[9fans] Config File parsing

[9fans] Config File parsing

[Mohanasundaram VIT]

global{
    verb
    test
    rl0
    rand (or) rand =0      [Two cases]
}

thread{
    frac_value = (0.2,(0.1,0.5))
    random_thread

}
OUTPUT should be this:

If i give the above input to lex and yacc, based upon the checking of
[ rand (or) rand=0 ]

if it is "rand", then it should print as " verb test rl0 rand
frac_value:L=0.1 frac_value:H=0.5"
if it is "rand=0", then it should print as " verb test rl0 rand=0
frac_value=0.2".
For this could someone please tell me how to write a lex and yacc
program.

Re: [9fans] Config File parsing

[erik quanstrom]

On Tue Feb 28 11:53:17 EST 2012, bakul@bitblocks.com wrote:
> I have almost always used a handwritten lexer as it seemed about the
> same amount of work and the end result is much smaller and easier to
> understand and lexers for different languages are not all that
> different so once you've written one it is pretty easy to write
> another; and somehow lex or flex interface never felt quite right.

for an extreme example, see /sys/src/cmd/upas/smtp/smtpd.y.

imho, the trick in lexing is to do as little as possible.  context rules
tend to sneak in in the lex phase.  for example, rc's free carets and
willingness to eat newlines under rules that seem obvious until they
need explaining.

- erik

Re: [9fans] Config File parsing

[Bakul Shah]

I have almost always used a handwritten lexer as it seemed about the same amount of work and the end result is much smaller and easier to understand and lexers for different languages are not all that different so once you've written one it is pretty easy to write another; and somehow lex or flex interface never felt quite right.

On Feb 27, 2012, at 8:03 PM, Nick LaForge <nicklaforge@gmail.com> wrote:

> Are you certain you want to use Lex?  If no, you may like this
> fascinating and instructive lecture by Rob Pike, which solves a lexing
> problem using Golang: http://www.youtube.com/watch?v=HxaD_trXwRE
> 
> If you have "The Unix Programming Environment" handy, you will also
> find a lucid tutorial of Lex and Yacc both (in the later chapters).
> 
> Nick
> 
> On 2/27/12, arnold@skeeve.com <arnold@skeeve.com> wrote:
>> O'Reilly's "lex & yacc" is somewhat more user-friendly a reference than
>> the dragon book, although the latter certainly has its value. :-)
>> 
>> Arnold
>> 
>> 
> 

Re: [9fans] Config File parsing

[Aram Hăvărneanu]

Nick LaForge wrote:
> If you have "The Unix Programming Environment" handy, you will also
> find a lucid tutorial of Lex and Yacc both (in the later chapters).

A great complement to this great book is the yacc paper in tenth
edition's manual.

-- 
Aram Hăvărneanu

Re: [9fans] Config File parsing

[Nick LaForge]

Are you certain you want to use Lex?  If no, you may like this
fascinating and instructive lecture by Rob Pike, which solves a lexing
problem using Golang: http://www.youtube.com/watch?v=HxaD_trXwRE

If you have "The Unix Programming Environment" handy, you will also
find a lucid tutorial of Lex and Yacc both (in the later chapters).

Nick

On 2/27/12, arnold@skeeve.com <arnold@skeeve.com> wrote:
> O'Reilly's "lex & yacc" is somewhat more user-friendly a reference than
> the dragon book, although the latter certainly has its value. :-)
>
> Arnold
>
>

Re: [9fans] Config File parsing

[Jack Norton]

On 2/27/2012 7:18 AM, erik quanstrom wrote:
>> For this could someone please tell me how to write a lex and yacc
>> program.
>
> you may wish to consult the dragon book.  just google it.
>
> - erik
>

FYI I just bought my copy on Amazon used for $3.48 USD ($3.99
shipping....).  It is a hardcopy in great shape too!

-Jack

Re: [9fans] Config File parsing

[arnold]

O'Reilly's "lex & yacc" is somewhat more user-friendly a reference than
the dragon book, although the latter certainly has its value. :-)

Arnold

Re: [9fans] Config File parsing

[erik quanstrom]

> For this could someone please tell me how to write a lex and yacc
> program.

you may wish to consult the dragon book.  just google it.

- erik