2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
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 ( RdrName, RdrNameMonoBinds )
15 import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds )
18 import Inst ( InstanceMapper )
19 import TcEnv ( getEnv_TyCons, tcLookupClassByKey )
20 import TcKind ( TcKind )
21 import TcGenDeriv -- Deriv stuff
22 import TcInstUtil ( InstInfo(..), mkInstanceRelatedIds, buildInstanceEnvs )
23 import TcSimplify ( tcSimplifyThetas )
25 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
26 import RnEnv ( newDfunName, bindLocatedLocalsRn )
27 import RnMonad ( RnM, RnDown, SDown, RnNameSupply,
28 renameSourceCode, thenRn, mapRn, returnRn )
30 import Bag ( Bag, emptyBag, unionBags, listToBag )
31 import Class ( classKey, Class )
32 import ErrUtils ( ErrMsg )
33 import MkId ( mkDictFunId )
34 import Id ( dataConArgTys, isNullaryDataCon )
35 import PrelInfo ( needsDataDeclCtxtClassKeys )
36 import Maybes ( maybeToBool )
37 import Name ( isLocallyDefined, getSrcLoc, Provenance,
38 Name{--O only-}, Module, NamedThing(..),
41 import SrcLoc ( mkGeneratedSrcLoc, SrcLoc )
42 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
43 tyConTheta, maybeTyConSingleCon, isDataTyCon,
44 isEnumerationTyCon, isAlgTyCon, TyCon
46 import Type ( GenType(..), TauType, mkTyVarTys, mkTyConApp,
47 mkSigmaTy, mkDictTy, isUnboxedType,
50 import TysPrim ( voidTy )
51 import TyVar ( GenTyVar, TyVar )
52 import Unique -- Keys stuff
53 import Bag ( bagToList )
54 import Util ( zipWithEqual, sortLt, removeDups, assoc, thenCmp )
58 %************************************************************************
60 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
62 %************************************************************************
66 data T a b = C1 (Foo a) (Bar b)
71 [NOTE: See end of these comments for what to do with
72 data (C a, D b) => T a b = ...
75 We want to come up with an instance declaration of the form
77 instance (Ping a, Pong b, ...) => Eq (T a b) where
80 It is pretty easy, albeit tedious, to fill in the code "...". The
81 trick is to figure out what the context for the instance decl is,
82 namely @Ping@, @Pong@ and friends.
84 Let's call the context reqd for the T instance of class C at types
85 (a,b, ...) C (T a b). Thus:
87 Eq (T a b) = (Ping a, Pong b, ...)
89 Now we can get a (recursive) equation from the @data@ decl:
91 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
92 u Eq (T b a) u Eq Int -- From C2
93 u Eq (T a a) -- From C3
95 Foo and Bar may have explicit instances for @Eq@, in which case we can
96 just substitute for them. Alternatively, either or both may have
97 their @Eq@ instances given by @deriving@ clauses, in which case they
98 form part of the system of equations.
100 Now all we need do is simplify and solve the equations, iterating to
101 find the least fixpoint. Notice that the order of the arguments can
102 switch around, as here in the recursive calls to T.
104 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
108 Eq (T a b) = {} -- The empty set
111 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
112 u Eq (T b a) u Eq Int -- From C2
113 u Eq (T a a) -- From C3
115 After simplification:
116 = Eq a u Ping b u {} u {} u {}
121 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
122 u Eq (T b a) u Eq Int -- From C2
123 u Eq (T a a) -- From C3
125 After simplification:
130 = Eq a u Ping b u Eq b u Ping a
132 The next iteration gives the same result, so this is the fixpoint. We
133 need to make a canonical form of the RHS to ensure convergence. We do
134 this by simplifying the RHS to a form in which
136 - the classes constrain only tyvars
137 - the list is sorted by tyvar (major key) and then class (minor key)
138 - no duplicates, of course
140 So, here are the synonyms for the ``equation'' structures:
143 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
144 -- The tyvars bind all the variables in the RHS
145 -- NEW: it's convenient to re-use InstInfo
146 -- We'll "panic" out some fields...
