什么是正确的方法来划分两个Int值来获得Float？ [英] What's the right way to divide two Int values to obtain a Float?

问题描述

我想在Haskell中分两个 Int 值并获得结果作为 Float 。我尝试这样做：

  foo :: Int  - > Int  - >浮动
 foo ab = fromRational $ a％b 
  

但GHC（版本6.12.1）告诉我对于表达式中 a 的推断类型'Int'，无法匹配预期的类型'整数'。

我明白为什么： fromRational 调用要求（％）产生一个 Ratio Integer ，所以操作数必须是 Integer 而不是 Int 。但是我分割的值远不及 Int 的范围限制，所以使用任意精度的bignum类型似乎是过度杀伤。 $ b

正确的做法是什么？我应该在我的操作数上调用到Integer ，还是有一个更好的方法（也许不涉及（％）和比率），我不知道？

解决方案

您必须将操作数转换为浮动 first 然后除，否则你将执行一个整数除法（无小数位）。

Laconic解决方案（需要 Data.Function
$ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ / pre>

  foo ab =（fromIntegral a）/（fromIntegral b）
  

with

  foo :: Int  - > Int  - >浮动
  

I'd like to divide two Int values in Haskell and obtain the result as a Float. I tried doing it like this:

foo :: Int -> Int -> Float
foo a b = fromRational $ a % b

but GHC (version 6.12.1) tells me "Couldn't match expected type 'Integer' against inferred type 'Int'" regarding the a in the expression.

I understand why: the fromRational call requires (%) to produce a Ratio Integer, so the operands need to be of type Integer rather than Int. But the values I'm dividing are nowhere near the Int range limit, so using an arbitrary-precision bignum type seems like overkill.

What's the right way to do this? Should I just call toInteger on my operands, or is there a better approach (maybe one not involving (%) and ratios) that I don't know about?

解决方案

You have to convert the operands to floats first and then divide, otherwise you'll perform an integer division (no decimal places).

Laconic solution (requires Data.Function)

foo = (/) `on` fromIntegral

which is short for

foo a b = (fromIntegral a) / (fromIntegral b)

with

foo :: Int -> Int -> Float

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