hiccup_to_html.rb

def to_html structure
  if structure.is_a? Hash
    structure.reduce([]) do |acc, (key, val)|
      acc + [[key.to_s, '="', val.to_s, '"'].join]
    end.join(' ')
  elsif structure.is_a? Array
    if structure[1].is_a? Hash
      tag, attrs, *children = structure.map { |s| to_html s}
      tag_and_attrs = structure[1].any? ? [tag, ' ', attrs].join : tag
    else
      tag, *children = structure.map { |s| to_html s}
    end

    ['<', tag_and_attrs || tag, '>', children.join, '</', tag, '>'].join
  else
    structure.to_s
  end
end