Restricted Monad experiment

restricted.tsx

import React from "react"
type Level = "read" | "read_write"

type Restricted<A, B> = (l: Level) => (a: A) => B

function restricted<A, B>(required: Level, whenAuth: (a: A) => B, whenNotAuth: () => B) {
  return (level: Level) => (a: A) => required === level
    ? whenAuth(a)
    : whenNotAuth();
}

function map<A, B, C>(fa: Restricted<A, B>, fn: (b: B) => C): Restricted<A, C> {
  return (level: Level) => (a: A) => fn(fa(level)(a))
}

//readonly chain: <R, A, B>(ma: ReaderT1<M, R, A>, f: (a: A) => ReaderT1<M, R, B>) => ReaderT1<M, R, B>
/**
 * instance Monad ((->) r) where
    f >>= k = \ r -> k (f r) r

    f = the function (r -> _)
    k = A -> (r -> _)

  Prelude> let bar = (const "max") >>= \r -> (words . (++r))
  Prelude> bar "david"
  ["davidmax"]

 */

function chain<A, B, C, D>(fa: Restricted<A, B>, fn: (b: B) => Restricted<B,D>): Restricted<A, D> {
  return (level: Level) => (a: A) => {
    const b = fa(level)(a);
    const fb = fn(b);
    return fb(level)(b);
  }
}

const restrictedRoute = restricted<string, JSX.Element>(
  "read_write",
  id => <AdminPanel />,
  () => <401 />,
);