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 TcEnv ( InstEnv, getEnvTyCons, tcSetInstEnv )
20 import TcGenDeriv -- Deriv stuff
21 import TcInstUtil ( InstInfo(..), buildInstanceEnv )
22 import TcSimplify ( tcSimplifyThetas )
24 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
25 import RnEnv ( newDFunName, bindLocatedLocalsRn )
26 import RnMonad ( RnNameSupply,
27 renameSourceCode, thenRn, mapRn, returnRn )
29 import Bag ( Bag, emptyBag, unionBags, listToBag )
30 import Class ( classKey, Class )
31 import ErrUtils ( dumpIfSet, Message, pprBagOfErrors )
32 import MkId ( mkDictFunId )
33 import Id ( mkVanillaId )
34 import DataCon ( dataConArgTys, isNullaryDataCon, isExistentialDataCon )
35 import PrelInfo ( needsDataDeclCtxtClassKeys )
36 import Maybes ( maybeToBool, catMaybes )
37 import Module ( ModuleName )
38 import Name ( isLocallyDefined, getSrcLoc,
42 import RdrName ( RdrName )
43 import RnMonad ( FixityEnv )
44 import SrcLoc ( mkGeneratedSrcLoc, SrcLoc )
45 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
46 tyConTheta, maybeTyConSingleCon, isDataTyCon,
47 isEnumerationTyCon, isAlgTyCon, TyCon
49 import Type ( TauType, mkTyVarTys, mkTyConApp,
50 mkSigmaTy, mkDictTy, isUnboxedType,
51 splitAlgTyConApp, classesToPreds
53 import TysWiredIn ( voidTy )
55 import Unique -- Keys stuff
56 import Bag ( bagToList )
57 import Util ( zipWithEqual, sortLt, removeDups, assoc, thenCmp )
61 %************************************************************************
63 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
65 %************************************************************************
69 data T a b = C1 (Foo a) (Bar b)
74 [NOTE: See end of these comments for what to do with
75 data (C a, D b) => T a b = ...
78 We want to come up with an instance declaration of the form
80 instance (Ping a, Pong b, ...) => Eq (T a b) where
83 It is pretty easy, albeit tedious, to fill in the code "...". The
84 trick is to figure out what the context for the instance decl is,
85 namely @Ping@, @Pong@ and friends.
87 Let's call the context reqd for the T instance of class C at types
88 (a,b, ...) C (T a b). Thus:
90 Eq (T a b) = (Ping a, Pong b, ...)
92 Now we can get a (recursive) equation from the @data@ decl:
94 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
95 u Eq (T b a) u Eq Int -- From C2
96 u Eq (T a a) -- From C3
98 Foo and Bar may have explicit instances for @Eq@, in which case we can
99 just substitute for them. Alternatively, either or both may have
100 their @Eq@ instances given by @deriving@ clauses, in which case they
101 form part of the system of equations.
103 Now all we need do is simplify and solve the equations, iterating to
104 find the least fixpoint. Notice that the order of the arguments can
105 switch around, as here in the recursive calls to T.
107 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
111 Eq (T a b) = {} -- The empty set
114 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
115 u Eq (T b a) u Eq Int -- From C2
116 u Eq (T a a) -- From C3
118 After simplification:
119 = Eq a u Ping b u {} u {} u {}
124 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
125 u Eq (T b a) u Eq Int -- From C2
126 u Eq (T a a) -- From C3
128 After simplification:
133 = Eq a u Ping b u Eq b u Ping a
135 The next iteration gives the same result, so this is the fixpoint. We
136 need to make a canonical form of the RHS to ensure convergence. We do
137 this by simplifying the RHS to a form in which
139 - the classes constrain only tyvars
140 - the list is sorted by tyvar (major key) and then class (minor key)
141 - no duplicates, of course
143 So, here are the synonyms for the ``equation'' structures:
146 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
147 -- The tyvars bind all the variables in the RHS
148 -- NEW: it's convenient to re-use InstInfo
149 -- We'll "panic" out some fields...
