# Please Forward: Ruby Quiz Submission **URL:** \ **Category:** ruby-talk\ **Created:** [4 February 2008 18:58 UTC](https://rubytalk.org/t/please-forward-ruby-quiz-submission/44258 "2008-02-04T18:58:19Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![James\_Edward\_Gray\_II](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@James\_Edward\_Gray\_II](https://rubytalk.org/u/James_Edward_Gray_II)\ **Post date:** [4 February 2008 18:58 UTC](https://rubytalk.org/t/please-forward-ruby-quiz-submission/44258/1 "2008-02-04T18:58:19Z")
> From: Alexander Stedile \ > Date: February 3, 2008 6:30:39 PM CST > To: submission@rubyquiz.com > Subject: Please Forward: Ruby Quiz Submission > > Hi! > > Here is my try for my second ruby quiz. I proved that it is possible to write a JSON parser in less than 100 lines. My (handmade) solution has 94. This would leave space for five more comment lines. 😉 > Looking forward to seeing your parsers and of course the nice quiz summary which I really appreciate. Thanks for that. > > By the way, I added a missing test. I had to do an extra check for that situation to my program. The reason is that the type is decided from the first character. And if there is a closing quotation mark at the end, it could be mistakenly interpreted as valid string 'a" "b'. >    assert\_raise(RuntimeError) { @parser.parse(%Q{"a" "b"}) } > I also do not check for control characters in strings, but anyway. > > As you see, I'm beginning to like eval. 🙂 And my solution heavily relies on regexp matching. The most important/tricky part is the String#split\_stateful method at the top of the code. > > Have fun, > Alex > \_\_\_\_\_\_ > class String > # Splits into sub-strings separated by ',' characters. Does not split > # contents within {}, , or "". \" does not end a string, \\" does. > # Checks if closing characters match previous opening ones. > def split\_stateful >    memb = # list of members identified >    delims = # stack of delimiters >    split('').each { |c| >      memb \<\< "" if memb.empty? >      case delims.last >      when '"' # quote mode >        c == '\\' and delims.push c >        c == '"' and delims.pop >      when '\\' # escape mode >        delims.pop >      else >        case c >        when '{', '[', '"' then delims.push c >        when ',' then ( memb \<\< ""; c="" ) if delims.empty? # next element >        when '}' then delims.pop == '{' or raise RuntimeError, "Non-matching }." >        when ']' then delims.pop == '[' or raise RuntimeError, "Non-matching]." >        end >      end >      memb[-1] += c >    } >    delims.empty? or raise RuntimeError, "No closing delimiter for #{delims.join(', ')}." >    memb > end > end > > class JSONParser > > NUM\_FORMAT = /^(-)?(0|[1-9][0-9]\*)(\.[0-9]+)?(E[+-]?([0-9]+))?$/i > > # parse\_value > def parse(code) >    code.strip! >    case code[0,1] >    when '"' then parse\_string(code) >    when /[-0-9]/ then parse\_number(code) >    when '{' then parse\_object(code) >    when '[' then parse\_array(code) >    else parse\_keyword(code) >    end > end > > def parse\_string(code) >    code =~ /^"(.\*)"$/ or raise RuntimeError, "String has no closing quotation mark." >    $\_ = $1 >    $\_ =~ /([^\\]|(\\\\)+)"/ and raise RuntimeError, "Non-escaped \" not allowed in string #{$\_}." >    gsub(/\\(.)/) { |m| >      case $1 >      when 'b', 'f', 'n', 'r', 't' >        eval('"\\%s"' % $1) >      when 'u' >        m # no change, handled later >      when '"', '/', '\\' >        $1 # strip \ character >      else >        raise RuntimeError, "No such escape sequence \\#{$1}." >      end >    } >    gsub(/\\u([A-F0-9]{4})/i) { "%c" % $1.hex } > end > > def parse\_number(code) >    code =~ NUM\_FORMAT or raise RuntimeError, "Invalid number #{code}." >    eval code > end > > def parse\_array(code) >    code =~ /^\[(.\*)\]$/ or raise RuntimeError, "No closing bracket for array #{code}." >    $1.split\_stateful.collect { |m| parse(m) } > end > > def parse\_object(code) >    code =~ /^\{(.\*)\}$/ or raise RuntimeError, "No closing bracket for object #{code}." >    object = {} >    $1.split\_stateful.each do |m| >      key, value = m.split(":", 2) >      object[parse\_string(key.strip)] = parse(value) >    end >    object > end > > def parse\_keyword(code) >    case code >    when 'true', 'false' then eval(code) >    when 'null' then nil >    else >      raise RuntimeError, "Syntax error: #{code}." >    end > end > end > **···** > > Begin forwarded message: