The Free On-line Dictionary of Computing (30 December 2018):
A dialect of Lisp developed at MIT AI Lab in
1966, known for its efficiency and programming facilities.
MacLisp was later used by Project MAC, Mathlab and
Macsyma. It ran on the PDP-10. It introduced the LEXPR
(a function with variable arity), macros, arrays, and
MacLisp was one of two main branches of LISP (the other being
Interlisp). In 1981 Common LISP was begun in an effort to
combine the best features of both.
["MACLISP Reference Manual", D.A. Moon
, TR Project MAC, MIT 1974].