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(..), collectLocatedMonoBinders )
14 import RdrHsSyn ( RdrNameMonoBinds )
15 import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds )
16 import CmdLineOpts ( DynFlag(..), DynFlags )
19 import TcEnv ( TcEnv, tcSetInstEnv, getTcGST, newDFunName )
20 import TcGenDeriv -- Deriv stuff
21 import TcInstUtil ( InstInfo(..), InstEnv,
22 pprInstInfo, simpleDFunClassTyCon, extendInstEnv )
23 import TcSimplify ( tcSimplifyThetas )
25 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
26 import RnEnv ( bindLocatedLocalsRn )
27 import RnMonad ( --RnNameSupply,
28 renameSourceCode, thenRn, mapRn, returnRn )
29 import HscTypes ( DFunId, GlobalSymbolTable, PersistentRenamerState )
31 import Bag ( Bag, emptyBag, unionBags, listToBag )
32 import Class ( classKey, Class )
33 import ErrUtils ( dumpIfSet_dyn, Message )
34 import MkId ( mkDictFunId )
35 import Id ( mkVanillaId, idType )
36 import DataCon ( dataConArgTys, isNullaryDataCon, isExistentialDataCon )
37 import PrelInfo ( needsDataDeclCtxtClassKeys )
38 import Maybes ( maybeToBool, catMaybes )
39 import Module ( Module )
40 import Name ( Name, isLocallyDefined, getSrcLoc, NamedThing(..) )
41 import RdrName ( RdrName )
42 --import RnMonad ( FixityEnv )
44 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
45 tyConTheta, maybeTyConSingleCon, isDataTyCon,
46 isEnumerationTyCon, isAlgTyCon, TyCon
48 import Type ( TauType, PredType(..), mkTyVarTys, mkTyConApp,
49 mkSigmaTy, splitSigmaTy, splitDictTy, mkDictTy,
50 isUnboxedType, splitAlgTyConApp, classesToPreds
52 import TysWiredIn ( voidTy )
55 import Bag ( bagToList )
56 import Util ( zipWithEqual, sortLt, thenCmp )
57 import ListSetOps ( removeDups, assoc )
61 %************************************************************************
63 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
65 %************************************************************************
69 data T a b = C1 (Foo a) (Bar b)
74 [NOTE: See end of these comments for what to do with
75 data (C a, D b) => T a b = ...
78 We want to come up with an instance declaration of the form
80 instance (Ping a, Pong b, ...) => Eq (T a b) where
83 It is pretty easy, albeit tedious, to fill in the code "...". The
84 trick is to figure out what the context for the instance decl is,
85 namely @Ping@, @Pong@ and friends.
87 Let's call the context reqd for the T instance of class C at types
88 (a,b, ...) C (T a b). Thus:
90 Eq (T a b) = (Ping a, Pong b, ...)
92 Now we can get a (recursive) equation from the @data@ decl:
94 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
95 u Eq (T b a) u Eq Int -- From C2
96 u Eq (T a a) -- From C3
98 Foo and Bar may have explicit instances for @Eq@, in which case we can
99 just substitute for them. Alternatively, either or both may have
100 their @Eq@ instances given by @deriving@ clauses, in which case they
101 form part of the system of equations.
103 Now all we need do is simplify and solve the equations, iterating to
104 find the least fixpoint. Notice that the order of the arguments can
105 switch around, as here in the recursive calls to T.
107 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
111 Eq (T a b) = {} -- The empty set
114 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
115 u Eq (T b a) u Eq Int -- From C2
116 u Eq (T a a) -- From C3
118 After simplification:
119 = Eq a u Ping b u {} u {} u {}
124 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
125 u Eq (T b a) u Eq Int -- From C2
126 u Eq (T a a) -- From C3
128 After simplification:
133 = Eq a u Ping b u Eq b u Ping a
135 The next iteration gives the same result, so this is the fixpoint. We
136 need to make a canonical form of the RHS to ensure convergence. We do
137 this by simplifying the RHS to a form in which
139 - the classes constrain only tyvars
140 - the list is sorted by tyvar (major key) and then class (minor key)
141 - no duplicates, of course
143 So, here are the synonyms for the ``equation'' structures:
146 type DerivEqn = (Name, Class, TyCon, [TyVar], DerivRhs)
147 -- The Name is the name for the DFun we'll build
148 -- The tyvars bind all the variables in the RHS
150 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
151 --[PredType] -- ... | Class Class [Type==TauType]
153 type DerivSoln = DerivRhs
157 A note about contexts on data decls
158 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
161 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
163 We will need an instance decl like:
165 instance (Read a, RealFloat a) => Read (Complex a) where
168 The RealFloat in the context is because the read method for Complex is bound
169 to construct a Complex, and doing that requires that the argument type is
172 But this ain't true for Show, Eq, Ord, etc, since they don't construct
173 a Complex; they only take them apart.