151 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
153 type DerivSoln = DerivRhs
157 A note about contexts on data decls
158 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
161 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
163 We will need an instance decl like:
165 instance (Read a, RealFloat a) => Read (Complex a) where
168 The RealFloat in the context is because the read method for Complex is bound
169 to construct a Complex, and doing that requires that the argument type is
172 But this ain't true for Show, Eq, Ord, etc, since they don't construct
173 a Complex; they only take them apart.
175 Our approach: identify the offending classes, and add the data type
176 context to the instance decl. The "offending classes" are
181 %************************************************************************
183 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
185 %************************************************************************
188 tcDeriving :: ModuleName -- name of module under scrutiny
189 -> FixityEnv -- for the deriving code (Show/Read.)
190 -> RnNameSupply -- for "renaming" bits of generated code
191 -> Bag InstInfo -- What we already know about instances
192 -> TcM s (Bag InstInfo, -- The generated "instance decls".
193 RenamedHsBinds) -- Extra generated bindings
195 tcDeriving modname fixs rn_name_supply inst_decl_infos_in
196 = recoverTc (returnTc (emptyBag, EmptyBinds)) $
198 -- Fish the "deriving"-related information out of the TcEnv
199 -- and make the necessary "equations".
200 makeDerivEqns `thenTc` \ eqns ->
202 returnTc (emptyBag, EmptyBinds)
205 -- Take the equation list and solve it, to deliver a list of
206 -- solutions, a.k.a. the contexts for the instance decls
207 -- required for the corresponding equations.
208 solveDerivEqns inst_decl_infos_in eqns `thenTc` \ new_inst_infos ->
210 -- Now augment the InstInfos, adding in the rather boring
211 -- actual-code-to-do-the-methods binds. We may also need to
212 -- generate extra not-one-inst-decl-specific binds, notably
213 -- "con2tag" and/or "tag2con" functions. We do these
216 gen_taggery_Names new_inst_infos `thenTc` \ nm_alist_etc ->
220 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
221 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
222 method_binds_s = map (gen_bind fixs) new_inst_infos
223 mbinders = bagToList (collectMonoBinders extra_mbinds)
225 -- Rename to get RenamedBinds.
226 -- The only tricky bit is that the extra_binds must scope over the
227 -- method bindings for the instances.
228 (dfun_names_w_method_binds, rn_extra_binds)
229 = renameSourceCode modname rn_name_supply (
230 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
231 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
232 mapRn rn_one method_binds_s `thenRn` \ dfun_names_w_method_binds ->
233 returnRn (dfun_names_w_method_binds, rn_extra_binds)
235 rn_one (cl_nm, tycon_nm, meth_binds)
236 = newDFunName (cl_nm, tycon_nm)
237 mkGeneratedSrcLoc `thenRn` \ dfun_name ->
238 rnMethodBinds meth_binds `thenRn` \ (rn_meth_binds, _) ->
239 returnRn (dfun_name, rn_meth_binds)
241 really_new_inst_infos = zipWith gen_inst_info
243 dfun_names_w_method_binds
245 ddump_deriv = ddump_deriving really_new_inst_infos rn_extra_binds
247 ioToTc (dumpIfSet opt_D_dump_deriv "Derived instances" ddump_deriv) `thenTc_`
249 returnTc (listToBag really_new_inst_infos, rn_extra_binds)
251 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
252 ddump_deriving inst_infos extra_binds
253 = vcat (map pp_info inst_infos) $$ ppr extra_binds
255 pp_info (InstInfo clas tvs [ty] inst_decl_theta _ mbinds _ _)
256 = ppr (mkSigmaTy tvs inst_decl_theta' (mkDictTy clas [ty]))
259 where inst_decl_theta' = classesToPreds inst_decl_theta
263 %************************************************************************
265 \subsection[TcDeriv-eqns]{Forming the equations}
267 %************************************************************************
269 @makeDerivEqns@ fishes around to find the info about needed derived
270 instances. Complicating factors:
273 We can only derive @Enum@ if the data type is an enumeration
274 type (all nullary data constructors).
277 We can only derive @Ix@ if the data type is an enumeration {\em
278 or} has just one data constructor (e.g., tuples).
