LISP-8

This document describes DECUS LISP-8, a LISP-like list processing language developed by William Neal for the PDP-8 computer, released in December 1970. Submitted by Ernest Hayden of the Speech Communications Research Laboratory, it was designed to provide an efficient and compact system for sophisticated list processing, particularly for natural language research, addressing the space limitations of previous LISP implementations on the PDP-8.

Key features and requirements:

• Platform: PDP-8 with 4K core memory and Extended Arithmetic Element (EAE).
• Efficiency: Prioritizes efficiency and smaller memory footprint for the PDP-8 by distinguishing between program and data, making it less flexible than LISP 1.5 but more suitable for small machines.
• Interpreter: Operates via an interpreter that evaluates arguments and executes primitives or subroutines.
• Primitives: Includes a comprehensive set of built-in functions for logical operations (AND, OR, NOT, EQ, GREATP, NULL, ATOM, NUMBER), list manipulation (HD, TL, SETHD, SETTL, CONS), I/O (LISTIN, LSTOUT), control flow (PROG, IF, COND, GO, RETURN), and arithmetic (PLUS, MINUS, TIMES).
• Subroutines: Supports user-defined recursive subroutines with formal variables, similar to algorithmic languages.
• Machine Language Integration: Allows calling machine language subroutines via the MACH primitive.
• Memory Management: Detailed storage representation for lists and atoms, and includes automatic garbage collection triggered when list storage is exhausted.
• Operational Procedures: Specifies how to assemble, initialize, and run LISP-8 programs, including parameters for memory allocation and I/O routines.
• Syntactic Sugaring: Describes a method for writing LISP-like expressions directly in PAL III assembly language using custom assembler modifications for improved readability.
• User Experience: Assumes familiarity with basic list processing concepts and LISP-like languages.