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, dataConOrigArgTys, isNullaryDataCon, isExistentialDataCon )
40 import Maybes ( maybeToBool, catMaybes )
41 import Name ( Name, getSrcLoc, nameUnique )
43 import RdrName ( RdrName )
45 import TyCon ( tyConTyVars, tyConDataCons, tyConArity,
46 tyConTheta, maybeTyConSingleCon, isDataTyCon,
47 isEnumerationTyCon, isRecursiveTyCon, TyCon
49 import TcType ( TcType, ThetaType, mkTyVarTys, mkTyConApp, getClassPredTys_maybe,
50 isUnLiftedType, mkClassPred, tyVarsOfTypes, tcSplitFunTys,
51 tcEqTypes, tcSplitAppTys, mkAppTys )
52 import Var ( TyVar, tyVarKind )
53 import VarSet ( mkVarSet, subVarSet )
55 import Util ( zipWithEqual, sortLt, notNull )
56 import ListSetOps ( removeDups, assoc )
60 %************************************************************************
62 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
64 %************************************************************************
68 data T a b = C1 (Foo a) (Bar b)
73 [NOTE: See end of these comments for what to do with
74 data (C a, D b) => T a b = ...
77 We want to come up with an instance declaration of the form
79 instance (Ping a, Pong b, ...) => Eq (T a b) where
82 It is pretty easy, albeit tedious, to fill in the code "...". The
83 trick is to figure out what the context for the instance decl is,
84 namely @Ping@, @Pong@ and friends.
86 Let's call the context reqd for the T instance of class C at types
87 (a,b, ...) C (T a b). Thus:
89 Eq (T a b) = (Ping a, Pong b, ...)
91 Now we can get a (recursive) equation from the @data@ decl:
93 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
94 u Eq (T b a) u Eq Int -- From C2
95 u Eq (T a a) -- From C3
97 Foo and Bar may have explicit instances for @Eq@, in which case we can
98 just substitute for them. Alternatively, either or both may have
99 their @Eq@ instances given by @deriving@ clauses, in which case they
100 form part of the system of equations.
102 Now all we need do is simplify and solve the equations, iterating to
103 find the least fixpoint. Notice that the order of the arguments can
104 switch around, as here in the recursive calls to T.
106 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
110 Eq (T a b) = {} -- The empty set
113 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
114 u Eq (T b a) u Eq Int -- From C2
115 u Eq (T a a) -- From C3
117 After simplification:
118 = Eq a u Ping b u {} u {} u {}
123 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
124 u Eq (T b a) u Eq Int -- From C2
125 u Eq (T a a) -- From C3
127 After simplification:
132 = Eq a u Ping b u Eq b u Ping a
134 The next iteration gives the same result, so this is the fixpoint. We
135 need to make a canonical form of the RHS to ensure convergence. We do
136 this by simplifying the RHS to a form in which
138 - the classes constrain only tyvars
139 - the list is sorted by tyvar (major key) and then class (minor key)
140 - no duplicates, of course
142 So, here are the synonyms for the ``equation'' structures:
145 type DerivEqn = (Name, Class, TyCon, [TyVar], DerivRhs)
146 -- The Name is the name for the DFun we'll build
147 -- The tyvars bind all the variables in the RHS
149 pprDerivEqn (n,c,tc,tvs,rhs)
150 = parens (hsep [ppr n, ppr c, ppr tc, ppr tvs] <+> equals <+> ppr rhs)
152 type DerivRhs = ThetaType
153 type DerivSoln = DerivRhs
157 [Data decl contexts] A note about contexts on data decls
158 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
161 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
163 We will need an instance decl like:
165 instance (Read a, RealFloat a) => Read (Complex a) where
168 The RealFloat in the context is because the read method for Complex is bound
169 to construct a Complex, and doing that requires that the argument type is
172 But this ain't true for Show, Eq, Ord, etc, since they don't construct
173 a Complex; they only take them apart.
