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(..), TyClDecl(..),
14 andMonoBindList, collectMonoBinders )
15 import RdrHsSyn ( RdrNameMonoBinds )
16 import RnHsSyn ( RenamedHsBinds, RenamedTyClDecl, RenamedHsPred )
17 import CmdLineOpts ( DynFlag(..) )
20 import TcEnv ( tcExtendTempInstEnv, newDFunName,
21 InstInfo(..), pprInstInfo, InstBindings(..),
22 pprInstInfoDetails, tcLookupTyCon, tcExtendTyVarEnv
24 import TcGenDeriv -- Deriv stuff
25 import InstEnv ( simpleDFunClassTyCon )
26 import TcMonoType ( tcHsPred )
27 import TcSimplify ( tcSimplifyDeriv )
29 import RnBinds ( rnMethodBinds, rnTopMonoBinds )
30 import RnEnv ( bindLocalsFV, extendTyVarEnvFVRn )
31 import TcRnMonad ( thenM, returnM, mapAndUnzipM )
32 import HscTypes ( DFunId )
34 import BasicTypes ( NewOrData(..) )
35 import Class ( className, classArity, classKey, classTyVars, classSCTheta, Class )
36 import Subst ( mkTyVarSubst, substTheta )
37 import ErrUtils ( dumpIfSet_dyn )
38 import MkId ( mkDictFunId )
39 import DataCon ( dataConOrigArgTys, isNullaryDataCon, isExistentialDataCon )
40 import Maybes ( maybeToBool, catMaybes )
41 import Name ( Name, getSrcLoc )
42 import Unique ( getUnique )
44 import RdrName ( RdrName )
46 import TyCon ( tyConTyVars, tyConDataCons, tyConArity,
47 tyConTheta, maybeTyConSingleCon, isDataTyCon,
48 isEnumerationTyCon, isRecursiveTyCon, TyCon
50 import TcType ( TcType, ThetaType, mkTyVarTy, mkTyVarTys, mkTyConApp,
51 getClassPredTys_maybe,
52 isUnLiftedType, mkClassPred, tyVarsOfTypes, tcSplitFunTys, isTypeKind,
53 tcEqTypes, tcSplitAppTys, mkAppTys, tcSplitDFunTy )
54 import Var ( TyVar, tyVarKind, idType, varName )
55 import VarSet ( mkVarSet, subVarSet )
57 import Util ( zipWithEqual, sortLt, notNull )
58 import ListSetOps ( removeDups, assoc )
62 %************************************************************************
64 \subsection[TcDeriv-intro]{Introduction to how we do deriving}
66 %************************************************************************
70 data T a b = C1 (Foo a) (Bar b)
75 [NOTE: See end of these comments for what to do with
76 data (C a, D b) => T a b = ...
79 We want to come up with an instance declaration of the form
81 instance (Ping a, Pong b, ...) => Eq (T a b) where
84 It is pretty easy, albeit tedious, to fill in the code "...". The
85 trick is to figure out what the context for the instance decl is,
86 namely @Ping@, @Pong@ and friends.
88 Let's call the context reqd for the T instance of class C at types
89 (a,b, ...) C (T a b). Thus:
91 Eq (T a b) = (Ping a, Pong b, ...)
93 Now we can get a (recursive) equation from the @data@ decl:
95 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
96 u Eq (T b a) u Eq Int -- From C2
97 u Eq (T a a) -- From C3
99 Foo and Bar may have explicit instances for @Eq@, in which case we can
100 just substitute for them. Alternatively, either or both may have
101 their @Eq@ instances given by @deriving@ clauses, in which case they
102 form part of the system of equations.
104 Now all we need do is simplify and solve the equations, iterating to
105 find the least fixpoint. Notice that the order of the arguments can
106 switch around, as here in the recursive calls to T.
