcDeriv ( tcDeriving ) where
11 #include "HsVersions.h"
13 import HsSyn ( HsBinds(..), MonoBinds(..), collectMonoBinders )
14 import RdrHsSyn ( RdrNameMonoBinds )
15 import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds )
16 import CmdLineOpts ( opt_D_dump_deriv )
19 import Inst ( InstanceMapper )
20 import TcEnv ( getEnvTyCons )
21 import TcGenDeriv -- Deriv stuff
22 import TcInstUtil ( InstInfo(..), buildInstanceEnvs )
23 import TcSimplify ( tcSimplifyThetas )
25 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
26 import RnEnv ( newDFunName, bindLocatedLocalsRn )
27 import RnMonad ( RnNameSupply,
28 renameSourceCode, thenRn, mapRn, returnRn )
30 import Bag ( Bag, emptyBag, unionBags, listToBag )
31 import Class ( classKey, Class )
32 import ErrUtils ( dumpIfSet, Message, pprBagOfErrors )
33 import MkId ( mkDictFunId )
34 import Id ( mkVanillaId )
35 import DataCon ( dataConArgTys, isNullaryDataCon, isExistentialDataCon )
36 import PrelInfo ( needsDataDeclCtxtClassKeys )
37 import Maybes ( maybeToBool, catMaybes )
38 import Module ( ModuleName )
39 import Name ( isLocallyDefined, getSrcLoc,
43 import RdrName ( RdrName )
44 import RnMonad ( Fixities )
45 import SrcLoc ( mkGeneratedSrcLoc, SrcLoc )
46 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
47 tyConTheta, maybeTyConSingleCon, isDataTyCon,
48 isEnumerationTyCon, isAlgTyCon, TyCon
50 import Type ( TauType, mkTyVarTys, mkTyConApp,
51 mkSigmaTy, mkDictTy, isUnboxedType,
52 splitAlgTyConApp, classesToPreds
54 import TysWiredIn ( voidTy )
56 import Unique -- Keys stuff
57 import Bag ( bagToList )
58 import Util ( zipWithEqual, sortLt, removeDups, assoc, thenCmp )
62 %************************************************************************
64 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
66 %************************************************************************
70 data T a b = C1 (Foo a) (Bar b)
75 [NOTE: See end of these comments for what to do with
76 data (C a, D b) => T a b = ...
79 We want to come up with an instance declaration of the form
81 instance (Ping a, Pong b, ...) => Eq (T a b) where
84 It is pretty easy, albeit tedious, to fill in the code "...". The
85 trick is to figure out what the context for the instance decl is,
86 namely @Ping@, @Pong@ and friends.
88 Let's call the context reqd for the T instance of class C at types
89 (a,b, ...) C (T a b). Thus:
91 Eq (T a b) = (Ping a, Pong b, ...)
93 Now we can get a (recursive) equation from the @data@ decl:
95 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
96 u Eq (T b a) u Eq Int -- From C2
97 u Eq (T a a) -- From C3
99 Foo and Bar may have explicit instances for @Eq@, in which case we can
100 just substitute for them. Alternatively, either or both may have
101 their @Eq@ instances given by @deriving@ clauses, in which case they
102 form part of the system of equations.
104 Now all we need do is simplify and solve the equations, iterating to
105 find the least fixpoint. Notice that the order of the arguments can
106 switch around, as here in the recursive calls to T.
108 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
112 Eq (T a b) = {} -- The empty set
115 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
116 u Eq (T b a) u Eq Int -- From C2
117 u Eq (T a a) -- From C3
119 After simplification:
120 = Eq a u Ping b u {} u {} u {}
125 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
126 u Eq (T b a) u Eq Int -- From C2
127 u Eq (T a a) -- From C3
129 After simplification:
134 = Eq a u Ping b u Eq b u Ping a
136 The next iteration gives the same result, so this is the fixpoint. We
137 need to make a canonical form of the RHS to ensure convergence. We do
138 this by simplifying the RHS to a form in which
140 - the classes constrain only tyvars
141 - the list is sorted by tyvar (major key) and then class (minor key)
142 - no duplicates, of course
144 So, here are the synonyms for the ``equation'' structures:
147 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
148 -- The tyvars bind all the variables in the RHS
149 -- NEW: it's convenient to re-use InstInfo
150 -- We'll "panic" out some fields...
