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(..),
40 import SrcLoc ( mkGeneratedSrcLoc, SrcLoc )
41 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
42 tyConTheta, maybeTyConSingleCon, isDataTyCon,
43 isEnumerationTyCon, isAlgTyCon, TyCon
45 import Type ( GenType(..), TauType, mkTyVarTys, mkTyConApp,
46 mkSigmaTy, mkDictTy, isUnboxedType,
49 import TysPrim ( voidTy )
50 import TyVar ( GenTyVar, TyVar )
51 import Unique -- Keys stuff
52 import Bag ( bagToList )
53 import Util ( zipWithEqual, sortLt, removeDups, assoc, thenCmp )
57 %************************************************************************
59 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
61 %************************************************************************
65 data T a b = C1 (Foo a) (Bar b)
70 [NOTE: See end of these comments for what to do with
71 data (C a, D b) => T a b = ...
74 We want to come up with an instance declaration of the form
76 instance (Ping a, Pong b, ...) => Eq (T a b) where
79 It is pretty easy, albeit tedious, to fill in the code "...". The
80 trick is to figure out what the context for the instance decl is,
81 namely @Ping@, @Pong@ and friends.
83 Let's call the context reqd for the T instance of class C at types
84 (a,b, ...) C (T a b). Thus:
86 Eq (T a b) = (Ping a, Pong b, ...)
88 Now we can get a (recursive) equation from the @data@ decl:
90 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
91 u Eq (T b a) u Eq Int -- From C2
92 u Eq (T a a) -- From C3
94 Foo and Bar may have explicit instances for @Eq@, in which case we can
95 just substitute for them. Alternatively, either or both may have
96 their @Eq@ instances given by @deriving@ clauses, in which case they
97 form part of the system of equations.
99 Now all we need do is simplify and solve the equations, iterating to
100 find the least fixpoint. Notice that the order of the arguments can
101 switch around, as here in the recursive calls to T.
103 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
107 Eq (T a b) = {} -- The empty set
110 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
111 u Eq (T b a) u Eq Int -- From C2
112 u Eq (T a a) -- From C3
114 After simplification:
115 = Eq a u Ping b u {} u {} u {}
120 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
121 u Eq (T b a) u Eq Int -- From C2
122 u Eq (T a a) -- From C3
124 After simplification:
129 = Eq a u Ping b u Eq b u Ping a
131 The next iteration gives the same result, so this is the fixpoint. We
132 need to make a canonical form of the RHS to ensure convergence. We do
133 this by simplifying the RHS to a form in which
135 - the classes constrain only tyvars
136 - the list is sorted by tyvar (major key) and then class (minor key)
137 - no duplicates, of course
139 So, here are the synonyms for the ``equation'' structures:
142 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
143 -- The tyvars bind all the variables in the RHS
144 -- NEW: it's convenient to re-use InstInfo
145 -- We'll "panic" out some fields...
147 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
149 type DerivSoln = DerivRhs
153 A note about contexts on data decls
154 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
157 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
159 We will need an instance decl like:
161 instance (Read a, RealFloat a) => Read (Complex a) where
164 The RealFloat in the context is because the read method for Complex is bound
165 to construct a Complex, and doing that requires that the argument type is
168 But this ain't true for Show, Eq, Ord, etc, since they don't construct
169 a Complex; they only take them apart.
171 Our approach: identify the offending classes, and add the data type
172 context to the instance decl. The "offending classes" are
177 %************************************************************************
179 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
181 %************************************************************************
184 tcDeriving :: Module -- name of module under scrutiny
185 -> RnNameSupply -- for "renaming" bits of generated code
186 -> Bag InstInfo -- What we already know about instances
187 -> TcM s (Bag InstInfo, -- The generated "instance decls".
188 RenamedHsBinds, -- Extra generated bindings
189 SDoc) -- Printable derived instance decls;
190 -- for debugging via -ddump-derivings.
192 tcDeriving modname rn_name_supply inst_decl_infos_in
193 = recoverTc (returnTc (emptyBag, EmptyBinds, empty)) $
195 -- Fish the "deriving"-related information out of the TcEnv
196 -- and make the necessary "equations".
