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(..), DynFlags )
20 import TcEnv ( tcSetInstEnv, newDFunName, InstInfo(..), pprInstInfo,
21 tcLookupClass, tcLookupTyCon, tcExtendTyVarEnv
23 import TcGenDeriv -- Deriv stuff
24 import InstEnv ( InstEnv, simpleDFunClassTyCon, extendInstEnv )
25 import TcMonoType ( tcHsPred )
26 import TcSimplify ( tcSimplifyThetas )
28 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
29 import RnEnv ( bindLocatedLocalsRn )
30 import RnMonad ( renameDerivedCode, thenRn, mapRn, returnRn )
31 import HscTypes ( DFunId, PersistentRenamerState )
33 import BasicTypes ( Fixity, NewOrData(..) )
34 import Class ( className, classKey, classTyVars, Class )
35 import ErrUtils ( dumpIfSet_dyn, Message )
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, isRecursiveTyCon
48 import TcType ( TcType, ThetaType, mkTyVarTys, mkTyConApp, getClassPredTys_maybe,
49 isUnLiftedType, mkClassPred, tyVarsOfTypes, tcSplitFunTys,
50 tcSplitTyConApp_maybe )
51 import Var ( TyVar, tyVarKind )
52 import VarSet ( mkVarSet, subVarSet )
54 import Util ( zipWithEqual, sortLt )
55 import ListSetOps ( removeDups, assoc )
57 import Maybe ( isJust )
59 import FastString ( FastString )
62 %************************************************************************
64 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
66 %************************************************************************
70 data T a b = C1 (Foo a) (Bar b)
75 [NOTE: See end of these comments for what to do with
76 data (C a, D b) => T a b = ...
79 We want to come up with an instance declaration of the form
81 instance (Ping a, Pong b, ...) => Eq (T a b) where
84 It is pretty easy, albeit tedious, to fill in the code "...". The
85 trick is to figure out what the context for the instance decl is,
86 namely @Ping@, @Pong@ and friends.
88 Let's call the context reqd for the T instance of class C at types
89 (a,b, ...) C (T a b). Thus:
91 Eq (T a b) = (Ping a, Pong b, ...)
93 Now we can get a (recursive) equation from the @data@ decl:
95 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
96 u Eq (T b a) u Eq Int -- From C2
97 u Eq (T a a) -- From C3
99 Foo and Bar may have explicit instances for @Eq@, in which case we can
100 just substitute for them. Alternatively, either or both may have
101 their @Eq@ instances given by @deriving@ clauses, in which case they
102 form part of the system of equations.
104 Now all we need do is simplify and solve the equations, iterating to
105 find the least fixpoint. Notice that the order of the arguments can
106 switch around, as here in the recursive calls to T.
108 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
112 Eq (T a b) = {} -- The empty set
115 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
116 u Eq (T b a) u Eq Int -- From C2
117 u Eq (T a a) -- From C3
119 After simplification:
120 = Eq a u Ping b u {} u {} u {}
125 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
126 u Eq (T b a) u Eq Int -- From C2
127 u Eq (T a a) -- From C3
129 After simplification:
134 = Eq a u Ping b u Eq b u Ping a
136 The next iteration gives the same result, so this is the fixpoint. We
137 need to make a canonical form of the RHS to ensure convergence. We do
138 this by simplifying the RHS to a form in which
140 - the classes constrain only tyvars
141 - the list is sorted by tyvar (major key) and then class (minor key)
142 - no duplicates, of course
144 So, here are the synonyms for the ``equation'' structures:
147 type DerivEqn = (Name, Class, TyCon, [TyVar], DerivRhs)
148 -- The Name is the name for the DFun we'll build
149 -- The tyvars bind all the variables in the RHS
151 type DerivRhs = 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 -> (Name -> Maybe Fixity) -- used in deriving Show and Read
191 -> [RenamedTyClDecl] -- All type constructors
192 -> TcM ([InstInfo], -- The generated "instance decls".
193 RenamedHsBinds) -- Extra generated bindings
195 tcDeriving prs mod inst_env get_fixity tycl_decls
196 = recoverTc (returnTc ([], EmptyBinds)) $
198 -- Fish the "deriving"-related information out of the TcEnv
199 -- and make the necessary "equations".