148 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
150 type DerivSoln = DerivRhs
154 A note about contexts on data decls
155 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
158 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
160 We will need an instance decl like:
162 instance (Read a, RealFloat a) => Read (Complex a) where
165 The RealFloat in the context is because the read method for Complex is bound
166 to construct a Complex, and doing that requires that the argument type is
169 But this ain't true for Show, Eq, Ord, etc, since they don't construct
170 a Complex; they only take them apart.
172 Our approach: identify the offending classes, and add the data type
173 context to the instance decl. The "offending classes" are
178 %************************************************************************
180 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
182 %************************************************************************
185 tcDeriving :: Module -- name of module under scrutiny
186 -> RnNameSupply -- for "renaming" bits of generated code
187 -> Bag InstInfo -- What we already know about instances
188 -> TcM s (Bag InstInfo, -- The generated "instance decls".
189 RenamedHsBinds, -- Extra generated bindings
190 SDoc) -- Printable derived instance decls;
191 -- for debugging via -ddump-derivings.
193 tcDeriving modname rn_name_supply inst_decl_infos_in
194 = recoverTc (returnTc (emptyBag, EmptyBinds, empty)) $
196 -- Fish the "deriving"-related information out of the TcEnv
197 -- and make the necessary "equations".
198 makeDerivEqns `thenTc` \ eqns ->
200 returnTc (emptyBag, EmptyBinds, text "No derivings")
203 -- Take the equation list and solve it, to deliver a list of
204 -- solutions, a.k.a. the contexts for the instance decls
205 -- required for the corresponding equations.
206 solveDerivEqns inst_decl_infos_in eqns `thenTc` \ new_inst_infos ->
208 -- Now augment the InstInfos, adding in the rather boring
209 -- actual-code-to-do-the-methods binds. We may also need to
210 -- generate extra not-one-inst-decl-specific binds, notably
211 -- "con2tag" and/or "tag2con" functions. We do these
214 gen_taggery_Names new_inst_infos `thenTc` \ nm_alist_etc ->
218 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
219 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
220 method_binds_s = map gen_bind new_inst_infos
221 mbinders = bagToList (collectMonoBinders extra_mbinds)
223 -- Rename to get RenamedBinds.
224 -- The only tricky bit is that the extra_binds must scope over the
225 -- method bindings for the instances.
226 (dfun_names_w_method_binds, rn_extra_binds)
227 = renameSourceCode modname rn_name_supply (
228 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
229 rnTopMonoBinds extra_mbinds [] `thenRn` \ rn_extra_binds ->
230 mapRn rn_one method_binds_s `thenRn` \ dfun_names_w_method_binds ->
231 returnRn (dfun_names_w_method_binds, rn_extra_binds)
233 rn_one (cl_nm, tycon_nm, meth_binds)
234 = newDfunName cl_nm tycon_nm
235 Nothing mkGeneratedSrcLoc `thenRn` \ dfun_name ->
236 rnMethodBinds meth_binds `thenRn` \ rn_meth_binds ->
237 returnRn (dfun_name, rn_meth_binds)
239 really_new_inst_infos = map (gen_inst_info modname)
240 (new_inst_infos `zip` dfun_names_w_method_binds)
242 ddump_deriv = ddump_deriving really_new_inst_infos rn_extra_binds
244 --pprTrace "derived:\n" (ddump_deriv) $
246 returnTc (listToBag really_new_inst_infos,
250 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])))
261 %************************************************************************
263 \subsection[TcDeriv-eqns]{Forming the equations}
265 %************************************************************************
267 @makeDerivEqns@ fishes around to find the info about needed derived
268 instances. Complicating factors:
271 We can only derive @Enum@ if the data type is an enumeration
272 type (all nullary data constructors).
275 We can only derive @Ix@ if the data type is an enumeration {\em
276 or} has just one data constructor (e.g., tuples).
279 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
283 makeDerivEqns :: TcM s [DerivEqn]
286 = tcGetEnv `thenNF_Tc` \ env ->
288 local_data_tycons = filter (\tc -> isLocallyDefined tc && isAlgTyCon tc)
291 if null local_data_tycons then
292 -- Bale out now; evalClass may not be loaded if there aren't any
295 tcLookupClassByKey evalClassKey `thenNF_Tc` \ eval_clas ->
297 think_about_deriving = need_deriving eval_clas local_data_tycons
298 (derive_these, _) = removeDups cmp_deriv think_about_deriving
299 eqns = map mk_eqn derive_these
301 mapTc chk_out think_about_deriving `thenTc_`
304 ------------------------------------------------------------------
305 need_deriving :: Class -> [TyCon] -> [(Class, TyCon)]
306 -- find the tycons that have `deriving' clauses;
307 -- we handle the "every datatype in Eval" by
308 -- doing a dummy "deriving" for it.