108 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
112 Eq (T a b) = {} -- The empty set
115 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
116 u Eq (T b a) u Eq Int -- From C2
117 u Eq (T a a) -- From C3
119 After simplification:
120 = Eq a u Ping b u {} u {} u {}
125 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
126 u Eq (T b a) u Eq Int -- From C2
127 u Eq (T a a) -- From C3
129 After simplification:
134 = Eq a u Ping b u Eq b u Ping a
136 The next iteration gives the same result, so this is the fixpoint. We
137 need to make a canonical form of the RHS to ensure convergence. We do
138 this by simplifying the RHS to a form in which
140 - the classes constrain only tyvars
141 - the list is sorted by tyvar (major key) and then class (minor key)
142 - no duplicates, of course
144 So, here are the synonyms for the ``equation'' structures:
147 type DerivEqn = (Name, Class, TyCon, [TyVar], DerivRhs)
148 -- The Name is the name for the DFun we'll build
149 -- The tyvars bind all the variables in the RHS
151 pprDerivEqn (n,c,tc,tvs,rhs)
152 = parens (hsep [ppr n, ppr c, ppr tc, ppr tvs] <+> equals <+> ppr rhs)
154 type DerivRhs = ThetaType
155 type DerivSoln = DerivRhs
159 [Data decl contexts] A note about contexts on data decls
160 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
163 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
165 We will need an instance decl like:
167 instance (Read a, RealFloat a) => Read (Complex a) where
170 The RealFloat in the context is because the read method for Complex is bound
171 to construct a Complex, and doing that requires that the argument type is
174 But this ain't true for Show, Eq, Ord, etc, since they don't construct
175 a Complex; they only take them apart.
177 Our approach: identify the offending classes, and add the data type
178 context to the instance decl. The "offending classes" are
182 FURTHER NOTE ADDED March 2002. In fact, Haskell98 now requires that
183 pattern matching against a constructor from a data type with a context
184 gives rise to the constraints for that context -- or at least the thinned
185 version. So now all classes are "offending".
189 %************************************************************************
191 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
193 %************************************************************************
196 tcDeriving :: [RenamedTyClDecl] -- All type constructors
197 -> TcM ([InstInfo], -- The generated "instance decls".
198 RenamedHsBinds, -- Extra generated bindings
199 FreeVars) -- These are free in the generated bindings
201 tcDeriving tycl_decls
202 = recoverM (returnM ([], EmptyBinds, emptyFVs)) $
203 getDOpts `thenM` \ dflags ->
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) ->
208 tcExtendTempInstEnv (map iDFunId newtype_inst_info) $
209 -- Add the newtype-derived instances to the inst env
210 -- before tacking the "ordinary" ones
212 deriveOrdinaryStuff ordinary_eqns `thenM` \ (ordinary_inst_info, binds, fvs) ->
214 inst_info = newtype_inst_info ++ ordinary_inst_info
217 ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
218 (ddump_deriving inst_info binds)) `thenM_`
220 returnM (inst_info, binds, fvs)
223 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
224 ddump_deriving inst_infos extra_binds
225 = vcat (map ppr_info inst_infos) $$ ppr extra_binds
227 ppr_info inst_info = pprInstInfo inst_info $$
228 nest 4 (pprInstInfoDetails inst_info)
229 -- pprInstInfo doesn't print much: only the type
231 -----------------------------------------
232 deriveOrdinaryStuff [] -- Short cut
233 = returnM ([], EmptyBinds, emptyFVs)
235 deriveOrdinaryStuff eqns
236 = -- Take the equation list and solve it, to deliver a list of
237 -- solutions, a.k.a. the contexts for the instance decls
238 -- required for the corresponding equations.
239 solveDerivEqns eqns `thenM` \ new_dfuns ->
241 -- Now augment the InstInfos, adding in the rather boring
242 -- actual-code-to-do-the-methods binds. We may also need to
243 -- generate extra not-one-inst-decl-specific binds, notably
244 -- "con2tag" and/or "tag2con" functions. We do these
246 gen_taggery_Names new_dfuns `thenM` \ nm_alist_etc ->
249 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
250 extra_mbinds = andMonoBindList extra_mbind_list
251 mbinders = collectMonoBinders extra_mbinds
253 mappM gen_bind new_dfuns `thenM` \ rdr_name_inst_infos ->
255 traceTc (text "tcDeriv" <+> vcat (map ppr rdr_name_inst_infos)) `thenM_`
256 getModule `thenM` \ this_mod ->
257 initRn (InterfaceMode this_mod) (
258 -- Rename to get RenamedBinds.
259 -- The only tricky bit is that the extra_binds must scope
260 -- over the method bindings for the instances.
261 bindLocalsFV (ptext (SLIT("deriving"))) mbinders $ \ _ ->
262 rnTopMonoBinds extra_mbinds [] `thenM` \ (rn_extra_binds, dus) ->
263 mapAndUnzipM rn_inst_info rdr_name_inst_infos `thenM` \ (rn_inst_infos, fvs_s) ->
264 returnM ((rn_inst_infos, rn_extra_binds),
265 duUses dus `plusFV` plusFVs fvs_s)
266 ) `thenM` \ ((rn_inst_infos, rn_extra_binds), fvs) ->
267 returnM (rn_inst_infos, rn_extra_binds, fvs)
270 rn_inst_info (dfun, binds)
271 = extendTyVarEnvFVRn (map varName tyvars) $
272 -- Bring the right type variables into scope
273 rnMethodBinds (className cls) [] binds `thenM` \ (rn_binds, fvs) ->
274 return (InstInfo { iDFunId = dfun, iBinds = VanillaInst rn_binds [] }, fvs)
276 (tyvars, _, cls, _) = tcSplitDFunTy (idType dfun)
280 %************************************************************************
282 \subsection[TcDeriv-eqns]{Forming the equations}
284 %************************************************************************
286 @makeDerivEqns@ fishes around to find the info about needed derived
287 instances. Complicating factors:
290 We can only derive @Enum@ if the data type is an enumeration
291 type (all nullary data constructors).
294 We can only derive @Ix@ if the data type is an enumeration {\em
295 or} has just one data constructor (e.g., tuples).
298 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
302 makeDerivEqns :: [RenamedTyClDecl]
303 -> TcM ([DerivEqn], -- Ordinary derivings
304 [InstInfo]) -- Special newtype derivings
306 makeDerivEqns tycl_decls
307 = mapAndUnzipM mk_eqn derive_these `thenM` \ (maybe_ordinaries, maybe_newtypes) ->
308 returnM (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
310 ------------------------------------------------------------------
311 derive_these :: [(NewOrData, Name, RenamedHsPred)]
312 -- Find the (nd, TyCon, Pred) pairs that must be `derived'
313 -- NB: only source-language decls have deriving, no imported ones do
314 derive_these = [ (nd, tycon, pred)
315 | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
318 ------------------------------------------------------------------
319 mk_eqn :: (NewOrData, Name, RenamedHsPred) -> TcM (Maybe DerivEqn, Maybe InstInfo)
320 -- We swizzle the tyvars and datacons out of the tycon
321 -- to make the rest of the equation
323 mk_eqn (new_or_data, tycon_name, pred)
324 = tcLookupTyCon tycon_name `thenM` \ tycon ->
325 addSrcLoc (getSrcLoc tycon) $
326 addErrCtxt (derivCtxt Nothing tycon) $
327 tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
328 -- the type variables for the type constructor
329 tcHsPred pred `thenM` \ pred' ->
330 case getClassPredTys_maybe pred' of
331 Nothing -> bale_out (malformedPredErr tycon pred)
332 Just (clas, tys) -> doptM Opt_GlasgowExts `thenM` \ gla_exts ->
333 mk_eqn_help gla_exts new_or_data tycon clas tys
335 ------------------------------------------------------------------
336 mk_eqn_help gla_exts DataType tycon clas tys
337 | Just err <- chk_out gla_exts clas tycon tys
338 = bale_out (derivingThingErr clas tys tycon tyvars err)
340 = new_dfun_name clas tycon `thenM` \ dfun_name ->
341 returnM (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
343 tyvars = tyConTyVars tycon
344 data_cons = tyConDataCons tycon
345 constraints = extra_constraints ++ ordinary_constraints
346 -- "extra_constraints": see note [Data decl contexts] above
347 extra_constraints = tyConTheta tycon
350 | clas `hasKey` typeableClassKey -- For the Typeable class, the constraints
351 -- don't involve the constructor ags, only
353 -- e.g. data T a b = ...
