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(..), TyClDecl(..),
14 collectLocatedMonoBinders )
15 import RdrHsSyn ( RdrNameMonoBinds )
16 import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds, RenamedTyClDecl, RenamedHsPred )
17 import CmdLineOpts ( DynFlag(..) )
20 import TcEnv ( tcSetInstEnv, newDFunName, InstInfo(..), pprInstInfo,
21 tcLookupTyCon, tcExtendTyVarEnv
23 import TcGenDeriv -- Deriv stuff
24 import InstEnv ( InstEnv, simpleDFunClassTyCon, extendInstEnv )
25 import TcMonoType ( tcHsPred )
26 import TcSimplify ( tcSimplifyDeriv )
28 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
29 import RnEnv ( bindLocatedLocalsRn )
30 import RnMonad ( renameDerivedCode, thenRn, mapRn, returnRn )
31 import HscTypes ( DFunId, PersistentRenamerState, FixityEnv )
33 import BasicTypes ( NewOrData(..) )
34 import Class ( className, classKey, classTyVars, Class )
35 import ErrUtils ( dumpIfSet_dyn )
36 import MkId ( mkDictFunId )
37 import DataCon ( dataConRepArgTys, isNullaryDataCon, isExistentialDataCon )
38 import PrelInfo ( needsDataDeclCtxtClassKeys )
39 import Maybes ( maybeToBool, catMaybes )
40 import Module ( Module )
41 import Name ( Name, getSrcLoc, nameUnique )
42 import RdrName ( RdrName )
44 import TyCon ( tyConTyVars, tyConDataCons, tyConArity, newTyConRep,
45 tyConTheta, maybeTyConSingleCon, isDataTyCon,
46 isEnumerationTyCon, TyCon
48 import TcType ( TcType, ThetaType, mkTyVarTys, mkTyConApp, getClassPredTys_maybe,
49 isUnLiftedType, mkClassPred, tyVarsOfTypes, tcSplitFunTys,
50 tcSplitTyConApp_maybe, tcEqTypes )
51 import Var ( TyVar, tyVarKind )
52 import VarSet ( mkVarSet, subVarSet )
54 import Util ( zipWithEqual, sortLt, notNull )
55 import ListSetOps ( removeDups, assoc )
57 import Maybe ( isJust )
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 = (Name, Class, TyCon, [TyVar], DerivRhs)
146 -- The Name is the name for the DFun we'll build
147 -- The tyvars bind all the variables in the RHS
149 pprDerivEqn (n,c,tc,tvs,rhs)
150 = parens (hsep [ppr n, ppr c, ppr tc, ppr tvs] <+> equals <+> ppr rhs)
152 type DerivRhs = ThetaType
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
180 FURTHER NOTE ADDED March 2002. In fact, Haskell98 now requires that
181 pattern matching against a constructor from a data type with a context
182 gives rise to the constraints for that context -- or at least the thinned
183 version. So now all classes are "offending".
187 %************************************************************************
189 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
191 %************************************************************************
194 tcDeriving :: PersistentRenamerState
195 -> Module -- name of module under scrutiny
196 -> InstEnv -- What we already know about instances
197 -> FixityEnv -- used in deriving Show and Read
198 -> [RenamedTyClDecl] -- All type constructors
199 -> TcM ([InstInfo], -- The generated "instance decls".
200 RenamedHsBinds) -- Extra generated bindings
202 tcDeriving prs mod inst_env get_fixity tycl_decls
203 = recoverTc (returnTc ([], EmptyBinds)) $
204 getDOptsTc `thenNF_Tc` \ dflags ->
206 -- Fish the "deriving"-related information out of the TcEnv
207 -- and make the necessary "equations".
