My biases

• big/complex UI
• heavy client
• 3d

The problem

UI Complexity

App Complexity

Solution

Sources

• Deprecating the Observer Pattern - Ingo Maier Tiark Rompf Martin Odersky
• Erik Meijer : What is means to be reactive ?
• StackOverflow : What's FRP ?

Goals

• Easy UI change
• Undo/Redo built-in
• Save/Load built-in

Concepts

• Streams & stream composition
• Events : next, error, end
• Types

My version : reactive2

• Python descriptors as stream
• document as hierarchy of stream 
• reversable events
• subsystems (IO, display, etc) communicate only via events and are peripheral

Python descriptors

myinstance.myattr=1 is translated by the interpreter as

   myinstance.__class__.myattr.__set__(myinstance, 1)

myinstance.__class__.myattr is a descriptor. And it's über cool. Because we can intercept assignment.

Reactive Python Descriptor

• react to assignment and send events when it happen
• wrap a single attribute

(in reactive2, see base.py)

The Document

• A hierarchy of objects
• with attributes wrapped by reactive descriptors
• the complete data of the app.

(in reactive2 see examples/todo.py)

The events

• only atomic operations : replace, append, insert, remove. 
• can be reversed
• can be applied to a reactive descriptor

(in reactive2 see event.py)

Subsystems

• read data from events, and translate them into domain
• may modify other part of the document.

Subsystem examples : History

• register to all wrapped attributes of the document. (tree descent)
• record N last events
• Undo/Redo is  reversing the last event, and applying it
• (psss... Save/Load is saving on disk all the events)

Subsystem examples :

3D display

• Main document has an 3d object list
• Via another subsystem, a new 3d object is added to it.
• It triggers an event that the 3d display listens to.
• The 3d display translated it into openGL/DirectX calls

Take away

• Works
• Extremist (all or nothing, architectural)
• Need thinking
• Not finished

No silver bullet

But Extremely useful

Connect !

• @LBdN
• https://bitbucket.org/lbarret/reactive2
• http://fr.linkedin.com/in/lionelbarretdenazaris