%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
Handles @deriving@ clauses on @data@ declarations.
\begin{code}
module TcDeriv ( tcDeriving ) where
#include "HsVersions.h"
import HsSyn
import DynFlags
import TcRnMonad
import FamInst
import TcEnv
import TcTyClsDecls( tcFamTyPats, tcAddFamInstCtxt )
import TcClassDcl( tcAddDeclCtxt )
import TcGenDeriv
import TcGenGenerics
import InstEnv
import Inst
import FamInstEnv
import TcHsType
import TcMType
import TcSimplify
import TcEvidence
import RnBinds
import RnEnv
import RnSource ( addTcgDUs )
import HscTypes
import Class
import Type
import ErrUtils
import MkId
import DataCon
import Maybes
import RdrName
import Name
import NameSet
import TyCon
import TcType
import Var
import VarSet
import PrelNames
import SrcLoc
import Util
import ListSetOps
import Outputable
import FastString
import Bag
import Control.Monad
import Data.List
\end{code}
%************************************************************************
%* *
Overview
%* *
%************************************************************************
Overall plan
~~~~~~~~~~~~
1. Convert the decls (i.e. data/newtype deriving clauses,
plus standalone deriving) to [EarlyDerivSpec]
2. Infer the missing contexts for the Left DerivSpecs
3. Add the derived bindings, generating InstInfos
\begin{code}
data DerivSpec = DS { ds_loc :: SrcSpan
, ds_orig :: CtOrigin
, ds_name :: Name
, ds_tvs :: [TyVar]
, ds_theta :: ThetaType
, ds_cls :: Class
, ds_tys :: [Type]
, ds_tc :: TyCon
, ds_tc_args :: [Type]
, ds_newtype :: Bool }
\end{code}
Example:
newtype instance T [a] = MkT (Tree a) deriving( C s )
==>
axiom T [a] = :RTList a
axiom :RTList a = Tree a
DS { ds_tvs = [a,s], ds_cls = C, ds_tys = [s, T [a]]
, ds_tc = :RTList, ds_tc_args = [a]
, ds_newtype = True }
\begin{code}
type DerivContext = Maybe ThetaType
type EarlyDerivSpec = Either DerivSpec DerivSpec
pprDerivSpec :: DerivSpec -> SDoc
pprDerivSpec (DS { ds_loc = l, ds_name = n, ds_tvs = tvs,
ds_cls = c, ds_tys = tys, ds_theta = rhs })
= parens (hsep [ppr l, ppr n, ppr tvs, ppr c, ppr tys]
<+> equals <+> ppr rhs)
instance Outputable DerivSpec where
ppr = pprDerivSpec
\end{code}
Inferring missing contexts
~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data T a b = C1 (Foo a) (Bar b)
| C2 Int (T b a)
| C3 (T a a)
deriving (Eq)
[NOTE: See end of these comments for what to do with
data (C a, D b) => T a b = ...
]
We want to come up with an instance declaration of the form
instance (Ping a, Pong b, ...) => Eq (T a b) where
x == y = ...
It is pretty easy, albeit tedious, to fill in the code "...". The
trick is to figure out what the context for the instance decl is,
namely @Ping@, @Pong@ and friends.
Let's call the context reqd for the T instance of class C at types
(a,b, ...) C (T a b). Thus:
Eq (T a b) = (Ping a, Pong b, ...)
Now we can get a (recursive) equation from the @data@ decl:
Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
u Eq (T b a) u Eq Int -- From C2
u Eq (T a a) -- From C3
Foo and Bar may have explicit instances for @Eq@, in which case we can
just substitute for them. Alternatively, either or both may have
their @Eq@ instances given by @deriving@ clauses, in which case they
form part of the system of equations.
Now all we need do is simplify and solve the equations, iterating to
find the least fixpoint. Notice that the order of the arguments can
switch around, as here in the recursive calls to T.
Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
We start with:
Eq (T a b) = {} -- The empty set
Next iteration:
Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
u Eq (T b a) u Eq Int -- From C2
u Eq (T a a) -- From C3
After simplification:
= Eq a u Ping b u {} u {} u {}
= Eq a u Ping b
Next iteration:
Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
u Eq (T b a) u Eq Int -- From C2
u Eq (T a a) -- From C3
After simplification:
= Eq a u Ping b
u (Eq b u Ping a)
u (Eq a u Ping a)
= Eq a u Ping b u Eq b u Ping a
The next iteration gives the same result, so this is the fixpoint. We
need to make a canonical form of the RHS to ensure convergence. We do
this by simplifying the RHS to a form in which
- the classes constrain only tyvars
- the list is sorted by tyvar (major key) and then class (minor key)
- no duplicates, of course
So, here are the synonyms for the ``equation'' structures:
Note [Data decl contexts]
~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
We will need an instance decl like:
instance (Read a, RealFloat a) => Read (Complex a) where
...
The RealFloat in the context is because the read method for Complex is bound
to construct a Complex, and doing that requires that the argument type is
in RealFloat.
But this ain't true for Show, Eq, Ord, etc, since they don't construct
a Complex; they only take them apart.
Our approach: identify the offending classes, and add the data type
context to the instance decl. The "offending classes" are
Read, Enum?
FURTHER NOTE ADDED March 2002. In fact, Haskell98 now requires that
pattern matching against a constructor from a data type with a context
gives rise to the constraints for that context -- or at least the thinned
version. So now all classes are "offending".
Note [Newtype deriving]
~~~~~~~~~~~~~~~~~~~~~~~
Consider this:
class C a b
instance C [a] Char
newtype T = T Char deriving( C [a] )
Notice the free 'a' in the deriving. We have to fill this out to
newtype T = T Char deriving( forall a. C [a] )
And then translate it to:
instance C [a] Char => C [a] T where ...
Note [Newtype deriving superclasses]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(See also Trac #1220 for an interesting exchange on newtype
deriving and superclasses.)
The 'tys' here come from the partial application in the deriving
clause. The last arg is the new instance type.
We must pass the superclasses; the newtype might be an instance
of them in a different way than the representation type
E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
Then the Show instance is not done via isomorphism; it shows
Foo 3 as "Foo 3"
The Num instance is derived via isomorphism, but the Show superclass
dictionary must the Show instance for Foo, *not* the Show dictionary
gotten from the Num dictionary. So we must build a whole new dictionary
not just use the Num one. The instance we want is something like:
instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
(+) = ((+)@a)
...etc...
