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 )
16 import CmdLineOpts ( DynFlag(..) )
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, Message )
34 import MkId ( mkDictFunId )
35 import Id ( mkVanillaId )
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, 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!
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 :: PersistentRenamerState
188 -> Module -- name of module under scrutiny
189 -> InstEnv -- What we already know about instances
190 -> TcM ([InstInfo], -- The generated "instance decls".
191 RenamedHsBinds) -- Extra generated bindings
193 tcDeriving prs mod inst_env_in local_tycons
194 = recoverTc (returnTc ([], EmptyBinds)) $
196 -- Fish the "deriving"-related information out of the TcEnv
197 -- and make the necessary "equations".
198 makeDerivEqns local_tycons `thenTc` \ eqns ->
200 returnTc ([], EmptyBinds)
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_env_in eqns `thenTc` \ new_dfuns ->
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_dfuns `thenTc` \ nm_alist_etc ->
216 tcGetEnv `thenNF_Tc` \ env ->
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 (getTcGST env)) new_dfuns
221 mbinders = collectLocatedMonoBinders 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 (rn_method_binds_s, rn_extra_binds)
227 = renameSourceCode mod prs (
228 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
229 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
230 mapRn rn_meths method_binds_s `thenRn` \ rn_method_binds_s ->
231 returnRn (rn_method_binds_s, rn_extra_binds)
234 mapNF_Tc gen_inst_info (new_dfuns `zip` rn_method_binds_s) `thenNF_Tc` \ new_inst_infos ->
236 ioToTc (dumpIfSet Opt_D_dump_deriv "Derived instances"
237 (ddump_deriving new_inst_infos rn_extra_binds)) `thenTc_`
239 returnTc (new_inst_infos, rn_extra_binds)
241 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
242 ddump_deriving inst_infos extra_binds
243 = vcat (map pprInstInfo inst_infos) $$ ppr extra_binds
246 -- Make a Real dfun instead of the dummy one we have so far
247 gen_inst_info (dfun, binds)
248 = InstInfo { iLocal = True,
249 iClass = clas, iTyVars = tyvars,
250 iTys = tys, iTheta = theta,
251 iDFunId = dfun, iBinds = binds,
252 iLoc = getSrcLoc dfun, iPrags = [] }
254 (tyvars, theta, tau) = splitSigmaTy dfun
255 (clas, tys) = splitDictTy tau
257 rn_meths meths = rnMethodBinds [] meths `thenRn` \ (meths', _) -> returnRn meths'
258 -- Ignore the free vars returned
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 :: Module -> [TyCon] -> TcM [DerivEqn]
286 makeDerivEqns this_mod local_tycons
288 think_about_deriving = need_deriving local_tycons
289 (derive_these, _) = removeDups cmp_deriv think_about_deriving
291 if null local_tycons then
292 returnTc [] -- Bale out now
294 mapTc mk_eqn derive_these `thenTc` \ maybe_eqns ->
295 returnTc (catMaybes maybe_eqns)
297 ------------------------------------------------------------------
298 need_deriving :: [TyCon] -> [(Class, TyCon)]
299 -- find the tycons that have `deriving' clauses;
301 need_deriving tycons_to_consider
302 = foldr (\ tycon acc -> [(clas,tycon) | clas <- tyConDerivings tycon] ++ acc)
306 ------------------------------------------------------------------
307 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
308 cmp_deriv (c1, t1) (c2, t2)
309 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
311 ------------------------------------------------------------------
312 mk_eqn :: (Class, TyCon) -> NF_TcM (Maybe DerivEqn)
313 -- we swizzle the tyvars and datacons out of the tycon
314 -- to make the rest of the equation
317 = case chk_out clas tycon of
318 Just err -> addErrTc err `thenNF_Tc_`
320 Nothing -> newDFunName this_mod clas tyvar_tys locn `thenNF_Tc` \ dfun_name ->
321 returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints))
323 clas_key = classKey clas
324 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
325 tyvar_tys = mkTyVarTys tyvars
326 data_cons = tyConDataCons tycon
327 locn = getSrcLoc tycon
329 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
331 -- "extra_constraints": see notes above about contexts on data decls
333 | offensive_class = tyConTheta tycon
336 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
338 mk_constraints data_con
340 | arg_ty <- instd_arg_tys,
341 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
