gistfile1.rb

require 'yaml'

def yacss(data)
  YAML.load(data).map do |item|
    item.map do |selector, properties|
      "#{selector} {\n" +
      properties.map do |property, value|
        "  #{property}: #{value};\n"
      end.join +
      "}\n"
    end.join
  end.join
end

YAML_TEXT = <<-YAML_TEXT
- body: &body               # setting a label
    height: 20px
    width: &width 30px      # setting another label

- .wadus span:
    width: *width           # using a label as a variable

- p:
    <<: *body               # using a label as a mixin
    color: "#fff"           # need to quote this as # opens a comment in YAML
    
                            # full reference at YAML.org =;-)
                            
YAML_TEXT

puts yacss(YAML_TEXT)

# Output:
#
# body {
#   height: 20px;
#   width: 30px;
# }
# .wadus span {
#   width: 30px;
# }
# p {
#   color: #fff;
#   height: 20px;
#   width: 30px;
# }