Planned Alternant r←(F∙G)y

This primitive or feature is planned, that is, it doesn't appear in the most recent released implementation of TinyAPL. Details may change before it is added!

F should be a reduction function. r is the alternant, i.e. the generalized determinant, of y, using F and G. How is that computed? I have no idea. I promise I'll do more research eventually but frankly I don't understand any of the documentation I've found so far (: