Hi, I'm testing a javascript based syntax highlighter for this blog. Let's see how it works:

 #Ducktyping: Does it walk like a duck? Does it quack like a duck?
 if arg1.responds_to? :capitalize
   puts "Then '#{arg1.capitalize}' must be a string.\n"
 else
   if arg1.responds_to? :modulo && arg1.responds_to? :numerator
     puts "Then '#{arg1.to_s}' must be an integer.\n"
   else
     if arg1.responds_to? :modulo && arg1.responds_to? :truncate
       puts "Then '#{arg1.to_s}' must be a float.\n"
     end
   end
 end

Whoops, guess not :( Anyone knows how to solve this issue?
Nice :) Actually I used this widget to make it work.

Update: I couldn't resist and I also implemented it in this wiki.