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"
11 module TcDeriv ( tcDeriving ) where
15 import HsSyn ( FixityDecl, Sig, HsBinds(..), Bind(..), MonoBinds(..),
16 GRHSsAndBinds, Match, HsExpr, HsLit, InPat,
17 ArithSeqInfo, Fake, MonoType )
18 import HsPragmas ( InstancePragmas(..) )
19 import RnHsSyn ( RenamedHsBinds(..), RenamedFixityDecl(..) )
20 import TcHsSyn ( TcIdOcc )
22 import TcMonad hiding ( rnMtoTcM )
23 import Inst ( InstOrigin(..), InstanceMapper(..) )
24 import TcEnv ( getEnv_TyCons )
25 import TcKind ( TcKind )
26 --import TcGenDeriv -- Deriv stuff
27 import TcInstUtil ( InstInfo(..), mkInstanceRelatedIds, buildInstanceEnvs )
28 import TcSimplify ( tcSimplifyThetas )
31 import RnUtils ( RnEnv(..) )
32 import RnBinds ( rnMethodBinds, rnTopBinds )
34 import Bag ( emptyBag{-ToDo:rm-}, Bag, isEmptyBag, unionBags, listToBag )
35 import Class ( GenClass, classKey )
36 import CmdLineOpts ( opt_CompilingPrelude )
37 import ErrUtils ( pprBagOfErrors, addErrLoc, Error(..) )
38 import Id ( dataConSig, dataConArity )
39 import Maybes ( assocMaybe, maybeToBool, Maybe(..) )
41 import PprType ( GenType, GenTyVar, GenClass, TyCon )
44 import SrcLoc ( mkGeneratedSrcLoc, mkUnknownSrcLoc, SrcLoc )
45 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
46 maybeTyConSingleCon, isEnumerationTyCon, TyCon )
47 import Type ( GenType(..), TauType(..), mkTyVarTys, applyTyCon,
48 mkSigmaTy, mkDictTy, isPrimType, instantiateTy,
49 getAppTyCon, getAppDataTyCon )
50 import TyVar ( GenTyVar )
51 import UniqFM ( emptyUFM )
52 import Unique -- Keys stuff
53 import Util ( zipWithEqual, zipEqual, sortLt, removeDups,
54 thenCmp, cmpList, panic, pprPanic, pprPanic# )
57 %************************************************************************
59 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
61 %************************************************************************
65 data T a b = C1 (Foo a) (Bar b)
70 We want to come up with an instance declaration of the form
72 instance (Ping a, Pong b, ...) => Eq (T a b) where
75 It is pretty easy, albeit tedious, to fill in the code "...". The
76 trick is to figure out what the context for the instance decl is,
77 namely @Ping@, @Pong@ and friends.
79 Let's call the context reqd for the T instance of class C at types
80 (a,b, ...) C (T a b). Thus:
82 Eq (T a b) = (Ping a, Pong b, ...)
84 Now we can get a (recursive) equation from the @data@ decl:
86 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
87 u Eq (T b a) u Eq Int -- From C2
88 u Eq (T a a) -- From C3
90 Foo and Bar may have explicit instances for @Eq@, in which case we can
91 just substitute for them. Alternatively, either or both may have
92 their @Eq@ instances given by @deriving@ clauses, in which case they
93 form part of the system of equations.
95 Now all we need do is simplify and solve the equations, iterating to
96 find the least fixpoint. Notice that the order of the arguments can
97 switch around, as here in the recursive calls to T.
99 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
103 Eq (T a b) = {} -- The empty set
106 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
107 u Eq (T b a) u Eq Int -- From C2
108 u Eq (T a a) -- From C3
110 After simplification:
111 = Eq a u Ping b u {} u {} u {}
116 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
117 u Eq (T b a) u Eq Int -- From C2
118 u Eq (T a a) -- From C3
120 After simplification:
125 = Eq a u Ping b u Eq b u Ping a
127 The next iteration gives the same result, so this is the fixpoint. We
128 need to make a canonical form of the RHS to ensure convergence. We do
129 this by simplifying the RHS to a form in which
131 - the classes constrain only tyvars
132 - the list is sorted by tyvar (major key) and then class (minor key)
133 - no duplicates, of course
135 So, here are the synonyms for the ``equation'' structures:
138 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
139 -- The tyvars bind all the variables in the RHS
140 -- NEW: it's convenient to re-use InstInfo
141 -- We'll "panic" out some fields...
