I''ll start by confessing that this comes originally from something I
worked on in Perl, and I''ve assumed, rightly or wrongly, that regular
expressions are regular expressions are regular expressions.
See
http://www.ilovejackdaniels.com/cheat-sheets/regular-expressions-cheat-sheet/
The context is that there are a whole pile of patterns that must be
preceded by .... .. well, not words or _some_ punctuation. Call them
"sort-of zero width". That is, white space, beginning of line and
some
opening sequences, call the ''[''and ('' and
''{'' for the sake of the
example, are allowed.
I''m trying to put the RE into a ''constant'' so that I
don''t have to keep
repeating it - all the DRY stuff about changes and so forth!
I''m trying to use RE''s lookahead.
This works in perl
$STARTWORD = qr/^|(?<=[\s\(\[\{])/m;
There is also the corresponding end word
$ENDWORD = qr/$|(?=[ \t\n\,\.\;\:\!\?\)])/om;
When I translate these into Ruby I get an error,
It doesn''t seem to like the lookbehind
The error message is
SyntaxError undefined (?...) sequence: /^|(?<=[\s\(])/
Well, possibly. Or it may be that it I''m having problems when
combining
it with an actual pattern.
What I''ve done is separate out the pattern to a constant (and tried to
eliminate things that might confuse the parser)
STARTWORD = %r{^|(?<=[\s\(])}m
An LO! The parser chokes on that.
Does it choke because there isn''t actually pattern being compared?
Well, maybe. If I remove the ''%r{'' stuff the parser
doesn''t choke.
But it doesn''t choke on
ENDWORD = %r{$|(?=[\s,.;:!?)])}m
And I seem to be getting confused when combining these with other
regular expressions because of this inconsistency.
Right now I don''t know if the problem is having the REs as constants.
Does this make them ''precompiled''?
ENDWORD.type ==> "Regexp"
so I''m presuming it is. In which case why can''t I precompile
STARTWORD?
So: Is it that Ruby can''t handle the ''?<=''
lookbehind assertion ... or
what? Am I completely hung up on a wrong track?
--
Any simple problem can be made insoluble if enough meetings are held to
discuss it.
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The ruby regular expression engine doesn''t support look-behind. http://en.wikipedia.org/wiki/Comparison_of_regular_expression_engines -- Posted via http://www.ruby-forum.com/. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
2008/1/16, Anton J Aylward <aja-XdPx9462FWc@public.gmane.org>:> So: Is it that Ruby can''t handle the ''?<='' lookbehind assertion ...As far as I know, look-behind assertions are not handled by Ruby 1.8.* but I think Oniguruma in 1.9 can. You should ask your question in Ruby-Talk mailing list, which is a better appropriate place for this kind of question. -- Jean-François. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe@googlegroups.com For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
John Harrison said the following on 16/01/08 12:43 PM:> The ruby regular expression engine doesn''t support look-behind. > > http://en.wikipedia.org/wiki/Comparison_of_regular_expression_engines{{ExpletiveDeleted!}} Suggestions? -- The state can''t give you free speech, and the state can''t take it away. You''re born with it, like your eyes, like your ears. Freedom is something you assume, then you wait for someone to try to take it away. The degree to which you resist is the degree to which you are free... --Utah Phillips --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Oniguruma http://oniguruma.rubyforge.org/ This engine is the RegExp engine for Ruby 1.9 and onwards, so you only need this gem for 1.8.x. Jason On Jan 16, 2008 1:06 PM, Anton J Aylward <aja-XdPx9462FWc@public.gmane.org> wrote:> > John Harrison said the following on 16/01/08 12:43 PM: > > The ruby regular expression engine doesn''t support look-behind. > > > > http://en.wikipedia.org/wiki/Comparison_of_regular_expression_engines > > {{ExpletiveDeleted!