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 ( 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, nameUnique )
43 import RdrName ( RdrName )
45 import TyCon ( tyConTyVars, tyConDataCons, tyConArity,
46 tyConTheta, maybeTyConSingleCon, isDataTyCon,
47 isEnumerationTyCon, isRecursiveTyCon, TyCon
49 import TcType ( TcType, ThetaType, mkTyVarTy, mkTyVarTys, mkTyConApp,
50 getClassPredTys_maybe,
51 isUnLiftedType, mkClassPred, tyVarsOfTypes, tcSplitFunTys, isTypeKind,
52 tcEqTypes, tcSplitAppTys, mkAppTys, tcSplitDFunTy )
53 import Var ( TyVar, tyVarKind, idType, varName )
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 ->
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) ->
207 tcExtendTempInstEnv (map iDFunId newtype_inst_info) $
208 -- Add the newtype-derived instances to the inst env
209 -- before tacking the "ordinary" ones
211 deriveOrdinaryStuff ordinary_eqns `thenM` \ (ordinary_inst_info, binds, fvs) ->
213 inst_info = newtype_inst_info ++ ordinary_inst_info
216 ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
217 (ddump_deriving inst_info binds)) `thenM_`
219 returnM (inst_info, binds, fvs)
222 ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
223 ddump_deriving inst_infos extra_binds
224 = vcat (map ppr_info inst_infos) $$ ppr extra_binds
226 ppr_info inst_info = pprInstInfo inst_info $$
227 nest 4 (pprInstInfoDetails inst_info)
228 -- pprInstInfo doesn't print much: only the type
230 -----------------------------------------
231 deriveOrdinaryStuff [] -- Short cut
232 = returnM ([], EmptyBinds, emptyFVs)
234 deriveOrdinaryStuff eqns
235 = -- Take the equation list and solve it, to deliver a list of
236 -- solutions, a.k.a. the contexts for the instance decls
237 -- required for the corresponding equations.
238 solveDerivEqns eqns `thenM` \ new_dfuns ->
240 -- Now augment the InstInfos, adding in the rather boring
241 -- actual-code-to-do-the-methods binds. We may also need to
242 -- generate extra not-one-inst-decl-specific binds, notably
243 -- "con2tag" and/or "tag2con" functions. We do these
245 gen_taggery_Names new_dfuns `thenM` \ nm_alist_etc ->
248 extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
249 extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
250 mbinders = collectMonoBinders extra_mbinds
252 mappM gen_bind new_dfuns `thenM` \ rdr_name_inst_infos ->
254 traceTc (text "tcDeriv" <+> vcat (map ppr rdr_name_inst_infos)) `thenM_`
255 getModule `thenM` \ this_mod ->
256 initRn (InterfaceMode this_mod) (
257 -- Rename to get RenamedBinds.
258 -- The only tricky bit is that the extra_binds must scope
259 -- over the method bindings for the instances.
260 bindLocalsFV (ptext (SLIT("deriving"))) mbinders $ \ _ ->
261 rnTopMonoBinds extra_mbinds [] `thenM` \ (rn_extra_binds, dus) ->
262 mapAndUnzipM rn_inst_info rdr_name_inst_infos `thenM` \ (rn_inst_infos, fvs_s) ->
263 returnM ((rn_inst_infos, rn_extra_binds),
264 duUses dus `plusFV` plusFVs fvs_s)
265 ) `thenM` \ ((rn_inst_infos, rn_extra_binds), fvs) ->
266 returnM (rn_inst_infos, rn_extra_binds, fvs)
269 rn_inst_info (dfun, binds)
270 = extendTyVarEnvFVRn (map varName tyvars) $
271 -- Bring the right type variables into scope
272 rnMethodBinds (className cls) [] binds `thenM` \ (rn_binds, fvs) ->
273 return (InstInfo { iDFunId = dfun, iBinds = VanillaInst rn_binds [] }, fvs)
275 (tyvars, _, cls, _) = tcSplitDFunTy (idType dfun)
279 %************************************************************************
281 \subsection[TcDeriv-eqns]{Forming the equations}
283 %************************************************************************
285 @makeDerivEqns@ fishes around to find the info about needed derived
286 instances. Complicating factors:
289 We can only derive @Enum@ if the data type is an enumeration
290 type (all nullary data constructors).
293 We can only derive @Ix@ if the data type is an enumeration {\em
294 or} has just one data constructor (e.g., tuples).
