rexpl is a sandbox to experiment and play with the Rubinius Virtual Machine and its bytecode instructions. It comes wrapped in a REPL (Read-Eval-Print Loop) à la IRB, so that anytime you can open a terminal, fire up rexpl, and start playing with instant feedback.
Its main feature is stack introspection, which means you can inspect what the stack looks like after each step of your instruction set.
How to use it?
$ gem install rexpl $ rexpl
Now you should see a welcome banner and an IRB-like prompt, and you're good to go! Just start typing some VM instructions and see what happens!
There are three extra commands to take advantage of the stack introspection:
listlists the instruction set of the current program.
resetempties the instruction set and starts a new program.
drawprints a visual representation of the stack after each instruction of your program.
When to use it?
Imagine you are bootstrapping a new language targeting the Rubinius VM and you
just implemented a particular AST node, but when you try to run the tests, you
keep getting nasty stack validation errors. Net stack underflow? What the heck
does this even mean? Where the hell is that extra
pop? Did this or that
instruction consume stack? Or maybe produce it? Oh fuck it, let's go fishing.
Don't panic. You always have your friends pen and paper ready to help you out, Read through the source code, and knowing what each instruction does, try to follow along and draw what the stack looks like at each step (does that sound familiar to you?). Or just fire up rexpl.