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Comment by katspaugh | Hacker News Reader

So Zork was written in Lisp? It had to be!

---

<ROUTINE V-ADVENT ()

  <TELL "A hollow voice says \"Fool.\"" CR>>

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MDL, actually, which was derived from LISP.

https://en.wikipedia.org/wiki/MDL_(programming_language)

I’m curious why they chose MDL rather than Lisp for it. Sure, it would have been ancient MACLISP or whatever, but why not leverage what was already in wide use at MIT at the time?

maybe they just made a mini-lisp and called it MDL?

It’s very Lispy, but it’s not strictly Lisp. Why, for instance, use “<“ and “>” to surround various forms but not others? If they were to make a mini-Lisp, I’d expect something more like Gnu Emacs Lisp, something that’s obviously a Lisp, but heavily influenced by the Lisps of the day. I’ve found a few old MDL manuals linked from Wikipedia, but none of them have any sort of “Here’s why we created MDL” section that I could find.

MDL is Grue Emacs Lisp ;)

Heh!

MDL is also from MIT and supposedly stood for More Datatypes than Lisp. According to wikipedia "MDL provides several enhancements to classic Lisp. It supports several built-in data types, including lists, strings and arrays, and user-defined data types. It offers multithreaded expression evaluation and coroutines."

Seems that most of it's novelties were eventually added into LISP proper.

MDL is what was in wide use at MIT at the time, the PDP-10 era. The M in MDL is sometimes "MIT" in the various backronyms of what it stood for. (Mostly it was apparently just short for "muddle", a self-deprecating description.)

(Also, to be technically correct, these source files aren't even MDL, they are a further descendant called ZIL [Zork Implementation Language].)

Yea, I get that MDL came from MIT, but I have to think that MACLISP was far more used at MIT at that time. But maybe not.

It sounds like from what I've read MACLISP and MDL were side-by-side for a while at MIT and something of a department choice. MACLISP sounds like the serious effort and I read MDL as the "hip" or maybe rebellious upstart with a weirder sense of humor (it was called Muddle and spelled MDL to make it seem like an appropriately serious acronym), which would also make some sense that Zork originated in that allowed to be sillier language.

(Also, in reading other comments around here, I've learned there's a deeper connection in MDL to Scheme than I knew before, so I hadn't realized the Lisp/Scheme split even has ties to this "competition" of Lisp languages at MIT.)

Because Zork was written on the MIT Dynamic Modeling PDP-10. MDL was an important part of the software ecosystem on that computer, but Lisp wasn't. On the other MIT PDP-10 computers, Maclisp reined.

Was there any particular reason they did that, or was it just a random coincidence (that was the team that wrote it and the hardware they had access to was that particular machine and that particular machine ran MDL, otherwise, it would have been MACLISP)? Was there anything about MDL that helped with writing an adventure game?

From one perspective ADVENT is just SHRDLU turned inside out, after all. (Though of course from another perspective it's a fancier WUMPUS.)

('ADVENT' is https://en.wikipedia.org/wiki/Colossal_Cave_Adventure , for anyone who isn't familar.)

A nice overview of the source code for that is:

http://literateprogramming.com/adventure.pdf

(This is not an original observation, to be clear: see eg. https://nickm.com/if/riddle_machines.html )

I remember playing it and finding a bunch of listings

  There is an enormous stack of line-printer paper here.  It is barely
  readable and totally unintelligible.

and:

  <DEFINE FEEL-FREE (LOSER)
    <TELL "FEEL FREE, CHOMPER!">
    <MEMQ ......
  The rest is, alas, unintelligible (as were the implementers).

I read a while back it’s a language called zil based on MDL.

https://the-rosebush.com/2025/07/studies-of-zil-part-2-how-d...

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