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 )
18 import Inst ( InstanceMapper )
19 import TcEnv ( getEnv_TyCons )
20 import TcGenDeriv -- Deriv stuff
21 import TcInstUtil ( InstInfo(..), buildInstanceEnvs )
22 import TcSimplify ( tcSimplifyThetas )
24 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
25 import RnEnv ( newDfunName, bindLocatedLocalsRn )
26 import RnMonad ( RnNameSupply,
27 renameSourceCode, thenRn, mapRn, returnRn )
29 import Bag ( Bag, emptyBag, unionBags, listToBag )
30 import Class ( classKey, Class )
31 import ErrUtils ( ErrMsg )
32 import MkId ( mkDictFunId )
33 import Id ( mkVanillaId )
34 import DataCon ( dataConArgTys, isNullaryDataCon )
35 import PrelInfo ( needsDataDeclCtxtClassKeys )
36 import Maybes ( maybeToBool )
37 import Name ( isLocallyDefined, getSrcLoc,
38 Name, 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 TysWiredIn ( voidTy )
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 think_about_deriving = need_deriving local_data_tycons
292 (derive_these, _) = removeDups cmp_deriv think_about_deriving
293 eqns = map mk_eqn derive_these
295 if null local_data_tycons then
296 returnTc [] -- Bale out now
298 mapTc chk_out think_about_deriving `thenTc_`
301 ------------------------------------------------------------------
302 need_deriving :: [TyCon] -> [(Class, TyCon)]
303 -- find the tycons that have `deriving' clauses;
305 need_deriving tycons_to_consider
306 = foldr (\ tycon acc -> [(clas,tycon) | clas <- tyConDerivings tycon] ++ acc)
310 ------------------------------------------------------------------
311 chk_out :: (Class, TyCon) -> TcM s ()
312 chk_out this_one@(clas, tycon)
314 clas_key = classKey clas
316 is_enumeration = isEnumerationTyCon tycon
317 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
319 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
320 nullary_why = SLIT("data type with all nullary constructors expected")
322 chk_clas clas_uniq clas_str clas_why cond
323 = if (clas_uniq == clas_key)
324 then checkTc cond (derivingThingErr clas_str clas_why tycon)
327 -- Are things OK for deriving Enum (if appropriate)?
328 chk_clas enumClassKey (SLIT("Enum")) nullary_why is_enumeration `thenTc_`
330 -- Are things OK for deriving Bounded (if appropriate)?
331 chk_clas boundedClassKey (SLIT("Bounded")) single_nullary_why
332 (is_enumeration || is_single_con) `thenTc_`
334 -- Are things OK for deriving Ix (if appropriate)?
335 chk_clas ixClassKey (SLIT("Ix.Ix")) single_nullary_why
336 (is_enumeration || is_single_con)
338 ------------------------------------------------------------------
339 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
340 cmp_deriv (c1, t1) (c2, t2)
341 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
343 ------------------------------------------------------------------
344 mk_eqn :: (Class, TyCon) -> DerivEqn
345 -- we swizzle the tyvars and datacons out of the tycon
346 -- to make the rest of the equation
349 = (clas, tycon, tyvars, constraints)
351 clas_key = classKey clas
352 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
353 tyvar_tys = mkTyVarTys tyvars
354 data_cons = tyConDataCons tycon
356 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
358 -- "extra_constraints": see notes above about contexts on data decls
360 | offensive_class = tyConTheta tycon
363 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
365 mk_constraints data_con
367 | arg_ty <- instd_arg_tys,
368 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
371 instd_arg_tys = dataConArgTys data_con tyvar_tys
374 %************************************************************************
376 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
378 %************************************************************************
380 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
381 terms, which is the final correct RHS for the corresponding original
385 Each (k,TyVarTy tv) in a solution constrains only a type
389 The (k,TyVarTy tv) pairs in a solution are canonically
390 ordered by sorting on type varible, tv, (major key) and then class, k,
395 solveDerivEqns :: Bag InstInfo
397 -> TcM s [InstInfo] -- Solns in same order as eqns.
398 -- This bunch is Absolutely minimal...
400 solveDerivEqns inst_decl_infos_in orig_eqns
401 = iterateDeriv initial_solutions
403 -- The initial solutions for the equations claim that each
404 -- instance has an empty context; this solution is certainly
405 -- in canonical form.