344 instd_arg_tys = dataConArgTys data_con tyvar_tys
346 ------------------------------------------------------------------
347 chk_out :: Class -> TyCon -> Maybe Message
349 | clas `hasKey` enumClassKey && not is_enumeration = bog_out nullary_why
350 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = bog_out single_nullary_why
351 | clas `hasKey` ixClassKey && not is_enumeration_or_single = bog_out single_nullary_why
352 | any isExistentialDataCon (tyConDataCons tycon) = Just (existentialErr clas tycon)
353 | otherwise = Nothing
355 is_enumeration = isEnumerationTyCon tycon
356 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
357 is_enumeration_or_single = is_enumeration || is_single_con
359 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
360 nullary_why = SLIT("data type with all nullary constructors expected")
362 bog_out why = Just (derivingThingErr clas tycon why)
365 %************************************************************************
367 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
369 %************************************************************************
371 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
372 terms, which is the final correct RHS for the corresponding original
376 Each (k,TyVarTy tv) in a solution constrains only a type
380 The (k,TyVarTy tv) pairs in a solution are canonically
381 ordered by sorting on type varible, tv, (major key) and then class, k,
386 solveDerivEqns :: InstEnv
388 -> TcM [DFunId] -- Solns in same order as eqns.
389 -- This bunch is Absolutely minimal...
391 solveDerivEqns inst_env_in orig_eqns
392 = iterateDeriv initial_solutions
394 -- The initial solutions for the equations claim that each
395 -- instance has an empty context; this solution is certainly
396 -- in canonical form.
397 initial_solutions :: [DerivSoln]
398 initial_solutions = [ [] | _ <- orig_eqns ]
400 ------------------------------------------------------------------
401 -- iterateDeriv calculates the next batch of solutions,
402 -- compares it with the current one; finishes if they are the
403 -- same, otherwise recurses with the new solutions.
404 -- It fails if any iteration fails
405 iterateDeriv :: [DerivSoln] ->TcM [DFunId]
406 iterateDeriv current_solns
407 = checkNoErrsTc (iterateOnce current_solns) `thenTc` \ (new_dfuns, new_solns) ->
408 if (current_solns == new_solns) then
411 iterateDeriv new_solns
413 ------------------------------------------------------------------
414 iterateOnce current_solns
415 = -- Extend the inst info from the explicit instance decls
416 -- with the current set of solutions, giving a
418 add_solns inst_env_in orig_eqns current_solns `thenNF_Tc` \ (new_dfuns, inst_env) ->
421 tcSetInstEnv inst_env (
422 listTc [ tcAddErrCtxt (derivCtxt tc) $
423 tcSimplifyThetas deriv_rhs
424 | (_, _,tc,_,deriv_rhs) <- orig_eqns ]
425 ) `thenTc` \ next_solns ->
427 -- Canonicalise the solutions, so they compare nicely
428 let canonicalised_next_solns = [ sortLt (<) next_soln | next_soln <- next_solns ]
430 returnTc (new_dfuns, canonicalised_next_solns)
434 add_solns :: InstEnv -- The global, non-derived ones
435 -> [DerivEqn] -> [DerivSoln]
436 -> ([DFunId], InstEnv)
437 -- the eqns and solns move "in lockstep"; we have the eqns
438 -- because we need the LHS info for addClassInstance.
440 add_solns inst_env_in eqns solns
441 = (new_dfuns, inst_env)
443 new_dfuns = zipWithEqual "add_solns" mk_deriv_dfun eqns solns
444 (inst_env, _) = extendInstEnv inst_env_in
445 -- Ignore the errors about duplicate instances.
446 -- We don't want repeated error messages
447 -- They'll appear later, when we do the top-level extendInstEnvs
449 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
450 = mkDictFunId dfun_name clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)] theta
453 %************************************************************************
455 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
457 %************************************************************************
459 After all the trouble to figure out the required context for the
460 derived instance declarations, all that's left is to chug along to
461 produce them. They will then be shoved into @tcInstDecls2@, which
462 will do all its usual business.
464 There are lots of possibilities for code to generate. Here are
465 various general remarks.
470 We want derived instances of @Eq@ and @Ord@ (both v common) to be
471 ``you-couldn't-do-better-by-hand'' efficient.
474 Deriving @Show@---also pretty common--- should also be reasonable good code.
477 Deriving for the other classes isn't that common or that big a deal.
484 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
487 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
490 We {\em normally} generate code only for the non-defaulted methods;
491 there are some exceptions for @Eq@ and (especially) @Ord@...
494 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
495 constructor's numeric (@Int#@) tag. These are generated by
496 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
497 these is around is given by @hasCon2TagFun@.
499 The examples under the different sections below will make this
503 Much less often (really just for deriving @Ix@), we use a
504 @_tag2con_<tycon>@ function. See the examples.
507 We use the renamer!!! Reason: we're supposed to be
508 producing @RenamedMonoBinds@ for the methods, but that means
509 producing correctly-uniquified code on the fly. This is entirely
510 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
511 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
512 the renamer. What a great hack!
516 -- Generate the method bindings for the required instance
517 -- (paired with class name, as we need that when generating dict
519 gen_bind :: GlobalSymbolTable -> DFunId -> RdrNameMonoBinds
520 gen_bind fixities dfun
521 | not (isLocallyDefined tycon) = EmptyMonoBinds
522 | clas `hasKey` showClassKey = gen_Show_binds fixities tycon
523 | clas `hasKey` readClassKey = gen_Read_binds fixities tycon
525 = assoc "gen_bind:bad derived class"
526 [(eqClassKey, gen_Eq_binds)
527 ,(ordClassKey, gen_Ord_binds)
528 ,(enumClassKey, gen_Enum_binds)
529 ,(boundedClassKey, gen_Bounded_binds)
530 ,(ixClassKey, gen_Ix_binds)
535 (clas, tycon) = simpleDFunClassTyCon dfun
539 %************************************************************************
541 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
543 %************************************************************************
548 con2tag_Foo :: Foo ... -> Int#
549 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
550 maxtag_Foo :: Int -- ditto (NB: not unboxed)
553 We have a @con2tag@ function for a tycon if:
556 We're deriving @Eq@ and the tycon has nullary data constructors.
559 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
563 We have a @tag2con@ function for a tycon if:
566 We're deriving @Enum@, or @Ix@ (enum type only???)
569 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
572 gen_taggery_Names :: [DFunId]
573 -> TcM [(RdrName, -- for an assoc list
574 TyCon, -- related tycon
577 gen_taggery_Names dfuns
578 = foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
579 foldlTc do_tag2con names_so_far tycons_of_interest
581 all_CTs = map simpleDFunClassTyCon dfuns
582 all_tycons = map snd all_CTs
583 (tycons_of_interest, _) = removeDups compare all_tycons
585 do_con2tag acc_Names tycon
586 | isDataTyCon tycon &&
587 ((we_are_deriving eqClassKey tycon
588 && any isNullaryDataCon (tyConDataCons tycon))
589 || (we_are_deriving ordClassKey tycon
590 && not (maybeToBool (maybeTyConSingleCon tycon)))
591 || (we_are_deriving enumClassKey tycon)
592 || (we_are_deriving ixClassKey tycon))
594 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
599 do_tag2con acc_Names tycon
600 | isDataTyCon tycon &&
601 (we_are_deriving enumClassKey tycon ||
602 we_are_deriving ixClassKey tycon
603 && isEnumerationTyCon tycon)
604 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
605 : (maxtag_RDR tycon, tycon, GenMaxTag)
610 we_are_deriving clas_key tycon
611 = is_in_eqns clas_key tycon all_CTs
613 is_in_eqns clas_key tycon [] = False
614 is_in_eqns clas_key tycon ((c,t):cts)
615 = (clas_key == classKey c && tycon == t)
616 || is_in_eqns clas_key tycon cts
620 derivingThingErr :: Class -> TyCon -> FAST_STRING -> Message
622 derivingThingErr clas tycon why
623 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr clas)],
624 hsep [ptext SLIT("for the type"), quotes (ppr tycon)],
627 existentialErr clas tycon
628 = sep [ptext SLIT("Can't derive any instances for type") <+> quotes (ppr tycon),
629 ptext SLIT("because it has existentially-quantified constructor(s)")]
632 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)