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 Id ( dataConArgTys, isNullaryDataCon, mkDictFunId )
34 import PrelInfo ( needsDataDeclCtxtClassKeys )
35 import Maybes ( maybeToBool )
36 import Name ( isLocallyDefined, getSrcLoc, Provenance,
37 Name{--O only-}, Module, NamedThing(..)
39 import SrcLoc ( mkGeneratedSrcLoc, SrcLoc )
40 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
41 tyConTheta, maybeTyConSingleCon, isDataTyCon,
42 isEnumerationTyCon, isAlgTyCon, TyCon
44 import Type ( GenType(..), TauType, mkTyVarTys, mkTyConApp,
45 mkSigmaTy, mkDictTy, isUnboxedType,
48 import TysPrim ( voidTy )
49 import TyVar ( GenTyVar, TyVar )
50 import Unique -- Keys stuff
51 import Bag ( bagToList )
52 import Util ( zipWithEqual, sortLt, removeDups, assoc, thenCmp )
56 %************************************************************************
58 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
60 %************************************************************************
64 data T a b = C1 (Foo a) (Bar b)
69 [NOTE: See end of these comments for what to do with
70 data (C a, D b) => T a b = ...
73 We want to come up with an instance declaration of the form
75 instance (Ping a, Pong b, ...) => Eq (T a b) where
78 It is pretty easy, albeit tedious, to fill in the code "...". The
79 trick is to figure out what the context for the instance decl is,
80 namely @Ping@, @Pong@ and friends.
82 Let's call the context reqd for the T instance of class C at types
83 (a,b, ...) C (T a b). Thus:
85 Eq (T a b) = (Ping a, Pong b, ...)
87 Now we can get a (recursive) equation from the @data@ decl:
89 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
90 u Eq (T b a) u Eq Int -- From C2
91 u Eq (T a a) -- From C3
93 Foo and Bar may have explicit instances for @Eq@, in which case we can
94 just substitute for them. Alternatively, either or both may have
95 their @Eq@ instances given by @deriving@ clauses, in which case they
96 form part of the system of equations.
98 Now all we need do is simplify and solve the equations, iterating to
99 find the least fixpoint. Notice that the order of the arguments can
100 switch around, as here in the recursive calls to T.
102 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
106 Eq (T a b) = {} -- The empty set
109 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
110 u Eq (T b a) u Eq Int -- From C2
111 u Eq (T a a) -- From C3
113 After simplification:
114 = Eq a u Ping b u {} u {} u {}
119 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
120 u Eq (T b a) u Eq Int -- From C2
121 u Eq (T a a) -- From C3
123 After simplification:
128 = Eq a u Ping b u Eq b u Ping a
130 The next iteration gives the same result, so this is the fixpoint. We
131 need to make a canonical form of the RHS to ensure convergence. We do
132 this by simplifying the RHS to a form in which
134 - the classes constrain only tyvars
135 - the list is sorted by tyvar (major key) and then class (minor key)
136 - no duplicates, of course
138 So, here are the synonyms for the ``equation'' structures:
141 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
142 -- The tyvars bind all the variables in the RHS
143 -- NEW: it's convenient to re-use InstInfo
144 -- We'll "panic" out some fields...
146 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
148 type DerivSoln = DerivRhs
152 A note about contexts on data decls
153 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
156 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
158 We will need an instance decl like:
160 instance (Read a, RealFloat a) => Read (Complex a) where
163 The RealFloat in the context is because the read method for Complex is bound
164 to construct a Complex, and doing that requires that the argument type is
167 But this ain't true for Show, Eq, Ord, etc, since they don't construct
168 a Complex; they only take them apart.
170 Our approach: identify the offending classes, and add the data type
171 context to the instance decl. The "offending classes" are
176 %************************************************************************
178 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
180 %************************************************************************
183 tcDeriving :: Module -- name of module under scrutiny
184 -> RnNameSupply -- for "renaming" bits of generated code
185 -> Bag InstInfo -- What we already know about instances
186 -> TcM s (Bag InstInfo, -- The generated "instance decls".