There may be a coercion needed which we get from the tycon for the newtype
when the dict is constructed in TcInstDcls.tcInstDecl2
Note [Unused constructors and deriving clauses]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
See Trac #3221. Consider
data T = T1 | T2 deriving( Show )
Are T1 and T2 unused? Well, no: the deriving clause expands to mention
both of them. So we gather defs/uses from deriving just like anything else.
%************************************************************************
%* *
\subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
%* *
%************************************************************************
\begin{code}
tcDeriving :: [LTyClDecl Name]
-> [LInstDecl Name]
-> [LDerivDecl Name]
-> TcM (TcGblEnv, Bag (InstInfo Name), HsValBinds Name)
tcDeriving tycl_decls inst_decls deriv_decls
= recoverM (do { g <- getGblEnv
; return (g, emptyBag, emptyValBindsOut)}) $
do {
is_boot <- tcIsHsBoot
; traceTc "tcDeriving" (ppr is_boot)
; early_specs <- makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
; (commonAuxs, auxDerivStuff) <- commonAuxiliaries $ map (either id id) early_specs
; overlap_flag <- getOverlapFlag
; let (infer_specs, given_specs) = splitEithers early_specs
; insts1 <- mapM (genInst True overlap_flag commonAuxs) given_specs
; final_specs <- extendLocalInstEnv (map (iSpec . fst) insts1) $
inferInstanceContexts overlap_flag infer_specs
; insts2 <- mapM (genInst False overlap_flag commonAuxs) final_specs
; let (inst_infos, deriv_stuff) = unzip (insts1 ++ insts2)
; loc <- getSrcSpanM
; let (binds, newTyCons, famInsts, extraInstances) =
genAuxBinds loc (unionManyBags (auxDerivStuff : deriv_stuff))
; (inst_info, rn_binds, rn_dus) <-
renameDeriv is_boot (inst_infos ++ (bagToList extraInstances)) binds
; dflags <- getDynFlags
; unless (isEmptyBag inst_info) $
liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
(ddump_deriving inst_info rn_binds newTyCons famInsts))
; let all_tycons = map ATyCon (bagToList newTyCons)
; gbl_env <- tcExtendGlobalEnv all_tycons $
tcExtendGlobalEnvImplicit (concatMap implicitTyThings all_tycons) $
tcExtendLocalFamInstEnv (bagToList famInsts) $
tcExtendLocalInstEnv (map iSpec (bagToList inst_info)) getGblEnv
; return (addTcgDUs gbl_env rn_dus, inst_info, rn_binds) }
where
ddump_deriving :: Bag (InstInfo Name) -> HsValBinds Name
-> Bag TyCon
-> Bag FamInst
-> SDoc
ddump_deriving inst_infos extra_binds repMetaTys repFamInsts
= hang (ptext (sLit "Derived instances:"))
2 (vcat (map (\i -> pprInstInfoDetails i $$ text "") (bagToList inst_infos))
$$ ppr extra_binds)
$$ hangP "Generic representation:" (
hangP "Generated datatypes for meta-information:"
(vcat (map ppr (bagToList repMetaTys)))
$$ hangP "Representation types:"
(vcat (map pprRepTy (bagToList repFamInsts))))
hangP s x = text "" $$ hang (ptext (sLit s)) 2 x
type CommonAuxiliary = MetaTyCons
type CommonAuxiliaries = [(TyCon, CommonAuxiliary)]
commonAuxiliaries :: [DerivSpec] -> TcM (CommonAuxiliaries, BagDerivStuff)
commonAuxiliaries = foldM snoc ([], emptyBag) where
snoc acc@(cas, stuff) (DS {ds_name = nm, ds_cls = cls, ds_tc = rep_tycon})
| getUnique cls `elem` [genClassKey, gen1ClassKey] =
extendComAux $ genGenericMetaTyCons rep_tycon (nameModule nm)
| otherwise = return acc
where extendComAux m
| any ((rep_tycon ==) . fst) cas = return acc
| otherwise = do (ca, new_stuff) <- m
return $ ((rep_tycon, ca) : cas, stuff `unionBags` new_stuff)
pprRepTy :: FamInst -> SDoc
pprRepTy fi
= pprFamInstHdr fi <+> ptext (sLit "=") <+> ppr (coAxiomRHS (famInstAxiom fi))
renameDeriv :: Bool
-> [InstInfo RdrName]
-> Bag (LHsBind RdrName, LSig RdrName)
-> TcM (Bag (InstInfo Name), HsValBinds Name, DefUses)
renameDeriv is_boot inst_infos bagBinds
| is_boot
= do { (rn_inst_infos, fvs) <- mapAndUnzipM rn_inst_info inst_infos
; return ( listToBag rn_inst_infos
, emptyValBindsOut, usesOnly (plusFVs fvs)) }
| otherwise
= discardWarnings $
do {
; (aux_binds, aux_sigs) <- mapAndUnzipBagM return bagBinds
; let aux_val_binds = ValBindsIn aux_binds (bagToList aux_sigs)
; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv aux_val_binds
; let bndrs = collectHsValBinders rn_aux_lhs
; bindLocalNames bndrs $
do { (rn_aux, dus_aux) <- rnValBindsRHS (LocalBindCtxt (mkNameSet bndrs)) rn_aux_lhs
; (rn_inst_infos, fvs_insts) <- mapAndUnzipM rn_inst_info inst_infos
; return (listToBag rn_inst_infos, rn_aux,
dus_aux `plusDU` usesOnly (plusFVs fvs_insts)) } }
where
rn_inst_info :: InstInfo RdrName -> TcM (InstInfo Name, FreeVars)
rn_inst_info info@(InstInfo { iBinds = NewTypeDerived coi tc })
= return ( info { iBinds = NewTypeDerived coi tc }
, mkFVs (map dataConName (tyConDataCons tc)))
rn_inst_info inst_info@(InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs standalone_deriv })
=
ASSERT( null sigs )
bindLocalNames (map Var.varName tyvars) $
do { (rn_binds, fvs) <- rnMethodBinds clas_nm (\_ -> []) binds
; let binds' = VanillaInst rn_binds [] standalone_deriv
; return (inst_info { iBinds = binds' }, fvs) }
where
(tyvars,_, clas,_) = instanceHead inst
clas_nm = className clas
\end{code}
Note [Newtype deriving and unused constructors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this (see Trac #1954):
module Bug(P) where
newtype P a = MkP (IO a) deriving Monad
If you compile with -fwarn-unused-binds you do not expect the warning
"Defined but not used: data consructor MkP". Yet the newtype deriving
code does not explicitly mention MkP, but it should behave as if you
had written
instance Monad P where
return x = MkP (return x)
...etc...
