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 HsPragmas ( InstancePragmas(..) )
15 import RdrHsSyn ( RdrName, RdrNameMonoBinds )
16 import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds, RenamedFixityDecl )
19 import Inst ( InstanceMapper )
20 import TcEnv ( TcIdOcc, getEnv_TyCons, tcLookupClassByKey )
21 import TcKind ( TcKind )
22 import TcGenDeriv -- Deriv stuff
23 import TcInstUtil ( InstInfo(..), mkInstanceRelatedIds, buildInstanceEnvs )
24 import TcSimplify ( tcSimplifyThetas )
26 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
27 import RnEnv ( newDfunName, bindLocatedLocalsRn )
28 import RnMonad ( RnM, RnDown, GDown, SDown, RnNameSupply(..),
29 setNameSupplyRn, renameSourceCode, thenRn, mapRn, returnRn )
31 import Bag ( Bag, emptyBag, isEmptyBag, unionBags, listToBag )
32 import Class ( classKey, Class )
33 import ErrUtils ( ErrMsg )
34 import Id ( dataConArgTys, isNullaryDataCon, mkDictFunId )
35 import PrelInfo ( needsDataDeclCtxtClassKeys )
36 import Maybes ( maybeToBool )
37 import Name ( isLocallyDefined, getSrcLoc, ExportFlag(..), Provenance,
38 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 UniqFM ( emptyUFM )
52 import Unique -- Keys stuff
53 import Bag ( bagToList )
54 import Util ( zipWithEqual, zipEqual, sortLt, removeDups, assoc,
60 %************************************************************************
62 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
64 %************************************************************************
68 data T a b = C1 (Foo a) (Bar b)
73 [NOTE: See end of these comments for what to do with
74 data (C a, D b) => T a b = ...
77 We want to come up with an instance declaration of the form
79 instance (Ping a, Pong b, ...) => Eq (T a b) where
82 It is pretty easy, albeit tedious, to fill in the code "...". The
83 trick is to figure out what the context for the instance decl is,
84 namely @Ping@, @Pong@ and friends.
86 Let's call the context reqd for the T instance of class C at types
87 (a,b, ...) C (T a b). Thus:
89 Eq (T a b) = (Ping a, Pong b, ...)
91 Now we can get a (recursive) equation from the @data@ decl:
93 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
94 u Eq (T b a) u Eq Int -- From C2
95 u Eq (T a a) -- From C3
97 Foo and Bar may have explicit instances for @Eq@, in which case we can
98 just substitute for them. Alternatively, either or both may have
99 their @Eq@ instances given by @deriving@ clauses, in which case they
100 form part of the system of equations.
102 Now all we need do is simplify and solve the equations, iterating to
103 find the least fixpoint. Notice that the order of the arguments can
104 switch around, as here in the recursive calls to T.
106 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
110 Eq (T a b) = {} -- The empty set
113 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
114 u Eq (T b a) u Eq Int -- From C2
115 u Eq (T a a) -- From C3
117 After simplification:
118 = Eq a u Ping b u {} u {} u {}
123 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
124 u Eq (T b a) u Eq Int -- From C2
125 u Eq (T a a) -- From C3
127 After simplification:
132 = Eq a u Ping b u Eq b u Ping a
134 The next iteration gives the same result, so this is the fixpoint. We
135 need to make a canonical form of the RHS to ensure convergence. We do
136 this by simplifying the RHS to a form in which
138 - the classes constrain only tyvars
139 - the list is sorted by tyvar (major key) and then class (minor key)
140 - no duplicates, of course
142 So, here are the synonyms for the ``equation'' structures:
145 type DerivEqn = (Class, TyCon, [TyVar], DerivRhs)
146 -- The tyvars bind all the variables in the RHS
147 -- NEW: it's convenient to re-use InstInfo
148 -- We'll "panic" out some fields...
