相关疑难解决方法(0)

我试图理解点运算符在这个Haskell代码中做了什么:

sumEuler = sum . (map euler) . mkList

整个源代码如下.

我的理解

点运算符将两个函数sum以及结果map euler和结果mkList作为输入.

但是,sum它不是函数,它是函数的参数,对吧？那么这里发生了什么？

还有,(map euler)做什么？

码

mkList :: Int -> [Int]
mkList n = [1..n-1]

euler :: Int -> Int
euler n = length (filter (relprime n) (mkList n))

sumEuler :: Int -> Int
sumEuler = sum . (map euler) . mkList

这是我在ghci中尝试做的事情:

import Data.Text
strip "  abc  "

我收到此错误消息:

<interactive>:1:6:
    Couldn't match expected type `Text' against inferred type `[Char]'
    In the first argument of `strip', namely `"  abc  "'
    In the expression: strip "  abc  "
    In the definition of `it': it = strip "  abc  "

我期待这个工作,因为它是在许多网页上给出的,包括这个答案:在Haskell中,你如何从字符串的开头和结尾修剪空格？

我究竟做错了什么？

我有一个字符串列表:

[" ix = index"," ctr = counter"," tbl = table"]

我想从它创建一个元组,如:

[("ix","index"),("ctr","counter"),("tbl","table")]

我甚至尝试过:

genTuple [] = []
genTuples (a:as)= do
                   i<-splitOn '=' a
                   genTuples as
                   return i

任何帮助都会受到赞赏谢谢.