haskell新手这个CLI有什么问题bmiTell函数

Question

我在以下bmiTell上得到parse error为什么？

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

您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

你试图在你的函数定义中使用guards，所以

weight/height^2 

应该

| weight/height^2 

其他人是相似的。

而@DiegoNolan在评论中指出，你应该把这个定义放在一个源文件中并加载到ghci。