So we want to signal a user of the data constructor 'MkP'. That's
what we do in rn_inst_info, and it's the only reason we have the TyCon
stored in NewTypeDerived.
%************************************************************************
%* *
From HsSyn to DerivSpec
%* *
%************************************************************************
@makeDerivSpecs@ fishes around to find the info about needed derived instances.
\begin{code}
makeDerivSpecs :: Bool
-> [LTyClDecl Name]
-> [LInstDecl Name]
-> [LDerivDecl Name]
-> TcM [EarlyDerivSpec]
makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
= do { eqns1 <- concatMapM (recoverM (return []) . deriveTyDecl) tycl_decls
; eqns2 <- concatMapM (recoverM (return []) . deriveInstDecl) inst_decls
; eqns3 <- mapAndRecoverM deriveStandalone deriv_decls
; let eqns = eqns1 ++ eqns2 ++ eqns3
; if is_boot then
do { unless (null eqns) (add_deriv_err (head eqns))
; return [] }
else return eqns }
where
add_deriv_err eqn
= setSrcSpan loc $
addErr (hang (ptext (sLit "Deriving not permitted in hs-boot file"))
2 (ptext (sLit "Use an instance declaration instead")))
where
loc = case eqn of { Left ds -> ds_loc ds; Right ds -> ds_loc ds }
deriveTyDecl :: LTyClDecl Name -> TcM [EarlyDerivSpec]
deriveTyDecl (L _ decl@(TyDecl { tcdLName = L _ tc_name
, tcdTyDefn = TyData { td_derivs = Just preds } }))
= tcAddDeclCtxt decl $
do { tc <- tcLookupTyCon tc_name
; let tvs = tyConTyVars tc
tys = mkTyVarTys tvs
; mapM (deriveTyData tvs tc tys) preds }
deriveTyDecl _ = return []
deriveInstDecl :: LInstDecl Name -> TcM [EarlyDerivSpec]
deriveInstDecl (L _ (FamInstD { lid_inst = fam_inst }))
= deriveFamInst fam_inst
deriveInstDecl (L _ (ClsInstD { cid_fam_insts = fam_insts }))
= concatMapM (deriveFamInst . unLoc) fam_insts
deriveFamInst :: FamInstDecl Name -> TcM [EarlyDerivSpec]
deriveFamInst decl@(FamInstDecl { fid_tycon = L _ tc_name, fid_pats = pats
, fid_defn = TyData { td_derivs = Just preds } })
= tcAddFamInstCtxt decl $
do { fam_tc <- tcLookupTyCon tc_name
; tcFamTyPats fam_tc pats (\_ -> return ()) $ \ tvs' pats' _ ->
mapM (deriveTyData tvs' fam_tc pats') preds }
deriveFamInst _ = return []
deriveStandalone :: LDerivDecl Name -> TcM EarlyDerivSpec
deriveStandalone (L loc (DerivDecl deriv_ty))
= setSrcSpan loc $
addErrCtxt (standaloneCtxt deriv_ty) $
do { traceTc "Standalone deriving decl for" (ppr deriv_ty)
; (tvs, theta, cls, inst_tys) <- tcHsInstHead TcType.InstDeclCtxt deriv_ty
; traceTc "Standalone deriving;" $ vcat
[ text "tvs:" <+> ppr tvs
, text "theta:" <+> ppr theta
, text "cls:" <+> ppr cls
, text "tys:" <+> ppr inst_tys ]
; let cls_tys = take (length inst_tys 1) inst_tys
inst_ty = last inst_tys
; traceTc "Standalone deriving:" $ vcat
[ text "class:" <+> ppr cls
, text "class types:" <+> ppr cls_tys
, text "type:" <+> ppr inst_ty ]
; mkEqnHelp StandAloneDerivOrigin tvs cls cls_tys inst_ty
(Just theta) }
deriveTyData :: [TyVar] -> TyCon -> [Type]
-> LHsType Name
-> TcM EarlyDerivSpec
deriveTyData tvs tc tc_args (L loc deriv_pred)
= setSrcSpan loc $
tcExtendTyVarEnv tvs $
do { (deriv_tvs, cls, cls_tys) <- tcHsDeriv deriv_pred
; let cls_tyvars = classTyVars cls
kind = tyVarKind (last cls_tyvars)
(arg_kinds, _) = splitKindFunTys kind
n_args_to_drop = length arg_kinds
n_args_to_keep = tyConArity tc n_args_to_drop
args_to_drop = drop n_args_to_keep tc_args
inst_ty = mkTyConApp tc (take n_args_to_keep tc_args)
inst_ty_kind = typeKind inst_ty
dropped_tvs = mkVarSet (mapCatMaybes getTyVar_maybe args_to_drop)
univ_tvs = (mkVarSet tvs `extendVarSetList` deriv_tvs)
`minusVarSet` dropped_tvs
; traceTc "derivTyData" (pprTvBndrs tvs $$ ppr tc $$ ppr tc_args $$
pprTvBndrs (varSetElems $ tyVarsOfTypes tc_args) $$ ppr inst_ty)
; checkTc (n_args_to_keep >= 0 && (inst_ty_kind `eqKind` kind))
(derivingKindErr tc cls cls_tys kind)
; checkTc (sizeVarSet dropped_tvs == n_args_to_drop &&
tyVarsOfTypes (inst_ty:cls_tys) `subVarSet` univ_tvs)
(derivingEtaErr cls cls_tys inst_ty)
; checkTc (not (isFamilyTyCon tc) || n_args_to_drop == 0)
(typeFamilyPapErr tc cls cls_tys inst_ty)
; mkEqnHelp DerivOrigin (varSetElemsKvsFirst univ_tvs) cls cls_tys inst_ty Nothing }
\end{code}
Note [Deriving, type families, and partial applications]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When there are no type families, it's quite easy:
newtype S a = MkS [a]
-- :CoS :: S ~ [] -- Eta-reduced
instance Eq [a] => Eq (S a) -- by coercion sym (Eq (:CoS a)) : Eq [a] ~ Eq (S a)
instance Monad [] => Monad S -- by coercion sym (Monad :CoS) : Monad [] ~ Monad S
When type familes are involved it's trickier:
data family T a b
newtype instance T Int a = MkT [a] deriving( Eq, Monad )
-- :RT is the representation type for (T Int a)
-- :CoF:R1T a :: T Int a ~ :RT a -- Not eta reduced
-- :Co:R1T :: :RT ~ [] -- Eta-reduced
instance Eq [a] => Eq (T Int a) -- easy by coercion
instance Monad [] => Monad (T Int) -- only if we can eta reduce???
