Fun with F#

Transcript

1. Fun with F# Emulating the Nokia Ringtone Composer ML (1973) Caml (1985) Ocaml (1996) F# (2005)
4. 7+2
5. (7+2)*3
6. When each piece of a program denotes a value (and nothing else) = the denotational semantic
7. public int Length(string s) string int Length(“dotnet”) = 6
8. public int Length(IEnumerable s) IEnumera ble int
9. The rule of good programming…
10. public int Length(IEnumerable s) Write functions that express their behaviour in their signature.
11. (7+2)*3 public int Add2Times3(int start) { return Times3(Add2(start)); } 7
12. Why?... These functions can be used without increasing complexity. i.e. they are composeable
13. Consequences • Mutable values cannot be allowed • Objects no longer make sense • Dependency injection is redundant • ‘Change tracking’ and tools like EF that rely on it are problematic
14. Reducing Accidental Complexity public static void Quicksort(int[] elements, int left, int right) { int i = left, j = right; int pivot = elements[(left + right) / 2]; while (i <= j) { while (elements[i] < pivot) { i++; } while (elements[j] > pivot) { j--; } if (i <= j) { int tmp = elements[i]; elements[i] = elements[j]; elements[j] = tmp; i++; j--; } } if (left < j) { Quicksort(elements, left, j); } if (i < right) { Quicksort(elements, i, right); } }
15. F# Equivalent let rec quicksort = function | [] -> [] | x :: xs -> let smaller = List.filter ((>) x) xs let larger = List.filter ((<=) x) xs quicksort smaller @ [x] @ quicksort larger
16. F# / C# Comparison F# / C# Comparison
17. // C# static int Square(int x) { var squared = x * x; return squared; } // F# let square x = x * x Functions
18. Immutable Values // C# var numbers = new List<int> { 1,2,3 }; numbers.Add(4); // F# let numbers = [3;2;1] let moreNumbers = 4 :: numbers
19. Data and Operations (C#) public class TwoNumbers { int fst; int snd; public TwoNumbers(int fst, int snd) { this.fst = fst; this.snd = snd; } public int Add() { return fst + snd; } }
20. Data and Operations (F#) type TwoNumbers = int * int let add ((fst,snd):TwoNumbers) = fst + snd
21. A function with 2 arguments let distance x y = x - y |> abs // val distance : x:int -> y:int -> int distance 5 2 // val it : int = 3
22. distance 5 2 + 1
23. 32f2 32#d2 32f2 8#d2 32#d2 32#d2 32f2 32g2 32f2 16.#d2 32- 16f2 8#d2 16#g2 32#g2 32#g2 32#g2 16g2 16.#d2 32- 8#a2 32#a2 32#a2 16#a2 16f2 16g2 8#g2 16g2 16g2 32g2 Jakob’ s Tune Emulato r
24. PCM is a digital representation of analogue audio Sample rate is the number of sampler per second Bit depth is the number of bits of information in each sample Encoding a Sound Wave -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Samples Sine
26. DEMO Signal_generator.fsx Wave_packer.fsx
27. Discriminated Unions type Day = Sunday | Monday | Tuesday | Wednesday | Thursday | Friday | Saturday
29. DEMO Du.fsx ComposerParsing.fsx
30. ASP.NET M VC Web Development Frameworks