208 makeDerivEqns tycl_decls `thenTc` \ (ordinary_eqns, newtype_inst_info) ->
210 -- Add the newtype-derived instances to the inst env
211 -- before tacking the "ordinary" ones
212 inst_env1 = extend_inst_env dflags inst_env
213 (map iDFunId newtype_inst_info)
215 deriveOrdinaryStuff mod prs inst_env1 get_fixity
216 ordinary_eqns `thenTc` \ (ordinary_inst_info, binds) ->
218 inst_info = newtype_inst_info ++ ordinary_inst_info
221 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
222 (ddump_deriving inst_info binds)) `thenTc_`
224 returnTc (inst_info, binds)
227 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
228 ddump_deriving inst_infos extra_binds
229 = vcat (map ppr_info inst_infos) $$ ppr extra_binds
231 ppr_info inst_info = pprInstInfo inst_info $$
232 nest 4 (ppr (iBinds inst_info))
233 -- pprInstInfo doesn't print much: only the type
235 -----------------------------------------
236 deriveOrdinaryStuff mod prs inst_env_in get_fixity [] -- Short cut
237 = returnTc ([], EmptyBinds)
239 deriveOrdinaryStuff mod prs inst_env_in get_fixity eqns
240 = -- Take the equation list and solve it, to deliver a list of
241 -- solutions, a.k.a. the contexts for the instance decls
242 -- required for the corresponding equations.
243 solveDerivEqns inst_env_in eqns `thenTc` \ new_dfuns ->
245 -- Now augment the InstInfos, adding in the rather boring
246 -- actual-code-to-do-the-methods binds. We may also need to
247 -- generate extra not-one-inst-decl-specific binds, notably
248 -- "con2tag" and/or "tag2con" functions. We do these
250 gen_taggery_Names new_dfuns `thenTc` \ nm_alist_etc ->
252 tcGetEnv `thenNF_Tc` \ env ->
253 getDOptsTc `thenNF_Tc` \ dflags ->
255 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
256 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
257 method_binds_s = map (gen_bind get_fixity) new_dfuns
258 mbinders = collectLocatedMonoBinders extra_mbinds
260 -- Rename to get RenamedBinds.
261 -- The only tricky bit is that the extra_binds must scope over the
262 -- method bindings for the instances.
263 (rn_method_binds_s, rn_extra_binds)
264 = renameDerivedCode dflags mod prs (
265 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
266 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
267 mapRn rn_meths method_binds_s `thenRn` \ rn_method_binds_s ->
268 returnRn (rn_method_binds_s, rn_extra_binds)
270 new_inst_infos = zipWith gen_inst_info new_dfuns rn_method_binds_s
272 returnTc (new_inst_infos, rn_extra_binds)
275 -- Make a Real dfun instead of the dummy one we have so far
276 gen_inst_info :: DFunId -> RenamedMonoBinds -> InstInfo
277 gen_inst_info dfun binds
278 = InstInfo { iDFunId = dfun, iBinds = binds, iPrags = [] }
280 rn_meths (cls, meths) = rnMethodBinds cls [] meths `thenRn` \ (meths', _) ->
281 returnRn meths' -- Ignore the free vars returned
285 %************************************************************************
287 \subsection[TcDeriv-eqns]{Forming the equations}
289 %************************************************************************
291 @makeDerivEqns@ fishes around to find the info about needed derived
292 instances. Complicating factors:
295 We can only derive @Enum@ if the data type is an enumeration
296 type (all nullary data constructors).
299 We can only derive @Ix@ if the data type is an enumeration {\em
300 or} has just one data constructor (e.g., tuples).
303 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
307 makeDerivEqns :: [RenamedTyClDecl]
308 -> TcM ([DerivEqn], -- Ordinary derivings
309 [InstInfo]) -- Special newtype derivings
311 makeDerivEqns tycl_decls
312 = mapAndUnzipTc mk_eqn derive_these `thenTc` \ (maybe_ordinaries, maybe_newtypes) ->
313 returnTc (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
315 ------------------------------------------------------------------
316 derive_these :: [(NewOrData, Name, RenamedHsPred)]
317 -- Find the (nd, TyCon, Pred) pairs that must be `derived'
318 -- NB: only source-language decls have deriving, no imported ones do
319 derive_these = [ (nd, tycon, pred)
320 | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
323 ------------------------------------------------------------------
324 mk_eqn :: (NewOrData, Name, RenamedHsPred) -> NF_TcM (Maybe DerivEqn, Maybe InstInfo)
325 -- We swizzle the tyvars and datacons out of the tycon
326 -- to make the rest of the equation
328 mk_eqn (new_or_data, tycon_name, pred)
329 = tcLookupTyCon tycon_name `thenNF_Tc` \ tycon ->
330 tcAddSrcLoc (getSrcLoc tycon) $