The "???" bit is that we don't build the :CoF thing in eta-reduced form
Henc the current typeFamilyPapErr, even though the instance makes sense.
After all, we can write it out
instance Monad [] => Monad (T Int) -- only if we can eta reduce???
return x = MkT [x]
... etc ...
\begin{code}
mkEqnHelp :: CtOrigin -> [TyVar] -> Class -> [Type] -> Type
-> DerivContext
-> TcRn EarlyDerivSpec
mkEqnHelp orig tvs cls cls_tys tc_app mtheta
| Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app
, isAlgTyCon tycon
= mk_alg_eqn tycon tc_args
| otherwise
= failWithTc (derivingThingErr False cls cls_tys tc_app
(ptext (sLit "The last argument of the instance must be a data or newtype application")))
where
bale_out msg = failWithTc (derivingThingErr False cls cls_tys tc_app msg)
mk_alg_eqn tycon tc_args
| className cls `elem` typeableClassNames
= do { dflags <- getDynFlags
; case checkTypeableConditions (dflags, tycon, tc_args) of
Just err -> bale_out err
Nothing -> mk_typeable_eqn orig tvs cls tycon tc_args mtheta }
| isDataFamilyTyCon tycon
, length tc_args /= tyConArity tycon
= bale_out (ptext (sLit "Unsaturated data family application"))
| otherwise
= do { (rep_tc, rep_tc_args) <- tcLookupDataFamInst tycon tc_args
; rdr_env <- getGlobalRdrEnv
; let hidden_data_cons = not (isWiredInName (tyConName rep_tc)) &&
(isAbstractTyCon rep_tc ||
any not_in_scope (tyConDataCons rep_tc))
not_in_scope dc = null (lookupGRE_Name rdr_env (dataConName dc))
; unless (isNothing mtheta || not hidden_data_cons)
(bale_out (derivingHiddenErr tycon))
; dflags <- getDynFlags
; if isDataTyCon rep_tc then
mkDataTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta
else
mkNewTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta }
\end{code}
%************************************************************************
%* *
Deriving data types
%* *
%************************************************************************
\begin{code}
mkDataTypeEqn :: CtOrigin
-> DynFlags
-> [Var]
-> Class
-> [Type]
-> TyCon
-> [Type]
-> TyCon
-> [Type]
-> DerivContext
-> TcRn EarlyDerivSpec
mkDataTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta
= case checkSideConditions dflags mtheta cls cls_tys rep_tc rep_tc_args of
CanDerive -> go_for_it
NonDerivableClass -> bale_out (nonStdErr cls)
DerivableClassError msg -> bale_out msg
where
go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
bale_out msg = failWithTc (derivingThingErr False cls cls_tys (mkTyConApp tycon tc_args) msg)
mk_data_eqn :: CtOrigin -> [TyVar] -> Class
-> TyCon -> [TcType] -> TyCon -> [TcType] -> DerivContext
-> TcM EarlyDerivSpec
mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
= do { loc <- getSrcSpanM
; dfun_name <- new_dfun_name cls tycon
; inferred_constraints <- inferConstraints cls inst_tys rep_tc rep_tc_args
; let spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = tvs
, ds_cls = cls, ds_tys = inst_tys
, ds_tc = rep_tc, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` inferred_constraints
, ds_newtype = False }
; return (if isJust mtheta then Right spec
else Left spec) }
where
inst_tys = [mkTyConApp tycon tc_args]
mk_typeable_eqn :: CtOrigin -> [TyVar] -> Class
-> TyCon -> [TcType] -> DerivContext
-> TcM EarlyDerivSpec
mk_typeable_eqn orig tvs cls tycon tc_args mtheta
| isNothing mtheta
= do { checkTc (cls `hasKey` typeableClassKey)
(ptext (sLit "Use deriving( Typeable ) on a data type declaration"))
; real_cls <- tcLookupClass (typeableClassNames !! tyConArity tycon)
; mk_typeable_eqn orig tvs real_cls tycon [] (Just []) }
| otherwise
= do { checkTc (null tc_args)
(ptext (sLit "Derived typeable instance must be of form (Typeable")
<> int (tyConArity tycon) <+> ppr tycon <> rparen)
; dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
; return (Right $
DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = []
, ds_cls = cls, ds_tys = [mkTyConApp tycon []]
, ds_tc = tycon, ds_tc_args = []
, ds_theta = mtheta `orElse` [], ds_newtype = False }) }
inferConstraints :: Class -> [TcType]
-> TyCon -> [TcType]
-> TcM ThetaType
inferConstraints cls inst_tys rep_tc rep_tc_args
| cls `hasKey` genClassKey
= return []
| cls `hasKey` gen1ClassKey
= ASSERT (length rep_tc_tvs > 0)
do { functorClass <- tcLookupClass functorClassName
; return (con_arg_constraints functorClass (get_gen1_constrained_tys last_tv)) }
| otherwise
= ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr rep_tc )
return (stupid_constraints ++ extra_constraints
++ sc_constraints
++ con_arg_constraints cls get_std_constrained_tys)
where
con_arg_constraints cls' get_constrained_tys
= [ mkClassPred cls' [arg_ty]
| data_con <- tyConDataCons rep_tc,
arg_ty <- ASSERT( isVanillaDataCon data_con )
get_constrained_tys $
dataConInstOrigArgTys data_con all_rep_tc_args,
not (isUnLiftedType arg_ty) ]
is_functor_like = getUnique cls `elem` functorLikeClassKeys
get_std_constrained_tys :: [Type] -> [Type]
get_std_constrained_tys tys
| is_functor_like = concatMap (deepSubtypesContaining last_tv) tys
| otherwise = tys
rep_tc_tvs = tyConTyVars rep_tc
last_tv = last rep_tc_tvs
all_rep_tc_args | cls `hasKey` gen1ClassKey || is_functor_like
= rep_tc_args ++ [mkTyVarTy last_tv]
| otherwise = rep_tc_args
sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys)
(classSCTheta cls)
stupid_constraints = substTheta subst (tyConStupidTheta rep_tc)
subst = zipTopTvSubst rep_tc_tvs all_rep_tc_args
extra_constraints
| cls `hasKey` dataClassKey
, all (isLiftedTypeKind . typeKind) rep_tc_args
= [mkClassPred cls [ty] | ty <- rep_tc_args]
| otherwise
= []
\end{code}
Note [Getting base classes]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Functor and Typeable are defined in package 'base', and that is not available
when compiling 'ghc-prim'. So we must be careful that 'deriving' for stuff in
ghc-prim does not use Functor or Typeable implicitly via these lookups.
