bierdown.rb

require 'parslet'

recipe = <<EOH
:1 oz: @1 :60 Minutes:
:1 oz: @2 :30 Minutes:
EOH

class BierDown < Parslet::Parser
  rule(:colon)      { match(':') }
  rule(:at)         { match('@') }
  rule(:number)     { match('[0-9]').repeat(1) }
  rule(:word)       { match('[a-zA-Z]').repeat(1) }
  rule(:space)      { match('\s') }
  rule(:space?)     { space.maybe }
  rule(:text)       { (colon.absent? >> at.absent? >> any).repeat(1) }

  rule(:modifier)   { colon >> number.as(:amount) >> space? >> word.as(:unit) >> colon }
  rule(:reference)  { str('@') >> number.as(:id) }

  rule(:line)       { (text | modifier | reference).repeat }
  root(:line)
end

tree = BierDown.new.parse(recipe)

tree.each do |item|
  puts "#{item[:amount]} #{item[:unit]}"
end