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(..), MonoBinds(..),
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 ( Unique, getUnique )
44 import RdrName ( RdrName )
46 import TyCon ( tyConTyVars, tyConDataCons, tyConArity,
47 tyConTheta, isProductTyCon, 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) ->
264 mapAndUnzipM rn_inst_info rdr_name_inst_infos `thenM` \ (pairs, fvs_s) ->
267 (rn_inst_infos, aux_binds_s) = unzip pairs
268 all_binds = rn_extra_binds `ThenBinds` foldr ThenBinds EmptyBinds aux_binds_s
270 returnM ((rn_inst_infos, all_binds),
271 duUses dus `plusFV` plusFVs fvs_s)
272 ) `thenM` \ ((rn_inst_infos, rn_extra_binds), fvs) ->
273 returnM (rn_inst_infos, rn_extra_binds, fvs)
276 rn_inst_info (dfun, (meth_binds, aux_binds))
277 = -- Rename the auxiliary bindings
278 bindLocalsFV (ptext (SLIT("deriving"))) mbinders $ \ _ ->
279 rnTopMonoBinds aux_binds [] `thenM` \ (rn_aux_binds, dus) ->
281 -- Bring the right type variables into scope
282 extendTyVarEnvFVRn (map varName tyvars) $
283 rnMethodBinds (className cls) [] meth_binds `thenM` \ (rn_meth_binds, fvs) ->
285 return ((InstInfo { iDFunId = dfun, iBinds = VanillaInst rn_meth_binds [] },
287 duUses dus `plusFV` fvs)
289 mbinders = collectMonoBinders aux_binds
290 (tyvars, _, cls, _) = tcSplitDFunTy (idType dfun)
294 %************************************************************************
296 \subsection[TcDeriv-eqns]{Forming the equations}
298 %************************************************************************
300 @makeDerivEqns@ fishes around to find the info about needed derived
301 instances. Complicating factors:
304 We can only derive @Enum@ if the data type is an enumeration
305 type (all nullary data constructors).
308 We can only derive @Ix@ if the data type is an enumeration {\em
309 or} has just one data constructor (e.g., tuples).
312 [See Appendix~E in the Haskell~1.2 report.] This code here deals w/
316 makeDerivEqns :: [RenamedTyClDecl]
317 -> TcM ([DerivEqn], -- Ordinary derivings
318 [InstInfo]) -- Special newtype derivings
320 makeDerivEqns tycl_decls
321 = mapAndUnzipM mk_eqn derive_these `thenM` \ (maybe_ordinaries, maybe_newtypes) ->
322 returnM (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
324 ------------------------------------------------------------------
325 derive_these :: [(NewOrData, Name, RenamedHsPred)]
326 -- Find the (nd, TyCon, Pred) pairs that must be `derived'
327 -- NB: only source-language decls have deriving, no imported ones do
328 derive_these = [ (nd, tycon, pred)
329 | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
332 ------------------------------------------------------------------
333 mk_eqn :: (NewOrData, Name, RenamedHsPred) -> TcM (Maybe DerivEqn, Maybe InstInfo)
334 -- We swizzle the tyvars and datacons out of the tycon
335 -- to make the rest of the equation
337 mk_eqn (new_or_data, tycon_name, pred)
338 = tcLookupTyCon tycon_name `thenM` \ tycon ->
339 addSrcLoc (getSrcLoc tycon) $
340 addErrCtxt (derivCtxt Nothing tycon) $
341 tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
342 -- the type variables for the type constructor
343 tcHsPred pred `thenM` \ pred' ->
344 case getClassPredTys_maybe pred' of
345 Nothing -> bale_out (malformedPredErr tycon pred)
346 Just (clas, tys) -> doptM Opt_GlasgowExts `thenM` \ gla_exts ->
347 mk_eqn_help gla_exts new_or_data tycon clas tys
349 ------------------------------------------------------------------
350 mk_eqn_help gla_exts DataType tycon clas tys
351 | Just err <- checkSideConditions gla_exts clas tycon tys
352 = bale_out (derivingThingErr clas tys tycon tyvars err)
354 = new_dfun_name clas tycon `thenM` \ dfun_name ->
355 returnM (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
357 tyvars = tyConTyVars tycon
358 data_cons = tyConDataCons tycon
359 constraints = extra_constraints ++ ordinary_constraints
360 -- "extra_constraints": see note [Data decl contexts] above
361 extra_constraints = tyConTheta tycon
364 | clas `hasKey` typeableClassKey -- For the Typeable class, the constraints
365 -- don't involve the constructor ags, only
367 -- e.g. data T a b = ...
