seq在haskell中代表什么

本文介绍了seq在haskell中代表什么的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我是Haskell的新手，刚刚来到懒惰的世界.我读到 seq 函数非常特殊，因为它强制使用严格的评估以便在某些情况下更有效.但我只是找不到 seq 的字面意思.也许严格评估Q * ???

I am new to haskell, and have just come to the lazy world proramming. I read that the seq function is very special because it forces to use a strict evaluation in order to be more efficient in some cases. But I just can't find what seq stand for literally. Maybe Strict Evaluation Q*???

推荐答案

seq 在返回第二个参数之前先评估其第一个参数.通常引入它是为了避免不必要的懒惰，从而提高性能.强制对功能进行评估.

seq evaluates its first argument before returning the second one. It is usually introduced to improve performance by avoiding unneeded laziness. It forces evaluation of the function.

seq :: a -> b -> b seq _ y = y

来自 prelude.hs

此函数定义包装在 #ifdef __HADDOCK __ 中，因此它将只能由haddock(文档工具)编译，而不能由实际的编译器！真实"序列在GHC.Prim中定义为

This function definition is wrapped in #ifdef __HADDOCK__ so it will only be compiled by haddock (the documentation tool), not by the actual compiler! The 'real' seq is defined in GHC.Prim as seq :: a -> b -> b; seq = let x = x in x.

这只是一个虚拟定义.基本上seq是特殊语法特别由编译器处理.您写了'seq评估其第一个参数"-但第一个定义显然没有做到这一点.

This is only a dummy definition. Basically seq is specially syntax handled particularly by the compiler. You wrote 'seq evaluates its first argument' - but first definition obviously does not do this.

通过 user2407038

更多阅读内容:

• 在HaskellWiki上
• 真实世界的Haskell.Chapter 25.分析和优化
• 在StackOverflow上
• 使Haskell程序更快，更小
• 如何避免seq