143 type DerivRhs = [(Class, TauType)] -- Same as a ThetaType!
145 type DerivSoln = DerivRhs
148 %************************************************************************
150 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
152 %************************************************************************
155 tcDeriving :: Module -- name of module under scrutiny
156 -> RnEnv -- for "renaming" bits of generated code
157 -> Bag InstInfo -- What we already know about instances
158 -> [RenamedFixityDecl] -- Fixity info; used by Read and Show
159 -> TcM s (Bag InstInfo, -- The generated "instance decls".
160 RenamedHsBinds, -- Extra generated bindings
161 PprStyle -> Pretty) -- Printable derived instance decls;
162 -- for debugging via -ddump-derivings.
164 tcDeriving modname rn_env inst_decl_infos_in fixities
165 = returnTc (trace "tcDeriving:ToDo" (emptyBag, EmptyBinds, \ x -> ppNil))
168 tcDeriving modname rn_env 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 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_rn_env nm_alist_etc `thenTc` \ extra_binds ->
208 mapTc (gen_inst_info maybe_mod fixities deriver_rn_env) 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 maybe_mod = if opt_CompilingPrelude then Nothing else Just mod_name
217 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> (PprStyle -> Pretty)
219 ddump_deriving inst_infos extra_binds sty
220 = ppAboves ((map pp_info inst_infos) ++ [ppr sty extra_binds])
222 pp_info (InstInfo clas tvs ty inst_decl_theta _ _ _ mbinds _ _ _ _)
223 = ppAbove (ppr sty (mkSigmaTy tvs inst_decl_theta (mkDictTy clas ty)))
228 %************************************************************************
230 \subsection[TcDeriv-eqns]{Forming the equations}
232 %************************************************************************
234 @makeDerivEqns@ fishes around to find the info about needed derived
235 instances. Complicating factors:
238 We can only derive @Enum@ if the data type is an enumeration
239 type (all nullary data constructors).
242 We can only derive @Ix@ if the data type is an enumeration {\em
243 or} has just one data constructor (e.g., tuples).
246 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
250 makeDerivEqns :: TcM s [DerivEqn]
253 = tcGetEnv `thenNF_Tc` \ env ->
255 tycons = getEnv_TyCons env
256 think_about_deriving = need_deriving tycons
258 mapTc (chk_out think_about_deriving) think_about_deriving `thenTc_`
260 (derive_these, _) = removeDups cmp_deriv think_about_deriving
261 eqns = map mk_eqn derive_these
265 ------------------------------------------------------------------
266 need_deriving :: [TyCon] -> [(Class, TyCon)]
267 -- find the tycons that have `deriving' clauses
269 need_deriving tycons_to_consider
270 = foldr ( \ tycon acc ->
271 case (tyConDerivings tycon) of
273 cs -> [ (clas,tycon) | clas <- cs ] ++ acc
278 ------------------------------------------------------------------
279 chk_out :: [(Class, TyCon)] -> (Class, TyCon) -> TcM s ()
280 chk_out whole_deriving_list this_one@(clas, tycon)
282 clas_key = classKey clas
285 -- Are things OK for deriving Enum (if appropriate)?
286 checkTc (clas_key == enumClassKey && not (isEnumerationTyCon tycon))
287 (derivingEnumErr tycon) `thenTc_`
289 -- Are things OK for deriving Ix (if appropriate)?
290 checkTc (clas_key == ixClassKey
291 && not (isEnumerationTyCon tycon
292 || maybeToBool (maybeTyConSingleCon tycon)))
293 (derivingIxErr tycon)
295 ------------------------------------------------------------------
296 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> TAG_
297 cmp_deriv (c1, t1) (c2, t2)
298 = (c1 `cmp` c2) `thenCmp` (t1 `cmp` t2)
300 ------------------------------------------------------------------
301 mk_eqn :: (Class, TyCon) -> DerivEqn
302 -- we swizzle the tyvars and datacons out of the tycon
303 -- to make the rest of the equation
306 = (clas, tycon, tyvars, constraints)
308 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
309 tyvar_tys = mkTyVarTys tyvars
310 data_cons = tyConDataCons tycon
311 constraints = concat (map mk_constraints data_cons)
313 mk_constraints data_con
314 = [ (clas, instantiateTy inst_env arg_ty)
316 not (isPrimType arg_ty) -- No constraints for primitive types
319 (con_tyvars, _, arg_tys, _) = dataConSig data_con
320 inst_env = con_tyvars `zipEqual` tyvar_tys
321 -- same number of tyvars in data constr and type constr!