152 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
154 type DerivSoln = DerivRhs
158 A note about contexts on data decls
159 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
162 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
164 We will need an instance decl like:
166 instance (Read a, RealFloat a) => Read (Complex a) where
169 The RealFloat in the context is because the read method for Complex is bound
170 to construct a Complex, and doing that requires that the argument type is
173 But this ain't true for Show, Eq, Ord, etc, since they don't construct
174 a Complex; they only take them apart.
176 Our approach: identify the offending classes, and add the data type
177 context to the instance decl. The "offending classes" are
182 %************************************************************************
184 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
186 %************************************************************************
189 tcDeriving :: ModuleName -- name of module under scrutiny
190 -> Fixities -- for the deriving code (Show/Read.)
191 -> RnNameSupply -- for "renaming" bits of generated code
192 -> Bag InstInfo -- What we already know about instances
193 -> TcM s (Bag InstInfo, -- The generated "instance decls".
194 RenamedHsBinds) -- Extra generated bindings
196 tcDeriving modname fixs rn_name_supply inst_decl_infos_in
197 = recoverTc (returnTc (emptyBag, EmptyBinds)) $
199 -- Fish the "deriving"-related information out of the TcEnv
200 -- and make the necessary "equations".
201 makeDerivEqns `thenTc` \ eqns ->
203 returnTc (emptyBag, EmptyBinds)
206 -- Take the equation list and solve it, to deliver a list of
207 -- solutions, a.k.a. the contexts for the instance decls
208 -- required for the corresponding equations.
209 solveDerivEqns inst_decl_infos_in eqns `thenTc` \ new_inst_infos ->
211 -- Now augment the InstInfos, adding in the rather boring
212 -- actual-code-to-do-the-methods binds. We may also need to
213 -- generate extra not-one-inst-decl-specific binds, notably
214 -- "con2tag" and/or "tag2con" functions. We do these
217 gen_taggery_Names new_inst_infos `thenTc` \ nm_alist_etc ->
221 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
222 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
223 method_binds_s = map (gen_bind fixs) new_inst_infos
224 mbinders = bagToList (collectMonoBinders extra_mbinds)
226 -- Rename to get RenamedBinds.
227 -- The only tricky bit is that the extra_binds must scope over the
228 -- method bindings for the instances.
229 (dfun_names_w_method_binds, rn_extra_binds)
230 = renameSourceCode modname rn_name_supply (
231 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
232 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
233 mapRn rn_one method_binds_s `thenRn` \ dfun_names_w_method_binds ->
234 returnRn (dfun_names_w_method_binds, rn_extra_binds)
236 rn_one (cl_nm, tycon_nm, meth_binds)
237 = newDFunName (cl_nm, tycon_nm)
238 mkGeneratedSrcLoc `thenRn` \ dfun_name ->
239 rnMethodBinds meth_binds `thenRn` \ (rn_meth_binds, _) ->
240 returnRn (dfun_name, rn_meth_binds)
242 really_new_inst_infos = zipWith gen_inst_info
244 dfun_names_w_method_binds
246 ddump_deriv = ddump_deriving really_new_inst_infos rn_extra_binds
248 ioToTc (dumpIfSet opt_D_dump_deriv "Derived instances" ddump_deriv) `thenTc_`
250 returnTc (listToBag really_new_inst_infos, rn_extra_binds)
252 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
253 ddump_deriving inst_infos extra_binds
254 = vcat (map pp_info inst_infos) $$ ppr extra_binds
256 pp_info (InstInfo clas tvs [ty] inst_decl_theta _ mbinds _ _)
257 = ppr (mkSigmaTy tvs inst_decl_theta' (mkDictTy clas [ty]))
260 where inst_decl_theta' = classesToPreds inst_decl_theta
264 %************************************************************************
266 \subsection[TcDeriv-eqns]{Forming the equations}
268 %************************************************************************
270 @makeDerivEqns@ fishes around to find the info about needed derived
271 instances. Complicating factors:
274 We can only derive @Enum@ if the data type is an enumeration
275 type (all nullary data constructors).
278 We can only derive @Ix@ if the data type is an enumeration {\em
279 or} has just one data constructor (e.g., tuples).
