Peter Christensen

Pedestal Lightning Talk Notes

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Tonight I gave a lightning talk about Pedestal at the San Francisco ClojureScript meetup. I’m still working through the tutorial so my understanding and experience are both limited, but this was a good chance to gather my thoughts.

Most people hadn’t worked with Pedestal so even though I’m still learning, there was a lot to share and a lot of good questions. Here are the notes I presented.

What is Pedestal?

  • Web applications, not pages
  • Designed for interactive, 2 way transfer of info to/from multiple sources
  • Framework, not Library. You put your code in the right place and Pedestal infrastructure calls it

Demo

http://www.infoq.com/presentations/pedestal-clojure, 5:32-8:00

What’s in the Box

  • Pedestal Services – for the server
  • Pedestal Applications – for the web client
  • Control flow via dataflow, messages, queues, not sequential logic
  • Easy recording/playback of messages
  • Separate concerns
    • Design without application code using a sequence of played-back messages
    • Develop client without the server using simulated backends that generated messages
    • Services and applications don’t even go in the same project

How Does It Work?

  • Application split into 3 layers:
    • Data model – data you’re holding
    • Application model – “shape” of the data in the rendered view
    • Rendered view
      • You can also cause non-rendering side effects: any side effects of changing data/application models, eg write to server, fire analytics
  • Handle inputs to update data model
  • Handle updates to data model to update application model, update downstream changes to data model, or send side-effects
  • Handle updates to application model by making targeted rendering updates
  • Queues for input, app-model, effects

Dataflow

derived-values-dataflow

Why I Like It

  • Makes data and UI changes functional rather than stateful
  • Separation of concerns makes each part of the app simpler
  • Record and replay of events makes designing and debugging more predictable
    • Reminds me of Rails up/down migrations for data consistency
  • Strong opinions different from other web frameworks and libraries and more inline with my software views
  • Reflects experience of experienced web devs
  • It’s Clojure-y!

Resources

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