175 Our approach: identify the offending classes, and add the data type
176 context to the instance decl. The "offending classes" are
180 FURTHER NOTE ADDED March 2002. In fact, Haskell98 now requires that
181 pattern matching against a constructor from a data type with a context
182 gives rise to the constraints for that context -- or at least the thinned
183 version. So now all classes are "offending".
187 %************************************************************************
189 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
191 %************************************************************************
194 tcDeriving :: [RenamedTyClDecl] -- All type constructors
195 -> TcM ([InstInfo], -- The generated "instance decls".
196 RenamedHsBinds, -- Extra generated bindings
197 FreeVars) -- These are free in the generated bindings
199 tcDeriving tycl_decls
200 = recoverM (returnM ([], EmptyBinds, emptyFVs)) $
201 getDOpts `thenM` \ dflags ->
202 tcGetInstEnv `thenM` \ inst_env ->
204 -- Fish the "deriving"-related information out of the TcEnv
205 -- and make the necessary "equations".
206 makeDerivEqns tycl_decls `thenM` \ (ordinary_eqns, newtype_inst_info) ->
208 -- Add the newtype-derived instances to the inst env
209 -- before tacking the "ordinary" ones
210 inst_env1 = extend_inst_env dflags inst_env
211 (map iDFunId newtype_inst_info)
213 deriveOrdinaryStuff inst_env1 ordinary_eqns `thenM` \ (ordinary_inst_info, binds, fvs) ->
215 inst_info = newtype_inst_info ++ ordinary_inst_info
218 ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
219 (ddump_deriving inst_info binds)) `thenM_`
221 returnM (inst_info, binds, fvs)
224 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
225 ddump_deriving inst_infos extra_binds
226 = vcat (map ppr_info inst_infos) $$ ppr extra_binds
228 ppr_info inst_info = pprInstInfo inst_info $$
229 nest 4 (pprInstInfoDetails inst_info)
230 -- pprInstInfo doesn't print much: only the type
232 -----------------------------------------
233 deriveOrdinaryStuff inst_env_in [] -- Short cut
234 = returnM ([], EmptyBinds, emptyFVs)
236 deriveOrdinaryStuff inst_env_in eqns
237 = -- Take the equation list and solve it, to deliver a list of
238 -- solutions, a.k.a. the contexts for the instance decls
239 -- required for the corresponding equations.
240 solveDerivEqns inst_env_in eqns `thenM` \ new_dfuns ->
242 -- Now augment the InstInfos, adding in the rather boring
243 -- actual-code-to-do-the-methods binds. We may also need to
244 -- generate extra not-one-inst-decl-specific binds, notably
245 -- "con2tag" and/or "tag2con" functions. We do these
247 gen_taggery_Names new_dfuns `thenM` \ nm_alist_etc ->
250 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
251 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
252 mbinders = collectMonoBinders extra_mbinds
254 mappM gen_bind new_dfuns `thenM` \ method_binds_s ->
256 traceTc (text "tcDeriv" <+> ppr method_binds_s) `thenM_`
257 getModule `thenM` \ this_mod ->
258 initRn (InterfaceMode this_mod) (
259 -- Rename to get RenamedBinds.
260 -- The only tricky bit is that the extra_binds must scope
261 -- over the method bindings for the instances.
262 bindLocalsFVRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
263 rnTopMonoBinds extra_mbinds [] `thenM` \ (rn_extra_binds, fvs) ->
264 mapAndUnzipM rn_meths method_binds_s `thenM` \ (rn_method_binds_s, fvs_s) ->
265 returnM ((rn_method_binds_s, rn_extra_binds),
266 fvs `plusFV` plusFVs fvs_s)
267 ) `thenM` \ ((rn_method_binds_s, rn_extra_binds), fvs) ->
269 new_inst_infos = zipWith gen_inst_info new_dfuns rn_method_binds_s
271 returnM (new_inst_infos, rn_extra_binds, fvs)
274 -- Make a Real dfun instead of the dummy one we have so far
275 gen_inst_info :: DFunId -> RenamedMonoBinds -> InstInfo
276 gen_inst_info dfun binds
277 = InstInfo { iDFunId = dfun, iBinds = VanillaInst binds [] }
279 rn_meths (cls, meths) = rnMethodBinds cls [] meths
283 %************************************************************************
285 \subsection[TcDeriv-eqns]{Forming the equations}
287 %************************************************************************
289 @makeDerivEqns@ fishes around to find the info about needed derived
290 instances. Complicating factors:
293 We can only derive @Enum@ if the data type is an enumeration
294 type (all nullary data constructors).
