Parslet a very cool Parsing Expression Grammar parser

Recently I made a japanese language learning tool, which is very cool :) . In this tool we need to create a mark language parser to parse like this [kanji|furigana], My colleague zete, use his very professional regexp skill to make a regexp to parse this text.

WORD_PARSER = /
  (?<kanji>   [\p{Han}\p{Hiragana}\p{Katakana}]+    ){0}
  (?<furi>    \p{Hiragana}+                         ){0}
  (?<oword>   [^\]]+                                ){0}
  (?<invalid> .                                     ){0}
  (?<word>    \[ \g<sp> \g<word_content> \g<sp> \]  ){0}

  (?<word_content> \g<kanji> \g<sp> \g<right> | \g<oword> ){0}
  (?<right>   \| \g<sp> \g<furi>                    ){0}
  (?<sp>      [\t\ ]*                               ){0}

  \g<word> | \g<invalid>
/ux

Look at above stunning regular expression. I never toughed this level of complexity of regexp. But later on when I was looking at http header parser, then found a good tool, called parslet. It just do the exactly same thing, and even could do more complicated things like parsing a language.

require 'parslet'
include Parslet

furidown = "[中国|ちゅうごく][雲南|うんなん][省|しょう][の][昆|こん][明|あきら][市|し][在住|ざいじゅう][の][27][歳|さい][の][アメリカ][人|じん][。]"

# Constructs a parser using a Parser Expression Grammar
class Furidown < Parslet::Parser
  rule(:space)      { match('\s').repeat(1) }
  rule(:space?)     { space.maybe }
  rule(:lbracket)   { str('[') >> space? }
  rule(:rbracket)   { str(']') >> space? }
  rule(:split)      { str("|") >> space? }
  rule(:kanji) { match('[^\]\|]').repeat.as(:kanji) }
  rule(:furigana) {split >> match('[^\]\[]').repeat.as(:furigana)}
  rule(:word) {lbracket >> kanji >> furigana.maybe >> rbracket}
  rule(:words) { word.repeat }
  root(:words)
end

parser = Furidown.new
p parser.parse(furidown)

# the result like
=> [{:kanji=>"中国"@1, :furigana=>"ちゅうごく"@8}, {:kanji=>"雲南"@25, :furigana=>"うんなん"@32}, {:kanji=>"省"@46, :furigana=>"しょう"@50}, {:kanji=>"の"@61}, {:kanji=>"昆"@66, :furigana=>"こん"@70}, {:kanji=>"明"@78, :furigana=>"あきら"@82}, {:kanji=>"市"@93, :furigana=>"し"@97}, {:kanji=>"在住"@102, :furigana=>"ざいじゅう"@109}, {:kanji=>"の"@126}, {:kanji=>"27"@131}, {:kanji=>"歳"@135, :furigana=>"さい"@139}, {:kanji=>"の"@147}, {:kanji=>"アメリカ"@152}, {:kanji=>"人"@166, :furigana=>"じん"@170}, {:kanji=>"。"@178}]