sxpf - S-Expression Framework

This is a framework to work with s-expressions. In contrast to some other implementations, there are three types of atoms: numbers, symbols and strings. Symbols are case-insensitive. A string may contain any sequence of unicode characters, using UTF-8 encoding. A number is a sequence of digits. An expression of the form (), (A), (A B), ..., is a pair list, where A and B are s-expressions. If it has the form (A . B) it is a pair.

The framework contains types, functions, and methods to create s-expressions, to encode them as a string, and to evaluate them. Evaluation creates a third atom type, which currently cannot be encoded fully in a s-expression: forms (aka functions). Forms can be special. In this case their arguments are not evaluated before calling the form.

Syntax

• ; starts a comment that lasts until end of line
• String = "CHAR*" is a sequence of characters, delimited by quotes
  • CHAR = any unicode character except from category C ("control") or an escaped character (ECHAR).
  • ECHAR a character sequence that starts with a backspace ```
    • \t = tabulator (code 9)
    • \n = new line (code 10)
    • \r = carriage return (code 13)
    • \xMN = character with code MN (hex digits)
    • \uMNOP = character with code MNOP (hex digits)
    • \UMNOPQR = character with code MNOPQR (hex digits)
    • any other character, excapt category C = the character itself, e.g. \\ = backslash, \" = quote.
• Symbol = a sequence of characters, except category C and Z ("separator"), and except ", (, ), [, ], ;, ..
• Number = a sequence of digits (0..9).
• Pair = ( Z* (s-expression (Z* s-sexpression)* (Z* . Z* s-expression)?)? Z* )
• Z = any unicode of category Z

Note

• Cyclic structures are currently not supported. Creating them will likely lead to a stack overflow when working with them.

Usage

• Zettelstore and its client library use this framework for transferring data and to help encoding some other data formats.
• My students will use it for various lectures / seminars.