fp_library/classes/
category.rs

1use crate::{classes::Semigroupoid, hkt::Apply1L2T};
2
3/// A type class for categories.
4///
5/// `Category` extends [`Semigroupoid`] with an identity element.
6///
7/// # Laws
8///
9/// `Category` instances must satisfy the identity law:
10/// * Identity: `compose(identity)(p) = compose(p)(identity)`.
11pub trait Category: Semigroupoid {
12	/// Returns the identity morphism.
13	///
14	/// # Type Signature
15	///
16	/// `forall a. Category c => () -> c a a`
17	///
18	/// # Returns
19	///
20	/// The identity morphism.
21	fn identity<'a, A: 'a>() -> Apply1L2T<'a, Self, A, A>;
22}
23
24/// Returns the identity morphism.
25///
26/// Free function version that dispatches to [the type class' associated function][`Category::identity`].
27///
28/// # Type Signature
29///
30/// `forall a. Category c => () -> c a a`
31///
32/// # Returns
33///
34/// The identity morphism.
35///
36/// # Examples
37///
38/// ```
39/// use fp_library::{brands::RcFnBrand, functions::category_identity};
40///
41/// assert_eq!(category_identity::<RcFnBrand, _>()(()), ());
42/// ```
43pub fn category_identity<'a, Brand: Category, A: 'a>() -> Apply1L2T<'a, Brand, A, A> {
44	Brand::identity::<'a, _>()
45}
fp_library/classes/category.rs

fp_library/classes/
category.rs