331 tcAddErrCtxt (derivCtxt Nothing tycon) $
332 tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
333 -- the type variables for the type constructor
334 tcHsPred pred `thenTc` \ pred' ->
335 case getClassPredTys_maybe pred' of
336 Nothing -> bale_out (malformedPredErr tycon pred)
337 Just (clas, tys) -> mk_eqn_help new_or_data tycon clas tys
339 ------------------------------------------------------------------
340 mk_eqn_help DataType tycon clas tys
341 | Just err <- chk_out clas tycon tys
342 = bale_out (derivingThingErr clas tys tycon tyvars err)
344 = new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
345 returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
347 tyvars = tyConTyVars tycon
348 data_cons = tyConDataCons tycon
349 constraints = extra_constraints ++
350 [ mkClassPred clas [arg_ty]
351 | data_con <- tyConDataCons tycon,
352 arg_ty <- dataConRepArgTys data_con,
353 -- Use the same type variables
354 -- as the type constructor,
355 -- hence no need to instantiate
356 not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
359 -- "extra_constraints": see notes above about contexts on data decls
360 extra_constraints = tyConTheta tycon
362 -- | offensive_class = tyConTheta tycon
364 -- offensive_class = classKey clas `elem` needsDataDeclCtxtClassKeys
367 mk_eqn_help NewType tycon clas tys
368 = doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
369 if can_derive_via_isomorphism && (gla_exts || standard_instance) then
370 -- Go ahead and use the isomorphism
371 new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
372 returnTc (Nothing, Just (NewTypeDerived (mk_dfun dfun_name)))
374 if standard_instance then
375 mk_eqn_help DataType tycon clas [] -- Go via bale-out route
377 bale_out cant_derive_err
379 -- Here is the plan for newtype derivings. We see
380 -- newtype T a1...an = T (t ak...an) deriving (C1...Cm)
381 -- where aj...an do not occur free in t, and the Ci are *partial applications* of
382 -- classes with the last parameter missing
384 -- We generate the instances
385 -- instance Ci (t ak...aj) => Ci (T a1...aj)
386 -- where T a1...aj is the partial application of the LHS of the correct kind
388 -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
390 kind = tyVarKind (last (classTyVars clas))
391 -- Kind of the thing we want to instance
392 -- e.g. argument kind of Monad, *->*
394 (arg_kinds, _) = tcSplitFunTys kind
395 n_args_to_drop = length arg_kinds
396 -- Want to drop 1 arg from (T s a) and (ST s a)
397 -- to get instance Monad (ST s) => Monad (T s)
399 (tyvars, rep_ty) = newTyConRep tycon
400 maybe_rep_app = tcSplitTyConApp_maybe rep_ty
401 Just (rep_tc, rep_ty_args) = maybe_rep_app
403 n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
404 tyvars_to_drop = drop n_tyvars_to_keep tyvars
405 tyvars_to_keep = take n_tyvars_to_keep tyvars
407 n_args_to_keep = tyConArity rep_tc - n_args_to_drop
408 args_to_drop = drop n_args_to_keep rep_ty_args
409 args_to_keep = take n_args_to_keep rep_ty_args
411 ctxt_pred = mkClassPred clas (tys ++ [mkTyConApp rep_tc args_to_keep])
413 mk_dfun dfun_name = mkDictFunId dfun_name clas tyvars
414 (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)] )
417 -- We can only do this newtype deriving thing if:
418 standard_instance = null tys && classKey clas `elem` derivableClassKeys
420 can_derive_via_isomorphism
421 = not (clas `hasKey` readClassKey) -- Never derive Read,Show this way
422 && not (clas `hasKey` showClassKey)
423 && n_tyvars_to_keep >= 0 -- Well kinded;
424 -- eg not: newtype T = T Int deriving( Monad )
425 && isJust maybe_rep_app -- The rep type is a type constructor app
426 && n_args_to_keep >= 0 -- Well kinded:
427 -- eg not: newtype T a = T Int deriving( Monad )
428 && eta_ok -- Eta reduction works
430 -- Check that eta reduction is OK
431 -- (a) the dropped-off args are identical
432 -- (b) the remaining type args mention
433 -- only the remaining type variables
434 eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
435 && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
437 cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
438 (ptext SLIT("too hard for cunning newtype deriving"))
440 bale_out err = addErrTc err `thenNF_Tc_` returnNF_Tc (Nothing, Nothing)
442 ------------------------------------------------------------------
443 chk_out :: Class -> TyCon -> [TcType] -> Maybe SDoc
444 chk_out clas tycon tys
445 | notNull tys = Just non_std_why
446 | not (getUnique clas `elem` derivableClassKeys) = Just non_std_why
