Made a useful tweak to the playground to better detect unresolved symbols https://squint-cljs.github.io/squint/?repl=true&src=KGRlZm4gZm9vIFt4XSAoKyB4IHkpKQooZm9vIDEp (the next step is to give a warning from the compiler itself, which is totally possible, but at least now JS complains too without spitting out undefined)