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 )
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
181 FURTHER NOTE ADDED March 2002. In fact, Haskell98 now requires that
182 pattern matching against a constructor from a data type with a context
183 gives rise to the constraints for that context -- or at least the thinned
184 version. So now all classes are "offending".
188 %************************************************************************
190 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
192 %************************************************************************
195 tcDeriving :: PersistentRenamerState
196 -> Module -- name of module under scrutiny
197 -> InstEnv -- What we already know about instances
198 -> FixityEnv -- used in deriving Show and Read
199 -> [RenamedTyClDecl] -- All type constructors
200 -> TcM ([InstInfo], -- The generated "instance decls".
201 RenamedHsBinds) -- Extra generated bindings
203 tcDeriving prs mod inst_env get_fixity tycl_decls
204 = recoverTc (returnTc ([], EmptyBinds)) $
205 getDOptsTc `thenNF_Tc` \ dflags ->
207 -- Fish the "deriving"-related information out of the TcEnv
208 -- and make the necessary "equations".
209 makeDerivEqns tycl_decls `thenTc` \ (ordinary_eqns, newtype_inst_info) ->
211 -- Add the newtype-derived instances to the inst env
212 -- before tacking the "ordinary" ones
213 inst_env1 = extend_inst_env dflags inst_env
214 (map iDFunId newtype_inst_info)
216 deriveOrdinaryStuff mod prs inst_env1 get_fixity
217 ordinary_eqns `thenTc` \ (ordinary_inst_info, binds) ->
219 inst_info = newtype_inst_info ++ ordinary_inst_info
222 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
223 (ddump_deriving inst_info binds)) `thenTc_`
225 returnTc (inst_info, binds)
228 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
229 ddump_deriving inst_infos extra_binds
230 = vcat (map ppr_info inst_infos) $$ ppr extra_binds
232 ppr_info inst_info = pprInstInfo inst_info $$
233 nest 4 (ppr (iBinds inst_info))
234 -- pprInstInfo doesn't print much: only the type
236 -----------------------------------------
237 deriveOrdinaryStuff mod prs inst_env_in get_fixity [] -- Short cut
238 = returnTc ([], EmptyBinds)
240 deriveOrdinaryStuff mod prs inst_env_in get_fixity eqns
241 = -- Take the equation list and solve it, to deliver a list of
242 -- solutions, a.k.a. the contexts for the instance decls
243 -- required for the corresponding equations.
244 solveDerivEqns inst_env_in eqns `thenTc` \ new_dfuns ->
246 -- Now augment the InstInfos, adding in the rather boring
247 -- actual-code-to-do-the-methods binds. We may also need to
248 -- generate extra not-one-inst-decl-specific binds, notably
249 -- "con2tag" and/or "tag2con" functions. We do these
251 gen_taggery_Names new_dfuns `thenTc` \ nm_alist_etc ->
253 tcGetEnv `thenNF_Tc` \ env ->
254 getDOptsTc `thenNF_Tc` \ dflags ->
256 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
257 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
258 method_binds_s = map (gen_bind get_fixity) new_dfuns
259 mbinders = collectLocatedMonoBinders extra_mbinds
261 -- Rename to get RenamedBinds.
262 -- The only tricky bit is that the extra_binds must scope over the
263 -- method bindings for the instances.
264 (rn_method_binds_s, rn_extra_binds)
265 = renameDerivedCode dflags mod prs (
266 bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
267 rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
268 mapRn rn_meths method_binds_s `thenRn` \ rn_method_binds_s ->
269 returnRn (rn_method_binds_s, rn_extra_binds)
271 new_inst_infos = zipWith gen_inst_info new_dfuns rn_method_binds_s
273 returnTc (new_inst_infos, rn_extra_binds)
276 -- Make a Real dfun instead of the dummy one we have so far
277 gen_inst_info :: DFunId -> RenamedMonoBinds -> InstInfo
278 gen_inst_info dfun binds
279 = InstInfo { iDFunId = dfun, iBinds = binds, iPrags = [] }
281 rn_meths (cls, meths) = rnMethodBinds cls [] meths `thenRn` \ (meths', _) ->
282 returnRn meths' -- Ignore the free vars returned
286 %************************************************************************
288 \subsection[TcDeriv-eqns]{Forming the equations}
290 %************************************************************************
292 @makeDerivEqns@ fishes around to find the info about needed derived
293 instances. Complicating factors:
296 We can only derive @Enum@ if the data type is an enumeration
297 type (all nullary data constructors).
300 We can only derive @Ix@ if the data type is an enumeration {\em
301 or} has just one data constructor (e.g., tuples).
