SLED: A Symbolic LISP Inspired by Scheme for DOS Environments

Introduction to SLED

SLED, or Schemy Lisp en DOS, is a new symbolic LISP implementation. It draws inspiration from Scheme and is designed for compatibility with Disk Operating System (DOS) environments, including FreeDOS, MS-DOS, and emulators like DOSBox. This project aims to provide a functional LISP for these retro computing platforms.

Core Features and Derivation

SLED is based on Kilo LISP but has been modified to remove certain features, such as macros, while enhancing others. It is classified as an Ur-Lisp, focusing on fundamental LISP principles. The implementation includes standard symbols, special forms, and built-in functions, with a detailed index available for reference.

Data Types in SLED

The two fundamental data types in SLED are Pairs and Atoms. Atoms are non-pairs and come in three variants: Symbols, Closures (functions), and Special Symbols. Symbols are unique names composed of specific character sets, with escape characters for other printable ASCII characters. Special Symbols, like 'nil', are predefined by SLED.

Pairs consist of a head and a tail, each capable of holding an atom or another pair. Pairs can be created using the '.' notation or the 'cons' built-in function. Pair elements are immutable. Lists are sequences of pairs where the last tail points to 'nil', and can be created using '()' or the 'list' function. The system also supports improper lists and association lists.

Quoting Mechanism

SLED includes a quoting mechanism to prevent evaluation of expressions. The 'quote' special form registers a symbol as data rather than code. A shorthand syntax, using the single quote character ('), is also available for convenience, allowing users to declare something as data directly.