197 makeDerivEqns `thenTc` \ eqns ->
199 returnTc (emptyBag, EmptyBinds, text "No derivings")
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 --pprTrace "derived:\n" (ddump_deriv) $
245 returnTc (listToBag really_new_inst_infos,
249 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
251 ddump_deriving inst_infos extra_binds
252 = vcat ((map pp_info inst_infos) ++ [ppr extra_binds])
254 pp_info (InstInfo clas tvs [ty] inst_decl_theta _ _ mbinds _ _)
255 = ($$) (ppr (mkSigmaTy tvs inst_decl_theta (mkDictTy clas [ty])))
260 %************************************************************************
262 \subsection[TcDeriv-eqns]{Forming the equations}
264 %************************************************************************
266 @makeDerivEqns@ fishes around to find the info about needed derived
267 instances. Complicating factors:
270 We can only derive @Enum@ if the data type is an enumeration
271 type (all nullary data constructors).
274 We can only derive @Ix@ if the data type is an enumeration {\em
275 or} has just one data constructor (e.g., tuples).
278 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
282 makeDerivEqns :: TcM s [DerivEqn]
285 = tcGetEnv `thenNF_Tc` \ env ->
287 local_data_tycons = filter (\tc -> isLocallyDefined tc && isAlgTyCon tc)
290 if null local_data_tycons then
291 -- Bale out now; evalClass may not be loaded if there aren't any
294 tcLookupClassByKey evalClassKey `thenNF_Tc` \ eval_clas ->
296 think_about_deriving = need_deriving eval_clas local_data_tycons
297 (derive_these, _) = removeDups cmp_deriv think_about_deriving
298 eqns = map mk_eqn derive_these
300 mapTc chk_out think_about_deriving `thenTc_`
303 ------------------------------------------------------------------
304 need_deriving :: Class -> [TyCon] -> [(Class, TyCon)]
305 -- find the tycons that have `deriving' clauses;
306 -- we handle the "every datatype in Eval" by
307 -- doing a dummy "deriving" for it.
309 need_deriving eval_clas tycons_to_consider
310 = foldr ( \ tycon acc ->
312 acc_plus = if isLocallyDefined tycon
313 then (eval_clas, tycon) : acc
316 case (tyConDerivings tycon) of
318 cs -> [ (clas,tycon) | clas <- cs ] ++ acc_plus
323 ------------------------------------------------------------------
324 chk_out :: (Class, TyCon) -> TcM s ()
325 chk_out this_one@(clas, tycon)
327 clas_key = classKey clas
329 is_enumeration = isEnumerationTyCon tycon
330 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
332 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
333 nullary_why = SLIT("data type with all nullary constructors expected")
335 chk_clas clas_uniq clas_str clas_why cond
336 = if (clas_uniq == clas_key)
337 then checkTc cond (derivingThingErr clas_str clas_why tycon)
340 -- Are things OK for deriving Enum (if appropriate)?
341 chk_clas enumClassKey (SLIT("Enum")) nullary_why is_enumeration `thenTc_`
343 -- Are things OK for deriving Bounded (if appropriate)?
344 chk_clas boundedClassKey (SLIT("Bounded")) single_nullary_why
345 (is_enumeration || is_single_con) `thenTc_`
347 -- Are things OK for deriving Ix (if appropriate)?
348 chk_clas ixClassKey (SLIT("Ix.Ix")) single_nullary_why
349 (is_enumeration || is_single_con)
351 ------------------------------------------------------------------
352 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
353 cmp_deriv (c1, t1) (c2, t2)
354 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
356 ------------------------------------------------------------------
357 mk_eqn :: (Class, TyCon) -> DerivEqn
358 -- we swizzle the tyvars and datacons out of the tycon
359 -- to make the rest of the equation
362 = (clas, tycon, tyvars, if_not_Eval constraints)
364 clas_key = classKey clas
365 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
366 tyvar_tys = mkTyVarTys tyvars
367 data_cons = tyConDataCons tycon
369 if_not_Eval cs = if clas_key == evalClassKey then [] else cs
371 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
373 -- "extra_constraints": see notes above about contexts on data decls
375 | offensive_class = tyConTheta tycon
378 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
380 mk_constraints data_con
382 | arg_ty <- instd_arg_tys,
383 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
386 instd_arg_tys = dataConArgTys data_con tyvar_tys
389 %************************************************************************
391 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
393 %************************************************************************
395 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
396 terms, which is the final correct RHS for the corresponding original
400 Each (k,TyVarTy tv) in a solution constrains only a type
404 The (k,TyVarTy tv) pairs in a solution are canonically
405 ordered by sorting on type varible, tv, (major key) and then class, k,
410 solveDerivEqns :: Bag InstInfo
412 -> TcM s [InstInfo] -- Solns in same order as eqns.
413 -- This bunch is Absolutely minimal...
415 solveDerivEqns inst_decl_infos_in orig_eqns
416 = iterateDeriv initial_solutions
418 -- The initial solutions for the equations claim that each
419 -- instance has an empty context; this solution is certainly
420 -- in canonical form.
