From: William James <w_a_x_man@...>
Date: 2005-12-14T20:12:41+09:00
Subject: Re: parsing literals

ako... wrote:
> hello,
>
> i need to write a function that would parse a string literal in another
> language. a string literal in this language is:
>
> STRING = "CHAR*"
> CHAR = any character except for " and \
>   | \"
>   | \\
>   | \/
>   | \u four hexadecimal digits
>
> the \u sequence specifies a character in UTF-16 encoding.
>
> for example: "abc", "", "a\"bc", "a\\b", "a\u12bfc"
>
> below is the code that i wrote. is this Ruby enough? can someone
> suggest improvements? a better style?
>
> thanks
> konstantin
>
> def parselit(s)
>   r = %r{\\"|\\/|\\\\|\\u[\da-f][\da-f][\da-f][\da-f]}i
>   s =~ /^"((?:[^"\\]|#{r})*)"$/ && $1.gsub(r) { |x| x =~ /\\u(.*)/ ?
> [$1.hex].pack('U*') : x[1..-1] }
> end
>
> puts parselit('"\u004e\"a"')

def parselit(s)

  re = %r{
           \\"
        |  \\/
        |  \\\\
        |  \\u [\da-f] {4}
  }xoi

  return nil   if s !~ /^".*"$/

  out = ""

  s[1..-2].scan( /\G (?: ( [^"\\]+ ) | ( #{re} ) )/x ){ |x|
    out <<
      if !x.last
        x.first
      else
        if x.last[0,2] == '\u'
          [x.last[2..-1].hex].pack('U*')
        else
          x.last[1..-1]
        end
      end

  }

  # Fail if whole string didn't match.
  if $~.post_match != ""
    nil
  else
    out
  end


end

puts parselit('"\u004e\"a"')
puts parselit('"\u004e\""a"')