355 -- instance (Typeable a, Typable b)
356 -- => Typeable (T a b) where
357 = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
359 = [ mkClassPred clas [arg_ty]
360 | data_con <- tyConDataCons tycon,
361 arg_ty <- dataConOrigArgTys data_con,
362 -- Use the same type variables
363 -- as the type constructor,
364 -- hence no need to instantiate
365 not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
368 mk_eqn_help gla_exts NewType tycon clas tys
369 | can_derive_via_isomorphism && (gla_exts || standard_class gla_exts clas)
370 = -- Go ahead and use the isomorphism
371 traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys) `thenM_`
372 new_dfun_name clas tycon `thenM` \ dfun_name ->
373 returnM (Nothing, Just (InstInfo { iDFunId = mk_dfun dfun_name,
374 iBinds = NewTypeDerived rep_tys }))
375 | standard_class gla_exts clas
376 = mk_eqn_help gla_exts DataType tycon clas tys -- Go via bale-out route
378 | otherwise -- Non-standard instance
379 = bale_out (if gla_exts then
380 cant_derive_err -- Too hard
382 non_std_err) -- Just complain about being a non-std instance
384 -- Here is the plan for newtype derivings. We see
385 -- newtype T a1...an = T (t ak...an) deriving (.., C s1 .. sm, ...)
386 -- where aj...an do not occur free in t, and the (C s1 ... sm) is a
387 -- *partial applications* of class C with the last parameter missing
389 -- We generate the instances
390 -- instance C s1 .. sm (t ak...aj) => C s1 .. sm (T a1...aj)
391 -- where T a1...aj is the partial application of the LHS of the correct kind
393 -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
394 -- instance Monad (ST s) => Monad (T s) where
395 -- fail = coerce ... (fail @ ST s)
397 clas_tyvars = classTyVars clas
398 kind = tyVarKind (last clas_tyvars)
399 -- Kind of the thing we want to instance
400 -- e.g. argument kind of Monad, *->*
402 (arg_kinds, _) = tcSplitFunTys kind
403 n_args_to_drop = length arg_kinds
404 -- Want to drop 1 arg from (T s a) and (ST s a)
405 -- to get instance Monad (ST s) => Monad (T s)
407 -- Note [newtype representation]
408 -- We must not use newTyConRep to get the representation
409 -- type, because that looks through all intermediate newtypes
410 -- To get the RHS of *this* newtype, just look at the data
411 -- constructor. For example
412 -- newtype B = MkB Int
413 -- newtype A = MkA B deriving( Num )
414 -- We want the Num instance of B, *not* the Num instance of Int,
415 -- when making the Num instance of A!