281 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
285 makeDerivEqns :: TcM s [DerivEqn]
288 = tcGetEnv `thenNF_Tc` \ env ->
290 local_data_tycons = filter (\tc -> isLocallyDefined tc && isAlgTyCon tc)
293 think_about_deriving = need_deriving local_data_tycons
294 (derive_these, _) = removeDups cmp_deriv think_about_deriving
295 eqns = map mk_eqn derive_these
297 if null local_data_tycons then
298 returnTc [] -- Bale out now
300 mapTc mk_eqn derive_these `thenTc` \ maybe_eqns ->
301 returnTc (catMaybes maybe_eqns)
303 ------------------------------------------------------------------
304 need_deriving :: [TyCon] -> [(Class, TyCon)]
305 -- find the tycons that have `deriving' clauses;
307 need_deriving tycons_to_consider
308 = foldr (\ tycon acc -> [(clas,tycon) | clas <- tyConDerivings tycon] ++ acc)
312 ------------------------------------------------------------------
313 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
314 cmp_deriv (c1, t1) (c2, t2)
315 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
317 ------------------------------------------------------------------
318 mk_eqn :: (Class, TyCon) -> NF_TcM s (Maybe DerivEqn)
319 -- we swizzle the tyvars and datacons out of the tycon
320 -- to make the rest of the equation
323 = case chk_out clas tycon of
324 Just err -> addErrTc err `thenNF_Tc_`
326 Nothing -> returnNF_Tc (Just (clas, tycon, tyvars, constraints))
328 clas_key = classKey clas
329 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
330 tyvar_tys = mkTyVarTys tyvars
331 data_cons = tyConDataCons tycon
333 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
335 -- "extra_constraints": see notes above about contexts on data decls
337 | offensive_class = tyConTheta tycon
340 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
342 mk_constraints data_con
344 | arg_ty <- instd_arg_tys,
345 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
348 instd_arg_tys = dataConArgTys data_con tyvar_tys
350 ------------------------------------------------------------------
351 chk_out :: Class -> TyCon -> Maybe Message
353 | clas `hasKey` enumClassKey && not is_enumeration = bog_out nullary_why
354 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = bog_out single_nullary_why
355 | clas `hasKey` ixClassKey && not is_enumeration_or_single = bog_out single_nullary_why
356 | any isExistentialDataCon (tyConDataCons tycon) = Just (existentialErr clas tycon)
357 | otherwise = Nothing
359 is_enumeration = isEnumerationTyCon tycon
360 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
361 is_enumeration_or_single = is_enumeration || is_single_con
363 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
364 nullary_why = SLIT("data type with all nullary constructors expected")
366 bog_out why = Just (derivingThingErr clas tycon why)
369 %************************************************************************
371 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
373 %************************************************************************
375 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
376 terms, which is the final correct RHS for the corresponding original
380 Each (k,TyVarTy tv) in a solution constrains only a type
384 The (k,TyVarTy tv) pairs in a solution are canonically
385 ordered by sorting on type varible, tv, (major key) and then class, k,
390 solveDerivEqns :: Bag InstInfo
392 -> TcM s [InstInfo] -- Solns in same order as eqns.
393 -- This bunch is Absolutely minimal...
395 solveDerivEqns inst_decl_infos_in orig_eqns
396 = iterateDeriv initial_solutions
398 -- The initial solutions for the equations claim that each
399 -- instance has an empty context; this solution is certainly
400 -- in canonical form.
401 initial_solutions :: [DerivSoln]
402 initial_solutions = [ [] | _ <- orig_eqns ]
404 ------------------------------------------------------------------
405 -- iterateDeriv calculates the next batch of solutions,
406 -- compares it with the current one; finishes if they are the
407 -- same, otherwise recurses with the new solutions.
