ref: 8dd4f85c85aa9ab7a5f1219efd694e6707f2718c
dir: /TODO/
* Stop comparing strings all the time * Stop copying the entire goal stack into every choicepoint * Stop creating choicepoints when it is not needed * How to implement builtins nicely? * Right now we copy and allocate a lot, but almost never free stuff. * Many builtins should really throw an error, but they just fail for now. * Exceptions (throw, catch) * Modules