It's more like Prolog with a maximum arity of 5 and about a thousand particles with complicated effects. The reference text says with some pride that it is "as simple as C++."
That will be Ithkuil with its weird complex rules and alien writing system made from a vast character set.
APL has a very simple ruleset once you sit down and learn it. The character set is large, though (a positive in my opinion, but not for everyone).