    module Data.Derive.Arbitrary(makeArbitrary) where
    {-
    import "QuickCheck" Test.QuickCheck

    example :: Custom

    instance Arbitrary (Sample a) where
        arbitrary = do
            x <- choose (0::Int,length [First{},Second{},Third{}] - 1)
            case x of
                0 -> do return (First)
                1 -> do x1 <- arbitrary
                        x2 <- arbitrary
                        return (Second x1 x2)
                2 -> do x1 <- arbitrary
                        return (Third x1)
                _ -> error "FATAL ERROR: Arbitrary instance, logic bug"

    test :: State
    instance (CoArbitrary s, Arbitrary s, Arbitrary a) => Arbitrary (State s a) where
        arbitrary = do x1 <- arbitrary
                       return (StateT x1)
    -}

    import Data.Derive.DSL.HSE
    import Data.List
    import Data.Generics.Uniplate.DataOnly

    -- GENERATED START

    import Data.Derive.DSL.DSL
    import Data.Derive.Internal.Derivation

    makeArbitrary :: Derivation
    makeArbitrary = derivationCustomDSL "Arbitrary" custom $
        List [Instance [] "Arbitrary" (List [App "InsDecl" (List [App
        "PatBind" (List [App "PVar" (List [App "Ident" (List [String
        "arbitrary"])]),App "UnGuardedRhs" (List [App "Do" (List [List [
        App "Generator" (List [App "PVar" (List [App "Ident" (List [String
        "x"])]),App "App" (List [App "Var" (List [App "UnQual" (List [App
        "Ident" (List [String "choose"])])]),App "Tuple" (List [App
        "Boxed" (List []),List [App "ExpTypeSig" (List [App "Lit" (List [
        App "Int" (List [Int 0])]),App "TyCon" (List [App "UnQual" (List [
        App "Ident" (List [String "Int"])])])]),App "InfixApp" (List [App
        "App" (List [App "Var" (List [App "UnQual" (List [App "Ident" (
        List [String "length"])])]),App "List" (List [MapCtor (App
        "RecConstr" (List [App "UnQual" (List [App "Ident" (List [CtorName
        ])]),List []]))])]),App "QVarOp" (List [App "UnQual" (List [App
        "Symbol" (List [String "-"])])]),App "Lit" (List [App "Int" (List
        [Int 1])])])]])])]),App "Qualifier" (List [App "Case" (List [App
        "Var" (List [App "UnQual" (List [App "Ident" (List [String "x"])])
        ]),Concat (List [MapCtor (App "Alt" (List [App "PLit" (List [App
        "Signless" (List []),App "Int" (List [CtorIndex])]),App
        "UnGuardedRhs" (List [App "Do" (List [Concat (List [MapField (App
        "Generator" (List [App "PVar" (List [App "Ident" (List [Concat (
        List [String "x",ShowInt FieldIndex])])]),App "Var" (List [App
        "UnQual" (List [App "Ident" (List [String "arbitrary"])])])])),
        List [App "Qualifier" (List [App "App" (List [App "Var" (List [App
        "UnQual" (List [App "Ident" (List [String "return"])])]),App
        "Paren" (List [Application (Concat (List [List [App "Con" (List [
        App "UnQual" (List [App "Ident" (List [CtorName])])])],MapField (
        App "Var" (List [App "UnQual" (List [App "Ident" (List [Concat (
        List [String "x",ShowInt FieldIndex])])])]))]))])])])]])])]),App
        "Nothing" (List [])])),List [App "Alt" (List [App "PWildCard" (
        List []),App "UnGuardedRhs" (List [App "App" (List [App "Var" (
        List [App "UnQual" (List [App "Ident" (List [String "error"])])]),
        App "Lit" (List [App "String" (List [String
        "FATAL ERROR: Arbitrary instance, logic bug"])])])]),App "Nothing"
        (List [])])]])])])]])]),App "Nothing" (List [])])])])]
    -- GENERATED STOP

    custom = customContext context

    -- Fix the context
    -- C a b => Arbitrary a, Arbitrary b
    -- a -> b => CoArbitrary a, Arbitrary b
    context :: FullDataDecl -> Context -> Context
    context (_,d) _ = nub $ concatMap (f True . snd) $ concatMap ctorDeclFields $ dataDeclCtors d
        where
            f b (TyVar x) = [ClassA (qname $ b ? "Arbitrary" $ "CoArbitrary") [TyVar x]]
            f b (TyFun x y) = f (not b) x ++ f b y
            f b x = concatMap (f b) (children x)