Re: PL-6 -- implementation language for Honeywell's CP-6
And bloody annoying it was to program in if you were used to PL/1.
Way back when, Aberdeen University were looking to replace their system and wanted Multics, unfortunately Honeywell had cancelled Multics and sold them CP-6 instead (features included a flat file system - no directories, just a bunch of files per user - and the world's worst text editor - no buffers, changes were made *immediately* in the original file, which was really fun if you were editing code over a noisy phone line).
So I ended up as part of the team implementing the "Rainbow books" (aka "Coloured books" https://en.wikipedia.org/wiki/Coloured_Book_protocols) used by JANET (the Joint Academic NETwork) in PL/6.
Some of the Multics PL/1 code was ported -which was no easy task. Fortunately I got to write the connection manager (conman) from scratch.
Not an experience I'd care to repeat.