var tokenize = function(input) { return replace(/\(/g, ' ( ') .replace(/\)/g, ' ) ') .trim() .split(/\s+/)

var tokenize = function(input) { return replace(/\(/g, ' ( ') .replace(/\)/g, ' ) ') .trim() .split(/\s+/); }; Code like this makes me a little upset. It'll completely break on simple cases: `(print "To close the REPL, type (quit).")` being an obvious example. I get that it's a toy example, but all too often it slides into tricking people that hard* problems are trivial. * - I'm aware that tokenization has been a solved problem for decades—what I'm trying to say is that it takes quite a bit more thought than the four-line implementation suggests.