class ActionDispatch::Journey::Format

def evaluate(hash)
  parts = @parts.dup
  @parameters.each do |index|
    param = parts[index]
    value = hash[param.name]
    return ''.freeze unless value
    parts[index] = param.escape value
  end
  @children.each { |index| parts[index] = parts[index].evaluate(hash) }
  parts.join
end