200 makeDerivEqns tycl_decls `thenTc` \ (ordinary_eqns, inst_info2) ->
202 deriveOrdinaryStuff mod prs inst_env get_fixity
203 ordinary_eqns `thenTc` \ (inst_info1, binds) ->
205 inst_info = inst_info2 ++ inst_info1 -- info2 usually empty
208 getDOptsTc `thenNF_Tc` \ dflags ->
209 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
210 (ddump_deriving inst_info binds)) `thenTc_`
212 returnTc (inst_info, binds)
215 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
216 ddump_deriving inst_infos extra_binds
217 = vcat (map pprInstInfo inst_infos) $$ ppr extra_binds
220 -----------------------------------------
221 deriveOrdinaryStuff mod prs inst_env_in get_fixity [] -- Short cut
222 = returnTc ([], EmptyBinds)
224 deriveOrdinaryStuff mod prs inst_env_in get_fixity eqns
225 = -- Take the equation list and solve it, to deliver a list of
226 -- solutions, a.k.a. the contexts for the instance decls
227 -- required for the corresponding equations.
228 solveDerivEqns inst_env_in eqns `thenTc` \ new_dfuns ->
230 -- Now augment the InstInfos, adding in the rather boring
231 -- actual-code-to-do-the-methods binds. We may also need to
232 -- generate extra not-one-inst-decl-specific binds, notably
233 -- "con2tag" and/or "tag2con" functions. We do these
235 gen_taggery_Names new_dfuns `thenTc` \ nm_alist_etc ->
237 tcGetEnv `thenNF_Tc` \ env ->
238 getDOptsTc `thenNF_Tc` \ dflags ->
240 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
241 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
242 method_binds_s = map (gen_bind get_fixity) new_dfuns
243 mbinders = collectLocatedMonoBinders extra_mbinds
245 -- Rename to get RenamedBinds.
246 -- The only tricky bit is that the extra_binds must scope over the
247 -- method bindings for the instances.
248 (rn_method_binds_s, rn_extra_binds)
249 = renameDerivedCode dflags mod prs (
250 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
251 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
252 mapRn rn_meths method_binds_s `thenRn` \ rn_method_binds_s ->
253 returnRn (rn_method_binds_s, rn_extra_binds)
255 new_inst_infos = zipWith gen_inst_info new_dfuns rn_method_binds_s
257 returnTc (new_inst_infos, rn_extra_binds)
260 -- Make a Real dfun instead of the dummy one we have so far
261 gen_inst_info :: DFunId -> RenamedMonoBinds -> InstInfo
262 gen_inst_info dfun binds
263 = InstInfo { iDFunId = dfun, iBinds = binds, iPrags = [] }
265 rn_meths (cls, meths) = rnMethodBinds cls [] meths `thenRn` \ (meths', _) ->
266 returnRn meths' -- Ignore the free vars returned
270 %************************************************************************
272 \subsection[TcDeriv-eqns]{Forming the equations}
274 %************************************************************************
276 @makeDerivEqns@ fishes around to find the info about needed derived
277 instances. Complicating factors:
280 We can only derive @Enum@ if the data type is an enumeration
281 type (all nullary data constructors).
284 We can only derive @Ix@ if the data type is an enumeration {\em
285 or} has just one data constructor (e.g., tuples).
