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Write on Lisp. Compile to Javascript. Can guess thoughts and generate missed code.

(: MetaJS)

Write on lisp. Compile to pure javascript without runtime dependencies. Enjoy compiler that can guess your thoughts and generate intentionally missed parts of code.

Knowledge-oriented programming language

MetaJS is yet another attempt to create better programming language for modern world. More about MetaJS background, why it was chosen Lisp-syntax and why it's compiled to Javascript, you can find on Project Coect aims to replace outdated Email and XMPP with modern universal communication protocol.

MetaJS for Coect plays the same role as Emacs Lisp for Emacs. MetaJS is written in MetaJS and can recompile itself. Look at the interactive MetaJS-documentation where you can try MetaJS without leaving your browser.

Knowledge-oriented programming as opposed to object-oriented or functional one gives main priority to semantic models of the program instead of building blocks of the program (objects or functions). Each semantic model (in the form that compiler can understand) is called logos.

You can find more information about semantic code transformations, examples of symbolic and entitative MetaJS to JavaScipt transformations in the metajs_semantic_code_transformations.pdf. Please look also at the high-level MetaJS language overview metajs_lisp.pdf.

Seamless integration with Javascript

MetaJS is compiled to Javascript code without runtime dependencies and don't use own datastructures (like for example ClojureScript does). MetaJS uses native Javascript's arrays as lists and so can perform in any Javascript environment without unnecessary overhead. JSON documents are valid MetaJS documents and so can be included with usual include. MetaJS tries to generate beautiful javascript code that passes JSHint without warnings. The generated code is compatible with EcmaScript5. For legacy browsers like IE8 it should be used es5-shim or other polyfill.

MetaJS is implemented in MetaJS and you can extend language easily by adding new macros. For example, to add support of yield keyword introduced in Javascript 1.7 just create a macro like:

(defmacro yield (x)
  `(js "yield %" ~x))

Feature highlights

MetaJS supports destructuring across all forms that accept name-value bindings:

(def actors ["Neo" "Trinity" "Morpheus"]
     [neo trinity morpheus] actors)
(let digits [1 2 3]
     [one two three] digits
  (set [one two three] digits))

Forms can be chained with well-known -> macro. For chaining methods calls often used in javascript libraries like jQuery or D3 there is also special syntax based on method hooks. For example let's look at following code-sample from D3 homepage:

    .delay(function(d, i) { return i * 10; })
    .attr("r", function(d) { return Math.sqrt(* scale); });

and rewrite it in MetaJS using hooks and short anonymous functions:

(d3 .selectAll "circle" .transition
    .duration 750
    .delay #(* %2 10)
    .attr "r" #(Math.sqrt (* %1 scale)))

To define a macro you can use standard Lisp syntax-quote, unquote and unquote-splicing:

(defmacro when (x & code)
  `(if ~x (do ~@code)))

Functions can have optional parameters and parameters with default values. Each parameter can be passed positionally or as keyword. In addition function can accept variable number of parameters that are accessible as list. Shortly syntax for keyword-only function parameters will be finalised.

;; 'a' is required, 'b' is required and associated with an entity 'Thing'
;; 'c' is optional, 'd' is optional and has default value 2, 'more' holds rest positional parameters
(defn demo-fn (a b:Thing c:? d:2 & more)
 (log a b c d more))
;; an example of the function call
(demo-fn "Just A" "noumenon" c:42)

You can embed variables inside interpolated strings that are started with #. Inside such strings $symbol is replaced with symbol's value and $=var replaced with pair name=value. For escaping $ itself use $$.

(= #"Hello, $nickname!" (str "Hello, " nickname "!"))

MetaJS is under active development. In the nearest plans is to finish javascript source maps support and explicit semantic code transformations. Then add namespaces and integrate support of Browserify. You can see full list of planned changes and offer your own.

How to install and try MetaJS

Firstly, please install Node.js.

If you want to install latest development version of MetaJS:

$ git clone
cd ./metajs
$ npm install
$ npm link .

If you don't plan to rebuild MetaJS and just want to try it:

$ npm install -g metajs

You have just installed MetaJS and become qualified for a MetaJS-developer T-shirt. It's time to dive into MetaJS:

$ metajs -x test/index.mjs # run MetaJS test suite
$ metajs --lint test/index.mjs # check unit tests for errors
$ metajs --lint --lint-log-level=1 test/index.mjs # show only Lint errors, hide warnings and hints
$ metajs # start TEPL (Translate Eval Print Loop)
$ metajs src/cli.mjs  # compile single file to stdout
$ metajs test/def.mjs test/hook.mjs --output ./ # compile 2 files to the working directory
$ metajs -e "(+ 2 2)" # advanced calculator
$ metajs --help # print help to stdout
$ make # rebuild MetaJS compiler and run test suite

If you use Emacs you will enjoy MetaJS-support for flymake mode. The simplest method is to use my fork of flymake, however you can also extend standard flymake with MetaJS support (use this changeset as a hint). With flymake you will receive MetaJS feedback in real-time mode during edithing the code.

How to get involved or learn more

Add any bugs or feature requests to the issues page. Follow @meta_js or d0gada on Twitter to receive latest metajs news. Like MetaJS page on Facebook. Join our mailing list. Please visit to find more docs and examples.

MetaJS allows compiler to generate source code. Will a computer create programs instead of a human?

The compiler will execute the instructions exactly as before, but in addition to grammar instructions, it will also execute semantic instructions defined specifically for your program.

Imagine that you're explaining how does your program work to a grandmother who knows nothing about programming — it's an old grammar compiler. Now imagine that you're explaining the same thing to a girl with a degree in computer science — it's a new semantic compiler. But you will have to explain it in both cases.