304 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
308 makeDerivEqns :: [RenamedTyClDecl]
309 -> TcM ([DerivEqn], -- Ordinary derivings
310 [InstInfo]) -- Special newtype derivings
312 makeDerivEqns tycl_decls
313 = mapAndUnzipTc mk_eqn derive_these `thenTc` \ (maybe_ordinaries, maybe_newtypes) ->
314 returnTc (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
316 ------------------------------------------------------------------
317 derive_these :: [(NewOrData, Name, RenamedHsPred)]
318 -- Find the (nd, TyCon, Pred) pairs that must be `derived'
319 -- NB: only source-language decls have deriving, no imported ones do
320 derive_these = [ (nd, tycon, pred)
321 | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
324 ------------------------------------------------------------------
325 mk_eqn :: (NewOrData, Name, RenamedHsPred) -> NF_TcM (Maybe DerivEqn, Maybe InstInfo)
326 -- We swizzle the tyvars and datacons out of the tycon
327 -- to make the rest of the equation
329 mk_eqn (new_or_data, tycon_name, pred)
330 = tcLookupTyCon tycon_name `thenNF_Tc` \ tycon ->
331 tcAddSrcLoc (getSrcLoc tycon) $
332 tcAddErrCtxt (derivCtxt Nothing tycon) $
333 tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
334 -- the type variables for the type constructor
335 tcHsPred pred `thenTc` \ pred' ->
336 case getClassPredTys_maybe pred' of
337 Nothing -> bale_out (malformedPredErr tycon pred)
338 Just (clas, tys) -> mk_eqn_help new_or_data tycon clas tys
340 ------------------------------------------------------------------
341 mk_eqn_help DataType tycon clas tys
342 | Just err <- chk_out clas tycon tys
343 = bale_out (derivingThingErr clas tys tycon tyvars err)
345 = new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
346 returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
348 tyvars = tyConTyVars tycon
349 data_cons = tyConDataCons tycon
350 constraints = extra_constraints ++
351 [ mkClassPred clas [arg_ty]
352 | data_con <- tyConDataCons tycon,
353 arg_ty <- dataConRepArgTys data_con,
354 -- Use the same type variables
355 -- as the type constructor,
356 -- hence no need to instantiate
357 not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
360 -- "extra_constraints": see notes above about contexts on data decls
361 extra_constraints = tyConTheta tycon
363 -- | offensive_class = tyConTheta tycon
365 -- offensive_class = classKey clas `elem` needsDataDeclCtxtClassKeys
368 mk_eqn_help NewType tycon clas tys
369 = doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
370 if can_derive_via_isomorphism && (gla_exts || standard_instance) then
371 -- Go ahead and use the isomorphism
372 new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
373 returnTc (Nothing, Just (NewTypeDerived (mk_dfun dfun_name)))
375 if standard_instance then
376 mk_eqn_help DataType tycon clas [] -- Go via bale-out route
378 bale_out cant_derive_err
380 -- Here is the plan for newtype derivings. We see
381 -- newtype T a1...an = T (t ak...an) deriving (C1...Cm)
382 -- where aj...an do not occur free in t, and the Ci are *partial applications* of
383 -- classes with the last parameter missing
385 -- We generate the instances
386 -- instance Ci (t ak...aj) => Ci (T a1...aj)
387 -- where T a1...aj is the partial application of the LHS of the correct kind
389 -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
391 kind = tyVarKind (last (classTyVars clas))
392 -- Kind of the thing we want to instance
393 -- e.g. argument kind of Monad, *->*
395 (arg_kinds, _) = tcSplitFunTys kind
396 n_args_to_drop = length arg_kinds
397 -- Want to drop 1 arg from (T s a) and (ST s a)
398 -- to get instance Monad (ST s) => Monad (T s)
400 (tyvars, rep_ty) = newTyConRep tycon
401 maybe_rep_app = tcSplitTyConApp_maybe rep_ty
402 Just (rep_tc, rep_ty_args) = maybe_rep_app
404 n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
405 tyvars_to_drop = drop n_tyvars_to_keep tyvars
406 tyvars_to_keep = take n_tyvars_to_keep tyvars
408 n_args_to_keep = tyConArity rep_tc - n_args_to_drop
409 args_to_drop = drop n_args_to_keep rep_ty_args
410 args_to_keep = take n_args_to_keep rep_ty_args
412 ctxt_pred = mkClassPred clas (tys ++ [mkTyConApp rep_tc args_to_keep])
414 mk_dfun dfun_name = mkDictFunId dfun_name clas tyvars
415 (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)] )
418 -- We can only do this newtype deriving thing if:
419 standard_instance = null tys && classKey clas `elem` derivableClassKeys
421 can_derive_via_isomorphism
422 = not (clas `hasKey` readClassKey) -- Never derive Read,Show this way
423 && not (clas `hasKey` showClassKey)
424 && n_tyvars_to_keep >= 0 -- Well kinded;
425 -- eg not: newtype T = T Int deriving( Monad )
426 && isJust maybe_rep_app -- The rep type is a type constructor app
427 && n_args_to_keep >= 0 -- Well kinded:
428 -- eg not: newtype T a = T Int deriving( Monad )
429 && eta_ok -- Eta reduction works
431 -- Check that eta reduction is OK
432 -- (a) the dropped-off args are identical
433 -- (b) the remaining type args mention
