KindFnEither
import type { KindFnEither } from "https://github.gh-proxy.cn/raw.githubusercontent.com/baetheus/fun/main/fn_either.ts";Specifies FnEither as a Higher Kinded Type, with covariant parameter A and B corresponding to the 0th and 1st indices of any Substitutions and a contravariant parameter D corresponding to the 0th index of any Substititions. The FnEither KindFnEither is unique in that it constrains the FnEither type to taking a single argument for the purposes of type substitution while the implementations of FnEither combinators such as map, flatmap, etc are mostly variadic (multiple arguments).
interface KindFnEither extends Kind {}