310 need_deriving eval_clas tycons_to_consider
311 = foldr ( \ tycon acc ->
313 acc_plus = if isLocallyDefined tycon
314 then (eval_clas, tycon) : acc
317 case (tyConDerivings tycon) of
319 cs -> [ (clas,tycon) | clas <- cs ] ++ acc_plus
324 ------------------------------------------------------------------
325 chk_out :: (Class, TyCon) -> TcM s ()
326 chk_out this_one@(clas, tycon)
328 clas_key = classKey clas
330 is_enumeration = isEnumerationTyCon tycon
331 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
333 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
334 nullary_why = SLIT("data type with all nullary constructors expected")
336 chk_clas clas_uniq clas_str clas_why cond
337 = if (clas_uniq == clas_key)
338 then checkTc cond (derivingThingErr clas_str clas_why tycon)
341 -- Are things OK for deriving Enum (if appropriate)?
342 chk_clas enumClassKey (SLIT("Enum")) nullary_why is_enumeration `thenTc_`
344 -- Are things OK for deriving Bounded (if appropriate)?
345 chk_clas boundedClassKey (SLIT("Bounded")) single_nullary_why
346 (is_enumeration || is_single_con) `thenTc_`
348 -- Are things OK for deriving Ix (if appropriate)?
349 chk_clas ixClassKey (SLIT("Ix.Ix")) single_nullary_why
350 (is_enumeration || is_single_con)
352 ------------------------------------------------------------------
353 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
354 cmp_deriv (c1, t1) (c2, t2)
355 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
357 ------------------------------------------------------------------
358 mk_eqn :: (Class, TyCon) -> DerivEqn
359 -- we swizzle the tyvars and datacons out of the tycon
360 -- to make the rest of the equation
363 = (clas, tycon, tyvars, if_not_Eval constraints)
365 clas_key = classKey clas
366 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
367 tyvar_tys = mkTyVarTys tyvars
368 data_cons = tyConDataCons tycon
370 if_not_Eval cs = if clas_key == evalClassKey then [] else cs
372 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
374 -- "extra_constraints": see notes above about contexts on data decls
376 | offensive_class = tyConTheta tycon
379 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
381 mk_constraints data_con
383 | arg_ty <- instd_arg_tys,
384 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
387 instd_arg_tys = dataConArgTys data_con tyvar_tys
390 %************************************************************************
392 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
394 %************************************************************************
396 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
397 terms, which is the final correct RHS for the corresponding original
401 Each (k,TyVarTy tv) in a solution constrains only a type
405 The (k,TyVarTy tv) pairs in a solution are canonically
406 ordered by sorting on type varible, tv, (major key) and then class, k,
411 solveDerivEqns :: Bag InstInfo
413 -> TcM s [InstInfo] -- Solns in same order as eqns.
414 -- This bunch is Absolutely minimal...
416 solveDerivEqns inst_decl_infos_in orig_eqns
417 = iterateDeriv initial_solutions
419 -- The initial solutions for the equations claim that each
420 -- instance has an empty context; this solution is certainly
421 -- in canonical form.
422 initial_solutions :: [DerivSoln]
423 initial_solutions = [ [] | _ <- orig_eqns ]
425 ------------------------------------------------------------------
426 -- iterateDeriv calculates the next batch of solutions,
427 -- compares it with the current one; finishes if they are the
428 -- same, otherwise recurses with the new solutions.