297 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
301 makeDerivEqns :: [RenamedTyClDecl]
302 -> TcM ([DerivEqn], -- Ordinary derivings
303 [InstInfo]) -- Special newtype derivings
305 makeDerivEqns tycl_decls
306 = mapAndUnzipM mk_eqn derive_these `thenM` \ (maybe_ordinaries, maybe_newtypes) ->
307 returnM (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
309 ------------------------------------------------------------------
310 derive_these :: [(NewOrData, Name, RenamedHsPred)]
311 -- Find the (nd, TyCon, Pred) pairs that must be `derived'
312 -- NB: only source-language decls have deriving, no imported ones do
313 derive_these = [ (nd, tycon, pred)
314 | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
317 ------------------------------------------------------------------
318 mk_eqn :: (NewOrData, Name, RenamedHsPred) -> TcM (Maybe DerivEqn, Maybe InstInfo)
319 -- We swizzle the tyvars and datacons out of the tycon
320 -- to make the rest of the equation
322 mk_eqn (new_or_data, tycon_name, pred)
323 = tcLookupTyCon tycon_name `thenM` \ tycon ->
324 addSrcLoc (getSrcLoc tycon) $
325 addErrCtxt (derivCtxt Nothing tycon) $
326 tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
327 -- the type variables for the type constructor
328 tcHsPred pred `thenM` \ pred' ->
329 case getClassPredTys_maybe pred' of
330 Nothing -> bale_out (malformedPredErr tycon pred)
331 Just (clas, tys) -> doptM Opt_GlasgowExts `thenM` \ gla_exts ->
332 mk_eqn_help gla_exts new_or_data tycon clas tys
334 ------------------------------------------------------------------
335 mk_eqn_help gla_exts DataType tycon clas tys
336 | Just err <- chk_out gla_exts clas tycon tys
337 = bale_out (derivingThingErr clas tys tycon tyvars err)
339 = new_dfun_name clas tycon `thenM` \ dfun_name ->
340 returnM (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
342 tyvars = tyConTyVars tycon
343 data_cons = tyConDataCons tycon
344 constraints = extra_constraints ++ ordinary_constraints
345 -- "extra_constraints": see note [Data decl contexts] above
346 extra_constraints = tyConTheta tycon
349 | clas `hasKey` typeableClassKey -- For the Typeable class, the constraints
350 -- don't involve the constructor ags, only
352 -- e.g. data T a b = ...
354 -- instance (Typeable a, Typable b)
355 -- => Typeable (T a b) where
356 = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
358 = [ mkClassPred clas [arg_ty]
359 | data_con <- tyConDataCons tycon,
360 arg_ty <- dataConOrigArgTys data_con,
361 -- Use the same type variables
362 -- as the type constructor,
363 -- hence no need to instantiate
364 not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
367 mk_eqn_help gla_exts NewType tycon clas tys
368 | can_derive_via_isomorphism && (gla_exts || standard_class gla_exts clas)
369 = -- Go ahead and use the isomorphism
370 traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys) `thenM_`
371 new_dfun_name clas tycon `thenM` \ dfun_name ->
372 returnM (Nothing, Just (InstInfo { iDFunId = mk_dfun dfun_name,
373 iBinds = NewTypeDerived rep_tys }))
374 | standard_class gla_exts clas
375 = mk_eqn_help gla_exts DataType tycon clas tys -- Go via bale-out route
377 | otherwise -- Non-standard instance
378 = bale_out (if gla_exts then
379 cant_derive_err -- Too hard
381 non_std_err) -- Just complain about being a non-std instance
383 -- Here is the plan for newtype derivings. We see
384 -- newtype T a1...an = T (t ak...an) deriving (.., C s1 .. sm, ...)
385 -- where aj...an do not occur free in t, and the (C s1 ... sm) is a
386 -- *partial applications* of class C with the last parameter missing
388 -- We generate the instances
389 -- instance C s1 .. sm (t ak...aj) => C s1 .. sm (T a1...aj)
390 -- where T a1...aj is the partial application of the LHS of the correct kind
392 -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
393 -- instance Monad (ST s) => Monad (T s) where
394 -- fail = coerce ... (fail @ ST s)
396 clas_tyvars = classTyVars clas
397 kind = tyVarKind (last clas_tyvars)
398 -- Kind of the thing we want to instance
399 -- e.g. argument kind of Monad, *->*
401 (arg_kinds, _) = tcSplitFunTys kind
402 n_args_to_drop = length arg_kinds
403 -- Want to drop 1 arg from (T s a) and (ST s a)
404 -- to get instance Monad (ST s) => Monad (T s)
406 -- Note [newtype representation]
407 -- We must not use newTyConRep to get the representation
408 -- type, because that looks through all intermediate newtypes
409 -- To get the RHS of *this* newtype, just look at the data
410 -- constructor. For example
411 -- newtype B = MkB Int
412 -- newtype A = MkA B deriving( Num )
413 -- We want the Num instance of B, *not* the Num instance of Int,
414 -- when making the Num instance of A!