}} > > Suggestions? > > -- > The state can''t give you free speech, and the state can''t take it away. > You''re born with it, like your eyes, like your ears. Freedom is > something you assume, then you wait for someone to try to take it away. > The degree to which you resist is the degree to which you are free... > --Utah Phillips > > > >--~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Jason Roelofs said the following on 16/01/08 01:21 PM:> Oniguruma > > http://oniguruma.rubyforge.org/ > > This engine is the RegExp engine for Ruby 1.9 and onwards, so you only > need this gem for 1.8.x.Roll on 1.9 then, because I get pages and pages of error messages when I try installing this gem, starting with oregexp.c:2:23: error: oniguruma.h: No such file or directory Now that can''t be because I don''t have the Ruby sources installed, can it? -- If God does not write LisP, God writes some code so similar to LisP as to make no difference. See also: http://xkcd.com/224/ --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
The Oniguruma gem is just a wrapper around the actual library. I haven''t installed this myself, though I assumed it would come with the needed code. You just need to install Oniguruma itself, then get the gem. Jason On Jan 17, 2008 2:08 PM, Anton J Aylward <aja-XdPx9462FWc@public.gmane.org> wrote:> > Jason Roelofs said the following on 16/01/08 01:21 PM: > > Oniguruma > > > > http://oniguruma.rubyforge.org/ > > > > This engine is the RegExp engine for Ruby 1.9 and onwards, so you only > > need this gem for 1.8.x. > > Roll on 1.9 then, because I get pages and pages of error messages when I > try installing this gem, starting with > > oregexp.c:2:23: error: oniguruma.h: No such file or directory > > Now that can''t be because I don''t have the Ruby sources installed, can it? > > -- > If God does not write LisP, God writes some code so similar to > LisP as to make no difference. > See also: http://xkcd.com/224/ > > > >--~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
The library can be found here: http://www.geocities.jp/kosako3/oniguruma/
I am trying to get look behind working as well. However, having got
past the errors, I am now wrestling with syntax:
** Starting Rails with development environment...
Exiting
/usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in
`gem_original_require'': ./lib/string_extensions.rb:4: undefined
(?...)
sequence: /[aeiou]|(?<![aeiou])y(?![aeiou])/ (SyntaxError)
./lib/string_extensions.rb:8: undefined (?...) sequence: /![aeiou]|(?
<=[aeiou])y(?=[aeiou])/ from /usr/local/lib/ruby/site_ruby/1.8/
rubygems/custom_require.rb:27:in `require''
It seems to be complaining about the look-behind and look-ahead
assertions in the following code fragment (which origuruma is
supposed
to support):
class String
def vowels
scan(/[aeiou]|(?<![aeiou])y(?![aeiou])/i)
end
def consonants
scan(/![aeiou]|(?<=[aeiou])y(?=[aeiou])/i)
end
end
According to this reference (http://www.geocities.jp/kosako3/oniguruma/
doc/RE.txt), the look behind and look ahead syntax that I am using
appears to be correct (ref section 7. Extended groups) but apparently
is not.
<stumped/>
On Jan 17, 1:27 pm, "Jason Roelofs"
<jameskil...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> The Oniguruma gem is just a wrapper around the actual library. I
haven''t
> installed this myself, though I assumed it would come with the needed code.
> You just need to install Oniguruma itself, then get the gem.
>
> Jason
>
> On Jan 17, 2008 2:08 PM, Anton J Aylward
<a...-XdPx9462FWc@public.gmane.org> wrote:
>
>
>
> > Jason Roelofs said the following on 16/01/08 01:21 PM:
> > > Oniguruma
>
> > >http://oniguruma.rubyforge.org/
>
> > > This engine is the RegExp engine for Ruby 1.9 and onwards, so you
only
> > > need this gem for 1.8.x.
>
> > Roll on 1.9 then, because I get pages and pages of error messages when
I
> > try installing this gem, starting with
>
> > oregexp.c:2:23: error: oniguruma.h: No such file or directory
>
> > Now that can''t be because I don''t have the Ruby
sources installed, can it?
>
> > --
> > If God does not write LisP, God writes some code so similar to
> > LisP as to make no difference.