416 tyvars = tyConTyVars tycon
417 rep_ty = head (dataConOrigArgTys (head (tyConDataCons tycon)))
418 (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
420 n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
421 tyvars_to_drop = drop n_tyvars_to_keep tyvars
422 tyvars_to_keep = take n_tyvars_to_keep tyvars
424 n_args_to_keep = length rep_ty_args - n_args_to_drop
425 args_to_drop = drop n_args_to_keep rep_ty_args
426 args_to_keep = take n_args_to_keep rep_ty_args
428 rep_tys = tys ++ [mkAppTys rep_fn args_to_keep]
429 rep_pred = mkClassPred clas rep_tys
430 -- rep_pred is the representation dictionary, from where
431 -- we are gong to get all the methods for the newtype dictionary
433 inst_tys = (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)])
434 -- The 'tys' here come from the partial application
435 -- in the deriving clause. The last arg is the new
438 -- We must pass the superclasses; the newtype might be an instance
439 -- of them in a different way than the representation type
440 -- E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
441 -- Then the Show instance is not done via isomprphism; it shows
443 -- The Num instance is derived via isomorphism, but the Show superclass
444 -- dictionary must the Show instance for Foo, *not* the Show dictionary
445 -- gotten from the Num dictionary. So we must build a whole new dictionary
446 -- not just use the Num one. The instance we want is something like:
447 -- instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
450 -- There's no 'corece' needed because after the type checker newtypes
453 sc_theta = substTheta (mkTyVarSubst clas_tyvars inst_tys)
456 -- If there are no tyvars, there's no need
457 -- to abstract over the dictionaries we need
458 dict_args | null tyvars = []
459 | otherwise = rep_pred : sc_theta
461 -- Finally! Here's where we build the dictionary Id
462 mk_dfun dfun_name = mkDictFunId dfun_name tyvars dict_args clas inst_tys
464 -------------------------------------------------------------------
465 -- Figuring out whether we can only do this newtype-deriving thing
467 right_arity = length tys + 1 == classArity clas
469 -- Never derive Read,Show,Typeable,Data this way
470 non_iso_classes = [readClassKey, showClassKey, typeableClassKey, dataClassKey]
471 can_derive_via_isomorphism
472 = not (getUnique clas `elem` non_iso_classes)
473 && right_arity -- Well kinded;
474 -- eg not: newtype T ... deriving( ST )
475 -- because ST needs *2* type params
476 && n_tyvars_to_keep >= 0 -- Type constructor has right kind:
477 -- eg not: newtype T = T Int deriving( Monad )
478 && n_args_to_keep >= 0 -- Rep type has right kind:
479 -- eg not: newtype T a = T Int deriving( Monad )
480 && eta_ok -- Eta reduction works
481 && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
482 -- newtype A = MkA [A]
484 -- instance Eq [A] => Eq A !!
486 -- Check that eta reduction is OK
487 -- (a) the dropped-off args are identical
488 -- (b) the remaining type args mention
489 -- only the remaining type variables
490 eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
491 && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
493 cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
494 (vcat [ptext SLIT("even with cunning newtype deriving:"),
495 if isRecursiveTyCon tycon then
496 ptext SLIT("the newtype is recursive")
498 if not right_arity then
499 quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("does not have arity 1")
501 if not (n_tyvars_to_keep >= 0) then
502 ptext SLIT("the type constructor has wrong kind")
503 else if not (n_args_to_keep >= 0) then
504 ptext SLIT("the representation type has wrong kind")
505 else if not eta_ok then
506 ptext SLIT("the eta-reduction property does not hold")
510 non_std_err = derivingThingErr clas tys tycon tyvars_to_keep
511 (vcat [non_std_why clas,
512 ptext SLIT("Try -fglasgow-exts for GHC's newtype-deriving extension")])
514 bale_out err = addErrTc err `thenM_` returnM (Nothing, Nothing)
516 standard_class gla_exts clas = key `elem` derivableClassKeys
517 || (gla_exts && (key == typeableClassKey || key == dataClassKey))
520 ------------------------------------------------------------------
521 chk_out :: Bool -> Class -> TyCon -> [TcType] -> Maybe SDoc
522 chk_out gla_exts clas tycon tys
523 | notNull tys = Just ty_args_why
524 | not (standard_class gla_exts clas) = Just (non_std_why clas)
525 | clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
526 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
527 | clas `hasKey` ixClassKey && not is_enumeration_or_single = Just single_nullary_why
528 | clas `hasKey` typeableClassKey && not all_type_kind = Just not_type_kind_why
529 | null data_cons = Just no_cons_why
530 | any isExistentialDataCon data_cons = Just existential_why
531 | otherwise = Nothing
533 data_cons = tyConDataCons tycon
534 is_enumeration = isEnumerationTyCon tycon
535 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
536 is_enumeration_or_single = is_enumeration || is_single_con
537 all_type_kind = all (isTypeKind . tyVarKind) (tyConTyVars tycon)
539 single_nullary_why = ptext SLIT("one constructor data type or type with all nullary constructors expected")
540 nullary_why = quotes (ppr tycon) <+> ptext SLIT("has non-nullary constructors")
541 no_cons_why = quotes (ppr tycon) <+> ptext SLIT("has no data constructors")
542 ty_args_why = quotes (ppr pred) <+> ptext SLIT("is not a class")
543 existential_why = quotes (ppr tycon) <+> ptext SLIT("has existentially-quantified constructor(s)")
544 not_type_kind_why = quotes (ppr tycon) <+> ptext SLIT("is parameterised over arguments of kind other than `*'")
546 pred = mkClassPred clas tys
548 non_std_why clas = quotes (ppr clas) <+> ptext SLIT("is not a derivable class")
550 new_dfun_name clas tycon -- Just a simple wrapper
551 = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
552 -- The type passed to newDFunName is only used to generate
553 -- a suitable string; hence the empty type arg list
556 %************************************************************************
558 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
560 %************************************************************************
562 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
563 terms, which is the final correct RHS for the corresponding original
567 Each (k,TyVarTy tv) in a solution constrains only a type
571 The (k,TyVarTy tv) pairs in a solution are canonically
572 ordered by sorting on type varible, tv, (major key) and then class, k,
577 solveDerivEqns :: [DerivEqn]
578 -> TcM [DFunId] -- Solns in same order as eqns.