282 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
286 makeDerivEqns :: TcM s [DerivEqn]
289 = tcGetEnv `thenNF_Tc` \ env ->
291 local_data_tycons = filter (\tc -> isLocallyDefined tc && isAlgTyCon tc)
294 think_about_deriving = need_deriving local_data_tycons
295 (derive_these, _) = removeDups cmp_deriv think_about_deriving
296 eqns = map mk_eqn derive_these
298 if null local_data_tycons then
299 returnTc [] -- Bale out now
301 mapTc mk_eqn derive_these `thenTc` \ maybe_eqns ->
302 returnTc (catMaybes maybe_eqns)
304 ------------------------------------------------------------------
305 need_deriving :: [TyCon] -> [(Class, TyCon)]
306 -- find the tycons that have `deriving' clauses;
308 need_deriving tycons_to_consider
309 = foldr (\ tycon acc -> [(clas,tycon) | clas <- tyConDerivings tycon] ++ acc)
313 ------------------------------------------------------------------
314 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
315 cmp_deriv (c1, t1) (c2, t2)
316 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
318 ------------------------------------------------------------------
319 mk_eqn :: (Class, TyCon) -> NF_TcM s (Maybe DerivEqn)
320 -- we swizzle the tyvars and datacons out of the tycon
321 -- to make the rest of the equation
324 = case chk_out clas tycon of
325 Just err -> addErrTc err `thenNF_Tc_`
327 Nothing -> returnNF_Tc (Just (clas, tycon, tyvars, constraints))
329 clas_key = classKey clas
330 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
331 tyvar_tys = mkTyVarTys tyvars
332 data_cons = tyConDataCons tycon
334 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
336 -- "extra_constraints": see notes above about contexts on data decls
338 | offensive_class = tyConTheta tycon
341 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
343 mk_constraints data_con
345 | arg_ty <- instd_arg_tys,
346 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
349 instd_arg_tys = dataConArgTys data_con tyvar_tys
351 ------------------------------------------------------------------
352 chk_out :: Class -> TyCon -> Maybe Message
354 | clas_key == enumClassKey && not is_enumeration = bog_out nullary_why
355 | clas_key == boundedClassKey && not is_enumeration_or_single = bog_out single_nullary_why
356 | clas_key == ixClassKey && not is_enumeration_or_single = bog_out single_nullary_why
357 | any isExistentialDataCon (tyConDataCons tycon) = Just (existentialErr clas tycon)
358 | otherwise = Nothing
360 clas_key = classKey clas
362 is_enumeration = isEnumerationTyCon tycon
363 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
364 is_enumeration_or_single = is_enumeration || is_single_con
366 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
367 nullary_why = SLIT("data type with all nullary constructors expected")
369 bog_out why = Just (derivingThingErr clas tycon why)
372 %************************************************************************
374 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
376 %************************************************************************
378 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
379 terms, which is the final correct RHS for the corresponding original
383 Each (k,TyVarTy tv) in a solution constrains only a type
387 The (k,TyVarTy tv) pairs in a solution are canonically
388 ordered by sorting on type varible, tv, (major key) and then class, k,
393 solveDerivEqns :: Bag InstInfo
395 -> TcM s [InstInfo] -- Solns in same order as eqns.
396 -- This bunch is Absolutely minimal...
398 solveDerivEqns inst_decl_infos_in orig_eqns
399 = iterateDeriv initial_solutions
401 -- The initial solutions for the equations claim that each
402 -- instance has an empty context; this solution is certainly
403 -- in canonical form.
404 initial_solutions :: [DerivSoln]
405 initial_solutions = [ [] | _ <- orig_eqns ]
407 ------------------------------------------------------------------
408 -- iterateDeriv calculates the next batch of solutions,
409 -- compares it with the current one; finishes if they are the
410 -- same, otherwise recurses with the new solutions.