150 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
152 type DerivSoln = DerivRhs
156 A note about contexts on data decls
157 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
160 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
162 We will need an instance decl like:
164 instance (Read a, RealFloat a) => Read (Complex a) where
167 The RealFloat in the context is because the read method for Complex is bound
168 to construct a Complex, and doing that requires that the argument type is
171 But this ain't true for Show, Eq, Ord, etc, since they don't construct
172 a Complex; they only take them apart.
174 Our approach: identify the offending classes, and add the data type
175 context to the instance decl. The "offending classes" are
180 %************************************************************************
182 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
184 %************************************************************************
187 tcDeriving :: Module -- name of module under scrutiny
188 -> RnNameSupply -- for "renaming" bits of generated code
189 -> Bag InstInfo -- What we already know about instances
190 -> TcM s (Bag InstInfo, -- The generated "instance decls".
191 RenamedHsBinds, -- Extra generated bindings
192 SDoc) -- Printable derived instance decls;
193 -- for debugging via -ddump-derivings.
195 tcDeriving modname rn_name_supply inst_decl_infos_in
196 = recoverTc (returnTc (emptyBag, EmptyBinds, empty)) $
198 -- Fish the "deriving"-related information out of the TcEnv
199 -- and make the necessary "equations".
200 makeDerivEqns `thenTc` \ eqns ->
202 returnTc (emptyBag, EmptyBinds, text "No derivings")
205 -- Take the equation list and solve it, to deliver a list of
206 -- solutions, a.k.a. the contexts for the instance decls
207 -- required for the corresponding equations.
208 solveDerivEqns inst_decl_infos_in eqns `thenTc` \ new_inst_infos ->
210 -- Now augment the InstInfos, adding in the rather boring
211 -- actual-code-to-do-the-methods binds. We may also need to
212 -- generate extra not-one-inst-decl-specific binds, notably
213 -- "con2tag" and/or "tag2con" functions. We do these
216 gen_taggery_Names new_inst_infos `thenTc` \ nm_alist_etc ->
220 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
221 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
222 method_binds_s = map gen_bind new_inst_infos
223 mbinders = bagToList (collectMonoBinders extra_mbinds)
225 -- Rename to get RenamedBinds.
226 -- The only tricky bit is that the extra_binds must scope over the
227 -- method bindings for the instances.
228 (dfun_names_w_method_binds, rn_extra_binds)
229 = renameSourceCode modname rn_name_supply (
230 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
231 rnTopMonoBinds extra_mbinds [] `thenRn` \ rn_extra_binds ->
232 mapRn rn_one method_binds_s `thenRn` \ dfun_names_w_method_binds ->
233 returnRn (dfun_names_w_method_binds, rn_extra_binds)
235 rn_one meth_binds = newDfunName 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 if null local_data_tycons then
292 -- Bale out now; evalClass may not be loaded if there aren't any
295 tcLookupClassByKey evalClassKey `thenNF_Tc` \ eval_clas ->
297 think_about_deriving = need_deriving eval_clas local_data_tycons
298 (derive_these, _) = removeDups cmp_deriv think_about_deriving
299 eqns = map mk_eqn derive_these
301 mapTc chk_out think_about_deriving `thenTc_`
304 ------------------------------------------------------------------
305 need_deriving :: Class -> [TyCon] -> [(Class, TyCon)]
306 -- find the tycons that have `deriving' clauses;
307 -- we handle the "every datatype in Eval" by
308 -- doing a dummy "deriving" for it.
