Why LuvvieScript?

The rise of DevOps and Continuous Delivery as state-of-the-art development approaches is driving low-impedance programming, where small teams of developers are able to take end-to-end changes and incrementally deliver them into production, because the number of language/skills layers in the stack has been dramatically reduced.

Most low-impedance stacks are binary stacks with Javascript or CoffeeScript in the browser and some server-side language on the back - but there are a couple of uni-stacks:

  • NodeJs
  • ClojureScript & Clojure

The mission is to make LuvvieScript & Erlang/OTP a low-impedance environment for developing web apps.

What Is LuvvieScript?

LuvvieScript is defined by its mission. LuvvieScript is:

  • a dom scripting language in the style of OTP Servers
  • a strict sub-set of Erlang capable of running client and server side

LuvvieScript is not:

  • a general purpose language
  • an implementation of the Erlang VM in the browser

The reason LuvvieScript does not aspire to be Erlang VM In The Browser follows from the very different operating environments client- and server-side.

Client Side Operating Environment

The client-side of a web application has the following characteristics:

  • low concurrency (approx 9 units of concurrency)
  • heavy-weight concurrency by Web Workers
  • no shared code between concurrent processes
  • code change by page refresh
  • little supervision
  • restart in the hands of the user not the programmer

Server-Side Operating Environment

The server-side operating environment has the following characteristics:

  • high concurrency (tens of thousands of concurrent processes)
  • light weight concurrency by Erlang processes
  • shared code via the Erlang VM and code loader
  • hot swapping and code management
  • OTP supervision and restart

The LuvvieScript Run-Time Environment

The working design for the LuvvieScript run-time is shown below: LuvvieScript Schematic

Different components of this view can be described as -alities - things that are specific to a particular application (the functionality of it) and -ilities attributes that are held in common across all applications. In normal Erlang development the VM, Erlang/OTP Supervision and server behaviours provide the -iliites (reliability, scalability, performability etc, etc) whereas the programmer delivers the -alities by writing (mostly) gen_server workers.

The LuvvieScript programmer writes the dom_servers that manipulate the models of the webpage as shown below: LuvvieScript Web Page Model Schematic

The intention is that the front end developer will write gen_server like code, all calls and casts:

handle_call(Msg, From, State) ->
    {NewState, SideEffects} = manipulate_state(Msg, State),
    NewState2 = handle_side_effects(SideEffects, State),
    Reply = `whatevs`,
    {reply, Reply, NewState2};

The messages themselves will normalise events:


The models that are programmed will operate on recursive records something like:

-record(tag, {
              type                      :: html()| pseudo_html(),
              id            = get_id()  :: opaque(),
              class         = []        :: [strings()],
              subscriptions = []        :: [dom_events()| pseudo_events()],
              attrs         = []        :: list(),
              inner         = []        :: [#tag{}]

The other components provide all the -ilities:

  • reliability
  • cross-browser compatibility
  • cachability
  • etc, etc

These are shown below: LuvvieScript Run Time Schematic

The Mailbox And VM is runs the inter-process mailbox. The actual job of rendering the page is handed off to the page rendering code. The intention is that the majority of the code in this part will be well tested Javascript libraries with a message passing wrapper.

The browser will not be considered part of the server-side cluster - but rather something more loosely connected - you could think of it as a bit like a C Port - you can communicate with it by sending and receiving messages as if it were a full node - but you can’t do RPC calls to it. There will be a server side cowboy handler implemented as part of LuvvieScript

The run-time will be configured using Erlang attributes. An Erlang module has only three components:

  • a mandatory module definition
  • a set of attributes
  • function definitions (or forms)

Erlang attributes are not strictly defined - there is a normal set of attributes that play conventional roles in different parts of the normal software cycle:

define    Macros                  Pre-compile Expansion
include                           Pre-compile Expansion

record   Syntactic Sugar          Compile Time
export                            Compile Time
spec      Limited Type Checking   Compile Time
type      Limited Type Checking   Compile Time

spec      Full Type Checking      Dialyzer
type      Full Type Checking      Dialyzer

author                            Run Time Tool Support
vsn                               Run Time Tool Support
date                              Run Time Tool Support

We will simply stuff all our run-time and configuration needs into a new set of attributes, something like this:

-dialect({luvviescript, {version, 1}}).
-require({javascript, [_underscore, jquery]}).
-require({luvviescript, [lists, sets]}).

Needless to say, all of this is subject to actual implementation.

Let me know what you think on Twitter.

If you have read this far you should follow @LuvvieScript or @gordonguthrie on Twitter.

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