The Folders Programming Language

Folders is an esoteric, non-textual programming language that uses directory containment and the alphabetical ordering of folder names as its sole syntax: code is a pure ordered tree rather than visible text. Conceived as a dematerialized form of code (inspired by Whitespace) it leans on the observation that on some systems folders occupy negligible or no recorded disk space - an experiment citing 352,449 folders with 0 bytes - so programs and data can be encoded entirely as nested folders. Implementations include a Windows-originating interpreter and a JavaScript emulator for other systems; an original implementation is hosted on GitHub. The project is maintained and updated (created 2015, updated 2026) by an author known for other esolangs.

Execution and data are determined by folder counts and positions: every command folder contains at least one child, the number of subfolders in the first (alphabetically earliest) child selects the command type, a second child encodes arguments, and some commands use a third. Expressions use the same count-based encoding. Temporary runtime state is held as folders whose names carry literal data, and preferred I/O is another folder tree (Folders FS), enabling programs to pass and persist information as directory structures. Programs can be visualized as nil-terminated nested lists, contour maps or branching trees; the language spec reduces to a compact mapping from child-count patterns to imperative operations.