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 ( 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 ( dumpIfSet, Message )
33 import MkId ( mkDictFunId )
34 import Id ( mkVanillaId )
35 import DataCon ( dataConArgTys, isNullaryDataCon )
36 import PrelInfo ( needsDataDeclCtxtClassKeys )
37 import Maybes ( maybeToBool )
38 import Module ( Module )
39 import Name ( isLocallyDefined, getSrcLoc,
43 import RdrName ( RdrName )
44 import RnMonad ( Fixities )
45 import SrcLoc ( mkGeneratedSrcLoc, SrcLoc )
46 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
47 tyConTheta, maybeTyConSingleCon, isDataTyCon,
48 isEnumerationTyCon, isAlgTyCon, TyCon
50 import Type ( TauType, mkTyVarTys, mkTyConApp,
51 mkSigmaTy, mkDictTy, isUnboxedType,
54 import TysWiredIn ( voidTy )
56 import Unique -- Keys stuff
57 import Bag ( bagToList )
58 import Util ( zipWithEqual, sortLt, removeDups, assoc, thenCmp )
62 %************************************************************************
64 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
66 %************************************************************************
70 data T a b = C1 (Foo a) (Bar b)
75 [NOTE: See end of these comments for what to do with
76 data (C a, D b) => T a b = ...
79 We want to come up with an instance declaration of the form
81 instance (Ping a, Pong b, ...) => Eq (T a b) where
84 It is pretty easy, albeit tedious, to fill in the code "...". The
85 trick is to figure out what the context for the instance decl is,
86 namely @Ping@, @Pong@ and friends.
88 Let's call the context reqd for the T instance of class C at types
89 (a,b, ...) C (T a b). Thus:
91 Eq (T a b) = (Ping a, Pong b, ...)
93 Now we can get a (recursive) equation from the @data@ decl:
95 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
96 u Eq (T b a) u Eq Int -- From C2
97 u Eq (T a a) -- From C3
99 Foo and Bar may have explicit instances for @Eq@, in which case we can
100 just substitute for them. Alternatively, either or both may have
101 their @Eq@ instances given by @deriving@ clauses, in which case they
102 form part of the system of equations.
104 Now all we need do is simplify and solve the equations, iterating to
105 find the least fixpoint. Notice that the order of the arguments can
106 switch around, as here in the recursive calls to T.
108 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
112 Eq (T a b) = {} -- The empty set
115 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
116 u Eq (T b a) u Eq Int -- From C2
117 u Eq (T a a) -- From C3
119 After simplification:
120 = Eq a u Ping b u {} u {} u {}
125 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
126 u Eq (T b a) u Eq Int -- From C2
127 u Eq (T a a) -- From C3
129 After simplification:
134 = Eq a u Ping b u Eq b u Ping a
136 The next iteration gives the same result, so this is the fixpoint. We
137 need to make a canonical form of the RHS to ensure convergence. We do
138 this by simplifying the RHS to a form in which
140 - the classes constrain only tyvars
141 - the list is sorted by tyvar (major key) and then class (minor key)
142 - no duplicates, of course
144 So, here are the synonyms for the ``equation'' structures:
147 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
148 -- The tyvars bind all the variables in the RHS
149 -- NEW: it's convenient to re-use InstInfo
150 -- We'll "panic" out some fields...
152 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
154 type DerivSoln = DerivRhs
158 A note about contexts on data decls
159 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
162 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
164 We will need an instance decl like:
166 instance (Read a, RealFloat a) => Read (Complex a) where
169 The RealFloat in the context is because the read method for Complex is bound
170 to construct a Complex, and doing that requires that the argument type is
173 But this ain't true for Show, Eq, Ord, etc, since they don't construct
174 a Complex; they only take them apart.
176 Our approach: identify the offending classes, and add the data type
177 context to the instance decl. The "offending classes" are
182 %************************************************************************
184 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
186 %************************************************************************
189 tcDeriving :: Module -- name of module under scrutiny
190 -> Fixities -- for the deriving code (Show/Read.)
