It's more straightforward than this. Think of it as a more comprehensive Yahoo Pipes or IFTTT, where the nice graphical interface is not yet released publicly. So for now developers can just write the raw JSON. Yes, a LISP interpreter would have done that job (as would a library written in some other programming language). However you are not allowed to download code into an iOS app (precisely for security reasons), and so we're downloading items from a predefined documented list of macros. This simplicity, in turn, makes creating a graphical interface a lot easier, without sacrificing the fact that the structure is as flexible as a functional programming language.