Intro to Functional Programming with Scala - #psuweb
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The document discusses functional programming principles and practices, referencing various programming languages and concepts such as immutability, purity, and side effects. It highlights programming mistakes like null references and introduces type-safe alternatives with the Option type in Scala. Additionally, it provides examples and resources for those looking to learn functional programming.
![An Example
def firstLarger(data: List[Int], threshold: Int): Int = ???](https://image.slidesharecdn.com/qcpqgwfzqpmozdqnvzbg-signature-48694b515c7671be15964332fc0a5dd1175476e46ffaea22fec70c2e7de2168d-poli-150622185321-lva1-app6892/85/Intro-to-Functional-Programming-with-Scala-psuweb-15-320.jpg)
![An Example
def firstLarger(data: List[Int], threshold: Int): Int = ???
val numbers = List(3, 2, 4, 7, 9, 8, 1)
firstLarger(numbers, 5) // returns 7
firstLarger(numbers, 10) // returns ?](https://image.slidesharecdn.com/qcpqgwfzqpmozdqnvzbg-signature-48694b515c7671be15964332fc0a5dd1175476e46ffaea22fec70c2e7de2168d-poli-150622185321-lva1-app6892/85/Intro-to-Functional-Programming-with-Scala-psuweb-16-320.jpg)
![Method Signatures & Error Signaling
public int firstLarger(final int[] data,
final int threshold) throws NoSuchElementException](https://image.slidesharecdn.com/qcpqgwfzqpmozdqnvzbg-signature-48694b515c7671be15964332fc0a5dd1175476e46ffaea22fec70c2e7de2168d-poli-150622185321-lva1-app6892/85/Intro-to-Functional-Programming-with-Scala-psuweb-17-320.jpg)
![Method Signatures & Error Signaling
/**
* ...
* @return null on error
*/
public Integer firstLarger(final int[] data, final int threshold)](https://image.slidesharecdn.com/qcpqgwfzqpmozdqnvzbg-signature-48694b515c7671be15964332fc0a5dd1175476e46ffaea22fec70c2e7de2168d-poli-150622185321-lva1-app6892/85/Intro-to-Functional-Programming-with-Scala-psuweb-18-320.jpg)
![Use the type system
Option[T]
Some(value: T) None](https://image.slidesharecdn.com/qcpqgwfzqpmozdqnvzbg-signature-48694b515c7671be15964332fc0a5dd1175476e46ffaea22fec70c2e7de2168d-poli-150622185321-lva1-app6892/85/Intro-to-Functional-Programming-with-Scala-psuweb-20-320.jpg)
![Option
sealed abstract class Option[T]
// wrapper around a value
final class Some[T](value: T) extends Option[T]
// Singleton marker for no value
// Not null. Safe to dereference.
object None extends Option](https://image.slidesharecdn.com/qcpqgwfzqpmozdqnvzbg-signature-48694b515c7671be15964332fc0a5dd1175476e46ffaea22fec70c2e7de2168d-poli-150622185321-lva1-app6892/85/Intro-to-Functional-Programming-with-Scala-psuweb-21-320.jpg)
![Scala Map
val people = Map("Frank" -> "N. Furter",
"Lady" -> "Gaga")
val frank = people.get("Frank")
frank: Option[String] = Some(N. Furter)
val bob = people.get("Bob")
bob: Option[String] = None](https://image.slidesharecdn.com/qcpqgwfzqpmozdqnvzbg-signature-48694b515c7671be15964332fc0a5dd1175476e46ffaea22fec70c2e7de2168d-poli-150622185321-lva1-app6892/85/Intro-to-Functional-Programming-with-Scala-psuweb-22-320.jpg)
![Signature
val numbers = List(3, 2, 4, 7, 9, 8, 1)
def firstLarger(data: List[Int], threshold: Int): Option[Int] = ???
firstLarger(numbers, 5) // Some(5)
firstLarger(numbers, 10) // None](https://image.slidesharecdn.com/qcpqgwfzqpmozdqnvzbg-signature-48694b515c7671be15964332fc0a5dd1175476e46ffaea22fec70c2e7de2168d-poli-150622185321-lva1-app6892/85/Intro-to-Functional-Programming-with-Scala-psuweb-23-320.jpg)
Intro to Functional Programming with Scala - #psuweb
- 1. Derek Morr, Penn State @derekmorr Functional Programming with
- 2. Demo code is at https://github.com/derekmorr/webconf2015
- 3. What’s your background? ● Java? C#? C++? ● Python, Ruby, JavaScript? ● Haskell, ML, Erlang, Lisp? ● F#? Scala? Clojure? ● Anything else?
- 7. Is this valid? x = x + 1
- 8. x = x + 1 if x is 5, then: 5 = 5 + 1 5 = 6 no, 5 ≠ 6
- 10. Purity // impure var a = 1 def incr() = { a += 1 } // pure def incr(a: Int) = { a + 1 }
- 11. An example find . -type f | grep foo | sort | uniq
- 12. What’s a side effect? A lot of stuff we do now: ● Reassigning variables ● Modifying data in-place ● Throwing exceptions ● Interacting w/ the external environment
- 13. What’s it like? Immutability Value In, Value Out Emphasis on data flow Descriptive, not imperative
- 14. Immutability OO makes code understandable by encapsulating moving parts. FP makes code understandable by minimizing moving parts. — Michael Feathers
- 15. An Example def firstLarger(data: List[Int], threshold: Int): Int = ???
- 16. An Example def firstLarger(data: List[Int], threshold: Int): Int = ??? val numbers = List(3, 2, 4, 7, 9, 8, 1) firstLarger(numbers, 5) // returns 7 firstLarger(numbers, 10) // returns ?
- 17. Method Signatures & Error Signaling public int firstLarger(final int[] data, final int threshold) throws NoSuchElementException
- 18. Method Signatures & Error Signaling /** * ... * @return null on error */ public Integer firstLarger(final int[] data, final int threshold)
- 19. “My Billion Dollar Mistake” “I call it my billion-dollar mistake. It was the invention of the null reference in 1965... This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.” - Sir Tony Hoare (2009) Null References: The Billion Dollar Mistake
- 20. Use the type system Option[T] Some(value: T) None
- 21. Option sealed abstract class Option[T] // wrapper around a value final class Some[T](value: T) extends Option[T] // Singleton marker for no value // Not null. Safe to dereference. object None extends Option
- 22. Scala Map val people = Map("Frank" -> "N. Furter", "Lady" -> "Gaga") val frank = people.get("Frank") frank: Option[String] = Some(N. Furter) val bob = people.get("Bob") bob: Option[String] = None
- 23. Signature val numbers = List(3, 2, 4, 7, 9, 8, 1) def firstLarger(data: List[Int], threshold: Int): Option[Int] = ??? firstLarger(numbers, 5) // Some(5) firstLarger(numbers, 10) // None
- 24. Demo
- 25. A Detour - Functional Lists List(1,2,3)
- 26. A Detour - Functional Lists 1 :: 2 :: 3 :: Nil synonym for empty list
- 27. A Detour - Functional Lists 1 :: 2 :: 3 :: Nil pronounced “cons”
- 28. A Detour - Functional Lists 1 :: 2 :: 3 :: Nil
- 29. A Detour - Functional Lists 1 :: 2 :: 3 :: Nil
- 30. A Detour - Functional Lists 1 :: 2 :: 3 :: NilList(1,2,3) =
- 31. A Detour - Functional Lists 1 :: 2 :: 3 :: Nil head tail (also a List)
- 32. A Detour - Functional Lists 1 :: 2 :: 3 :: Nil head tail
- 33. A Detour - Functional Lists 1 :: 2 :: 3 :: Nil head tail
- 34. A Detour - Functional Lists 1 :: 2 :: 3 :: Nil
- 35. A nice overview of Scala
- 36. If you want to learn FP - short
- 37. FP for OO folks
- 38. If you want to learn FP - long
- 39. Two good books First 11 chapters online for free. Some chapters online for free. 40% off at manning.com w/ code tsfp14
- 40. Pattern Matching Slides: Czech Scala Enthusiasts: Pattern Matching and Case Classes (1h45) See also their blog.
- 41. Questions?
Editor's Notes
- #4: ask what they want to get out of talk, langs used, who’s used underscore ?
- #5: Scala is #14 #25 in TIOBE
- #7: F#, Scala, Clojure are functional. Rust has functional elements.
- #10: pure function. value in value out. no side effects. side effects = reach outside box for variable access or io. or exceptions.
- #12: No state. Not mutating a variable, we’re streaming data thru functions. Data isn’t changed during processing.
- #17: Btw, ??? is valid scala - it’s a symbolic method name for undefined methods. Handy in code instead of TODO
- #20: Famous computer scientist. Invented Quicksort. Won Turing Award, John von Neumann Medal, Kyoto Prize, Fellow of Royal Society & Royal Academy of Engineering. Even in “null-safe” languages like Ruby, nil is a bad idea - http://www.sandimetz.com/blog/2014/12/19/suspicions-of-nil Also, NULLs in SQL are a bad idea: https://www.youtube.com/watch?v=BC-OBmreMHY
- #22: explain “sealed” keyword