2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1994
4 \section[TcDeriv]{Deriving}
6 Handles @deriving@ clauses on @data@ declarations.
9 #include "HsVersions.h"
17 import HsSyn ( FixityDecl, Sig, HsBinds(..), Bind(..), MonoBinds(..),
18 GRHSsAndBinds, Match, HsExpr, HsLit, InPat,
19 ArithSeqInfo, Fake, MonoType )
20 import HsPragmas ( InstancePragmas(..) )
21 import RnHsSyn ( RenamedHsBinds(..), RenamedFixityDecl(..) )
22 import TcHsSyn ( TcIdOcc )
25 import Inst ( InstOrigin(..), InstanceMapper(..) )
26 import TcEnv ( getEnv_TyCons )
27 import TcKind ( TcKind )
28 import TcGenDeriv -- Deriv stuff
29 import TcInstUtil ( InstInfo(..), mkInstanceRelatedIds, buildInstanceEnvs )
30 import TcSimplify ( tcSimplifyThetas )
33 import RnUtils ( GlobalNameMappers(..), GlobalNameMapper(..) )
34 import RnBinds4 ( rnMethodBinds, rnTopBinds )
36 import Bag ( Bag, isEmptyBag, unionBags, listToBag )
37 import Class ( GenClass, getClassKey )
38 import ErrUtils ( pprBagOfErrors, addErrLoc, TcError(..) )
39 import Id ( getDataConSig, getDataConArity )
40 import Maybes ( assocMaybe, maybeToBool, Maybe(..) )
41 import Name ( Name(..) )
42 import NameTypes ( mkPreludeCoreName, Provenance(..) )
44 import PprType ( GenType, GenTyVar, GenClass, TyCon )
47 import ProtoName ( eqProtoName, ProtoName(..), Name )
48 import SrcLoc ( mkGeneratedSrcLoc, mkUnknownSrcLoc, SrcLoc )
49 import TyCon ( getTyConTyVars, getTyConDataCons, getTyConDerivings,
50 maybeTyConSingleCon, isEnumerationTyCon, TyCon )
51 import Type ( GenType(..), TauType(..), mkTyVarTys, applyTyCon,
52 mkSigmaTy, mkDictTy, isPrimType, instantiateTy,
53 getAppTyCon, getAppDataTyCon )
54 import TyVar ( GenTyVar )
55 import UniqFM ( eltsUFM )
56 import Unique -- Keys stuff
57 import Util ( zipWithEqual, zipEqual, sortLt, removeDups,
58 thenCmp, cmpList, panic, pprPanic, pprPanic# )
61 %************************************************************************
63 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
65 %************************************************************************
69 data T a b = C1 (Foo a) (Bar b)
74 We want to come up with an instance declaration of the form
76 instance (Ping a, Pong b, ...) => Eq (T a b) where
79 It is pretty easy, albeit tedious, to fill in the code "...". The
80 trick is to figure out what the context for the instance decl is,
81 namely @Ping@, @Pong@ and friends.
83 Let's call the context reqd for the T instance of class C at types
84 (a,b, ...) C (T a b). Thus:
86 Eq (T a b) = (Ping a, Pong b, ...)
88 Now we can get a (recursive) equation from the @data@ decl:
90 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
91 u Eq (T b a) u Eq Int -- From C2
92 u Eq (T a a) -- From C3
94 Foo and Bar may have explicit instances for @Eq@, in which case we can
95 just substitute for them. Alternatively, either or both may have
96 their @Eq@ instances given by @deriving@ clauses, in which case they
97 form part of the system of equations.
99 Now all we need do is simplify and solve the equations, iterating to
100 find the least fixpoint. Notice that the order of the arguments can
101 switch around, as here in the recursive calls to T.
103 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
107 Eq (T a b) = {} -- The empty set
110 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
111 u Eq (T b a) u Eq Int -- From C2
112 u Eq (T a a) -- From C3
114 After simplification:
115 = Eq a u Ping b u {} u {} u {}
120 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
121 u Eq (T b a) u Eq Int -- From C2
122 u Eq (T a a) -- From C3
124 After simplification:
129 = Eq a u Ping b u Eq b u Ping a
131 The next iteration gives the same result, so this is the fixpoint. We
132 need to make a canonical form of the RHS to ensure convergence. We do
133 this by simplifying the RHS to a form in which
135 - the classes constrain only tyvars
136 - the list is sorted by tyvar (major key) and then class (minor key)
137 - no duplicates, of course
139 So, here are the synonyms for the ``equation'' structures:
142 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
143 -- The tyvars bind all the variables in the RHS
144 -- NEW: it's convenient to re-use InstInfo
145 -- We'll "panic" out some fields...
