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Functional Programming Principles & Patterns
The document covers the principles and patterns of functional programming, including key concepts such as pure functions, higher-order functions, immutability, and laziness. It highlights the benefits of functional programming like testability and modularity, as well as use cases in various fields. Additionally, the document provides resources for further learning and examples in Java and JavaScript.
Functional Programming Principles & Patterns
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- 2. Agenda ● Introduction toFunctional Programming ● Principles ● Concepts ● Patterns ● Q & A Code-examples are written in Java and JavaScript
- 3. Introduction to FunctionalProgramming ● 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 ● Noside-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 DataStructures ● 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 andConquer ● Can provide elegant solutions for complex problems ● Not as complicated to do, if one knows how ;)
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- 19. Concepts ● Declarative vs.Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 20. Laziness ● Evaluation isdeferred to the last possible moment ● Avoids needless calculations ● Working with infinite data structures ● Works very well with declarative programming
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- 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
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- 28. Concepts ● Declarative vs.Imperative ● Pure Functions ● Higher Order Functions (+Lambdas) ● Immutability ● Recursion ● Laziness ● map/filter/reduce/zip/flatMap ● Currying
- 29. Currying ● Concept byHaskell 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
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- 33. Patterns ● GOF-Patterns inFunctional 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)
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- 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
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- 42. Advanced Topics ● Monoids/ Functors / Applicatives ● Algebraic Structures in general ● Monads ● Transducers ● ...
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- 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