429 -- It fails if any iteration fails
430 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
431 iterateDeriv current_solns
432 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_inst_infos, new_solns) ->
433 if (current_solns == new_solns) then
434 returnTc new_inst_infos
436 iterateDeriv new_solns
438 ------------------------------------------------------------------
439 iterateOnce current_solns
440 = -- Extend the inst info from the explicit instance decls
441 -- with the current set of solutions, giving a
443 add_solns inst_decl_infos_in orig_eqns current_solns
444 `thenNF_Tc` \ (new_inst_infos, inst_mapper) ->
446 class_to_inst_env cls = inst_mapper cls
450 listTc [ tcAddErrCtxt (derivCtxt tc) $
451 tcSimplifyThetas class_to_inst_env deriv_rhs
452 | (_,tc,_,deriv_rhs) <- orig_eqns ] `thenTc` \ next_solns ->
454 -- Canonicalise the solutions, so they compare nicely
455 let canonicalised_next_solns
456 = [ sortLt (<) next_soln | next_soln <- next_solns ]
458 returnTc (new_inst_infos, canonicalised_next_solns)
462 add_solns :: Bag InstInfo -- The global, non-derived ones
463 -> [DerivEqn] -> [DerivSoln]
464 -> NF_TcM s ([InstInfo], -- The new, derived ones
466 -- the eqns and solns move "in lockstep"; we have the eqns
467 -- because we need the LHS info for addClassInstance.
469 add_solns inst_infos_in eqns solns
471 = discardErrsTc (buildInstanceEnvs all_inst_infos) `thenNF_Tc` \ inst_mapper ->
472 -- We do the discard-errs so that we don't get repeated error messages
473 -- about duplicate instances.
474 -- They'll appear later, when we do the top-level buildInstanceEnvs.
476 returnNF_Tc (new_inst_infos, inst_mapper)
478 new_inst_infos = zipWithEqual "add_solns" mk_deriv_inst_info eqns solns
480 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
482 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
483 = InstInfo clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
485 (my_panic "dfun_theta")
489 (my_panic "binds") (getSrcLoc tycon)
490 (my_panic "upragmas")
493 = mkDictFunId (getName tycon) dummy_dfun_ty bottom bottom
494 -- The name is getSrcLoc'd in an error message
496 bottom = panic "dummy_dfun_id"
498 dummy_dfun_ty = mkSigmaTy tyvars theta voidTy
499 -- All we need from the dfun is its "theta" part, used during
500 -- equation simplification (tcSimplifyThetas). The final
501 -- dfun_id will have the superclass dictionaries as arguments too,
502 -- but that'll be added after the equations are solved. For now,
503 -- it's enough just to make a dummy dfun with the simple theta part.
505 -- The part after the theta is dummied here as voidTy; actually it's
506 -- (C (T a b)), but it doesn't seem worth constructing it.
507 -- We can't leave it as a panic because to get the theta part we
508 -- have to run down the type!
510 my_panic str = panic "add_soln" -- pprPanic ("add_soln:"++str) (hsep [char ':', ppr clas, ppr tycon])
513 %************************************************************************
515 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
517 %************************************************************************
519 After all the trouble to figure out the required context for the
520 derived instance declarations, all that's left is to chug along to
521 produce them. They will then be shoved into @tcInstDecls2@, which
522 will do all its usual business.
524 There are lots of possibilities for code to generate. Here are
525 various general remarks.
530 We want derived instances of @Eq@ and @Ord@ (both v common) to be
531 ``you-couldn't-do-better-by-hand'' efficient.
534 Deriving @Show@---also pretty common--- should also be reasonable good code.
537 Deriving for the other classes isn't that common or that big a deal.
544 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
547 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
550 We {\em normally} generate code only for the non-defaulted methods;
551 there are some exceptions for @Eq@ and (especially) @Ord@...
554 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
555 constructor's numeric (@Int#@) tag. These are generated by
556 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
557 these is around is given by @hasCon2TagFun@.
559 The examples under the different sections below will make this
563 Much less often (really just for deriving @Ix@), we use a
564 @_tag2con_<tycon>@ function. See the examples.
567 We use the renamer!!! Reason: we're supposed to be
568 producing @RenamedMonoBinds@ for the methods, but that means
569 producing correctly-uniquified code on the fly. This is entirely
570 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
571 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
572 the renamer. What a great hack!
