Haskell 中的 I/O 是函数式的吗? [英] I/O in Haskell is Functional?

问题描述

我刚刚开始看看 Haskell(我以前的 FP 经验是在 Scheme 中)，我遇到此代码:

I'm just starting to take a look at Haskell (my previous FP experience is in Scheme), and I came across this code:

do { putStrLn "ABCDE" ; putStrLn "12345" }

对我来说，这是过程式编程，如果有的话——尤其是因为副作用的连续性.

To me, this is procedural programming, if anything -- especially because of the consecutive nature of side effects.

有人能解释一下这段代码在任何方面的功能"吗?

Would someone please explain how this code is "functional" in any respect?

推荐答案

虽然它看起来是一个过程程序，但上面的语法被翻译成一个函数式程序，如下所示:

While it appears to be a procedural program, the above syntax is translated into a functional program, like so:

   do { putStrLn "ABCDE" ; putStrLn "12345" }
=>
   IO ( s -> case (putStrLn "ABCDE" s) of
                  ( new_s, _ ) -> case (putStrLn "12345" new_s) of
                                      ( new_new_s, _) -> ((), new_new_s))

也就是说，一系列嵌套函数有一个独特的世界参数贯穿它们，程序性地"对原始函数的调用进行排序.此设计支持将命令式编程编码为函数式语言.

That is, a series of nested functions that have a unique world parameter threaded through them, sequencing calls to primitive functions "procedurally". This design supports an encoding of imperative programming into a functional language.

对基于此设计的语义决策的最佳介绍是 "The Awkward Squad" 论文，

The best introduction to the semantic decisions underlying this design is "The Awkward Squad" paper,

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