type IResult<A, B, C> = Result<A, (B, C)>;

pub fn one_of<I, T, Error>(list: T) -> impl Fn(I) -> IResult<I, char, Error> {
    Ok
}

pub fn escaped<P1, P2, T, O, Input, Error>(normal: P1, control: T, escapable: P2)
    -> impl FnOnce(Input) -> IResult<Input, Input, Error>
where
    P1: Fn(Input) -> IResult<Input, O, Error>,
    P2: Fn(Input) -> IResult<Input, O, Error>,
{
    Ok
}

fn main() {
    let alpha = Ok::<_, (_, ())>;
    escaped(alpha, '\\', one_of(""))("abcd");
}