187 RenamedHsBinds, -- Extra generated bindings
188 SDoc) -- Printable derived instance decls;
189 -- for debugging via -ddump-derivings.
191 tcDeriving modname rn_name_supply inst_decl_infos_in
192 = recoverTc (returnTc (emptyBag, EmptyBinds, empty)) $
194 -- Fish the "deriving"-related information out of the TcEnv
195 -- and make the necessary "equations".
196 makeDerivEqns `thenTc` \ eqns ->
198 returnTc (emptyBag, EmptyBinds, text "No derivings")
201 -- Take the equation list and solve it, to deliver a list of
202 -- solutions, a.k.a. the contexts for the instance decls
203 -- required for the corresponding equations.
204 solveDerivEqns inst_decl_infos_in eqns `thenTc` \ new_inst_infos ->
206 -- Now augment the InstInfos, adding in the rather boring
207 -- actual-code-to-do-the-methods binds. We may also need to
208 -- generate extra not-one-inst-decl-specific binds, notably
209 -- "con2tag" and/or "tag2con" functions. We do these
212 gen_taggery_Names new_inst_infos `thenTc` \ nm_alist_etc ->
216 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
217 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
218 method_binds_s = map gen_bind new_inst_infos
219 mbinders = bagToList (collectMonoBinders extra_mbinds)
221 -- Rename to get RenamedBinds.
222 -- The only tricky bit is that the extra_binds must scope over the
223 -- method bindings for the instances.
224 (dfun_names_w_method_binds, rn_extra_binds)
225 = renameSourceCode modname rn_name_supply (
226 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
227 rnTopMonoBinds extra_mbinds [] `thenRn` \ rn_extra_binds ->
228 mapRn rn_one method_binds_s `thenRn` \ dfun_names_w_method_binds ->
229 returnRn (dfun_names_w_method_binds, rn_extra_binds)
231 rn_one meth_binds = newDfunName Nothing mkGeneratedSrcLoc `thenRn` \ dfun_name ->
232 rnMethodBinds meth_binds `thenRn` \ rn_meth_binds ->
233 returnRn (dfun_name, rn_meth_binds)
235 really_new_inst_infos = map (gen_inst_info modname)
236 (new_inst_infos `zip` dfun_names_w_method_binds)
238 ddump_deriv = ddump_deriving really_new_inst_infos rn_extra_binds
240 --pprTrace "derived:\n" (ddump_deriv) $
242 returnTc (listToBag really_new_inst_infos,
246 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
248 ddump_deriving inst_infos extra_binds
249 = vcat ((map pp_info inst_infos) ++ [ppr extra_binds])
251 pp_info (InstInfo clas tvs [ty] inst_decl_theta _ _ mbinds _ _)
252 = ($$) (ppr (mkSigmaTy tvs inst_decl_theta (mkDictTy clas [ty])))
257 %************************************************************************
259 \subsection[TcDeriv-eqns]{Forming the equations}
261 %************************************************************************
263 @makeDerivEqns@ fishes around to find the info about needed derived
264 instances. Complicating factors:
267 We can only derive @Enum@ if the data type is an enumeration
268 type (all nullary data constructors).
271 We can only derive @Ix@ if the data type is an enumeration {\em
272 or} has just one data constructor (e.g., tuples).
275 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
279 makeDerivEqns :: TcM s [DerivEqn]
282 = tcGetEnv `thenNF_Tc` \ env ->
284 local_data_tycons = filter (\tc -> isLocallyDefined tc && isAlgTyCon tc)
287 if null local_data_tycons then
288 -- Bale out now; evalClass may not be loaded if there aren't any
291 tcLookupClassByKey evalClassKey `thenNF_Tc` \ eval_clas ->
293 think_about_deriving = need_deriving eval_clas local_data_tycons
294 (derive_these, _) = removeDups cmp_deriv think_about_deriving
295 eqns = map mk_eqn derive_these
297 mapTc chk_out think_about_deriving `thenTc_`
300 ------------------------------------------------------------------
301 need_deriving :: Class -> [TyCon] -> [(Class, TyCon)]
302 -- find the tycons that have `deriving' clauses;
303 -- we handle the "every datatype in Eval" by
304 -- doing a dummy "deriving" for it.