175 Our approach: identify the offending classes, and add the data type
176 context to the instance decl. The "offending classes" are
181 %************************************************************************
183 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
185 %************************************************************************
188 tcDeriving :: PersistentRenamerState
189 -> Module -- name of module under scrutiny
190 -> InstEnv -- What we already know about instances
191 -> [TyCon] -- "local_tycons" ???
192 -> TcM ([InstInfo], -- The generated "instance decls".
193 RenamedHsBinds) -- Extra generated bindings
195 tcDeriving prs mod inst_env_in local_tycons
196 = recoverTc (returnTc ([], EmptyBinds)) $
198 -- Fish the "deriving"-related information out of the TcEnv
199 -- and make the necessary "equations".
200 makeDerivEqns mod local_tycons `thenTc` \ eqns ->
202 returnTc ([], EmptyBinds)
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_env_in eqns `thenTc` \ new_dfuns ->
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_dfuns `thenTc` \ nm_alist_etc ->
218 tcGetEnv `thenNF_Tc` \ env ->
219 getDOptsTc `thenTc` \ dflags ->
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 (getTcGST env)) new_dfuns
224 mbinders = collectLocatedMonoBinders 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 (rn_method_binds_s, rn_extra_binds)
230 = renameSourceCode dflags mod prs (
231 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
232 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
233 mapRn rn_meths method_binds_s `thenRn` \ rn_method_binds_s ->
234 returnRn (rn_method_binds_s, rn_extra_binds)
237 new_inst_infos = map gen_inst_info (new_dfuns `zip` rn_method_binds_s)
240 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
241 (ddump_deriving new_inst_infos rn_extra_binds)) `thenTc_`
243 returnTc (new_inst_infos, rn_extra_binds)
245 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
246 ddump_deriving inst_infos extra_binds
247 = vcat (map pprInstInfo inst_infos) $$ ppr extra_binds
250 -- Make a Real dfun instead of the dummy one we have so far
251 gen_inst_info :: (DFunId, RenamedMonoBinds) -> InstInfo
252 gen_inst_info (dfun, binds)
253 = InstInfo { iLocal = True,
254 iClass = clas, iTyVars = tyvars,
255 iTys = tys, iTheta = theta,
258 iLoc = getSrcLoc dfun, iPrags = [] }
260 (tyvars, theta, tau) = splitSigmaTy (idType dfun)
261 (clas, tys) = splitDictTy tau
263 rn_meths meths = rnMethodBinds [] meths `thenRn` \ (meths', _) -> returnRn meths'
264 -- Ignore the free vars returned
268 %************************************************************************
270 \subsection[TcDeriv-eqns]{Forming the equations}
272 %************************************************************************
274 @makeDerivEqns@ fishes around to find the info about needed derived
275 instances. Complicating factors:
278 We can only derive @Enum@ if the data type is an enumeration
279 type (all nullary data constructors).
282 We can only derive @Ix@ if the data type is an enumeration {\em
283 or} has just one data constructor (e.g., tuples).
