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(..),
15 import RdrHsSyn ( RdrNameMonoBinds )
16 import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds, RenamedTyClDecl, RenamedHsPred )
17 import CmdLineOpts ( DynFlag(..) )
20 import TcEnv ( tcGetInstEnv, tcSetInstEnv, newDFunName,
21 InstInfo(..), pprInstInfo, InstBindings(..),
22 pprInstInfoDetails, tcLookupTyCon, tcExtendTyVarEnv
24 import TcGenDeriv -- Deriv stuff
25 import InstEnv ( InstEnv, simpleDFunClassTyCon, extendInstEnv )
26 import TcMonoType ( tcHsPred )
27 import TcSimplify ( tcSimplifyDeriv )
29 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
30 import RnEnv ( bindLocalsFVRn )
31 import TcRnMonad ( thenM, returnM, mapAndUnzipM )
32 import HscTypes ( DFunId )
34 import BasicTypes ( NewOrData(..) )
35 import Class ( className, classKey, classTyVars, classSCTheta, Class )
36 import Subst ( mkTyVarSubst, substTheta )
37 import ErrUtils ( dumpIfSet_dyn )
38 import MkId ( mkDictFunId )
39 import DataCon ( dataConRepArgTys, isNullaryDataCon, isExistentialDataCon )
40 import Maybes ( maybeToBool, catMaybes )
41 import Name ( Name, getSrcLoc, nameUnique )
43 import RdrName ( RdrName )
45 import TyCon ( tyConTyVars, tyConDataCons, tyConArity, newTyConRep,
46 tyConTheta, maybeTyConSingleCon, isDataTyCon,
47 isEnumerationTyCon, isRecursiveTyCon, TyCon
49 import TcType ( TcType, ThetaType, mkTyVarTys, mkTyConApp, getClassPredTys_maybe,
50 isUnLiftedType, mkClassPred, tyVarsOfTypes, tcSplitFunTys,
52 import Type ( splitAppTys )
53 import Var ( TyVar, tyVarKind )
54 import VarSet ( mkVarSet, subVarSet )
56 import Util ( zipWithEqual, sortLt, notNull )
57 import ListSetOps ( removeDups, assoc )
61 %************************************************************************
63 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
65 %************************************************************************
69 data T a b = C1 (Foo a) (Bar b)
74 [NOTE: See end of these comments for what to do with
75 data (C a, D b) => T a b = ...
78 We want to come up with an instance declaration of the form
80 instance (Ping a, Pong b, ...) => Eq (T a b) where
83 It is pretty easy, albeit tedious, to fill in the code "...". The
84 trick is to figure out what the context for the instance decl is,
85 namely @Ping@, @Pong@ and friends.
87 Let's call the context reqd for the T instance of class C at types
88 (a,b, ...) C (T a b). Thus:
90 Eq (T a b) = (Ping a, Pong b, ...)
92 Now we can get a (recursive) equation from the @data@ decl:
94 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
95 u Eq (T b a) u Eq Int -- From C2
96 u Eq (T a a) -- From C3
98 Foo and Bar may have explicit instances for @Eq@, in which case we can
99 just substitute for them. Alternatively, either or both may have
100 their @Eq@ instances given by @deriving@ clauses, in which case they
101 form part of the system of equations.
103 Now all we need do is simplify and solve the equations, iterating to
104 find the least fixpoint. Notice that the order of the arguments can
105 switch around, as here in the recursive calls to T.
107 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
111 Eq (T a b) = {} -- The empty set
114 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
115 u Eq (T b a) u Eq Int -- From C2
116 u Eq (T a a) -- From C3
118 After simplification:
119 = Eq a u Ping b u {} u {} u {}
124 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
125 u Eq (T b a) u Eq Int -- From C2
126 u Eq (T a a) -- From C3
128 After simplification:
133 = Eq a u Ping b u Eq b u Ping a
135 The next iteration gives the same result, so this is the fixpoint. We
136 need to make a canonical form of the RHS to ensure convergence. We do
137 this by simplifying the RHS to a form in which
139 - the classes constrain only tyvars
140 - the list is sorted by tyvar (major key) and then class (minor key)
141 - no duplicates, of course
143 So, here are the synonyms for the ``equation'' structures:
146 type DerivEqn = (Name, Class, TyCon, [TyVar], DerivRhs)
147 -- The Name is the name for the DFun we'll build
148 -- The tyvars bind all the variables in the RHS
150 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 [Data decl contexts] 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 :: [RenamedTyClDecl] -- All type constructors
196 -> TcM ([InstInfo], -- The generated "instance decls".