191 -> RnNameSupply -- for "renaming" bits of generated code
192 -> Bag InstInfo -- What we already know about instances
193 -> TcM s (Bag InstInfo, -- The generated "instance decls".
194 RenamedHsBinds) -- Extra generated bindings
196 tcDeriving modname fixs rn_name_supply inst_decl_infos_in
197 = recoverTc (returnTc (emptyBag, EmptyBinds)) $
199 -- Fish the "deriving"-related information out of the TcEnv
200 -- and make the necessary "equations".
201 makeDerivEqns `thenTc` \ eqns ->
203 returnTc (emptyBag, EmptyBinds)
206 -- Take the equation list and solve it, to deliver a list of
207 -- solutions, a.k.a. the contexts for the instance decls
208 -- required for the corresponding equations.
209 solveDerivEqns inst_decl_infos_in eqns `thenTc` \ new_inst_infos ->
211 -- Now augment the InstInfos, adding in the rather boring
212 -- actual-code-to-do-the-methods binds. We may also need to
213 -- generate extra not-one-inst-decl-specific binds, notably
214 -- "con2tag" and/or "tag2con" functions. We do these
217 gen_taggery_Names new_inst_infos `thenTc` \ nm_alist_etc ->
221 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
222 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
223 method_binds_s = map (gen_bind fixs) new_inst_infos
224 mbinders = bagToList (collectMonoBinders extra_mbinds)
226 -- Rename to get RenamedBinds.
227 -- The only tricky bit is that the extra_binds must scope over the
228 -- method bindings for the instances.
229 (dfun_names_w_method_binds, rn_extra_binds)
230 = renameSourceCode modname rn_name_supply (
231 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
232 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
233 mapRn rn_one method_binds_s `thenRn` \ dfun_names_w_method_binds ->
234 returnRn (dfun_names_w_method_binds, rn_extra_binds)
236 rn_one (cl_nm, tycon_nm, meth_binds)
237 = newDFunName cl_nm tycon_nm
238 Nothing mkGeneratedSrcLoc `thenRn` \ dfun_name ->
239 rnMethodBinds meth_binds `thenRn` \ (rn_meth_binds, _) ->
240 returnRn (dfun_name, rn_meth_binds)
242 really_new_inst_infos = map (gen_inst_info modname)
243 (new_inst_infos `zip` dfun_names_w_method_binds)
245 ddump_deriv = ddump_deriving really_new_inst_infos rn_extra_binds
247 ioToTc (dumpIfSet opt_D_dump_deriv "Derived instances" ddump_deriv) `thenTc_`
249 returnTc (listToBag really_new_inst_infos, rn_extra_binds)
251 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]))
262 %************************************************************************
264 \subsection[TcDeriv-eqns]{Forming the equations}
266 %************************************************************************
268 @makeDerivEqns@ fishes around to find the info about needed derived
269 instances. Complicating factors:
272 We can only derive @Enum@ if the data type is an enumeration
273 type (all nullary data constructors).
276 We can only derive @Ix@ if the data type is an enumeration {\em
277 or} has just one data constructor (e.g., tuples).
280 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
284 makeDerivEqns :: TcM s [DerivEqn]
287 = tcGetEnv `thenNF_Tc` \ env ->
289 local_data_tycons = filter (\tc -> isLocallyDefined tc && isAlgTyCon tc)
292 think_about_deriving = need_deriving local_data_tycons
293 (derive_these, _) = removeDups cmp_deriv think_about_deriving
294 eqns = map mk_eqn derive_these
296 if null local_data_tycons then
297 returnTc [] -- Bale out now
299 mapTc chk_out think_about_deriving `thenTc_`
302 ------------------------------------------------------------------
303 need_deriving :: [TyCon] -> [(Class, TyCon)]
304 -- find the tycons that have `deriving' clauses;
306 need_deriving tycons_to_consider
307 = foldr (\ tycon acc -> [(clas,tycon) | clas <- tyConDerivings tycon] ++ acc)
311 ------------------------------------------------------------------
312 chk_out :: (Class, TyCon) -> TcM s ()
313 chk_out this_one@(clas, tycon)
315 clas_key = classKey clas
317 is_enumeration = isEnumerationTyCon tycon
318 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
320 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
321 nullary_why = SLIT("data type with all nullary constructors expected")
323 chk_clas clas_uniq clas_str clas_why cond
324 = if (clas_uniq == clas_key)
325 then checkTc cond (derivingThingErr clas_str clas_why tycon)
328 -- Are things OK for deriving Enum (if appropriate)?
