Basic monadic IO implementation

IO.js

const IO = (function(io) {
  
  io.return = x => () => x;
  io.unit = io.return;
  io.of = io.return;
  io.bind = a => fa => () => fa(a())();
  io.flatten = aa => io.bind(aa)(a => io.bind(a)(ar => io.return(ar)));
  io.join = io.flatten
  io.takeLeft = a => b => io.bind(a)(ar => io.bind(b)(_ => io.return(ar)));
  io.takeRight = a => b => io.bind(a)(_ => b);
  
  io.pure = io.return;
  io.ap = af => a => io.bind(af)(f => io.bind(a)(ar => io.return(f(ar))));
  
  io.fmap = f => a => io.ap(io.return(f))(a);
  
  io.io = fn => (...args) => io.bind(io.return(args))((args) => io.return(fn(...args)));
  io.run = a => a();
  
  
  return Object.freeze(io);
 
})({});

// utils

function sequence(ms, M) {
  return ms.reduce((acc, m) => M.bind(acc)(l => M.bind(m)(mr => M.return(l.concat([mr])))), M.return([]));
}

function run(m, M) {
  return M.run(m)
}



// example:

const print = IO.io(console.log)

const prompt = IO.io(window.prompt)

function doStuffReturnIO(x) {
  if(typeof +x === "number" && Number.isNaN(+x) === false) {
    return print(`Ho ricevuto un numero: ${x}`)
  } else if(typeof x === "string") {
    return print(`Ho ricevuto una stringa: ${x}`)
  } else {
    return print(`Ho ricevuto un boh: `, JSON.stringify(x, null, 4))
  }
}

const readFromUserThenDoStuff = IO.bind(prompt("Inserisci qualcosa :)"))(doStuffReturnIO)

const readFromUserThenDoStuff3TimesAfterGreetBeforeByeBye = sequence(
  [ 
    print("Benvenuto"),
    readFromUserThenDoStuff,
    readFromUserThenDoStuff,
    readFromUserThenDoStuff,
    print("Alla prossima!"),
  ],
  IO
)

IO.run(readFromUserThenDoStuff3TimesAfterGreetBeforeByeBye)