[zerr]

> you are going to be paying for Dyalog

Not really. As I see APL is ISO standardized and there are many implementations.

[jetti]

There are many implementations but not as many that are active (here is a brief list https://en.wikipedia.org/wiki/APL_(programming_language)#Mod...). Dyalog provides more than just a interpreter/compiler but an entire development environment.