APL demonstration 1975 

Cool vintage REPL

Yes, he could (and probably should have) called UNIT from BOX. The old Selectric terminal brings back memories. For longer running expressions, the keyboard would lock up until done. To let the user know program was still runnng, the typeball would nod back and forth, creating a clicking sound. I spent many nights at home trying to get to sleep while a long running program was running on the terminal, which was connected to the remote mainframe via an acoustic coupler running at 134 baud.

APL's key innovation was that it made it possible to interactively program computers on very slow printing terminals in a timesharing environment. To on the other hand, be programming in Basic or Fortran at the time on such a terminal, just the printing out of the program could take pages and pages of printout and would be too time consuming to be considered, "interactive." The time it took to print out an APL program while developing it, was very short due to the character efficiency of the symbol and matrix oriented language, and APL provided a single-line oriented editor that further optimized interactive development on the printing terminals. APL code lines could be dozens of characters long, where editing rather than re-typing lines was an important feature.

This - the memory of youth. APL could really work wonders, especially after the introduction of arbitrary arrays. Programming APL - is a game оf mind and grace. But it is the language of mathematics, not programmers. Sectarian bit.

Such a clear and well thought-out introduction. The latter segment really helped me understand what inner- and outer products in APL do.

I used one of those terminals when I learned APL back in high school. This is a good demo that I can refer people to for getting a basic understanding of what the language is like. GNU APL and NARS2000 are good freeware interpreters for people who want to experiment.

Thanks for posting this - I've had a fondness for APL which seems recent but which actually stretches back around 10 years now. I'm only a dabbler, never really got any good!

I wish he had called UNIT inside of BOX. Does anyone know if calling function within other functions was supported? Also, HOLY CRAP this is cool.

Excellent video! I still use APL\11 sometimes.

Wow. As soon as a heard that teletype, I was transported back to being a little kid in the 1970's and watching the Six Million Dollar Man opening credits (search youtube - they won't let me attach the link to the video in a comment)

Mind blown.

So, you can't make a function that takes three or more arguments?

7:23 2*5+1 = 12. in APL back then you actually needed brackets for that cool. Its easier to read with brackets anyway.

Awesome! a want to program some APL