# Regex dynamic count modifier {min, max}?

**URL:** <https://www.ruby-forum.com/t/regex-dynamic-count-modifier-min-max/128490>\
**Category:** Ruby\
**Created:** [February 8, 2008, 2:03am UTC](https://www.ruby-forum.com/t/regex-dynamic-count-modifier-min-max/128490 "2008-02-08T02:03:23Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [February 8, 2008, 2:03am UTC](https://www.ruby-forum.com/t/regex-dynamic-count-modifier-min-max/128490/1 "2008-02-08T02:03:23Z")

</div>

Here is an idea and tell me if it could be accomplished by some other  
means.

To parse a logic statement like this:

fn:function3(fn:function2(fn:function1(xargs)))

Using a regex sorta like so to grep the function-start-pattern(s) :

/\A((fn:[\w-]+)[]_([]_)+\z/i

It would be nice to ensure the proper count of ‘)’, without confusion if  
say  
the xargs had ‘)’ literal or escaped string value(s) in there.

One way is to provide a count ref for function-start-pattern, so I could  
then group a pattern for match on post-xargs ‘)’ and force the {min,max}  
count by some backref to count-of-(function-start-pattern) =X and put  
that  
in there for the (function-end-pattern)+{X,X}.

Then it might be something like this (ignore the lack of a match on  
possible  
xargs for now) :

/\A((fn:[\w-]+)[]_([]_)+[]\*()){$#1,$#1}\z/i

Where $#1 would be the count ref of the first group etc. Then there  
would be  
matching count-left-side-( and count-right-side-).

Or I don’t understand enuf about the internals of regex to know that  
this is  
impossible.

-ntcm

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**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [February 8, 2008, 3:35am UTC](https://www.ruby-forum.com/t/regex-dynamic-count-modifier-min-max/128490/2 "2008-02-08T03:35:26Z")

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On Feb 7, 7:02 pm, jOhn [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> /\A((fn:[\w-]+)[]_([]_)+\z/i  
> xargs for now) :
> 
> /\A((fn:[\w-]+)[]_([]_)+[]\*()){$#1,$#1}\z/i
> 
> Where $#1 would be the count ref of the first group etc. Then there would be  
> matching count-left-side-( and count-right-side-).
> 
> Or I don’t understand enuf about the internals of regex to know that this is  
> impossible.
> 
> -ntcm

Could you use the awk statement to further parse here?

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<div class="post-metadata">

**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [February 8, 2008, 9:09am UTC](https://www.ruby-forum.com/t/regex-dynamic-count-modifier-min-max/128490/3 "2008-02-08T09:09:12Z")

</div>

2008/2/8, jOhn [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> /\A((fn:[\w-]+)[]_([]_)+[]\*()){$#1,$#1}\z/i
> 
> Where $#1 would be the count ref of the first group etc. Then there would be  
> matching count-left-side-( and count-right-side-).
> 
> Or I don’t understand enuf about the internals of regex to know that this is  
> impossible.

Parsing nested structures is not possible with standard regular  
expressions. IIRC they added something to Perl regexps to do that and  
it may be possible with Ruby 1.9; but I do not know the 1.9 regexp  
engine good enough to answer that off the top of my head.

So the usual approach is to use a context free grammar and parser.  
You can find parser generators in the RAA.

If you just want to ensure counts match you could do something like  
this:

raise “brackets do not match!” if  
str.scan(/(/).size != str.scan(/)/).size

However, this does not ensure proper nesting. I bit more sophisticated:

c = 0  
str.scan /[()]/ do |m|  
case m  
when “(”  
c += 1  
when “)”  
c -= 1  
raise “Mismatch at ‘#$`’” if c \< 0  
else  
raise “Programming error”  
end  
end  
raise “Mismatch” unless c == 0

But now you get pretty close to a decent parser. 🙂

Kind regards

robert

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<div class="post-metadata">

**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [February 8, 2008, 10:20am UTC](https://www.ruby-forum.com/t/regex-dynamic-count-modifier-min-max/128490/4 "2008-02-08T10:20:28Z")

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> To parse a logic statement like this:
> 
> fn:function3(fn:function2(fn:function1(xargs)))

Are you looking for something like this (ruby19):

def get\_fns(string, count=0)  
m = /(?  
fn:[\w-]+  
\s\*(\s\*  
(\g|[^)]_)  
\s_)  
)\s\*/xi.match(string)  
if m  
n = /^(fn:[\w-]+)(\s\*)((.\*?))$/.match(m[‘fn’])  
puts “FN #{count}: #{n[1]} with args #{n[3]}”  
get\_fns(n[3], count + 1)  
end  
end  
a = “foo fn:function3(fn:function2(fn:function1(xargs))) foo(bar) bar”  
get\_fns(a)

> a = “foo fn:function3(fn:function2(fn:function1(xargs))) foo(bar) bar”  
> get\_fns(a)  
> FN 0: fn:function3 with args fn:function2(fn:function1(xargs))  
> FN 1: fn:function2 with args fn:function1(xargs)  
> FN 2: fn:function1 with args xargs  
> =\> nil

Regards,  
Thomas.

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**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [February 8, 2008, 11:21pm UTC](https://www.ruby-forum.com/t/regex-dynamic-count-modifier-min-max/128490/5 "2008-02-08T23:21:39Z")

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I modified slightly to avoid parenthesis within quotes or double quotes

def get\_fns(string, count=0)  
m = /(?  
fn:[\w-]+  
\s\*(\s\*  
(\g|(".+")_(’.+’)_[^)]_)  
\s_)  
)\s\*/xi.match(string)  
if m  
n = /^(fn:[\w-]+)(\s\*)((.\*?))$/.match(m[‘fn’])  
puts “FN #{count}: #{n[1]} with args #{n[3]}”  
get\_fns(n[3], count + 1)  
end  
end

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<div class="post-metadata">

**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [February 8, 2008, 4:40pm UTC](https://www.ruby-forum.com/t/regex-dynamic-count-modifier-min-max/128490/6 "2008-02-08T16:40:44Z")

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wow good job thomas.

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<div class="post-metadata">

**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [February 9, 2008, 7:25am UTC](https://www.ruby-forum.com/t/regex-dynamic-count-modifier-min-max/128490/7 "2008-02-09T07:25:53Z")

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> (\g|(“.+”)_(‘.+’)_[^)]\*)

In this case you’ll probably have to take care of strings like “foo  
"bar"” etc.

I tend to use the regexp from my JSON-quiz solution:  
[http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/289684](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/289684)