147 type DerivRhs = [(Class, TauType)] -- Same as a ThetaType!
149 type DerivSoln = DerivRhs
152 %************************************************************************
154 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
156 %************************************************************************
159 tcDeriving :: FAST_STRING -- name of module under scrutiny
160 -> GlobalNameMappers -- for "renaming" bits of generated code
161 -> Bag InstInfo -- What we already know about instances
162 -> [RenamedFixityDecl] -- Fixity info; used by Read and Show
163 -> TcM s (Bag InstInfo, -- The generated "instance decls".
164 RenamedHsBinds, -- Extra generated bindings
165 PprStyle -> Pretty) -- Printable derived instance decls;
166 -- for debugging via -ddump-derivings.
168 tcDeriving modname renamer_name_funs inst_decl_infos_in fixities
169 = -- Fish the "deriving"-related information out of the TcEnv
170 -- and make the necessary "equations".
171 makeDerivEqns `thenTc` \ eqns ->
173 -- Take the equation list and solve it, to deliver a list of
174 -- solutions, a.k.a. the contexts for the instance decls
175 -- required for the corresponding equations.
176 solveDerivEqns modname inst_decl_infos_in eqns
177 `thenTc` \ new_inst_infos ->
179 -- Now augment the InstInfos, adding in the rather boring
180 -- actual-code-to-do-the-methods binds. We may also need to
181 -- generate extra not-one-inst-decl-specific binds, notably
182 -- "con2tag" and/or "tag2con" functions. We do these
185 gen_taggery_Names eqns `thenTc` \ nm_alist_etc ->
187 nm_alist = [ (pn, n) | (pn,n,_,_) <- nm_alist_etc ]
189 -- We have the renamer's final "name funs" in our hands
190 -- (they were passed in). So we can handle ProtoNames
191 -- that refer to anything "out there". But our generated
192 -- code may also mention "con2tag" (etc.). So we need
193 -- to augment to "name funs" to include those.
194 (rn_val_gnf, rn_tc_gnf) = renamer_name_funs
196 deriv_val_gnf pname = case (assoc_maybe nm_alist pname) of
198 Nothing -> rn_val_gnf pname
200 deriver_name_funs = (deriv_val_gnf, rn_tc_gnf)
202 assoc_maybe [] _ = Nothing
203 assoc_maybe ((k,v) : vs) key
204 = if k `eqProtoName` key then Just v else assoc_maybe vs key
206 gen_tag_n_con_binds deriver_name_funs nm_alist_etc `thenTc` \ extra_binds ->
208 mapTc (gen_inst_info modname fixities deriver_name_funs) new_inst_infos
209 `thenTc` \ really_new_inst_infos ->
211 returnTc (listToBag really_new_inst_infos,
213 ddump_deriving really_new_inst_infos extra_binds)
215 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> (PprStyle -> Pretty)
217 ddump_deriving inst_infos extra_binds sty
218 = ppAboves ((map pp_info inst_infos) ++ [ppr sty extra_binds])
220 pp_info (InstInfo clas tvs ty inst_decl_theta _ _ _ mbinds _ _ _ _)
221 = ppAbove (ppr sty (mkSigmaTy tvs inst_decl_theta (mkDictTy clas ty)))
226 %************************************************************************
228 \subsection[TcDeriv-eqns]{Forming the equations}
230 %************************************************************************
232 @makeDerivEqns@ fishes around to find the info about needed derived
233 instances. Complicating factors:
236 We can only derive @Enum@ if the data type is an enumeration
237 type (all nullary data constructors).
240 We can only derive @Ix@ if the data type is an enumeration {\em
241 or} has just one data constructor (e.g., tuples).
244 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
248 makeDerivEqns :: TcM s [DerivEqn]
251 = tcGetEnv `thenNF_Tc` \ env ->
253 tycons = getEnv_TyCons env
254 think_about_deriving = need_deriving tycons
256 mapTc (chk_out think_about_deriving) think_about_deriving `thenTc_`
258 (derive_these, _) = removeDups cmp_deriv think_about_deriving
259 eqns = map mk_eqn derive_these
263 ------------------------------------------------------------------
264 need_deriving :: [TyCon] -> [(Class, TyCon)]
265 -- find the tycons that have `deriving' clauses
267 need_deriving tycons_to_consider
268 = foldr ( \ tycon acc ->
269 case (getTyConDerivings tycon) of
271 cs -> [ (clas,tycon) | clas <- cs ] ++ acc
276 ------------------------------------------------------------------
277 chk_out :: [(Class, TyCon)] -> (Class, TyCon) -> TcM s ()
278 chk_out whole_deriving_list this_one@(clas, tycon)
280 clas_key = getClassKey clas
283 -- Are things OK for deriving Enum (if appropriate)?