576 -- Generate the method bindings for the required instance
577 -- (paired with class name, as we need that when generating dict
579 gen_bind :: InstInfo -> ({-class-}OccName, {-tyCon-}OccName, RdrNameMonoBinds)
580 gen_bind (InstInfo clas _ [ty] _ _ _ _ _ _)
582 = (clas_nm, tycon_nm, EmptyMonoBinds)
584 = (clas_nm, tycon_nm,
585 assoc "gen_bind:bad derived class"
586 [(eqClassKey, gen_Eq_binds)
587 ,(ordClassKey, gen_Ord_binds)
588 ,(enumClassKey, gen_Enum_binds)
589 ,(evalClassKey, gen_Eval_binds)
590 ,(boundedClassKey, gen_Bounded_binds)
591 ,(showClassKey, gen_Show_binds)
592 ,(readClassKey, gen_Read_binds)
593 ,(ixClassKey, gen_Ix_binds)
598 clas_nm = nameOccName (getName clas)
599 tycon_nm = nameOccName (getName tycon)
600 from_here = isLocallyDefined tycon
601 (tycon,_,_) = splitAlgTyConApp ty
604 gen_inst_info :: Module -- Module name
605 -> (InstInfo, (Name, RenamedMonoBinds)) -- the main stuff to work on
606 -> InstInfo -- the gen'd (filled-in) "instance decl"
608 gen_inst_info modname
609 (InstInfo clas tyvars tys@(ty:_) inst_decl_theta _ _ _ locn _, (dfun_name, meth_binds))
611 -- Generate the various instance-related Ids
612 InstInfo clas tyvars tys inst_decl_theta
617 (dfun_id, dfun_theta) = mkInstanceRelatedIds
622 from_here = isLocallyDefined tycon
623 (tycon,_,_) = splitAlgTyConApp ty
627 %************************************************************************
629 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
631 %************************************************************************
636 con2tag_Foo :: Foo ... -> Int#
637 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
638 maxtag_Foo :: Int -- ditto (NB: not unboxed)
641 We have a @con2tag@ function for a tycon if:
644 We're deriving @Eq@ and the tycon has nullary data constructors.
647 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
651 We have a @tag2con@ function for a tycon if:
654 We're deriving @Enum@, or @Ix@ (enum type only???)
657 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
660 gen_taggery_Names :: [InstInfo]
661 -> TcM s [(RdrName, -- for an assoc list
662 TyCon, -- related tycon
665 gen_taggery_Names inst_infos
666 = --pprTrace "gen_taggery:\n" (vcat [hsep [ppr c, ppr t] | (c,t) <- all_CTs]) $
667 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
668 foldlTc do_tag2con names_so_far tycons_of_interest
670 all_CTs = [ (c, get_tycon ty) | (InstInfo c _ [ty] _ _ _ _ _ _) <- inst_infos ]
672 get_tycon ty = case splitAlgTyConApp ty of { (tc, _, _) -> tc }
674 all_tycons = map snd all_CTs
675 (tycons_of_interest, _) = removeDups compare all_tycons
677 do_con2tag acc_Names tycon
678 | isDataTyCon tycon &&
679 (we_are_deriving eqClassKey tycon
680 && any isNullaryDataCon (tyConDataCons tycon))
681 || (we_are_deriving ordClassKey tycon
682 && not (maybeToBool (maybeTyConSingleCon tycon)))
683 || (we_are_deriving enumClassKey tycon)
684 || (we_are_deriving ixClassKey tycon)
686 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
691 do_tag2con acc_Names tycon
692 = if (we_are_deriving enumClassKey tycon)
693 || (we_are_deriving ixClassKey tycon)
695 returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
696 : (maxtag_RDR tycon, tycon, GenMaxTag)
701 we_are_deriving clas_key tycon
702 = is_in_eqns clas_key tycon all_CTs
704 is_in_eqns clas_key tycon [] = False
705 is_in_eqns clas_key tycon ((c,t):cts)
706 = (clas_key == classKey c && tycon == t)
707 || is_in_eqns clas_key tycon cts
712 derivingThingErr :: FAST_STRING -> FAST_STRING -> TyCon -> ErrMsg
714 derivingThingErr thing why tycon
715 = hang (hsep [ptext SLIT("Can't make a derived instance of"), ptext thing])
716 0 (hang (hsep [ptext SLIT("for the type"), quotes (ppr tycon)])
717 0 (parens (ptext why)))
720 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)