Note [Deriving and unboxed types]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We have some special hacks to support things like
data T = MkT Int# deriving( Ord, Show )
Specifically
* For Show we use TcGenDeriv.box_if_necy to box the Int# into an Int
(which we know how to show)
* For Eq, Ord, we ust TcGenDeriv.primOrdOps to give Ord operations
on some primitive types
It's all a bit ad hoc.
\begin{code}
data DerivStatus = CanDerive
| DerivableClassError SDoc
| NonDerivableClass
checkSideConditions :: DynFlags -> DerivContext -> Class -> [TcType]
-> TyCon -> [Type]
-> DerivStatus
checkSideConditions dflags mtheta cls cls_tys rep_tc rep_tc_args
| Just cond <- sideConditions mtheta cls
= case (cond (dflags, rep_tc, rep_tc_args)) of
Just err -> DerivableClassError err
Nothing | null cls_tys -> CanDerive
| otherwise -> DerivableClassError ty_args_why
| otherwise = NonDerivableClass
where
ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class")
checkTypeableConditions :: Condition
checkTypeableConditions = checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK
nonStdErr :: Class -> SDoc
nonStdErr cls = quotes (ppr cls) <+> ptext (sLit "is not a derivable class")
sideConditions :: DerivContext -> Class -> Maybe Condition
sideConditions mtheta cls
| cls_key == eqClassKey = Just (cond_std `andCond` cond_args cls)
| cls_key == ordClassKey = Just (cond_std `andCond` cond_args cls)
| cls_key == showClassKey = Just (cond_std `andCond` cond_args cls)
| cls_key == readClassKey = Just (cond_std `andCond` cond_args cls)
| cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration)
| cls_key == ixClassKey = Just (cond_std `andCond` cond_enumOrProduct cls)
| cls_key == boundedClassKey = Just (cond_std `andCond` cond_enumOrProduct cls)
| cls_key == dataClassKey = Just (checkFlag Opt_DeriveDataTypeable `andCond`
cond_std `andCond` cond_args cls)
| cls_key == functorClassKey = Just (checkFlag Opt_DeriveFunctor `andCond`
cond_functorOK True)
| cls_key == foldableClassKey = Just (checkFlag Opt_DeriveFoldable `andCond`
cond_functorOK False)
| cls_key == traversableClassKey = Just (checkFlag Opt_DeriveTraversable `andCond`
cond_functorOK False)
| cls_key == genClassKey = Just (cond_RepresentableOk `andCond`
checkFlag Opt_DeriveGeneric)
| cls_key == gen1ClassKey = Just (cond_Representable1Ok `andCond`
checkFlag Opt_DeriveGeneric)
| otherwise = Nothing
where
cls_key = getUnique cls
cond_std = cond_stdOK mtheta
type Condition = (DynFlags, TyCon, [Type]) -> Maybe SDoc
orCond :: Condition -> Condition -> Condition
orCond c1 c2 tc
= case c1 tc of
Nothing -> Nothing
Just x -> case c2 tc of
Nothing -> Nothing
Just y -> Just (x $$ ptext (sLit " or") $$ y)
andCond :: Condition -> Condition -> Condition
andCond c1 c2 tc = case c1 tc of
Nothing -> c2 tc
Just x -> Just x
cond_stdOK :: DerivContext -> Condition
cond_stdOK (Just _) _
= Nothing
cond_stdOK Nothing (_, rep_tc, _)
| null data_cons = Just (no_cons_why rep_tc $$ suggestion)
| not (null con_whys) = Just (vcat con_whys $$ suggestion)
| otherwise = Nothing
where
suggestion = ptext (sLit "Possible fix: use a standalone deriving declaration instead")
data_cons = tyConDataCons rep_tc
con_whys = mapCatMaybes check_con data_cons
check_con :: DataCon -> Maybe SDoc
check_con con
| isVanillaDataCon con
, all isTauTy (dataConOrigArgTys con) = Nothing
| otherwise = Just (badCon con (ptext (sLit "must have a Haskell-98 type")))
no_cons_why :: TyCon -> SDoc
no_cons_why rep_tc = quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "must have at least one data constructor")
cond_RepresentableOk :: Condition
cond_RepresentableOk (_, tc, tc_args) = canDoGenerics tc tc_args
cond_Representable1Ok :: Condition
cond_Representable1Ok (_, tc, tc_args) = canDoGenerics1 tc tc_args
cond_enumOrProduct :: Class -> Condition
cond_enumOrProduct cls = cond_isEnumeration `orCond`
(cond_isProduct `andCond` cond_args cls)
cond_args :: Class -> Condition
cond_args cls (_, tc, _)
= case bad_args of
[] -> Nothing
(ty:_) -> Just (hang (ptext (sLit "Don't know how to derive") <+> quotes (ppr cls))
2 (ptext (sLit "for type") <+> quotes (ppr ty)))
where
bad_args = [ arg_ty | con <- tyConDataCons tc
, arg_ty <- dataConOrigArgTys con
, isUnLiftedType arg_ty
, not (ok_ty arg_ty) ]
cls_key = classKey cls
ok_ty arg_ty
| cls_key == eqClassKey = check_in arg_ty ordOpTbl
| cls_key == ordClassKey = check_in arg_ty ordOpTbl
| cls_key == showClassKey = check_in arg_ty boxConTbl
| otherwise = False
