Re: [dev] lex and yacc

From: Markus Wichmann <nullplan_AT_gmx.net>
Date: Sun, 10 Mar 2019 06:17:16 +0100

On Sat, Mar 09, 2019 at 06:59:38PM +0000, sylvain.bertrand_AT_gmail.com wrote:
> Hi,
>
> I am coding a little/simple custom language parser, and I was wondering if there
> are "suckless" grade alternatives to flex and bison, anyone? But wait...
>
> That said and as of today, I still don't agree with myself on the usefullness
> of lex/yacc in the first place. For instance, I am puzzled by line/column
> tracking, which can be tricky (for instance C preprocessor/compiler accurate
> line/column tracking with line-return escaping with lex/yacc??)
>
> Maybe it's not an implementation issue of lex and yacc... they may actually
> be _not_ suckless at all. Any thoughts on this?
>
> --
> Sylvain
>

Well, other people have made that point before: Why use a regex to
identify a token when a simple loop will do?

So for lexing, usually a simple token parser in C will do the job
better. And for parsing, you get the problem that yacc will create an
LALR parser, which is a bottom-up parser. Which may be faster but
doesn't allow for good error messages on faulty input ("error: expected
this, that, or the other token before this one"). That's why top-down
recursive-descent parsers (or LL(1) parsers) are superior. Maybe
supplemented with a shunting-yard algorithm to get the binary
expressions right without having to call layer after layer of functions.

Ciao,
Markus
Received on Sun Mar 10 2019 - 06:17:16 CET