计算字符串列表中的回文数，Haskell [英] Count number of palindromes in a list of strings, Haskell

问题描述

  isPalindrome：返回一个字符串列表，并返回一个字符串的个数。 ：字符串 - > Bool 
 isPalindrome w = w ==反向w 
 
 countPalindromes :: [String]  - > Int 
 countPalindromes ss = length filter（== isPalindrome）ss 
  

我知道函数长度应用于两个参数而不是一个。我只是不知道如何解决这个问题？

解决方案

您可以使用括号来影响函数应用程序：

  countPalindromes ss = length（filter（== isPalindrome）ss）
  

括号会导致整个表达式 filter（== isPalindrome）ss 被分组到一个单词中，并且其结果被传递至长度。

这会让您接触到下一个错误;我鼓励你仔细阅读，看看你是否能从这里自己取得进展，然后开一个新问题，如果你花费了十五分钟的时间试图了解它，而没有取得进展。

The function countPalindromes receives a list of strings and returns a count of how many of the strings are palindromes.

isPalindrome :: String -> Bool
isPalindrome w = w == reverse w

countPalindromes :: [String] -> Int
countPalindromes ss = length filter (== isPalindrome) ss 

I know that the function length is applied to two arguments instead of one. I just don't know how to fix this?

解决方案

You may use parentheses to affect function application:

countPalindromes ss = length (filter (== isPalindrome) ss)

The parentheses will cause the entire expression filter (== isPalindrome) ss to be grouped into a single term, and its result passed on to length.

This will get you to the next error; I encourage you to read it carefully and see if you can make progress from here yourself, then open a fresh question if you spend, say, fifteen minutes trying to understand it without making progress.

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