Abstract the data path

[ctford]

In the example you presented at ClojureX, knowledge of the core.async channel and the location of the counter's state leaked into the messages and view.

I've refactored this example to remove that coupling. handle-with! is a piece of generic machinery that uses an fmap function and a view function to wire up a component to where to find its state in the overall model. This could easily be pushed into Petrol's core, and possibly replace send!.

You could easily write helpers that would construct fmap and view from a path, though it's not necessary that they use a path at all - you might want to e.g. use a model containing seconds with a component that expects minutes.

This may or may not match your plans for Petrol, but I thought it would be fun to use lens functions to make the wiring up simpler.

[ctford]

Thinking about it, handle-with! could also be written in terms of get and set, rather than update. Might make it simpler to grok?

And if you rolled it into core, you could keep ui-channel private.