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Pavel Kaygorodov <>


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A Common Lisp library to build fully dynamic web interfaces

The main idea of this library is to vanish a border between frontend and backend as much as possible. You can develop a CL application using REPL and SLIME on a backend, but some of you functions and macros can be declared as browser-side (b-s) with defun-f and defmacro-f respectively:

(require :omg)
(defpackage mytest (:use cl omg))
(in-package :mytest)
(defun-f js-add (x y)
  (+ x y)) ;; this code will be executed in a browser

The (start-server) function starts clack web server on default port 7500 (can be changed by setting omg::*port* variable). Now, in the html-code you can inject the following line:

<script src='http://localhost:7500/j' type='text/javascript'></script>

or just open a page http://localhost:7500/ (a blank page with js-injection code).

Now you call a browser-side function, just executing it in REPL, for example:

MYTEST> (js-add 1 2)
;; (3)

The function call will be converted to javascript with JSCL and sent to the browser via websocket, where the code will be executed and result will be returned to the backend. The result in this example will be returned as a list, because we are not specified a session (see below) and the code will be executed in all connected browsers, and the list of result values will be returned.

The more complicated example you can find in in example.lisp file, where omgui package is used to manipulate DOM objects.

OMGUI package

OMG package is all-sufficient and can be used as is to control a frontend. You can execute any JS code on the browser-side using JSCL FFI:

(defun-f jslog (&rest args) ;; call console.log(...args)
  "Log function for js"
  (apply (jscl::oget (jscl::%js-vref "console") "log") args)

But many of useful JS and DOM-manipulating functions are provided by omgui package, where you can find the following functions:

  • (create-element type ...attrs) - create and return a DOM element (like document.createElement()). You can provide attributes in JS notation. For example:

    (create-element "div" :|innerHTML| "Some text" :|style.fontWeight| "lighter")
  • (append-element element &optional parent) - append DOM element as a child to the parent. If the parent is omitted, the element will be appended to document.

  • (check-element ID) - check if DOM element with ID exists.

  • (remove-element element) - remove element from DOM.

  • (element-width) (element-height) - return element dimensions in pixels.

  • (get-element-id element) - return DOM ID of the element. If the element has no ID, a random ID will be created and assigned to it.

  • (js-get-element-by-id ID) - get DOM element by ID

  • (parent-element element) returns a parent of DOM element

  • (page-width) (page-height) (visible-width) (visible-height) (visible-left) (visible-top) - get browser page dimensions.

  • (execute-after time callback) - execute the (callback) after time, where time specified in seconds.

  • (jsfloor num) (jsmax ...nums) (jsmin ...nums) (jsrandom) (jssin) (jscos) - JS Math functions Math.floor(), Math.max(), Math.min(), Math.random(), Math.sin() and Math.cos().

  • (jslog ...args) - wrapper for console.log()

  • (prevent-page-close) (allow-page-close) - prevent and allow page closing.

  • (disable-back-button) (enable-back-button) - disable/enable "back" button in browser.

  • (disable-scroll) (enable-scroll) - disable/enable page scroll.

  • (make-js-object :attr1 value1 attr2 value2 ...) - return a JS dict object with specefied keys and values.

  • (make-js-function name lambda) - create an JS function from lambda which can be accesssed via

  • (load-js-script url &optional callback) - load JS script from url. The optional callback lambda will be executed then the script is succesfully loaded.

  • (register-hash-cb hash cb) - register a callback to call when URL hash part changes. With this function you can, for example, automatically mark session as debug one, when you open URL like http://localhost:7500/#debug:

    (defun-r debug-me ()
      (set-debug-session (current-session-id)))
    (defun-r my-boot ()
      (register-hash-cb "#debug" (lambda () (debug-me))))
    (add-to-boot '(my-boot))

    If the page is loaded with the registered hash part, the callback will be executed immediately during register-hash-cb call.