284 checkTc (clas_key == enumClassKey && not (isEnumerationTyCon tycon))
285 (derivingEnumErr tycon) `thenTc_`
287 -- Are things OK for deriving Ix (if appropriate)?
288 checkTc (clas_key == ixClassKey
289 && not (isEnumerationTyCon tycon
290 || maybeToBool (maybeTyConSingleCon tycon)))
291 (derivingIxErr tycon)
293 ------------------------------------------------------------------
294 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> TAG_
295 cmp_deriv (c1, t1) (c2, t2)
296 = (c1 `cmp` c2) `thenCmp` (t1 `cmp` t2)
298 ------------------------------------------------------------------
299 mk_eqn :: (Class, TyCon) -> DerivEqn
300 -- we swizzle the tyvars and datacons out of the tycon
301 -- to make the rest of the equation
304 = (clas, tycon, tyvars, constraints)
306 tyvars = getTyConTyVars tycon -- ToDo: Do we need new tyvars ???
307 tyvar_tys = mkTyVarTys tyvars
308 data_cons = getTyConDataCons tycon
309 constraints = concat (map mk_constraints data_cons)
311 mk_constraints data_con
312 = [ (clas, instantiateTy inst_env arg_ty)
314 not (isPrimType arg_ty) -- No constraints for primitive types
317 (con_tyvars, _, arg_tys, _) = getDataConSig data_con
318 inst_env = con_tyvars `zipEqual` tyvar_tys
319 -- same number of tyvars in data constr and type constr!
322 %************************************************************************
324 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
326 %************************************************************************
328 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
329 terms, which is the final correct RHS for the corresponding original
333 Each (k,UniTyVarTemplate tv) in a solution constrains only a type
337 The (k,UniTyVarTemplate tv) pairs in a solution are canonically
338 ordered by sorting on type varible, tv, (major key) and then class, k,
343 solveDerivEqns :: FAST_STRING
346 -> TcM s [InstInfo] -- Solns in same order as eqns.
347 -- This bunch is Absolutely minimal...
349 solveDerivEqns modname inst_decl_infos_in orig_eqns
350 = iterateDeriv initial_solutions
352 -- The initial solutions for the equations claim that each
353 -- instance has an empty context; this solution is certainly
354 -- in canonical form.
355 initial_solutions :: [DerivSoln]
356 initial_solutions = [ [] | _ <- orig_eqns ]
358 -- iterateDeriv calculates the next batch of solutions,
359 -- compares it with the current one; finishes if they are the
360 -- same, otherwise recurses with the new solutions.
362 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
364 iterateDeriv current_solns
365 = -- Extend the inst info from the explicit instance decls
366 -- with the current set of solutions, giving a
368 add_solns modname inst_decl_infos_in orig_eqns current_solns
369 `thenTc` \ (new_inst_infos, inst_mapper) ->
371 -- Simplify each RHS, using a DerivingOrigin containing an
372 -- inst_mapper reflecting the previous solution
374 mk_deriv_origin clas ty
375 = DerivingOrigin inst_mapper clas tycon
377 (tycon,_) = getAppTyCon ty
379 listTc [ tcSimplifyThetas mk_deriv_origin rhs
380 | (_, _, _, rhs) <- orig_eqns
381 ] `thenTc` \ next_solns ->
383 -- Canonicalise the solutions, so they compare nicely
384 let canonicalised_next_solns
385 = [ sortLt lt_rhs next_soln | next_soln <- next_solns ] in
387 if current_solns `eq_solns` canonicalised_next_solns then
388 returnTc new_inst_infos
390 iterateDeriv canonicalised_next_solns
393 ------------------------------------------------------------------
394 lt_rhs r1 r2 = case cmp_rhs r1 r2 of { LT_ -> True; _ -> False }
395 eq_solns s1 s2 = case cmp_solns s1 s2 of { EQ_ -> True; _ -> False }
396 cmp_solns s1 s2 = cmpList (cmpList cmp_rhs) s1 s2
397 cmp_rhs (c1, TyVarTy tv1) (c2, TyVarTy tv2)
398 = (tv1 `cmp` tv2) `thenCmp` (c1 `cmp` c2)
400 cmp_rhs other_1 other_2
401 = pprPanic# "tcDeriv:cmp_rhs:" (ppCat [ppr PprDebug other_1, ppr PprDebug other_2])
407 add_solns :: FAST_STRING
408 -> Bag InstInfo -- The global, non-derived ones
409 -> [DerivEqn] -> [DerivSoln]
410 -> TcM s ([InstInfo], -- The new, derived ones
412 -- the eqns and solns move "in lockstep"; we have the eqns
413 -- because we need the LHS info for addClassInstance.
