SLip — a Lisp system in JavaScript

Features

Update (Oct. 2025): a lot of CL features have been implemented, such that I was able to compile Closette source code almost as-is, with only trivial changes. There's still a long way to go, but this is becoming Common Lisp!

• Self-hosting compiler
• Lexical and dynamic variables
• TAGBODY/GO, THROW/CATCH, BLOCK/RETURN, UNWIND-PROTECT
• Tail call optimization
• Scheme-like first-class continuations (not to be used with unwind-protect though)
• Scheme-like named LET — useful for looping via recursion.
• Separate function/variable namespace (that might be a “misfeature”, depending how you look at it).
• Common Lisp-like symbols/package system
• Standard CL lambda keywords (&optional, &rest, &key etc), with good performance
• Multiple-values with good performance — MULTIPLE-VALUE-BIND should be as fast as LET, and returning multiple values from a function should not involve any measurable performance penalty when only the main value is expected.
• Proper setters (SETF along with the underlying machinery — DEFINE-SETF-EXPANDER etc.)
• Type system (DEFTYPE, TYPEP, TYPECASE); no SUBTYPEP for now.
• Structures (DEFSTRUCT)
• CLOS — via Closette
• Both structures and classes are integrated with the type system, but however not with themselves yet; that is, DEFSTRUCT doesn't also define a class.
• Condition system based on CLOS (HANDLER-BIND, HANDLER-CASE, IGNORE-ERRORS)
• LOOP, FORMAT and a pretty printer (incomplete but still useful)
• List and sequence functions (FIND, REMOVE-IF etc.); but sequence functions only operate on lists for now.
• A (tiny) subset of ansi-test, which was instrumental for maintaining my sanity while developing this.
• Tons of primitive functions
• A simple “foreign function interface” for writing functions in JavaScript
• Most basic datatypes are unboxed—strings, numbers, vectors, regexps—so they can be freely passed around to JavaScript functions
• Literal regexps — #/seriously/i
• Green threads with a simple scheduler
• An in-browser development environment inspired by Emacs and SLIME (based on Ymacs).

Live demo

Start hacking!