# Any parser \*for\* regular expressions? **URL:** \ **Category:** ruby-talk\ **Created:** [16 February 2012 17:53 UTC](https://rubytalk.org/t/any-parser-for-regular-expressions/64897 "2012-02-16T17:53:21Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Brian\_Candler](https://avatars.discourse-cdn.com/v4/letter/b/5f9b8f/32.png) [@Brian\_Candler](https://rubytalk.org/u/Brian_Candler)\ **Post date:** [16 February 2012 17:53 UTC](https://rubytalk.org/t/any-parser-for-regular-expressions/64897/1 "2012-02-16T17:53:21Z")
Is there some existing code (preferably ruby) which can take a regular expression and build a parse tree from it? e.g. I want to turn "^(foo|(bar|baz)\*|qux)$" into something like this:      \     / | \ \ | \      \    / | \ foo \<\*\> qux        \>      \      / \    bar baz or some equivalent representation of the regular expression itself. (The trouble is, when you google for 'ruby regular expression parser' you get all sorts of parsers written \*using\* regular expressions, not parsers \*for\* regular expressions!) Thanks, Brian. > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Alex\_Chaffee](https://avatars.discourse-cdn.com/v4/letter/a/da6949/32.png) [@Alex\_Chaffee](https://rubytalk.org/u/Alex_Chaffee)\ **Post date:** [16 February 2012 18:11 UTC](https://rubytalk.org/t/any-parser-for-regular-expressions/64897/2 "2012-02-16T18:11:51Z")
A better search term might be "regular expression grammar" since a grammar is what a regular expression parser would require. Here's one I just found for Perl regexes: [http://www.cs.sfu.ca/~cameron/Teaching/384/99-3/regexp-plg.html](http://www.cs.sfu.ca/~cameron/Teaching/384/99-3/regexp-plg.html) via [Regex BNF Grammar - Stack Overflow](http://stackoverflow.com/questions/265457/regex-grammar) If I were you I'd use the Perl one as a starting point for writing a Treetop grammar for Ruby regexes. Or ask around on the Treetop list and see if someone's already done that. > **[GitHub - nathansobo/treetop: A Ruby-based parsing DSL based on parsing...](https://github.com/nathansobo/treetop)** > > A Ruby-based parsing DSL based on parsing expression grammars. - GitHub - nathansobo/treetop: A Ruby-based parsing DSL based on parsing expression grammars. [http://thingsaaronmade.com/blog/a-quick-intro-to-writing-a-parser-using-treetop.html](http://thingsaaronmade.com/blog/a-quick-intro-to-writing-a-parser-using-treetop.html) [http://groups.google.com/group/treetop-dev](http://groups.google.com/group/treetop-dev) > **···** > > On Thu, Feb 16, 2012 at 9:53 AM, Brian Candler \ wrote: > > > Is there some existing code (preferably ruby) which can take a regular > > expression and > > build a parse tree from it? e.g. I want to turn > > > > "^(foo|(bar|baz)\*|qux)$" > > > > into something like this: > > > > ``` > > <seq> > > > > ``` > > > > / | \ > > \ | \ > > \ > > / | \ > > foo \<\*\> qux > > \> > > \ > > / \ > > bar baz > > > > or some equivalent representation of the regular expression itself. > > > > (The trouble is, when you google for 'ruby regular expression parser' > > you get all sorts of parsers written \*using\* regular expressions, not > > parsers \*for\* regular expressions!) > > > > Thanks, > > > > Brian. > > > > -- > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). > > -- > Alex Chaffee - alex@stinky.com > [http://alexchaffee.com](http://alexchaffee.com) > [http://twitter.com/alexch](http://twitter.com/alexch) ---
**Author:** ![Ammar\_Ali](https://avatars.discourse-cdn.com/v4/letter/a/73ab20/32.png) [@Ammar\_Ali](https://rubytalk.org/u/Ammar_Ali)\ **Post date:** [16 February 2012 19:01 UTC](https://rubytalk.org/t/any-parser-for-regular-expressions/64897/3 "2012-02-16T19:01:06Z")
I wrote one a while ago. It doesn't exactly produce a tree like you described, but it does provide outputs that I think can be easily used to create such a tree. [GitHub - ammar/regexp\_parser: A regular expression parser library for Ruby](https://github.com/ammar/regexp_parser) [regexp\_parser | RubyGems.org | your community gem host](https://rubygems.org/gems/regexp_parser) I only have one public, and simple, project that uses it so far:   [GitHub - ammar/meta\_re: An experimental regular expression "preprocessor"](https://github.com/ammar/meta_re) HTH, Ammar > **···** > > On Thu, Feb 16, 2012 at 7:53 PM, Brian Candler \ wrote: > > > Is there some existing code (preferably ruby) which can take a regular > > expression and build a parse tree from it? ---
**Author:** ![Jesus\_Gabriel\_y\_Gala](https://avatars.discourse-cdn.com/v4/letter/j/96bed5/32.png) [@Jesus\_Gabriel\_y\_Gala](https://rubytalk.org/u/Jesus_Gabriel_y_Gala)\ **Post date:** [16 February 2012 19:43 UTC](https://rubytalk.org/t/any-parser-for-regular-expressions/64897/4 "2012-02-16T19:43:37Z")
I don't have a good answer for your problem, but this question reminded me of an old rubyquiz I have fond memories of 🙂 [http://www.rubyquiz.com/quiz143.html](http://www.rubyquiz.com/quiz143.html) Jesus. > **···** > > On Thu, Feb 16, 2012 at 6:53 PM, Brian Candler \ wrote: > > > Is there some existing code (preferably ruby) which can take a regular > > expression and > > build a parse tree from it? e.g. I want to turn > > > > "^(foo|(bar|baz)\*|qux)$" > > > > into something like this: > > > > ``` > > <seq> > > > > ``` > > > > / | \ > > \ | \ > > \ > > / | \ > > foo \<\*\> qux > > \> > > \ > > / \ > > bar baz > > > > or some equivalent representation of the regular expression itself. > > > > (The trouble is, when you google for 'ruby regular expression parser' > > you get all sorts of parsers written \*using\* regular expressions, not > > parsers \*for\* regular expressions!) ---
**Author:** ![Brian\_Candler](https://avatars.discourse-cdn.com/v4/letter/b/5f9b8f/32.png) [@Brian\_Candler](https://rubytalk.org/u/Brian_Candler)\ **Post date:** [16 February 2012 19:22 UTC](https://rubytalk.org/t/any-parser-for-regular-expressions/64897/5 "2012-02-16T19:22:12Z")
Ammar Ali wrote in post #1047200: > I wrote one a while ago. It doesn't exactly produce a tree like you > described, but it does provide outputs that I think can be easily used > to > create such a tree. > > [GitHub - ammar/regexp\_parser: A regular expression parser library for Ruby](https://github.com/ammar/regexp_parser) That looks like just the job, thank you! > **···** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).