From: dblack@...
Date: 2003-10-09T20:08:23+09:00
Subject: Re: case where regex range should raise

Hi --

On Thu, 9 Oct 2003, Robert Klemme wrote:

>
> Interestingly enough negative values do not cause errors but do not match
> either:
>
> irb(main):008:0> /f{-1,2}/ =~ "aaffff"
> => nil
>
> IMHO this should either raise an error or match, since there are more
> than -1 "f"'s in the string.

This is also similar to the case Guy showed:

  irb(main):004:0> /a{-1,2}/.match("a{-1,2}")[0]
  => "a{-1,2}"

However....

  irb(main):005:0> /{-1,2}/.match("{-1,2}")[0]
  SyntaxError: compile error
  (irb):5: invalid regular expression; there's no previous pattern, to
  which '{' would define cardinality at 1: /{-1,2}/

So apparently if a { is encountered, the algorithm is:

  1. is there a previous pattern to apply it to?
     a. no: error
     b. yes: is it a plausible {} range?
        i. yes: apply it
       ii. no: treat it as a literal string

One might argue that 1b should come first.


David

-- 
David Alan Black
home: dblack@superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav