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    Scheme based powerful lisp interpreter written in JavaScript
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    LIPS - Scheme Based Powerful Lisp Language

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    LIPS is a powerful Scheme-based, Lisp language written in JavaScript. It is based on the Scheme dialect and the R5RS/R7RS specifications. It has extensions to make it easier to interact with JavaScript. It work both in the browser and with Node.js.

    The name is a recursive acronym which stands for LIPS Is Pretty Simple.


    Web REPL Demo


    • Literal regular expression.
    • Asynchronous execution (auto resolving of promises).
    • Possibility to add new syntax (similar to vectors and object).
    • Numerical tower and Big Integer support.
    • Powerful introspection.
    • Great integration with JavaScript.
    • Auto formatting lisp of code (pretty print)
    • Lisp and hygienic Scheme macros and macroexpand.
    • Builtin help system.


    To install you can use npm (or yarn)
    NOTE: The version that is on NPM is heavily outdated, use beta version:

    npm install @jcubic/lips@beta

    or yarn:

    yarn add @jcubic/lips@beta

    then include the file in the script tag. You can grab the version from

    or from jsDelivr (that's seems a bit faster)

    Bookmarklet REPL

    You can also run the REPL on any page while you learn Scheme using the bookmarklet:

    Create any link in your bookmarks, edit it and copy paste the content of that file. Affter you click on the link it will create the REPL at the bottom of the page. (NOTE: It may not work on every page because of content security policy; e.g. or

    If you have trouble with creating the bookmarklet you can open LISP Scheme home page where you can find a link that you can drag to your bookmarks.


    The simplest way is to include the lips code in the script tag:

    <script type="text/x-scheme" bootstrap>
    (let ((what "world")
          (greet "hello"))
       (display (string-append greet " " what)))

    or use the src attribute:

    <script type="text/x-scheme" bootstrap src="example.scm"></script>

    Bootstrapping Scheme system

    Big part of LIPS is written in LIPS itself, but to use full power of LIPS you need to load those additional Scheme files. The easiest way is to add bootstrap attribute on first script tag with text/x-scheme type. By default it will use CDN from jsdelivr. To load each file using builtin load function (that will fetch the file using AJAX and evaluate it).

    <script src="" bootstrap></script>

    You can also specify the path where LIPS should search for standard library.

    <script src=""

    You can use bootstrap="./std.xcb" if there is std.xcb file in local directory. You can also bootstrap with std.scm or std.min.scm but xcb file is the fastest, because it's already parsed and compiled into binary format.

    Running LIPS programmatically

    var {exec} = require('@jcubic/lips'); // node
    // or
    var {exec} = lips; // browser
    exec(string).then(function(results) {
         results.forEach(function(result) {

    When running exec you will also need to bootstrap the language and loaded files from /lib/ directory.

    Documentation about beta version can be found in Wiki.

    Standalone executable

    NOTE: Executable don't require bootstrapping lib files.

    If you install lips globally with:

    npm install -g @jcubic/lips@beta

    you can run the interpreter from the terminal:

    LIPS: Scheme interactive terminal

    You can also run code in a string with:

    lips -c '(let ((what "World")) (display (string-append "Hello " what)))'

    and you can run a file using:

    cat > foo.scm <<EOF
    (let ((what "World"))
      (display (string-append "Hello " what))
    lips foo.scm

    You can also write executable files that use lips using shebang (SRFI-22)

    cat foo.scm
    #!/usr/bin/env lips
    (let ((what "World"))
      (display (string-append "Hello " what))
    chmod a+x foo.scm

    Executables also return a S-Expression according to SRFI-176 use lips --version or lips -V.

    FOSDEM'23 Presentation [Video]

    FOSDEM 2023 - LIPS Scheme: Powerful introspection and extensibility


    Because LIPS is tree walking interpreter sometimes it may be slow. Especially if you want to process long arrays and use callback function. If the array is quite large each pice of code inside the callback may slow down the processing. For example see:

    script reference.scm

    That generates reference documentation for all builtin functions and macros. The slow part is (names.sort name-compare) (Array::sort) that take quite time to calculate, because the array with functions and macros is quite large. If you came into performance issue, you can write the part of the code in JavaScript. If you want to do this in LIPS Scheme you can use something like this:

    (let ((fn (self.eval "(function(a, b) {
                             /* any complex code in JS */
                             return a.localeCompare(b);
       (arr.sort fn))

    Another example of slow performace is using LIPS with React, the more code you put into components the slower the app will become.


    The issue with performance is tracked in #197.

    Supported SRFI


    description spec
    Feature-based conditional expansion construct SRFI-0
    Homogeneous numeric vector datatypes SRFI-4
    Basic String Ports SRFI-6
    Running Scheme Scripts on Unix SRFI-22
    Error reporting mechanism SRFI-23
    Basic Syntax-rules Extensions SRFI-46
    Version flag SRFI-176

    require (load "./lib/srfi/<number>.scm")

    They should be loaded as R7RS libraries in final 1.0.0 version

    description spec
    List Library SRFI-1
    AND-LET*: an AND with local bindings, a guarded LET* special form SRFI-2
    receive: Binding to multiple values SRFI-8
    #, external form SRFI-10
    Notation for Specializing Parameters without Currying SRFI-26
    Basic hash tables SRFI-69
    An interface to access environment variables SRFI-98
    Boxes SRFI-111
    Syntactic combiners for binary predicates SRFI-156



    • [x] Full support for R5RS
    • [ ] Full support for R7RS
      • [ ] R7RS libraries (import/export/define-library).
      • [ ] Continuations.
      • [ ] Tail Call Optimization (TCO).
      • [ ] Fully tested Numerical Tower.
    • [x] Fully working binary compiler (for faster parsing and loading std lib).
    • [ ] Finish syntax-rules (ignore limitations of current approach).
      • [ ] Objects.
      • [ ] Vectors.


    • [ ] Picture language (possibly inspired by P5.js).
    • [ ] Stepper/Debugger.
    • [ ] Allow to use read/port in syntax extensions (similar to CL reader macros).
    • [ ] Proper expansion time for both macro system.
    • [ ] Fully working and tested R7RS hygienic Macros (syntax-rules).
    • [ ] All recursive function in JS don't consume stack.

    WIP Side projects

    • [ ] KISS (chrome extension REPL).
    • [ ] SMILE (Web IDE), need to start over.



    Released under MIT license
    Copyright (c) 2018-2021 Jakub T. Jankiewicz

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