sx - symbolic expressions

Sx is a collection of libraries and frameworks to work with s-expressions.

See for more information on its project page.

Types

Sx support the following atomic, immutable types:

• Numbers contain numeric values. Currently, only integer values are supported. There is no maximum or minimum integer value. They optionally start with a + or - sign and contain only digits 0, ..., 9.
• Strings are UTF-8 encoded Unicode character sequences. They are delimited by " characters. Special characters inside the string, like the " character itself, are escaped by the \ character.
• Symbols are sequences of printable / visible Unicode characters. They are typically used to bind them to values within an environment. Another use case is symbolic computation. A symbol allows to store additional values by providing an association list (a-list), a list of pairs. Symbols can be compared for equality quite efficients, since they are interned by their associated symbol factory.

Sx supports nested lists. A list is delimited by parentheses: ( ... ). Within a list, all values are separated by space characters, including new line. Lists can be nested. Internally, lists are created by pairs. The first part of a pair, called "car", contains the actual value stored at the beginning of a list. The second part, called "cdr", typically links to the next pair. This allows multiple lists to share elements. A proper list is a list, where the last elements second part is the empty list. The last element of a list may be a pair, where the second part references a values except a list. Such lists are improper lists. Since the second part may reference any value, even earlier elements of a list, lists may be circular. Single pairs are denoted as (X . Y), where the car references S and the cdr references Y (Y is not a list).

All other types supported by Sx cannot be specified via the reader.