Implement history_arg_extract about rb-readline

[rdp]

Just ran into this today.

>> some_stuff/home/wilkboar/local_installs/lib/ruby/site_ruby/1.8/rbreadline.rb:7365:in `rl_yank_nth_arg_internal': undefined method `history_arg_extract' for RbReadline:Module (NoMethodError)
        from /home/wilkboar/local_installs/lib/ruby/site_ruby/1.8/rbreadline.rb:7425:in `rl_yank_last_arg'
        from /home/wilkboar/local_installs/lib/ruby/site_ruby/1.8/rbreadline.rb:4254:in `send'
        from /home/wilkboar/local_installs/lib/ruby/site_ruby/1.8/rbreadline.rb:4254:in `_rl_dispatch_subseq'
        from /home/wilkboar/local_installs/lib/ruby/site_ruby/1.8/rbreadline.rb:4263:in `_rl_dispatch_subseq'
        from /home/wilkboar/local_installs/lib/ruby/site_ruby/1.8/rbreadline.rb:4243:in `_rl_dispatch'
        from /home/wilkboar/local_installs/lib/ruby/site_ruby/1.8/rbreadline.rb:4660:in `readline_internal_charloop'
        from /home/wilkboar/local_installs/lib/ruby/site_ruby/1.8/rbreadline.rb:4734:in `readline_internal'
        from /home/wilkboar/local_installs/lib/ruby/site_ruby/1.8/rbreadline.rb:4756:in `readline'
         ... 18 levels...
        from /home/wilkboar/local_installs/lib/ruby/1.8/irb.rb:70:in `start'
        from /home/wilkboar/local_installs/lib/ruby/1.8/irb.rb:69:in `catch'
        from /home/wilkboar/local_installs/lib/ruby/1.8/irb.rb:69:in `start'
        from /home1/wilkboar/local_installs/bin/irb:13

[Spakman]

I've been looking at GNU Readline for porting this. Unfortunately, it's not quite as straightforward as I would like (things like the tokenization of strings using multiple delimiters and returning multiple args make it trickier than you might think).

For Urchin I'm using a very dumbed-down version, which simply splits on spaces that haven't been backslash-escaped:

module RbReadline
  def self.history_arg_extract(first, last, string)
    if first != "$" || last != "$"
      fail "RbReadline.history_arg_extract called with currently unsupported args."
    end

    words = string.split
    while words.size > 1 && words[-2][-1].chr == "\\"
      words[-2] = "#{words[-2]} #{words.last}"
      words.pop
    end
    words.last
  end
end

I'm considering committing this to rb-readline as it is probably generally useful until we get a full implementation.

@rdp - would this suffice for your use case?

[rdp]

sure go for it