288 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
292 makeDerivEqns :: [RenamedTyClDecl]
293 -> TcM ([DerivEqn], -- Ordinary derivings
294 [InstInfo]) -- Special newtype derivings
296 makeDerivEqns tycl_decls
297 = mapAndUnzipTc mk_eqn derive_these `thenTc` \ (maybe_ordinaries, maybe_newtypes) ->
298 returnTc (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
300 ------------------------------------------------------------------
301 derive_these :: [(NewOrData, Name, RenamedHsPred)]
302 -- Find the (nd, TyCon, Pred) pairs that must be `derived'
303 -- NB: only source-language decls have deriving, no imported ones do
304 derive_these = [ (nd, tycon, pred)
305 | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
308 ------------------------------------------------------------------
309 mk_eqn :: (NewOrData, Name, RenamedHsPred) -> NF_TcM (Maybe DerivEqn, Maybe InstInfo)
310 -- We swizzle the tyvars and datacons out of the tycon
311 -- to make the rest of the equation
313 mk_eqn (new_or_data, tycon_name, pred)
314 = tcLookupTyCon tycon_name `thenNF_Tc` \ tycon ->
315 tcAddSrcLoc (getSrcLoc tycon) $
316 tcAddErrCtxt (derivCtxt tycon) $
317 tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
318 -- the type variables for the type constructor
319 tcHsPred pred `thenTc` \ pred' ->
320 case getClassPredTys_maybe pred' of
321 Nothing -> bale_out (malformedPredErr tycon pred)
322 Just (clas, tys) -> mk_eqn_help new_or_data tycon clas tys
324 ------------------------------------------------------------------
325 mk_eqn_help DataType tycon clas tys
326 | Just err <- chk_out clas tycon tys
327 = bale_out (derivingThingErr clas tys tycon tyvars err)
329 = new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
330 returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
332 tyvars = tyConTyVars tycon
333 data_cons = tyConDataCons tycon
334 constraints = extra_constraints ++
335 [ mkClassPred clas [arg_ty]
336 | data_con <- tyConDataCons tycon,
337 arg_ty <- dataConRepArgTys data_con,
338 -- Use the same type variables
339 -- as the type constructor,
340 -- hence no need to instantiate
341 not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
345 -- "extra_constraints": see notes above about contexts on data decls
346 extra_constraints | offensive_class = tyConTheta tycon
349 offensive_class = classKey clas `elem` needsDataDeclCtxtClassKeys
352 mk_eqn_help NewType tycon clas tys
353 = doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
354 if can_derive_via_isomorphism && (gla_exts || standard_instance) then
355 -- Go ahead and use the isomorphism
356 new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
357 returnTc (Nothing, Just (NewTypeDerived (mk_dfun dfun_name)))
359 if standard_instance then
360 mk_eqn_help DataType tycon clas [] -- Go via bale-out route
362 bale_out cant_derive_err
364 -- Here is the plan for newtype derivings. We see
365 -- newtype T a1...an = T (t ak...an) deriving (C1...Cm)
366 -- where aj...an do not occur free in t, and the Ci are *partial applications* of
367 -- classes with the last parameter missing
369 -- We generate the instances
370 -- instance Ci (t ak...aj) => Ci (T a1...aj)
371 -- where T a1...aj is the partial application of the LHS of the correct kind
373 -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
375 kind = tyVarKind (last (classTyVars clas))
376 -- Kind of the thing we want to instance
377 -- e.g. argument kind of Monad, *->*
379 (arg_kinds, _) = tcSplitFunTys kind
380 n_args_to_drop = length arg_kinds
381 -- Want to drop 1 arg from (T s a) and (ST s a)
382 -- to get instance Monad (ST s) => Monad (T s)
384 (tyvars, rep_ty) = newTyConRep tycon
385 maybe_rep_app = tcSplitTyConApp_maybe rep_ty
386 Just (rep_tc, rep_ty_args) = maybe_rep_app
388 n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
389 tyvars_to_keep = ASSERT( n_tyvars_to_keep >= 0 && n_tyvars_to_keep <= length tyvars )
390 take n_tyvars_to_keep tyvars -- Kind checking should ensure this
392 n_args_to_keep = tyConArity rep_tc - n_args_to_drop
393 args_to_keep = ASSERT( n_args_to_keep >= 0 && n_args_to_keep <= length rep_ty_args )
394 take n_args_to_keep rep_ty_args
396 ctxt_pred = mkClassPred clas (tys ++ [mkTyConApp rep_tc args_to_keep])
398 mk_dfun dfun_name = mkDictFunId dfun_name clas tyvars
399 (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)] )
402 -- We can only do this newtype deriving thing if:
403 standard_instance = null tys && classKey clas `elem` derivableClassKeys
405 can_derive_via_isomorphism
406 = not (clas `hasKey` readClassKey) -- Never derive Read,Show this way