197 RenamedHsBinds, -- Extra generated bindings
198 FreeVars) -- These are free in the generated bindings
200 tcDeriving tycl_decls
201 = recoverM (returnM ([], EmptyBinds, emptyFVs)) $
202 getDOpts `thenM` \ dflags ->
203 tcGetInstEnv `thenM` \ inst_env ->
205 -- Fish the "deriving"-related information out of the TcEnv
206 -- and make the necessary "equations".
207 makeDerivEqns tycl_decls `thenM` \ (ordinary_eqns, newtype_inst_info) ->
209 -- Add the newtype-derived instances to the inst env
210 -- before tacking the "ordinary" ones
211 inst_env1 = extend_inst_env dflags inst_env
212 (map iDFunId newtype_inst_info)
214 deriveOrdinaryStuff inst_env1 ordinary_eqns `thenM` \ (ordinary_inst_info, binds, fvs) ->
216 inst_info = newtype_inst_info ++ ordinary_inst_info
219 ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
220 (ddump_deriving inst_info binds)) `thenM_`
222 returnM (inst_info, binds, fvs)
225 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
226 ddump_deriving inst_infos extra_binds
227 = vcat (map ppr_info inst_infos) $$ ppr extra_binds
229 ppr_info inst_info = pprInstInfo inst_info $$
230 nest 4 (pprInstInfoDetails inst_info)
231 -- pprInstInfo doesn't print much: only the type
233 -----------------------------------------
234 deriveOrdinaryStuff inst_env_in [] -- Short cut
235 = returnM ([], EmptyBinds, emptyFVs)
237 deriveOrdinaryStuff inst_env_in eqns
238 = -- Take the equation list and solve it, to deliver a list of
239 -- solutions, a.k.a. the contexts for the instance decls
240 -- required for the corresponding equations.
241 solveDerivEqns inst_env_in eqns `thenM` \ new_dfuns ->
243 -- Now augment the InstInfos, adding in the rather boring
244 -- actual-code-to-do-the-methods binds. We may also need to
245 -- generate extra not-one-inst-decl-specific binds, notably
246 -- "con2tag" and/or "tag2con" functions. We do these
248 gen_taggery_Names new_dfuns `thenM` \ nm_alist_etc ->
251 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
252 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
253 mbinders = collectMonoBinders extra_mbinds
255 mappM gen_bind new_dfuns `thenM` \ method_binds_s ->
257 traceTc (text "tcDeriv" <+> ppr method_binds_s) `thenM_`
258 getModule `thenM` \ this_mod ->
259 initRn (InterfaceMode this_mod) (
260 -- Rename to get RenamedBinds.
261 -- The only tricky bit is that the extra_binds must scope
262 -- over the method bindings for the instances.
263 bindLocalsFVRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
264 rnTopMonoBinds extra_mbinds [] `thenM` \ (rn_extra_binds, fvs) ->
265 mapAndUnzipM rn_meths method_binds_s `thenM` \ (rn_method_binds_s, fvs_s) ->
266 returnM ((rn_method_binds_s, rn_extra_binds),
267 fvs `plusFV` plusFVs fvs_s)
268 ) `thenM` \ ((rn_method_binds_s, rn_extra_binds), fvs) ->
270 new_inst_infos = zipWith gen_inst_info new_dfuns rn_method_binds_s
272 returnM (new_inst_infos, rn_extra_binds, fvs)
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 = VanillaInst binds [] }
280 rn_meths (cls, meths) = rnMethodBinds cls [] meths
284 %************************************************************************
286 \subsection[TcDeriv-eqns]{Forming the equations}
288 %************************************************************************
290 @makeDerivEqns@ fishes around to find the info about needed derived
291 instances. Complicating factors:
294 We can only derive @Enum@ if the data type is an enumeration
295 type (all nullary data constructors).
