Haskell点运算符 [英] Haskell dot operator

问题描述

我尝试在Haskell中开发一个简单的平均函数。
这似乎工作：

  lst = [1,3] 
 
x = fromIntegral （sum lst）
y = fromIntegral（length lst）
 $ b $ = x / y 
  

但为什么下面的版本不工作？

  lst = [1,3] 
 
x = fromIntegral.sum lst 
y = fromIntegral.length lst 
 
z = x / y 
  

解决方案

你被运算符haskell的优先规则绊倒了。 >当你写

  x = fromIntegral.sum lst 
   b 
 
 
 Haskell认为它与 
 
 
  x = fromIntegral。（总和lst）
  
你打算写的是： 
 
 
  x =（fromIntegral.sum）lst 
  
 
I try to develop a simple average function in Haskell.
This seems to work:
lst = [1, 3]

x = fromIntegral (sum lst)
y = fromIntegral(length lst)

z = x / y
But why doesn't the following version work?
lst = [1, 3]

x = fromIntegral.sum lst
y = fromIntegral.length lst

z = x / y

解决方案
You're getting tripped up by haskell's precedence rules for operators, which are confusing.

When you write
x = fromIntegral.sum lst
Haskell sees that as the same as:
x = fromIntegral.(sum lst)
What you meant to write was:
x = (fromIntegral.sum) lst


                        
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