407 && not (clas `hasKey` showClassKey)
408 && not (isRecursiveTyCon tycon) -- Newtype isn't recursive
409 && isJust maybe_rep_app -- The rep type is a type constructor app
410 && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
411 -- and the tyvars are all in scope
413 cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
414 SLIT("too hard for cunning newtype deriving")
417 bale_out err = addErrTc err `thenNF_Tc_` returnNF_Tc (Nothing, Nothing)
419 ------------------------------------------------------------------
420 chk_out :: Class -> TyCon -> [TcType] -> Maybe FastString
421 chk_out clas tycon tys
422 | not (null tys) = Just non_std_why
423 | not (getUnique clas `elem` derivableClassKeys) = Just non_std_why
424 | clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
425 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
426 | clas `hasKey` ixClassKey && not is_enumeration_or_single = Just single_nullary_why
427 | null data_cons = Just no_cons_why
428 | any isExistentialDataCon data_cons = Just existential_why
429 | otherwise = Nothing
431 data_cons = tyConDataCons tycon
432 is_enumeration = isEnumerationTyCon tycon
433 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
434 is_enumeration_or_single = is_enumeration || is_single_con
436 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
437 nullary_why = SLIT("data type with all nullary constructors expected")
438 no_cons_why = SLIT("type has no data constructors")
439 non_std_why = SLIT("not a derivable class")
440 existential_why = SLIT("it has existentially-quantified constructor(s)")
442 new_dfun_name clas tycon -- Just a simple wrapper
443 = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
444 -- The type passed to newDFunName is only used to generate
445 -- a suitable string; hence the empty type arg list
448 %************************************************************************
450 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
452 %************************************************************************
454 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
455 terms, which is the final correct RHS for the corresponding original
459 Each (k,TyVarTy tv) in a solution constrains only a type
463 The (k,TyVarTy tv) pairs in a solution are canonically
464 ordered by sorting on type varible, tv, (major key) and then class, k,
469 solveDerivEqns :: InstEnv
471 -> TcM [DFunId] -- Solns in same order as eqns.
472 -- This bunch is Absolutely minimal...
474 solveDerivEqns inst_env_in orig_eqns
475 = iterateDeriv initial_solutions
477 -- The initial solutions for the equations claim that each
478 -- instance has an empty context; this solution is certainly
479 -- in canonical form.
480 initial_solutions :: [DerivSoln]
481 initial_solutions = [ [] | _ <- orig_eqns ]
483 ------------------------------------------------------------------
484 -- iterateDeriv calculates the next batch of solutions,
485 -- compares it with the current one; finishes if they are the
486 -- same, otherwise recurses with the new solutions.
487 -- It fails if any iteration fails
488 iterateDeriv :: [DerivSoln] ->TcM [DFunId]
489 iterateDeriv current_solns
490 = checkNoErrsTc (iterateOnce current_solns)
491 `thenTc` \ (new_dfuns, new_solns) ->
492 if (current_solns == new_solns) then
495 iterateDeriv new_solns
497 ------------------------------------------------------------------
498 iterateOnce current_solns
499 = -- Extend the inst info from the explicit instance decls
500 -- with the current set of solutions, giving a
501 getDOptsTc `thenNF_Tc` \ dflags ->
502 let (new_dfuns, inst_env) =
503 add_solns dflags inst_env_in orig_eqns current_solns
506 tcSetInstEnv inst_env (
507 listTc [ tcAddSrcLoc (getSrcLoc tc) $
508 tcAddErrCtxt (derivCtxt tc) $
509 tcSimplifyThetas deriv_rhs
510 | (_, _,tc,_,deriv_rhs) <- orig_eqns ]
511 ) `thenTc` \ next_solns ->
513 -- Canonicalise the solutions, so they compare nicely
514 let canonicalised_next_solns = [ sortLt (<) next_soln | next_soln <- next_solns ]
516 returnTc (new_dfuns, canonicalised_next_solns)
520 add_solns :: DynFlags
521 -> InstEnv -- The global, non-derived ones
522 -> [DerivEqn] -> [DerivSoln]
523 -> ([DFunId], InstEnv)
524 -- the eqns and solns move "in lockstep"; we have the eqns
525 -- because we need the LHS info for addClassInstance.
527 add_solns dflags inst_env_in eqns solns
528 = (new_dfuns, inst_env)
530 new_dfuns = zipWithEqual "add_solns" mk_deriv_dfun eqns solns
531 (inst_env, _) = extendInstEnv dflags inst_env_in new_dfuns
532 -- Ignore the errors about duplicate instances.