324 %************************************************************************
326 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
328 %************************************************************************
330 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
331 terms, which is the final correct RHS for the corresponding original
335 Each (k,UniTyVarTemplate tv) in a solution constrains only a type
339 The (k,UniTyVarTemplate tv) pairs in a solution are canonically
340 ordered by sorting on type varible, tv, (major key) and then class, k,
345 solveDerivEqns :: Bag InstInfo
347 -> TcM s [InstInfo] -- Solns in same order as eqns.
348 -- This bunch is Absolutely minimal...
350 solveDerivEqns inst_decl_infos_in orig_eqns
351 = iterateDeriv initial_solutions
353 -- The initial solutions for the equations claim that each
354 -- instance has an empty context; this solution is certainly
355 -- in canonical form.
356 initial_solutions :: [DerivSoln]
357 initial_solutions = [ [] | _ <- orig_eqns ]
359 -- iterateDeriv calculates the next batch of solutions,
360 -- compares it with the current one; finishes if they are the
361 -- same, otherwise recurses with the new solutions.
363 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
365 iterateDeriv current_solns
366 = -- Extend the inst info from the explicit instance decls
367 -- with the current set of solutions, giving a
369 add_solns inst_decl_infos_in orig_eqns current_solns
370 `thenTc` \ (new_inst_infos, inst_mapper) ->
372 -- Simplify each RHS, using a DerivingOrigin containing an
373 -- inst_mapper reflecting the previous solution
375 mk_deriv_origin clas ty
376 = DerivingOrigin inst_mapper clas tycon
378 (tycon,_) = getAppTyCon ty
380 listTc [ tcSimplifyThetas mk_deriv_origin rhs
381 | (_, _, _, rhs) <- orig_eqns
382 ] `thenTc` \ next_solns ->
384 -- Canonicalise the solutions, so they compare nicely
385 let canonicalised_next_solns
386 = [ sortLt lt_rhs next_soln | next_soln <- next_solns ] in
388 if current_solns `eq_solns` canonicalised_next_solns then
389 returnTc new_inst_infos
391 iterateDeriv canonicalised_next_solns
394 ------------------------------------------------------------------
395 lt_rhs r1 r2 = case cmp_rhs r1 r2 of { LT_ -> True; _ -> False }
396 eq_solns s1 s2 = case cmp_solns s1 s2 of { EQ_ -> True; _ -> False }
397 cmp_solns s1 s2 = cmpList (cmpList cmp_rhs) s1 s2
398 cmp_rhs (c1, TyVarTy tv1) (c2, TyVarTy tv2)
399 = (tv1 `cmp` tv2) `thenCmp` (c1 `cmp` c2)
401 cmp_rhs other_1 other_2
402 = pprPanic# "tcDeriv:cmp_rhs:" (ppCat [ppr PprDebug other_1, ppr PprDebug other_2])
408 add_solns :: FAST_STRING
409 -> Bag InstInfo -- The global, non-derived ones
410 -> [DerivEqn] -> [DerivSoln]
411 -> TcM s ([InstInfo], -- The new, derived ones
413 -- the eqns and solns move "in lockstep"; we have the eqns
414 -- because we need the LHS info for addClassInstance.
416 add_solns inst_infos_in eqns solns
417 = buildInstanceEnvs all_inst_infos `thenTc` \ inst_mapper ->
418 returnTc (new_inst_infos, inst_mapper)
420 new_inst_infos = zipWithEqual mk_deriv_inst_info eqns solns
422 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
424 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
425 = InstInfo clas tyvars (applyTyCon tycon (mkTyVarTys tyvars))
427 theta -- Blarg. This is the dfun_theta slot,
428 -- which is needed by buildInstanceEnv;
429 -- This works ok for solving the eqns, and
430 -- gen_eqns sets it to its final value
431 -- (incl super class dicts) before we
432 -- finally return it.
