A pure functional language like Haskell might offer type hierarchies, discriminated unions, quantification, existential types, and so on, but OOP languages typically lack these things.

象Haskell那样的纯函数型语言可以提供类型层次结构、区别合并、量化、存在类型等等，但OOP语言通常缺乏这些功能。

youdao

Haskell is quite possibly the most extremely limiting language in common use: there is one way to do everything, mathematically pure functional programming. You have strong, expressive static typing.

通常情况下，Haskell可能是限制最严格的语言：一种方式可以做所有的事情，这就是数学上纯函数式语言。

youdao