434 -- only the remaining type variables
435 eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
436 && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
438 cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
439 SLIT("too hard for cunning newtype deriving")
442 bale_out err = addErrTc err `thenNF_Tc_` returnNF_Tc (Nothing, Nothing)
444 ------------------------------------------------------------------
445 chk_out :: Class -> TyCon -> [TcType] -> Maybe FastString
446 chk_out clas tycon tys
447 | notNull tys = Just non_std_why
448 | not (getUnique clas `elem` derivableClassKeys) = Just non_std_why
449 | clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
450 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
451 | clas `hasKey` ixClassKey && not is_enumeration_or_single = Just single_nullary_why
452 | null data_cons = Just no_cons_why
453 | any isExistentialDataCon data_cons = Just existential_why
454 | otherwise = Nothing
456 data_cons = tyConDataCons tycon
457 is_enumeration = isEnumerationTyCon tycon
458 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
459 is_enumeration_or_single = is_enumeration || is_single_con
461 single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
462 nullary_why = SLIT("data type with all nullary constructors expected")
463 no_cons_why = SLIT("type has no data constructors")
464 non_std_why = SLIT("not a derivable class")
465 existential_why = SLIT("it has existentially-quantified constructor(s)")
467 new_dfun_name clas tycon -- Just a simple wrapper
468 = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
469 -- The type passed to newDFunName is only used to generate
470 -- a suitable string; hence the empty type arg list
473 %************************************************************************
475 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
477 %************************************************************************
479 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
480 terms, which is the final correct RHS for the corresponding original
484 Each (k,TyVarTy tv) in a solution constrains only a type
488 The (k,TyVarTy tv) pairs in a solution are canonically
489 ordered by sorting on type varible, tv, (major key) and then class, k,
494 solveDerivEqns :: InstEnv
496 -> TcM [DFunId] -- Solns in same order as eqns.
497 -- This bunch is Absolutely minimal...
499 solveDerivEqns inst_env_in orig_eqns
500 = iterateDeriv 1 initial_solutions
502 -- The initial solutions for the equations claim that each
503 -- instance has an empty context; this solution is certainly
504 -- in canonical form.
505 initial_solutions :: [DerivSoln]
506 initial_solutions = [ [] | _ <- orig_eqns ]
508 ------------------------------------------------------------------
509 -- iterateDeriv calculates the next batch of solutions,
510 -- compares it with the current one; finishes if they are the
511 -- same, otherwise recurses with the new solutions.
512 -- It fails if any iteration fails
513 iterateDeriv :: Int -> [DerivSoln] ->TcM [DFunId]
514 iterateDeriv n current_solns
515 | n > 20 -- Looks as if we are in an infinite loop
516 -- This can happen if we have -fallow-undecidable-instances
517 -- (See TcSimplify.tcSimplifyDeriv.)
518 = pprPanic "solveDerivEqns: probable loop"
519 (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
521 = getDOptsTc `thenNF_Tc` \ dflags ->
523 dfuns = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
524 inst_env = extend_inst_env dflags inst_env_in dfuns
527 -- Extend the inst info from the explicit instance decls
528 -- with the current set of solutions, and simplify each RHS
529 tcSetInstEnv inst_env $
530 mapTc gen_soln orig_eqns
531 ) `thenTc` \ new_solns ->
532 if (current_solns == new_solns) then
535 iterateDeriv (n+1) new_solns
537 ------------------------------------------------------------------
539 gen_soln (_, clas, tc,tyvars,deriv_rhs)
540 = tcAddSrcLoc (getSrcLoc tc) $
541 tcAddErrCtxt (derivCtxt (Just clas) tc) $
542 tcSimplifyDeriv tyvars deriv_rhs `thenTc` \ theta ->
543 returnTc (sortLt (<) theta) -- Canonicalise before returning the soluction
547 extend_inst_env dflags inst_env new_dfuns
550 (new_inst_env, _errs) = extendInstEnv dflags inst_env new_dfuns
551 -- Ignore the errors about duplicate instances.
552 -- We don't want repeated error messages
553 -- They'll appear later, when we do the top-level extendInstEnvs
555 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
556 = mkDictFunId dfun_name clas tyvars
557 [mkTyConApp tycon (mkTyVarTys tyvars)]
561 %************************************************************************
563 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
565 %************************************************************************
567 After all the trouble to figure out the required context for the
568 derived instance declarations, all that's left is to chug along to
569 produce them. They will then be shoved into @tcInstDecls2@, which
570 will do all its usual business.