434 (panic "add_soln:dfun_id") (panic "add_soln:const_meth_ids")
435 (panic "add_soln:binds") (panic "add_soln:from_here")
436 (panic "add_soln:modname") mkGeneratedSrcLoc
437 (panic "add_soln:upragmas")
439 bottom bottom bottom bottom bottom mkGeneratedSrcLoc bottom
441 bottom = panic "add_soln"
445 %************************************************************************
447 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
449 %************************************************************************
451 After all the trouble to figure out the required context for the
452 derived instance declarations, all that's left is to chug along to
453 produce them. They will then be shoved into @tcInstDecls2@, which
454 will do all its usual business.
456 There are lots of possibilities for code to generate. Here are
457 various general remarks.
462 We want derived instances of @Eq@ and @Ord@ (both v common) to be
463 ``you-couldn't-do-better-by-hand'' efficient.
466 Deriving @Text@---also pretty common, usually just for
467 @show@---should also be reasonable good code.
470 Deriving for the other classes isn't that common or that big a deal.
477 Deriving @Ord@ is done mostly with our non-standard @tagCmp@ method.
480 Deriving @Eq@ also uses @tagCmp@, if we're deriving @Ord@, too.
483 We {\em normally} generated code only for the non-defaulted methods;
484 there are some exceptions for @Eq@ and (especially) @Ord@...
487 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
488 constructor's numeric (@Int#@) tag. These are generated by
489 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
490 these is around is given by @hasCon2TagFun@.
493 The examples under the different sections below will make this
497 Much less often (really just for deriving @Ix@), we use a
498 @_tag2con_<tycon>@ function. See the examples.
501 We use Pass~4 of the renamer!!! Reason: we're supposed to be
502 producing @RenamedMonoBinds@ for the methods, but that means
503 producing correctly-uniquified code on the fly. This is entirely
504 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
505 So, instead, we produce @ProtoNameMonoBinds@ then heave 'em through
506 the renamer. What a great hack!
510 gen_inst_info :: Maybe Module -- Module name; Nothing => Prelude
511 -> [RenamedFixityDecl] -- all known fixities;
512 -- may be needed for Text
513 -> RnEnv -- lookup stuff for names we may use
514 -> InstInfo -- the main stuff to work on
515 -> TcM s InstInfo -- the gen'd (filled-in) "instance decl"
517 gen_inst_info modname fixities deriver_rn_env
518 info@(InstInfo clas tyvars ty inst_decl_theta _ _ _ _ _ _ locn _)
520 -- Generate the various instance-related Ids
522 True {-from_here-} modname
526 [{-no user pragmas-}]
527 `thenTc` \ (dfun_id, dfun_theta, const_meth_ids) ->
529 -- Generate the bindings for the new instance declaration,
530 -- rename it, and check for errors
532 (tycon,_,_) = getAppDataTyCon ty
535 | clas_key == eqClassKey = gen_Eq_binds tycon
536 | clas_key == showClassKey = gen_Show_binds fixities tycon
537 | clas_key == ordClassKey = gen_Ord_binds tycon
538 | clas_key == enumClassKey = gen_Enum_binds tycon
539 | clas_key == ixClassKey = gen_Ix_binds tycon
540 | clas_key == readClassKey = gen_Read_binds fixities tycon
541 | clas_key == binaryClassKey = gen_Binary_binds tycon
542 | otherwise = panic "gen_inst_info:bad derived class"
544 rnMtoTcM deriver_rn_env (
545 setExtraRn emptyUFM{-no fixities-} $
546 rnMethodBinds clas_Name proto_mbinds
547 ) `thenNF_Tc` \ (mbinds, errs) ->
549 if not (isEmptyBag errs) then
550 pprPanic "gen_inst_info:renamer errs!\n"
551 (ppAbove (pprBagOfErrors PprDebug errs) (ppr PprDebug proto_mbinds))