Creating SVG elements

You can create SVG elements with make-svg function. The function accepts parameter pairs like :|attributename| value for attributes and (tag-name ...attributes and subtags) for inner elements. For exanple, the following code will return SVG-object with circle:

(make-svg :|viewBox| "0 0 100 100"
          '(circle :|cx| 50 :|cy| 50 :|r| 50 :|fill| "red"))

The following function returns animated spinner:

(defun-f make-spinner ()
  (let* ((width 20)
         (ncirc 10)
         (r (/ width 2))
         (rc (/ width 6)))
    (apply #'make-svg
           `(:|viewBox| ,(format nil "0 0 ~A ~A" width width)
             ,@(loop for i below ncirc
                     for ang = (* i (/ (* 2 pi) ncirc))
                 `(circle :|cx| ,(+ r (* (- r rc) (jscos ang)))
                          :|cy| ,(+ r (* -1 (- r rc) (jssin ang)))
                          :|r| 0
                          :|fill| "#505050"
                          (animate :|attributeName| "r"
                                   :|from| ,rc
                                   :|to| ,(* rc (/ 3 (+ ncirc 2)))
                                   :|begin| ,(format nil "~As" (/ (- ncirc i 1) ncirc))
                                   :|dur| "1s"
                                   :|repeatCount| "indefinite")
                          (animate :|attributeName| "fill-opacity"
                                   :|from| 1
                                   :|to| 0
                                   :|begin| ,(format nil "~As" (/ (- ncirc i 1) ncirc))
                                   :|dur| "1s"
                                   :|repeatCount| "indefinite")))))))

Modal dialogs

You can display modal dialog in the browser using the modal-dialog macro:

  (print (modal-dialog "Dialog header"
                       "Dialog text"))
                       :lines (list :line1 "field 1"
                                    :line2 "field 2"
                                    :buttons (list (list "OK" #'dialog-ok)
                                                   (list "Cancel" #'close-current-dialog))))
;; ((:line1 "Text in the line 1"))
    (:line2 "Text in the line 2")

This code will display a modal dialog in debug session and print the result, returned as a plist or nil if the Cancel button was pressed.

You can provide validation functions for input lines in the form ... :line1 (list "field1" #'func), where #'func can be a browser-side or RPC function. Also you can provide (lambda (s) ...) as a validator function, and even a #'any-backend-function but you will get a security warning in last case. The function must accept a string as an argument and return an (optionally) modified string which will replace the string in the input field. See the example.lisp.

You callbacks can use the following supplementary functions:

  • (close-current-dialog) - close current modal dialog, modal-dialog will return nil.

  • (dialog-ok) - close current modal dialog, modal-dialog will return data entered in fields.

  • (get-dialog-data) - returns plist with dialog data, can be called anytime on frontend or backend.

Yotube player

  • (add-youtube-player element &key onready onstatechange onqualitychange onratechange onerror onapichange width height video-id) - add YouTube player on the page. The video-id is a string with YouTube video ID; element must be parent element for the player; width and height -- player dimensions; onready, onstatechange, onqualitychange, onratechange, onerror and onapichange - the callbacks. See the example.lisp.


  • All browser-side functions must be declared in your own package(s), not in CL-USER. See How it works for details.

  • The library tested in SBCL, but may work in other CL impementations too. The browser code will be executed in JSCL environment, where not all of the standard CL library functions are implemented yet, so you have to respect JCSL limitations on browser-side.

  • All the function parameters and their results must be serializable via standard LISP reader/writer, so you cannot return, for example, DOM object from browser-side function to backend, and put a hash-table as a parameter to browser-side function when calling it on backend. But you can use any allowed data types while you are still on backend or browser-side, if a b-s function will be called only by another b-s functions it can return DOM objects. Also, you can pass a lambdas as arguments of b-s functions, they will be compiled and executed on browser-side. The backend functions can be passed as parameter to bs-functions, they will work on the backend, while called on brower-side, but you will get a security warning during compilation.

  • Lists can be passed as parameters to b-s functions, but they must be implicitly constructed with LIST function, quotes and backquotes cannot be used:

    (some-bs-function (list a b c)) ;; will work
    (some-bs-function '(a b c)) ;; will not work

    This is because the CL macros cannot distinct function calls and lists, constructed by quotation and quasiquotations. The second line will be threated as (some-bs-function (a b c)).

  • CLOS on browser-side is not implemented yet. And there may be some fundamental difficulties to implement it (see How it works section).

  • There is no error propagation yet between browser and backend. If bs-function causes a error, nil will be returned.