572 There are lots of possibilities for code to generate. Here are
573 various general remarks.
578 We want derived instances of @Eq@ and @Ord@ (both v common) to be
579 ``you-couldn't-do-better-by-hand'' efficient.
582 Deriving @Show@---also pretty common--- should also be reasonable good code.
585 Deriving for the other classes isn't that common or that big a deal.
592 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
595 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
598 We {\em normally} generate code only for the non-defaulted methods;
599 there are some exceptions for @Eq@ and (especially) @Ord@...
602 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
603 constructor's numeric (@Int#@) tag. These are generated by
604 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
605 these is around is given by @hasCon2TagFun@.
607 The examples under the different sections below will make this
611 Much less often (really just for deriving @Ix@), we use a
612 @_tag2con_<tycon>@ function. See the examples.
615 We use the renamer!!! Reason: we're supposed to be
616 producing @RenamedMonoBinds@ for the methods, but that means
617 producing correctly-uniquified code on the fly. This is entirely
618 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
619 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
620 the renamer. What a great hack!
624 -- Generate the method bindings for the required instance
625 -- (paired with class name, as we need that when renaming
627 gen_bind :: FixityEnv -> DFunId -> (Name, RdrNameMonoBinds)
628 gen_bind get_fixity dfun
631 cls_nm = className clas
632 (clas, tycon) = simpleDFunClassTyCon dfun
634 binds = assoc "gen_bind:bad derived class" gen_list
635 (nameUnique cls_nm) tycon
637 gen_list = [(eqClassKey, gen_Eq_binds)
638 ,(ordClassKey, gen_Ord_binds)
639 ,(enumClassKey, gen_Enum_binds)
640 ,(boundedClassKey, gen_Bounded_binds)
641 ,(ixClassKey, gen_Ix_binds)
642 ,(showClassKey, gen_Show_binds get_fixity)
643 ,(readClassKey, gen_Read_binds get_fixity)
648 %************************************************************************
650 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
652 %************************************************************************
657 con2tag_Foo :: Foo ... -> Int#
658 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
659 maxtag_Foo :: Int -- ditto (NB: not unlifted)
662 We have a @con2tag@ function for a tycon if:
665 We're deriving @Eq@ and the tycon has nullary data constructors.
668 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
672 We have a @tag2con@ function for a tycon if:
675 We're deriving @Enum@, or @Ix@ (enum type only???)
678 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
681 gen_taggery_Names :: [DFunId]
682 -> TcM [(RdrName, -- for an assoc list
683 TyCon, -- related tycon
686 gen_taggery_Names dfuns
687 = foldlTc do_con2tag [] tycons_of_interest `thenTc` \ names_so_far ->
688 foldlTc do_tag2con names_so_far tycons_of_interest
690 all_CTs = map simpleDFunClassTyCon dfuns
691 all_tycons = map snd all_CTs
692 (tycons_of_interest, _) = removeDups compare all_tycons
694 do_con2tag acc_Names tycon
695 | isDataTyCon tycon &&
696 ((we_are_deriving eqClassKey tycon
697 && any isNullaryDataCon (tyConDataCons tycon))
698 || (we_are_deriving ordClassKey tycon
699 && not (maybeToBool (maybeTyConSingleCon tycon)))
700 || (we_are_deriving enumClassKey tycon)
701 || (we_are_deriving ixClassKey tycon))
703 = returnTc ((con2tag_RDR tycon, tycon, GenCon2Tag)
708 do_tag2con acc_Names tycon
709 | isDataTyCon tycon &&
710 (we_are_deriving enumClassKey tycon ||
711 we_are_deriving ixClassKey tycon
712 && isEnumerationTyCon tycon)
713 = returnTc ( (tag2con_RDR tycon, tycon, GenTag2Con)
714 : (maxtag_RDR tycon, tycon, GenMaxTag)
719 we_are_deriving clas_key tycon
720 = is_in_eqns clas_key tycon all_CTs
722 is_in_eqns clas_key tycon [] = False
723 is_in_eqns clas_key tycon ((c,t):cts)
724 = (clas_key == classKey c && tycon == t)
725 || is_in_eqns clas_key tycon cts
729 derivingThingErr clas tys tycon tyvars why
730 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
733 pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
735 malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
737 derivCtxt :: Maybe Class -> TyCon -> SDoc
738 derivCtxt maybe_cls tycon
739 = ptext SLIT("When deriving") <+> cls <+> ptext SLIT("for type") <+> quotes (ppr tycon)
741 cls = case maybe_cls of
742 Nothing -> ptext SLIT("instances")
743 Just c -> ptext SLIT("the") <+> quotes (ppr c) <+> ptext SLIT("instance")