I worked with GNU APL for a while and really liked it. It's also possible to extend it with the C foreign function interface (FFI). The best way I found to input the APL2 symbols with my normal keyboard was with a customized XCompose definition where the input chords are mnemonics of the actual symbols: https://gist.github.com/smartmic/cdb8b0b3936ab965213748813b6...

Old RMS song, to the tune of "row row row your boat":

Rho, rho, rho of x, always equals 1

Rho's dimension, rho rho rank; APL is fun!

APL was developed in the 1960s. Between then and whenever its symbols were added to Unicode (U+2336 and following, at least), how were its symbols encoded?