[webkit-dev] What is the reason for changing JavaScript parser from bison parser(LR) to Top-To-Down Recursion parser?

[PandaCanFly]

In my opinion, the bison parser implements LR analyzer, handwritten parser implements Top-To-Down analyzer. I remember some compiling book says "LR analyzer is better and faster than Top-To-Down analyzer". So, your opinon confuses me. Could you give me more information about speed of handwritten parser?




At 2011-11-30 15:47:43,"Oliver Hunt" <oliver at apple.com> wrote:
The handwritten parser has numerous benefits over the old bison generated one, the most basic being:
 * It's more than 2 times faster than the bison parser
 * It doesn't require complete duplication of the grammar to support strict mode (and can identify strict mode in the first place)
 * It fixes a number of bugs inherent in the bison parser due to the way automatic semicolon insertion was implemented.


There are a number of other benefits, but those are the most obvious.


--Oliver


On Nov 29, 2011, at 11:38 PM, PandaCanFly wrote:


Hello everyone,
    I am researching WEBKIT and coming up against difficulty about Javascript parser。As I Know, WEBKIT of old version uses the bison parser to interpret javascript code. But WEBKIT of recently version doesn't uses bison parser. Instead, WEBKIT of recently version uses Top-To-Down Recursion parser.
    I have some details to add. 1) WEBKIT using bison parser has a source file named "Grammar.cpp". 2) I know WEBKIT with 38688 version number uses bison parser.
I hope someone can give me some explanation, thanks.


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