421 initial_solutions :: [DerivSoln]
422 initial_solutions = [ [] | _ <- orig_eqns ]
424 ------------------------------------------------------------------
425 -- iterateDeriv calculates the next batch of solutions,
426 -- compares it with the current one; finishes if they are the
427 -- same, otherwise recurses with the new solutions.
428 -- It fails if any iteration fails
429 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
430 iterateDeriv current_solns
431 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_inst_infos, new_solns) ->
432 if (current_solns == new_solns) then
433 returnTc new_inst_infos
435 iterateDeriv new_solns
437 ------------------------------------------------------------------
438 iterateOnce current_solns
439 = -- Extend the inst info from the explicit instance decls
440 -- with the current set of solutions, giving a
442 add_solns inst_decl_infos_in orig_eqns current_solns
443 `thenNF_Tc` \ (new_inst_infos, inst_mapper) ->
445 class_to_inst_env cls = inst_mapper cls
449 listTc [ tcAddErrCtxt (derivCtxt tc) $
450 tcSimplifyThetas class_to_inst_env deriv_rhs
451 | (_,tc,_,deriv_rhs) <- orig_eqns ] `thenTc` \ next_solns ->
453 -- Canonicalise the solutions, so they compare nicely
454 let canonicalised_next_solns
455 = [ sortLt (<) next_soln | next_soln <- next_solns ]
457 returnTc (new_inst_infos, canonicalised_next_solns)
461 add_solns :: Bag InstInfo -- The global, non-derived ones
462 -> [DerivEqn] -> [DerivSoln]
463 -> NF_TcM s ([InstInfo], -- The new, derived ones
465 -- the eqns and solns move "in lockstep"; we have the eqns
466 -- because we need the LHS info for addClassInstance.
468 add_solns inst_infos_in eqns solns
470 = discardErrsTc (buildInstanceEnvs all_inst_infos) `thenNF_Tc` \ inst_mapper ->
471 -- We do the discard-errs so that we don't get repeated error messages
472 -- about duplicate instances.
473 -- They'll appear later, when we do the top-level buildInstanceEnvs.
475 returnNF_Tc (new_inst_infos, inst_mapper)
477 new_inst_infos = zipWithEqual "add_solns" mk_deriv_inst_info eqns solns
479 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
481 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
482 = InstInfo clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
484 (my_panic "dfun_theta")
488 (my_panic "binds") (getSrcLoc tycon)
489 (my_panic "upragmas")
492 = mkDictFunId (getName tycon) dummy_dfun_ty bottom bottom
493 -- The name is getSrcLoc'd in an error message
495 bottom = panic "dummy_dfun_id"
497 dummy_dfun_ty = mkSigmaTy tyvars theta voidTy
498 -- All we need from the dfun is its "theta" part, used during
499 -- equation simplification (tcSimplifyThetas). The final
500 -- dfun_id will have the superclass dictionaries as arguments too,
501 -- but that'll be added after the equations are solved. For now,
502 -- it's enough just to make a dummy dfun with the simple theta part.
504 -- The part after the theta is dummied here as voidTy; actually it's
505 -- (C (T a b)), but it doesn't seem worth constructing it.
506 -- We can't leave it as a panic because to get the theta part we
507 -- have to run down the type!
509 my_panic str = panic "add_soln" -- pprPanic ("add_soln:"++str) (hsep [char ':', ppr clas, ppr tycon])
512 %************************************************************************
514 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
516 %************************************************************************
518 After all the trouble to figure out the required context for the
519 derived instance declarations, all that's left is to chug along to
520 produce them. They will then be shoved into @tcInstDecls2@, which
521 will do all its usual business.
523 There are lots of possibilities for code to generate. Here are
524 various general remarks.
529 We want derived instances of @Eq@ and @Ord@ (both v common) to be
530 ``you-couldn't-do-better-by-hand'' efficient.
533 Deriving @Show@---also pretty common--- should also be reasonable good code.
536 Deriving for the other classes isn't that common or that big a deal.
543 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
546 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
549 We {\em normally} generate code only for the non-defaulted methods;
550 there are some exceptions for @Eq@ and (especially) @Ord@...
553 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
554 constructor's numeric (@Int#@) tag. These are generated by
555 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
556 these is around is given by @hasCon2TagFun@.
558 The examples under the different sections below will make this
562 Much less often (really just for deriving @Ix@), we use a
563 @_tag2con_<tycon>@ function. See the examples.
