pub trait Plus<F, A>where
Self: Alt<F, A>,
F: HKT1<T<A> = Self>,{
// Required method
fn empty() -> F::T<A>;
}Expand description
Plus adds an identity (empty) value to Alt.
Laws
The Plus identity value must be a no-op on either side
of an alt, e.g.
use naan::prelude::*;
assert_eq!(Option::pure("hello").alt(Option::empty()),
Option::pure("hello"));
// Generalized:
fn assert_empty_is_identity<F, A, T>(t: T)
where T: PartialEq + core::fmt::Debug + Clone + Plus<F, A>,
F: HKT1<T<A> = T>
{
assert_eq!(t.clone().alt(T::empty()), t.clone());
assert_eq!(T::empty().alt(t.clone()), t);
}
assert_empty_is_identity(Some("hello"));
assert_empty_is_identity(vec!["hello"]);