Text.ParserCombinators.Parsec和Text.Parsec有什么区别 [英] What's the difference between Text.ParserCombinators.Parsec and Text.Parsec

问题描述

 文本
 Text.Parsec 
 Text.Parsec.ByteString 
 Text.Parsec.ByteString.Lazy 
 Text.Parsec.Char 
 Text.Parsec.Combinator 
 Text.Parsec.Error 
 Text.Parsec.Expr 
 Text.Parsec.Language 
 Text.Parsec.Perm 
文本。 Parsec.Pos 
 Text.Parsec.Prim 
 Text.Parsec.String 
 Text.Parsec.Token 
 ParserCombinators 
 Text.ParserCombinators.Parsec 
 Text。 ParserCombinators.Parsec.Char 
 Text.ParserCombinators.Parsec.Combinator 
 Text.ParserCombinators.Parsec.Error 
 Text.ParserCombinators.Parsec.Expr 
 Text.ParserCombinators.Parsec.Language 
 Text.ParserCombinators.Parsec.Perm 
 Text.ParserCombinators.Parsec.Pos 
 Text.ParserCombinators.Parsec.Prim 
 Text.ParserCombinators.Parsec.Token 
  

它们是否一样？

解决方案

目前有两种广泛使用的专业Parsec 2和
Parsec 3的版本。

我的建议只是使用Parsec 3的最新版本。但是如果你想要
进行有意识的选择，继续阅读。

Parsec 3中的新功能

Monad Transformer

Parsec 3引入了一个monad转换器， ParsecT ，可用于将
解析与其他一元效果组合在一起。

Streams

尽管Parsec 2允许您选择令牌类型（当您
需要时将词法分析从解析中分离出来），令牌总是被排列成列表中的
。列表可能不是存储
大文本的最有效的数据结构。

Parsec 3可以使用任意流 - 数据具有列表式
接口的结构。您可以定义自己的流，但Parsec 3还包含基于ByteString（用于 Char - 基于
解析）的流行
和高效Stream实现，通过 Text.Parsec.ByteString 和
Text.Parsec.ByteString.Lazy p>

选择Parsec 2的理由

需要更少的扩展名

Parsec 3提供的高级功能并不是免费的：要实现它们
需要几种语言扩展。

这两个版本都不是Haskell-2010 （即都使用扩展），但是
Parsec 2使用的扩展比Parsec 3少，所以任何给定的编译器
都可以编译Parsec 2的机会要高于Parsec 3的那些。

到目前为止，这两个版本都与GHC一起工作，而Parsec 2也是报告到
使用JHC构建，包括ded作为JHC的标准库之一。

表现

最初（即从3.0版开始）Parsec 3比
Parsec 2慢得多。但是，改善Parsec 3性能的工作已完成，
和3.1版本的Parsec 3只比Parsec 2
稍微慢一些（基准： 1 ， 2 ）。

兼容层

可以在Parsec 3中重新实现所有的Parsec 2 API。这个
兼容层由Parsec 3包在模块层次结构
下提供 Text.ParserCombinators.Parsec （与Parsec 2相同的层次结构）
，而新的Parsec 3 API可在 Text.Parsec 层次结构。

这意味着您可以使用Parsec 3作为Parsec 2的直接替代品。

Text
    Text.Parsec
        Text.Parsec.ByteString
            Text.Parsec.ByteString.Lazy
        Text.Parsec.Char
        Text.Parsec.Combinator
        Text.Parsec.Error
        Text.Parsec.Expr
        Text.Parsec.Language
        Text.Parsec.Perm
        Text.Parsec.Pos
        Text.Parsec.Prim
        Text.Parsec.String
        Text.Parsec.Token
    ParserCombinators
        Text.ParserCombinators.Parsec
            Text.ParserCombinators.Parsec.Char
            Text.ParserCombinators.Parsec.Combinator
            Text.ParserCombinators.Parsec.Error
            Text.ParserCombinators.Parsec.Expr
            Text.ParserCombinators.Parsec.Language
            Text.ParserCombinators.Parsec.Perm
            Text.ParserCombinators.Parsec.Pos
            Text.ParserCombinators.Parsec.Prim
            Text.ParserCombinators.Parsec.Token

Are they the same?

解决方案

At the moment there are two widely used major versions of Parsec, Parsec 2 and Parsec 3.

My advice is simply to use the latest release of Parsec 3. But if you want to make a conscious choice, read on.

New in Parsec 3

Monad Transformer

Parsec 3 introduces a monad transformer, ParsecT, which can be used to combine parsing with other monadic effects.

Streams

Although Parsec 2 lets you to choose the token type (which is useful when you want to separate lexical analysis from the parsing), the tokens are always arranged into lists. List may be not the most efficient data structure to store large texts.

Parsec 3 can work with arbitrary streams -- data structures with list-like interface. You can define your own streams, but Parsec 3 also includes a popular and efficient Stream implementation based on ByteString (for Char-based parsing), exposed through the modules Text.Parsec.ByteString and Text.Parsec.ByteString.Lazy.

Reasons to prefer Parsec 2

Less extensions required

Advanced features provided by Parsec 3 do not come for free: to implement them several language extensions are required.

Neither of the two versions is Haskell-2010 (i.e. both use extensions), but Parsec 2 uses less extensions than Parsec 3, so chances that any given compiler can compile Parsec 2 are higher than those for Parsec 3.

By this time both versions work with GHC, while Parsec 2 is also reported to build with JHC and is included as one of the JHC's standard libraries.

Performance

Originally (i.e. as of 3.0 version) Parsec 3 was considerably slower than Parsec 2. However, work on improving Parsec 3 performance has been done, and as of version 3.1 Parsec 3 is only slightly slower than Parsec 2 (benchmarks: 1, 2).

Compatibility layer

It has been possible to "reimplement" all of the Parsec 2 API in Parsec 3. This compatibility layer is provided by the Parsec 3 package under the module hierarchy Text.ParserCombinators.Parsec (the same hierarchy which is used by Parsec 2), while the new Parsec 3 API is available under the Text.Parsec hierarchy.

This means that you can use Parsec 3 as a drop-in replacement for Parsec 2.

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