298 We can only derive @Ix@ if the data type is an enumeration {\em
299 or} has just one data constructor (e.g., tuples).
302 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
306 makeDerivEqns :: [RenamedTyClDecl]
307 -> TcM ([DerivEqn], -- Ordinary derivings
308 [InstInfo]) -- Special newtype derivings
310 makeDerivEqns tycl_decls
311 = mapAndUnzipM mk_eqn derive_these `thenM` \ (maybe_ordinaries, maybe_newtypes) ->
312 returnM (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
314 ------------------------------------------------------------------
315 derive_these :: [(NewOrData, Name, RenamedHsPred)]
316 -- Find the (nd, TyCon, Pred) pairs that must be `derived'
317 -- NB: only source-language decls have deriving, no imported ones do
318 derive_these = [ (nd, tycon, pred)
319 | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
322 ------------------------------------------------------------------
323 mk_eqn :: (NewOrData, Name, RenamedHsPred) -> TcM (Maybe DerivEqn, Maybe InstInfo)
324 -- We swizzle the tyvars and datacons out of the tycon
325 -- to make the rest of the equation
327 mk_eqn (new_or_data, tycon_name, pred)
328 = tcLookupTyCon tycon_name `thenM` \ tycon ->
329 addSrcLoc (getSrcLoc tycon) $
330 addErrCtxt (derivCtxt Nothing tycon) $
331 tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
332 -- the type variables for the type constructor
333 tcHsPred pred `thenM` \ pred' ->
334 case getClassPredTys_maybe pred' of
335 Nothing -> bale_out (malformedPredErr tycon pred)
336 Just (clas, tys) -> mk_eqn_help new_or_data tycon clas tys
338 ------------------------------------------------------------------
339 mk_eqn_help DataType tycon clas tys
340 | Just err <- chk_out clas tycon tys
341 = bale_out (derivingThingErr clas tys tycon tyvars err)
343 = new_dfun_name clas tycon `thenM` \ dfun_name ->
344 returnM (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
346 tyvars = tyConTyVars tycon
347 data_cons = tyConDataCons tycon
348 constraints = extra_constraints ++
349 [ mkClassPred clas [arg_ty]
350 | data_con <- tyConDataCons tycon,
351 arg_ty <- dataConRepArgTys data_con,
352 -- Use the same type variables
353 -- as the type constructor,
354 -- hence no need to instantiate
355 not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
358 -- "extra_constraints": see note [Data decl contexts] above
359 extra_constraints = tyConTheta tycon
361 mk_eqn_help NewType tycon clas tys
362 = doptM Opt_GlasgowExts `thenM` \ gla_exts ->
363 if can_derive_via_isomorphism && (gla_exts || standard_instance) then
364 -- Go ahead and use the isomorphism
365 new_dfun_name clas tycon `thenM` \ dfun_name ->
366 returnM (Nothing, Just (InstInfo { iDFunId = mk_dfun dfun_name,
367 iBinds = NewTypeDerived rep_tys }))
369 if standard_instance then
370 mk_eqn_help DataType tycon clas [] -- Go via bale-out route
372 bale_out cant_derive_err
374 -- Here is the plan for newtype derivings. We see
375 -- newtype T a1...an = T (t ak...an) deriving (.., C s1 .. sm, ...)
376 -- where aj...an do not occur free in t, and the (C s1 ... sm) is a
377 -- *partial applications* of class C with the last parameter missing
379 -- We generate the instances
380 -- instance C s1 .. sm (t ak...aj) => C s1 .. sm (T a1...aj)
381 -- where T a1...aj is the partial application of the LHS of the correct kind
383 -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
384 -- instance Monad (ST s) => Monad (T s) where
385 -- fail = coerce ... (fail @ ST s)
387 clas_tyvars = classTyVars clas
388 kind = tyVarKind (last clas_tyvars)
389 -- Kind of the thing we want to instance
390 -- e.g. argument kind of Monad, *->*
392 (arg_kinds, _) = tcSplitFunTys kind
393 n_args_to_drop = length arg_kinds
394 -- Want to drop 1 arg from (T s a) and (ST s a)
395 -- to get instance Monad (ST s) => Monad (T s)
397 (tyvars, rep_ty) = newTyConRep tycon
398 (rep_fn, rep_ty_args) = splitAppTys rep_ty
400 n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
401 tyvars_to_drop = drop n_tyvars_to_keep tyvars
402 tyvars_to_keep = take n_tyvars_to_keep tyvars
404 n_args_to_keep = length rep_ty_args - n_args_to_drop
405 args_to_drop = drop n_args_to_keep rep_ty_args
406 args_to_keep = take n_args_to_keep rep_ty_args
408 rep_tys = tys ++ [mkAppTys rep_fn args_to_keep]
409 rep_pred = mkClassPred clas rep_tys
410 -- rep_pred is the representation dictionary, from where
411 -- we are gong to get all the methods for the newtype dictionary
413 inst_tys = (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)])
414 -- The 'tys' here come from the partial application
415 -- in the deriving clause. The last arg is the new
418 -- We must pass the superclasses; the newtype might be an instance
419 -- of them in a different way than the representation type
420 -- E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
421 -- Then the Show instance is not done via isomprphism; it shows
423 -- The Num instance is derived via isomorphism, but the Show superclass
424 -- dictionary must the Show instance for Foo, *not* the Show dictionary
425 -- gotten from the Num dictionary. So we must build a whole new dictionary
426 -- not just use the Num one. The instance we want is something like:
427 -- instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
430 -- There's no 'corece' needed because after the type checker newtypes
433 sc_theta = substTheta (mkTyVarSubst clas_tyvars inst_tys)
436 -- If there are no tyvars, there's no need
437 -- to abstract over the dictionaries we need
438 dict_args | null tyvars = []
439 | otherwise = rep_pred : sc_theta
441 -- Finally! Here's where we build the dictionary Id
442 mk_dfun dfun_name = mkDictFunId dfun_name tyvars dict_args clas inst_tys
444 -------------------------------------------------------------------
445 -- Figuring out whether we can only do this newtype-deriving thing
447 standard_instance = null tys && classKey clas `elem` derivableClassKeys
449 can_derive_via_isomorphism
450 = not (clas `hasKey` readClassKey) -- Never derive Read,Show this way
451 && not (clas `hasKey` showClassKey)
452 && n_tyvars_to_keep >= 0 -- Well kinded;
453 -- eg not: newtype T = T Int deriving( Monad )
454 && n_args_to_keep >= 0 -- Well kinded:
455 -- eg not: newtype T a = T Int deriving( Monad )
456 && eta_ok -- Eta reduction works
457 && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
458 -- newtype A = MkA [A]
460 -- instance Eq [A] => Eq A !!
462 -- Check that eta reduction is OK
463 -- (a) the dropped-off args are identical
464 -- (b) the remaining type args mention
465 -- only the remaining type variables
466 eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
467 && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
469 cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
470 (vcat [ptext SLIT("too hard for cunning newtype deriving"),
471 ppr n_tyvars_to_keep,
474 ppr (isRecursiveTyCon tycon)
477 bale_out err = addErrTc err `thenM_` returnM (Nothing, Nothing)
479 ------------------------------------------------------------------
480 chk_out :: Class -> TyCon -> [TcType] -> Maybe SDoc
481 chk_out clas tycon tys
482 | notNull tys = Just non_std_why
483 | not (getUnique clas `elem` derivableClassKeys) = Just non_std_why
484 | clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
485 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
486 | clas `hasKey` ixClassKey && not is_enumeration_or_single = Just single_nullary_why
487 | null data_cons = Just no_cons_why
488 | any isExistentialDataCon data_cons = Just existential_why
489 | otherwise = Nothing
491 data_cons = tyConDataCons tycon
492 is_enumeration = isEnumerationTyCon tycon
493 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
494 is_enumeration_or_single = is_enumeration || is_single_con
496 single_nullary_why = ptext SLIT("one constructor data type or type with all nullary constructors expected")
497 nullary_why = ptext SLIT("data type with all nullary constructors expected")
498 no_cons_why = ptext SLIT("type has no data constructors")
499 non_std_why = ptext SLIT("not a derivable class")
500 existential_why = ptext SLIT("it has existentially-quantified constructor(s)")
502 new_dfun_name clas tycon -- Just a simple wrapper
503 = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
504 -- The type passed to newDFunName is only used to generate
505 -- a suitable string; hence the empty type arg list
508 %************************************************************************
510 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
512 %************************************************************************
514 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
515 terms, which is the final correct RHS for the corresponding original
519 Each (k,TyVarTy tv) in a solution constrains only a type
523 The (k,TyVarTy tv) pairs in a solution are canonically
524 ordered by sorting on type varible, tv, (major key) and then class, k,
529 solveDerivEqns :: InstEnv
531 -> TcM [DFunId] -- Solns in same order as eqns.
