TypeScript port of the first half of John De Goes "FP to the max" (https://www.youtube.com/watch?v=sxudIMiOo68)

fp-ts-to-the-max-I.ts

import { log } from 'fp-ts/lib/Console'
import { none, Option, some } from 'fp-ts/lib/Option'
import { randomInt } from 'fp-ts/lib/Random'
import { fromIO, Task, task } from 'fp-ts/lib/Task'
import { createInterface } from 'readline'

//
// helpers
//

const getStrLn: Task<string> = new Task(
  () =>
    new Promise(resolve => {
      const rl = createInterface({
        input: process.stdin,
        output: process.stdout
      })
      rl.question('> ', answer => {
        rl.close()
        resolve(answer)
      })
    })
)

const putStrLn = (message: string): Task<void> => fromIO(log(message))

const random = fromIO(randomInt(1, 5))

const parse = (s: string): Option<number> => {
  const i = +s
  return isNaN(i) || i % 1 !== 0 ? none : some(i)
}

//
// game
//

const checkContinue = (name: string): Task<boolean> =>
  putStrLn(`Do you want to continue, ${name}?`)
    .chain(() => getStrLn)
    .chain(answer => {
      switch (answer.toLowerCase()) {
        case 'y':
          return task.of(true)
        case 'n':
          return task.of(false)
        default:
          return checkContinue(name)
      }
    })

const gameLoop = (name: string): Task<void> =>
  random.chain(secret =>
    putStrLn(`Dear ${name}, please guess a number from 1 to 5`)
      .chain(() =>
        getStrLn.chain(guess =>
          parse(guess).fold(
            putStrLn('You did not enter an integer!'),
            x =>
              x === secret
                ? putStrLn(`You guessed right, ${name}!`)
                : putStrLn(`You guessed wrong, ${name}! The number was: ${secret}`)
          )
        )
      )
      .chain(() => checkContinue(name))
      .chain(shouldContinue => (shouldContinue ? gameLoop(name) : task.of(undefined)))
  )

const main: Task<void> = putStrLn('What is your name?')
  .chain(() => getStrLn)
  .chain(name => putStrLn(`Hello, ${name} welcome to the game!`).chain(() => gameLoop(name)))

main.run()