这个CLI bmiTell函数有问题

Question

关于bmiTell，我得到parse error为什么会这样？

Prelude> :{
Prelude| let  bmiTell :: Double -> Double -> String
Prelude| bmiTell weight height
Prelude|   weight / height ^ 2 <= 18.5 = "You're underweight, you emo, you!"
Prelude|   weight / height ^ 2 <= 25.0 = "You're supposedly normal. Pffft, I bet you're ugly!"
Prelude|   weight / height ^ 2 <= 30.0 = "You're fat! Lose some weight, fatty!"
Prelude|   otherwise = "You're a whale, congratulations!"
Prelude| :}

<interactive>:19:1: parse error on input `bmiTell'

Answer 1

你的缩进正在抛弃解析器。看看这个：

Prelude> :{
Prelude| let bmiTell :: Double -> Double -> String
Prelude| bmiTell weight height = undefined
Prelude| :}

<interactive>:6:1: parse error on input `bmiTell'
Prelude> :{
Prelude| let bmiTell :: Double -> Double -> String
Prelude|     bmiTell weight height = undefined
Prelude| :}
Prelude>

Answer 2

您正在尝试在函数定义中使用guards，所以

weight / height ^ 2 

应该是

| weight / height ^ 2 

其他人也很相似。

正如@DiegoNolan在评论中指出的那样，你真的应该把这个定义放在一个源文件中并加载到ghci。