LISP 1.5 Programmer's Manual

The LISP language is designed primarily for symbolic data processing used
for symbolic calculations in differential and integral calculus, electrical circuit
theory, mathematical logic, game playing, and other fields of artificial
intelligence.The manual describes LISP, a formal mathematical language. LISP differs
from most programming languages in three important ways. The first way is in the
nature of the data. In the LISP language, all data are in the form of symbolic
expressions usually referred to as S-expressions, of indefinite length, and which
have a branching tree-type of structure, so that significant subexpressions can be
readily isolated. In the LISP system, the bulk of the available memory is used for
storing S-expressions in the form of list structures. The second distinction is that
the LISP language is the source language itself which specifies in what way the
S-expressions are to be processed. Third, LISP can interpret and execute programs
written in the form of S-expressions. Thus, like machine language, and unlike most
other high level languages, it can be used to generate programs for further
executions.