369 -- instance (Typeable a, Typable b)
370 -- => Typeable (T a b) where
371 = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
373 = [ mkClassPred clas [arg_ty]
374 | data_con <- tyConDataCons tycon,
375 arg_ty <- dataConOrigArgTys data_con,
376 -- Use the same type variables
377 -- as the type constructor,
378 -- hence no need to instantiate
379 not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
382 mk_eqn_help gla_exts NewType tycon clas tys
383 | can_derive_via_isomorphism && (gla_exts || standard_class gla_exts clas)
384 = -- Go ahead and use the isomorphism
385 traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys) `thenM_`
386 new_dfun_name clas tycon `thenM` \ dfun_name ->
387 returnM (Nothing, Just (InstInfo { iDFunId = mk_dfun dfun_name,
388 iBinds = NewTypeDerived rep_tys }))
389 | standard_class gla_exts clas
390 = mk_eqn_help gla_exts DataType tycon clas tys -- Go via bale-out route
392 | otherwise -- Non-standard instance
393 = bale_out (if gla_exts then
394 cant_derive_err -- Too hard
396 non_std_err) -- Just complain about being a non-std instance
398 -- Here is the plan for newtype derivings. We see
399 -- newtype T a1...an = T (t ak...an) deriving (.., C s1 .. sm, ...)
400 -- where aj...an do not occur free in t, and the (C s1 ... sm) is a
401 -- *partial applications* of class C with the last parameter missing
403 -- We generate the instances
404 -- instance C s1 .. sm (t ak...aj) => C s1 .. sm (T a1...aj)
405 -- where T a1...aj is the partial application of the LHS of the correct kind
407 -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
408 -- instance Monad (ST s) => Monad (T s) where
409 -- fail = coerce ... (fail @ ST s)
411 clas_tyvars = classTyVars clas
412 kind = tyVarKind (last clas_tyvars)
413 -- Kind of the thing we want to instance
414 -- e.g. argument kind of Monad, *->*
416 (arg_kinds, _) = tcSplitFunTys kind
417 n_args_to_drop = length arg_kinds
418 -- Want to drop 1 arg from (T s a) and (ST s a)
419 -- to get instance Monad (ST s) => Monad (T s)
421 -- Note [newtype representation]
422 -- We must not use newTyConRep to get the representation
423 -- type, because that looks through all intermediate newtypes
424 -- To get the RHS of *this* newtype, just look at the data
425 -- constructor. For example
426 -- newtype B = MkB Int
427 -- newtype A = MkA B deriving( Num )
428 -- We want the Num instance of B, *not* the Num instance of Int,
429 -- when making the Num instance of A!
430 tyvars = tyConTyVars tycon
431 rep_ty = head (dataConOrigArgTys (head (tyConDataCons tycon)))
432 (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
434 n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
435 tyvars_to_drop = drop n_tyvars_to_keep tyvars
436 tyvars_to_keep = take n_tyvars_to_keep tyvars
438 n_args_to_keep = length rep_ty_args - n_args_to_drop
439 args_to_drop = drop n_args_to_keep rep_ty_args
440 args_to_keep = take n_args_to_keep rep_ty_args
442 rep_tys = tys ++ [mkAppTys rep_fn args_to_keep]
443 rep_pred = mkClassPred clas rep_tys
444 -- rep_pred is the representation dictionary, from where
445 -- we are gong to get all the methods for the newtype dictionary
447 inst_tys = (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)])
448 -- The 'tys' here come from the partial application
449 -- in the deriving clause. The last arg is the new
452 -- We must pass the superclasses; the newtype might be an instance
453 -- of them in a different way than the representation type
454 -- E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
455 -- Then the Show instance is not done via isomprphism; it shows
457 -- The Num instance is derived via isomorphism, but the Show superclass
458 -- dictionary must the Show instance for Foo, *not* the Show dictionary
459 -- gotten from the Num dictionary. So we must build a whole new dictionary
460 -- not just use the Num one. The instance we want is something like:
461 -- instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
464 -- There's no 'corece' needed because after the type checker newtypes
467 sc_theta = substTheta (mkTyVarSubst clas_tyvars inst_tys)
470 -- If there are no tyvars, there's no need
471 -- to abstract over the dictionaries we need
472 dict_args | null tyvars = []
473 | otherwise = rep_pred : sc_theta
475 -- Finally! Here's where we build the dictionary Id
476 mk_dfun dfun_name = mkDictFunId dfun_name tyvars dict_args clas inst_tys
478 -------------------------------------------------------------------
479 -- Figuring out whether we can only do this newtype-deriving thing
481 right_arity = length tys + 1 == classArity clas
483 -- Never derive Read,Show,Typeable,Data this way
484 non_iso_classes = [readClassKey, showClassKey, typeableClassKey, dataClassKey]
485 can_derive_via_isomorphism
486 = not (getUnique clas `elem` non_iso_classes)
487 && right_arity -- Well kinded;
488 -- eg not: newtype T ... deriving( ST )
489 -- because ST needs *2* type params
490 && n_tyvars_to_keep >= 0 -- Type constructor has right kind:
491 -- eg not: newtype T = T Int deriving( Monad )
492 && n_args_to_keep >= 0 -- Rep type has right kind:
493 -- eg not: newtype T a = T Int deriving( Monad )
494 && eta_ok -- Eta reduction works
495 && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
496 -- newtype A = MkA [A]
498 -- instance Eq [A] => Eq A !!
