[jaybosamiya]

Your whitelisting is quite good!

I still haven't been able to do complete code execution yet, but have reasons to believe it might be possible.

Simply using `x1` as input causes it to print "deadbeef11 is not defined". Additionally, parens are allowed, and there is the `=>` arrow syntax for defining functions. Thus, we have a way to define variables, a way to define lambda abstractions, as well as a way to perform applications. Therefore, we have the untyped lambda calculus. This is Turing complete, so I have reason to believe that it should be possible to execute arbitrary code. I just need to find some time to do so :)

Update: `(x1=>x1(x1))(x1=>x1(x1))` gives "Too much recursion" :D