286 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
290 makeDerivEqns :: Module -> [TyCon] -> TcM [DerivEqn]
292 makeDerivEqns this_mod local_tycons
294 think_about_deriving = need_deriving local_tycons
295 (derive_these, _) = removeDups cmp_deriv think_about_deriving
297 if null local_tycons then
298 returnTc [] -- Bale out now
300 mapTc mk_eqn derive_these `thenTc` \ maybe_eqns ->
301 returnTc (catMaybes maybe_eqns)
303 ------------------------------------------------------------------
304 need_deriving :: [TyCon] -> [(Class, TyCon)]
305 -- find the tycons that have `deriving' clauses;
307 need_deriving tycons_to_consider
308 = foldr (\ tycon acc -> [(clas,tycon) | clas <- tyConDerivings tycon] ++ acc)
312 ------------------------------------------------------------------
313 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
314 cmp_deriv (c1, t1) (c2, t2)
315 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
317 ------------------------------------------------------------------
318 mk_eqn :: (Class, TyCon) -> NF_TcM (Maybe DerivEqn)
319 -- we swizzle the tyvars and datacons out of the tycon
320 -- to make the rest of the equation
323 = case chk_out clas tycon of
324 Just err -> addErrTc err `thenNF_Tc_`
326 Nothing -> newDFunName this_mod clas tyvar_tys locn `thenNF_Tc` \ dfun_name ->
327 returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints))
329 clas_key = classKey clas
330 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
331 tyvar_tys = mkTyVarTys tyvars
332 data_cons = tyConDataCons tycon
333 locn = getSrcLoc tycon
335 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
337 -- "extra_constraints": see notes above about contexts on data decls
339 | offensive_class = tyConTheta tycon
342 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
344 mk_constraints data_con
346 | arg_ty <- instd_arg_tys,
347 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
350 instd_arg_tys = dataConArgTys data_con tyvar_tys
352 ------------------------------------------------------------------
353 chk_out :: Class -> TyCon -> Maybe Message
355 | clas `hasKey` enumClassKey && not is_enumeration = bog_out nullary_why
356 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = bog_out single_nullary_why
357 | clas `hasKey` ixClassKey && not is_enumeration_or_single = bog_out single_nullary_why
358 | any isExistentialDataCon (tyConDataCons tycon) = Just (existentialErr clas tycon)
359 | otherwise = Nothing
361 is_enumeration = isEnumerationTyCon tycon
362 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
363 is_enumeration_or_single = is_enumeration || is_single_con
365 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
366 nullary_why = SLIT("data type with all nullary constructors expected")
368 bog_out why = Just (derivingThingErr clas tycon why)
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 :: InstEnv
394 -> TcM [DFunId] -- Solns in same order as eqns.
395 -- This bunch is Absolutely minimal...
397 solveDerivEqns inst_env_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 [DFunId]
412 iterateDeriv current_solns
413 = checkNoErrsTc (iterateOnce current_solns)
414 `thenTc` \ (new_dfuns, new_solns) ->
415 if (current_solns == new_solns) then
418 iterateDeriv new_solns
420 ------------------------------------------------------------------
421 iterateOnce current_solns
422 = -- Extend the inst info from the explicit instance decls
423 -- with the current set of solutions, giving a
424 getDOptsTc `thenTc` \ dflags ->
425 let (new_dfuns, inst_env) =
426 add_solns dflags inst_env_in orig_eqns current_solns
429 tcSetInstEnv inst_env (
430 listTc [ tcAddErrCtxt (derivCtxt tc) $
431 tcSimplifyThetas deriv_rhs
432 | (_, _,tc,_,deriv_rhs) <- orig_eqns ]
433 ) `thenTc` \ next_solns ->
435 -- Canonicalise the solutions, so they compare nicely
436 let canonicalised_next_solns = [ sortLt (<) next_soln | next_soln <- next_solns ]
438 returnTc (new_dfuns, canonicalised_next_solns)
442 add_solns :: DynFlags
443 -> InstEnv -- The global, non-derived ones
444 -> [DerivEqn] -> [DerivSoln]
445 -> ([DFunId], InstEnv)
446 -- the eqns and solns move "in lockstep"; we have the eqns
447 -- because we need the LHS info for addClassInstance.
449 add_solns dflags inst_env_in eqns solns
450 = (new_dfuns, inst_env)
452 new_dfuns = zipWithEqual "add_solns" mk_deriv_dfun eqns solns
453 (inst_env, _) = extendInstEnv dflags inst_env_in new_dfuns
454 -- Ignore the errors about duplicate instances.
455 -- We don't want repeated error messages
456 -- They'll appear later, when we do the top-level extendInstEnvs
458 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
459 = mkDictFunId dfun_name clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
460 (map pair2PredType theta)
462 pair2PredType (clas, tautypes) = Class clas tautypes
465 %************************************************************************
467 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
469 %************************************************************************
471 After all the trouble to figure out the required context for the
472 derived instance declarations, all that's left is to chug along to
473 produce them. They will then be shoved into @tcInstDecls2@, which
474 will do all its usual business.
