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![Fizzbuzz Imperative
public class FizzBuzz{
public static void main(String[] args){
for(int i= 1; i <= 100; i++){
if(i % 15 == 0{
System.out.println(„FizzBuzz");
}else if(i % 3 == 0){
System.out.println("Fizz");
}else if(i % 5 == 0){
System.out.println("Buzz");
}else{
System.out.println(i);
} } } }](https://image.slidesharecdn.com/fregeatjdd-intrduction-151023120657-lva1-app6891/75/JDD2015-Frege-Introducing-purely-functional-programming-on-the-JVM-Dierk-Konig-22-2048.jpg)
![Fizzbuzz Logical
fizzes = cycle ["", "", "fizz"]
buzzes = cycle ["", "", "", "", "buzz"]
pattern = zipWith (++) fizzes buzzes
fizzbuzz = zipWith (max . show) [1..] pattern
main _ = do
for (take 100 fizzbuzz) println](https://image.slidesharecdn.com/fregeatjdd-intrduction-151023120657-lva1-app6891/75/JDD2015-Frege-Introducing-purely-functional-programming-on-the-JVM-Dierk-Konig-23-2048.jpg)
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JDD2015: Frege - Introducing purely functional programming on the JVM - Dierk König
The document introduces Frege, a purely functional programming language on the JVM, emphasizing its differences from traditional programming models by eliminating mutable state and side effects. It highlights the advantages of using pure functions, such as type safety and ease of reasoning, while demonstrating practical applications like the 'FizzBuzz' example. Additionally, it promotes Frege's accessibility to Java programmers and its alignment with functional programming principles.
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Similar to JDD2015: Frege - Introducing purely functional programming on the JVM - Dierk König
JDD2015: Frege - Introducing purely functional programming on the JVM - Dierk König
- 1. Frege Introduction to purelyfunctional programming on the JVM
- 2.
- 3. Takeaway Frege is fundamentallydifferent based on science and practical
- 4. Why do wecare? a = 1 b = 2 c = b b = a a = c 1 1 2 1 2 2 1 1 22 1 2 time1 time2 time3 state1 state2 state3
- 5. Operational Reasoning a = 1 b = 2 c = b b = a a = c 1 1 2 12 2 1 1 2 2 1 2 time1 time2 time3 state1 state2 state3
- 6.
- 7. Using functions a = 1 b = 2 1 1 2 21 swap(a,b) = (b,a)
- 8. The Key Idea Assignmentschange state and introduce time. Statements do side effects. Let’s just remove them!
- 9. Pure Functions Java T foo(Pair<T,U> p) {…} Frege foo :: (α,β) -> α What could possiblyhappen? What could possibly happen?
- 10. Pure Functions Java T foo(Pair<T,U> p) {…} Frege foo :: (α,β) -> α Everything! State changes, file or db access, missile launch,… a is returned
- 11. can be cached(memoized) can be evaluated lazily can be evaluated in advance can be evaluated concurrently can be eliminated in common subexpressions can be optimized Pure Functions
- 12. Is my methodpure? Let the type system find out!
- 13. Java Interoperability do notmix OO and FP combine them
- 14. Java -> Frege Scripting:JSR 223 Service: compile *.fr file call static method simple
- 15. pure native encodejava.net.URLEncoder.encode :: String -> String encode “Dierk König“ native millis java.lang.System.currentTimeMillis :: () -> IO Long millis () millis () past = millis () - 1000 Does not compile! Frege -> Java This is a key distinction between Frege and other JVM languages! even Java can be pure
- 16. allows calling Java butnever unprotected! is explicit about effects just like Haskell Frege
- 17. Type System Global typeinference and thus more safety and less work for the programmer You don’t need to specify any types at all! But sometimes you do anyway…
- 18. Mutable I/O Mutable Mutable Keep the messout! Pure Computation Pure Computation Pure Computation
- 19. Mutable I/O Mutable Mutable Keep the messout! Pure Computation Pure Computation Pure Computation Ok, these are Monads. Be brave. Think of them as contexts that the type system propagates and makes un-escapable. Thread- safe by design! Checked by compiler
- 20. Java Java Java Service Based Design Frege Frege Frege Atypical integration option: use Frege code for services
- 21.
- 22.
- 23.
- 24. Fizzbuzz Comparison Imperative Logical Conditionals4 0 Operators 7 1 Nesting level 3 0 Sequencing sensitive transparent Maintainability - - - +
- 25. History Java promise: „Nomore pointers!“ But NullPointerExceptions (?)
- 26. Frege is different NoMore But state no state (unless declared) statements expressions (+ „do“ notation) assignments definitions variables ST monad as „agent“ interfaces type classes classes & objects algebraic data types inheritance parametric polymorphism null references Maybe NullPointerExceptions Bottom, error
- 27.
- 28. Frege in comparison safe Java Groovy Frege Haskell conceptby Simon Peyton-Jones Frege makes the Haskell spirit accessible to the Java programmer and provides a new level of safety. apply logic run computers practical
- 29. Why Frege Robustness underparallel execution Robustness under composition Robustness under increments Robustness under refactoring Enables local and equational reasoning Best way to learn FP
- 30.
- 31. Gottlob Frege "As Ithink about acts of integrity and grace, I realise that there is nothing in my knowledge that compares with Frege’s dedication to truth… It was almost superhuman.“ —Bertrand Russel "Not many people managed to create a revolution in thought. Frege did.“ —Graham Priest Lecture on Gottlob Frege: http://www.youtube.com/watch?v=foITiYYu2bc
- 32. Dierk König Canoo mittie Join thetutorial tomorrow