Haskell是一种纯函数式语言,它突破了传统的面向对象语言.但是,请考虑Alan Kay关于OOP“真实”含义的以下引用：

OOP to me means only messaging, local retention and protection and hiding of state-process, and extreme late-binding of all things. It can be done in Smalltalk and in LISP. There are possibly other systems in which this is possible, but I’m not aware of them. — Alan Kay

后来：

I thought of objects being like biological cells and/or individual computers on a network, only able to communicate with messages (so messaging came at the very beginning — it took a while to see how to do messaging in a programming language efficiently enough to be useful).

我很好奇在Haskell中可以在多大程度上实现这种编程风格.特别是,是否可以将Haskell程序构造为一系列(类似的)封装对象,它们来回传递消息？

注意：我正在寻找特定于Haskell的示例,而不是大型函数语言(当发生冲突时).

最佳答案

only messaging, local retention and protection and hiding of
state-process

like biological cells and/or individual computers on a network, only
able to communicate with messages

我相信某些Haskell编程模式在某种程度上确实类似于Kay的描述.

在像conduit,pipes或streaming这样的流式库中,通常将计算构建为由不同阶段组成的管道.管道的每个部分都完全独立于其他部分,并且可以保持其自己的私有状态(您也可以在管道中具有“共享”状态).

拓扑往往是线性和单向的.也就是说,像管道ZipSink这样的抽象 – 以及foldl包中的Folds的Applicative实例 – 让你构建分支出来的“树状”拓扑.管道可以是bidirectional,虽然我没有看到很多使用它的例子.

然后是arrowized functional reactive programming.它可以让你构建自动机箭头的“电路”can even include loops.电路的每个部分都可以保持自己的状态.正如netwire FRP库的描述所述：

This library provides interfaces for and implements wire arrows useful
both for functional reactive programming (FRP) and locally stateful
programming (LSP).

从auto库的文档：

auto works by providing a type that encapsulates value stream
transformers, or locally stateful functions; by specifying your
program as a (potentially cyclic) graph of relationships between value
streams, you create a way of declaring a system based simply on static
relationships between quantities.

Instead of a state monad type solution, where all functions have
access to a rigid global state, auto works by specifying relationships
which each exist independently and on their own, without any global
state.