408 -- It fails if any iteration fails
409 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
410 iterateDeriv current_solns
411 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_inst_infos, new_solns) ->
412 if (current_solns == new_solns) then
413 returnTc new_inst_infos
415 iterateDeriv new_solns
417 ------------------------------------------------------------------
418 iterateOnce current_solns
419 = -- Extend the inst info from the explicit instance decls
420 -- with the current set of solutions, giving a
422 add_solns inst_decl_infos_in orig_eqns current_solns
423 `thenNF_Tc` \ (new_inst_infos, inst_env) ->
427 tcSetInstEnv inst_env (
428 listTc [ tcAddErrCtxt (derivCtxt tc) $
429 tcSimplifyThetas deriv_rhs
430 | (_,tc,_,deriv_rhs) <- orig_eqns ]
431 ) `thenTc` \ next_solns ->
433 -- Canonicalise the solutions, so they compare nicely
434 let canonicalised_next_solns
435 = [ sortLt (<) next_soln | next_soln <- next_solns ]
437 returnTc (new_inst_infos, canonicalised_next_solns)
441 add_solns :: Bag InstInfo -- The global, non-derived ones
442 -> [DerivEqn] -> [DerivSoln]
443 -> NF_TcM s ([InstInfo], -- The new, derived ones
445 -- the eqns and solns move "in lockstep"; we have the eqns
446 -- because we need the LHS info for addClassInstance.
448 add_solns inst_infos_in eqns solns
450 = discardErrsTc (buildInstanceEnv all_inst_infos) `thenNF_Tc` \ inst_env ->
451 -- We do the discard-errs so that we don't get repeated error messages
452 -- about duplicate instances.
453 -- They'll appear later, when we do the top-level buildInstanceEnv.
455 returnNF_Tc (new_inst_infos, inst_env)
457 new_inst_infos = zipWithEqual "add_solns" mk_deriv_inst_info eqns solns
459 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
461 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
462 = InstInfo clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
465 (my_panic "binds") (getSrcLoc tycon)
466 (my_panic "upragmas")
469 = mkVanillaId (getName tycon) dummy_dfun_ty
470 -- The name is getSrcLoc'd in an error message
472 theta' = classesToPreds theta
473 dummy_dfun_ty = mkSigmaTy tyvars theta' voidTy
474 -- All we need from the dfun is its "theta" part, used during
475 -- equation simplification (tcSimplifyThetas). The final
476 -- dfun_id will have the superclass dictionaries as arguments too,
477 -- but that'll be added after the equations are solved. For now,
478 -- it's enough just to make a dummy dfun with the simple theta part.
480 -- The part after the theta is dummied here as voidTy; actually it's
481 -- (C (T a b)), but it doesn't seem worth constructing it.
482 -- We can't leave it as a panic because to get the theta part we
483 -- have to run down the type!
485 my_panic str = panic "add_soln" -- pprPanic ("add_soln:"++str) (hsep [char ':', ppr clas, ppr tycon])
488 %************************************************************************
490 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
492 %************************************************************************
494 After all the trouble to figure out the required context for the
495 derived instance declarations, all that's left is to chug along to
496 produce them. They will then be shoved into @tcInstDecls2@, which
497 will do all its usual business.
499 There are lots of possibilities for code to generate. Here are
500 various general remarks.
505 We want derived instances of @Eq@ and @Ord@ (both v common) to be
506 ``you-couldn't-do-better-by-hand'' efficient.
509 Deriving @Show@---also pretty common--- should also be reasonable good code.
512 Deriving for the other classes isn't that common or that big a deal.
519 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
522 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
525 We {\em normally} generate code only for the non-defaulted methods;
526 there are some exceptions for @Eq@ and (especially) @Ord@...
529 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
530 constructor's numeric (@Int#@) tag. These are generated by
531 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
532 these is around is given by @hasCon2TagFun@.
534 The examples under the different sections below will make this
538 Much less often (really just for deriving @Ix@), we use a
539 @_tag2con_<tycon>@ function. See the examples.
542 We use the renamer!!! Reason: we're supposed to be
543 producing @RenamedMonoBinds@ for the methods, but that means
544 producing correctly-uniquified code on the fly. This is entirely
545 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
546 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
547 the renamer. What a great hack!
