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 ( Fixity, 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, tyVarsOfTheta )
51 import Var ( TyVar, tyVarKind )
52 import VarSet ( mkVarSet, subVarSet )
54 import Util ( zipWithEqual, sortLt )
55 import ListSetOps ( removeDups, assoc )
57 import Maybe ( isJust )
58 import FastString ( FastString )
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 pprDerivEqn (n,c,tc,tvs,rhs)
151 = parens (hsep [ppr n, ppr c, ppr tc, ppr tvs] <+> equals <+> ppr rhs)
153 type DerivRhs = ThetaType
154 type DerivSoln = DerivRhs
158 A note about contexts on data decls
159 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
162 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
164 We will need an instance decl like:
166 instance (Read a, RealFloat a) => Read (Complex a) where
169 The RealFloat in the context is because the read method for Complex is bound
170 to construct a Complex, and doing that requires that the argument type is
173 But this ain't true for Show, Eq, Ord, etc, since they don't construct
174 a Complex; they only take them apart.
176 Our approach: identify the offending classes, and add the data type
177 context to the instance decl. The "offending classes" are
182 %************************************************************************
184 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
186 %************************************************************************
189 tcDeriving :: PersistentRenamerState
190 -> Module -- name of module under scrutiny
191 -> InstEnv -- What we already know about instances
192 -> FixityEnv -- used in deriving Show and Read
193 -> [RenamedTyClDecl] -- All type constructors
194 -> TcM ([InstInfo], -- The generated "instance decls".
195 RenamedHsBinds) -- Extra generated bindings
197 tcDeriving prs mod inst_env get_fixity tycl_decls
198 = recoverTc (returnTc ([], EmptyBinds)) $
199 getDOptsTc `thenNF_Tc` \ dflags ->
201 -- Fish the "deriving"-related information out of the TcEnv
202 -- and make the necessary "equations".
203 makeDerivEqns tycl_decls `thenTc` \ (ordinary_eqns, newtype_inst_info) ->
205 -- Add the newtype-derived instances to the inst env
206 -- before tacking the "ordinary" ones
207 inst_env1 = extend_inst_env dflags inst_env
208 (map iDFunId newtype_inst_info)
210 deriveOrdinaryStuff mod prs inst_env1 get_fixity
211 ordinary_eqns `thenTc` \ (ordinary_inst_info, binds) ->
213 inst_info = newtype_inst_info ++ ordinary_inst_info
216 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
217 (ddump_deriving inst_info binds)) `thenTc_`
219 returnTc (inst_info, binds)
222 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
223 ddump_deriving inst_infos extra_binds
224 = vcat (map pprInstInfo inst_infos) $$ ppr extra_binds
227 -----------------------------------------
228 deriveOrdinaryStuff mod prs inst_env_in get_fixity [] -- Short cut
229 = returnTc ([], EmptyBinds)
231 deriveOrdinaryStuff mod prs inst_env_in get_fixity eqns
232 = -- Take the equation list and solve it, to deliver a list of
233 -- solutions, a.k.a. the contexts for the instance decls
234 -- required for the corresponding equations.
235 solveDerivEqns inst_env_in eqns `thenTc` \ new_dfuns ->
237 -- Now augment the InstInfos, adding in the rather boring
238 -- actual-code-to-do-the-methods binds. We may also need to
239 -- generate extra not-one-inst-decl-specific binds, notably
240 -- "con2tag" and/or "tag2con" functions. We do these
242 gen_taggery_Names new_dfuns `thenTc` \ nm_alist_etc ->
244 tcGetEnv `thenNF_Tc` \ env ->
245 getDOptsTc `thenNF_Tc` \ dflags ->
247 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
248 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
249 method_binds_s = map (gen_bind get_fixity) new_dfuns
250 mbinders = collectLocatedMonoBinders extra_mbinds
252 -- Rename to get RenamedBinds.
253 -- The only tricky bit is that the extra_binds must scope over the
254 -- method bindings for the instances.