check_in :: Type -> [(Type,a)] -> Bool
check_in arg_ty tbl = any (eqType arg_ty . fst) tbl
cond_isEnumeration :: Condition
cond_isEnumeration (_, rep_tc, _)
| isEnumerationTyCon rep_tc = Nothing
| otherwise = Just why
where
why = sep [ quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "must be an enumeration type")
, ptext (sLit "(an enumeration consists of one or more nullary, non-GADT constructors)") ]
cond_isProduct :: Condition
cond_isProduct (_, rep_tc, _)
| isProductTyCon rep_tc = Nothing
| otherwise = Just why
where
why = quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "must have precisely one constructor")
cond_typeableOK :: Condition
cond_typeableOK (_, tc, _)
| tyConArity tc > 7 = Just too_many
| not (all (isSubOpenTypeKind . tyVarKind) (tyConTyVars tc))
= Just bad_kind
| otherwise = Nothing
where
too_many = quotes (pprSourceTyCon tc) <+>
ptext (sLit "must have 7 or fewer arguments")
bad_kind = quotes (pprSourceTyCon tc) <+>
ptext (sLit "must only have arguments of kind `*'")
functorLikeClassKeys :: [Unique]
functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey]
cond_functorOK :: Bool -> Condition
cond_functorOK allowFunctions (_, rep_tc, _)
| null tc_tvs
= Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
<+> ptext (sLit "must have some type parameters"))
| not (null bad_stupid_theta)
= Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
<+> ptext (sLit "must not have a class context") <+> pprTheta bad_stupid_theta)
| otherwise
= msum (map check_con data_cons)
where
tc_tvs = tyConTyVars rep_tc
Just (_, last_tv) = snocView tc_tvs
bad_stupid_theta = filter is_bad (tyConStupidTheta rep_tc)
is_bad pred = last_tv `elemVarSet` tyVarsOfType pred
data_cons = tyConDataCons rep_tc
check_con con = msum (check_vanilla con : foldDataConArgs (ft_check con) con)
check_vanilla :: DataCon -> Maybe SDoc
check_vanilla con | isVanillaDataCon con = Nothing
| otherwise = Just (badCon con existential)
ft_check :: DataCon -> FFoldType (Maybe SDoc)
ft_check con = FT { ft_triv = Nothing, ft_var = Nothing
, ft_co_var = Just (badCon con covariant)
, ft_fun = \x y -> if allowFunctions then x `mplus` y
else Just (badCon con functions)
, ft_tup = \_ xs -> msum xs
, ft_ty_app = \_ x -> x
, ft_bad_app = Just (badCon con wrong_arg)
, ft_forall = \_ x -> x }
existential = ptext (sLit "must not have existential arguments")
covariant = ptext (sLit "must not use the type variable in a function argument")
functions = ptext (sLit "must not contain function types")
wrong_arg = ptext (sLit "must use the type variable only as the last argument of a data type")
checkFlag :: ExtensionFlag -> Condition
checkFlag flag (dflags, _, _)
| xopt flag dflags = Nothing
| otherwise = Just why
where
why = ptext (sLit "You need -X") <> text flag_str
<+> ptext (sLit "to derive an instance for this class")
flag_str = case [ s | (s, f, _) <- xFlags, f==flag ] of
[s] -> s
other -> pprPanic "checkFlag" (ppr other)
std_class_via_iso :: Class -> Bool
std_class_via_iso clas
= classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
non_iso_class :: Class -> Bool
non_iso_class cls
= classKey cls `elem` ([ readClassKey, showClassKey, dataClassKey
, genClassKey, gen1ClassKey] ++ typeableClassKeys)
typeableClassKeys :: [Unique]
typeableClassKeys = map getUnique typeableClassNames
new_dfun_name :: Class -> TyCon -> TcM Name
new_dfun_name clas tycon
= do { loc <- getSrcSpanM
; newDFunName clas [mkTyConApp tycon []] loc }
badCon :: DataCon -> SDoc -> SDoc
badCon con msg = ptext (sLit "Constructor") <+> quotes (ppr con) <+> msg
\end{code}
Note [Superclasses of derived instance]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In general, a derived instance decl needs the superclasses of the derived
class too. So if we have
data T a = ...deriving( Ord )
then the initial context for Ord (T a) should include Eq (T a). Often this is
redundant; we'll also generate an Ord constraint for each constructor argument,
and that will probably generate enough constraints to make the Eq (T a) constraint
be satisfied too. But not always; consider:
data S a = S
instance Eq (S a)
instance Ord (S a)
data T a = MkT (S a) deriving( Ord )
instance Num a => Eq (T a)
The derived instance for (Ord (T a)) must have a (Num a) constraint!
Similarly consider:
data T a = MkT deriving( Data, Typeable )
Here there *is* no argument field, but we must nevertheless generate
a context for the Data instances:
instance Typable a => Data (T a) where ...