551 -- Generate the method bindings for the required instance
552 -- (paired with class name, as we need that when generating dict
554 gen_bind :: FixityEnv -> InstInfo -> ({-class-}OccName, {-tyCon-}OccName, RdrNameMonoBinds)
555 gen_bind fixities (InstInfo clas _ [ty] _ _ _ _ _)
557 = (clas_nm, tycon_nm, EmptyMonoBinds)
558 | clas `hasKey` showClassKey
559 = (clas_nm, tycon_nm, gen_Show_binds fixities tycon)
560 | clas `hasKey` readClassKey
561 = (clas_nm, tycon_nm, gen_Read_binds fixities tycon)
563 = (clas_nm, tycon_nm,
564 assoc "gen_bind:bad derived class"
565 [(eqClassKey, gen_Eq_binds)
566 ,(ordClassKey, gen_Ord_binds)
567 ,(enumClassKey, gen_Enum_binds)
568 ,(boundedClassKey, gen_Bounded_binds)
569 ,(ixClassKey, gen_Ix_binds)
574 clas_nm = nameOccName (getName clas)
575 tycon_nm = nameOccName (getName tycon)
576 from_here = isLocallyDefined tycon
577 (tycon,_,_) = splitAlgTyConApp ty
579 gen_inst_info :: InstInfo
580 -> (Name, RenamedMonoBinds)
581 -> InstInfo -- the gen'd (filled-in) "instance decl"
583 gen_inst_info (InstInfo clas tyvars tys@(ty:_) inst_decl_theta _ _ locn _)
584 (dfun_name, meth_binds)
586 -- Generate the various instance-related Ids
587 InstInfo clas tyvars tys inst_decl_theta
592 dfun_id = mkDictFunId dfun_name clas tyvars tys inst_decl_theta
594 from_here = isLocallyDefined tycon
595 (tycon,_,_) = splitAlgTyConApp ty
599 %************************************************************************
601 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
603 %************************************************************************
608 con2tag_Foo :: Foo ... -> Int#
609 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
610 maxtag_Foo :: Int -- ditto (NB: not unboxed)
613 We have a @con2tag@ function for a tycon if:
616 We're deriving @Eq@ and the tycon has nullary data constructors.
619 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
623 We have a @tag2con@ function for a tycon if:
626 We're deriving @Enum@, or @Ix@ (enum type only???)
629 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
632 gen_taggery_Names :: [InstInfo]
633 -> TcM s [(RdrName, -- for an assoc list
634 TyCon, -- related tycon
637 gen_taggery_Names inst_infos
638 = --pprTrace "gen_taggery:\n" (vcat [hsep [ppr c, ppr t] | (c,t) <- all_CTs]) $
639 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
640 foldlTc do_tag2con names_so_far tycons_of_interest
642 all_CTs = [ (c, get_tycon ty) | (InstInfo c _ [ty] _ _ _ _ _) <- inst_infos ]
644 get_tycon ty = case splitAlgTyConApp ty of { (tc, _, _) -> tc }
646 all_tycons = map snd all_CTs
647 (tycons_of_interest, _) = removeDups compare all_tycons
649 do_con2tag acc_Names tycon
650 | isDataTyCon tycon &&
651 ((we_are_deriving eqClassKey tycon
652 && any isNullaryDataCon (tyConDataCons tycon))
653 || (we_are_deriving ordClassKey tycon
654 && not (maybeToBool (maybeTyConSingleCon tycon)))
655 || (we_are_deriving enumClassKey tycon)
656 || (we_are_deriving ixClassKey tycon))
658 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
663 do_tag2con acc_Names tycon
664 | isDataTyCon tycon &&
665 (we_are_deriving enumClassKey tycon ||
666 we_are_deriving ixClassKey tycon
667 && isEnumerationTyCon tycon)
668 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
669 : (maxtag_RDR tycon, tycon, GenMaxTag)
674 we_are_deriving clas_key tycon
675 = is_in_eqns clas_key tycon all_CTs
677 is_in_eqns clas_key tycon [] = False
678 is_in_eqns clas_key tycon ((c,t):cts)
679 = (clas_key == classKey c && tycon == t)
680 || is_in_eqns clas_key tycon cts
685 derivingThingErr :: Class -> TyCon -> FAST_STRING -> Message
687 derivingThingErr clas tycon why
688 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr clas)],
689 hsep [ptext SLIT("for the type"), quotes (ppr tycon)],
692 existentialErr clas tycon
693 = sep [ptext SLIT("Can't derive any instances for type") <+> quotes (ppr tycon),
694 ptext SLIT("because it has existentially-quantified constructor(s)")]
697 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)