579 -- This bunch is Absolutely minimal...
581 solveDerivEqns orig_eqns
582 = iterateDeriv 1 initial_solutions
584 -- The initial solutions for the equations claim that each
585 -- instance has an empty context; this solution is certainly
586 -- in canonical form.
587 initial_solutions :: [DerivSoln]
588 initial_solutions = [ [] | _ <- orig_eqns ]
590 ------------------------------------------------------------------
591 -- iterateDeriv calculates the next batch of solutions,
592 -- compares it with the current one; finishes if they are the
593 -- same, otherwise recurses with the new solutions.
594 -- It fails if any iteration fails
595 iterateDeriv :: Int -> [DerivSoln] ->TcM [DFunId]
596 iterateDeriv n current_solns
597 | n > 20 -- Looks as if we are in an infinite loop
598 -- This can happen if we have -fallow-undecidable-instances
599 -- (See TcSimplify.tcSimplifyDeriv.)
600 = pprPanic "solveDerivEqns: probable loop"
601 (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
604 dfuns = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
607 -- Extend the inst info from the explicit instance decls
608 -- with the current set of solutions, and simplify each RHS
609 tcExtendTempInstEnv dfuns $
610 mappM gen_soln orig_eqns
611 ) `thenM` \ new_solns ->
612 if (current_solns == new_solns) then
615 iterateDeriv (n+1) new_solns
617 ------------------------------------------------------------------
619 gen_soln (_, clas, tc,tyvars,deriv_rhs)
620 = addSrcLoc (getSrcLoc tc) $
621 addErrCtxt (derivCtxt (Just clas) tc) $
622 tcSimplifyDeriv tyvars deriv_rhs `thenM` \ theta ->
623 returnM (sortLt (<) theta) -- Canonicalise before returning the soluction
625 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
626 = mkDictFunId dfun_name tyvars theta
627 clas [mkTyConApp tycon (mkTyVarTys tyvars)]
630 %************************************************************************
632 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
634 %************************************************************************
636 After all the trouble to figure out the required context for the
637 derived instance declarations, all that's left is to chug along to
638 produce them. They will then be shoved into @tcInstDecls2@, which
639 will do all its usual business.
641 There are lots of possibilities for code to generate. Here are
642 various general remarks.
647 We want derived instances of @Eq@ and @Ord@ (both v common) to be
648 ``you-couldn't-do-better-by-hand'' efficient.
651 Deriving @Show@---also pretty common--- should also be reasonable good code.
654 Deriving for the other classes isn't that common or that big a deal.
661 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
664 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
667 We {\em normally} generate code only for the non-defaulted methods;
668 there are some exceptions for @Eq@ and (especially) @Ord@...
671 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
672 constructor's numeric (@Int#@) tag. These are generated by
673 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
674 these is around is given by @hasCon2TagFun@.
676 The examples under the different sections below will make this
680 Much less often (really just for deriving @Ix@), we use a
681 @_tag2con_<tycon>@ function. See the examples.