297 We can only derive @Ix@ if the data type is an enumeration {\em
298 or} has just one data constructor (e.g., tuples).
301 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
305 makeDerivEqns :: [RenamedTyClDecl]
306 -> TcM ([DerivEqn], -- Ordinary derivings
307 [InstInfo]) -- Special newtype derivings
309 makeDerivEqns tycl_decls
310 = mapAndUnzipM mk_eqn derive_these `thenM` \ (maybe_ordinaries, maybe_newtypes) ->
311 returnM (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
313 ------------------------------------------------------------------
314 derive_these :: [(NewOrData, Name, RenamedHsPred)]
315 -- Find the (nd, TyCon, Pred) pairs that must be `derived'
316 -- NB: only source-language decls have deriving, no imported ones do
317 derive_these = [ (nd, tycon, pred)
318 | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
321 ------------------------------------------------------------------
322 mk_eqn :: (NewOrData, Name, RenamedHsPred) -> TcM (Maybe DerivEqn, Maybe InstInfo)
323 -- We swizzle the tyvars and datacons out of the tycon
324 -- to make the rest of the equation
326 mk_eqn (new_or_data, tycon_name, pred)
327 = tcLookupTyCon tycon_name `thenM` \ tycon ->
328 addSrcLoc (getSrcLoc tycon) $
329 addErrCtxt (derivCtxt Nothing tycon) $
330 tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
331 -- the type variables for the type constructor
332 tcHsPred pred `thenM` \ pred' ->
333 case getClassPredTys_maybe pred' of
334 Nothing -> bale_out (malformedPredErr tycon pred)
335 Just (clas, tys) -> mk_eqn_help new_or_data tycon clas tys
337 ------------------------------------------------------------------
338 mk_eqn_help DataType tycon clas tys
339 | Just err <- chk_out clas tycon tys
340 = bale_out (derivingThingErr clas tys tycon tyvars err)
342 = new_dfun_name clas tycon `thenM` \ dfun_name ->
343 returnM (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
345 tyvars = tyConTyVars tycon
346 data_cons = tyConDataCons tycon
347 constraints = extra_constraints ++
348 [ mkClassPred clas [arg_ty]
349 | data_con <- tyConDataCons tycon,
350 arg_ty <- dataConRepArgTys data_con, -- dataConOrigArgTys???
351 -- Use the same type variables
352 -- as the type constructor,
353 -- hence no need to instantiate
354 not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
357 -- "extra_constraints": see note [Data decl contexts] above
358 extra_constraints = tyConTheta tycon
360 mk_eqn_help NewType tycon clas tys
361 = doptM Opt_GlasgowExts `thenM` \ gla_exts ->
362 if can_derive_via_isomorphism && (gla_exts || standard_instance) then
363 -- Go ahead and use the isomorphism
364 traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys) `thenM_`
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 -- Note [newtype representation]
398 -- We must not use newTyConRep to get the representation
399 -- type, because that looks through all intermediate newtypes
400 -- To get the RHS of *this* newtype, just look at the data
401 -- constructor. For example
402 -- newtype B = MkB Int
403 -- newtype A = MkA B deriving( Num )
404 -- We want the Num instance of B, *not* the Num instance of Int,
405 -- when making the Num instance of A!
