PMaps

Principled and Powerful Maps

Presented at NE Scala 2018

Transcript

1. PMAPS
2. INTRO • My name is Jason Liberman • Studied Pure Math and Philosophy at UPenn • Previously worked at an investment bank • Self-taught, Scala was the first programming language I learned in formal setting • Life outside of Scala: • Avid reader (lots of philosophy) • Book store dreams
3. BRIDGEWATER • Investment Engineer at Bridgewater Associates • Largest hedge fund in the world • Manage $160bn for our clients • Author / implement investment logic in code (primarily Scala) • Team of ~50 engineers, we are incredibly passionate about Scala training and generally building a great community • Come talk to me if interested in learning more!
4. MAPS - CONTEXT • Maps / Key-Value pair collections are used everywhere • Scala’s immutable Map collection is fast and incredibly useful • Scala Map shortcomings? • Birth of PMaps
5. AGENDA • Define some important qualities I think key-value pair collections should have • Some ways in which Maps seem to be falling short • Introduce PMaps and how they compensate • Questions
6. TAKEAWAYS • Often easy to build something small that makes code authoring a lot simpler! • Define algebra • Enforce algebra • Add syntax
7. WHAT IS THE KEY TO KEY-VALUE COLLECTIONS? • Performant • Principled: • Operations are well-defined, transparent, and reflected in the types • Powerful: • Clean, concise, expressive logic • Lift algebra / logic to collection level
8. MAPS THAT GET YOU LOST • Case 1: Defaults
9. MAPS THAT GET YOU LOST • Defaults on Scala Maps: • Not principled: • I want a strongly typed identification that I have something fundamentally different • Function vs. Partial Function
10. MAPS THAT GET YOU LOST • Case 2: Dropped Keys
11. MAPS THAT GET YOU LOST • Dropped Keys: • Not principled: • Silently dropping colliding keys • Not powerful: • Would ideally want to use the fact that quantity sold can be summed for a given author!
12. VERBOSE KEY ITERATIONS
13. VERBOSE KEY ITERATIONS • Not powerful • I know that my quantities can be added, all I really want to do is this: • In other words LIFT the algebra on QuantitySold to the collection level
14. PRINCIPLED AND POWERFUL MAPS PMAPS • Simple wrapper class around a Map
15. DEFAULTS • Always know whether I am working with a Function or Partial Function
16. DROPPED KEYS • Dropped keys throw an exception
17. DROPPED KEYS • Alternative methods available to ‘add’ values with the same keys
18. VERBOSE KEY ITERATIONS
19. ALGEBRA AT COLLECTION LEVEL
20. JOINS • Maps are just functions (as long as they have a default) • So can’t I just do this?
21. JOINS • outerJoin, for example: • Or leftJoins:
22. JOINS • Can apply logic to joined values at collection level: • Joins only defined when it makes sense, e.g. no leftJoins on PMapWDefaults
23. LIFTING ALGEBRA TO COLLECTION • Lifting algebra of V to PMap level • If V is a Monoid, so is PMap[K, V] • If V is a Vector Space, so is PMap[K, V] • Prove this, and you get syntax for free (e.g. from Spire)
24. ALGEBRA AT COLLECTION LEVEL
25. ALGEBRA AT COLLECTION LEVEL
26. HOW THIS WORKS • Type Classes • Prove if V is Monoid, then PMapWDefault[K, V] is Monoid • Numeric type classes and algebraic syntax and from Spire • Dependent types to avoid nested tuples and return reasonable types from Joins
27. TAKEAWAYS • Often easy to build something small that makes code authoring a lot simpler! • Define algebra • Enforce algebra • Add syntax
28. IN CONCLUSION • You can find the code on github: • https://github.com/jasonliberman8/PMaps • Suggestions? Thoughts? Please find me after.
29. QUESTIONS?