684 We use the renamer!!! Reason: we're supposed to be
685 producing @RenamedMonoBinds@ for the methods, but that means
686 producing correctly-uniquified code on the fly. This is entirely
687 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
688 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
689 the renamer. What a great hack!
693 -- Generate the method bindings for the required instance
694 -- (paired with DFunId, as we need that when renaming
696 gen_bind :: DFunId -> TcM (DFunId, RdrNameMonoBinds)
698 = getFixityEnv `thenM` \ fix_env ->
700 (clas, tycon) = simpleDFunClassTyCon dfun
701 gen_binds_fn = assoc "gen_bind:bad derived class"
702 gen_list (getUnique clas)
704 gen_list = [(eqClassKey, gen_Eq_binds)
705 ,(ordClassKey, gen_Ord_binds)
706 ,(enumClassKey, gen_Enum_binds)
707 ,(boundedClassKey, gen_Bounded_binds)
708 ,(ixClassKey, gen_Ix_binds)
709 ,(showClassKey, gen_Show_binds fix_env)
710 ,(readClassKey, gen_Read_binds fix_env)
711 ,(typeableClassKey,gen_Typeable_binds)
712 ,(dataClassKey, gen_Data_binds)
715 returnM (dfun, gen_binds_fn tycon)
719 %************************************************************************
721 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
723 %************************************************************************
728 con2tag_Foo :: Foo ... -> Int#
729 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
730 maxtag_Foo :: Int -- ditto (NB: not unlifted)
733 We have a @con2tag@ function for a tycon if:
736 We're deriving @Eq@ and the tycon has nullary data constructors.
739 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
743 We have a @tag2con@ function for a tycon if:
746 We're deriving @Enum@, or @Ix@ (enum type only???)
749 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
752 gen_taggery_Names :: [DFunId]
753 -> TcM [(RdrName, -- for an assoc list
754 TyCon, -- related tycon
757 gen_taggery_Names dfuns
758 = foldlM do_con2tag [] tycons_of_interest `thenM` \ names_so_far ->
759 foldlM do_tag2con names_so_far tycons_of_interest
761 all_CTs = map simpleDFunClassTyCon dfuns
762 all_tycons = map snd all_CTs
763 (tycons_of_interest, _) = removeDups compare all_tycons
765 do_con2tag acc_Names tycon
766 | isDataTyCon tycon &&
767 ((we_are_deriving eqClassKey tycon
768 && any isNullaryDataCon (tyConDataCons tycon))
769 || (we_are_deriving ordClassKey tycon
770 && not (maybeToBool (maybeTyConSingleCon tycon)))
771 || (we_are_deriving enumClassKey tycon)
772 || (we_are_deriving ixClassKey tycon))
774 = returnM ((con2tag_RDR tycon, tycon, GenCon2Tag)
779 do_tag2con acc_Names tycon
780 | isDataTyCon tycon &&
781 (we_are_deriving enumClassKey tycon ||
782 we_are_deriving ixClassKey tycon
783 && isEnumerationTyCon tycon)
784 = returnM ( (tag2con_RDR tycon, tycon, GenTag2Con)
785 : (maxtag_RDR tycon, tycon, GenMaxTag)
790 we_are_deriving clas_key tycon
791 = is_in_eqns clas_key tycon all_CTs
793 is_in_eqns clas_key tycon [] = False
794 is_in_eqns clas_key tycon ((c,t):cts)
795 = (clas_key == classKey c && tycon == t)
796 || is_in_eqns clas_key tycon cts
800 derivingThingErr clas tys tycon tyvars why
801 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
804 pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
806 malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
808 derivCtxt :: Maybe Class -> TyCon -> SDoc
809 derivCtxt maybe_cls tycon
810 = ptext SLIT("When deriving") <+> cls <+> ptext SLIT("for type") <+> quotes (ppr tycon)
812 cls = case maybe_cls of
813 Nothing -> ptext SLIT("instances")
814 Just c -> ptext SLIT("the") <+> quotes (ppr c) <+> ptext SLIT("instance")