[英]Haskell filtered string to list
I want a fuction where you put in a String like "Hello I am 25 years old!" 我想要一个函数,在其中输入“你好,我25岁!”之类的字符串。 and get a list out of it like ["hello","i","am","years","old"].
并从中获取列表,例如[“ hello”,“ i”,“ am”,“年”,“旧”]。 So it should put all uppercase letters in lowercase and delete everything that isnt a letter.
因此,应将所有大写字母都小写,并删除所有不包含字母的内容。 It should just use Data.List and Data.Char.
它应该只使用Data.List和Data.Char。 I know i should use words on the String and then filter it but i just cant figure it out (yes im new to Haskell).
我知道我应该在字符串上使用单词,然后对其进行过滤,但是我无法弄清楚(是Haskell的新手)。
toString :: String -> [String]
toString str = ...
At the risk of answering a homework question: 冒着回答作业问题的风险:
import Data.Char
toString :: String -> [String]
toString str = filter (not . null) . map (map toLower . filter isAlpha) . words $ str
Prelude Data.Char> toString "Hello I am 25 years old!"
["hello", "i", "am", "years", "old"]
This would be my workflow: Use hoogle and work with the type signatures you need. 这就是我的工作流程:使用hoogle并使用所需的类型签名。
On how to get a list of words: You need a function foo
that does "one two three" -> ["one", "two", "three"] so it has the type signature: String -> [String]
. 关于如何获取单词列表:您需要一个函数
foo
,该函数执行“ one two two”-> [“ one”,“ two”,“ three”],因此它具有类型签名: String -> [String]
。 Search for exactly this type signature via hoogle and you will find the function words
second in the result list. 通过hoogle精确搜索此类型签名,您将在结果列表中第二找到功能
words
。
a method which does uppercase would mostly like have the type signature Char -> Char
. 一个大写的方法通常希望具有类型签名
Char -> Char
。 Type this into hoogle and you will find toUpper
in third in the list. 将其键入到hoogle中,您将在列表的第三部分找到
toUpper
。
is a letter: Char -> Bool 是一个字母:Char-> Bool
next open ghci and try out the functions. 接下来打开ghci并尝试功能。 IE:
IE浏览器:
ghci> :t toUpper -- will print the type of isUpper
<interactive>:1:1: Not in scope: 'isUpper'
-- you need to import Data.Char <interactive>:1:1: Not in scope: 'isUpper'
您需要导入Data.Char
ghci> import Data.Char
-- so let´s import Data.Char ghci> import Data.Char
所以让我们导入Data.Char
ghci> toUpper "abc"
ghci> words "a quick brown fox"
ghci> :t map
ghci> map toUpper ["a", "quick"]
... and so on ... 等等
You`ll still need to figure out how to put these parts together with map and filter but again I´d advice you to have a close look at the types. 您仍然需要弄清楚如何将这些部分与地图和过滤器放在一起,但是我还是建议您仔细看一下这些类型。
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