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 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, 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 -> (Name -> Maybe Fixity) -- used in deriving Show and Read
192 -> [TyCon] -- "local_tycons" ???
193 -> TcM ([InstInfo], -- The generated "instance decls".
194 RenamedHsBinds) -- Extra generated bindings
196 tcDeriving prs mod inst_env_in get_fixity local_tycons
197 = recoverTc (returnTc ([], EmptyBinds)) $
199 -- Fish the "deriving"-related information out of the TcEnv
200 -- and make the necessary "equations".
201 makeDerivEqns mod local_tycons `thenTc` \ eqns ->
203 returnTc ([], EmptyBinds)
206 -- Take the equation list and solve it, to deliver a list of
207 -- solutions, a.k.a. the contexts for the instance decls
208 -- required for the corresponding equations.
209 solveDerivEqns inst_env_in eqns `thenTc` \ new_dfuns ->
211 -- Now augment the InstInfos, adding in the rather boring
212 -- actual-code-to-do-the-methods binds. We may also need to
213 -- generate extra not-one-inst-decl-specific binds, notably
214 -- "con2tag" and/or "tag2con" functions. We do these
217 gen_taggery_Names new_dfuns `thenTc` \ nm_alist_etc ->
219 tcGetEnv `thenNF_Tc` \ env ->
220 getDOptsTc `thenTc` \ dflags ->
222 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
223 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
224 method_binds_s = map (gen_bind get_fixity) new_dfuns
225 mbinders = collectLocatedMonoBinders extra_mbinds
227 -- Rename to get RenamedBinds.
228 -- The only tricky bit is that the extra_binds must scope over the
229 -- method bindings for the instances.
230 (rn_method_binds_s, rn_extra_binds)
231 = renameSourceCode dflags mod prs (
232 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
233 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
234 mapRn rn_meths method_binds_s `thenRn` \ rn_method_binds_s ->
235 returnRn (rn_method_binds_s, rn_extra_binds)
238 new_inst_infos = map gen_inst_info (new_dfuns `zip` rn_method_binds_s)
241 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
242 (ddump_deriving new_inst_infos rn_extra_binds)) `thenTc_`
244 returnTc (new_inst_infos, rn_extra_binds)
246 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
247 ddump_deriving inst_infos extra_binds
248 = vcat (map pprInstInfo inst_infos) $$ ppr extra_binds
251 -- Make a Real dfun instead of the dummy one we have so far
252 gen_inst_info :: (DFunId, RenamedMonoBinds) -> InstInfo
253 gen_inst_info (dfun, binds)
254 = InstInfo { iLocal = True,
255 iClass = clas, iTyVars = tyvars,
256 iTys = tys, iTheta = theta,
259 iLoc = getSrcLoc dfun, iPrags = [] }
261 (tyvars, theta, tau) = splitSigmaTy (idType dfun)
262 (clas, tys) = splitDictTy tau
264 rn_meths meths = rnMethodBinds [] meths `thenRn` \ (meths', _) -> returnRn meths'
265 -- Ignore the free vars returned
269 %************************************************************************
271 \subsection[TcDeriv-eqns]{Forming the equations}
273 %************************************************************************
275 @makeDerivEqns@ fishes around to find the info about needed derived
276 instances. Complicating factors:
279 We can only derive @Enum@ if the data type is an enumeration
280 type (all nullary data constructors).
283 We can only derive @Ix@ if the data type is an enumeration {\em
284 or} has just one data constructor (e.g., tuples).
287 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
291 makeDerivEqns :: Module -> [TyCon] -> TcM [DerivEqn]
293 makeDerivEqns this_mod local_tycons
295 think_about_deriving = need_deriving local_tycons
296 (derive_these, _) = removeDups cmp_deriv think_about_deriving
298 if null local_tycons then
299 returnTc [] -- Bale out now
301 mapTc mk_eqn derive_these `thenTc` \ maybe_eqns ->
302 returnTc (catMaybes maybe_eqns)
304 ------------------------------------------------------------------
305 need_deriving :: [TyCon] -> [(Class, TyCon)]
306 -- find the tycons that have `deriving' clauses;
308 need_deriving tycons_to_consider
309 = foldr (\ tycon acc -> [(clas,tycon) | clas <- tyConDerivings tycon] ++ acc)
313 ------------------------------------------------------------------
314 cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
315 cmp_deriv (c1, t1) (c2, t2)
316 = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
318 ------------------------------------------------------------------
319 mk_eqn :: (Class, TyCon) -> NF_TcM (Maybe DerivEqn)
320 -- we swizzle the tyvars and datacons out of the tycon
321 -- to make the rest of the equation
324 = case chk_out clas tycon of
325 Just err -> addErrTc err `thenNF_Tc_`
327 Nothing -> newDFunName this_mod clas tyvar_tys locn `thenNF_Tc` \ dfun_name ->
328 returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints))
330 clas_key = classKey clas
331 tyvars = tyConTyVars tycon -- ToDo: Do we need new tyvars ???
