Executing YARV (in JRuby)

I guess the title says it all. Oh, it doesn't? You want what? A tutorial on how to play with this? Well, alright then.

What you will need to get started is first and foremost JRuby trunk. Download and build that. You will also need either a very recent version of YARV or Ruby trunk. Download either and build that too. I have the source in $YARV_SRC and $RUBY_TRUNK_SRC. I've also installed them with suffixes, so I have ruby-yarv and ruby-trunk globally available. That's a quite good setup.

Before compiling some Ruby, we need to change the change the compile-script slightly. So open up the file in $YARV_SRC/tool/compile.rb and disable the peephole_optimization and inline_const_cache, since JRuby doesn't really support these features yet. If you use Ruby trunk, you also need to do a global search-and-replace in this file, from YARVCore to VM.

Now you're finished to compile something. The goal for this execution have been to get an iterative fibonacci sequence running, so save this code in a file called fib.rb:

def fib_iter_ruby(n)
  i = 0
  j = 1
  cur = 1
  while cur <= n
    k = i
    i = j
    j = k + j
    cur = cur + 1
  end
  i
end

puts fib_iter_ruby(5000)

Next, compile this file:

ruby-yarv $YARV_SRC/tool/compile.rb -o fib.rbc fib.rb

Modify as needed if you use Ruby trunk instead. Now, how to run this? With the y-flag to JRuby:

jruby -y fib.rbc

As you can see, simple files like this just work. Of course, there are much missing yet, but basic interpretation works really nice. Some more additions to the YARV machine will come quite soon, probably. But the next step will be to implement a compiler for YARV too. From that point it should be possible to execute Ruby-files in JRuby in several different ways; by regular interpretation, YARV compilation, YARV interpretation, Java bytecode AOT compiling, Java bytecode JIT compiling and also possibly Rubinius interpretation. The future is, as always, interesting.