---
language: F#
contributors:
    - ["Scott Wlaschin", "http://fsharpforfunandprofit.com/"]
translators:
    - ["Mustafa Zengin", "http://zengin.github.com/"]
filename: learnfsharp.fs
---

F# fonksiyonel ve nesne tabanlı, genel amaçlı bir programlama dilidir. Bedava ve açık kaynaklıdır ve Linux, Mac, Windows ve dahasında çalışır.

Hataları derleme zamanında yakalayan çok güçlü bir tip sistemine sahiptir, ancak tip çıkarımı yaptığından dinamik bir dil gibi görünür.

F#'ın söz dizimi C-stili dillerden farklıdır:

* Küme parantezi kod bloklarını ayırmak için kullanılmaz. Bunun yerine Python'da olduğu gibi girinti kullanılır.
* Parametreleri birbirinden ayırmak için virgül yerine boşluk karakteri kullanılır.

Aşağıdaki kodu denemek istiyorsanız, [tryfsharp.org](http://www.tryfsharp.org/Create)'a gidin be interaktif REPL'e kodu yapıştırın.

```csharp

// tek satır yorumlar ikili bölme işareti kullanılır
(* çok satırlı yorumlar (* . . . *) ikilisini kullanır

-çok satırlı yorumun sonu- *)

// ================================================
// Temel Söz Dizimi
// ================================================

// ------ "Değişkenler" (tam da değil) ------
// "let" anahtar kelimesi (değişmez) değer tanımlar
let myInt = 5
let myFloat = 3.14
let myString = "hello"           // tip bilgisi olmamasına dikkat

// ------ Listeler ------
let twoToFive = [2; 3; 4; 5]        // Köşeli parantezler listeleri oluşturur,
                                 // değerler ise noktalı virgülle ayrılır.
let oneToFive = 1 :: twoToFive   // :: yeni birinci elemanı olan bir liste oluşturur.
// Sonuç: [1; 2; 3; 4; 5]
let zeroToFive = [0; 1] @ twoToFive   // @ iki listeyi birbirine ekler.

// ÖNEMLİ: virgüller hiçbir zaman ayraç olarak kullanılmaz, sadece noktalı virgüller!

// ------ Fonksiyonlar ------
// "let" anahtar kelimesi isimlendirilmiş fonksiyonları da tanımlar.
let square x = x * x          // Parantez kullanılmadığına dikkat.
square 3                      // Şimdi fonksiyonu uygula. Yine parantez yok.

let add x y = x + y           // add (x,y) kullanmayın! Bu tamamen başka bir anlama geliyor.
add 2 3                       // Şimdi fonksiyonu uygula.

// çok satırlı bir fonksiyon tanımlamak için sadece girinti kullan. Noktalıı virgül gerekmez.
let evens list =
   let isEven x = x % 2 = 0     // "isEven"ı alt fonksiyon olarak tanımla
   List.filter isEven list    // List.filter boolean bir fonksiyon ve
                              // üzerinde çalışılacak bir liste parametrelerinden oluşan
                              // bir kütüphane fonksiyonu
                              
evens oneToFive               // Şimdi fonksiyonu uygula.

// Parantezleri önceliği netleştirmek için kullanabilirsin. Bu örnekte
// "map"i önce iki argümanla uygula, sonra sonuç üzerinde "sum" uygula.
// Parantezler olmasaydı, "List.map" List.sum'ın ilk argümanı olurdu.
let sumOfSquaresTo100 =
   List.sum ( List.map square [1..100] )

// Bir operasyonun sonucunu bir sonrakine "|>" kullanarak besleyebilirsin.
// Veri beslemek F#'ta UNIX'te olduğu gibi yaygındır..

// Burada sumOfSquares fonksiyonunun veri beslemeyle yazılmış hali var:
let sumOfSquaresTo100piped =
   [1..100] |> List.map square |> List.sum  // "square" önceden tanımlanmıştı

// Lambda'ları (anonim fonksiyonları) "fun" anahtar kelimesiyle tanımlayabilirsin
let sumOfSquaresTo100withFun =
   [1..100] |> List.map (fun x -> x * x) |> List.sum

// F#'ta "return" anahtar kelimesi yoktur. Bir fonksiyon
// her zaman son kullanılan ifadeyi döndürür.

// ------ Kalıp eşleştirme ------
// Match..with.. çok güçlü bir case/switch türevidir.
let simplePatternMatch =
   let x = "a"
   match x with
    | "a" -> printfn "x is a"
    | "b" -> printfn "x is b"
    | _ -> printfn "x is something else"   // alt çizgi bütün kalıplarla eşleşir

// F# varsayılan olarak null'lara izin vermez -- Option tipini kullanıp
// kalıp eşleştirme yapmalısın.
// Some(..) ve None, Nullable tipler gibidir.
let validValue = Some(99)
let invalidValue = None

// Bu örnekte, match..with "Some" ve "None"la eşleştirme yapıyor,
// ve ayrıca "Some" içerisindeki değeri de çıkarıyor.
let optionPatternMatch input =
   match input with
