![What is a function?
Maths: a function maps input to output.
f : R -> R
f(x) = x * x
Programming: a function receives input, performs actions, returns output.
int main( int argc, const char* argv[] ) {
printf( "nHello Worldnn" );
}
OO Programming: a function is a method on an object
class HelloWorldApp {
public static void main(String[] args) {
System.out.println("Hello World!"); // Display the string.](https://image.slidesharecdn.com/whenlifegivesyoufunctionsmakefunctionalprograms-160908092120/85/When-life-gives-you-functions-make-functional-programs-8-320.jpg)
![Let’s Ask (more) Celebrity Programmers
“Functional programming is about writing pure functions, about removing hidden
inputs and outputs as far as we can, so that [our code just describes] a
relationship between inputs and outputs.”
- @krisajenkins
“What if instead of telling the computer what to do, we told the computer what
things are.”
- @_K_E_L_S_E_Y
“2+2 is functional programming [...] the proper OO way is:
x = new int(2); x.add(2); return x;”
- @chris__martin](https://image.slidesharecdn.com/whenlifegivesyoufunctionsmakefunctionalprograms-160908092120/85/When-life-gives-you-functions-make-functional-programs-13-320.jpg)
![Programming with Higher-Order Functions
Traditional
var nums = [1, 2, 3];
var result = [];
for(num in nums) {
result.push(num * 10);
}
Functional
var nums = [1, 2, 3];
var result =
nums.map(function(num) {
return num * 10;
});
[1, 2, 3] ---> [10, 20, 30]](https://image.slidesharecdn.com/whenlifegivesyoufunctionsmakefunctionalprograms-160908092120/85/When-life-gives-you-functions-make-functional-programs-23-320.jpg)
![Minimize Location of Side-Effects
A function is said to have a Side-Effect if it mutates state or has an observable
interaction.
public static void main(String[] args) {
System.out.println("Hello World!"); // ← Side Effect!
}
Pure functions don’t have Side Effects (Referential Transparency)
Handling side-effects is necessary for interacting with the real world!](https://image.slidesharecdn.com/whenlifegivesyoufunctionsmakefunctionalprograms-160908092120/85/When-life-gives-you-functions-make-functional-programs-29-320.jpg)
When life gives you functions make functional programs!
- 1. When Life Gives you Functions Make Functional Programs! aaron levin 07.09.2016
- 2. Thank you Ellen, Duana, and Open Tech School!
- 3. Outline 1. Who is Aaron Levin? 2. What is Functional Programming? 3. How Functional Programming Can Benefit You 4. 🎉🎉🎉🎉
- 4. Who is Aaron Levin MSc Pure Mathematics Started Programming at age 30 👴 Building Recommender Systems at SoundCloud But also have worked as: Taco Conjurer @ TacoTime 🌮 Telemarketer @ The WeedMan 🌿 Rare Record Dealer @ eBay 🌮 Music Director @ Community Radio Station 📻
- 5. Who is Aaron Levin (really) First programming job in Scala. Was once paid actual Real World™ money to write Haskell Wrote authentication framework for http library servant. Author of a few Haskell libraries: - free-vl - haskell-kubernetes
- 6. What is Functional Programming?
- 7. Wait, what is a function?
- 8. What is a function? Maths: a function maps input to output. f : R -> R f(x) = x * x Programming: a function receives input, performs actions, returns output. int main( int argc, const char* argv[] ) { printf( "nHello Worldnn" ); } OO Programming: a function is a method on an object class HelloWorldApp { public static void main(String[] args) { System.out.println("Hello World!"); // Display the string.
- 9. How can we program with functions?
- 10. Functional Programming Languages Functional Languages LISP Clojure Erlang Haskell OCaml SML Languages with Functional Features Javascript Ruby Python Java (8) C++ Who can know what to make of this one?
- 11. With so many functional languages, what makes a language functional?
- 12. Let’s ask celebrity programmers! “You are programming with functions? Then you are doing functional programming. And your language is a functional programming language.” - @raganwald “A programming paradigm, a coding style, a mindset, a sexy, buzz-wordy trend” - @AnjanaVakil “Functional programming is a style of programming which models computations as the evaluation of expressions.” - Haskell.org
- 13. Let’s Ask (more) Celebrity Programmers “Functional programming is about writing pure functions, about removing hidden inputs and outputs as far as we can, so that [our code just describes] a relationship between inputs and outputs.” - @krisajenkins “What if instead of telling the computer what to do, we told the computer what things are.” - @_K_E_L_S_E_Y “2+2 is functional programming [...] the proper OO way is: x = new int(2); x.add(2); return x;” - @chris__martin
- 15. Things Associated With Functional Programming Higher-Order Functions Immutability Purity Pattern Matching Lazy Evaluation Recursion Type Inference Algebraic Data Types
- 16. ...
