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, newDFunName )
20 import TcGenDeriv -- Deriv stuff
21 import InstEnv ( 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, PersistentRenamerState )
31 import BasicTypes ( Fixity )
32 import Class ( classKey, Class )
33 import ErrUtils ( dumpIfSet_dyn, Message )
34 import MkId ( mkDictFunId )
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 )
41 import RdrName ( RdrName )
43 import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
44 tyConTheta, maybeTyConSingleCon, isDataTyCon,
45 isEnumerationTyCon, TyCon
47 import Type ( TauType, PredType(..), mkTyVarTys, mkTyConApp,
48 splitDFunTy, isUnboxedType
52 import Util ( zipWithEqual, sortLt, thenCmp )
53 import ListSetOps ( removeDups, assoc )
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 = (Name, Class, TyCon, [TyVar], DerivRhs)
143 -- The Name is the name for the DFun we'll build
144 -- The tyvars bind all the variables in the RHS
146 type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
147 --[PredType] -- ... | Class Class [Type==TauType]
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 :: PersistentRenamerState
185 -> Module -- name of module under scrutiny
186 -> InstEnv -- What we already know about instances
187 -> (Name -> Maybe Fixity) -- used in deriving Show and Read
188 -> [TyCon] -- "local_tycons" ???
189 -> TcM ([InstInfo], -- The generated "instance decls".
190 RenamedHsBinds) -- Extra generated bindings
192 tcDeriving prs mod inst_env_in get_fixity local_tycons
193 = recoverTc (returnTc ([], EmptyBinds)) $
195 -- Fish the "deriving"-related information out of the TcEnv
196 -- and make the necessary "equations".
197 makeDerivEqns mod local_tycons `thenTc` \ eqns ->
199 returnTc ([], EmptyBinds)
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_env_in eqns `thenTc` \ new_dfuns ->
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_dfuns `thenTc` \ nm_alist_etc ->
215 tcGetEnv `thenNF_Tc` \ env ->
216 getDOptsTc `thenTc` \ dflags ->
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 get_fixity) 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 dflags 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 new_inst_infos = map gen_inst_info (new_dfuns `zip` rn_method_binds_s)
237 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
238 (ddump_deriving new_inst_infos rn_extra_binds)) `thenTc_`
240 returnTc (new_inst_infos, rn_extra_binds)
242 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
243 ddump_deriving inst_infos extra_binds
244 = vcat (map pprInstInfo inst_infos) $$ ppr extra_binds
247 -- Make a Real dfun instead of the dummy one we have so far
248 gen_inst_info :: (DFunId, RenamedMonoBinds) -> InstInfo
249 gen_inst_info (dfun, binds)
250 = InstInfo { iLocal = True,
251 iClass = clas, iTyVars = tyvars,
252 iTys = tys, iTheta = theta,
255 iLoc = getSrcLoc dfun, iPrags = [] }
257 (tyvars, theta, clas, tys) = splitDFunTy (idType dfun)
259 rn_meths meths = rnMethodBinds [] meths `thenRn` \ (meths', _) -> returnRn meths'
260 -- Ignore the free vars returned
264 %************************************************************************
266 \subsection[TcDeriv-eqns]{Forming the equations}
268 %************************************************************************
270 @makeDerivEqns@ fishes around to find the info about needed derived
271 instances. Complicating factors:
274 We can only derive @Enum@ if the data type is an enumeration
275 type (all nullary data constructors).
278 We can only derive @Ix@ if the data type is an enumeration {\em
279 or} has just one data constructor (e.g., tuples).