    | Some i -> printfn "input is an int=%d" i
    | None -> printfn "input is missing"

optionPatternMatch validValue
optionPatternMatch invalidValue

// ------ Printing ------
// The printf/printfn functions are similar to the
// Console.Write/WriteLine functions in C#.
printfn "Printing an int %i, a float %f, a bool %b" 1 2.0 true
printfn "A string %s, and something generic %A" "hello" [1; 2; 3; 4]

// There are also sprintf/sprintfn functions for formatting data
// into a string, similar to String.Format in C#.

// ================================================
// More on functions
// ================================================

// F# is a true functional language -- functions are first
// class entities and can be combined easily to make powerful
// constructs

// Modules are used to group functions together
// Indentation is needed for each nested module.
module FunctionExamples =

    // define a simple adding function
    let add x y = x + y

    // basic usage of a function
    let a = add 1 2
    printfn "1 + 2 = %i" a

    // partial application to "bake in" parameters
    let add42 = add 42
    let b = add42 1
    printfn "42 + 1 = %i" b

    // composition to combine functions
    let add1 = add 1
    let add2 = add 2
    let add3 = add1 >> add2
    let c = add3 7
    printfn "3 + 7 = %i" c

    // higher order functions
    [1..10] |> List.map add3 |> printfn "new list is %A"

    // lists of functions, and more
    let add6 = [add1; add2; add3] |> List.reduce (>>)
    let d = add6 7
    printfn "1 + 2 + 3 + 7 = %i" d

// ================================================
// Lists and collection
// ================================================

// There are three types of ordered collection:
// * Lists are most basic immutable collection.
// * Arrays are mutable and more efficient when needed.
// * Sequences are lazy and infinite (e.g. an enumerator).
//
// Other collections include immutable maps and sets
// plus all the standard .NET collections

module ListExamples =

    // lists use square brackets
    let list1 = ["a"; "b"]
    let list2 = "c" :: list1    // :: is prepending
    let list3 = list1 @ list2   // @ is concat

    // list comprehensions (aka generators)
    let squares = [for i in 1..10 do yield i * i]

    // prime number generator
    let rec sieve = function
        | (p::xs) -> p :: sieve [ for x in xs do if x % p > 0 then yield x ]
        | []      -> []
    let primes = sieve [2..50]
    printfn "%A" primes

    // pattern matching for lists
    let listMatcher aList =
        match aList with
        | [] -> printfn "the list is empty"
        | [first] -> printfn "the list has one element %A " first
        | [first; second] -> printfn "list is %A and %A" first second
        | _ -> printfn "the list has more than two elements"

    listMatcher [1; 2; 3; 4]
    listMatcher [1; 2]
    listMatcher [1]
    listMatcher []

    // recursion using lists
    let rec sum aList =
        match aList with
        | [] -> 0
        | x::xs -> x + sum xs
    sum [1..10]

    // -----------------------------------------
    // Standard library functions
    // -----------------------------------------

    // map
    let add3 x = x + 3
    [1..10] |> List.map add3

    // filter
    let even x = x % 2 = 0
    [1..10] |> List.filter even

    // many more -- see documentation

module ArrayExamples =

    // arrays use square brackets with bar
    let array1 = [| "a"; "b" |]
    let first = array1.[0]        // indexed access using dot

    // pattern matching for arrays is same as for lists
    let arrayMatcher aList =
        match aList with
        | [| |] -> printfn "the array is empty"
        | [| first |] -> printfn "the array has one element %A " first
        | [| first; second |] -> printfn "array is %A and %A" first second
        | _ -> printfn "the array has more than two elements"

    arrayMatcher [| 1; 2; 3; 4 |]

    // Standard library functions just as for List

    [| 1..10 |]
    |> Array.map (fun i -> i + 3)
    |> Array.filter (fun i -> i % 2 = 0)
    |> Array.iter (printfn "value is %i. ")


module SequenceExamples =

    // sequences use curly braces
