**MDL** (pronounced //"muddle"//; a backronym for //Model Development Language//) is a Lisp-descended programming language developed at MIT in the 1970s. It was used to develop the initial version of the game [[tutorials:zork|Zork]].

On twenex.org, run the MDL interpreter with the command ''MDL105'':

  [KANKAN] PUBLIC:<~>@ MDL105
  MUDDLE 105 IN OPERATION.
  LISTENING-AT-LEVEL 1 PROCESS 1
  
Quit MDL by pressing **Ctrl-C**.

After typing an expression in the interpreter, press the **Esc** key (represented with **$** in manuals; used instead of the more common **Enter** key) to have MDL process what you've typed.

Create source files with any editor. Save the file with the extension ".MUD".

Load source files into the MDL interpreter with the function ''FLOAD'':

  <FLOAD "DEV:<DIR>FILE">
  
(You can omit the ''DEV:<DIR>'' portion of the file specification if you set the ''MDL:'' logical name to the device and directory where your MDL source files are stored.)

====== References ======

  * M. Dornbrook, M. Blank. [[http://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TR-292.pdf|The MDL Programming Language Primer]]. Massachusetts Institute of Technology, Laboratory for Computer Science, 1980. Retrieved 2022-03-12. 
  * S. Galley, G. Pfister. [[http://ifarchive.org/if-archive/programming/mdl/manuals/MDL_Programming_Language.pdf|The MDL Programming Language]]. Massachusetts Institute of Technology, Laboratory for Computer Science, 1979. Retrieved 2022-03-12. 
  * P.D. Lebling. [[http://ifarchive.org/if-archive/programming/mdl/manuals/MDL_Programming_Environment.pdf|The MDL Programming Environment]]. Massachusetts Institute of Technology, Laboratory for Computer Science, 1980. Retrieved 2022-03-12. 
  * [[https://en.wikipedia.org/wiki/MDL_(programming_language)|MDL (programming language)]]. Wikipedia. Retrieved 2022-03-12.