406 initial_solutions :: [DerivSoln]
407 initial_solutions = [ [] | _ <- orig_eqns ]
409 ------------------------------------------------------------------
410 -- iterateDeriv calculates the next batch of solutions,
411 -- compares it with the current one; finishes if they are the
412 -- same, otherwise recurses with the new solutions.
413 -- It fails if any iteration fails
414 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
415 iterateDeriv current_solns
416 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_inst_infos, new_solns) ->
417 if (current_solns == new_solns) then
418 returnTc new_inst_infos
420 iterateDeriv new_solns
422 ------------------------------------------------------------------
423 iterateOnce current_solns
424 = -- Extend the inst info from the explicit instance decls
425 -- with the current set of solutions, giving a
427 add_solns inst_decl_infos_in orig_eqns current_solns
428 `thenNF_Tc` \ (new_inst_infos, inst_mapper) ->
430 class_to_inst_env cls = inst_mapper cls
434 listTc [ tcAddErrCtxt (derivCtxt tc) $
435 tcSimplifyThetas class_to_inst_env deriv_rhs
436 | (_,tc,_,deriv_rhs) <- orig_eqns ] `thenTc` \ next_solns ->
438 -- Canonicalise the solutions, so they compare nicely
439 let canonicalised_next_solns
440 = [ sortLt (<) next_soln | next_soln <- next_solns ]
442 returnTc (new_inst_infos, canonicalised_next_solns)
446 add_solns :: Bag InstInfo -- The global, non-derived ones
447 -> [DerivEqn] -> [DerivSoln]
448 -> NF_TcM s ([InstInfo], -- The new, derived ones
450 -- the eqns and solns move "in lockstep"; we have the eqns
451 -- because we need the LHS info for addClassInstance.
453 add_solns inst_infos_in eqns solns
455 = discardErrsTc (buildInstanceEnvs all_inst_infos) `thenNF_Tc` \ inst_mapper ->
456 -- We do the discard-errs so that we don't get repeated error messages
457 -- about duplicate instances.
458 -- They'll appear later, when we do the top-level buildInstanceEnvs.
460 returnNF_Tc (new_inst_infos, inst_mapper)
462 new_inst_infos = zipWithEqual "add_solns" mk_deriv_inst_info eqns solns
464 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
466 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
467 = InstInfo clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
470 (my_panic "binds") (getSrcLoc tycon)
471 (my_panic "upragmas")
474 = mkVanillaId (getName tycon) dummy_dfun_ty
475 -- The name is getSrcLoc'd in an error message
477 dummy_dfun_ty = mkSigmaTy tyvars theta voidTy
478 -- All we need from the dfun is its "theta" part, used during
479 -- equation simplification (tcSimplifyThetas). The final
480 -- dfun_id will have the superclass dictionaries as arguments too,
481 -- but that'll be added after the equations are solved. For now,
482 -- it's enough just to make a dummy dfun with the simple theta part.
484 -- The part after the theta is dummied here as voidTy; actually it's
485 -- (C (T a b)), but it doesn't seem worth constructing it.
486 -- We can't leave it as a panic because to get the theta part we
487 -- have to run down the type!
489 my_panic str = panic "add_soln" -- pprPanic ("add_soln:"++str) (hsep [char ':', ppr clas, ppr tycon])
492 %************************************************************************
494 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
496 %************************************************************************
498 After all the trouble to figure out the required context for the
499 derived instance declarations, all that's left is to chug along to
500 produce them. They will then be shoved into @tcInstDecls2@, which
501 will do all its usual business.
503 There are lots of possibilities for code to generate. Here are
504 various general remarks.
509 We want derived instances of @Eq@ and @Ord@ (both v common) to be
510 ``you-couldn't-do-better-by-hand'' efficient.
513 Deriving @Show@---also pretty common--- should also be reasonable good code.
516 Deriving for the other classes isn't that common or that big a deal.
523 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
526 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
529 We {\em normally} generate code only for the non-defaulted methods;
530 there are some exceptions for @Eq@ and (especially) @Ord@...
533 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
534 constructor's numeric (@Int#@) tag. These are generated by
535 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
536 these is around is given by @hasCon2TagFun@.
538 The examples under the different sections below will make this
542 Much less often (really just for deriving @Ix@), we use a
543 @_tag2con_<tycon>@ function. See the examples.
546 We use the renamer!!! Reason: we're supposed to be
547 producing @RenamedMonoBinds@ for the methods, but that means
548 producing correctly-uniquified code on the fly. This is entirely
549 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
550 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
551 the renamer. What a great hack!
