ParadigmsMulti-paradigm: functional, procedural, reflective, meta
Designed byRichard Greenblatt
Jon L. White
DeveloperMIT: Project MAC
First appearedJuly 1966; 57 years ago (1966-07)
Typing disciplinedynamic, strong
Implementation languageAssembly language, PL/I
PlatformPDP-6, PDP-10
OSIncompatible Timesharing System, TOPS-10, TOPS-20, Multics
Filename extensions.lisp, .fasl
Influenced by
Lisp 1.5
Common Lisp

Maclisp (or MACLISP, sometimes styled MacLisp or MacLISP) is a programming language, a dialect of the language Lisp. It originated at the Massachusetts Institute of Technology's (MIT) Project MAC[1] (from which it derived its prefix) in the late 1960s and was based on Lisp 1.5.[2] Richard Greenblatt was the main developer of the original codebase for the PDP-6;[1] Jon L. White was responsible for its later maintenance and development. The name Maclisp began 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.[3] Maclisp departs from Lisp 1.5 by using a value cell to access and store the dynamic values of variables;[4] Lisp 1.5 used a linear search of an association list to determine a variable's value.[5] The Maclisp variable evaluation is faster but has different variable semantics. Maclisp also employed reader macros to make more readable input and output, termed input/output (I/O). 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.[6] Maclisp also has a load-on-demand feature.[7]

Maclisp began 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, Timesharing / Total Operating System, TOPS-10 and TOPS-20. The original implementation was in assembly language, but a later implementation on Multics used PL/I. Maclisp developed considerably in its lifetime. Major features[which?] were added which in other language systems would typically correspond to major release numbers.[dubious ]

Maclisp was used to implement the Macsyma computer algebra system (CAS) or symbolic algebra program. Macsyma's development also drove several features[which?] in Maclisp. The SHRDLU blocks-world program was written in Maclisp, and so the language was in widespread use in the artificial intelligence (AI) research community through the early 1980s. It was also used to implement other programming languages, such as Planner and Scheme. Multics Maclisp was used to implement the first Lisp-based Emacs.

Maclisp was an influential Lisp implementation, but is no longer maintained actively. It now runs on PDP-10 emulators and can be used for experimenting with early AI programs.

1958 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020
 LISP 1, 1.5, LISP 2(abandoned)
 Lisp Machine Lisp
 Scheme  R5RS  R6RS  R7RS small
 ZIL (Zork Implementation Language)
 Franz Lisp
 Common Lisp  ANSI standard
 Le Lisp
 MIT Scheme
 Chez Scheme
 Emacs Lisp
 PLT Scheme  Racket
 GNU Guile
 Visual LISP


Maclisp began with a small, fixed number of data types: cons cell, atom (later termed symbol), integer, and floating-point number. Later additions included: arrays, which were never first-class data types; arbitrary-precision integers (bignums); strings; and tuples. All objects (except inums) were implemented as pointers, and their data type was determined by the block of memory into which it pointed, with a special case for small numbers (inums).

Programs could be interpreted or compiled. Compiled behavior was the same as interpreted except that local variables were lexical by default in compiled code, unless declared SPECIAL,[8] and no error checking was done for inline operations such as CAR and CDR. The Ncomplr compiler (mid-1970s) introduced fast numeric support to Lisp languages, generating machine code (instructions) for arithmetic rather than calling interpretive routines which dispatched on data type. This made Lisp arithmetic comparable in speed to Fortran for scalar operations (though Fortran array and loop implementation remained much faster).

The original version was limited by the 18-bit word memory address of the PDP-10, and considerable effort was expended in keeping the implementation lean and simple. Multics Maclisp had a far larger address space, but was costly to use. When the memory and processing power of the PDP-10 were exceeded, the Lisp Machine was invented: Lisp Machine Lisp is the direct descendant of Maclisp. Several other Lisp dialects were also in use, and the need to unify the community resulted in the modern Common Lisp language.


Maclisp was named for Project MAC, and is unrelated to Apple's Macintosh (Mac) computer, which it predates by decades or to John McCarthy. The various Lisp systems for the Macintosh have no particular similarity to Maclisp.[9]


  1. ^ a b Levy, Steven (1984). Hackers: Heroes of the Computer Revolution. Doubleday. ISBN 0-385-19195-2.
  2. ^ Project MAC Progress Report IV: July 1966 to July 1967 (PDF) (Report). n.d. p. 19. Archived from the original (PDF) on March 8, 2016. The higher-level language used for most of the vision laboratory program is the PDP-6 LISP System. This system is based chiefly on the LISP 1.5 programming language, but has been extensively modified in a number of ways. These include many new functions and services, including facilities for linking with programs written in other languages.
  3. ^ Moon 1974, p. 1
  4. ^ Moon 1974, p. 47
  5. ^ Lisp 1.5 p. 13, evaluating an atom e in the environment a is done with (cdr (assoc e a)). That involves a linear search of the association list a. A more involved description with global constants and errors is given on p. 71; it does a linear search of the property list before searching the association list.
  6. ^ Maclisp uses defun; Lisp 1.5 uses define.
  7. ^ Moon 1974, p. 107; the autoload property.
  8. ^ Pitman, Kent (December 16, 2007). "The Revised Maclisp Manual (The Pitmanual), Sunday Morning Edition". HyperMeta, Inc. Declarations and the Compiler, Concept "Variables". Retrieved October 20, 2018. If the variable to be bound has been declared to be special, the binding is compiled as code to imitate the way the interpreter binds variables.
  9. ^ Pitman, Kent (December 16, 2007). "The Revised Maclisp Manual (The Pitmanual), Sunday Morning Edition". HyperMeta Inc. p. 1 FAQ q1. Retrieved October 20, 2018. Project MAC had nothing to do with the Apple "Mac". And neither did MACLISP.