(Originally "Muddle"). C. Reeve, Carl Hewitt and GeraldSussman, Dynamic Modeling Group, MIT ca. 1971. Intended as a

successor to Lisp, and a possible base for Planner-70.

Basically LISP 1.5 with data types and arrays. Many of its

features were advanced at the time (I/O, interrupt handling

and coroutining), and were incorporated into later LISP

dialects ("optional", "rest" and "aux" markers). In the mid

80's there was an effort to use bytecoding to make the

language portable. CLU was first implemented in MDL. Infocom

wrote Zork in MDL, and used it as the basis for the ZIL

interpreter.