415 tyvars = tyConTyVars tycon
416 rep_ty = head (dataConOrigArgTys (head (tyConDataCons tycon)))
417 (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
419 n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
420 tyvars_to_drop = drop n_tyvars_to_keep tyvars
421 tyvars_to_keep = take n_tyvars_to_keep tyvars
423 n_args_to_keep = length rep_ty_args - n_args_to_drop
424 args_to_drop = drop n_args_to_keep rep_ty_args
425 args_to_keep = take n_args_to_keep rep_ty_args
427 rep_tys = tys ++ [mkAppTys rep_fn args_to_keep]
428 rep_pred = mkClassPred clas rep_tys
429 -- rep_pred is the representation dictionary, from where
430 -- we are gong to get all the methods for the newtype dictionary
432 inst_tys = (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)])
433 -- The 'tys' here come from the partial application
434 -- in the deriving clause. The last arg is the new
437 -- We must pass the superclasses; the newtype might be an instance
438 -- of them in a different way than the representation type
439 -- E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
440 -- Then the Show instance is not done via isomprphism; it shows
442 -- The Num instance is derived via isomorphism, but the Show superclass
443 -- dictionary must the Show instance for Foo, *not* the Show dictionary
444 -- gotten from the Num dictionary. So we must build a whole new dictionary
445 -- not just use the Num one. The instance we want is something like:
446 -- instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
449 -- There's no 'corece' needed because after the type checker newtypes
452 sc_theta = substTheta (mkTyVarSubst clas_tyvars inst_tys)
455 -- If there are no tyvars, there's no need
456 -- to abstract over the dictionaries we need
457 dict_args | null tyvars = []
458 | otherwise = rep_pred : sc_theta
460 -- Finally! Here's where we build the dictionary Id
461 mk_dfun dfun_name = mkDictFunId dfun_name tyvars dict_args clas inst_tys
463 -------------------------------------------------------------------
464 -- Figuring out whether we can only do this newtype-deriving thing
466 right_arity = length tys + 1 == classArity clas
468 can_derive_via_isomorphism
469 = not (clas `hasKey` readClassKey) -- Never derive Read,Show,Typeable this way
470 && not (clas `hasKey` showClassKey)
471 && not (clas `hasKey` typeableClassKey)
472 && right_arity -- Well kinded;
473 -- eg not: newtype T ... deriving( ST )
474 -- because ST needs *2* type params
475 && n_tyvars_to_keep >= 0 -- Type constructor has right kind:
476 -- eg not: newtype T = T Int deriving( Monad )
477 && n_args_to_keep >= 0 -- Rep type has right kind:
478 -- eg not: newtype T a = T Int deriving( Monad )
479 && eta_ok -- Eta reduction works
480 && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
481 -- newtype A = MkA [A]
483 -- instance Eq [A] => Eq A !!
485 -- Check that eta reduction is OK
486 -- (a) the dropped-off args are identical
487 -- (b) the remaining type args mention
488 -- only the remaining type variables
489 eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
490 && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
492 cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
493 (vcat [ptext SLIT("even with cunning newtype deriving:"),
494 if isRecursiveTyCon tycon then
495 ptext SLIT("the newtype is recursive")
497 if not right_arity then
498 quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("does not have arity 1")
500 if not (n_tyvars_to_keep >= 0) then
501 ptext SLIT("the type constructor has wrong kind")
502 else if not (n_args_to_keep >= 0) then
503 ptext SLIT("the representation type has wrong kind")
504 else if not eta_ok then
505 ptext SLIT("the eta-reduction property does not hold")
509 non_std_err = derivingThingErr clas tys tycon tyvars_to_keep
510 (vcat [non_std_why clas,
511 ptext SLIT("Try -fglasgow-exts for GHC's newtype-deriving extension")])
513 bale_out err = addErrTc err `thenM_` returnM (Nothing, Nothing)
515 standard_class gla_exts clas = key `elem` derivableClassKeys
516 || (gla_exts && (key == typeableClassKey || key == traverseClassKey))
519 ------------------------------------------------------------------
520 chk_out :: Bool -> Class -> TyCon -> [TcType] -> Maybe SDoc
521 chk_out gla_exts clas tycon tys
522 | notNull tys = Just ty_args_why
523 | not (standard_class gla_exts clas) = Just (non_std_why clas)
524 | clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
525 | clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
526 | clas `hasKey` ixClassKey && not is_enumeration_or_single = Just single_nullary_why