447 | clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
448 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
449 | clas `hasKey` ixClassKey && not is_enumeration_or_single = Just single_nullary_why
450 | null data_cons = Just no_cons_why
451 | any isExistentialDataCon data_cons = Just existential_why
452 | otherwise = Nothing
454 data_cons = tyConDataCons tycon
455 is_enumeration = isEnumerationTyCon tycon
456 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
457 is_enumeration_or_single = is_enumeration || is_single_con
459 single_nullary_why = ptext SLIT("one constructor data type or type with all nullary constructors expected")
460 nullary_why = ptext SLIT("data type with all nullary constructors expected")
461 no_cons_why = ptext SLIT("type has no data constructors")
462 non_std_why = ptext SLIT("not a derivable class")
463 existential_why = ptext SLIT("it has existentially-quantified constructor(s)")
465 new_dfun_name clas tycon -- Just a simple wrapper
466 = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
467 -- The type passed to newDFunName is only used to generate
468 -- a suitable string; hence the empty type arg list
471 %************************************************************************
473 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
475 %************************************************************************
477 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
478 terms, which is the final correct RHS for the corresponding original
482 Each (k,TyVarTy tv) in a solution constrains only a type
486 The (k,TyVarTy tv) pairs in a solution are canonically
487 ordered by sorting on type varible, tv, (major key) and then class, k,
492 solveDerivEqns :: InstEnv
494 -> TcM [DFunId] -- Solns in same order as eqns.
495 -- This bunch is Absolutely minimal...
497 solveDerivEqns inst_env_in orig_eqns
498 = iterateDeriv 1 initial_solutions
500 -- The initial solutions for the equations claim that each
501 -- instance has an empty context; this solution is certainly
502 -- in canonical form.
503 initial_solutions :: [DerivSoln]
504 initial_solutions = [ [] | _ <- orig_eqns ]
506 ------------------------------------------------------------------
507 -- iterateDeriv calculates the next batch of solutions,
508 -- compares it with the current one; finishes if they are the
509 -- same, otherwise recurses with the new solutions.
510 -- It fails if any iteration fails
511 iterateDeriv :: Int -> [DerivSoln] ->TcM [DFunId]
512 iterateDeriv n current_solns
513 | n > 20 -- Looks as if we are in an infinite loop
514 -- This can happen if we have -fallow-undecidable-instances
515 -- (See TcSimplify.tcSimplifyDeriv.)
516 = pprPanic "solveDerivEqns: probable loop"
517 (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
519 = getDOptsTc `thenNF_Tc` \ dflags ->
521 dfuns = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
522 inst_env = extend_inst_env dflags inst_env_in dfuns
525 -- Extend the inst info from the explicit instance decls
526 -- with the current set of solutions, and simplify each RHS
527 tcSetInstEnv inst_env $
528 mapTc gen_soln orig_eqns
529 ) `thenTc` \ new_solns ->
530 if (current_solns == new_solns) then
533 iterateDeriv (n+1) new_solns
535 ------------------------------------------------------------------
537 gen_soln (_, clas, tc,tyvars,deriv_rhs)
538 = tcAddSrcLoc (getSrcLoc tc) $
539 tcAddErrCtxt (derivCtxt (Just clas) tc) $
540 tcSimplifyDeriv tyvars deriv_rhs `thenTc` \ theta ->
541 returnTc (sortLt (<) theta) -- Canonicalise before returning the soluction
545 extend_inst_env dflags inst_env new_dfuns
548 (new_inst_env, _errs) = extendInstEnv dflags inst_env new_dfuns
549 -- Ignore the errors about duplicate instances.
550 -- We don't want repeated error messages
551 -- They'll appear later, when we do the top-level extendInstEnvs
553 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
554 = mkDictFunId dfun_name clas tyvars
555 [mkTyConApp tycon (mkTyVarTys tyvars)]
559 %************************************************************************
561 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
563 %************************************************************************
565 After all the trouble to figure out the required context for the
566 derived instance declarations, all that's left is to chug along to
567 produce them. They will then be shoved into @tcInstDecls2@, which
568 will do all its usual business.
570 There are lots of possibilities for code to generate. Here are
571 various general remarks.
