[sotojuan]

Sorry, but isn't that the point? Why do I need to know what `sum` does behind the scenes? Same with `map`, `reduce`, etc. Those functions exist to avoid a `for` loop or other forms of imperative iteration for common uses.

Either way, I seem to remember that Clojure does have a REPL function to show you the source code for any function. You can use that to know what's going on behind the scenes.