Clang parser是完全手写的吗？ 第1页

是。

A single unified parser for C, Objective C, C++, and Objective C++

Clang is the "C Language Family Front-end", which means we intend to support the most popular members of the C family. We are convinced that the right parsing technology for this class of languages is a hand-built recursive-descent parser. Because it is plain C++ code, recursive descent makes it very easy for new developers to understand the code, it easily supports ad-hoc rules and other strange hacks required by C/C++, and makes it straight-forward to implement excellent diagnostics and error recovery.

We believe that implementing C/C++/ObjC in a single unified parser makes the end result easier to maintain and evolve than maintaining a separate C and C++ parser which must be bugfixed and maintained independently of each other.

因为要加各种奇怪的功能还是手写的parser更容易实现和理解。

用parser generator的话总会有别扭的地方要跟那个generator“抗争”一下，反而麻烦。

其实GCC的C++ parser从GCC 3.4系列开始也改为手写的了。

• A hand-written recursive-descent C++ parser has replaced the YACC-derived C++ parser from previous GCC releases. The new parser contains much improved infrastructure needed for better parsing of C++ source codes, handling of extensions, and clean separation (where possible) between proper semantics analysis and parsing. The new parser fixes many bugs that were found in the old parser.

而GCC的C和Objective-C parser从GCC 4.1系列开始也改为手写的了。

• The old Bison-based C and Objective-C parser has been replaced by a new, faster hand-written recursive-descent parser.

当然，还是有人觉得用parser generator更好。例如这里：

来自

的Ira Baxter认为坊间传闻C++ parser用generator不好写不是因为generator这个概念不好，而是因为用的parsing算法太落后了——传统的parser generator很多都是用LALR(1)的，例如bison的默认模式。

他认为如果用更强力的parsing算法，例如

，问题就迎刃而解了。

嗯这个还是见仁见智。召唤

大神来发表对GLR的见解 >_<

有兴趣的同学可以看看一个用GLR的C++ parser，

的

，就跟

的回答说的一样，在parse阶段其实parse出了多份有歧义的AST，然后通过类型检查把不合理的删除掉，得到最终的干净的AST。

Clang官网文档有对比Clang parser与Elsa parser的段落：