500 -- Check that eta reduction is OK
501 -- (a) the dropped-off args are identical
502 -- (b) the remaining type args mention
503 -- only the remaining type variables
504 eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
505 && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
507 cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
508 (vcat [ptext SLIT("even with cunning newtype deriving:"),
509 if isRecursiveTyCon tycon then
510 ptext SLIT("the newtype is recursive")
512 if not right_arity then
513 quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("does not have arity 1")
515 if not (n_tyvars_to_keep >= 0) then
516 ptext SLIT("the type constructor has wrong kind")
517 else if not (n_args_to_keep >= 0) then
518 ptext SLIT("the representation type has wrong kind")
519 else if not eta_ok then
520 ptext SLIT("the eta-reduction property does not hold")
524 non_std_err = derivingThingErr clas tys tycon tyvars_to_keep
525 (vcat [non_std_why clas,
526 ptext SLIT("Try -fglasgow-exts for GHC's newtype-deriving extension")])
528 bale_out err = addErrTc err `thenM_` returnM (Nothing, Nothing)
529 standard_class gla_exts clas = key `elem` derivableClassKeys
530 || (gla_exts && (key == typeableClassKey || key == dataClassKey))
537 new_dfun_name clas tycon -- Just a simple wrapper
538 = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
539 -- The type passed to newDFunName is only used to generate
540 -- a suitable string; hence the empty type arg list
543 ------------------------------------------------------------------
544 -- Check side conditions that dis-allow derivability for particular classes
545 -- This is *apart* from the newtype-deriving mechanism
547 checkSideConditions :: Bool -> Class -> TyCon -> [TcType] -> Maybe SDoc
548 checkSideConditions gla_exts clas tycon tys
550 = Just ty_args_why -- e.g. deriving( Foo s )
552 = case [cond | (key,cond) <- sideConditions, key == getUnique clas] of
553 [] -> Just (non_std_why clas)
554 [cond] -> cond (gla_exts, tycon)
555 other -> pprPanic "checkSideConditions" (ppr clas)
557 ty_args_why = quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("is not a class")
559 non_std_why clas = quotes (ppr clas) <+> ptext SLIT("is not a derivable class")
561 sideConditions :: [(Unique, Condition)]
563 = [ (eqClassKey, cond_std),
564 (ordClassKey, cond_std),
565 (readClassKey, cond_std),
566 (showClassKey, cond_std),
567 (enumClassKey, cond_std `andCond` cond_isEnumeration),
568 (ixClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)),
569 (boundedClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)),
570 (typeableClassKey, cond_glaExts `andCond` cond_allTypeKind),
571 (dataClassKey, cond_glaExts `andCond` cond_std)
574 type Condition = (Bool, TyCon) -> Maybe SDoc -- Nothing => OK
576 orCond :: Condition -> Condition -> Condition
579 Nothing -> Nothing -- c1 succeeds
580 Just x -> case c2 tc of -- c1 fails
582 Just y -> Just (x $$ ptext SLIT(" and") $$ y)
585 andCond c1 c2 tc = case c1 tc of
586 Nothing -> c2 tc -- c1 succeeds
587 Just x -> Just x -- c1 fails
589 cond_std :: Condition
590 cond_std (gla_exts, tycon)
591 | any isExistentialDataCon data_cons = Just existential_why
592 | null data_cons = Just no_cons_why
593 | otherwise = Nothing
595 data_cons = tyConDataCons tycon
596 no_cons_why = quotes (ppr tycon) <+> ptext SLIT("has no data constructors")
597 existential_why = quotes (ppr tycon) <+> ptext SLIT("has existentially-quantified constructor(s)")
599 cond_isEnumeration :: Condition
600 cond_isEnumeration (gla_exts, tycon)
601 | isEnumerationTyCon tycon = Nothing
602 | otherwise = Just why
604 why = quotes (ppr tycon) <+> ptext SLIT("has non-nullary constructors")
606 cond_isProduct :: Condition
607 cond_isProduct (gla_exts, tycon)
608 | isProductTyCon tycon = Nothing
609 | otherwise = Just why
611 why = quotes (ppr tycon) <+> ptext SLIT("has more than one constructor")
613 cond_allTypeKind :: Condition
614 cond_allTypeKind (gla_exts, tycon)
615 | all (isTypeKind . tyVarKind) (tyConTyVars tycon) = Nothing
616 | otherwise = Just why
618 why = quotes (ppr tycon) <+> ptext SLIT("is parameterised over arguments of kind other than `*'")
620 cond_glaExts :: Condition
621 cond_glaExts (gla_exts, tycon) | gla_exts = Nothing
622 | otherwise = Just why
624 why = ptext SLIT("You need -fglasgow-exts to derive an instance for this class")
627 %************************************************************************
629 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
631 %************************************************************************
633 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
634 terms, which is the final correct RHS for the corresponding original
638 Each (k,TyVarTy tv) in a solution constrains only a type
642 The (k,TyVarTy tv) pairs in a solution are canonically
643 ordered by sorting on type varible, tv, (major key) and then class, k,
648 solveDerivEqns :: [DerivEqn]
649 -> TcM [DFunId] -- Solns in same order as eqns.
650 -- This bunch is Absolutely minimal...
652 solveDerivEqns orig_eqns
653 = iterateDeriv 1 initial_solutions
655 -- The initial solutions for the equations claim that each
656 -- instance has an empty context; this solution is certainly
657 -- in canonical form.
658 initial_solutions :: [DerivSoln]
659 initial_solutions = [ [] | _ <- orig_eqns ]
661 ------------------------------------------------------------------
662 -- iterateDeriv calculates the next batch of solutions,
663 -- compares it with the current one; finishes if they are the
664 -- same, otherwise recurses with the new solutions.
665 -- It fails if any iteration fails
666 iterateDeriv :: Int -> [DerivSoln] ->TcM [DFunId]
667 iterateDeriv n current_solns
668 | n > 20 -- Looks as if we are in an infinite loop
669 -- This can happen if we have -fallow-undecidable-instances
670 -- (See TcSimplify.tcSimplifyDeriv.)
671 = pprPanic "solveDerivEqns: probable loop"
672 (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
675 dfuns = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
678 -- Extend the inst info from the explicit instance decls
679 -- with the current set of solutions, and simplify each RHS
680 tcExtendTempInstEnv dfuns $
681 mappM gen_soln orig_eqns
682 ) `thenM` \ new_solns ->
683 if (current_solns == new_solns) then
686 iterateDeriv (n+1) new_solns
688 ------------------------------------------------------------------
690 gen_soln (_, clas, tc,tyvars,deriv_rhs)
691 = addSrcLoc (getSrcLoc tc) $
692 addErrCtxt (derivCtxt (Just clas) tc) $
693 tcSimplifyDeriv tyvars deriv_rhs `thenM` \ theta ->
694 returnM (sortLt (<) theta) -- Canonicalise before returning the soluction
696 mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
697 = mkDictFunId dfun_name tyvars theta
698 clas [mkTyConApp tycon (mkTyVarTys tyvars)]
701 %************************************************************************
703 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
705 %************************************************************************
707 After all the trouble to figure out the required context for the
708 derived instance declarations, all that's left is to chug along to
709 produce them. They will then be shoved into @tcInstDecls2@, which
710 will do all its usual business.
712 There are lots of possibilities for code to generate. Here are
713 various general remarks.
718 We want derived instances of @Eq@ and @Ord@ (both v common) to be
719 ``you-couldn't-do-better-by-hand'' efficient.
722 Deriving @Show@---also pretty common--- should also be reasonable good code.
725 Deriving for the other classes isn't that common or that big a deal.
732 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
735 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
738 We {\em normally} generate code only for the non-defaulted methods;
739 there are some exceptions for @Eq@ and (especially) @Ord@...
742 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
743 constructor's numeric (@Int#@) tag. These are generated by
744 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
745 these is around is given by @hasCon2TagFun@.
747 The examples under the different sections below will make this
751 Much less often (really just for deriving @Ix@), we use a
752 @_tag2con_<tycon>@ function. See the examples.