329 chk_clas enumClassKey (SLIT("Enum")) nullary_why is_enumeration `thenTc_`
331 -- Are things OK for deriving Bounded (if appropriate)?
332 chk_clas boundedClassKey (SLIT("Bounded")) single_nullary_why
333 (is_enumeration || is_single_con) `thenTc_`
335 -- Are things OK for deriving Ix (if appropriate)?
336 chk_clas ixClassKey (SLIT("Ix.Ix")) single_nullary_why
337 (is_enumeration || is_single_con)
339 ------------------------------------------------------------------
340 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
341 cmp_deriv (c1, t1) (c2, t2)
342 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
344 ------------------------------------------------------------------
345 mk_eqn :: (Class, TyCon) -> DerivEqn
346 -- we swizzle the tyvars and datacons out of the tycon
347 -- to make the rest of the equation
350 = (clas, tycon, tyvars, constraints)
352 clas_key = classKey clas
353 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
354 tyvar_tys = mkTyVarTys tyvars
355 data_cons = tyConDataCons tycon
357 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
359 -- "extra_constraints": see notes above about contexts on data decls
361 | offensive_class = tyConTheta tycon
364 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
366 mk_constraints data_con
368 | arg_ty <- instd_arg_tys,
369 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
372 instd_arg_tys = dataConArgTys data_con tyvar_tys
375 %************************************************************************
377 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
379 %************************************************************************
381 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
382 terms, which is the final correct RHS for the corresponding original
386 Each (k,TyVarTy tv) in a solution constrains only a type
390 The (k,TyVarTy tv) pairs in a solution are canonically
391 ordered by sorting on type varible, tv, (major key) and then class, k,
396 solveDerivEqns :: Bag InstInfo
398 -> TcM s [InstInfo] -- Solns in same order as eqns.
399 -- This bunch is Absolutely minimal...
401 solveDerivEqns inst_decl_infos_in orig_eqns
402 = iterateDeriv initial_solutions
404 -- The initial solutions for the equations claim that each
405 -- instance has an empty context; this solution is certainly
406 -- in canonical form.
407 initial_solutions :: [DerivSoln]
408 initial_solutions = [ [] | _ <- orig_eqns ]
410 ------------------------------------------------------------------
411 -- iterateDeriv calculates the next batch of solutions,
412 -- compares it with the current one; finishes if they are the
413 -- same, otherwise recurses with the new solutions.
414 -- It fails if any iteration fails
415 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
416 iterateDeriv current_solns
417 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_inst_infos, new_solns) ->
418 if (current_solns == new_solns) then
419 returnTc new_inst_infos
421 iterateDeriv new_solns
423 ------------------------------------------------------------------
424 iterateOnce current_solns
425 = -- Extend the inst info from the explicit instance decls
426 -- with the current set of solutions, giving a
428 add_solns inst_decl_infos_in orig_eqns current_solns
429 `thenNF_Tc` \ (new_inst_infos, inst_mapper) ->
431 class_to_inst_env cls = inst_mapper cls
435 listTc [ tcAddErrCtxt (derivCtxt tc) $
436 tcSimplifyThetas class_to_inst_env deriv_rhs
437 | (_,tc,_,deriv_rhs) <- orig_eqns ] `thenTc` \ next_solns ->
439 -- Canonicalise the solutions, so they compare nicely
440 let canonicalised_next_solns
441 = [ sortLt (<) next_soln | next_soln <- next_solns ]
443 returnTc (new_inst_infos, canonicalised_next_solns)
447 add_solns :: Bag InstInfo -- The global, non-derived ones
448 -> [DerivEqn] -> [DerivSoln]
449 -> NF_TcM s ([InstInfo], -- The new, derived ones
451 -- the eqns and solns move "in lockstep"; we have the eqns
452 -- because we need the LHS info for addClassInstance.