255 (rn_method_binds_s, rn_extra_binds)
256 = renameDerivedCode dflags mod prs (
257 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
258 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
259 mapRn rn_meths method_binds_s `thenRn` \ rn_method_binds_s ->
260 returnRn (rn_method_binds_s, rn_extra_binds)
262 new_inst_infos = zipWith gen_inst_info new_dfuns rn_method_binds_s
264 returnTc (new_inst_infos, rn_extra_binds)
267 -- Make a Real dfun instead of the dummy one we have so far
268 gen_inst_info :: DFunId -> RenamedMonoBinds -> InstInfo
269 gen_inst_info dfun binds
270 = InstInfo { iDFunId = dfun, iBinds = binds, iPrags = [] }
272 rn_meths (cls, meths) = rnMethodBinds cls [] meths `thenRn` \ (meths', _) ->
273 returnRn meths' -- Ignore the free vars returned
277 %************************************************************************
279 \subsection[TcDeriv-eqns]{Forming the equations}
281 %************************************************************************
283 @makeDerivEqns@ fishes around to find the info about needed derived
284 instances. Complicating factors:
287 We can only derive @Enum@ if the data type is an enumeration
288 type (all nullary data constructors).
291 We can only derive @Ix@ if the data type is an enumeration {\em
292 or} has just one data constructor (e.g., tuples).
295 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
299 makeDerivEqns :: [RenamedTyClDecl]
300 -> TcM ([DerivEqn], -- Ordinary derivings
301 [InstInfo]) -- Special newtype derivings
303 makeDerivEqns tycl_decls
304 = mapAndUnzipTc mk_eqn derive_these `thenTc` \ (maybe_ordinaries, maybe_newtypes) ->
305 returnTc (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
307 ------------------------------------------------------------------
308 derive_these :: [(NewOrData, Name, RenamedHsPred)]
309 -- Find the (nd, TyCon, Pred) pairs that must be `derived'
310 -- NB: only source-language decls have deriving, no imported ones do
311 derive_these = [ (nd, tycon, pred)
312 | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
315 ------------------------------------------------------------------
316 mk_eqn :: (NewOrData, Name, RenamedHsPred) -> NF_TcM (Maybe DerivEqn, Maybe InstInfo)
317 -- We swizzle the tyvars and datacons out of the tycon
318 -- to make the rest of the equation
320 mk_eqn (new_or_data, tycon_name, pred)
321 = tcLookupTyCon tycon_name `thenNF_Tc` \ tycon ->
322 tcAddSrcLoc (getSrcLoc tycon) $
323 tcAddErrCtxt (derivCtxt Nothing tycon) $
324 tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
325 -- the type variables for the type constructor
326 tcHsPred pred `thenTc` \ pred' ->
327 case getClassPredTys_maybe pred' of
328 Nothing -> bale_out (malformedPredErr tycon pred)
329 Just (clas, tys) -> mk_eqn_help new_or_data tycon clas tys
331 ------------------------------------------------------------------
332 mk_eqn_help DataType tycon clas tys
333 | Just err <- chk_out clas tycon tys
334 = bale_out (derivingThingErr clas tys tycon tyvars err)
336 = new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
337 returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
339 tyvars = tyConTyVars tycon
340 data_cons = tyConDataCons tycon
341 constraints = extra_constraints ++
342 [ mkClassPred clas [arg_ty]
343 | data_con <- tyConDataCons tycon,
344 arg_ty <- dataConRepArgTys data_con,
345 -- Use the same type variables
346 -- as the type constructor,
347 -- hence no need to instantiate
348 not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
352 -- "extra_constraints": see notes above about contexts on data decls
353 extra_constraints | offensive_class = tyConTheta tycon
356 offensive_class = classKey clas `elem` needsDataDeclCtxtClassKeys
359 mk_eqn_help NewType tycon clas tys
360 = doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
361 if can_derive_via_isomorphism && (gla_exts || standard_instance) then
362 -- Go ahead and use the isomorphism
363 new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
364 returnTc (Nothing, Just (NewTypeDerived (mk_dfun dfun_name)))
366 if standard_instance then
367 mk_eqn_help DataType tycon clas [] -- Go via bale-out route
369 bale_out cant_derive_err
371 -- Here is the plan for newtype derivings. We see
372 -- newtype T a1...an = T (t ak...an) deriving (C1...Cm)
