haskell：过滤具有特定符号的字符串，例如'！' 列表中？

Question

I have a list of Strings : ["1*1", "ab!c", "cde2", "efghi!"] I want to sort out every string with an '!' . My first idea was : filter (map elem '!' (list)) list String with map elem '!' (list), but thats not really working because it only checkups the String as itself and not the elements of the Strings in that List...

thanks for your help!

Answer 1

You mapped too much.

filter ('!' `elem`) list

should work for you....

Explanation:

You have a list of strings [String] . A string is a list of chars, because String = [Char] ...

So basically you have a list of lists. [[Char]] Since elem works by checking if a single element exists in a list, you can just call elem on each list item from your outer list.