什么是“纯粹”用“纯粹功能语言”来表示？ [英] What does "pure" mean in "pure functional language"?

问题描述

Haskell被称为纯功能语言。

在这种情况下，纯意味着什么？这对程序员有什么影响？

解决方案

在纯函数式语言中，不要做任何有副作用的事情。

副作用意味着评估一个表达式会改变一些内部状态，以后会导致评估同一表达式产生不同的结果。在纯粹的函数式语言中，您可以使用相同的参数来按照您的要求评估相同的表达式，并且始终返回相同的值，因为没有可改变的状态。

例如，一个纯粹的函数式语言不能有一个赋值运算符或输入/输出，尽管出于实际的目的，甚至纯粹的函数式语言经常会调用不纯粹的库来执行I / O操作。

Haskell has been called a "pure functional language."

What does "pure" mean in this context? What consequences does this have for a programmer?

解决方案

In a pure functional language, you can't do anything that has a side effect.

A side effect would mean that evaluating an expression changes some internal state that would later cause evaluating the same expression to have a different result. In a pure functional language you can evaluate the same expression as often as you want with the same arguments, and it would always return the same value, because there is no state to change.

For example, a pure functional language cannot have an assignment operator or do input/output, although for practical purposes, even pure functional languages often call impure libraries to do I/O.

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