476 There are lots of possibilities for code to generate. Here are
477 various general remarks.
482 We want derived instances of @Eq@ and @Ord@ (both v common) to be
483 ``you-couldn't-do-better-by-hand'' efficient.
486 Deriving @Show@---also pretty common--- should also be reasonable good code.
489 Deriving for the other classes isn't that common or that big a deal.
496 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
499 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
502 We {\em normally} generate code only for the non-defaulted methods;
503 there are some exceptions for @Eq@ and (especially) @Ord@...
506 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
507 constructor's numeric (@Int#@) tag. These are generated by
508 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
509 these is around is given by @hasCon2TagFun@.
511 The examples under the different sections below will make this
515 Much less often (really just for deriving @Ix@), we use a
516 @_tag2con_<tycon>@ function. See the examples.
519 We use the renamer!!! Reason: we're supposed to be
520 producing @RenamedMonoBinds@ for the methods, but that means
521 producing correctly-uniquified code on the fly. This is entirely
522 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
523 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
524 the renamer. What a great hack!
528 -- Generate the method bindings for the required instance
529 -- (paired with class name, as we need that when generating dict
531 gen_bind :: GlobalSymbolTable -> DFunId -> RdrNameMonoBinds
532 gen_bind fixities dfun
533 | not (isLocallyDefined tycon) = EmptyMonoBinds
534 | clas `hasKey` showClassKey = gen_Show_binds fixities tycon
535 | clas `hasKey` readClassKey = gen_Read_binds fixities tycon
537 = assoc "gen_bind:bad derived class"
538 [(eqClassKey, gen_Eq_binds)
539 ,(ordClassKey, gen_Ord_binds)
540 ,(enumClassKey, gen_Enum_binds)
541 ,(boundedClassKey, gen_Bounded_binds)
542 ,(ixClassKey, gen_Ix_binds)
547 (clas, tycon) = simpleDFunClassTyCon dfun
551 %************************************************************************
553 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
555 %************************************************************************
560 con2tag_Foo :: Foo ... -> Int#
561 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
562 maxtag_Foo :: Int -- ditto (NB: not unboxed)
565 We have a @con2tag@ function for a tycon if:
568 We're deriving @Eq@ and the tycon has nullary data constructors.
571 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
575 We have a @tag2con@ function for a tycon if:
578 We're deriving @Enum@, or @Ix@ (enum type only???)
581 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
584 gen_taggery_Names :: [DFunId]
585 -> TcM [(RdrName, -- for an assoc list
586 TyCon, -- related tycon
589 gen_taggery_Names dfuns
590 = foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
591 foldlTc do_tag2con names_so_far tycons_of_interest
593 all_CTs = map simpleDFunClassTyCon dfuns
594 all_tycons = map snd all_CTs
595 (tycons_of_interest, _) = removeDups compare all_tycons
597 do_con2tag acc_Names tycon
598 | isDataTyCon tycon &&
599 ((we_are_deriving eqClassKey tycon
600 && any isNullaryDataCon (tyConDataCons tycon))
601 || (we_are_deriving ordClassKey tycon
602 && not (maybeToBool (maybeTyConSingleCon tycon)))
603 || (we_are_deriving enumClassKey tycon)
604 || (we_are_deriving ixClassKey tycon))
606 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
611 do_tag2con acc_Names tycon
612 | isDataTyCon tycon &&
613 (we_are_deriving enumClassKey tycon ||
614 we_are_deriving ixClassKey tycon
615 && isEnumerationTyCon tycon)
616 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
617 : (maxtag_RDR tycon, tycon, GenMaxTag)
622 we_are_deriving clas_key tycon
623 = is_in_eqns clas_key tycon all_CTs
625 is_in_eqns clas_key tycon [] = False
626 is_in_eqns clas_key tycon ((c,t):cts)
627 = (clas_key == classKey c && tycon == t)
628 || is_in_eqns clas_key tycon cts
632 derivingThingErr :: Class -> TyCon -> FAST_STRING -> Message
634 derivingThingErr clas tycon why
635 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr clas)],
636 hsep [ptext SLIT("for the type"), quotes (ppr tycon)],
639 existentialErr clas tycon
640 = sep [ptext SLIT("Can't derive any instances for type") <+> quotes (ppr tycon),
641 ptext SLIT("because it has existentially-quantified constructor(s)")]
644 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)