282 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
286 makeDerivEqns :: Module -> [TyCon] -> TcM [DerivEqn]
288 makeDerivEqns this_mod local_tycons
290 think_about_deriving = need_deriving local_tycons
291 (derive_these, _) = removeDups cmp_deriv think_about_deriving
293 if null local_tycons then
294 returnTc [] -- Bale out now
296 mapTc mk_eqn derive_these `thenTc` \ maybe_eqns ->
297 returnTc (catMaybes maybe_eqns)
299 ------------------------------------------------------------------
300 need_deriving :: [TyCon] -> [(Class, TyCon)]
301 -- find the tycons that have `deriving' clauses;
303 need_deriving tycons_to_consider
304 = foldr (\ tycon acc -> [(clas,tycon) | clas <- tyConDerivings tycon] ++ acc)
308 ------------------------------------------------------------------
309 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
310 cmp_deriv (c1, t1) (c2, t2)
311 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
313 ------------------------------------------------------------------
314 mk_eqn :: (Class, TyCon) -> NF_TcM (Maybe DerivEqn)
315 -- we swizzle the tyvars and datacons out of the tycon
316 -- to make the rest of the equation
319 = case chk_out clas tycon of
320 Just err -> addErrTc err `thenNF_Tc_`
322 Nothing -> newDFunName this_mod clas tyvar_tys locn `thenNF_Tc` \ dfun_name ->
323 returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints))
325 clas_key = classKey clas
326 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
327 tyvar_tys = mkTyVarTys tyvars
328 data_cons = tyConDataCons tycon
329 locn = getSrcLoc tycon
331 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
333 -- "extra_constraints": see notes above about contexts on data decls
335 | offensive_class = tyConTheta tycon
338 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
340 mk_constraints data_con
342 | arg_ty <- instd_arg_tys,
343 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
346 instd_arg_tys = dataConArgTys data_con tyvar_tys
348 ------------------------------------------------------------------
349 chk_out :: Class -> TyCon -> Maybe Message
351 | clas `hasKey` enumClassKey && not is_enumeration = bog_out nullary_why
352 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = bog_out single_nullary_why
353 | clas `hasKey` ixClassKey && not is_enumeration_or_single = bog_out single_nullary_why
354 | any isExistentialDataCon (tyConDataCons tycon) = Just (existentialErr clas tycon)
355 | otherwise = Nothing
357 is_enumeration = isEnumerationTyCon tycon
358 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
359 is_enumeration_or_single = is_enumeration || is_single_con
361 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
362 nullary_why = SLIT("data type with all nullary constructors expected")
364 bog_out why = Just (derivingThingErr clas tycon why)
367 %************************************************************************
369 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
371 %************************************************************************
373 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
374 terms, which is the final correct RHS for the corresponding original
378 Each (k,TyVarTy tv) in a solution constrains only a type
382 The (k,TyVarTy tv) pairs in a solution are canonically
383 ordered by sorting on type varible, tv, (major key) and then class, k,
388 solveDerivEqns :: InstEnv
390 -> TcM [DFunId] -- Solns in same order as eqns.
391 -- This bunch is Absolutely minimal...
393 solveDerivEqns inst_env_in orig_eqns
394 = iterateDeriv initial_solutions
396 -- The initial solutions for the equations claim that each
397 -- instance has an empty context; this solution is certainly
398 -- in canonical form.
399 initial_solutions :: [DerivSoln]
400 initial_solutions = [ [] | _ <- orig_eqns ]
402 ------------------------------------------------------------------
403 -- iterateDeriv calculates the next batch of solutions,
404 -- compares it with the current one; finishes if they are the
405 -- same, otherwise recurses with the new solutions.
406 -- It fails if any iteration fails
407 iterateDeriv :: [DerivSoln] ->TcM [DFunId]
408 iterateDeriv current_solns
409 = checkNoErrsTc (iterateOnce current_solns)
410 `thenTc` \ (new_dfuns, new_solns) ->
411 if (current_solns == new_solns) then
414 iterateDeriv new_solns
416 ------------------------------------------------------------------
417 iterateOnce current_solns
418 = -- Extend the inst info from the explicit instance decls
419 -- with the current set of solutions, giving a
420 getDOptsTc `thenTc` \ dflags ->
421 let (new_dfuns, inst_env) =
422 add_solns dflags inst_env_in orig_eqns current_solns
425 tcSetInstEnv inst_env (
426 listTc [ tcAddErrCtxt (derivCtxt tc) $
427 tcSimplifyThetas deriv_rhs
428 | (_, _,tc,_,deriv_rhs) <- orig_eqns ]
429 ) `thenTc` \ next_solns ->
431 -- Canonicalise the solutions, so they compare nicely
432 let canonicalised_next_solns = [ sortLt (<) next_soln | next_soln <- next_solns ]
434 returnTc (new_dfuns, canonicalised_next_solns)
438 add_solns :: DynFlags
439 -> InstEnv -- The global, non-derived ones
440 -> [DerivEqn] -> [DerivSoln]
441 -> ([DFunId], InstEnv)
442 -- the eqns and solns move "in lockstep"; we have the eqns
443 -- because we need the LHS info for addClassInstance.
445 add_solns dflags inst_env_in eqns solns
446 = (new_dfuns, inst_env)
448 new_dfuns = zipWithEqual "add_solns" mk_deriv_dfun eqns solns
449 (inst_env, _) = extendInstEnv dflags inst_env_in new_dfuns
450 -- Ignore the errors about duplicate instances.
