Comment by kasbah

Rob Pike also implemented an APL-like big number calculator in Go more recently: https://github.com/robpike/ivy

>The author has never used APL. It's a chicken and egg problem. (...) All testing has been done with tryapl.org.

There are also a few free software implementations of APL most notably GNU APL. I have been sticking to that while learning APL. https://www.gnu.org/software/apl/