sonic-pi

https://github.com/sonic-pi-net/sonic-pi

C++

Code. Music. Live.

Parslet.dynamic

Designates a piece of the parser as being dynamic. Dynamic parsers can
either return a parser at runtime, which will be applied on the input, or
return a result from a parse. 

Dynamic parse pieces are never cached and can introduce performance
abnormalitites - use sparingly where other constructs fail. 

Example: 
  # Parses either 'a' or 'b', depending on the weather
  dynamic { rand() < 0.5 ? str('a') : str('b') }

Source | Google | Stack overflow

Edit

git clone [email protected]:sonic-pi-net/sonic-pi.git

cd sonic-pi

open app/server/ruby/vendor/parslet/lib/parslet.rb

Contribute

# Make a new branch

git checkout -b -your-name--update-docs-Parslet-dynamic-for-pr

# Commit to git

git add app/server/ruby/vendor/parslet/lib/parslet.rbgit commit -m "better docs for Parslet.dynamic"

# Open pull request

gem install hub # on a mac you can `brew install hub`

hub fork

git push <your name> -your-name--update-docs-Parslet-dynamic-for-pr

hub pull-request

# Celebrate!