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 ( RdrName, RdrNameMonoBinds )
15 import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds )
16 import CmdLineOpts ( opt_D_dump_deriv )
19 import Inst ( InstanceMapper )
20 import TcEnv ( getEnvTyCons )
21 import TcGenDeriv -- Deriv stuff
22 import TcInstUtil ( InstInfo(..), buildInstanceEnvs )
23 import TcSimplify ( tcSimplifyThetas )
25 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
26 import RnEnv ( newDFunName, bindLocatedLocalsRn )
27 import RnMonad ( RnNameSupply,
28 renameSourceCode, thenRn, mapRn, returnRn )
30 import Bag ( Bag, emptyBag, unionBags, listToBag )
31 import Class ( classKey, Class )
32 import ErrUtils ( ErrMsg, dumpIfSet )
33 import MkId ( mkDictFunId )
34 import Id ( mkVanillaId )
35 import DataCon ( dataConArgTys, isNullaryDataCon )
36 import PrelInfo ( needsDataDeclCtxtClassKeys )
37 import Maybes ( maybeToBool )
38 import Name ( isLocallyDefined, getSrcLoc,
39 Name, Module, NamedThing(..),
42 import SrcLoc ( mkGeneratedSrcLoc, SrcLoc )
43 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
44 tyConTheta, maybeTyConSingleCon, isDataTyCon,
45 isEnumerationTyCon, isAlgTyCon, TyCon
47 import Type ( TauType, mkTyVarTys, mkTyConApp,
48 mkSigmaTy, mkDictTy, isUnboxedType,
51 import TysWiredIn ( voidTy )
53 import Unique -- Keys stuff
54 import Bag ( bagToList )
55 import Util ( zipWithEqual, sortLt, removeDups, assoc, thenCmp )
59 %************************************************************************
61 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
63 %************************************************************************
67 data T a b = C1 (Foo a) (Bar b)
72 [NOTE: See end of these comments for what to do with
73 data (C a, D b) => T a b = ...
76 We want to come up with an instance declaration of the form
78 instance (Ping a, Pong b, ...) => Eq (T a b) where
81 It is pretty easy, albeit tedious, to fill in the code "...". The
82 trick is to figure out what the context for the instance decl is,
83 namely @Ping@, @Pong@ and friends.
85 Let's call the context reqd for the T instance of class C at types
86 (a,b, ...) C (T a b). Thus:
88 Eq (T a b) = (Ping a, Pong b, ...)
90 Now we can get a (recursive) equation from the @data@ decl:
92 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
93 u Eq (T b a) u Eq Int -- From C2
94 u Eq (T a a) -- From C3
96 Foo and Bar may have explicit instances for @Eq@, in which case we can
97 just substitute for them. Alternatively, either or both may have
98 their @Eq@ instances given by @deriving@ clauses, in which case they
99 form part of the system of equations.
101 Now all we need do is simplify and solve the equations, iterating to
102 find the least fixpoint. Notice that the order of the arguments can
103 switch around, as here in the recursive calls to T.
105 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
109 Eq (T a b) = {} -- The empty set
112 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
113 u Eq (T b a) u Eq Int -- From C2
114 u Eq (T a a) -- From C3
116 After simplification:
117 = Eq a u Ping b u {} u {} u {}
122 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
123 u Eq (T b a) u Eq Int -- From C2
124 u Eq (T a a) -- From C3
126 After simplification:
131 = Eq a u Ping b u Eq b u Ping a
133 The next iteration gives the same result, so this is the fixpoint. We
134 need to make a canonical form of the RHS to ensure convergence. We do
135 this by simplifying the RHS to a form in which
137 - the classes constrain only tyvars
138 - the list is sorted by tyvar (major key) and then class (minor key)
139 - no duplicates, of course
141 So, here are the synonyms for the ``equation'' structures:
144 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
145 -- The tyvars bind all the variables in the RHS
146 -- NEW: it's convenient to re-use InstInfo
147 -- We'll "panic" out some fields...
149 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
151 type DerivSoln = DerivRhs
155 A note about contexts on data decls
156 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
159 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
161 We will need an instance decl like:
163 instance (Read a, RealFloat a) => Read (Complex a) where
166 The RealFloat in the context is because the read method for Complex is bound
167 to construct a Complex, and doing that requires that the argument type is
170 But this ain't true for Show, Eq, Ord, etc, since they don't construct
171 a Complex; they only take them apart.
173 Our approach: identify the offending classes, and add the data type
174 context to the instance decl. The "offending classes" are
179 %************************************************************************
181 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
183 %************************************************************************
186 tcDeriving :: Module -- name of module under scrutiny
187 -> RnNameSupply -- for "renaming" bits of generated code
188 -> Bag InstInfo -- What we already know about instances
189 -> TcM s (Bag InstInfo, -- The generated "instance decls".
190 RenamedHsBinds) -- Extra generated bindings
192 tcDeriving modname rn_name_supply inst_decl_infos_in
193 = recoverTc (returnTc (emptyBag, EmptyBinds)) $
195 -- Fish the "deriving"-related information out of the TcEnv
196 -- and make the necessary "equations".
197 makeDerivEqns `thenTc` \ eqns ->
199 returnTc (emptyBag, EmptyBinds)
202 -- Take the equation list and solve it, to deliver a list of
203 -- solutions, a.k.a. the contexts for the instance decls
204 -- required for the corresponding equations.
205 solveDerivEqns inst_decl_infos_in eqns `thenTc` \ new_inst_infos ->
207 -- Now augment the InstInfos, adding in the rather boring
208 -- actual-code-to-do-the-methods binds. We may also need to
209 -- generate extra not-one-inst-decl-specific binds, notably
210 -- "con2tag" and/or "tag2con" functions. We do these
213 gen_taggery_Names new_inst_infos `thenTc` \ nm_alist_etc ->
217 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
218 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
219 method_binds_s = map gen_bind new_inst_infos
220 mbinders = bagToList (collectMonoBinders extra_mbinds)
222 -- Rename to get RenamedBinds.
223 -- The only tricky bit is that the extra_binds must scope over the
224 -- method bindings for the instances.
225 (dfun_names_w_method_binds, rn_extra_binds)
226 = renameSourceCode modname rn_name_supply (
227 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
228 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
229 mapRn rn_one method_binds_s `thenRn` \ dfun_names_w_method_binds ->
230 returnRn (dfun_names_w_method_binds, rn_extra_binds)
232 rn_one (cl_nm, tycon_nm, meth_binds)
233 = newDFunName cl_nm tycon_nm
234 Nothing mkGeneratedSrcLoc `thenRn` \ dfun_name ->
235 rnMethodBinds meth_binds `thenRn` \ (rn_meth_binds, _) ->
236 returnRn (dfun_name, rn_meth_binds)
238 really_new_inst_infos = map (gen_inst_info modname)
239 (new_inst_infos `zip` dfun_names_w_method_binds)
241 ddump_deriv = ddump_deriving really_new_inst_infos rn_extra_binds
243 ioToTc (dumpIfSet opt_D_dump_deriv "Derived instances" ddump_deriv) `thenTc_`
245 returnTc (listToBag really_new_inst_infos, rn_extra_binds)
247 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]))
258 %************************************************************************
260 \subsection[TcDeriv-eqns]{Forming the equations}
262 %************************************************************************
264 @makeDerivEqns@ fishes around to find the info about needed derived
265 instances. Complicating factors:
268 We can only derive @Enum@ if the data type is an enumeration
269 type (all nullary data constructors).
272 We can only derive @Ix@ if the data type is an enumeration {\em
273 or} has just one data constructor (e.g., tuples).
276 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
280 makeDerivEqns :: TcM s [DerivEqn]
283 = tcGetEnv `thenNF_Tc` \ env ->
285 local_data_tycons = filter (\tc -> isLocallyDefined tc && isAlgTyCon tc)
288 think_about_deriving = need_deriving local_data_tycons
289 (derive_these, _) = removeDups cmp_deriv think_about_deriving
290 eqns = map mk_eqn derive_these
292 if null local_data_tycons then
293 returnTc [] -- Bale out now
295 mapTc chk_out think_about_deriving `thenTc_`
298 ------------------------------------------------------------------
299 need_deriving :: [TyCon] -> [(Class, TyCon)]
300 -- find the tycons that have `deriving' clauses;
302 need_deriving tycons_to_consider
303 = foldr (\ tycon acc -> [(clas,tycon) | clas <- tyConDerivings tycon] ++ acc)
307 ------------------------------------------------------------------
308 chk_out :: (Class, TyCon) -> TcM s ()
309 chk_out this_one@(clas, tycon)
311 clas_key = classKey clas
313 is_enumeration = isEnumerationTyCon tycon
314 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
316 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
317 nullary_why = SLIT("data type with all nullary constructors expected")
319 chk_clas clas_uniq clas_str clas_why cond
320 = if (clas_uniq == clas_key)
321 then checkTc cond (derivingThingErr clas_str clas_why tycon)
324 -- Are things OK for deriving Enum (if appropriate)?
