Promise - 嵌套函數不起作用

我想知道為什么以下代碼不起作用，畢竟它只是嵌套函數：

var calculus = new Promise((resolve, reject) => (resolve) => resolve(3))

var calculus2 = new Promise((resolve, reject) => {
  () => resolve(4)
})

calculus.then((result) => console.log(result))
calculus2.then((result) => console.log(result))