    let seq1 = seq { yield "a"; yield "b" }

    // sequences can use yield and
    // can contain subsequences
    let strange = seq {
        // "yield" adds one element
        yield 1; yield 2;

        // "yield!" adds a whole subsequence
        yield! [5..10]
        yield! seq {
            for i in 1..10 do
              if i % 2 = 0 then yield i }}
    // test
    strange |> Seq.toList


    // Sequences can be created using "unfold"
    // Here's the fibonacci series
    let fib = Seq.unfold (fun (fst,snd) ->
        Some(fst + snd, (snd, fst + snd))) (0,1)

    // test
    let fib10 = fib |> Seq.take 10 |> Seq.toList
    printf "first 10 fibs are %A" fib10


// ================================================
// Data Types
// ================================================

module DataTypeExamples =

    // All data is immutable by default

    // Tuples are quick 'n easy anonymous types
    // -- Use a comma to create a tuple
    let twoTuple = 1, 2
    let threeTuple = "a", 2, true

    // Pattern match to unpack
    let x, y = twoTuple  // sets x = 1, y = 2

    // ------------------------------------
    // Record types have named fields
    // ------------------------------------

    // Use "type" with curly braces to define a record type
    type Person = {First:string; Last:string}

    // Use "let" with curly braces to create a record
    let person1 = {First="John"; Last="Doe"}

    // Pattern match to unpack
    let {First = first} = person1    // sets first="John"

    // ------------------------------------
    // Union types (aka variants) have a set of choices
    // Only case can be valid at a time.
    // ------------------------------------

    // Use "type" with bar/pipe to define a union type
    type Temp =
        | DegreesC of float
        | DegreesF of float

    // Use one of the cases to create one
    let temp1 = DegreesF 98.6
    let temp2 = DegreesC 37.0

    // Pattern match on all cases to unpack
    let printTemp = function
       | DegreesC t -> printfn "%f degC" t
       | DegreesF t -> printfn "%f degF" t

    printTemp temp1
    printTemp temp2

    // ------------------------------------
    // Recursive types
    // ------------------------------------

    // Types can be combined recursively in complex ways
    // without having to create subclasses
    type Employee =
      | Worker of Person
      | Manager of Employee list

    let jdoe = {First="John"; Last="Doe"}
    let worker = Worker jdoe

    // ------------------------------------
    // Modeling with types
    // ------------------------------------

    // Union types are great for modeling state without using flags
    type EmailAddress =
        | ValidEmailAddress of string
        | InvalidEmailAddress of string

    let trySendEmail email =
        match email with // use pattern matching
        | ValidEmailAddress address -> ()   // send
        | InvalidEmailAddress address -> () // don't send

    // The combination of union types and record types together
    // provide a great foundation for domain driven design.
    // You can create hundreds of little types that accurately
    // reflect the domain.

    type CartItem = { ProductCode: string; Qty: int }
    type Payment = Payment of float
    type ActiveCartData = { UnpaidItems: CartItem list }
    type PaidCartData = { PaidItems: CartItem list; Payment: Payment}

    type ShoppingCart =
        | EmptyCart  // no data
        | ActiveCart of ActiveCartData
        | PaidCart of PaidCartData

    // ------------------------------------
    // Built in behavior for types
    // ------------------------------------

    // Core types have useful "out-of-the-box" behavior, no coding needed.
    // * Immutability
    // * Pretty printing when debugging
    // * Equality and comparison
    // * Serialization

    // Pretty printing using %A
    printfn "twoTuple=%A,\nPerson=%A,\nTemp=%A,\nEmployee=%A"
             twoTuple person1 temp1 worker

    // Equality and comparison built in.
    // Here's an example with cards.
    type Suit = Club | Diamond | Spade | Heart
    type Rank = Two | Three | Four | Five | Six | Seven | Eight