310 need_deriving eval_clas tycons_to_consider
311 = foldr ( \ tycon acc ->
313 acc_plus = if isLocallyDefined tycon
314 then (eval_clas, tycon) : acc
317 case (tyConDerivings tycon) of
319 cs -> [ (clas,tycon) | clas <- cs ] ++ acc_plus
324 ------------------------------------------------------------------
325 chk_out :: (Class, TyCon) -> TcM s ()
326 chk_out this_one@(clas, tycon)
328 clas_key = classKey clas
330 is_enumeration = isEnumerationTyCon tycon
331 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
333 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
334 nullary_why = SLIT("data type with all nullary constructors expected")
336 chk_clas clas_uniq clas_str clas_why cond
337 = if (clas_uniq == clas_key)
338 then checkTc cond (derivingThingErr clas_str clas_why tycon)
341 -- Are things OK for deriving Enum (if appropriate)?
342 chk_clas enumClassKey (SLIT("Enum")) nullary_why is_enumeration `thenTc_`
344 -- Are things OK for deriving Bounded (if appropriate)?
345 chk_clas boundedClassKey (SLIT("Bounded")) single_nullary_why
346 (is_enumeration || is_single_con) `thenTc_`
348 -- Are things OK for deriving Ix (if appropriate)?
349 chk_clas ixClassKey (SLIT("Ix.Ix")) single_nullary_why
350 (is_enumeration || is_single_con)
352 ------------------------------------------------------------------
353 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
354 cmp_deriv (c1, t1) (c2, t2)
355 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
357 ------------------------------------------------------------------
358 mk_eqn :: (Class, TyCon) -> DerivEqn
359 -- we swizzle the tyvars and datacons out of the tycon
360 -- to make the rest of the equation
363 = (clas, tycon, tyvars, if_not_Eval constraints)
365 clas_key = classKey clas
366 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
367 tyvar_tys = mkTyVarTys tyvars
368 data_cons = tyConDataCons tycon
370 if_not_Eval cs = if clas_key == evalClassKey then [] else cs
372 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
374 -- "extra_constraints": see notes above about contexts on data decls
376 | offensive_class = tyConTheta tycon
379 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
381 mk_constraints data_con
383 | arg_ty <- instd_arg_tys,
384 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
387 instd_arg_tys = dataConArgTys data_con tyvar_tys
390 %************************************************************************
392 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
394 %************************************************************************
396 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
397 terms, which is the final correct RHS for the corresponding original
401 Each (k,TyVarTy tv) in a solution constrains only a type
405 The (k,TyVarTy tv) pairs in a solution are canonically
406 ordered by sorting on type varible, tv, (major key) and then class, k,
411 solveDerivEqns :: Bag InstInfo
413 -> TcM s [InstInfo] -- Solns in same order as eqns.
414 -- This bunch is Absolutely minimal...
416 solveDerivEqns inst_decl_infos_in orig_eqns
417 = iterateDeriv initial_solutions
419 -- The initial solutions for the equations claim that each
420 -- instance has an empty context; this solution is certainly
421 -- in canonical form.
422 initial_solutions :: [DerivSoln]
423 initial_solutions = [ [] | _ <- orig_eqns ]
425 ------------------------------------------------------------------
426 -- iterateDeriv calculates the next batch of solutions,
427 -- compares it with the current one; finishes if they are the
428 -- same, otherwise recurses with the new solutions.
429 -- It fails if any iteration fails
430 iterateDeriv :: [DerivSoln] ->TcM s [InstInfo]
431 iterateDeriv current_solns
432 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_inst_infos, new_solns) ->
433 if (current_solns == new_solns) then
434 returnTc new_inst_infos
436 iterateDeriv new_solns
438 ------------------------------------------------------------------
439 iterateOnce current_solns
440 = -- Extend the inst info from the explicit instance decls
441 -- with the current set of solutions, giving a
443 add_solns inst_decl_infos_in orig_eqns current_solns
444 `thenNF_Tc` \ (new_inst_infos, inst_mapper) ->
446 class_to_inst_env cls = inst_mapper cls
450 listTc [ tcAddErrCtxt (derivCtxt tc) $
451 tcSimplifyThetas class_to_inst_env deriv_rhs
452 | (_,tc,_,deriv_rhs) <- orig_eqns ] `thenTc` \ next_solns ->
454 -- Canonicalise the solutions, so they compare nicely
455 let canonicalised_next_solns
456 = [ sortLt (<) next_soln | next_soln <- next_solns ]
458 returnTc (new_inst_infos, canonicalised_next_solns)
462 add_solns :: Bag InstInfo -- The global, non-derived ones
463 -> [DerivEqn] -> [DerivSoln]
464 -> NF_TcM s ([InstInfo], -- The new, derived ones
466 -- the eqns and solns move "in lockstep"; we have the eqns
467 -- because we need the LHS info for addClassInstance.