How it works

There are the following macros to define browser-side functions, macros and variables:

  • defun-f
  • defmacro-f
  • defvar-f
  • defparameter-f

Also you can define RPC-functions, with

  • defun-r

Browser-side functions

defun-f has similar syntax as a defun, but defines macro with the same name, instead of function. The macro has to check its arguments and evaluate only some of them on backend, passing the rest to the browser-side as is. For example:

(some-bs-function "value1" ;; will be passed as is
                  (some-backend-function) ;; will be evaluated on backend and the result will be passed as a parameter
                  (another-bs-function) ;; will be passed as is and evaluated on browser-side
                  #'another-bs-function ;; will be passed as is
                  (lambda (x) (+ x 1)) ;; will be passed as is and evaluated on browser-side
                  #'another-backend-function) ;; will be automatically converted to RPC-call, security warning will be printed

Just after websocket connection, the browser-side has no declared symbols and functions. When you trying to execute (some-bs-function) the symbol some-bs-function will be undeclared (in browser) and the library will ask backend for the symbol via synchronous XHR query and will get it as an already compiled to JS code. You can change this behavior by setting the omg::*local-compile* variable to nil, after that the CL code will be sent as is and compiled in browser before execution. This can provide a bit more compatibility, but code compilation will be much slower. The omg::*local-compile* may be changed on-the-fly without browser page reloading.

The library determines which symbols must be fetched from backend just by their packages: if the package still not exists, it will be created on-the-fly with defpackage, cl and jscl packages will be used. All created packages will be marked as remote and the library will try to fetch unknown symbols from that packages from the backend. This is the reason, why you cannot define browser-side functions just in CL-USER.

The CLOS is not implemented in browser-side. It is implemented in JSCL, but I see no way to catch access to undefined methods if several methods are defined with same names. If you are know how to implement this - tell me :)

Browser-side macros

Browser-side macros are called while code is compiled to JS and must be evaluated on the browser side. So, if you are use such macros while the omg::*local-compile* is set to T (by default), JSCL will parse the code and execute code of each macro in the browser, get the results and finish the compilation using them. This means that while local compilation is enabled, macro expansion will be rather expensive, especially, if you are using recursive macros.

Browser-side variables and parameters

You can declare browser-side variables and parameters with defvar-f and defparameter-f. They a similar to standard defvar and defparameter, but the symbols will be available to browser-side functions. This is one-way availability: if the variable will be changed on browser-side, backend will see no update, also, the data will not be updated on other connected browsers. If you are changing such variable or parameter on the backend, the changes will be seen only for newly connected browsers or by browser, which are not fetched they yet.

RPC functions

Due to security reasons, you can call only some specially marked functions of backend from browser side. You can declare them with defun-r macro, which acts as standard defun, but places the function name in the list of allowed RPC functions. The RPC function can be simply called on browser-side as any other function.

Also, you can asynchronously call any RPC function using async-bind macro:

(async-bind (res (some-rpc-function arg1 arg2))
  (jslog res) ;; The code will be executed asynchronously after RPC call completion


Each connected browser starts a new session which is determined by unique random symbol - session ID. When RPC-function is called from browser-side, it will be executed in the session context, so, it will execute all bs-functions in the specific browser. You can implicitly set the current session by executing a code inside with-session macro:

(with-session (find-session 'ASDXCASA) ;; find a session object by ID
  (some-bs-function)) ;; will be called in session 'ASDXCASA

If you are executing bs-function without session, it will be executed in ALL connected browsers and a list of results will be returned.

The library provides some other utility functions to work with sessions:

  • (set-debug-session session) - execute this function to mark specific session as debug.
  • (in-debug-session code) - execute a code in the debug session. If there are no active debug session a warning will be printed and code will not executed.

Boot functions

Just after connection, the some boot code will be executed in browser. You can control this using the following functions:

  • (add-to-boot code) - add some code to boot sequence. This function can be called more then once to to codes which will be executed sequentally in the order of addition. The code must be a lisp form, for _example:

    (add-to-boot '(jslog "Hi!")) ;; print "Hi!" to JS console.

    If you want to execute some backend code, use RPC call:

    (defun-r my-boot ()
      (print "New browser is connected!")
      (set-debug-session (current-session-id))) ;; Mark the session as debug
    (add-to-boot '(my-boot))
  • (rm-from-boot code) - remove code from boot sequence.

REMOTE-EXEC function

You can use (remote-exec cmd [nowait]) function to execute any CL code cmd in the browser. This function has optional argument nowait - set it to T if you are not needed to return value(s) and the function will return nil immediately.

Adding a custom HTML into default document body

The default HTML page returned for "/" just contains the main js script link, but you can add any extra HTML into document body, for example to display "Loading..." message:

 (add-to-root-html "<span id='loadBanner'>The page is loading, please wait...</span>")
 (add-to-boot '(remove-element (js-get-element-by-id "loadBanner")))

Dependencies (4)

  • bordeaux-threads
  • clack
  • trivial-utf-8
  • websocket-driver

Dependents (0)

    • GitHub
    • Quicklisp