envmonad.ts

// created by KatagiriSo Rodhos Soft

type EnvMonad<T,E> = (env:E) => T

const unit = <T,E>(t:T) => (env:E) => t;
const bind = <T1,T2,E>(e:EnvMonad<T1,E>, f:(t1:T1)=>EnvMonad<T2,E>) => {
    return (env:E) => f(e(env))(env)
}

function envMonadTest() {
    const f = (i:number) => (env:number) => i*env;

    const m = unit<number, number>(10);
    const mm = bind(m, f);
    const ans = mm(5); // env 5
    console.log("ans == ", ans) // 10*5 = 50;

}

envMonadTest();