                | Nine | Ten | Jack | Queen | King | Ace

    let hand = [ Club, Ace; Heart, Three; Heart, Ace;
                 Spade, Jack; Diamond, Two; Diamond, Ace ]

    // sorting
    List.sort hand |> printfn "sorted hand is (low to high) %A"
    List.max hand |> printfn "high card is %A"
    List.min hand |> printfn "low card is %A"


// ================================================
// Active patterns
// ================================================

module ActivePatternExamples =

    // F# has a special type of pattern matching called "active patterns"
    // where the pattern can be parsed or detected dynamically.

    // "banana clips" are the syntax for active patterns

    // for example, define an "active" pattern to match character types...
    let (|Digit|Letter|Whitespace|Other|) ch =
       if System.Char.IsDigit(ch) then Digit
       else if System.Char.IsLetter(ch) then Letter
       else if System.Char.IsWhiteSpace(ch) then Whitespace
       else Other

    // ... and then use it to make parsing logic much clearer
    let printChar ch =
      match ch with
      | Digit -> printfn "%c is a Digit" ch
      | Letter -> printfn "%c is a Letter" ch
      | Whitespace -> printfn "%c is a Whitespace" ch
      | _ -> printfn "%c is something else" ch

    // print a list
    ['a'; 'b'; '1'; ' '; '-'; 'c'] |> List.iter printChar

    // -----------------------------------
    // FizzBuzz using active patterns
    // -----------------------------------

    // You can create partial matching patterns as well
    // Just use underscore in the definition, and return Some if matched.
    let (|MultOf3|_|) i = if i % 3 = 0 then Some MultOf3 else None
    let (|MultOf5|_|) i = if i % 5 = 0 then Some MultOf5 else None

    // the main function
    let fizzBuzz i =
      match i with
      | MultOf3 & MultOf5 -> printf "FizzBuzz, "
      | MultOf3 -> printf "Fizz, "
      | MultOf5 -> printf "Buzz, "
      | _ -> printf "%i, " i

    // test
    [1..20] |> List.iter fizzBuzz

// ================================================
// Conciseness
// ================================================

module AlgorithmExamples =

    // F# has a high signal/noise ratio, so code reads
    // almost like the actual algorithm

    // ------ Example: define sumOfSquares function ------
    let sumOfSquares n =
       [1..n]              // 1) take all the numbers from 1 to n
       |> List.map square  // 2) square each one
       |> List.sum         // 3) sum the results

    // test
    sumOfSquares 100 |> printfn "Sum of squares = %A"

    // ------ Example: define a sort function ------
    let rec sort list =
       match list with
       // If the list is empty
       | [] ->
            []                            // return an empty list
       // If the list is not empty
       | firstElem::otherElements ->      // take the first element
            let smallerElements =         // extract the smaller elements
                otherElements             // from the remaining ones
                |> List.filter (fun e -> e < firstElem)
                |> sort                   // and sort them
            let largerElements =          // extract the larger ones
                otherElements             // from the remaining ones
                |> List.filter (fun e -> e >= firstElem)
                |> sort                   // and sort them
            // Combine the 3 parts into a new list and return it
            List.concat [smallerElements; [firstElem]; largerElements]

    // test
    sort [1; 5; 23; 18; 9; 1; 3] |> printfn "Sorted = %A"

// ================================================
// Asynchronous Code
// ================================================

module AsyncExample =

    // F# has built-in features to help with async code
    // without encountering the "pyramid of doom"
    //
    // The following example downloads a set of web pages in parallel.

    open System.Net
    open System
    open System.IO
    open Microsoft.FSharp.Control.CommonExtensions

    // Fetch the contents of a URL asynchronously
    let fetchUrlAsync url =
        async {   // "async" keyword and curly braces
