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 CATCH/THROW. 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.