Maclisp

MACLISP (or Maclisp, sometimes styled MacLisp or MacLISP) is a dialect of the Lisp programming language. It originated at MIT's Project MAC (from which it derived its prefix) in the late 1960s and was based on Lisp 1.5.Richard Greenblatt was the main developer of the original codebase for the PDP-6; Jon L. White was responsible for its later maintenance and development. The name 'Maclisp' started being used in the early 1970s to distinguish it from other forks of PDP-6 Lisp, notably BBN Lisp.

Maclisp is a descendant of Lisp 1.5. Maclisp departs from Lisp 1.5 by using a "value cell" to access and store the dynamic values of variables; Lisp 1.5 used a linear search of an association list to determine a variable's value. The Maclisp variable evaluation is faster but has different variable semantics. Maclisp also employed reader macros to make more readable input and output. Instead of entering (QUOTE A), one could enter 'A to get the same s-expression. Although both implementations put functions on the property list, Maclisp uses different syntax to define functions. Maclisp also has a load-on-demand feature.

Maclisp started on Digital Equipment Corporation PDP-6 and PDP-10 computers running the Incompatible Timesharing System (ITS); later it was ported to all other PDP-10 operating systems, for example, TOPS-10 and TOPS-20. The original implementation was in assembly language, but a later implemented on Multics used PL/I. Maclisp developed considerably in its lifetime. Major features were added which in other language systems would typically correspond to major release numbers.

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