566 We use the renamer!!! Reason: we're supposed to be
567 producing @RenamedMonoBinds@ for the methods, but that means
568 producing correctly-uniquified code on the fly. This is entirely
569 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
570 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
571 the renamer. What a great hack!
575 -- Generate the method bindings for the required instance
576 -- (paired with class name, as we need that when generating dict
578 gen_bind :: InstInfo -> ({-class-}OccName, {-tyCon-}OccName, RdrNameMonoBinds)
579 gen_bind (InstInfo clas _ [ty] _ _ _ _ _ _)
581 = (clas_nm, tycon_nm, EmptyMonoBinds)
583 = (clas_nm, tycon_nm,
584 assoc "gen_bind:bad derived class"
585 [(eqClassKey, gen_Eq_binds)
586 ,(ordClassKey, gen_Ord_binds)
587 ,(enumClassKey, gen_Enum_binds)
588 ,(evalClassKey, gen_Eval_binds)
589 ,(boundedClassKey, gen_Bounded_binds)
590 ,(showClassKey, gen_Show_binds)
591 ,(readClassKey, gen_Read_binds)
592 ,(ixClassKey, gen_Ix_binds)
597 clas_nm = nameOccName (getName clas)
598 tycon_nm = nameOccName (getName tycon)
599 from_here = isLocallyDefined tycon
600 (tycon,_,_) = splitAlgTyConApp ty
603 gen_inst_info :: Module -- Module name
604 -> (InstInfo, (Name, RenamedMonoBinds)) -- the main stuff to work on
605 -> InstInfo -- the gen'd (filled-in) "instance decl"
607 gen_inst_info modname
608 (InstInfo clas tyvars tys@(ty:_) inst_decl_theta _ _ _ locn _, (dfun_name, meth_binds))
610 -- Generate the various instance-related Ids
611 InstInfo clas tyvars tys inst_decl_theta
616 (dfun_id, dfun_theta) = mkInstanceRelatedIds
621 from_here = isLocallyDefined tycon
622 (tycon,_,_) = splitAlgTyConApp ty
626 %************************************************************************
628 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
630 %************************************************************************
635 con2tag_Foo :: Foo ... -> Int#
636 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
637 maxtag_Foo :: Int -- ditto (NB: not unboxed)
640 We have a @con2tag@ function for a tycon if:
643 We're deriving @Eq@ and the tycon has nullary data constructors.
646 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
650 We have a @tag2con@ function for a tycon if:
653 We're deriving @Enum@, or @Ix@ (enum type only???)
656 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
659 gen_taggery_Names :: [InstInfo]
660 -> TcM s [(RdrName, -- for an assoc list
661 TyCon, -- related tycon
664 gen_taggery_Names inst_infos
665 = --pprTrace "gen_taggery:\n" (vcat [hsep [ppr c, ppr t] | (c,t) <- all_CTs]) $
666 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
667 foldlTc do_tag2con names_so_far tycons_of_interest
669 all_CTs = [ (c, get_tycon ty) | (InstInfo c _ [ty] _ _ _ _ _ _) <- inst_infos ]
671 get_tycon ty = case splitAlgTyConApp ty of { (tc, _, _) -> tc }
673 all_tycons = map snd all_CTs
674 (tycons_of_interest, _) = removeDups compare all_tycons
676 do_con2tag acc_Names tycon
677 | isDataTyCon tycon &&
678 (we_are_deriving eqClassKey tycon
679 && any isNullaryDataCon (tyConDataCons tycon))
680 || (we_are_deriving ordClassKey tycon
681 && not (maybeToBool (maybeTyConSingleCon tycon)))
682 || (we_are_deriving enumClassKey tycon)
683 || (we_are_deriving ixClassKey tycon)
685 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
690 do_tag2con acc_Names tycon
691 = if (we_are_deriving enumClassKey tycon)
692 || (we_are_deriving ixClassKey tycon)
694 returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
695 : (maxtag_RDR tycon, tycon, GenMaxTag)
700 we_are_deriving clas_key tycon
701 = is_in_eqns clas_key tycon all_CTs
703 is_in_eqns clas_key tycon [] = False
704 is_in_eqns clas_key tycon ((c,t):cts)
705 = (clas_key == classKey c && tycon == t)
706 || is_in_eqns clas_key tycon cts
711 derivingThingErr :: FAST_STRING -> FAST_STRING -> TyCon -> ErrMsg
713 derivingThingErr thing why tycon
714 = hang (hsep [ptext SLIT("Can't make a derived instance of"), ptext thing])
715 0 (hang (hsep [ptext SLIT("for the type"), quotes (ppr tycon)])
716 0 (parens (ptext why)))
719 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)