> > See also:http://xkcd.com/224/
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Thanks for all the help everyone. The problem was solved with the help
from pullmonkey on Rails Forum! Here is the solution:
Objective:
1. Extract vowels and consonants from a string
2. Handle the conditional treatment of ''y'' as a vowel under
the
following circumstances:
- y is a vowel if it is surrounded by consonants
- y is a consonant if it is adjacent to a vowel
Here is the code that works:
def vowels(name_str)
reg =
Oniguruma::ORegexp.new(''[aeiou]|(?<![aeiou])y(?![aeiou])'')
reg.match_all(name_str).to_s.scan(/./)
end
def consonants(name_str)
reg =
Oniguruma::ORegexp.new(''[bcdfghjklmnpqrstvwx]|(?<=[aeiou])y|
y(?=[aeiou])'')
reg.match_all(name_str).to_s.scan(/./)
end
(Note, the .scan(/./) can be eliminated to return an array)
The major problem was getting the code to accurately treat "y" as a
consonant. The key to solving this problem was to:
1. define unconditional consonants explicitly (i.e.,
[bcdfghjklmnpqrstvwx]) -- not as [^aeiou] which automatically includes
"y" thus OVER-RIDING any conditional reatment of "y" that
follows
2. define conditional "y" regexp assertions independently, i.e.,
"| (?
<=[aeiou]) y | y (?=[aeiou])" -- not "|(?<=[aeiou]) y
(?=[aeiou])"
which only matches "y" preceded AND followed by a vowel, not preceded
OR followed by a vowel
HTH.
On Feb 4, 8:36 am, Dondi
<Donovan.Dil...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> The library can be found here:http://www.geocities.jp/kosako3/oniguruma/
>
> I am trying to get look behind working as well. However, having got
> past the errors, I am now wrestling with syntax:
>
> ** Starting Rails with development environment...
> Exiting
> /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in
> `gem_original_require'': ./lib/string_extensions.rb:4: undefined
> (?...)
> sequence: /[aeiou]|(?<![aeiou])y(?![aeiou])/ (SyntaxError)
> ./lib/string_extensions.rb:8: undefined (?...) sequence: /![aeiou]|(?
> <=[aeiou])y(?=[aeiou])/ from /usr/local/lib/ruby/site_ruby/1.8/
> rubygems/custom_require.rb:27:in `require''
> It seems to be complaining about the look-behind and look-ahead
> assertions in the following code fragment (which origuruma is
> supposed
> to support):
> class String
> def vowels
> scan(/[aeiou]|(?<![aeiou])y(?![aeiou])/i)
> end
> def consonants
> scan(/![aeiou]|(?<=[aeiou])y(?=[aeiou])/i)
> end
> end
> According to this reference (http://www.geocities.jp/kosako3/oniguruma/
> doc/RE.txt), the look behind and look ahead syntax that I am using
> appears to be correct (ref section 7. Extended groups) but apparently
> is not.
>
> <stumped/>
>
> On Jan 17, 1:27 pm, "Jason Roelofs"
<jameskil...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > The Oniguruma gem is just a wrapper around the actual library. I
haven''t
> > installed this myself, though I assumed it would come with the needed
code.
> > You just need to install Oniguruma itself, then get the gem.
>
> > Jason
>
> > On Jan 17, 2008 2:08 PM, Anton J Aylward
<a...-XdPx9462FWc@public.gmane.org> wrote:
>
> > > Jason Roelofs said the following on 16/01/08 01:21 PM:
> > > > Oniguruma
>
> > > >http://oniguruma.rubyforge.org/
>
> > > > This engine is the RegExp engine for Ruby 1.9 and onwards,
so you only
> > > > need this gem for 1.8.x.
>
> > > Roll on 1.9 then, because I get pages and pages of error messages
when I
> > > try installing this gem, starting with
>
> > > oregexp.c:2:23: error: oniguruma.h: No such file or directory
>
> > > Now that can''t be because I don''t have the Ruby
sources installed, can it?
>
> > > --
> > > If God does not write LisP, God writes some code so similar to
> > > LisP as to make no difference.
> > > See also:http://xkcd.com/224/
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