532 -- This bunch is Absolutely minimal...
534 solveDerivEqns inst_env_in orig_eqns
535 = iterateDeriv 1 initial_solutions
537 -- The initial solutions for the equations claim that each
538 -- instance has an empty context; this solution is certainly
539 -- in canonical form.
540 initial_solutions :: [DerivSoln]
541 initial_solutions = [ [] | _ <- orig_eqns ]
543 ------------------------------------------------------------------
544 -- iterateDeriv calculates the next batch of solutions,
545 -- compares it with the current one; finishes if they are the
546 -- same, otherwise recurses with the new solutions.
547 -- It fails if any iteration fails
548 iterateDeriv :: Int -> [DerivSoln] ->TcM [DFunId]
549 iterateDeriv n current_solns
550 | n > 20 -- Looks as if we are in an infinite loop
551 -- This can happen if we have -fallow-undecidable-instances
552 -- (See TcSimplify.tcSimplifyDeriv.)
553 = pprPanic "solveDerivEqns: probable loop"
554 (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
556 = getDOpts `thenM` \ dflags ->
558 dfuns = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
559 inst_env = extend_inst_env dflags inst_env_in dfuns
562 -- Extend the inst info from the explicit instance decls
563 -- with the current set of solutions, and simplify each RHS
564 tcSetInstEnv inst_env $
565 mappM gen_soln orig_eqns
566 ) `thenM` \ new_solns ->
567 if (current_solns == new_solns) then
570 iterateDeriv (n+1) new_solns
572 ------------------------------------------------------------------
574 gen_soln (_, clas, tc,tyvars,deriv_rhs)
575 = addSrcLoc (getSrcLoc tc) $
576 addErrCtxt (derivCtxt (Just clas) tc) $
577 tcSimplifyDeriv tyvars deriv_rhs `thenM` \ theta ->
578 returnM (sortLt (<) theta) -- Canonicalise before returning the soluction
582 extend_inst_env dflags inst_env new_dfuns
585 (new_inst_env, _errs) = extendInstEnv dflags inst_env new_dfuns
586 -- Ignore the errors about duplicate instances.
587 -- We don't want repeated error messages
588 -- They'll appear later, when we do the top-level extendInstEnvs
590 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
591 = mkDictFunId dfun_name tyvars theta
592 clas [mkTyConApp tycon (mkTyVarTys tyvars)]
595 %************************************************************************
597 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
599 %************************************************************************
601 After all the trouble to figure out the required context for the
602 derived instance declarations, all that's left is to chug along to
603 produce them. They will then be shoved into @tcInstDecls2@, which
604 will do all its usual business.
606 There are lots of possibilities for code to generate. Here are
607 various general remarks.
612 We want derived instances of @Eq@ and @Ord@ (both v common) to be
613 ``you-couldn't-do-better-by-hand'' efficient.
616 Deriving @Show@---also pretty common--- should also be reasonable good code.
619 Deriving for the other classes isn't that common or that big a deal.
626 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
629 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
632 We {\em normally} generate code only for the non-defaulted methods;
633 there are some exceptions for @Eq@ and (especially) @Ord@...
636 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
637 constructor's numeric (@Int#@) tag. These are generated by
638 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
639 these is around is given by @hasCon2TagFun@.