- 17. Take a step back breathe Let’s start over
- 19. There are lots of things to program with: objects, statements, relations, instructions, messages
- 20. There are lots of things to program with: functions!
- 21. Functional Programming Is 1. Programming with Functions that are Higher-Order 2. Programming with Data that is Immutable 3. Designing Systems that minimize the location of Side-Effects
- 22. Programming with Higher-Order Functions A Higher-Order Function may take another function as an argument. Allows you to pass functions to functions! Most prevalent example: call-backs.
- 23. Programming with Higher-Order Functions Traditional var nums = [1, 2, 3]; var result = []; for(num in nums) { result.push(num * 10); } Functional var nums = [1, 2, 3]; var result = nums.map(function(num) { return num * 10; }); [1, 2, 3] ---> [10, 20, 30]
- 24. Programming with Higher-Order Functions Benefits: 1. No indexing / out-of-bounds issues 2. Don’t care about array structure 3. Don’t care about how to iterate through structure 4. Could work for anything that can be traversed! Trees, etc.
- 25. Programming with Immutable Data Immutable data cannot be changed after it is created. Cannot score++ with an immutable score!
- 26. Programming with Immutable Data def collision_points(self, other): if self.collide(other) and other.is_coin: state.high_score++ elif self.collide(other): state.high_score = 0 def collision_points(self, other, state): new_state = copy(state) if self.collide(other) and other.is_coin: new_state.high_score++ elif self.collide(other): new_state.high_score = 0 return new_state
- 27. Programming with Immutable Data def collision_points(self, other): if self.collide(other) and other.is_coin: state.high_score = state.high_score + 1 elif self.collide(other): state.high_score = 0 def collision_points(self, other): if self.collide(other) and other.is_coin: return {‘mutate’: ‘increment’, ‘amount’: 1} elif self.collide(other): return {‘mutate’: ‘reset’, ‘amount’: 0} else: return None return facts! a description of how to change the world!
- 28. Programming with Immutable Data Benefits 1. Know exactly where and how state is modified 2. Easier to test 3. Can share data with concurrent threads / processes safely 4. Easily parallelizable 5. Easily persisted to disk 6. Basically everything is 100000000% satisfaction guaranteed better when things are immutable
- 29. Minimize Location of Side-Effects A function is said to have a Side-Effect if it mutates state or has an observable interaction. public static void main(String[] args) { System.out.println("Hello World!"); // ← Side Effect! } Pure functions don’t have Side Effects (Referential Transparency) Handling side-effects is necessary for interacting with the real world!
- 30. Minimize Location of Side-Effects
- 31. Values Pure function Function interfacing with outside world Minimize Location of Side-Effects The Outside World™ Manage Program State Open files Connect to DB Receive HTTP Req. Receive Mouse Input Talk to GPU Read stdin Output to stdout Launch programs Send UDP packets request.body.rewind request.body
- 32. Minimize Location of Side-Effects Benefits 1. Don’t have to remember things 2. How do I know if someone “already read it”? Don’t have to understand the entire program! 3. Test core algorithms more easily
- 34. Functional Programming Is 1. Programming with Functions that are Higher-Order 2. Programming with Data that is Immutable 3. Designing Systems that minimize the location of Side-Effects
- 35. Why don’t we always program with functions?
- 36. Why Don’t We Always Program With Functions? Some languages don’t support it (Java <7) Requires thinking very deeply about program architecture. Is not always performant Many APIs are written in a non-FP style (e.g. java’s old Time library)
- 37. What are the benefits of Functional Programming?
- 38. Benefits of Functional Programming Safer Easier to understand your programs Easier to debug your programs Easier to test your programs Make APIs easier to use Make static typing systems more powerful It’s fun! It’s simple!
- 39. What next?
- 40. What Next? 1. Try re-writing programs in a more functional style! 2. Learn a functional language! (Haskell or OCaml) 3. How to encode data (numbers, lists, strings) as functions! (Church-encoding) Thanks! Ende.