                  // creates an "async" object
            let req = WebRequest.Create(Uri(url))
            use! resp = req.AsyncGetResponse()
                // use! is async assignment
            use stream = resp.GetResponseStream()
                // "use" triggers automatic close()
                // on resource at end of scope
            use reader = new IO.StreamReader(stream)
            let html = reader.ReadToEnd()
            printfn "finished downloading %s" url
            }

    // a list of sites to fetch
    let sites = ["http://www.bing.com";
                 "http://www.google.com";
                 "http://www.microsoft.com";
                 "http://www.amazon.com";
                 "http://www.yahoo.com"]

    // do it
    sites
    |> List.map fetchUrlAsync  // make a list of async tasks
    |> Async.Parallel          // set up the tasks to run in parallel
    |> Async.RunSynchronously  // start them off

// ================================================
// .NET compatibility
// ================================================

module NetCompatibilityExamples =

    // F# can do almost everything C# can do, and it integrates
    // seamlessly with .NET or Mono libraries.

    // ------- work with existing library functions  -------

    let (i1success, i1) = System.Int32.TryParse("123");
    if i1success then printfn "parsed as %i" i1 else printfn "parse failed"

    // ------- Implement interfaces on the fly! -------

    // create a new object that implements IDisposable
    let makeResource name =
       { new System.IDisposable
         with member this.Dispose() = printfn "%s disposed" name }

    let useAndDisposeResources =
        use r1 = makeResource "first resource"
        printfn "using first resource"
        for i in [1..3] do
            let resourceName = sprintf "\tinner resource %d" i
            use temp = makeResource resourceName
            printfn "\tdo something with %s" resourceName
        use r2 = makeResource "second resource"
        printfn "using second resource"
        printfn "done."

    // ------- Object oriented code -------

    // F# is also a fully fledged OO language.
    // It supports classes, inheritance, virtual methods, etc.

    // interface with generic type
    type IEnumerator<'a> =
        abstract member Current : 'a
        abstract MoveNext : unit -> bool

    // abstract base class with virtual methods
    [<AbstractClass>]
    type Shape() =
        // readonly properties
        abstract member Width : int with get
        abstract member Height : int with get
        // non-virtual method
        member this.BoundingArea = this.Height * this.Width
        // virtual method with base implementation
        abstract member Print : unit -> unit
        default this.Print () = printfn "I'm a shape"

    // concrete class that inherits from base class and overrides
    type Rectangle(x:int, y:int) =
        inherit Shape()
        override this.Width = x
        override this.Height = y
        override this.Print ()  = printfn "I'm a Rectangle"

    // test
    let r = Rectangle(2, 3)
    printfn "The width is %i" r.Width
    printfn "The area is %i" r.BoundingArea
    r.Print()

    // ------- extension methods  -------

    // Just as in C#, F# can extend existing classes with extension methods.
    type System.String with
       member this.StartsWithA = this.StartsWith "A"

    // test
    let s = "Alice"
    printfn "'%s' starts with an 'A' = %A" s s.StartsWithA

    // ------- events  -------

    type MyButton() =
        let clickEvent = new Event<_>()

        [<CLIEvent>]
        member this.OnClick = clickEvent.Publish

        member this.TestEvent(arg) =
            clickEvent.Trigger(this, arg)

    // test
    let myButton = new MyButton()
    myButton.OnClick.Add(fun (sender, arg) ->
            printfn "Click event with arg=%O" arg)

    myButton.TestEvent("Hello World!")

```

## More Information

For more demonstrations of F#, go to the [Try F#](http://www.tryfsharp.org/Learn) site, or my [why use F#](http://fsharpforfunandprofit.com/why-use-fsharp/) series.

Read more about F# at [fsharp.org](http://fsharp.org/).