755 We use the renamer!!! Reason: we're supposed to be
756 producing @RenamedMonoBinds@ for the methods, but that means
757 producing correctly-uniquified code on the fly. This is entirely
758 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
759 So, instead, we produce @RdrNameMonoBinds@ then heave 'em through
760 the renamer. What a great hack!
764 -- Generate the method bindings for the required instance
765 -- (paired with DFunId, as we need that when renaming
767 gen_bind :: DFunId -> TcM (DFunId, (RdrNameMonoBinds, RdrNameMonoBinds))
769 = getFixityEnv `thenM` \ fix_env ->
771 (clas, tycon) = simpleDFunClassTyCon dfun
772 gen_binds_fn = assoc "gen_bind:bad derived class"
773 gen_list (getUnique clas)
775 gen_list = [(eqClassKey, no_aux_binds gen_Eq_binds)
776 ,(ordClassKey, no_aux_binds gen_Ord_binds)
777 ,(enumClassKey, no_aux_binds gen_Enum_binds)
778 ,(boundedClassKey, no_aux_binds gen_Bounded_binds)
779 ,(ixClassKey, no_aux_binds gen_Ix_binds)
780 ,(showClassKey, no_aux_binds (gen_Show_binds fix_env))
781 ,(readClassKey, no_aux_binds (gen_Read_binds fix_env))
782 ,(typeableClassKey,no_aux_binds gen_Typeable_binds)
783 ,(dataClassKey, gen_Data_binds fix_env)
786 -- Used for generators that don't need to produce
787 -- any auxiliary bindings
788 no_aux_binds f tc = (f tc, EmptyMonoBinds)
790 returnM (dfun, gen_binds_fn tycon)
794 %************************************************************************
796 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
798 %************************************************************************
803 con2tag_Foo :: Foo ... -> Int#
804 tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
805 maxtag_Foo :: Int -- ditto (NB: not unlifted)
808 We have a @con2tag@ function for a tycon if:
811 We're deriving @Eq@ and the tycon has nullary data constructors.
814 Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
818 We have a @tag2con@ function for a tycon if:
821 We're deriving @Enum@, or @Ix@ (enum type only???)
824 If we have a @tag2con@ function, we also generate a @maxtag@ constant.
827 gen_taggery_Names :: [DFunId]
828 -> TcM [(RdrName, -- for an assoc list
829 TyCon, -- related tycon
832 gen_taggery_Names dfuns
833 = foldlM do_con2tag [] tycons_of_interest `thenM` \ names_so_far ->
834 foldlM do_tag2con names_so_far tycons_of_interest
836 all_CTs = map simpleDFunClassTyCon dfuns
837 all_tycons = map snd all_CTs
838 (tycons_of_interest, _) = removeDups compare all_tycons
840 do_con2tag acc_Names tycon
841 | isDataTyCon tycon &&
842 ((we_are_deriving eqClassKey tycon
843 && any isNullaryDataCon (tyConDataCons tycon))
844 || (we_are_deriving ordClassKey tycon
845 && not (isProductTyCon tycon))
846 || (we_are_deriving enumClassKey tycon)
847 || (we_are_deriving ixClassKey tycon))
849 = returnM ((con2tag_RDR tycon, tycon, GenCon2Tag)
854 do_tag2con acc_Names tycon
855 | isDataTyCon tycon &&
856 (we_are_deriving enumClassKey tycon ||
857 we_are_deriving ixClassKey tycon
858 && isEnumerationTyCon tycon)
859 = returnM ( (tag2con_RDR tycon, tycon, GenTag2Con)
860 : (maxtag_RDR tycon, tycon, GenMaxTag)
865 we_are_deriving clas_key tycon
866 = is_in_eqns clas_key tycon all_CTs
868 is_in_eqns clas_key tycon [] = False
869 is_in_eqns clas_key tycon ((c,t):cts)
870 = (clas_key == classKey c && tycon == t)
871 || is_in_eqns clas_key tycon cts
875 derivingThingErr clas tys tycon tyvars why
876 = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
879 pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
881 malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
883 derivCtxt :: Maybe Class -> TyCon -> SDoc
884 derivCtxt maybe_cls tycon
885 = ptext SLIT("When deriving") <+> cls <+> ptext SLIT("for type") <+> quotes (ppr tycon)
887 cls = case maybe_cls of
888 Nothing -> ptext SLIT("instances")
889 Just c -> ptext SLIT("the") <+> quotes (ppr c) <+> ptext SLIT("instance")