elm-architecture

Hello there, fellow Haskeller! This library is an attempt to build an Elm-like framework in Haskell.

It uses sdl2 and sdl-ttf for rendering.

Basics

The app is built on 4 pillars. They define everything that the does, and displays.

1. Model - This defines the state of the app
2. View - This defines how the app looks for a particular instance of Model.
3. Update - This defines how the app updates itself in response to user interactions.
4. Action - This defines how an effectful(having side-effects) task can be triggered from the UI.

Flow

Types

The function that is responsible for creating and displaying your entire app is this one:

elmArchitecture :: (Eq msg, Eq model)
    => model                                    -- Initial Model
    -> (model -> App msg)                       -- The view function
    -> (msg -> model -> (model, Maybe action))  -- The update function
    -> (action -> IO msg)                       -- The action handler, for side-effects
    -> IO ()

As you can see, most of the types above are user-defined, the only exception being App.

Users familiar with Elm will also notice the similarity between the generic action type used here and Cmd type used in Elm. My main rationale for not following the Elm way here is the difference between a browser app and an actual app.

Browser applications are restricted in many ways, for example, writing to a file on the user's system. Haskell applications, on the other hand, are not restricted, Haskell being a full fledged programming language. Actions can be thought of as analogous to subscriptions.

TODO

• Implement border width (make sure font doesn't override border, change the cropping rectangle)
• Add documentation for view types, including App.
• Add documentation for examples, inside examples directory.
• Add more rendering capabilities (scrolling etc).
• Make action handling async.
• Add a font cache.
• Make all data types strict.
• Add as a library to Hackage/Stackage.