373 -- where aj...an do not occur free in t, and the Ci are *partial applications* of
374 -- classes with the last parameter missing
376 -- We generate the instances
377 -- instance Ci (t ak...aj) => Ci (T a1...aj)
378 -- where T a1...aj is the partial application of the LHS of the correct kind
380 -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
382 kind = tyVarKind (last (classTyVars clas))
383 -- Kind of the thing we want to instance
384 -- e.g. argument kind of Monad, *->*
386 (arg_kinds, _) = tcSplitFunTys kind
387 n_args_to_drop = length arg_kinds
388 -- Want to drop 1 arg from (T s a) and (ST s a)
389 -- to get instance Monad (ST s) => Monad (T s)
391 (tyvars, rep_ty) = newTyConRep tycon
392 maybe_rep_app = tcSplitTyConApp_maybe rep_ty
393 Just (rep_tc, rep_ty_args) = maybe_rep_app
395 n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
396 tyvars_to_drop = drop n_tyvars_to_keep tyvars
397 tyvars_to_keep = take n_tyvars_to_keep tyvars
399 n_args_to_keep = tyConArity rep_tc - n_args_to_drop
400 args_to_drop = drop n_args_to_keep rep_ty_args
401 args_to_keep = take n_args_to_keep rep_ty_args
403 ctxt_pred = mkClassPred clas (tys ++ [mkTyConApp rep_tc args_to_keep])
405 mk_dfun dfun_name = mkDictFunId dfun_name clas tyvars
406 (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)] )
409 -- We can only do this newtype deriving thing if:
410 standard_instance = null tys && classKey clas `elem` derivableClassKeys
412 can_derive_via_isomorphism
413 = not (clas `hasKey` readClassKey) -- Never derive Read,Show this way
414 && not (clas `hasKey` showClassKey)
415 && n_tyvars_to_keep >= 0 -- Well kinded;
416 -- eg not: newtype T = T Int deriving( Monad )
417 && isJust maybe_rep_app -- The rep type is a type constructor app
418 && n_args_to_keep >= 0 -- Well kinded:
419 -- eg not: newtype T a = T Int deriving( Monad )
420 && eta_ok -- Eta reduction works
422 -- Check that eta reduction is OK
423 -- (a) the dropped-off args are identical
424 -- (b) the remaining type args mention
425 -- only the remaining type variables
426 eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
427 && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
429 cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
430 SLIT("too hard for cunning newtype deriving")
433 bale_out err = addErrTc err `thenNF_Tc_` returnNF_Tc (Nothing, Nothing)
435 ------------------------------------------------------------------
436 chk_out :: Class -> TyCon -> [TcType] -> Maybe FastString
437 chk_out clas tycon tys
438 | not (null tys) = Just non_std_why
439 | not (getUnique clas `elem` derivableClassKeys) = Just non_std_why
440 | clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
441 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
442 | clas `hasKey` ixClassKey && not is_enumeration_or_single = Just single_nullary_why
443 | null data_cons = Just no_cons_why
444 | any isExistentialDataCon data_cons = Just existential_why
445 | otherwise = Nothing
447 data_cons = tyConDataCons tycon
448 is_enumeration = isEnumerationTyCon tycon
449 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
450 is_enumeration_or_single = is_enumeration || is_single_con
452 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
453 nullary_why = SLIT("data type with all nullary constructors expected")
454 no_cons_why = SLIT("type has no data constructors")
455 non_std_why = SLIT("not a derivable class")
456 existential_why = SLIT("it has existentially-quantified constructor(s)")
458 new_dfun_name clas tycon -- Just a simple wrapper
459 = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
460 -- The type passed to newDFunName is only used to generate
461 -- a suitable string; hence the empty type arg list
464 %************************************************************************
466 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
468 %************************************************************************
470 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
471 terms, which is the final correct RHS for the corresponding original
475 Each (k,TyVarTy tv) in a solution constrains only a type
479 The (k,TyVarTy tv) pairs in a solution are canonically
480 ordered by sorting on type varible, tv, (major key) and then class, k,
485 solveDerivEqns :: InstEnv
487 -> TcM [DFunId] -- Solns in same order as eqns.
