many high schools were teaching mathematics with APL! There are quite a few textbooks to learn math with APL [1] or J [2] syntax. Iverson originally wrote APL as a superior syntax for math, the programming implementation came a few years later.
[1] https://alexalejandre.com/about/#apl [2] https://code.jsoftware.com/wiki/Books#Math_for_the_Layman
As an example, I listened to a, now defunct, podcast about Type Theory. Wild esoteric stuff.