Function lambda_calculus::data::result::option_err

pub fn option_err() -> Term

Applied to a lambda-encoded Result it produces a lambda-encoded Option containing the Err value.

OPTION_ERR ≡ λa.a (λx.NONE) SOME ≡ λ 1 (λ NONE) SOME

Example

use lambda_calculus::data::result::option_err;
use lambda_calculus::data::option::none;
use lambda_calculus::*;

let ok_one: Result<usize, usize> = Ok(1);
let err_two: Result<usize, usize> = Err(2);

assert_eq!(beta(app(option_err(), ok_one.into_church()), NOR, 0), none());
assert_eq!(beta(app(option_err(), err_two.into_church()), NOR, 0), Some(2).into_church());