Sad Path Programming using the 'with' Command in Elixir

Inspired by this video, I used the 'with' macro in Elixir to cleanly refactor some code.

The problem I was trying to solve was that on module had a handle_event function that matched on the type of the first argument

def handle_event(%Events.TitleChanged{title: title}), do: ...

But there were an increasing number of Event types. So this module was getting quite long and I wanted to split it into several modules that would each handle one group of events.

I split it into 3 sections, and made a default function for each of them return :not_handled.

def handle_event(_), do: :not_handled

Then I used  `with` (as shown below), to keep trying until I find one that handles it.

	def handle_event(persisted_event) do
	with :not_handled <- ActionFramework.handle_event(persisted_event),
	:not_handled <- Action.handle_event(persisted_event),
	:not_handled <- Comment.handle_event(persisted_event) do
	:error
	else
	_ -> :ok
	end
	end

view raw handle_event.ex hosted with ❤ by GitHub