monad

monad

// monad.js
const Monad = x => ({
    map: f => Monad(f(x)),
    fold: f => f(x),
    toString: () => `Monad(${x})`
})
const dollarToYuan = str =>
    Monad(str)
    .map(s => s.replace(/\$+/g, '￥'))
    .fold(x => x)
    // .toString()
// dollarToYuan('$5.00')