def fib(n)
  {n => :fixnum}

  if n < 2
    n
  else
    fib(n - 1) + fib(n - 2)
  end
end
~/NetBeansProjects/jruby ➔ jruby -rcompiler/duby/plugin/math lib/ruby/site_ruby/1.8/compiler/duby/c_compiler.rb fib.rb
~/NetBeansProjects/jruby ➔ cat fib.rb.c
int fib(int n) {;
if (n < 2) {n} else {fib(n - 1) + fib(n - 2)};
}