%************************************************************************
%* *
Deriving newtypes
%* *
%************************************************************************
\begin{code}
mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class
-> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
-> DerivContext
-> TcRn EarlyDerivSpec
mkNewTypeEqn orig dflags tvs
cls cls_tys tycon tc_args rep_tycon rep_tc_args mtheta
| can_derive_via_isomorphism && (newtype_deriving || std_class_via_iso cls)
= do { traceTc "newtype deriving:" (ppr tycon <+> ppr rep_tys <+> ppr all_preds)
; dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
; let spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = varSetElemsKvsFirst dfun_tvs
, ds_cls = cls, ds_tys = inst_tys
, ds_tc = rep_tycon, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` all_preds
, ds_newtype = True }
; return (if isJust mtheta then Right spec
else Left spec) }
| otherwise
= case checkSideConditions dflags mtheta cls cls_tys rep_tycon rep_tc_args of
CanDerive -> go_for_it
DerivableClassError msg
| can_derive_via_isomorphism -> bale_out (msg $$ suggest_nd)
| otherwise -> bale_out msg
NonDerivableClass
| newtype_deriving -> bale_out cant_derive_err
| can_derive_via_isomorphism -> bale_out (non_std $$ suggest_nd)
| otherwise -> bale_out non_std
where
newtype_deriving = xopt Opt_GeneralizedNewtypeDeriving dflags
go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta
bale_out msg = failWithTc (derivingThingErr newtype_deriving cls cls_tys inst_ty msg)
non_std = nonStdErr cls
suggest_nd = ptext (sLit "Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")
nt_eta_arity = length (fst (newTyConEtadRhs rep_tycon))
rep_inst_ty = newTyConInstRhs rep_tycon rep_tc_args
rep_tys = cls_tys ++ [rep_inst_ty]
rep_pred = mkClassPred cls rep_tys
cls_tyvars = classTyVars cls
dfun_tvs = tyVarsOfTypes inst_tys
inst_ty = mkTyConApp tycon tc_args
inst_tys = cls_tys ++ [inst_ty]
sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys)
(classSCTheta cls)
all_preds = rep_pred : sc_theta
can_derive_via_isomorphism
= not (non_iso_class cls)
&& arity_ok
&& eta_ok
&& ats_ok
arity_ok = length cls_tys + 1 == classArity cls
eta_ok = nt_eta_arity <= length rep_tc_args
ats_ok = null (classATs cls)
cant_derive_err
= vcat [ ppUnless arity_ok arity_msg
, ppUnless eta_ok eta_msg
, ppUnless ats_ok ats_msg ]
arity_msg = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1")
eta_msg = ptext (sLit "cannot eta-reduce the representation type enough")
ats_msg = ptext (sLit "the class has associated types")
\end{code}
Note [Recursive newtypes]
~~~~~~~~~~~~~~~~~~~~~~~~~
Newtype deriving works fine, even if the newtype is recursive.
e.g. newtype S1 = S1 [T1 ()]
newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
Remember, too, that type families are curretly (conservatively) given
a recursive flag, so this also allows newtype deriving to work
for type famillies.
We used to exclude recursive types, because we had a rather simple
minded way of generating the instance decl:
newtype A = MkA [A]
instance Eq [A] => Eq A -- Makes typechecker loop!
But now we require a simple context, so it's ok.
%************************************************************************
%* *
\subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
%* *
%************************************************************************
A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
terms, which is the final correct RHS for the corresponding original
equation.
\begin{itemize}
\item
Each (k,TyVarTy tv) in a solution constrains only a type
variable, tv.
\item
The (k,TyVarTy tv) pairs in a solution are canonically
ordered by sorting on type varible, tv, (major key) and then class, k,
(minor key)
\end{itemize}
\begin{code}
inferInstanceContexts :: OverlapFlag -> [DerivSpec] -> TcM [DerivSpec]
inferInstanceContexts _ [] = return []
inferInstanceContexts oflag infer_specs
= do { traceTc "inferInstanceContexts" $ vcat (map pprDerivSpec infer_specs)
; iterate_deriv 1 initial_solutions }
where
initial_solutions :: [ThetaType]
initial_solutions = [ [] | _ <- infer_specs ]
iterate_deriv :: Int -> [ThetaType] -> TcM [DerivSpec]
iterate_deriv n current_solns
| n > 20
= pprPanic "solveDerivEqns: probable loop"
(vcat (map pprDerivSpec infer_specs) $$ ppr current_solns)
| otherwise
= do {
let inst_specs = zipWithEqual "add_solns" (mkInstance oflag)
current_solns infer_specs
; new_solns <- checkNoErrs $
extendLocalInstEnv inst_specs $
mapM gen_soln infer_specs
; let eqList :: (a -> b -> Bool) -> [a] -> [b] -> Bool
eqList f xs ys = length xs == length ys && and (zipWith f xs ys)
; if (eqList (eqList eqType) current_solns new_solns) then
return [ spec { ds_theta = soln }
| (spec, soln) <- zip infer_specs current_solns ]
else
iterate_deriv (n+1) new_solns }
gen_soln :: DerivSpec -> TcM [PredType]
gen_soln (DS { ds_loc = loc, ds_orig = orig, ds_tvs = tyvars
, ds_cls = clas, ds_tys = inst_tys, ds_theta = deriv_rhs })
= setSrcSpan loc $
addErrCtxt (derivInstCtxt the_pred) $
do { theta <- simplifyDeriv orig the_pred tyvars deriv_rhs
; traceTc "TcDeriv" (ppr deriv_rhs $$ ppr theta)
; return (sortBy cmpType theta) }
where
the_pred = mkClassPred clas inst_tys
mkInstance :: OverlapFlag -> ThetaType -> DerivSpec -> ClsInst
mkInstance overlap_flag theta
(DS { ds_name = dfun_name
, ds_tvs = tyvars, ds_cls = clas, ds_tys = tys })
= mkLocalInstance dfun overlap_flag
where
dfun = mkDictFunId dfun_name tyvars theta clas tys
extendLocalInstEnv :: [ClsInst] -> TcM a -> TcM a
extendLocalInstEnv dfuns thing_inside
= do { env <- getGblEnv
; let inst_env' = extendInstEnvList (tcg_inst_env env) dfuns
env' = env { tcg_inst_env = inst_env' }
; setGblEnv env' thing_inside }
\end{code}
%************************************************************************
%* *
\subsection[TcDeriv-normal-binds]{Bindings for the various classes}
%* *
%************************************************************************
After all the trouble to figure out the required context for the
derived instance declarations, all that's left is to chug along to
produce them. They will then be shoved into @tcInstDecls2@, which
will do all its usual business.
There are lots of possibilities for code to generate. Here are
various general remarks.
PRINCIPLES:
\begin{itemize}
\item
We want derived instances of @Eq@ and @Ord@ (both v common) to be
``you-couldn't-do-better-by-hand'' efficient.
\item
Deriving @Show@---also pretty common--- should also be reasonable good code.
\item
Deriving for the other classes isn't that common or that big a deal.
\end{itemize}
PRAGMATICS:
\begin{itemize}
\item
Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
\item
Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
\item
We {\em normally} generate code only for the non-defaulted methods;
there are some exceptions for @Eq@ and (especially) @Ord@...