454 add_solns inst_infos_in eqns solns
456 = discardErrsTc (buildInstanceEnvs all_inst_infos) `thenNF_Tc` \ inst_mapper ->
457 -- We do the discard-errs so that we don't get repeated error messages
458 -- about duplicate instances.
459 -- They'll appear later, when we do the top-level buildInstanceEnvs.
461 returnNF_Tc (new_inst_infos, inst_mapper)
463 new_inst_infos = zipWithEqual "add_solns" mk_deriv_inst_info eqns solns
465 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
467 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
468 = InstInfo clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
471 (my_panic "binds") (getSrcLoc tycon)
472 (my_panic "upragmas")
475 = mkVanillaId (getName tycon) dummy_dfun_ty
476 -- The name is getSrcLoc'd in an error message
478 dummy_dfun_ty = mkSigmaTy tyvars theta voidTy
479 -- All we need from the dfun is its "theta" part, used during
480 -- equation simplification (tcSimplifyThetas). The final
481 -- dfun_id will have the superclass dictionaries as arguments too,
482 -- but that'll be added after the equations are solved. For now,
483 -- it's enough just to make a dummy dfun with the simple theta part.
485 -- The part after the theta is dummied here as voidTy; actually it's
486 -- (C (T a b)), but it doesn't seem worth constructing it.
487 -- We can't leave it as a panic because to get the theta part we
488 -- have to run down the type!
490 my_panic str = panic "add_soln" -- pprPanic ("add_soln:"++str) (hsep [char ':', ppr clas, ppr tycon])
493 %************************************************************************
495 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
497 %************************************************************************
499 After all the trouble to figure out the required context for the
500 derived instance declarations, all that's left is to chug along to
501 produce them. They will then be shoved into @tcInstDecls2@, which
502 will do all its usual business.
504 There are lots of possibilities for code to generate. Here are
505 various general remarks.
510 We want derived instances of @Eq@ and @Ord@ (both v common) to be
511 ``you-couldn't-do-better-by-hand'' efficient.
514 Deriving @Show@---also pretty common--- should also be reasonable good code.
517 Deriving for the other classes isn't that common or that big a deal.
524 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
527 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
530 We {\em normally} generate code only for the non-defaulted methods;
531 there are some exceptions for @Eq@ and (especially) @Ord@...
534 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
535 constructor's numeric (@Int#@) tag. These are generated by
536 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
537 these is around is given by @hasCon2TagFun@.
539 The examples under the different sections below will make this
543 Much less often (really just for deriving @Ix@), we use a
544 @_tag2con_<tycon>@ function. See the examples.
547 We use the renamer!!! Reason: we're supposed to be
548 producing @RenamedMonoBinds@ for the methods, but that means
549 producing correctly-uniquified code on the fly. This is entirely
550 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
551 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
552 the renamer. What a great hack!
