Haskell：如何解析一个IO输入字符串到一个Float（或Int或其他）？ [英] Haskell: How to parse an IO input string into a Float (or Int or whatever)?

问题描述

然而，每次我尝试解析这个函数的时候，输入字符串到浮动我不断收到错误。我试过的每一个方法都没有让我把用户输入的数据变成一个Float，这就是我所需要的。

我的练习程序（不是我试图解决的实际问题）是：

$ $ $ $ $ $ c $ main $
putStrLn请输入一个数字。
inputjar&​​lt; - getLine
read :: read a =>字符串 - > a
putStrLn（read inputjar :: Int）

编辑

还有一个问题。

如何将输入的字符串转换为我可以用于计算的东西？

例如，如何输入字符串以便我可以执行下列操作：

 （var + var）/ 2 
  

解决方案

  main = do 
 putStrLn请输入一个数字。 
 inputjar < -  readLn 
 print（inputjar :: Int）
  

是一种更好的方式，因为它立即修复了我们正在阅读的字符串：

$ $ p $ $ $ $ $ $ $ $ $ $ $ $ $ putStrLn 请输入一个数字。
inputjar :: Int< - readLn
print inputjar

{ - ＃LANGUAGE ScopedTypeVariables＃ - }

I am trying to make a program that takes a Float number inputted by the user via keyboard and does stuff with it.

However every time I try to parse the inputted String into a Float I keep getting errors. Every single method I've tried has failed to allow me to take user inputted data and turn it into a Float, which is what I need.

My practice program (not the actual problem I'm trying to solve) is:

main = do
    putStrLn "Please input a number."
    inputjar <- getLine
    read :: read a => String -> a
    putStrLn( read inputjar :: Int)

Edit

A further question.

How do I take the inputted string and turn it into something I can use in a calculation?

For example, how do I take the inputted string so that I can do something like:

(var + var) / 2

解决方案

main = do
   putStrLn "Please input a number."
   inputjar <- readLn
   print (inputjar :: Int)

This is in a way nicer since it immediately fixes what we're reading the string as:

main = do
   putStrLn "Please input a number."
   inputjar :: Int  <- readLn
   print inputjar

but it requires {-#LANGUAGE ScopedTypeVariables#-}

这篇关于Haskell：如何解析一个IO输入字符串到一个Float（或Int或其他）？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！