411 -- It fails if any iteration fails
412 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
413 iterateDeriv current_solns
414 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_inst_infos, new_solns) ->
415 if (current_solns == new_solns) then
416 returnTc new_inst_infos
418 iterateDeriv new_solns
420 ------------------------------------------------------------------
421 iterateOnce current_solns
422 = -- Extend the inst info from the explicit instance decls
423 -- with the current set of solutions, giving a
425 add_solns inst_decl_infos_in orig_eqns current_solns
426 `thenNF_Tc` \ (new_inst_infos, inst_mapper) ->
428 class_to_inst_env cls = inst_mapper cls
432 listTc [ tcAddErrCtxt (derivCtxt tc) $
433 tcSimplifyThetas class_to_inst_env deriv_rhs
434 | (_,tc,_,deriv_rhs) <- orig_eqns ] `thenTc` \ next_solns ->
436 -- Canonicalise the solutions, so they compare nicely
437 let canonicalised_next_solns
438 = [ sortLt (<) next_soln | next_soln <- next_solns ]
440 returnTc (new_inst_infos, canonicalised_next_solns)
444 add_solns :: Bag InstInfo -- The global, non-derived ones
445 -> [DerivEqn] -> [DerivSoln]
446 -> NF_TcM s ([InstInfo], -- The new, derived ones
448 -- the eqns and solns move "in lockstep"; we have the eqns
449 -- because we need the LHS info for addClassInstance.
451 add_solns inst_infos_in eqns solns
453 = discardErrsTc (buildInstanceEnvs all_inst_infos) `thenNF_Tc` \ inst_mapper ->
454 -- We do the discard-errs so that we don't get repeated error messages
455 -- about duplicate instances.
456 -- They'll appear later, when we do the top-level buildInstanceEnvs.
458 returnNF_Tc (new_inst_infos, inst_mapper)
460 new_inst_infos = zipWithEqual "add_solns" mk_deriv_inst_info eqns solns
462 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
464 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
465 = InstInfo clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
468 (my_panic "binds") (getSrcLoc tycon)
469 (my_panic "upragmas")
472 = mkVanillaId (getName tycon) dummy_dfun_ty
473 -- The name is getSrcLoc'd in an error message
475 theta' = classesToPreds theta
476 dummy_dfun_ty = mkSigmaTy tyvars theta' voidTy
477 -- All we need from the dfun is its "theta" part, used during
478 -- equation simplification (tcSimplifyThetas). The final
479 -- dfun_id will have the superclass dictionaries as arguments too,
480 -- but that'll be added after the equations are solved. For now,
481 -- it's enough just to make a dummy dfun with the simple theta part.
483 -- The part after the theta is dummied here as voidTy; actually it's
484 -- (C (T a b)), but it doesn't seem worth constructing it.
485 -- We can't leave it as a panic because to get the theta part we
486 -- have to run down the type!
488 my_panic str = panic "add_soln" -- pprPanic ("add_soln:"++str) (hsep [char ':', ppr clas, ppr tycon])
491 %************************************************************************
493 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
495 %************************************************************************
497 After all the trouble to figure out the required context for the
498 derived instance declarations, all that's left is to chug along to
499 produce them. They will then be shoved into @tcInstDecls2@, which
500 will do all its usual business.
502 There are lots of possibilities for code to generate. Here are
503 various general remarks.
508 We want derived instances of @Eq@ and @Ord@ (both v common) to be
509 ``you-couldn't-do-better-by-hand'' efficient.
512 Deriving @Show@---also pretty common--- should also be reasonable good code.
515 Deriving for the other classes isn't that common or that big a deal.
522 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
525 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
528 We {\em normally} generate code only for the non-defaulted methods;
529 there are some exceptions for @Eq@ and (especially) @Ord@...
532 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
533 constructor's numeric (@Int#@) tag. These are generated by
534 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
535 these is around is given by @hasCon2TagFun@.
537 The examples under the different sections below will make this
541 Much less often (really just for deriving @Ix@), we use a
542 @_tag2con_<tycon>@ function. See the examples.
545 We use the renamer!!! Reason: we're supposed to be
546 producing @RenamedMonoBinds@ for the methods, but that means
547 producing correctly-uniquified code on the fly. This is entirely
548 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
549 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
550 the renamer. What a great hack!