527 | clas `hasKey` typeableClassKey && not all_type_kind = Just not_type_kind_why
528 | null data_cons = Just no_cons_why
529 | any isExistentialDataCon data_cons = Just existential_why
530 | otherwise = Nothing
532 data_cons = tyConDataCons tycon
533 is_enumeration = isEnumerationTyCon tycon
534 is_single_con = maybeToBool (maybeTyConSingleCon tycon)
535 is_enumeration_or_single = is_enumeration || is_single_con
536 all_type_kind = all (isTypeKind . tyVarKind) (tyConTyVars tycon)
538 single_nullary_why = ptext SLIT("one constructor data type or type with all nullary constructors expected")
539 nullary_why = quotes (ppr tycon) <+> ptext SLIT("has non-nullary constructors")
540 no_cons_why = quotes (ppr tycon) <+> ptext SLIT("has no data constructors")
541 ty_args_why = quotes (ppr pred) <+> ptext SLIT("is not a class")
542 existential_why = quotes (ppr tycon) <+> ptext SLIT("has existentially-quantified constructor(s)")
543 not_type_kind_why = quotes (ppr tycon) <+> ptext SLIT("is parameterised over arguments of kind other than `*'")
545 pred = mkClassPred clas tys
547 non_std_why clas = quotes (ppr clas) <+> ptext SLIT("is not a derivable class")
549 new_dfun_name clas tycon -- Just a simple wrapper
550 = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
551 -- The type passed to newDFunName is only used to generate
552 -- a suitable string; hence the empty type arg list
555 %************************************************************************
557 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
559 %************************************************************************
561 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
562 terms, which is the final correct RHS for the corresponding original
566 Each (k,TyVarTy tv) in a solution constrains only a type
570 The (k,TyVarTy tv) pairs in a solution are canonically
571 ordered by sorting on type varible, tv, (major key) and then class, k,
576 solveDerivEqns :: [DerivEqn]
577 -> TcM [DFunId] -- Solns in same order as eqns.
578 -- This bunch is Absolutely minimal...
580 solveDerivEqns orig_eqns
581 = iterateDeriv 1 initial_solutions
583 -- The initial solutions for the equations claim that each
584 -- instance has an empty context; this solution is certainly
585 -- in canonical form.
586 initial_solutions :: [DerivSoln]
587 initial_solutions = [ [] | _ <- orig_eqns ]
589 ------------------------------------------------------------------
590 -- iterateDeriv calculates the next batch of solutions,
591 -- compares it with the current one; finishes if they are the
592 -- same, otherwise recurses with the new solutions.
593 -- It fails if any iteration fails
594 iterateDeriv :: Int -> [DerivSoln] ->TcM [DFunId]
595 iterateDeriv n current_solns
596 | n > 20 -- Looks as if we are in an infinite loop
597 -- This can happen if we have -fallow-undecidable-instances
598 -- (See TcSimplify.tcSimplifyDeriv.)
599 = pprPanic "solveDerivEqns: probable loop"
600 (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
603 dfuns = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
606 -- Extend the inst info from the explicit instance decls
607 -- with the current set of solutions, and simplify each RHS
608 tcExtendTempInstEnv dfuns $
609 mappM gen_soln orig_eqns
610 ) `thenM` \ new_solns ->
611 if (current_solns == new_solns) then
614 iterateDeriv (n+1) new_solns
616 ------------------------------------------------------------------
618 gen_soln (_, clas, tc,tyvars,deriv_rhs)
619 = addSrcLoc (getSrcLoc tc) $
620 addErrCtxt (derivCtxt (Just clas) tc) $
621 tcSimplifyDeriv tyvars deriv_rhs `thenM` \ theta ->
622 returnM (sortLt (<) theta) -- Canonicalise before returning the soluction
624 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
625 = mkDictFunId dfun_name tyvars theta
626 clas [mkTyConApp tycon (mkTyVarTys tyvars)]
629 %************************************************************************
631 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
633 %************************************************************************
635 After all the trouble to figure out the required context for the
636 derived instance declarations, all that's left is to chug along to
637 produce them. They will then be shoved into @tcInstDecls2@, which
638 will do all its usual business.
640 There are lots of possibilities for code to generate. Here are
641 various general remarks.
646 We want derived instances of @Eq@ and @Ord@ (both v common) to be
647 ``you-couldn't-do-better-by-hand'' efficient.