576 We want derived instances of @Eq@ and @Ord@ (both v common) to be
577 ``you-couldn't-do-better-by-hand'' efficient.
580 Deriving @Show@---also pretty common--- should also be reasonable good code.
583 Deriving for the other classes isn't that common or that big a deal.
590 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
593 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
596 We {\em normally} generate code only for the non-defaulted methods;
597 there are some exceptions for @Eq@ and (especially) @Ord@...
600 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
601 constructor's numeric (@Int#@) tag. These are generated by
602 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
603 these is around is given by @hasCon2TagFun@.
605 The examples under the different sections below will make this
609 Much less often (really just for deriving @Ix@), we use a
610 @_tag2con_<tycon>@ function. See the examples.
613 We use the renamer!!! Reason: we're supposed to be
614 producing @RenamedMonoBinds@ for the methods, but that means
615 producing correctly-uniquified code on the fly. This is entirely
616 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
617 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
618 the renamer. What a great hack!
622 -- Generate the method bindings for the required instance
623 -- (paired with class name, as we need that when renaming
625 gen_bind :: FixityEnv -> DFunId -> (Name, RdrNameMonoBinds)
626 gen_bind get_fixity dfun
629 cls_nm = className clas
630 (clas, tycon) = simpleDFunClassTyCon dfun
632 binds = assoc "gen_bind:bad derived class" gen_list
633 (nameUnique cls_nm) tycon
635 gen_list = [(eqClassKey, gen_Eq_binds)
636 ,(ordClassKey, gen_Ord_binds)
637 ,(enumClassKey, gen_Enum_binds)
638 ,(boundedClassKey, gen_Bounded_binds)
639 ,(ixClassKey, gen_Ix_binds)
640 ,(showClassKey, gen_Show_binds get_fixity)
641 ,(readClassKey, gen_Read_binds get_fixity)
646 %************************************************************************
648 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
650 %************************************************************************
655 con2tag_Foo :: Foo ... -> Int#
656 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
657 maxtag_Foo :: Int -- ditto (NB: not unlifted)
660 We have a @con2tag@ function for a tycon if:
663 We're deriving @Eq@ and the tycon has nullary data constructors.
666 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
670 We have a @tag2con@ function for a tycon if:
673 We're deriving @Enum@, or @Ix@ (enum type only???)
676 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
679 gen_taggery_Names :: [DFunId]
680 -> TcM [(RdrName, -- for an assoc list
681 TyCon, -- related tycon
684 gen_taggery_Names dfuns
685 = foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
686 foldlTc do_tag2con names_so_far tycons_of_interest
688 all_CTs = map simpleDFunClassTyCon dfuns
689 all_tycons = map snd all_CTs
690 (tycons_of_interest, _) = removeDups compare all_tycons
692 do_con2tag acc_Names tycon
693 | isDataTyCon tycon &&
694 ((we_are_deriving eqClassKey tycon
695 && any isNullaryDataCon (tyConDataCons tycon))
696 || (we_are_deriving ordClassKey tycon
697 && not (maybeToBool (maybeTyConSingleCon tycon)))
698 || (we_are_deriving enumClassKey tycon)
699 || (we_are_deriving ixClassKey tycon))
701 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
706 do_tag2con acc_Names tycon
707 | isDataTyCon tycon &&
708 (we_are_deriving enumClassKey tycon ||
709 we_are_deriving ixClassKey tycon
710 && isEnumerationTyCon tycon)
711 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
712 : (maxtag_RDR tycon, tycon, GenMaxTag)
717 we_are_deriving clas_key tycon
718 = is_in_eqns clas_key tycon all_CTs
720 is_in_eqns clas_key tycon [] = False
721 is_in_eqns clas_key tycon ((c,t):cts)
722 = (clas_key == classKey c && tycon == t)
723 || is_in_eqns clas_key tycon cts
727 derivingThingErr clas tys tycon tyvars why
728 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
731 pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
733 malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
735 derivCtxt :: Maybe Class -> TyCon -> SDoc
736 derivCtxt maybe_cls tycon
737 = ptext SLIT("When deriving") <+> cls <+> ptext SLIT("for type") <+> quotes (ppr tycon)
739 cls = case maybe_cls of
740 Nothing -> ptext SLIT("instances")
741 Just c -> ptext SLIT("the") <+> quotes (ppr c) <+> ptext SLIT("instance")