elm-vextab

This is a simple Elm 0.18 module that wraps VexTab which is a language for creating and editing musical scores. Vextab itself is an open-source javascript project and is still in a pre-alpha stage.

VexTab renders a score by side-effect. You must create a canvas tag in your web page, assign it an id and initialise the module with this id in the configuration. You can then ask it to render some VexTab text - if it is valid then the score will appear in the canvas, otherwise an error will be returned. You do not need to incorporate the canvas into your elm view.

Integrating the module

Because we are wrapping a javascript module, our only option is to use ports, and so the integration of the various pieces of javascript that go to make up a final web page have to be assembled by hand - see basic.html for an example.

The module exposes the following:

    Model, Msg(RequestRenderScore), init, update, subscriptions 

This can be imported into a main elm program using the normal conventions. It is usually sensible to initialise vextab when the program starts. For example, here we have provided a canvas with an id of vextab:

    defaultConfig : Config
    defaultConfig =
        { canvasDivId = "#vextab"
        , canvasX = 10
        , canvasY = 10
        , canvasWidth = 1200
        , scale = 0.8
        }

    init : ( Model, Cmd Msg )
    init =
        let
            ( vextabModel, vextabCmd ) =
                VexTab.init defaultConfig
        in
            { text = sampleVexText
            , vextab = vextabModel
            }
                ! [ Cmd.map VexTabMsg vextabCmd ]

The Model used by the module in fact only contains a possible error message which will be returned if the module cannot be initialised or if the text cannot be parsed.

It exposes a single message - RequestRenderScore which you use to request that sample text is rendered. There are two subscriptions:

    initialisedSub
    renderedSub

although normally there is no need to register these - instead, you may simply check for any error in the vextab model after either initialising or after requesting a score rendering.