Introducing citrus-mode

Citrus is a library for Parsing Expressions in Ruby.

This is a simple grammar in Citrus for addition. As you can see, the grammar language very simple:

grammar Addition
  rule additive
    number plus (additive | number)
  end

  rule number
    [0-9]+ space
  end

  rule plus
    '+' space
  end

  rule space
    [ \t]*
  end
end

The way to use the grammar is:

require 'citrus'

Citrus.load 'addition'

m = Addition.parse '1 + 2 + 3'
m.value # 6

I wrote citrus-mode, which is a major mode for Emacs to edit Citrus files.