306 need_deriving eval_clas tycons_to_consider
307 = foldr ( \ tycon acc ->
309 acc_plus = if isLocallyDefined tycon
310 then (eval_clas, tycon) : acc
313 case (tyConDerivings tycon) of
315 cs -> [ (clas,tycon) | clas <- cs ] ++ acc_plus
320 ------------------------------------------------------------------
321 chk_out :: (Class, TyCon) -> TcM s ()
322 chk_out this_one@(clas, tycon)
324 clas_key = classKey clas
326 is_enumeration = isEnumerationTyCon tycon
327 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
329 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
330 nullary_why = SLIT("data type with all nullary constructors expected")
332 chk_clas clas_uniq clas_str clas_why cond
333 = if (clas_uniq == clas_key)
334 then checkTc cond (derivingThingErr clas_str clas_why tycon)
337 -- Are things OK for deriving Enum (if appropriate)?
338 chk_clas enumClassKey (SLIT("Enum")) nullary_why is_enumeration `thenTc_`
340 -- Are things OK for deriving Bounded (if appropriate)?
341 chk_clas boundedClassKey (SLIT("Bounded")) single_nullary_why
342 (is_enumeration || is_single_con) `thenTc_`
344 -- Are things OK for deriving Ix (if appropriate)?
345 chk_clas ixClassKey (SLIT("Ix.Ix")) single_nullary_why
346 (is_enumeration || is_single_con)
348 ------------------------------------------------------------------
349 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
350 cmp_deriv (c1, t1) (c2, t2)
351 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
353 ------------------------------------------------------------------
354 mk_eqn :: (Class, TyCon) -> DerivEqn
355 -- we swizzle the tyvars and datacons out of the tycon
356 -- to make the rest of the equation
359 = (clas, tycon, tyvars, if_not_Eval constraints)
361 clas_key = classKey clas
362 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
363 tyvar_tys = mkTyVarTys tyvars
364 data_cons = tyConDataCons tycon
366 if_not_Eval cs = if clas_key == evalClassKey then [] else cs
368 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
370 -- "extra_constraints": see notes above about contexts on data decls
372 | offensive_class = tyConTheta tycon
375 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
377 mk_constraints data_con
379 | arg_ty <- instd_arg_tys,
380 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
383 instd_arg_tys = dataConArgTys data_con tyvar_tys
386 %************************************************************************
388 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
390 %************************************************************************
392 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
393 terms, which is the final correct RHS for the corresponding original
397 Each (k,TyVarTy tv) in a solution constrains only a type
401 The (k,TyVarTy tv) pairs in a solution are canonically
402 ordered by sorting on type varible, tv, (major key) and then class, k,
407 solveDerivEqns :: Bag InstInfo
409 -> TcM s [InstInfo] -- Solns in same order as eqns.
410 -- This bunch is Absolutely minimal...
412 solveDerivEqns inst_decl_infos_in orig_eqns
413 = iterateDeriv initial_solutions
415 -- The initial solutions for the equations claim that each
416 -- instance has an empty context; this solution is certainly
417 -- in canonical form.
418 initial_solutions :: [DerivSoln]
419 initial_solutions = [ [] | _ <- orig_eqns ]
421 ------------------------------------------------------------------
422 -- iterateDeriv calculates the next batch of solutions,
423 -- compares it with the current one; finishes if they are the
424 -- same, otherwise recurses with the new solutions.
425 -- It fails if any iteration fails
426 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
427 iterateDeriv current_solns
428 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_inst_infos, new_solns) ->
429 if (current_solns == new_solns) then
430 returnTc new_inst_infos
432 iterateDeriv new_solns
434 ------------------------------------------------------------------
435 iterateOnce current_solns
436 = -- Extend the inst info from the explicit instance decls
437 -- with the current set of solutions, giving a
439 add_solns inst_decl_infos_in orig_eqns current_solns
440 `thenNF_Tc` \ (new_inst_infos, inst_mapper) ->
442 class_to_inst_env cls = inst_mapper cls
446 listTc [ tcAddErrCtxt (derivCtxt tc) $
447 tcSimplifyThetas class_to_inst_env deriv_rhs
448 | (_,tc,_,deriv_rhs) <- orig_eqns ] `thenTc` \ next_solns ->
450 -- Canonicalise the solutions, so they compare nicely
451 let canonicalised_next_solns
452 = [ sortLt (<) next_soln | next_soln <- next_solns ]
454 returnTc (new_inst_infos, canonicalised_next_solns)
458 add_solns :: Bag InstInfo -- The global, non-derived ones
459 -> [DerivEqn] -> [DerivSoln]
460 -> NF_TcM s ([InstInfo], -- The new, derived ones
462 -- the eqns and solns move "in lockstep"; we have the eqns
463 -- because we need the LHS info for addClassInstance.
465 add_solns inst_infos_in eqns solns
467 = discardErrsTc (buildInstanceEnvs all_inst_infos) `thenNF_Tc` \ inst_mapper ->
468 -- We do the discard-errs so that we don't get repeated error messages
469 -- about duplicate instances.
470 -- They'll appear later, when we do the top-level buildInstanceEnvs.
472 returnNF_Tc (new_inst_infos, inst_mapper)
474 new_inst_infos = zipWithEqual "add_solns" mk_deriv_inst_info eqns solns
476 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
478 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
479 = InstInfo clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
481 (my_panic "dfun_theta")
485 (my_panic "binds") (getSrcLoc tycon)
486 (my_panic "upragmas")
489 = mkDictFunId (getName tycon) dummy_dfun_ty bottom bottom
490 -- The name is getSrcLoc'd in an error message
492 bottom = panic "dummy_dfun_id"
494 dummy_dfun_ty = mkSigmaTy tyvars theta voidTy
495 -- All we need from the dfun is its "theta" part, used during
496 -- equation simplification (tcSimplifyThetas). The final
497 -- dfun_id will have the superclass dictionaries as arguments too,
498 -- but that'll be added after the equations are solved. For now,
499 -- it's enough just to make a dummy dfun with the simple theta part.
501 -- The part after the theta is dummied here as voidTy; actually it's
502 -- (C (T a b)), but it doesn't seem worth constructing it.
503 -- We can't leave it as a panic because to get the theta part we
504 -- have to run down the type!
506 my_panic str = panic "add_soln" -- pprPanic ("add_soln:"++str) (hsep [char ':', ppr clas, ppr tycon])
509 %************************************************************************
511 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
513 %************************************************************************
515 After all the trouble to figure out the required context for the
516 derived instance declarations, all that's left is to chug along to
517 produce them. They will then be shoved into @tcInstDecls2@, which
518 will do all its usual business.
520 There are lots of possibilities for code to generate. Here are
521 various general remarks.
526 We want derived instances of @Eq@ and @Ord@ (both v common) to be
527 ``you-couldn't-do-better-by-hand'' efficient.
530 Deriving @Show@---also pretty common--- should also be reasonable good code.
533 Deriving for the other classes isn't that common or that big a deal.
540 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
543 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
546 We {\em normally} generate code only for the non-defaulted methods;
547 there are some exceptions for @Eq@ and (especially) @Ord@...
550 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
551 constructor's numeric (@Int#@) tag. These are generated by
552 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
553 these is around is given by @hasCon2TagFun@.
555 The examples under the different sections below will make this
559 Much less often (really just for deriving @Ix@), we use a
560 @_tag2con_<tycon>@ function. See the examples.
563 We use the renamer!!! Reason: we're supposed to be
564 producing @RenamedMonoBinds@ for the methods, but that means
565 producing correctly-uniquified code on the fly. This is entirely
566 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
567 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
568 the renamer. What a great hack!