406 tyvars = tyConTyVars tycon
407 rep_ty = head (dataConOrigArgTys (head (tyConDataCons tycon)))
408 (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
410 n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
411 tyvars_to_drop = drop n_tyvars_to_keep tyvars
412 tyvars_to_keep = take n_tyvars_to_keep tyvars
414 n_args_to_keep = length rep_ty_args - n_args_to_drop
415 args_to_drop = drop n_args_to_keep rep_ty_args
416 args_to_keep = take n_args_to_keep rep_ty_args
418 rep_tys = tys ++ [mkAppTys rep_fn args_to_keep]
419 rep_pred = mkClassPred clas rep_tys
420 -- rep_pred is the representation dictionary, from where
421 -- we are gong to get all the methods for the newtype dictionary
423 inst_tys = (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)])
424 -- The 'tys' here come from the partial application
425 -- in the deriving clause. The last arg is the new
428 -- We must pass the superclasses; the newtype might be an instance
429 -- of them in a different way than the representation type
430 -- E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
431 -- Then the Show instance is not done via isomprphism; it shows
433 -- The Num instance is derived via isomorphism, but the Show superclass
434 -- dictionary must the Show instance for Foo, *not* the Show dictionary
435 -- gotten from the Num dictionary. So we must build a whole new dictionary
436 -- not just use the Num one. The instance we want is something like:
437 -- instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
440 -- There's no 'corece' needed because after the type checker newtypes
443 sc_theta = substTheta (mkTyVarSubst clas_tyvars inst_tys)
446 -- If there are no tyvars, there's no need
447 -- to abstract over the dictionaries we need
448 dict_args | null tyvars = []
449 | otherwise = rep_pred : sc_theta
451 -- Finally! Here's where we build the dictionary Id
452 mk_dfun dfun_name = mkDictFunId dfun_name tyvars dict_args clas inst_tys
454 -------------------------------------------------------------------
455 -- Figuring out whether we can only do this newtype-deriving thing
457 standard_instance = null tys && classKey clas `elem` derivableClassKeys
459 can_derive_via_isomorphism
460 = not (clas `hasKey` readClassKey) -- Never derive Read,Show this way
461 && not (clas `hasKey` showClassKey)
462 && n_tyvars_to_keep >= 0 -- Well kinded;
463 -- eg not: newtype T = T Int deriving( Monad )
464 && n_args_to_keep >= 0 -- Well kinded:
465 -- eg not: newtype T a = T Int deriving( Monad )
466 && eta_ok -- Eta reduction works
467 && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
468 -- newtype A = MkA [A]
470 -- instance Eq [A] => Eq A !!
472 -- Check that eta reduction is OK
473 -- (a) the dropped-off args are identical
474 -- (b) the remaining type args mention
475 -- only the remaining type variables
476 eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
477 && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
479 cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
480 (vcat [ptext SLIT("too hard for cunning newtype deriving"),
481 ppr n_tyvars_to_keep,
484 ppr (isRecursiveTyCon tycon)
487 bale_out err = addErrTc err `thenM_` returnM (Nothing, Nothing)
489 ------------------------------------------------------------------
490 chk_out :: Class -> TyCon -> [TcType] -> Maybe SDoc
491 chk_out clas tycon tys
492 | notNull tys = Just non_std_why
493 | not (getUnique clas `elem` derivableClassKeys) = Just non_std_why
494 | clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
495 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
496 | clas `hasKey` ixClassKey && not is_enumeration_or_single = Just single_nullary_why
497 | null data_cons = Just no_cons_why
498 | any isExistentialDataCon data_cons = Just existential_why
499 | otherwise = Nothing
501 data_cons = tyConDataCons tycon
502 is_enumeration = isEnumerationTyCon tycon
503 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
504 is_enumeration_or_single = is_enumeration || is_single_con
506 single_nullary_why = ptext SLIT("one constructor data type or type with all nullary constructors expected")
507 nullary_why = ptext SLIT("data type with all nullary constructors expected")
508 no_cons_why = ptext SLIT("type has no data constructors")
509 non_std_why = ptext SLIT("not a derivable class")
510 existential_why = ptext SLIT("it has existentially-quantified constructor(s)")
512 new_dfun_name clas tycon -- Just a simple wrapper
513 = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
514 -- The type passed to newDFunName is only used to generate
515 -- a suitable string; hence the empty type arg list
518 %************************************************************************
520 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
522 %************************************************************************
524 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
525 terms, which is the final correct RHS for the corresponding original
529 Each (k,TyVarTy tv) in a solution constrains only a type
533 The (k,TyVarTy tv) pairs in a solution are canonically
534 ordered by sorting on type varible, tv, (major key) and then class, k,
539 solveDerivEqns :: InstEnv
541 -> TcM [DFunId] -- Solns in same order as eqns.
