十进制和二进制数字处理 [英] Decimal and binary number handling

问题描述

我正在研究能够将十进制转换为二进制值的代码。与其他语言相比，haskell需要几行代码才能实现。以下是我编制的代码。

  binaryToDec :: [Int]  - > Int 
 binaryToDec [] = [] 
 binaryToDec（x：xs）=（+）（x * 2 ^（length xs））
  

这段代码给出了一个我试图弄清楚的错误。但我不能。

  Assignment.hs：61：18：
无法与实际类型为'[Int' a0]'
在表达式中：[] 
在`binaryToDec'的等式中：binaryToDec [] = [] 
  

我该怎么办？

解决方案

  binaryToDec :: [Int]  - > Int 
  

也就是说 binaryToDec 是一个函数，它以 Int s作为参数列表，并返回一个 Int 作为结果。

  binaryToDec [] = [] 
  

这就是说，当 binaryToDec 的参数是一个空列表时，其结果是一个空列表。

空白列表不是 Int ，所以这是一个错误。解决方案： code> binaryToDec [] 应计算到等式的右边。

但这不是全部...

  binaryToDec（x：xs）=（+）（x * 2 ^（length xs））
  

也就是说，当 binaryToDec 的参数是 not 是一个空列表，其结果是一个将 x * 2 ^（length xs）添加到其参数的函数。 / p>

函数不是 Int ，所以这也是一个错误。解决方案：找出你想添加到 x * 2 ^（长度xs）



---

以前的错误消息让你难住。所以让我们一行一行地解构错误信息：

• Assignment.hs：61：18 ：

  
  
  

  这给出了编译器判断出现错误的行上的文件名，行号和近似位置。




• 无法与实际类型为[[a0]'的预期类型'Int'匹配

  
  
  

  这意味着周围的上下文需要类型 Int 的值，但是提供的值是类型 [a0] 。 （ a0 这里的意思是不知道，所以编译器会发现你提供了一个列表，但还没有算出它的列表。）在表达式中：[]

  
  
  

  这是表达式类型 [a0] ，但预期类型为 Int 。这并不总是出现你的错误 - 只是编译器在发现错误的地方 - 但在这种情况下，是，你的错误是： [ ] 显然不是 Int 。

  
  
  如果错误是<在等号左边的code> [] ，错误信息会引用模式 [] 而不是表达式 [] 。）
code>在binaryToDec方程中：binaryToDec [] = []




这只是给你更多的上下文关于编译器发现错误的地方。

I'm working on a code which capable of converting decimal to a binary value. Comparing to other languages haskell needs few lines of code to bring this up. Below is the code i worked out.

binaryToDec :: [Int] -> Int
binaryToDec [] = []
binaryToDec (x:xs) = (+) (x * 2 ^(length xs))

this code gives an error which i tried so hard to figure out. but i couldn't.

Assignment.hs:61:18:
    Couldn't match expected type `Int' with actual type `[a0]'
    In the expression: []
    In an equation for `binaryToDec': binaryToDec [] = []

what should i do?

解决方案

binaryToDec :: [Int] -> Int

That says that binaryToDec is a function, which takes a list of Ints as its parameter, and returns an Int as its result.

binaryToDec [] = []

That says that when binaryToDec's parameter is an empty list, its result is an empty list.

An empty list is not an Int, so this is an error.

Solution: decide what binaryToDec [] should evaluate to, and use that on the right hand side of the equation.

But that's not all...

binaryToDec (x:xs) = (+) (x * 2 ^(length xs))

That says that when binaryToDec's parameter is not an empty list, its result is a function that adds x * 2 ^(length xs) to its parameter.

A function is not an Int, so this is also an error.

Solution: work out what you want to add to x * 2 ^(length xs), and, er, add it.

---

You have been stumped by error messages like this before. So let's deconstruct the error message line-by-line:

• Assignment.hs:61:18:

  This gives the filename, line number and approximate position on the line where the compiler decided there was an error.

• Couldn't match expected type `Int' with actual type `[a0]'

  This means that the surrounding context expected a value of type Int, but the value provided was of type [a0]. (a0 here means "don't know", so the compiler's worked out that you provided a list, but hasn't worked out what it's a list of.)

• In the expression: []

  This is the expression that has type [a0], but was expected to have type Int. This is not always where your mistake is --- just where the compiler was when it noticed something was wrong --- but in this case it is where your mistake is: [] is clearly not an Int.

  (n.b. If the error was the [] on the left of the equals sign, the error message would have referred to the pattern [] instead of the expression [].)

• In an equation for `binaryToDec': binaryToDec [] = []

  This is just giving you a bit more context about where the compiler found the error.

这篇关于十进制和二进制数字处理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！