Joshua T Kalis (he/him/his)

Lambda Jam 2014

Transit (format)

"Transit is a format and set of libraries for conveying values between applications written in different programming languages." - http://blog.cognitect.com/blog/2014/7/22/transit

JSON Deficits

• Few types
• Repetition
• Bloated

Transit Goals

1. Schema-less (self-describing "at the bottom")
2. Extensible
3. Performant
4. Reach the browser

Transit Links

• http://blog.cognitect.com/blog/2014/7/22/transit
• https://github.com/cognitect/transit-format

Reactive Programming

Let the data flow.

Reactive - Traits/Goals

• Responsive
• Scalable
• Resilient
• Event-driven

Responsive + Event-driven

a = b + c

Imperative - Statically assign the result of the computation on the right to the identifier on the left.

When b or c change, a will not change.

Reactive - Create a relationship between the identifier on the left and the computation on the right.

When b or c change, a will re-evaluate.

Reactive - Notes

• Loosely coupled
• Composable
• Distributed(-able)
• Failures are first-class
  • Handling errors is just another event (type)
• Async-friendly

Interactive vs. Reactive

Interactive - Programs respond at the speed of the interactions.

• Will create/require backpressure in massive data streams

Reactive - Programs respond at the speed of the environment.

• Backpressure will (not likely) be necessary in massive data streams with horizontal scaling

Design and Architecture for Actors

System design for process-based concurrency

Synonyms

Actor === Agent === Process

Process-based Concurrency Mantra

1. Processes are not threads.
2. Processes are really cheap.
3. Goto 1.

Supervision Hierarchy Map

Imagine a soda vending machine; this might be a - over-simplified - diagram of its actors.

    +------------+
    |   System   |
    | Supervisor |
    +------------+
      /        \
     /          \
+---------+ +------------+
| Cooling | |  Vending   |
| System  | | Supervisor |
+---------+ +------------+
              /        \
             /          \
       +-----------+ +----------+
       | Selection | |   Soda   |
       |  Handler  | | Fetching |
       +-----------+ +----------+

• From top down, coarse to fine grained responsibility.
• One process for every truly concurrent activity.
• Failure in a non-dependant process should have zero direct affect.

Let it Crash

"Did you try and turn it off and back on again?"

No Joke

Return to a known "good" state of a system.

Random Stuff

"... debugging ... is a powerful exercise in the learning process." - Gerald Jay Sussman

"Because, physics." - Erik Meijer