556 -- Generate the method bindings for the required instance
557 -- (paired with class name, as we need that when generating dict
559 gen_bind :: Fixities -> InstInfo -> ({-class-}OccName, {-tyCon-}OccName, RdrNameMonoBinds)
560 gen_bind fixities (InstInfo clas _ [ty] _ _ _ _ _)
562 = (clas_nm, tycon_nm, EmptyMonoBinds)
563 | ckey == showClassKey
564 = (clas_nm, tycon_nm, gen_Show_binds fixities tycon)
565 | ckey == readClassKey
566 = (clas_nm, tycon_nm, gen_Read_binds fixities tycon)
568 = (clas_nm, tycon_nm,
569 assoc "gen_bind:bad derived class"
570 [(eqClassKey, gen_Eq_binds)
571 ,(ordClassKey, gen_Ord_binds)
572 ,(enumClassKey, gen_Enum_binds)
573 ,(boundedClassKey, gen_Bounded_binds)
574 ,(ixClassKey, gen_Ix_binds)
579 clas_nm = nameOccName (getName clas)
580 tycon_nm = nameOccName (getName tycon)
581 from_here = isLocallyDefined tycon
582 (tycon,_,_) = splitAlgTyConApp ty
586 gen_inst_info :: Module -- Module name
587 -> (InstInfo, (Name, RenamedMonoBinds)) -- the main stuff to work on
588 -> InstInfo -- the gen'd (filled-in) "instance decl"
590 gen_inst_info modname
591 (InstInfo clas tyvars tys@(ty:_) inst_decl_theta _ _ locn _, (dfun_name, meth_binds))
593 -- Generate the various instance-related Ids
594 InstInfo clas tyvars tys inst_decl_theta
599 dfun_id = mkDictFunId dfun_name clas tyvars tys inst_decl_theta
601 from_here = isLocallyDefined tycon
602 (tycon,_,_) = splitAlgTyConApp ty
606 %************************************************************************
608 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
610 %************************************************************************
615 con2tag_Foo :: Foo ... -> Int#
616 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
617 maxtag_Foo :: Int -- ditto (NB: not unboxed)
620 We have a @con2tag@ function for a tycon if:
623 We're deriving @Eq@ and the tycon has nullary data constructors.
626 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
630 We have a @tag2con@ function for a tycon if:
633 We're deriving @Enum@, or @Ix@ (enum type only???)
636 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
639 gen_taggery_Names :: [InstInfo]
640 -> TcM s [(RdrName, -- for an assoc list
641 TyCon, -- related tycon
644 gen_taggery_Names inst_infos
645 = --pprTrace "gen_taggery:\n" (vcat [hsep [ppr c, ppr t] | (c,t) <- all_CTs]) $
646 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
647 foldlTc do_tag2con names_so_far tycons_of_interest
649 all_CTs = [ (c, get_tycon ty) | (InstInfo c _ [ty] _ _ _ _ _) <- inst_infos ]
651 get_tycon ty = case splitAlgTyConApp ty of { (tc, _, _) -> tc }
653 all_tycons = map snd all_CTs
654 (tycons_of_interest, _) = removeDups compare all_tycons
656 do_con2tag acc_Names tycon
657 | isDataTyCon tycon &&
658 ((we_are_deriving eqClassKey tycon
659 && any isNullaryDataCon (tyConDataCons tycon))
660 || (we_are_deriving ordClassKey tycon
661 && not (maybeToBool (maybeTyConSingleCon tycon)))
662 || (we_are_deriving enumClassKey tycon)
663 || (we_are_deriving ixClassKey tycon))
665 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
670 do_tag2con acc_Names tycon
671 | isDataTyCon tycon &&
672 (we_are_deriving enumClassKey tycon ||
673 we_are_deriving ixClassKey tycon
674 && isEnumerationTyCon tycon)
675 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
676 : (maxtag_RDR tycon, tycon, GenMaxTag)
681 we_are_deriving clas_key tycon
682 = is_in_eqns clas_key tycon all_CTs
684 is_in_eqns clas_key tycon [] = False
685 is_in_eqns clas_key tycon ((c,t):cts)
686 = (clas_key == classKey c && tycon == t)
687 || is_in_eqns clas_key tycon cts
692 derivingThingErr :: FAST_STRING -> FAST_STRING -> TyCon -> Message
694 derivingThingErr thing why tycon
695 = hang (hsep [ptext SLIT("Can't make a derived instance of"), ptext thing])
696 0 (hang (hsep [ptext SLIT("for the type"), quotes (ppr tycon)])
697 0 (parens (ptext why)))
700 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)