415 add_solns modname inst_infos_in eqns solns
416 = buildInstanceEnvs all_inst_infos `thenTc` \ inst_mapper ->
417 returnTc (new_inst_infos, inst_mapper)
419 new_inst_infos = zipWithEqual mk_deriv_inst_info eqns solns
421 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
423 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
424 = InstInfo clas tyvars (applyTyCon tycon (mkTyVarTys tyvars))
426 theta -- Blarg. This is the dfun_theta slot,
427 -- which is needed by buildInstanceEnv;
428 -- This works ok for solving the eqns, and
429 -- gen_eqns sets it to its final value
430 -- (incl super class dicts) before we
431 -- finally return it.
433 (panic "add_soln:dfun_id") (panic "add_soln:const_meth_ids")
434 (panic "add_soln:binds") (panic "add_soln:from_here")
435 (panic "add_soln:modname") mkGeneratedSrcLoc
436 (panic "add_soln:upragmas")
438 bottom bottom bottom bottom bottom mkGeneratedSrcLoc bottom
440 bottom = panic "add_soln"
444 %************************************************************************
446 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
448 %************************************************************************
450 After all the trouble to figure out the required context for the
451 derived instance declarations, all that's left is to chug along to
452 produce them. They will then be shoved into @tcInstDecls2@, which
453 will do all its usual business.
455 There are lots of possibilities for code to generate. Here are
456 various general remarks.
461 We want derived instances of @Eq@ and @Ord@ (both v common) to be
462 ``you-couldn't-do-better-by-hand'' efficient.
465 Deriving @Text@---also pretty common, usually just for
466 @show@---should also be reasonable good code.
469 Deriving for the other classes isn't that common or that big a deal.
476 Deriving @Ord@ is done mostly with our non-standard @tagCmp@ method.
479 Deriving @Eq@ also uses @tagCmp@, if we're deriving @Ord@, too.
482 We {\em normally} generated code only for the non-defaulted methods;
483 there are some exceptions for @Eq@ and (especially) @Ord@...
486 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
487 constructor's numeric (@Int#@) tag. These are generated by
488 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
489 these is around is given by @hasCon2TagFun@.
492 The examples under the different sections below will make this
496 Much less often (really just for deriving @Ix@), we use a
497 @_tag2con_<tycon>@ function. See the examples.
500 We use Pass~4 of the renamer!!! Reason: we're supposed to be
501 producing @RenamedMonoBinds@ for the methods, but that means
502 producing correctly-uniquified code on the fly. This is entirely
503 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
504 So, instead, we produce @ProtoNameMonoBinds@ then heave 'em through
505 the renamer. What a great hack!
509 gen_inst_info :: FAST_STRING -- Module name
510 -> [RenamedFixityDecl] -- all known fixities;
511 -- may be needed for Text
512 -> GlobalNameMappers -- lookup stuff for names we may use
513 -> InstInfo -- the main stuff to work on
514 -> TcM s InstInfo -- the gen'd (filled-in) "instance decl"
516 gen_inst_info modname fixities deriver_name_funs
517 info@(InstInfo clas tyvars ty inst_decl_theta _ _ _ _ _ _ locn _)
519 -- Generate the various instance-related Ids
521 True {-from_here-} modname
525 [{-no user pragmas-}]
526 `thenTc` \ (dfun_id, dfun_theta, const_meth_ids) ->
528 -- Generate the bindings for the new instance declaration,
529 -- rename it, and check for errors
531 (tycon,_,_) = getAppDataTyCon ty
534 | clas_key == eqClassKey = gen_Eq_binds tycon
535 | clas_key == showClassKey = gen_Show_binds fixities tycon
536 | clas_key == ordClassKey = gen_Ord_binds tycon
537 | clas_key == enumClassKey = gen_Enum_binds tycon
538 | clas_key == ixClassKey = gen_Ix_binds tycon
539 | clas_key == readClassKey = gen_Read_binds fixities tycon
540 | clas_key == binaryClassKey = gen_Binary_binds tycon