542 -- This bunch is Absolutely minimal...
544 solveDerivEqns inst_env_in orig_eqns
545 = iterateDeriv 1 initial_solutions
547 -- The initial solutions for the equations claim that each
548 -- instance has an empty context; this solution is certainly
549 -- in canonical form.
550 initial_solutions :: [DerivSoln]
551 initial_solutions = [ [] | _ <- orig_eqns ]
553 ------------------------------------------------------------------
554 -- iterateDeriv calculates the next batch of solutions,
555 -- compares it with the current one; finishes if they are the
556 -- same, otherwise recurses with the new solutions.
557 -- It fails if any iteration fails
558 iterateDeriv :: Int -> [DerivSoln] ->TcM [DFunId]
559 iterateDeriv n current_solns
560 | n > 20 -- Looks as if we are in an infinite loop
561 -- This can happen if we have -fallow-undecidable-instances
562 -- (See TcSimplify.tcSimplifyDeriv.)
563 = pprPanic "solveDerivEqns: probable loop"
564 (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
566 = getDOpts `thenM` \ dflags ->
568 dfuns = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
569 inst_env = extend_inst_env dflags inst_env_in dfuns
572 -- Extend the inst info from the explicit instance decls
573 -- with the current set of solutions, and simplify each RHS
574 tcSetInstEnv inst_env $
575 mappM gen_soln orig_eqns
576 ) `thenM` \ new_solns ->
577 if (current_solns == new_solns) then
580 iterateDeriv (n+1) new_solns
582 ------------------------------------------------------------------
584 gen_soln (_, clas, tc,tyvars,deriv_rhs)
585 = addSrcLoc (getSrcLoc tc) $
586 addErrCtxt (derivCtxt (Just clas) tc) $
587 tcSimplifyDeriv tyvars deriv_rhs `thenM` \ theta ->
588 returnM (sortLt (<) theta) -- Canonicalise before returning the soluction
592 extend_inst_env dflags inst_env new_dfuns
595 (new_inst_env, _errs) = extendInstEnv dflags inst_env new_dfuns
596 -- Ignore the errors about duplicate instances.
597 -- We don't want repeated error messages
598 -- They'll appear later, when we do the top-level extendInstEnvs
600 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
601 = mkDictFunId dfun_name tyvars theta
602 clas [mkTyConApp tycon (mkTyVarTys tyvars)]
605 %************************************************************************
607 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
609 %************************************************************************
611 After all the trouble to figure out the required context for the
612 derived instance declarations, all that's left is to chug along to
613 produce them. They will then be shoved into @tcInstDecls2@, which
614 will do all its usual business.
616 There are lots of possibilities for code to generate. Here are
617 various general remarks.
622 We want derived instances of @Eq@ and @Ord@ (both v common) to be
623 ``you-couldn't-do-better-by-hand'' efficient.
626 Deriving @Show@---also pretty common--- should also be reasonable good code.
629 Deriving for the other classes isn't that common or that big a deal.
636 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
639 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
642 We {\em normally} generate code only for the non-defaulted methods;
643 there are some exceptions for @Eq@ and (especially) @Ord@...
646 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
647 constructor's numeric (@Int#@) tag. These are generated by
648 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
649 these is around is given by @hasCon2TagFun@.
651 The examples under the different sections below will make this
655 Much less often (really just for deriving @Ix@), we use a
656 @_tag2con_<tycon>@ function. See the examples.