555 -- Generate the method bindings for the required instance
556 -- (paired with class name, as we need that when generating dict
558 gen_bind :: InstInfo -> ({-class-}OccName, {-tyCon-}OccName, RdrNameMonoBinds)
559 gen_bind (InstInfo clas _ [ty] _ _ _ _ _)
561 = (clas_nm, tycon_nm, EmptyMonoBinds)
563 = (clas_nm, tycon_nm,
564 assoc "gen_bind:bad derived class"
565 [(eqClassKey, gen_Eq_binds)
566 ,(ordClassKey, gen_Ord_binds)
567 ,(enumClassKey, gen_Enum_binds)
568 ,(boundedClassKey, gen_Bounded_binds)
569 ,(showClassKey, gen_Show_binds)
570 ,(readClassKey, gen_Read_binds)
571 ,(ixClassKey, gen_Ix_binds)
576 clas_nm = nameOccName (getName clas)
577 tycon_nm = nameOccName (getName tycon)
578 from_here = isLocallyDefined tycon
579 (tycon,_,_) = splitAlgTyConApp ty
582 gen_inst_info :: Module -- Module name
583 -> (InstInfo, (Name, RenamedMonoBinds)) -- the main stuff to work on
584 -> InstInfo -- the gen'd (filled-in) "instance decl"
586 gen_inst_info modname
587 (InstInfo clas tyvars tys@(ty:_) inst_decl_theta _ _ locn _, (dfun_name, meth_binds))
589 -- Generate the various instance-related Ids
590 InstInfo clas tyvars tys inst_decl_theta
595 dfun_id = mkDictFunId dfun_name clas tyvars tys inst_decl_theta
597 from_here = isLocallyDefined tycon
598 (tycon,_,_) = splitAlgTyConApp ty
602 %************************************************************************
604 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
606 %************************************************************************
611 con2tag_Foo :: Foo ... -> Int#
612 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
613 maxtag_Foo :: Int -- ditto (NB: not unboxed)
616 We have a @con2tag@ function for a tycon if:
619 We're deriving @Eq@ and the tycon has nullary data constructors.
622 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
626 We have a @tag2con@ function for a tycon if:
629 We're deriving @Enum@, or @Ix@ (enum type only???)
632 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
635 gen_taggery_Names :: [InstInfo]
636 -> TcM s [(RdrName, -- for an assoc list
637 TyCon, -- related tycon
640 gen_taggery_Names inst_infos
641 = --pprTrace "gen_taggery:\n" (vcat [hsep [ppr c, ppr t] | (c,t) <- all_CTs]) $
642 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
643 foldlTc do_tag2con names_so_far tycons_of_interest
645 all_CTs = [ (c, get_tycon ty) | (InstInfo c _ [ty] _ _ _ _ _) <- inst_infos ]
647 get_tycon ty = case splitAlgTyConApp ty of { (tc, _, _) -> tc }
649 all_tycons = map snd all_CTs
650 (tycons_of_interest, _) = removeDups compare all_tycons
652 do_con2tag acc_Names tycon
653 | isDataTyCon tycon &&
654 ((we_are_deriving eqClassKey tycon
655 && any isNullaryDataCon (tyConDataCons tycon))
656 || (we_are_deriving ordClassKey tycon
657 && not (maybeToBool (maybeTyConSingleCon tycon)))
658 || (we_are_deriving enumClassKey tycon)
659 || (we_are_deriving ixClassKey tycon))
661 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
666 do_tag2con acc_Names tycon
667 | isDataTyCon tycon &&
668 (we_are_deriving enumClassKey tycon ||
669 we_are_deriving ixClassKey tycon)
670 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
671 : (maxtag_RDR tycon, tycon, GenMaxTag)
676 we_are_deriving clas_key tycon
677 = is_in_eqns clas_key tycon all_CTs
679 is_in_eqns clas_key tycon [] = False
680 is_in_eqns clas_key tycon ((c,t):cts)
681 = (clas_key == classKey c && tycon == t)
682 || is_in_eqns clas_key tycon cts
687 derivingThingErr :: FAST_STRING -> FAST_STRING -> TyCon -> ErrMsg
689 derivingThingErr thing why tycon
690 = hang (hsep [ptext SLIT("Can't make a derived instance of"), ptext thing])
691 0 (hang (hsep [ptext SLIT("for the type"), quotes (ppr tycon)])
692 0 (parens (ptext why)))
695 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)