541 | otherwise = panic "gen_inst_info:bad derived class"
543 rn4MtoTcM deriver_name_funs (
544 rnMethodBinds clas_Name proto_mbinds
545 ) `thenNF_Tc` \ (mbinds, errs) ->
547 if not (isEmptyBag errs) then
548 pprPanic "gen_inst_info:renamer errs!\n"
549 (ppAbove (pprBagOfErrors PprDebug errs) (ppr PprDebug proto_mbinds))
551 --pprTrace "derived binds:" (ppr PprDebug proto_mbinds) $
555 from_here = isLocallyDefined tycon -- If so, then from here
557 returnTc (InstInfo clas tyvars ty inst_decl_theta
558 dfun_theta dfun_id const_meth_ids
559 (if from_here then mbinds else EmptyMonoBinds)
560 from_here modname locn [])
562 clas_key = getClassKey clas
564 = let (mod, nm) = getOrigName clas in
565 ClassName clas_key (mkPreludeCoreName mod nm) []
568 %************************************************************************
570 \subsection[TcGenDeriv-con2tag-tag2con]{Generating extra binds (@con2tag@ and @tag2con@)}
572 %************************************************************************
576 con2tag_Foo :: Foo ... -> Int#
577 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
578 maxtag_Foo :: Int -- ditto (NB: not unboxed)
581 gen_tag_n_con_binds :: GlobalNameMappers
582 -> [(ProtoName, Name, TyCon, TagThingWanted)]
583 -> TcM s RenamedHsBinds
585 gen_tag_n_con_binds deriver_name_funs nm_alist_etc
587 proto_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
588 proto_mbinds = foldr AndMonoBinds EmptyMonoBinds proto_mbind_list
591 rn4MtoTcM deriver_name_funs (
592 rnTopBinds (SingleBind (RecBind proto_mbinds))
593 ) `thenNF_Tc` \ (binds, errs) ->
595 if not (isEmptyBag errs) then
596 panic "gen_inst_info:renamer errs (2)!"
601 %************************************************************************
603 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
605 %************************************************************************
607 We have a @con2tag@ function for a tycon if:
610 We're deriving @Eq@ and the tycon has nullary data constructors.
613 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
617 We have a @tag2con@ function for a tycon if:
620 We're deriving @Enum@, or @Ix@ (enum type only???)
623 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
626 gen_taggery_Names :: [DerivEqn]
627 -> TcM s [(ProtoName, Name, -- for an assoc list
628 TyCon, -- related tycon
631 gen_taggery_Names eqns
633 all_tycons = [ tc | (_, tc, _, _) <- eqns ]
634 (tycons_of_interest, _) = removeDups cmp all_tycons
636 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
637 foldlTc do_tag2con names_so_far tycons_of_interest
639 do_con2tag acc_Names tycon
640 = if (we_are_deriving eqClassKey tycon
641 && any ( (== 0).getDataConArity ) (getTyConDataCons tycon))
642 || (we_are_deriving ordClassKey tycon
643 && not (maybeToBool (maybeTyConSingleCon tycon)))
644 || (we_are_deriving enumClassKey tycon)
645 || (we_are_deriving ixClassKey tycon)
647 tcGetUnique `thenNF_Tc` ( \ u ->
648 returnTc ((con2tag_PN tycon, ValName u (con2tag_FN tycon), tycon, GenCon2Tag)
653 do_tag2con acc_Names tycon
654 = if (we_are_deriving enumClassKey tycon)
655 || (we_are_deriving ixClassKey tycon)
657 tcGetUnique `thenNF_Tc` \ u1 ->
658 tcGetUnique `thenNF_Tc` \ u2 ->
659 returnTc ( (tag2con_PN tycon, ValName u1 (tag2con_FN tycon), tycon, GenTag2Con)
660 : (maxtag_PN tycon, ValName u2 (maxtag_FN tycon), tycon, GenMaxTag)
665 we_are_deriving clas_key tycon
666 = is_in_eqns clas_key tycon eqns
668 is_in_eqns clas_key tycon [] = False
669 is_in_eqns clas_key tycon ((c,t,_,_):eqns)
670 = (clas_key == getClassKey c && tycon == t)
671 || is_in_eqns clas_key tycon eqns
676 derivingEnumErr :: TyCon -> TcError
677 derivingEnumErr tycon
678 = addErrLoc (getSrcLoc tycon) "Can't derive an instance of `Enum'" ( \ sty ->
679 ppBesides [ppStr "type `", ppr sty tycon, ppStr "'"] )
681 derivingIxErr :: TyCon -> TcError
683 = addErrLoc (getSrcLoc tycon) "Can't derive an instance of `Ix'" ( \ sty ->
684 ppBesides [ppStr "type `", ppr sty tycon, ppStr "'"] )