554 -- Generate the method bindings for the required instance
555 -- (paired with class name, as we need that when generating dict
557 gen_bind :: Fixities -> InstInfo -> ({-class-}OccName, {-tyCon-}OccName, RdrNameMonoBinds)
558 gen_bind fixities (InstInfo clas _ [ty] _ _ _ _ _)
560 = (clas_nm, tycon_nm, EmptyMonoBinds)
561 | ckey == showClassKey
562 = (clas_nm, tycon_nm, gen_Show_binds fixities tycon)
563 | ckey == readClassKey
564 = (clas_nm, tycon_nm, gen_Read_binds fixities tycon)
566 = (clas_nm, tycon_nm,
567 assoc "gen_bind:bad derived class"
568 [(eqClassKey, gen_Eq_binds)
569 ,(ordClassKey, gen_Ord_binds)
570 ,(enumClassKey, gen_Enum_binds)
571 ,(boundedClassKey, gen_Bounded_binds)
572 ,(ixClassKey, gen_Ix_binds)
577 clas_nm = nameOccName (getName clas)
578 tycon_nm = nameOccName (getName tycon)
579 from_here = isLocallyDefined tycon
580 (tycon,_,_) = splitAlgTyConApp ty
584 gen_inst_info :: InstInfo
585 -> (Name, RenamedMonoBinds)
586 -> InstInfo -- the gen'd (filled-in) "instance decl"
588 gen_inst_info (InstInfo clas tyvars tys@(ty:_) inst_decl_theta _ _ locn _)
589 (dfun_name, meth_binds)
591 -- Generate the various instance-related Ids
592 InstInfo clas tyvars tys inst_decl_theta
597 dfun_id = mkDictFunId dfun_name clas tyvars tys inst_decl_theta
599 from_here = isLocallyDefined tycon
600 (tycon,_,_) = splitAlgTyConApp ty
604 %************************************************************************
606 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
608 %************************************************************************
613 con2tag_Foo :: Foo ... -> Int#
614 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
615 maxtag_Foo :: Int -- ditto (NB: not unboxed)
618 We have a @con2tag@ function for a tycon if:
621 We're deriving @Eq@ and the tycon has nullary data constructors.
624 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
628 We have a @tag2con@ function for a tycon if:
631 We're deriving @Enum@, or @Ix@ (enum type only???)
634 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
637 gen_taggery_Names :: [InstInfo]
638 -> TcM s [(RdrName, -- for an assoc list
639 TyCon, -- related tycon
642 gen_taggery_Names inst_infos
643 = --pprTrace "gen_taggery:\n" (vcat [hsep [ppr c, ppr t] | (c,t) <- all_CTs]) $
644 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
645 foldlTc do_tag2con names_so_far tycons_of_interest
647 all_CTs = [ (c, get_tycon ty) | (InstInfo c _ [ty] _ _ _ _ _) <- inst_infos ]
649 get_tycon ty = case splitAlgTyConApp ty of { (tc, _, _) -> tc }
651 all_tycons = map snd all_CTs
652 (tycons_of_interest, _) = removeDups compare all_tycons
654 do_con2tag acc_Names tycon
655 | isDataTyCon tycon &&
656 ((we_are_deriving eqClassKey tycon
657 && any isNullaryDataCon (tyConDataCons tycon))
658 || (we_are_deriving ordClassKey tycon
659 && not (maybeToBool (maybeTyConSingleCon tycon)))
660 || (we_are_deriving enumClassKey tycon)
661 || (we_are_deriving ixClassKey tycon))
663 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
668 do_tag2con acc_Names tycon
669 | isDataTyCon tycon &&
670 (we_are_deriving enumClassKey tycon ||
671 we_are_deriving ixClassKey tycon
672 && isEnumerationTyCon tycon)
673 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
674 : (maxtag_RDR tycon, tycon, GenMaxTag)
679 we_are_deriving clas_key tycon
680 = is_in_eqns clas_key tycon all_CTs
682 is_in_eqns clas_key tycon [] = False
683 is_in_eqns clas_key tycon ((c,t):cts)
684 = (clas_key == classKey c && tycon == t)
685 || is_in_eqns clas_key tycon cts
690 derivingThingErr :: Class -> TyCon -> FAST_STRING -> Message
692 derivingThingErr clas tycon why
693 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr clas)],
694 hsep [ptext SLIT("for the type"), quotes (ppr tycon)],
697 existentialErr clas tycon
698 = sep [ptext SLIT("Can't derive any instances for type") <+> quotes (ppr tycon),
699 ptext SLIT("because it has existentially-quantified constructor(s)")]
702 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)