451 -- We don't want repeated error messages
452 -- They'll appear later, when we do the top-level extendInstEnvs
454 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
455 = mkDictFunId dfun_name clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
456 (map pair2PredType theta)
458 pair2PredType (clas, tautypes) = Class clas tautypes
461 %************************************************************************
463 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
465 %************************************************************************
467 After all the trouble to figure out the required context for the
468 derived instance declarations, all that's left is to chug along to
469 produce them. They will then be shoved into @tcInstDecls2@, which
470 will do all its usual business.
472 There are lots of possibilities for code to generate. Here are
473 various general remarks.
478 We want derived instances of @Eq@ and @Ord@ (both v common) to be
479 ``you-couldn't-do-better-by-hand'' efficient.
482 Deriving @Show@---also pretty common--- should also be reasonable good code.
485 Deriving for the other classes isn't that common or that big a deal.
492 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
495 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
498 We {\em normally} generate code only for the non-defaulted methods;
499 there are some exceptions for @Eq@ and (especially) @Ord@...
502 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
503 constructor's numeric (@Int#@) tag. These are generated by
504 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
505 these is around is given by @hasCon2TagFun@.
507 The examples under the different sections below will make this
511 Much less often (really just for deriving @Ix@), we use a
512 @_tag2con_<tycon>@ function. See the examples.
515 We use the renamer!!! Reason: we're supposed to be
516 producing @RenamedMonoBinds@ for the methods, but that means
517 producing correctly-uniquified code on the fly. This is entirely
518 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
519 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
520 the renamer. What a great hack!
524 -- Generate the method bindings for the required instance
525 -- (paired with class name, as we need that when generating dict
527 gen_bind :: (Name -> Maybe Fixity) -> DFunId -> RdrNameMonoBinds
528 gen_bind get_fixity dfun
529 | not (isLocallyDefined tycon) = EmptyMonoBinds
530 | clas `hasKey` showClassKey = gen_Show_binds get_fixity tycon
531 | clas `hasKey` readClassKey = gen_Read_binds get_fixity tycon
533 = assoc "gen_bind:bad derived class"
534 [(eqClassKey, gen_Eq_binds)
535 ,(ordClassKey, gen_Ord_binds)
536 ,(enumClassKey, gen_Enum_binds)
537 ,(boundedClassKey, gen_Bounded_binds)
538 ,(ixClassKey, gen_Ix_binds)
543 (clas, tycon) = simpleDFunClassTyCon dfun
547 %************************************************************************
549 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
551 %************************************************************************
556 con2tag_Foo :: Foo ... -> Int#
557 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
558 maxtag_Foo :: Int -- ditto (NB: not unboxed)
561 We have a @con2tag@ function for a tycon if:
564 We're deriving @Eq@ and the tycon has nullary data constructors.
567 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
571 We have a @tag2con@ function for a tycon if:
574 We're deriving @Enum@, or @Ix@ (enum type only???)
577 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
580 gen_taggery_Names :: [DFunId]
581 -> TcM [(RdrName, -- for an assoc list
582 TyCon, -- related tycon
585 gen_taggery_Names dfuns
586 = foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
587 foldlTc do_tag2con names_so_far tycons_of_interest
589 all_CTs = map simpleDFunClassTyCon dfuns
590 all_tycons = map snd all_CTs
591 (tycons_of_interest, _) = removeDups compare all_tycons
593 do_con2tag acc_Names tycon
594 | isDataTyCon tycon &&
595 ((we_are_deriving eqClassKey tycon
596 && any isNullaryDataCon (tyConDataCons tycon))
597 || (we_are_deriving ordClassKey tycon
598 && not (maybeToBool (maybeTyConSingleCon tycon)))
599 || (we_are_deriving enumClassKey tycon)
600 || (we_are_deriving ixClassKey tycon))
602 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
607 do_tag2con acc_Names tycon
608 | isDataTyCon tycon &&
609 (we_are_deriving enumClassKey tycon ||
610 we_are_deriving ixClassKey tycon
611 && isEnumerationTyCon tycon)
612 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
613 : (maxtag_RDR tycon, tycon, GenMaxTag)
618 we_are_deriving clas_key tycon
619 = is_in_eqns clas_key tycon all_CTs
621 is_in_eqns clas_key tycon [] = False
622 is_in_eqns clas_key tycon ((c,t):cts)
623 = (clas_key == classKey c && tycon == t)
624 || is_in_eqns clas_key tycon cts
628 derivingThingErr :: Class -> TyCon -> FAST_STRING -> Message
630 derivingThingErr clas tycon why
631 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr clas)],
632 hsep [ptext SLIT("for the type"), quotes (ppr tycon)],
635 existentialErr clas tycon
636 = sep [ptext SLIT("Can't derive any instances for type") <+> quotes (ppr tycon),
637 ptext SLIT("because it has existentially-quantified constructor(s)")]
640 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)