650 Deriving @Show@---also pretty common--- should also be reasonable good code.
653 Deriving for the other classes isn't that common or that big a deal.
660 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
663 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
666 We {\em normally} generate code only for the non-defaulted methods;
667 there are some exceptions for @Eq@ and (especially) @Ord@...
670 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
671 constructor's numeric (@Int#@) tag. These are generated by
672 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
673 these is around is given by @hasCon2TagFun@.
675 The examples under the different sections below will make this
679 Much less often (really just for deriving @Ix@), we use a
680 @_tag2con_<tycon>@ function. See the examples.
683 We use the renamer!!! Reason: we're supposed to be
684 producing @RenamedMonoBinds@ for the methods, but that means
685 producing correctly-uniquified code on the fly. This is entirely
686 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
687 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
688 the renamer. What a great hack!
692 -- Generate the method bindings for the required instance
693 -- (paired with DFunId, as we need that when renaming
695 gen_bind :: DFunId -> TcM (DFunId, RdrNameMonoBinds)
697 = getFixityEnv `thenM` \ fix_env ->
699 (clas, tycon) = simpleDFunClassTyCon dfun
700 gen_binds_fn = assoc "gen_bind:bad derived class"
701 gen_list (getUnique clas)
703 gen_list = [(eqClassKey, gen_Eq_binds)
704 ,(ordClassKey, gen_Ord_binds)
705 ,(enumClassKey, gen_Enum_binds)
706 ,(boundedClassKey, gen_Bounded_binds)
707 ,(ixClassKey, gen_Ix_binds)
708 ,(showClassKey, gen_Show_binds fix_env)
709 ,(readClassKey, gen_Read_binds fix_env)
710 ,(typeableClassKey,gen_Typeable_binds)
713 returnM (dfun, gen_binds_fn tycon)
717 %************************************************************************
719 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
721 %************************************************************************
726 con2tag_Foo :: Foo ... -> Int#
727 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
728 maxtag_Foo :: Int -- ditto (NB: not unlifted)
731 We have a @con2tag@ function for a tycon if:
734 We're deriving @Eq@ and the tycon has nullary data constructors.
737 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
741 We have a @tag2con@ function for a tycon if:
744 We're deriving @Enum@, or @Ix@ (enum type only???)
747 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
750 gen_taggery_Names :: [DFunId]
751 -> TcM [(RdrName, -- for an assoc list
752 TyCon, -- related tycon
755 gen_taggery_Names dfuns
756 = foldlM do_con2tag [] tycons_of_interest `thenM` \ names_so_far ->
757 foldlM do_tag2con names_so_far tycons_of_interest
759 all_CTs = map simpleDFunClassTyCon dfuns
760 all_tycons = map snd all_CTs
761 (tycons_of_interest, _) = removeDups compare all_tycons
763 do_con2tag acc_Names tycon
764 | isDataTyCon tycon &&
765 ((we_are_deriving eqClassKey tycon
766 && any isNullaryDataCon (tyConDataCons tycon))
767 || (we_are_deriving ordClassKey tycon
768 && not (maybeToBool (maybeTyConSingleCon tycon)))
769 || (we_are_deriving enumClassKey tycon)
770 || (we_are_deriving ixClassKey tycon))
772 = returnM ((con2tag_RDR tycon, tycon, GenCon2Tag)
777 do_tag2con acc_Names tycon
778 | isDataTyCon tycon &&
779 (we_are_deriving enumClassKey tycon ||
780 we_are_deriving ixClassKey tycon
781 && isEnumerationTyCon tycon)
782 = returnM ( (tag2con_RDR tycon, tycon, GenTag2Con)
783 : (maxtag_RDR tycon, tycon, GenMaxTag)
788 we_are_deriving clas_key tycon
789 = is_in_eqns clas_key tycon all_CTs
791 is_in_eqns clas_key tycon [] = False
792 is_in_eqns clas_key tycon ((c,t):cts)
793 = (clas_key == classKey c && tycon == t)
794 || is_in_eqns clas_key tycon cts
798 derivingThingErr clas tys tycon tyvars why
799 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
802 pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
804 malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
806 derivCtxt :: Maybe Class -> TyCon -> SDoc
807 derivCtxt maybe_cls tycon
808 = ptext SLIT("When deriving") <+> cls <+> ptext SLIT("for type") <+> quotes (ppr tycon)
810 cls = case maybe_cls of
811 Nothing -> ptext SLIT("instances")
812 Just c -> ptext SLIT("the") <+> quotes (ppr c) <+> ptext SLIT("instance")