659 We use the renamer!!! Reason: we're supposed to be
660 producing @RenamedMonoBinds@ for the methods, but that means
661 producing correctly-uniquified code on the fly. This is entirely
662 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
663 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
664 the renamer. What a great hack!
668 -- Generate the method bindings for the required instance
669 -- (paired with class name, as we need that when renaming
671 gen_bind :: DFunId -> TcM (Name, RdrNameMonoBinds)
673 = getFixityEnv `thenM` \ fix_env ->
674 returnM (cls_nm, gen_binds_fn fix_env cls_nm tycon)
676 cls_nm = className clas
677 (clas, tycon) = simpleDFunClassTyCon dfun
679 gen_binds_fn fix_env cls_nm
680 = assoc "gen_bind:bad derived class"
681 gen_list (nameUnique cls_nm)
683 gen_list = [(eqClassKey, gen_Eq_binds)
684 ,(ordClassKey, gen_Ord_binds)
685 ,(enumClassKey, gen_Enum_binds)
686 ,(boundedClassKey, gen_Bounded_binds)
687 ,(ixClassKey, gen_Ix_binds)
688 ,(showClassKey, gen_Show_binds fix_env)
689 ,(readClassKey, gen_Read_binds fix_env)
694 %************************************************************************
696 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
698 %************************************************************************
703 con2tag_Foo :: Foo ... -> Int#
704 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
705 maxtag_Foo :: Int -- ditto (NB: not unlifted)
708 We have a @con2tag@ function for a tycon if:
711 We're deriving @Eq@ and the tycon has nullary data constructors.
714 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
718 We have a @tag2con@ function for a tycon if:
721 We're deriving @Enum@, or @Ix@ (enum type only???)
724 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
727 gen_taggery_Names :: [DFunId]
728 -> TcM [(RdrName, -- for an assoc list
729 TyCon, -- related tycon
732 gen_taggery_Names dfuns
733 = foldlM do_con2tag [] tycons_of_interest `thenM` \ names_so_far ->
734 foldlM do_tag2con names_so_far tycons_of_interest
736 all_CTs = map simpleDFunClassTyCon dfuns
737 all_tycons = map snd all_CTs
738 (tycons_of_interest, _) = removeDups compare all_tycons
740 do_con2tag acc_Names tycon
741 | isDataTyCon tycon &&
742 ((we_are_deriving eqClassKey tycon
743 && any isNullaryDataCon (tyConDataCons tycon))
744 || (we_are_deriving ordClassKey tycon
745 && not (maybeToBool (maybeTyConSingleCon tycon)))
746 || (we_are_deriving enumClassKey tycon)
747 || (we_are_deriving ixClassKey tycon))
749 = returnM ((con2tag_RDR tycon, tycon, GenCon2Tag)
754 do_tag2con acc_Names tycon
755 | isDataTyCon tycon &&
756 (we_are_deriving enumClassKey tycon ||
757 we_are_deriving ixClassKey tycon
758 && isEnumerationTyCon tycon)
759 = returnM ( (tag2con_RDR tycon, tycon, GenTag2Con)
760 : (maxtag_RDR tycon, tycon, GenMaxTag)
765 we_are_deriving clas_key tycon
766 = is_in_eqns clas_key tycon all_CTs
768 is_in_eqns clas_key tycon [] = False
769 is_in_eqns clas_key tycon ((c,t):cts)
770 = (clas_key == classKey c && tycon == t)
771 || is_in_eqns clas_key tycon cts
775 derivingThingErr clas tys tycon tyvars why
776 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
779 pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
781 malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
783 derivCtxt :: Maybe Class -> TyCon -> SDoc
784 derivCtxt maybe_cls tycon
785 = ptext SLIT("When deriving") <+> cls <+> ptext SLIT("for type") <+> quotes (ppr tycon)
787 cls = case maybe_cls of
788 Nothing -> ptext SLIT("instances")
789 Just c -> ptext SLIT("the") <+> quotes (ppr c) <+> ptext SLIT("instance")