Tree-sitter Grammar for Emacs Lisp

A simple tree-sitter grammar for elisp.

Syntax supported:

• Atoms (integers, floats, strings, characters, symbols)
• Lists (normal syntax (a b) and dotted (a . b))
• Vectors
• Quoting and unquoting (', #', `, ,, ,@)
• Some special read syntax ($#, ##, #("foo" 1 2 x))
• Bytecode literals (#[1 2 3 4])
• Special forms (let etc)
• Comments

Currently unsupported:

• Autoload cookies
• Definitions (e.g. defun, defvar, defmacro)

Limitations

Elisp is a lisp-2 with user-defined macros. A simple parser cannot detect if e.g. (foo (let ...)) is a function call with a let expression argument, or a macro call where let means something else.

Currently tree-sitter-elisp treats everything as an s-expression. This is accurate, but makes this package less useful for generating a summary of file contents, or for syntax highlighting.

Emacs itself has more information that it can use. Emacs will highlight macro calls based on which macros are defined in the current instance. Some elisp packages also offer custom highlighting logic, such as dash-fontify-mode in dash.el.

Developing

Check out the repo, then use npm to install dependencies.

$ npm install

You can then parse your favourite elisp files.

$ npm run parse ~/.emacs.d/init.el

The grammar itself is in grammar.js. You'll need to regenerate the code after editing the grammar.

$ npm run generate

This project also contains a few tests.

$ npm test

You can also run this parser against your .emacs.d to confirm it can parse everything.

$ npm run parse -- '/home/wilfred/.emacs.d/**/*.el' --quiet --stat

Why?

The best place to read and write elisp is of course Emacs.

However, there is a growing ecosystem of tools built on top of tree-sitter, such as GitHub. This project should allow them to support emacs lisp too.

Related Projects

tree-sitter-clojure is another tree-sitter package for the lisp family. It's a useful project to compare with, and has notes discussing lisp-specific challenges.

language-emacs-lisp is a textmate grammar for elisp that's used for Atom and GitHub.