ref: ee4298a2cfbbd9e015cfc775d9d714a9f5035846
dir: /TODO/
1) Add a repl 2) Figure out how to print the final bindings after running a query 3) Stop comparing strings all the time 4) Stop copying the entire goal stack into every choicepoint 5) Stop creating choicepoints when it is not needed 6) How to implement builtins nicely?