I was a co-op student at IBM Canada in 1986-87. I got sorted (think sorting hat - hiring was generic) into the APL cohort. We had a fun course at the beginnin

I was a co-op student at IBM Canada in 1986-87. I got sorted (think sorting hat - hiring was generic) into the APL cohort. We had a fun course at the beginning and then I was shipped off into ... get this ... a marketing group. So here I sit in front of a then very fancy 3279 terminal writing my little APL programs to do what they wanted - mostly extract/reformat/summarize data from one sort of file format to another. Was this a particularly good fit for APL? Not really, but if all you have is a hammer... Anwyay one day I poked around in other APL code that was on the system and visible to me, and ran one program and wham... the screen on the 3279, which to that point I'd only known as a nice colour text terminal - exploded into fancy graphics. Mind blown. How did they do that? I never found out, because the program that did that was, as you say, "write only" - it looked like screenfuls of random noise. But yes, APL was used in the mainstream, at least in the IBM internal world, as late as the mid 1980s. Maybe the use was artificial - you know, train new cohorts of co-op students in it and make them use it for real work - as a sort of dogfooding, don't know.