488 -- This bunch is Absolutely minimal...
490 solveDerivEqns inst_env_in orig_eqns
491 = iterateDeriv 1 initial_solutions
493 -- The initial solutions for the equations claim that each
494 -- instance has an empty context; this solution is certainly
495 -- in canonical form.
496 initial_solutions :: [DerivSoln]
497 initial_solutions = [ [] | _ <- orig_eqns ]
499 ------------------------------------------------------------------
500 -- iterateDeriv calculates the next batch of solutions,
501 -- compares it with the current one; finishes if they are the
502 -- same, otherwise recurses with the new solutions.
503 -- It fails if any iteration fails
504 iterateDeriv :: Int -> [DerivSoln] ->TcM [DFunId]
505 iterateDeriv n current_solns
506 | n > 20 -- Looks as if we are in an infinite loop
507 -- This can happen if we have -fallow-undecidable-instances
508 -- (See TcSimplify.tcSimplifyDeriv.)
509 = pprPanic "solveDerivEqns: probable loop"
510 (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
512 = getDOptsTc `thenNF_Tc` \ dflags ->
514 dfuns = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
515 inst_env = extend_inst_env dflags inst_env_in dfuns
518 -- Extend the inst info from the explicit instance decls
519 -- with the current set of solutions, and simplify each RHS
520 tcSetInstEnv inst_env $
521 mapTc gen_soln orig_eqns
522 ) `thenTc` \ new_solns ->
523 if (current_solns == new_solns) then
526 iterateDeriv (n+1) new_solns
528 ------------------------------------------------------------------
530 gen_soln (_, clas, tc,tyvars,deriv_rhs)
531 = tcAddSrcLoc (getSrcLoc tc) $
532 tcAddErrCtxt (derivCtxt (Just clas) tc) $
533 tcSimplifyDeriv tyvars deriv_rhs `thenTc` \ theta ->
534 returnTc (sortLt (<) theta) -- Canonicalise before returning the soluction
538 extend_inst_env dflags inst_env new_dfuns
541 (new_inst_env, _errs) = extendInstEnv dflags inst_env new_dfuns
542 -- Ignore the errors about duplicate instances.
543 -- We don't want repeated error messages
544 -- They'll appear later, when we do the top-level extendInstEnvs
546 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
547 = mkDictFunId dfun_name clas tyvars
548 [mkTyConApp tycon (mkTyVarTys tyvars)]
552 %************************************************************************
554 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
556 %************************************************************************
558 After all the trouble to figure out the required context for the
559 derived instance declarations, all that's left is to chug along to
560 produce them. They will then be shoved into @tcInstDecls2@, which
561 will do all its usual business.
563 There are lots of possibilities for code to generate. Here are
564 various general remarks.
569 We want derived instances of @Eq@ and @Ord@ (both v common) to be
570 ``you-couldn't-do-better-by-hand'' efficient.
573 Deriving @Show@---also pretty common--- should also be reasonable good code.
576 Deriving for the other classes isn't that common or that big a deal.
583 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
586 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
589 We {\em normally} generate code only for the non-defaulted methods;
590 there are some exceptions for @Eq@ and (especially) @Ord@...
593 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
594 constructor's numeric (@Int#@) tag. These are generated by
595 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
596 these is around is given by @hasCon2TagFun@.
598 The examples under the different sections below will make this
602 Much less often (really just for deriving @Ix@), we use a
603 @_tag2con_<tycon>@ function. See the examples.
606 We use the renamer!!! Reason: we're supposed to be
607 producing @RenamedMonoBinds@ for the methods, but that means
608 producing correctly-uniquified code on the fly. This is entirely
609 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
610 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
611 the renamer. What a great hack!
615 -- Generate the method bindings for the required instance
616 -- (paired with class name, as we need that when renaming
618 gen_bind :: FixityEnv -> DFunId -> (Name, RdrNameMonoBinds)
619 gen_bind get_fixity dfun
622 cls_nm = className clas
623 (clas, tycon) = simpleDFunClassTyCon dfun
625 binds = assoc "gen_bind:bad derived class" gen_list
626 (nameUnique cls_nm) tycon
628 gen_list = [(eqClassKey, gen_Eq_binds)
629 ,(ordClassKey, gen_Ord_binds)
630 ,(enumClassKey, gen_Enum_binds)
631 ,(boundedClassKey, gen_Bounded_binds)
632 ,(ixClassKey, gen_Ix_binds)
633 ,(showClassKey, gen_Show_binds get_fixity)
634 ,(readClassKey, gen_Read_binds get_fixity)
639 %************************************************************************
641 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
643 %************************************************************************
648 con2tag_Foo :: Foo ... -> Int#
649 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
650 maxtag_Foo :: Int -- ditto (NB: not unlifted)
653 We have a @con2tag@ function for a tycon if:
656 We're deriving @Eq@ and the tycon has nullary data constructors.
659 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
663 We have a @tag2con@ function for a tycon if:
666 We're deriving @Enum@, or @Ix@ (enum type only???)
669 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
672 gen_taggery_Names :: [DFunId]
673 -> TcM [(RdrName, -- for an assoc list
674 TyCon, -- related tycon
677 gen_taggery_Names dfuns
678 = foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
679 foldlTc do_tag2con names_so_far tycons_of_interest
681 all_CTs = map simpleDFunClassTyCon dfuns
682 all_tycons = map snd all_CTs
683 (tycons_of_interest, _) = removeDups compare all_tycons
685 do_con2tag acc_Names tycon
686 | isDataTyCon tycon &&
687 ((we_are_deriving eqClassKey tycon
688 && any isNullaryDataCon (tyConDataCons tycon))
689 || (we_are_deriving ordClassKey tycon
690 && not (maybeToBool (maybeTyConSingleCon tycon)))
691 || (we_are_deriving enumClassKey tycon)
692 || (we_are_deriving ixClassKey tycon))
694 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
699 do_tag2con acc_Names tycon
700 | isDataTyCon tycon &&
701 (we_are_deriving enumClassKey tycon ||
702 we_are_deriving ixClassKey tycon
703 && isEnumerationTyCon tycon)
704 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
705 : (maxtag_RDR tycon, tycon, GenMaxTag)
710 we_are_deriving clas_key tycon
711 = is_in_eqns clas_key tycon all_CTs
713 is_in_eqns clas_key tycon [] = False
714 is_in_eqns clas_key tycon ((c,t):cts)
715 = (clas_key == classKey c && tycon == t)
716 || is_in_eqns clas_key tycon cts
720 derivingThingErr clas tys tycon tyvars why
721 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
724 pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
726 malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
728 derivCtxt :: Maybe Class -> TyCon -> SDoc
729 derivCtxt maybe_cls tycon
730 = ptext SLIT("When deriving") <+> cls <+> ptext SLIT("for type") <+> quotes (ppr tycon)
732 cls = case maybe_cls of
733 Nothing -> ptext SLIT("instances")
734 Just c -> ptext SLIT("the") <+> quotes (ppr c) <+> ptext SLIT("instance")