Haskell将整数转换为Int？ [英] Haskell Convert Integer to Int?

问题描述

是否可以将整数转换为Int？另一个方向是可能的：toInteger。我知道Integer能够存储更大的值，但有时需要一个对话来使用std-lib函数。我试过（n :: Int）和其他代码样本，我发现 - 但没有什么工作。

Is it possible to cast an Integer to an Int? The other direction is possible: toInteger. I know that Integer is able to store bigger values, but sometimes a conversation is needed to use std-lib functions. I tried ( n :: Int) and other code samples I found - but nothing works.

takeN :: Integer -> [a] -> [a]
takeN n l = take n l

推荐答案

使用 fromIntegral 。

takeN :: Integer -> [a] -> [a]
takeN n l = take (fromIntegral n) l

$ c> fromIntegral ::（Integral a，Num b）=> a - > b ，所以有时你需要一个额外的类型注释（例如（fromIntegral n :: Int）），但通常编译器可以推断哪个类型

Note that fromIntegral :: (Integral a, Num b) => a -> b, so sometimes you will need an extra type annotation (e.g. (fromIntegral n :: Int)), but usually the compiler can infer which type you want.

在您的示例的特殊情况下，在 Data.List 中有 genericTake ::（Integral i）=> i - > [a] - > [a] ，它执行与相同的操作，但使用更一般的类型。

In the special case of your example, in Data.List there is genericTake :: (Integral i) => i -> [a] -> [a], which does the same thing as take but with a more general type.

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