325 chk_clas enumClassKey (SLIT("Enum")) nullary_why is_enumeration `thenTc_`
327 -- Are things OK for deriving Bounded (if appropriate)?
328 chk_clas boundedClassKey (SLIT("Bounded")) single_nullary_why
329 (is_enumeration || is_single_con) `thenTc_`
331 -- Are things OK for deriving Ix (if appropriate)?
332 chk_clas ixClassKey (SLIT("Ix.Ix")) single_nullary_why
333 (is_enumeration || is_single_con)
335 ------------------------------------------------------------------
336 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
337 cmp_deriv (c1, t1) (c2, t2)
338 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
340 ------------------------------------------------------------------
341 mk_eqn :: (Class, TyCon) -> DerivEqn
342 -- we swizzle the tyvars and datacons out of the tycon
343 -- to make the rest of the equation
346 = (clas, tycon, tyvars, constraints)
348 clas_key = classKey clas
349 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
350 tyvar_tys = mkTyVarTys tyvars
351 data_cons = tyConDataCons tycon
353 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
355 -- "extra_constraints": see notes above about contexts on data decls
357 | offensive_class = tyConTheta tycon
360 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
362 mk_constraints data_con
364 | arg_ty <- instd_arg_tys,
365 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
368 instd_arg_tys = dataConArgTys data_con tyvar_tys
371 %************************************************************************
373 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
375 %************************************************************************
377 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
378 terms, which is the final correct RHS for the corresponding original
382 Each (k,TyVarTy tv) in a solution constrains only a type
386 The (k,TyVarTy tv) pairs in a solution are canonically
387 ordered by sorting on type varible, tv, (major key) and then class, k,
392 solveDerivEqns :: Bag InstInfo
394 -> TcM s [InstInfo] -- Solns in same order as eqns.
395 -- This bunch is Absolutely minimal...
397 solveDerivEqns inst_decl_infos_in orig_eqns
398 = iterateDeriv initial_solutions
400 -- The initial solutions for the equations claim that each
401 -- instance has an empty context; this solution is certainly
402 -- in canonical form.
403 initial_solutions :: [DerivSoln]
404 initial_solutions = [ [] | _ <- orig_eqns ]
406 ------------------------------------------------------------------
407 -- iterateDeriv calculates the next batch of solutions,
408 -- compares it with the current one; finishes if they are the
409 -- same, otherwise recurses with the new solutions.
410 -- It fails if any iteration fails
411 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
412 iterateDeriv current_solns
413 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_inst_infos, new_solns) ->
414 if (current_solns == new_solns) then
415 returnTc new_inst_infos
417 iterateDeriv new_solns
419 ------------------------------------------------------------------
420 iterateOnce current_solns
421 = -- Extend the inst info from the explicit instance decls
422 -- with the current set of solutions, giving a
424 add_solns inst_decl_infos_in orig_eqns current_solns
425 `thenNF_Tc` \ (new_inst_infos, inst_mapper) ->
427 class_to_inst_env cls = inst_mapper cls
431 listTc [ tcAddErrCtxt (derivCtxt tc) $
432 tcSimplifyThetas class_to_inst_env deriv_rhs
433 | (_,tc,_,deriv_rhs) <- orig_eqns ] `thenTc` \ next_solns ->
435 -- Canonicalise the solutions, so they compare nicely
436 let canonicalised_next_solns
437 = [ sortLt (<) next_soln | next_soln <- next_solns ]
439 returnTc (new_inst_infos, canonicalised_next_solns)
443 add_solns :: Bag InstInfo -- The global, non-derived ones
444 -> [DerivEqn] -> [DerivSoln]
445 -> NF_TcM s ([InstInfo], -- The new, derived ones
447 -- the eqns and solns move "in lockstep"; we have the eqns
448 -- because we need the LHS info for addClassInstance.
450 add_solns inst_infos_in eqns solns
452 = discardErrsTc (buildInstanceEnvs all_inst_infos) `thenNF_Tc` \ inst_mapper ->
453 -- We do the discard-errs so that we don't get repeated error messages
454 -- about duplicate instances.
455 -- They'll appear later, when we do the top-level buildInstanceEnvs.