469 add_solns inst_infos_in eqns solns
471 = discardErrsTc (buildInstanceEnvs all_inst_infos) `thenNF_Tc` \ inst_mapper ->
472 -- We do the discard-errs so that we don't get repeated error messages
473 -- about duplicate instances.
474 -- They'll appear later, when we do the top-level buildInstanceEnvs.
476 returnNF_Tc (new_inst_infos, inst_mapper)
478 new_inst_infos = zipWithEqual "add_solns" mk_deriv_inst_info eqns solns
480 all_inst_infos = inst_infos_in `unionBags` listToBag new_inst_infos
482 mk_deriv_inst_info (clas, tycon, tyvars, _) theta
483 = InstInfo clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
485 (my_panic "dfun_theta")
489 (my_panic "binds") (getSrcLoc tycon)
490 (my_panic "upragmas")
493 = mkDictFunId (getName tycon) dummy_dfun_ty bottom bottom
494 -- The name is getSrcLoc'd in an error message
496 bottom = panic "dummy_dfun_id"
498 dummy_dfun_ty = mkSigmaTy tyvars theta voidTy
499 -- All we need from the dfun is its "theta" part, used during
500 -- equation simplification (tcSimplifyThetas). The final
501 -- dfun_id will have the superclass dictionaries as arguments too,
502 -- but that'll be added after the equations are solved. For now,
503 -- it's enough just to make a dummy dfun with the simple theta part.
505 -- The part after the theta is dummied here as voidTy; actually it's
506 -- (C (T a b)), but it doesn't seem worth constructing it.
507 -- We can't leave it as a panic because to get the theta part we
508 -- have to run down the type!
510 my_panic str = panic "add_soln" -- pprPanic ("add_soln:"++str) (hsep [char ':', ppr clas, ppr tycon])
513 %************************************************************************
515 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
517 %************************************************************************
519 After all the trouble to figure out the required context for the
520 derived instance declarations, all that's left is to chug along to
521 produce them. They will then be shoved into @tcInstDecls2@, which
522 will do all its usual business.
524 There are lots of possibilities for code to generate. Here are
525 various general remarks.
530 We want derived instances of @Eq@ and @Ord@ (both v common) to be
531 ``you-couldn't-do-better-by-hand'' efficient.
534 Deriving @Show@---also pretty common--- should also be reasonable good code.
537 Deriving for the other classes isn't that common or that big a deal.
544 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
547 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
550 We {\em normally} generate code only for the non-defaulted methods;
551 there are some exceptions for @Eq@ and (especially) @Ord@...
554 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
555 constructor's numeric (@Int#@) tag. These are generated by
556 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
557 these is around is given by @hasCon2TagFun@.
559 The examples under the different sections below will make this
563 Much less often (really just for deriving @Ix@), we use a
564 @_tag2con_<tycon>@ function. See the examples.
567 We use the renamer!!! Reason: we're supposed to be
568 producing @RenamedMonoBinds@ for the methods, but that means
569 producing correctly-uniquified code on the fly. This is entirely
570 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
571 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
572 the renamer. What a great hack!
