pattern.rb

require 'parslet'

module Rip::Parser::Atoms
  class Pattern < Parslet::Atoms::Base
    attr_reader :pattern

    def initialize(pattern)
      super()
      @pattern = pattern
    end

    def try(source, context, consume_all)
      match_count = source.match(pattern)

      case
      when match_count
        succ(source.consume(match_count))
      when source.chars_left.zero?
        context.err(self, source, 'Premature end of input')
      else
        context.err(self, source, "Failed to match #{pattern}")
      end
    end
  end
end

module Parslet
  def pattern(regular_expression)
    Rip::Parser::Atoms::Pattern.new(regular_expression)
  end
  module_function :pattern
end