Functional Programming Principles & Patterns
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A talk on functional programming principles, patterns and examples for people who come from object oriented languages
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Functional Programming Principles & Patterns
- 1. Functional Programming Principles & Patterns
- 2. Agenda ● Introduction to Functional Programming ● Principles ● Concepts ● Patterns ● Q & A Code-examples are written in Java and JavaScript
- 3. Introduction to Functional Programming ● Benefits ○ Declarative (what vs. how) ○ Scalability / Concurrency ○ Testability ○ Composability & Modularity ○ Ability to reason about programs / Simplicity ○ ... ○ In our case: Broadening our Horizon ● Use-cases ○ Mathematical programming ○ Distributed Systems ○ High Concurrency ○ GUI programming (new!) ○ ...
- 4. Functional Programming Languages ● Common Lisp ● Haskell ● SML ● Clojure ● Scala ● Erlang ● (Java) ● (JavaScript) ● ...
- 5. Concepts ● Declarative vs. Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 6. Declarative vs. Imperative ● Defining WHAT to do vs. HOW to do it ● Expressive ● Improve / Optimize underlying algorithms ● Eliminate Side-effects as much as possible
- 7. Declarative vs. Imperative - Example
- 8. Concepts ● Declarative vs. Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 9. Pure Functions ● No side-effects ● Referential Transparency (caching, ...) ● Thread-safe ● Compiler-Optimizations ● ...
- 10. Concepts ● Declarative vs. Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 11. Higher Order Functions ● Critical concept in FP ● Functions can take functions as arguments ● Functions can return functions ● Enables functional composition
- 12. Higher Order Functions - Example #1
- 13. Higher Order Functions - Example #2
- 14. Concepts ● Declarative vs. Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 15. Immutability ● Persistent Data Structures ● Every time a data structure would be mutated, a new one is returned instead ● Simplifies state management and mutation tracking ● Enables optimizations ● Works well with pure functions ● Memory overhead is mitigated by sharing (Tries)
- 16. Concepts ● Declarative vs. Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 17. Recursion ● Divide and Conquer ● Can provide elegant solutions for complex problems ● Not as complicated to do, if one knows how ;)
- 18. Recursion #1
- 19. Concepts ● Declarative vs. Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 20. Laziness ● Evaluation is deferred to the last possible moment ● Avoids needless calculations ● Working with infinite data structures ● Works very well with declarative programming
- 21. Laziness Example
- 22. Concepts ● Declarative vs. Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 23. map / Filter / Reduce / Zip ● Backbone of functional programming
- 24. map
- 25. Filter
- 26. Reduce
- 27. Zip
- 28. Concepts ● Declarative vs. Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 29. Currying ● Concept by Haskell Curry ● Translating a function that takes multiple arguments into a sequence of functions which all take 1 argument ● e.g.: add(a, b) AND add(a)(b) ● Improves reusability and composition ● In some languages (Haskell, F#) functions are curried by default
- 30. Currying - Example #1
- 31. Currying - Example #2
- 32. Currying - Example #3
- 33. Patterns ● GOF-Patterns in Functional Style ● Memoization ● Advanced Currying ● Immutability in practice ● Maybe / Optional ● Outlook: Advanced Topics
- 34. GOF Patterns vs. Functional Programming
- 35. GOF - Decorator (wrapper function)
- 36. GOF - Strategy (higher order functions)
- 37. Memoization (Caching Technique - Java)
- 38. Memoization (Caching Technique - JS)
- 39. Immutability in practice ● Data Structures don’t necessarily need to be persistent in nature ● Use map / filter / reduce ● Examples in JS:
- 40. Maybe / Optional ● Pattern for handling absent (e.g.: Null) values ● Avoid annoying if (x==null) checks ● Great for declarative API’s ● Your business logic doesn’t need to deal with null values, it can just use Maybe()’s ○ At the end, when the actual value is needed, the Maybe can be evaluated and the null can be handled
- 41. Maybe / Optional
- 42. Advanced Topics ● Monoids / Functors / Applicatives ● Algebraic Structures in general ● Monads ● Transducers ● ...
- 43. Q & A
- 45. Resources #1 ● https://vimeo.com/113588389 ● http://looprecur.com/blog/ ● https://www.youtube.com/playlist?list=PLK_hdtAJ4KqX0JOs_KMAmUNTNMRYhWEaC ● http://www.infoq.com/presentations/Simple-Made-Easy ● http://www.infoq.com/presentations/Clojure-Design-Patterns ● https://www.manning.com/books/functional-programming-in-java ● https://dzone.com/articles/functional-programming-java-8 ● http://www.vasinov.com/blog/16-months-of-functional-programming/ ● https://www.reddit.com/r/functionalprogramming/ ● https://github.com/jhusain/learnrxjava/ ● http://reactivex.io/learnrx/ ● http://blog.jhades.org/java-8-how-to-use-optional/
- 46. Resources #2 ● http://javascriptair.com/episodes/2015-12-30/ ● http://www.amazon.de/Purely-Functional-Data-Structures-Okasaki/dp/0521663504/ref=sr_1_1?ie=UTF8&qid=1452875910&sr=8-1&k eywords=functional+data+structures ● http://www.amazon.de/Functional-Thinking-Paradigm-Over-Syntax/dp/1449365515/ref=sr_1_1?ie=UTF8&qid=1452875871&sr=8-1&k eywords=functional+thinking ● http://www.amazon.de/Becoming-Functional-Joshua-Backfield/dp/1449368174/ref=sr_1_1?ie=UTF8&qid=1452875879&sr=8-1&keyw ords=becoming+functional ● http://www.amazon.de/Functional-JavaScript-Introducing-Programming-Underscore-js/dp/1449360726/ref=sr_1_1?ie=UTF8&qid=145 2875887&sr=8-1&keywords=functional+javascript ● https://github.com/MostlyAdequate/mostly-adequate-guide