JSON Parser

json_parser.rb

require 'rubygems'
require 'parslet'

#This needs a few more 'as' calls to annotate the output 
class JSONParser < Parslet::Parser
  rule(:space)              { match('[\s\n]').repeat(1)}
  rule(:space?)             { space.maybe }
  rule(:digit)              { match('[0-9]') }
  rule(:hexdigit)           { match('[0-9a-fA-F]') }
  rule(:comma)              { space? >> str(',') >> space? }
  rule(:colon)              { space? >> str(':') >> space? }

  rule(:number)             { space? >> str('-').maybe >> 
                                (str('0') | (match('[1-9]') >> digit.repeat)) >> 
                                (str('.') >> digit.repeat).maybe >> 
                                ((str('e')| str('E')) >> (str('+')|str('-')).maybe >> digit.repeat ).maybe }

  rule(:escaped_character)  { str('\\') >> (match('["\\\\/bfnrt]') | (str('u') >> hexdigit.repeat(4,4))) }

  rule(:string){ 
     str('"') >> (
        escaped_character | str('"').absent? >> any
     ).repeat.as(:string) >> str('"') 
  }

  rule(:value){ 
     (string | 
      number | 
      object | 
      array  | 
      str('true').as(:true) | 
      str('false').as(:false) | 
      str('null').as(:null)).as(:val) 
}

  rule(:entry)              { string >> colon >> value }
  rule(:pair_list)          { entry>> (comma >> entry).repeat }
  rule(:object)             { str('{') >> space? >> pair_list.maybe >> space? >> str('}') }

  rule(:value_list)         { value >> (comma >> value).repeat }
  rule(:array)              { str('[') >> space? >> value_list.maybe >> space? >> str(']')}

  rule(:json)               { space? >> value >> space?}
  root(:json)
end

I just found someone else has written one too.. https://gist.github.com/966020