572 -- Generate the method bindings for the required instance
573 gen_bind :: InstInfo -> RdrNameMonoBinds
574 gen_bind (InstInfo clas _ [ty] _ _ _ _ _ _)
578 = assoc "gen_inst_info:bad derived class"
579 [(eqClassKey, gen_Eq_binds)
580 ,(ordClassKey, gen_Ord_binds)
581 ,(enumClassKey, gen_Enum_binds)
582 ,(evalClassKey, gen_Eval_binds)
583 ,(boundedClassKey, gen_Bounded_binds)
584 ,(showClassKey, gen_Show_binds)
585 ,(readClassKey, gen_Read_binds)
586 ,(ixClassKey, gen_Ix_binds)
591 from_here = isLocallyDefined tycon
592 (tycon,_,_) = splitAlgTyConApp ty
595 gen_inst_info :: Module -- Module name
596 -> (InstInfo, (Name, RenamedMonoBinds)) -- the main stuff to work on
597 -> InstInfo -- the gen'd (filled-in) "instance decl"
599 gen_inst_info modname
600 (InstInfo clas tyvars tys@(ty:_) inst_decl_theta _ _ _ locn _, (dfun_name, meth_binds))
602 -- Generate the various instance-related Ids
603 InstInfo clas tyvars tys inst_decl_theta
608 (dfun_id, dfun_theta) = mkInstanceRelatedIds
613 from_here = isLocallyDefined tycon
614 (tycon,_,_) = splitAlgTyConApp ty
618 %************************************************************************
620 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
622 %************************************************************************
627 con2tag_Foo :: Foo ... -> Int#
628 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
629 maxtag_Foo :: Int -- ditto (NB: not unboxed)
632 We have a @con2tag@ function for a tycon if:
635 We're deriving @Eq@ and the tycon has nullary data constructors.
638 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
642 We have a @tag2con@ function for a tycon if:
645 We're deriving @Enum@, or @Ix@ (enum type only???)
648 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
651 gen_taggery_Names :: [InstInfo]
652 -> TcM s [(RdrName, -- for an assoc list
653 TyCon, -- related tycon
656 gen_taggery_Names inst_infos
657 = --pprTrace "gen_taggery:\n" (vcat [hsep [ppr c, ppr t] | (c,t) <- all_CTs]) $
658 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
659 foldlTc do_tag2con names_so_far tycons_of_interest
661 all_CTs = [ (c, get_tycon ty) | (InstInfo c _ [ty] _ _ _ _ _ _) <- inst_infos ]
663 get_tycon ty = case splitAlgTyConApp ty of { (tc, _, _) -> tc }
665 all_tycons = map snd all_CTs
666 (tycons_of_interest, _) = removeDups compare all_tycons
668 do_con2tag acc_Names tycon
669 | isDataTyCon tycon &&
670 (we_are_deriving eqClassKey tycon
671 && any isNullaryDataCon (tyConDataCons tycon))
672 || (we_are_deriving ordClassKey tycon
673 && not (maybeToBool (maybeTyConSingleCon tycon)))
674 || (we_are_deriving enumClassKey tycon)
675 || (we_are_deriving ixClassKey tycon)
677 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
682 do_tag2con acc_Names tycon
683 = if (we_are_deriving enumClassKey tycon)
684 || (we_are_deriving ixClassKey tycon)
686 returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
687 : (maxtag_RDR tycon, tycon, GenMaxTag)
692 we_are_deriving clas_key tycon
693 = is_in_eqns clas_key tycon all_CTs
695 is_in_eqns clas_key tycon [] = False
696 is_in_eqns clas_key tycon ((c,t):cts)
697 = (clas_key == classKey c && tycon == t)
698 || is_in_eqns clas_key tycon cts
703 derivingThingErr :: FAST_STRING -> FAST_STRING -> TyCon -> ErrMsg
705 derivingThingErr thing why tycon
706 = hang (hsep [ptext SLIT("Can't make a derived instance of"), ptext thing])
707 0 (hang (hsep [ptext SLIT("for the type"), quotes (ppr tycon)])
708 0 (parens (ptext why)))
711 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)