\item
Sometimes we use a @_con2tag_@ function, which returns a data
constructor's numeric (@Int#@) tag. These are generated by
@gen_tag_n_con_binds@, and the heuristic for deciding if one of
these is around is given by @hasCon2TagFun@.
The examples under the different sections below will make this
clearer.
\item
Much less often (really just for deriving @Ix@), we use a
@_tag2con_@ function. See the examples.
\item
We use the renamer!!! Reason: we're supposed to be
producing @LHsBinds Name@ for the methods, but that means
producing correctly-uniquified code on the fly. This is entirely
possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
So, instead, we produce @MonoBinds RdrName@ then heave 'em through
the renamer. What a great hack!
\end{itemize}
\begin{code}
genInst :: Bool
-> OverlapFlag
-> CommonAuxiliaries
-> DerivSpec -> TcM (InstInfo RdrName, BagDerivStuff)
genInst standalone_deriv oflag comauxs
spec@(DS { ds_tvs = tvs, ds_tc = rep_tycon, ds_tc_args = rep_tc_args
, ds_theta = theta, ds_newtype = is_newtype
, ds_name = name, ds_cls = clas })
| is_newtype
= return (InstInfo { iSpec = inst_spec
, iBinds = NewTypeDerived co rep_tycon }, emptyBag)
| otherwise
= do { fix_env <- getFixityEnv
; (meth_binds, deriv_stuff) <- genDerivStuff (getSrcSpan name)
fix_env clas name rep_tycon
(lookup rep_tycon comauxs)
; let inst_info = InstInfo { iSpec = inst_spec
, iBinds = VanillaInst meth_binds []
standalone_deriv }
; return ( inst_info, deriv_stuff) }
where
inst_spec = mkInstance oflag theta spec
co1 = case tyConFamilyCoercion_maybe rep_tycon of
Just co_con -> mkTcAxInstCo co_con rep_tc_args
Nothing -> id_co
co2 = mkTcAxInstCo (newTyConCo rep_tycon) rep_tc_args
co = mkTcForAllCos tvs (co1 `mkTcTransCo` co2)
id_co = mkTcReflCo (mkTyConApp rep_tycon rep_tc_args)
genDerivStuff :: SrcSpan -> FixityEnv -> Class -> Name -> TyCon
-> Maybe CommonAuxiliary
-> TcM (LHsBinds RdrName, BagDerivStuff)
genDerivStuff loc fix_env clas name tycon comaux_maybe
| className clas `elem` typeableClassNames
= return (gen_Typeable_binds loc tycon, emptyBag)
| ck `elem` [genClassKey, gen1ClassKey]
= let gk = if ck == genClassKey then Gen0 else Gen1
Just metaTyCons = comaux_maybe
in do
(binds, faminst) <- gen_Generic_binds gk tycon metaTyCons (nameModule name)
return (binds, DerivFamInst faminst `consBag` emptyBag)
| otherwise
= do dflags <- getDynFlags
case assocMaybe (gen_list dflags) (getUnique clas) of
Just gen_fn -> return (gen_fn loc tycon)
Nothing -> pprPanic "genDerivStuff: bad derived class" (ppr clas)
where
ck = classKey clas
gen_list :: DynFlags
-> [(Unique, SrcSpan -> TyCon -> (LHsBinds RdrName, BagDerivStuff))]
gen_list dflags
= [(eqClassKey, gen_Eq_binds)
,(ordClassKey, gen_Ord_binds)
,(enumClassKey, gen_Enum_binds)
,(boundedClassKey, gen_Bounded_binds)
,(ixClassKey, gen_Ix_binds)
,(showClassKey, gen_Show_binds fix_env)
,(readClassKey, gen_Read_binds fix_env)
,(dataClassKey, gen_Data_binds dflags)
,(functorClassKey, gen_Functor_binds)
,(foldableClassKey, gen_Foldable_binds)
,(traversableClassKey, gen_Traversable_binds)
]
\end{code}
%************************************************************************
%* *
\subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
%* *
%************************************************************************
\begin{code}
derivingKindErr :: TyCon -> Class -> [Type] -> Kind -> MsgDoc
derivingKindErr tc cls cls_tys cls_kind
= hang (ptext (sLit "Cannot derive well-kinded instance of form")
<+> quotes (pprClassPred cls cls_tys <+> parens (ppr tc <+> ptext (sLit "..."))))
2 (ptext (sLit "Class") <+> quotes (ppr cls)
<+> ptext (sLit "expects an argument of kind") <+> quotes (pprKind cls_kind))
derivingEtaErr :: Class -> [Type] -> Type -> MsgDoc
derivingEtaErr cls cls_tys inst_ty
= sep [ptext (sLit "Cannot eta-reduce to an instance of form"),
nest 2 (ptext (sLit "instance (...) =>")
<+> pprClassPred cls (cls_tys ++ [inst_ty]))]
typeFamilyPapErr :: TyCon -> Class -> [Type] -> Type -> MsgDoc
typeFamilyPapErr tc cls cls_tys inst_ty
= hang (ptext (sLit "Derived instance") <+> quotes (pprClassPred cls (cls_tys ++ [inst_ty])))
2 (ptext (sLit "requires illegal partial application of data type family") <+> ppr tc)
derivingThingErr :: Bool -> Class -> [Type] -> Type -> MsgDoc -> MsgDoc
derivingThingErr newtype_deriving clas tys ty why
= sep [(hang (ptext (sLit "Can't make a derived instance of"))
2 (quotes (ppr pred))
$$ nest 2 extra) <> colon,
nest 2 why]
where
extra | newtype_deriving = ptext (sLit "(even with cunning newtype deriving)")
| otherwise = empty
pred = mkClassPred clas (tys ++ [ty])
derivingHiddenErr :: TyCon -> SDoc
derivingHiddenErr tc
= hang (ptext (sLit "The data constructors of") <+> quotes (ppr tc) <+> ptext (sLit "are not all in scope"))
2 (ptext (sLit "so you cannot derive an instance for it"))
standaloneCtxt :: LHsType Name -> SDoc
standaloneCtxt ty = hang (ptext (sLit "In the stand-alone deriving instance for"))
2 (quotes (ppr ty))
derivInstCtxt :: PredType -> MsgDoc
derivInstCtxt pred
= ptext (sLit "When deriving the instance for") <+> parens (ppr pred)
\end{code}