576 -- Generate the method bindings for the required instance
577 gen_bind :: InstInfo -> RdrNameMonoBinds
578 gen_bind (InstInfo clas _ [ty] _ _ _ _ _ _)
582 = assoc "gen_inst_info:bad derived class"
583 [(eqClassKey, gen_Eq_binds)
584 ,(ordClassKey, gen_Ord_binds)
585 ,(enumClassKey, gen_Enum_binds)
586 ,(evalClassKey, gen_Eval_binds)
587 ,(boundedClassKey, gen_Bounded_binds)
588 ,(showClassKey, gen_Show_binds)
589 ,(readClassKey, gen_Read_binds)
590 ,(ixClassKey, gen_Ix_binds)
595 from_here = isLocallyDefined tycon
596 (tycon,_,_) = splitAlgTyConApp ty
599 gen_inst_info :: Module -- Module name
600 -> (InstInfo, (Name, RenamedMonoBinds)) -- the main stuff to work on
601 -> InstInfo -- the gen'd (filled-in) "instance decl"
603 gen_inst_info modname
604 (InstInfo clas tyvars tys@(ty:_) inst_decl_theta _ _ _ locn _, (dfun_name, meth_binds))
606 -- Generate the various instance-related Ids
607 InstInfo clas tyvars tys inst_decl_theta
612 (dfun_id, dfun_theta) = mkInstanceRelatedIds
617 from_here = isLocallyDefined tycon
618 (tycon,_,_) = splitAlgTyConApp ty
622 %************************************************************************
624 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
626 %************************************************************************
631 con2tag_Foo :: Foo ... -> Int#
632 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
633 maxtag_Foo :: Int -- ditto (NB: not unboxed)
636 We have a @con2tag@ function for a tycon if:
639 We're deriving @Eq@ and the tycon has nullary data constructors.
642 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
646 We have a @tag2con@ function for a tycon if:
649 We're deriving @Enum@, or @Ix@ (enum type only???)
652 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
655 gen_taggery_Names :: [InstInfo]
656 -> TcM s [(RdrName, -- for an assoc list
657 TyCon, -- related tycon
660 gen_taggery_Names inst_infos
661 = --pprTrace "gen_taggery:\n" (vcat [hsep [ppr c, ppr t] | (c,t) <- all_CTs]) $
662 foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
663 foldlTc do_tag2con names_so_far tycons_of_interest
665 all_CTs = [ (c, get_tycon ty) | (InstInfo c _ [ty] _ _ _ _ _ _) <- inst_infos ]
667 get_tycon ty = case splitAlgTyConApp ty of { (tc, _, _) -> tc }
669 all_tycons = map snd all_CTs
670 (tycons_of_interest, _) = removeDups compare all_tycons
672 do_con2tag acc_Names tycon
673 | isDataTyCon tycon &&
674 (we_are_deriving eqClassKey tycon
675 && any isNullaryDataCon (tyConDataCons tycon))
676 || (we_are_deriving ordClassKey tycon
677 && not (maybeToBool (maybeTyConSingleCon tycon)))
678 || (we_are_deriving enumClassKey tycon)
679 || (we_are_deriving ixClassKey tycon)
681 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
686 do_tag2con acc_Names tycon
687 = if (we_are_deriving enumClassKey tycon)
688 || (we_are_deriving ixClassKey tycon)
690 returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
691 : (maxtag_RDR tycon, tycon, GenMaxTag)
696 we_are_deriving clas_key tycon
697 = is_in_eqns clas_key tycon all_CTs
699 is_in_eqns clas_key tycon [] = False
700 is_in_eqns clas_key tycon ((c,t):cts)
701 = (clas_key == classKey c && tycon == t)
702 || is_in_eqns clas_key tycon cts
707 derivingThingErr :: FAST_STRING -> FAST_STRING -> TyCon -> ErrMsg
709 derivingThingErr thing why tycon
710 = hang (hsep [ptext SLIT("Can't make a derived instance of"), ptext thing])
711 0 (hang (hsep [ptext SLIT("for the type"), quotes (ppr tycon)])
712 0 (parens (ptext why)))
715 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)