457 returnNF_Tc (new_inst_infos, inst_mapper)
459 new_inst_infos = zipWithEqual "add_solns" mk_deriv_inst_info eqns solns
461 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
463 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
464 = InstInfo clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
467 (my_panic "binds") (getSrcLoc tycon)
468 (my_panic "upragmas")
471 = mkVanillaId (getName tycon) dummy_dfun_ty
472 -- The name is getSrcLoc'd in an error message
474 dummy_dfun_ty = mkSigmaTy tyvars theta voidTy
475 -- All we need from the dfun is its "theta" part, used during
476 -- equation simplification (tcSimplifyThetas). The final
477 -- dfun_id will have the superclass dictionaries as arguments too,
478 -- but that'll be added after the equations are solved. For now,
479 -- it's enough just to make a dummy dfun with the simple theta part.
481 -- The part after the theta is dummied here as voidTy; actually it's
482 -- (C (T a b)), but it doesn't seem worth constructing it.
483 -- We can't leave it as a panic because to get the theta part we
484 -- have to run down the type!
486 my_panic str = panic "add_soln" -- pprPanic ("add_soln:"++str) (hsep [char ':', ppr clas, ppr tycon])
489 %************************************************************************
491 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
493 %************************************************************************
495 After all the trouble to figure out the required context for the
496 derived instance declarations, all that's left is to chug along to
497 produce them. They will then be shoved into @tcInstDecls2@, which
498 will do all its usual business.
500 There are lots of possibilities for code to generate. Here are
501 various general remarks.
506 We want derived instances of @Eq@ and @Ord@ (both v common) to be
507 ``you-couldn't-do-better-by-hand'' efficient.
510 Deriving @Show@---also pretty common--- should also be reasonable good code.
513 Deriving for the other classes isn't that common or that big a deal.
520 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
523 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
526 We {\em normally} generate code only for the non-defaulted methods;
527 there are some exceptions for @Eq@ and (especially) @Ord@...
530 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
531 constructor's numeric (@Int#@) tag. These are generated by
532 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
533 these is around is given by @hasCon2TagFun@.
535 The examples under the different sections below will make this
539 Much less often (really just for deriving @Ix@), we use a
540 @_tag2con_<tycon>@ function. See the examples.
543 We use the renamer!!! Reason: we're supposed to be
544 producing @RenamedMonoBinds@ for the methods, but that means
545 producing correctly-uniquified code on the fly. This is entirely
546 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
547 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
548 the renamer. What a great hack!
552 -- Generate the method bindings for the required instance
553 -- (paired with class name, as we need that when generating dict
555 gen_bind :: InstInfo -> ({-class-}OccName, {-tyCon-}OccName, RdrNameMonoBinds)
556 gen_bind (InstInfo clas _ [ty] _ _ _ _ _)
558 = (clas_nm, tycon_nm, EmptyMonoBinds)
560 = (clas_nm, tycon_nm,
561 assoc "gen_bind:bad derived class"
562 [(eqClassKey, gen_Eq_binds)
563 ,(ordClassKey, gen_Ord_binds)
564 ,(enumClassKey, gen_Enum_binds)
565 ,(boundedClassKey, gen_Bounded_binds)
566 ,(showClassKey, gen_Show_binds)
567 ,(readClassKey, gen_Read_binds)
568 ,(ixClassKey, gen_Ix_binds)
573 clas_nm = nameOccName (getName clas)
574 tycon_nm = nameOccName (getName tycon)
575 from_here = isLocallyDefined tycon
576 (tycon,_,_) = splitAlgTyConApp ty
579 gen_inst_info :: Module -- Module name
580 -> (InstInfo, (Name, RenamedMonoBinds)) -- the main stuff to work on
581 -> InstInfo -- the gen'd (filled-in) "instance decl"
583 gen_inst_info modname
584 (InstInfo clas tyvars tys@(ty:_) inst_decl_theta _ _ locn _, (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 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
668 : (maxtag_RDR tycon, tycon, GenMaxTag)
673 we_are_deriving clas_key tycon
674 = is_in_eqns clas_key tycon all_CTs
676 is_in_eqns clas_key tycon [] = False
677 is_in_eqns clas_key tycon ((c,t):cts)
678 = (clas_key == classKey c && tycon == t)
679 || is_in_eqns clas_key tycon cts
684 derivingThingErr :: FAST_STRING -> FAST_STRING -> TyCon -> ErrMsg
686 derivingThingErr thing why tycon
687 = hang (hsep [ptext SLIT("Can't make a derived instance of"), ptext thing])
688 0 (hang (hsep [ptext SLIT("for the type"), quotes (ppr tycon)])
689 0 (parens (ptext why)))
692 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)