641 The examples under the different sections below will make this
645 Much less often (really just for deriving @Ix@), we use a
646 @_tag2con_<tycon>@ function. See the examples.
649 We use the renamer!!! Reason: we're supposed to be
650 producing @RenamedMonoBinds@ for the methods, but that means
651 producing correctly-uniquified code on the fly. This is entirely
652 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
653 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
654 the renamer. What a great hack!
658 -- Generate the method bindings for the required instance
659 -- (paired with class name, as we need that when renaming
661 gen_bind :: DFunId -> TcM (Name, RdrNameMonoBinds)
663 = getFixityEnv `thenM` \ fix_env ->
664 returnM (cls_nm, gen_binds_fn fix_env cls_nm tycon)
666 cls_nm = className clas
667 (clas, tycon) = simpleDFunClassTyCon dfun
669 gen_binds_fn fix_env cls_nm
670 = assoc "gen_bind:bad derived class"
671 gen_list (nameUnique cls_nm)
673 gen_list = [(eqClassKey, gen_Eq_binds)
674 ,(ordClassKey, gen_Ord_binds)
675 ,(enumClassKey, gen_Enum_binds)
676 ,(boundedClassKey, gen_Bounded_binds)
677 ,(ixClassKey, gen_Ix_binds)
678 ,(showClassKey, gen_Show_binds fix_env)
679 ,(readClassKey, gen_Read_binds fix_env)
684 %************************************************************************
686 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
688 %************************************************************************
693 con2tag_Foo :: Foo ... -> Int#
694 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
695 maxtag_Foo :: Int -- ditto (NB: not unlifted)
698 We have a @con2tag@ function for a tycon if:
701 We're deriving @Eq@ and the tycon has nullary data constructors.
704 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
708 We have a @tag2con@ function for a tycon if:
711 We're deriving @Enum@, or @Ix@ (enum type only???)
714 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
717 gen_taggery_Names :: [DFunId]
718 -> TcM [(RdrName, -- for an assoc list
719 TyCon, -- related tycon
722 gen_taggery_Names dfuns
723 = foldlM do_con2tag [] tycons_of_interest `thenM` \ names_so_far ->
724 foldlM do_tag2con names_so_far tycons_of_interest
726 all_CTs = map simpleDFunClassTyCon dfuns
727 all_tycons = map snd all_CTs
728 (tycons_of_interest, _) = removeDups compare all_tycons
730 do_con2tag acc_Names tycon
731 | isDataTyCon tycon &&
732 ((we_are_deriving eqClassKey tycon
733 && any isNullaryDataCon (tyConDataCons tycon))
734 || (we_are_deriving ordClassKey tycon
735 && not (maybeToBool (maybeTyConSingleCon tycon)))
736 || (we_are_deriving enumClassKey tycon)
737 || (we_are_deriving ixClassKey tycon))
739 = returnM ((con2tag_RDR tycon, tycon, GenCon2Tag)
744 do_tag2con acc_Names tycon
745 | isDataTyCon tycon &&
746 (we_are_deriving enumClassKey tycon ||
747 we_are_deriving ixClassKey tycon
748 && isEnumerationTyCon tycon)
749 = returnM ( (tag2con_RDR tycon, tycon, GenTag2Con)
750 : (maxtag_RDR tycon, tycon, GenMaxTag)
755 we_are_deriving clas_key tycon
756 = is_in_eqns clas_key tycon all_CTs
758 is_in_eqns clas_key tycon [] = False
759 is_in_eqns clas_key tycon ((c,t):cts)
760 = (clas_key == classKey c && tycon == t)
761 || is_in_eqns clas_key tycon cts
765 derivingThingErr clas tys tycon tyvars why
766 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
769 pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
771 malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
773 derivCtxt :: Maybe Class -> TyCon -> SDoc
774 derivCtxt maybe_cls tycon
775 = ptext SLIT("When deriving") <+> cls <+> ptext SLIT("for type") <+> quotes (ppr tycon)
777 cls = case maybe_cls of
778 Nothing -> ptext SLIT("instances")
779 Just c -> ptext SLIT("the") <+> quotes (ppr c) <+> ptext SLIT("instance")