553 --pprTrace "derived binds:" (ppr PprDebug proto_mbinds) $
557 from_here = isLocallyDefined tycon -- If so, then from here
559 returnTc (InstInfo clas tyvars ty inst_decl_theta
560 dfun_theta dfun_id const_meth_ids
561 (if from_here then mbinds else EmptyMonoBinds)
562 from_here modname locn [])
564 clas_key = classKey clas
566 = let (mod, nm) = moduleNamePair clas in
567 ClassName clas_key (mkPreludeCoreName mod nm) []
570 %************************************************************************
572 \subsection[TcGenDeriv-con2tag-tag2con]{Generating extra binds (@con2tag@ and @tag2con@)}
574 %************************************************************************
578 con2tag_Foo :: Foo ... -> Int#
579 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
580 maxtag_Foo :: Int -- ditto (NB: not unboxed)
583 gen_tag_n_con_binds :: RnEnv
584 -> [(RdrName, RnName, TyCon, TagThingWanted)]
585 -> TcM s RenamedHsBinds
587 gen_tag_n_con_binds deriver_rn_env nm_alist_etc
589 proto_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
590 proto_mbinds = foldr AndMonoBinds EmptyMonoBinds proto_mbind_list
593 rnMtoTcM deriver_rn_env (
594 setExtraRn emptyUFM{-no fixities-} $
595 rnTopBinds (SingleBind (RecBind proto_mbinds))
596 ) `thenNF_Tc` \ (binds, errs) ->
598 if not (isEmptyBag errs) then
599 panic "gen_inst_info:renamer errs (2)!"
604 %************************************************************************
606 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
608 %************************************************************************
610 We have a @con2tag@ function for a tycon if:
613 We're deriving @Eq@ and the tycon has nullary data constructors.
616 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
620 We have a @tag2con@ function for a tycon if:
623 We're deriving @Enum@, or @Ix@ (enum type only???)
626 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
629 gen_taggery_Names :: [DerivEqn]
630 -> TcM s [(RdrName, RnName, -- for an assoc list
631 TyCon, -- related tycon
634 gen_taggery_Names eqns
636 all_tycons = [ tc | (_, tc, _, _) <- eqns ]
637 (tycons_of_interest, _) = removeDups cmp all_tycons
639 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
640 foldlTc do_tag2con names_so_far tycons_of_interest
642 do_con2tag acc_Names tycon
643 = if (we_are_deriving eqClassKey tycon
644 && any ( (== 0).dataConArity ) (tyConDataCons tycon))
645 || (we_are_deriving ordClassKey tycon
646 && not (maybeToBool (maybeTyConSingleCon tycon)))
647 || (we_are_deriving enumClassKey tycon)
648 || (we_are_deriving ixClassKey tycon)
650 tcGetUnique `thenNF_Tc` ( \ u ->
651 returnTc ((con2tag_PN tycon, ValName u (con2tag_FN tycon), tycon, GenCon2Tag)
656 do_tag2con acc_Names tycon
657 = if (we_are_deriving enumClassKey tycon)
658 || (we_are_deriving ixClassKey tycon)
660 tcGetUnique `thenNF_Tc` \ u1 ->
661 tcGetUnique `thenNF_Tc` \ u2 ->
662 returnTc ( (tag2con_PN tycon, ValName u1 (tag2con_FN tycon), tycon, GenTag2Con)
663 : (maxtag_PN tycon, ValName u2 (maxtag_FN tycon), tycon, GenMaxTag)
668 we_are_deriving clas_key tycon
669 = is_in_eqns clas_key tycon eqns
671 is_in_eqns clas_key tycon [] = False
672 is_in_eqns clas_key tycon ((c,t,_,_):eqns)
673 = (clas_key == classKey c && tycon == t)
674 || is_in_eqns clas_key tycon eqns
679 derivingEnumErr :: TyCon -> Error
680 derivingEnumErr tycon
681 = addErrLoc (getSrcLoc tycon) "Can't derive an instance of `Enum'" ( \ sty ->
682 ppBesides [ppStr "type `", ppr sty tycon, ppStr "'"] )
684 derivingIxErr :: TyCon -> Error
686 = addErrLoc (getSrcLoc tycon) "Can't derive an instance of `Ix'" ( \ sty ->
687 ppBesides [ppStr "type `", ppr sty tycon, ppStr "'"] )