Promise - 嵌套函数不起作用

我想知道为什么以下代码不起作用，毕竟它只是嵌套函数：

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))