Maclisp (orMACLISP, sometimes styledMacLisp orMacLISP) is aprogramming language, adialect of the languageLisp. It originated at theMassachusetts 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 thePDP-6;^[1] Jon L. White was responsible for its later maintenance and development. The nameMaclisp began being used in the early 1970s to distinguish it from otherforks of PDP-6 Lisp, notablyBBN Lisp.

Maclisp is a descendant ofLisp 1.5.^[3] Maclisp departs from Lisp 1.5 by using avalue cell to access and store the dynamic values ofvariables;^[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 readableinput andoutput, termedinput/output (I/O). Instead of entering(QUOTE A), one could enter'A to get the sames-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 onDigital Equipment CorporationPDP-6 andPDP-10 computers running theIncompatible Timesharing System (ITS); later it was ported to all other PDP-10 operating systems, for example,Timesharing / Total Operating System,TOPS-10 andTOPS-20. The original implementation was inassembly language, but a later implementation onMultics usedPL/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 –discuss]}

Maclisp was used to implement theMacsymacomputer algebra system (CAS) or symbolic algebra program. Macsyma's development also drove several features^[which?] in Maclisp. TheSHRDLU blocks-world program was written in Maclisp, and so the language was in widespread use in theartificial intelligence (AI) research community through the early 1980s. It was also used to implement other programming languages, such asPlanner andScheme. Multics Maclisp was used to implement the first Lisp-basedEmacs.

Maclisp was an influential Lisp implementation, but is no longer maintained actively.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

Maclisp began with a small, fixed number ofdata types:cons cell, atom (later termedsymbol),integer, andfloating-point number. Later additions included:arrays, which were never first-class data types;arbitrary-precision integers (bignums);strings; andtuples. All objects (except inums) were implemented aspointers, 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 beinterpreted orcompiled. 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, generatingmachine code (instructions) for arithmetic rather than calling interpretive routines which dispatched on data type. This made Lisp arithmetic comparable in speed toFortran for scalar operations (though Fortran array and loop implementation remained much faster).

The original version was limited by the 18-bit wordmemory 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 thePDP-10 were exceeded, theLisp Machine was invented:Lisp Machine Lisp is the direct descendant of Maclisp. Several otherLisp dialects were also in use, and the need to unify the community resulted in the modernCommon Lisp language.

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

• http://www.softwarepreservation.org/projects/LISP/maclisp_family/ contains a bibliography of Maclisp.
  • John L. White. An Interim LISP User's Guide. Artificial Intelligence Memo No. 190, Project MAC, Massachusetts Institute of Technology, March 1970, 87 pages.ftp://publications.ai.mit.edu/ai-publications/pdf/AIM-190.pdf states "'MACLISP' refers to the PDP/6 implementation of the programming language LISP in use at the Artificial Intelligence Group of Project MAC."
  • "In 1973 and 1974,David A. Moon led an effort to implement MacLisp on the Honeywell 6180 under Multics. As a part of this project he wrote the first truly comprehensive reference manual for Maclisp, which became familiarly known as the 'Moonual'." [Steele and Gabriel 1993]
  • Jon L. White [JONL], Eric Rosen [ECR],Richard M. Stallman [RMS],Guy L. Steele Jr. [GLS], Howard I. Cannon [HIC], Bob Kerns [RWK]. LISP News. MacLisp release notes.
  • Jon L. White. LISP: Program is Data: A Historical Perspective on MacLISP. Proceedings of the 1977 MACSYMA Users' Conference. NASA Scientific and Technical Information Office (Washington, D.C., July 1977), pages 181–189.PDF
• McCarthy, John; Abrahams, Paul W.; Edwards, Daniel J.; Hart, Timothy P.; Levin, Michael I. (1985) [1962].LISP 1.5 Programmer's Manual (2nd ed.).MIT Press.ISBN 0-262-13011-4.
• Moon, David (1974).Maclisp Reference Manual(PDF).Archived(PDF) from the original on 2011-10-05.
• The Revised Maclisp Manual (1983) byKent Pitman
• The Multics MACLISP compiler (1977) byBernard Greenberg

• Lisp programming language family
• Lisp (programming language)
• Multics software

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