Editing Maclisp (section)

==History==
Maclisp is a descendant of [[Lisp 1.5]].<ref>{{harvnb|Moon|1974|p=1}}</ref>  Maclisp departs from Lisp 1.5 by using a ''value cell'' to access and store the dynamic values of [[Variable (computer science)|variables]];<ref>{{harvnb|Moon|1974|p=47}}</ref> Lisp 1.5 used a linear search of an association list to determine a variable's value.<ref>Lisp 1.5 p. 13, evaluating an atom <code>e</code> in the environment <code>a</code> is done with <code>(cdr (assoc e a))</code>.  That involves a linear search of the association list <code>a</code>. 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.</ref>  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 <code>(QUOTE A)</code>, one could enter <code>'A</code> to get the same [[s-expression]]. Although both implementations put functions on the property list, Maclisp uses different syntax to define functions.<ref>Maclisp uses <code>defun</code>; Lisp 1.5 uses <code>define</code>.</ref>  Maclisp also has a load-on-demand feature.<ref>{{harvnb|Moon|1974|p=107}}; the <code>autoload</code> property.</ref>

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|date=March 2016}} were added which in other language systems would typically correspond to major release numbers.{{dubious|date=March 2016}}<!-- distinguish the langage and the library; LET, SETF, and LOOP, for example, did not change the language. Compare with UNWIND-PROTECT. -->

Maclisp was used to implement the [[Macsyma]] [[computer algebra system]] (CAS) or symbolic algebra program. Macsyma's development also drove several features{{which|date=March 2016}}<!-- BIGNUM and what else? --> 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 (programming language)|Planner]] and [[Scheme (programming language)|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 [[emulator]]s and can be used for experimenting with early AI programs.

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