From: Bill Kelly <billk@...>
Date: 2004-04-14T07:56:12+09:00
Subject: Re: New Ruby questions...


From: "Jeff Massung" <jma@NOSPAM.mfire.com>
>
> I've just started Ruby a couple days ago (man this is cool). Coming from 
> the embedded world of Forth and C, being able to do some string parsing 
> easily is what I'm looking forward to. So, onto a couple questions that I 
> can't seem to find the answers to:

26952 DUP 255 AND EMIT 256 / EMIT     ( :-)

> Quickly, the "teach myself" project is a simple ARM assembler. I've done 
> it numerous times, and it is something I'm familiar and comfortable with 
> (let alone something I need ATM).
> 
> 1. How can a regexp get the longer of two possibilities that are 
> ambiguous? For example, I need to be able to strip out register names:
> 
> registers = '(r0|r1|r2|r3...|r10|r11|r12...)'
> 
> In the regular expression, how can I get it to find r10 or r11 instead of 
> stopping at r1? I get the same problem with opcode mnemonics (like B 
> instead of BX or BL).

Try putting the longer strings first in the alternation
sequence...

irb --simple-prompt
>> puts $& if "r11" =~ /r1|r2|r11/     # shorter strings first
r1

>> puts $& if "r11" =~ /r11|r2|r1/     # longer strings first
r11


Alternately, you could use lookahead assertions to
specify the character following the token is some
kind of token separating character, like...

This "\b" insists a "word boundary" occurs at that point
in the pattern:

>> puts $& if "r11" =~ /(r1|r2|r11)\b/
r11

I think the "\b" is essentially equivalent to:
>> puts $& if "r11" =~ /(r1|r2|r11)(?![A-Za-z0-9_])/
r11


Regards,

Bill