533 -- We don't want repeated error messages
534 -- They'll appear later, when we do the top-level extendInstEnvs
536 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
537 = mkDictFunId dfun_name clas tyvars
538 [mkTyConApp tycon (mkTyVarTys tyvars)]
542 %************************************************************************
544 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
546 %************************************************************************
548 After all the trouble to figure out the required context for the
549 derived instance declarations, all that's left is to chug along to
550 produce them. They will then be shoved into @tcInstDecls2@, which
551 will do all its usual business.
553 There are lots of possibilities for code to generate. Here are
554 various general remarks.
559 We want derived instances of @Eq@ and @Ord@ (both v common) to be
560 ``you-couldn't-do-better-by-hand'' efficient.
563 Deriving @Show@---also pretty common--- should also be reasonable good code.
566 Deriving for the other classes isn't that common or that big a deal.
573 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
576 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
579 We {\em normally} generate code only for the non-defaulted methods;
580 there are some exceptions for @Eq@ and (especially) @Ord@...
583 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
584 constructor's numeric (@Int#@) tag. These are generated by
585 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
586 these is around is given by @hasCon2TagFun@.
588 The examples under the different sections below will make this
592 Much less often (really just for deriving @Ix@), we use a
593 @_tag2con_<tycon>@ function. See the examples.
596 We use the renamer!!! Reason: we're supposed to be
597 producing @RenamedMonoBinds@ for the methods, but that means
598 producing correctly-uniquified code on the fly. This is entirely
599 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
600 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
601 the renamer. What a great hack!
605 -- Generate the method bindings for the required instance
606 -- (paired with class name, as we need that when renaming
608 gen_bind :: (Name -> Maybe Fixity) -> DFunId -> (Name, RdrNameMonoBinds)
609 gen_bind get_fixity dfun
612 cls_nm = className clas
613 (clas, tycon) = simpleDFunClassTyCon dfun
615 binds = assoc "gen_bind:bad derived class" gen_list
616 (nameUnique cls_nm) tycon
618 gen_list = [(eqClassKey, gen_Eq_binds)
619 ,(ordClassKey, gen_Ord_binds)
620 ,(enumClassKey, gen_Enum_binds)
621 ,(boundedClassKey, gen_Bounded_binds)
622 ,(ixClassKey, gen_Ix_binds)
623 ,(showClassKey, gen_Show_binds get_fixity)
624 ,(readClassKey, gen_Read_binds get_fixity)
629 %************************************************************************
631 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
633 %************************************************************************
638 con2tag_Foo :: Foo ... -> Int#
639 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
640 maxtag_Foo :: Int -- ditto (NB: not unlifted)
643 We have a @con2tag@ function for a tycon if:
646 We're deriving @Eq@ and the tycon has nullary data constructors.
649 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
653 We have a @tag2con@ function for a tycon if:
656 We're deriving @Enum@, or @Ix@ (enum type only???)
659 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
662 gen_taggery_Names :: [DFunId]
663 -> TcM [(RdrName, -- for an assoc list
664 TyCon, -- related tycon
667 gen_taggery_Names dfuns
668 = foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
669 foldlTc do_tag2con names_so_far tycons_of_interest
671 all_CTs = map simpleDFunClassTyCon dfuns
672 all_tycons = map snd all_CTs
673 (tycons_of_interest, _) = removeDups compare all_tycons
675 do_con2tag acc_Names tycon
676 | isDataTyCon tycon &&
677 ((we_are_deriving eqClassKey tycon
678 && any isNullaryDataCon (tyConDataCons tycon))
679 || (we_are_deriving ordClassKey tycon
680 && not (maybeToBool (maybeTyConSingleCon tycon)))
681 || (we_are_deriving enumClassKey tycon)
682 || (we_are_deriving ixClassKey tycon))
684 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
689 do_tag2con acc_Names tycon
690 | isDataTyCon tycon &&
691 (we_are_deriving enumClassKey tycon ||
692 we_are_deriving ixClassKey tycon
693 && isEnumerationTyCon tycon)
694 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
695 : (maxtag_RDR tycon, tycon, GenMaxTag)
700 we_are_deriving clas_key tycon
701 = is_in_eqns clas_key tycon all_CTs
703 is_in_eqns clas_key tycon [] = False
704 is_in_eqns clas_key tycon ((c,t):cts)
705 = (clas_key == classKey c && tycon == t)
706 || is_in_eqns clas_key tycon cts
710 derivingThingErr clas tys tycon tyvars why
711 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
714 pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
716 malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
719 = ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)