Nabab

https://clojars.org/nabab

French word nabab comes from نواب and refers to an Indian ruler within the Mogul empire.

The name of this lightweighted library stands for Not an ABstraction ABove. Its mere goal is to handle vars created by core.async and describe how data flow between channels.

Links

• Litterate source with syntactic hilighting
• Naiad or aide might better fit your needs, check it.
• GitHub repository

Rationale

core.async is simple but not easy

From Naiad:

core.async is simple but not easy. That is to say, it is possible to write simple maintainable using core.async but it is not a easy task.

core.async is great. However, when using it, I’ve always been puzzled by code organisation problem: where to keep channel Vars so they’re both simple to retrieve and reason about?

A graph is quite easy to grasp

I’ve chosen a declarative, data-oriented approach based on a graph representation of the data flow:

• A channel is pictured as a node of the graph when data reside before being processed.
• Processing functions (such as pipeline, go-loop, and pipe) are edges of this graph. In nabab they are called ::transitions.
• Most of the time a message is delivered to one channel but sometimes you need to dispatch it to several ones. This nicely fits the publisher-subscriber architecture pattern.

Because this is a graph, you can analyse it with any graph processing tool. Because a graph is visual, it’s much more easy to grasp. Because publisher-subscriber is naturally implemented atop channels in core.async, this design choice is idiomatic and doesn’t prevent you to design your architecture the way you want.

Nabab implements this representation.

Minimal working example

(def some-transition
  {:nabab/subscribed-topics #{:topic/input}
   :nabab/doc-published-topics {:topic/input #{:topic/output}}
   :nabab/pipeline-transducer (map #(-> %
                                        (update :message/content inc)
                                        (assoc :message/topic :topic/output)))})

(def minimal-graph
  {:nabab/fixed-buffer-size 2
   :nabab/dispatch-ifn :message/topic
   :nabab/transitions {:some-transition some-transition}})

Why not Naiad

Why haven’t I used Naiad?

• Writing a library is a great exercice
• It doesn’t provide visualisation capability
• It’s abstraction over core.async but I don’t want it. I just want raw core.async with a lightweight tool to make code structure simpler and more legible.