okay so, i finally found the DOS FPS game i'd played the demo of as a kid!!! i could remember it being in 3D, with configurable sound card options, a kind of sci-fi รฆsthetic, some outdoor sections with brown being the predominant colour, but also prominant use of electric blue...
based on those details i knew it had to be from the mid-to-late 90's. sure enough, it's Domination (1998), apparently also known Rex Blade: The Battle Begins.

playing it now, i understand why I didn't keep playing: it sucks.
the reason i was reminded of it and wanted to find it again today is that i remembered the sound card options, and wondered if it had General MIDI i could try out with my new (old) MIDI module. sure enough, it has both FM synthesis and MIDI, and both OSTs suck. lmao.
BUT.
one neat thing about Domination is that there's a "terminal" in the game, that you can walk up to. and it's an actual terminal! it looks like an Apple II, but it has CLS, DIR, HELP, SYSTEM, VER, and more.

but then i see REX++ and wonder what it does. i figure that, considering the game's main character is named Rex Blade, it might unlock something.
but no. it's... an honest-to-god FULLY FEATURED PROGRAMMING LANGUAGE????

this is one of SEVERAL examples. yeah, you can actually run it:

and yes i did of course test whether you can edit the example and run arbitrary code, in case for some reason it's not a real interpreter. and yes, you can.
what. what!!!!!
i must emphasise: as far as i can tell this is a run-of-the-mill 3D shooty game. it's not even a fucking action RPG. this is not a developer console, it's literally an in-game item. what the fuck is this doing here. did they spend all the development effort on the toy programming language rather than the game
also. after playing with it, it dawned on me...
while this doesn't seem to be compatible with REXX, it must be named after it or its predecessor REX.
DID THEY NAME THE MAIN CHARACTER OF THE GAME AFTER THE PROGRAMMING LANGUAGE
this is just the deepest nerd shit and i can only respect it. shame about the game