I understand regular expressions, but can someone please explain this:
re = %r/((?<pg>\((?:\\[()]|[^()]|\g<pg>)*\)))/
By the way, this only works with the Oniguruma engine (Ruby 1.9).
So, now that there is the capability to match balanced parens and so
forth, does this mean that the new regular expression engine can be
used to construct simple parsers (matching language constructs)?
%r/ ... /
-- regexp delimter (why they didn't just use / ... /, I don't know)
( ... )
-- non-capturing group - (normally would be capturing, but see
http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt, part 10, case 3)
-- seems rather useless, given that the only contained item is a
capturing group
(?<pg> ... )
-- capturing named group (see http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt,
part 7)
\( .. \)
-- literal parentheses surrounding pattern
(?: ... | ... | ... )*
-- non-capturing group of 3 alternatives, repeated 0 or more times
\\[()]
-- escaped literal parens
[^()]
-- anything except parens
\g<pg>
-- match the pg-named pattern here (recursive sub-exp - see
http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt, part 9)
On Nov 18, 8:50 pm, Wayne Magor <Wayne.Ma...@gmail.com> wrote:
I understand regular expressions, but can someone please explain this:
re = %r/((?<pg>\((?:\\[()]|[^()]|\g<pg>)*\)))/
By the way, this only works with the Oniguruma engine (Ruby 1.9).
So, now that there is the capability to match balanced parens and so
forth, does this mean that the new regular expression engine can be
used to construct simple parsers (matching language constructs)?
No, translated to 1.8, the regex would be:
%r/((\((?:\\[()]|[^()]|\2)*\)))/
On Nov 18, 2007, at 17:55 , Wayne Magor wrote:
I understand regular expressions, but can someone please explain this:
re = %r/((?<pg>\((?:\\[()]|[^()]|\g<pg>)*\)))/
By the way, this only works with the Oniguruma engine (Ruby 1.9).
So, now that there is the capability to match balanced parens and so
forth, does this mean that the new regular expression engine can be
used to construct simple parsers (matching language constructs)?
--
Poor workers blame their tools. Good workers build better tools. The
best workers get their tools to do the work for them. -- Syndicate Wars
Thanks, I understand nearly everything now. It really shows the power
of the oniguruma engine for regular expressions. By the way, the comma
caused a Japanese site to come up. For people's reference the manual
for onigurama is at:
http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt
That's a great reference, but I still didn't understand this:
Noah Easterly wrote:
\\[()]
-- escaped literal parens
What is that pattern? I've never seen that before. What does it match?
Where can I read about that?
Why would that be there since a new open paren should start another
instance of <pg>, shouldn't it?
So, obviously, I'm still a little confused.
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Posted via http://www.ruby-forum.com/\.
Noah Easterly wrote:
I understand regular expressions, but can someone please explain this:
re = %r/((?<pg>\((?:\\[()]|[^()]|\g<pg>)*\)))/
snip
(?: ... | ... | ... )*
-- non-capturing group of 3 alternatives, repeated 0 or more times
\\[()]
-- escaped literal parens
[^()]
-- anything except parens
\g<pg>
-- match the pg-named pattern here
Ok, so there are 3 alternatives in the non-capturing group:
1. An open or close parenthesis
2. Any character except a paren
3. A pattern that starts with an open paren
Am I the only one that finds this strange?
On Nov 18, 8:50 pm, Wayne Magor <Wayne.Ma...@gmail.com> wrote:
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Posted via http://www.ruby-forum.com/\.
"\(" or "\)"
On Nov 20, 2007, at 14:42 , Wayne Magor wrote:
Noah Easterly wrote:
\\[()]
-- escaped literal parensWhat is that pattern? I've never seen that before. What does it match?
Where can I read about that?
--
Poor workers blame their tools. Good workers build better tools. The
best workers get their tools to do the work for them. -- Syndicate Wars
Noah Easterly wrote:
>> I understand regular expressions, but can someone please explain this:>> re = %r/((?<pg>\((?:\\[()]|[^()]|\g<pg>)*\)))/
snip
> (?: ... | ... | ... )*
> -- non-capturing group of 3 alternatives, repeated 0 or more times
> \\[()]
> -- escaped literal parens
> [^()]
> -- anything except parens
> \g<pg>
> -- match the pg-named pattern hereOk, so there are 3 alternatives in the non-capturing group:
1. An open or close parenthesis
correction. As Eric said above, an escaped (read, with leading
backslash) parenthesis.
2. Any character except a paren
yup.
3. A pattern that starts with an open paren
AND ends in a close paren, and contains only, non-parens, escaped
parens, and balanced pairs of parens.
Am I the only one that finds this strange?
Doubtful :). You may be one of the ones to which this is new, though.
I find it strange that only recognize parenthesis escapes, and not
escaped backslashes. So you can do something like:
( \( )
and match correctly, but there's no way to do a balanced pair of
parentheses containing just a backslash:
(\) -- no
(\\) -- no
(\\\) -- no
(\ ) -- matches, but has an extra space.
I would have replaced '\\[()]' by '\\[()\\]' so that '(\\)' would
match.
On Nov 21, 9:11 am, Wayne Magor <wema...@hotmail.com> wrote:
> On Nov 18, 8:50 pm, Wayne Magor <Wayne.Ma...@gmail.com> wrote:
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Posted viahttp://www.ruby-forum.com/.