332 tyvar_tys = mkTyVarTys tyvars
333 data_cons = tyConDataCons tycon
334 locn = getSrcLoc tycon
336 constraints = extra_constraints ++ concat (map mk_constraints data_cons)
338 -- "extra_constraints": see notes above about contexts on data decls
340 | offensive_class = tyConTheta tycon
343 offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
345 mk_constraints data_con
347 | arg_ty <- instd_arg_tys,
348 not (isUnboxedType arg_ty) -- No constraints for unboxed types?
351 instd_arg_tys = dataConArgTys data_con tyvar_tys
353 ------------------------------------------------------------------
354 chk_out :: Class -> TyCon -> Maybe Message
356 | clas `hasKey` enumClassKey && not is_enumeration = bog_out nullary_why
357 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = bog_out single_nullary_why
358 | clas `hasKey` ixClassKey && not is_enumeration_or_single = bog_out single_nullary_why
359 | any isExistentialDataCon (tyConDataCons tycon) = Just (existentialErr clas tycon)
360 | otherwise = Nothing
362 is_enumeration = isEnumerationTyCon tycon
363 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
364 is_enumeration_or_single = is_enumeration || is_single_con
366 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
367 nullary_why = SLIT("data type with all nullary constructors expected")
369 bog_out why = Just (derivingThingErr clas tycon why)
372 %************************************************************************
374 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
376 %************************************************************************
378 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
379 terms, which is the final correct RHS for the corresponding original
383 Each (k,TyVarTy tv) in a solution constrains only a type
387 The (k,TyVarTy tv) pairs in a solution are canonically
388 ordered by sorting on type varible, tv, (major key) and then class, k,
393 solveDerivEqns :: InstEnv
395 -> TcM [DFunId] -- Solns in same order as eqns.
396 -- This bunch is Absolutely minimal...
398 solveDerivEqns inst_env_in orig_eqns
399 = iterateDeriv initial_solutions
401 -- The initial solutions for the equations claim that each
402 -- instance has an empty context; this solution is certainly
403 -- in canonical form.
404 initial_solutions :: [DerivSoln]
405 initial_solutions = [ [] | _ <- orig_eqns ]
407 ------------------------------------------------------------------
408 -- iterateDeriv calculates the next batch of solutions,
409 -- compares it with the current one; finishes if they are the
410 -- same, otherwise recurses with the new solutions.
411 -- It fails if any iteration fails
412 iterateDeriv :: [DerivSoln] ->TcM [DFunId]
413 iterateDeriv current_solns
414 = checkNoErrsTc (iterateOnce current_solns)
415 `thenTc` \ (new_dfuns, new_solns) ->
416 if (current_solns == new_solns) then
419 iterateDeriv new_solns
421 ------------------------------------------------------------------
422 iterateOnce current_solns
423 = -- Extend the inst info from the explicit instance decls
424 -- with the current set of solutions, giving a
425 getDOptsTc `thenTc` \ dflags ->
426 let (new_dfuns, inst_env) =
427 add_solns dflags inst_env_in orig_eqns current_solns
430 tcSetInstEnv inst_env (
431 listTc [ tcAddErrCtxt (derivCtxt tc) $
432 tcSimplifyThetas deriv_rhs
433 | (_, _,tc,_,deriv_rhs) <- orig_eqns ]
434 ) `thenTc` \ next_solns ->
436 -- Canonicalise the solutions, so they compare nicely
437 let canonicalised_next_solns = [ sortLt (<) next_soln | next_soln <- next_solns ]
439 returnTc (new_dfuns, canonicalised_next_solns)
443 add_solns :: DynFlags
444 -> InstEnv -- The global, non-derived ones
445 -> [DerivEqn] -> [DerivSoln]
446 -> ([DFunId], InstEnv)
447 -- the eqns and solns move "in lockstep"; we have the eqns
448 -- because we need the LHS info for addClassInstance.
450 add_solns dflags inst_env_in eqns solns
451 = (new_dfuns, inst_env)
453 new_dfuns = zipWithEqual "add_solns" mk_deriv_dfun eqns solns
454 (inst_env, _) = extendInstEnv dflags inst_env_in new_dfuns
455 -- Ignore the errors about duplicate instances.
456 -- We don't want repeated error messages
457 -- They'll appear later, when we do the top-level extendInstEnvs
459 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
460 = mkDictFunId dfun_name clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
461 (map pair2PredType theta)
463 pair2PredType (clas, tautypes) = Class clas tautypes
466 %************************************************************************
468 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
470 %************************************************************************
472 After all the trouble to figure out the required context for the
473 derived instance declarations, all that's left is to chug along to
474 produce them. They will then be shoved into @tcInstDecls2@, which
475 will do all its usual business.
477 There are lots of possibilities for code to generate. Here are
478 various general remarks.
483 We want derived instances of @Eq@ and @Ord@ (both v common) to be
484 ``you-couldn't-do-better-by-hand'' efficient.
487 Deriving @Show@---also pretty common--- should also be reasonable good code.
490 Deriving for the other classes isn't that common or that big a deal.
497 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
500 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
503 We {\em normally} generate code only for the non-defaulted methods;
504 there are some exceptions for @Eq@ and (especially) @Ord@...
507 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
508 constructor's numeric (@Int#@) tag. These are generated by
509 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
510 these is around is given by @hasCon2TagFun@.
512 The examples under the different sections below will make this
516 Much less often (really just for deriving @Ix@), we use a
517 @_tag2con_<tycon>@ function. See the examples.
520 We use the renamer!!! Reason: we're supposed to be
521 producing @RenamedMonoBinds@ for the methods, but that means
522 producing correctly-uniquified code on the fly. This is entirely
523 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
524 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
525 the renamer. What a great hack!
529 -- Generate the method bindings for the required instance
530 -- (paired with class name, as we need that when generating dict
532 gen_bind :: (Name -> Maybe Fixity) -> DFunId -> RdrNameMonoBinds
533 gen_bind get_fixity dfun
534 | not (isLocallyDefined tycon) = EmptyMonoBinds
535 | clas `hasKey` showClassKey = gen_Show_binds get_fixity tycon
536 | clas `hasKey` readClassKey = gen_Read_binds get_fixity tycon
538 = assoc "gen_bind:bad derived class"
539 [(eqClassKey, gen_Eq_binds)
540 ,(ordClassKey, gen_Ord_binds)
541 ,(enumClassKey, gen_Enum_binds)
542 ,(boundedClassKey, gen_Bounded_binds)
543 ,(ixClassKey, gen_Ix_binds)
548 (clas, tycon) = simpleDFunClassTyCon dfun
552 %************************************************************************
554 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
556 %************************************************************************
561 con2tag_Foo :: Foo ... -> Int#
562 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
563 maxtag_Foo :: Int -- ditto (NB: not unboxed)
566 We have a @con2tag@ function for a tycon if:
569 We're deriving @Eq@ and the tycon has nullary data constructors.
572 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
576 We have a @tag2con@ function for a tycon if:
579 We're deriving @Enum@, or @Ix@ (enum type only???)
582 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
585 gen_taggery_Names :: [DFunId]
586 -> TcM [(RdrName, -- for an assoc list
587 TyCon, -- related tycon
590 gen_taggery_Names dfuns
591 = foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
592 foldlTc do_tag2con names_so_far tycons_of_interest
594 all_CTs = map simpleDFunClassTyCon dfuns
595 all_tycons = map snd all_CTs
596 (tycons_of_interest, _) = removeDups compare all_tycons
598 do_con2tag acc_Names tycon
599 | isDataTyCon tycon &&
600 ((we_are_deriving eqClassKey tycon
601 && any isNullaryDataCon (tyConDataCons tycon))
602 || (we_are_deriving ordClassKey tycon
603 && not (maybeToBool (maybeTyConSingleCon tycon)))
604 || (we_are_deriving enumClassKey tycon)
605 || (we_are_deriving ixClassKey tycon))
607 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
612 do_tag2con acc_Names tycon
613 | isDataTyCon tycon &&
614 (we_are_deriving enumClassKey tycon ||
615 we_are_deriving ixClassKey tycon
616 && isEnumerationTyCon tycon)
617 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
618 : (maxtag_RDR tycon, tycon, GenMaxTag)
623 we_are_deriving clas_key tycon
624 = is_in_eqns clas_key tycon all_CTs
626 is_in_eqns clas_key tycon [] = False
627 is_in_eqns clas_key tycon ((c,t):cts)
628 = (clas_key == classKey c && tycon == t)
629 || is_in_eqns clas_key tycon cts
633 derivingThingErr :: Class -> TyCon -> FAST_STRING -> Message
635 derivingThingErr clas tycon why
636 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr clas)],
637 hsep [ptext SLIT("for the type"), quotes (ppr tycon)],
640 existentialErr clas tycon
641 = sep [ptext SLIT("Can't derive any instances for type") <+> quotes (ppr tycon),
642 ptext SLIT("because it has existentially-quantified constructor(s)")]
645 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)