F Sharp (programming language)

F # is a functional programming language developed by Microsoft for the. NET Framework. F # is related to the languages ​​OCaml and ML, the syntax of the language, therefore, are very similar. Many OCaml programs that avoid unusual constructs and Caml - specific libraries, can therefore be compiled without change with F #.

In addition to the ingredients of functional programming are included in F # object-oriented and imperative language constructs.

Originally F # was developed as a research project by Microsoft Research, presently there will be continued by Microsoft's development department. F # is as part of Visual Studio 2010 for the first time officially supported and delivered. In addition, it is also available as an extension to Visual Studio 2008. In November 2010, F #, and associated compiler and libraries under the Apache License 2.0 was released.

Some language features

Variables

In F # there are no variables as in other programming languages. However, there are functions that always have the same return value. These are in F # declared with the let keyword and defined.

Let pi = 3.1415927 F # has type inference, that is, types of expressions are determined automatically. For example, pi automatically gets the type of floating-point literal.

Let is no variable assignment, but a declaration, ie the source

Let pi = 3.1415927      let pi = 10.0 can not be compiled because the value of pi is declared twice in the same scope. If the value of a variable in the program sequence to be changed, this must also be indicated in the declaration:

Let mutable x = 0 / / x is characterized by the " mutable " keyword as a variable      x < - 5 / / x, a new value is assigned      printfn "% i" x / / returns 5 from To change values ​​in retrospect is also possible through the use of so-called reference cells:

Let x = ref 0 / / x is of type " int ref" is therefore a reference to an integer      x: = 5 / / x is a new value is assigned to      printfn "% i"! x / / Using the "! " operator x is dereferenced. Returns 5. functions

Functions are declared like other values ​​using let:

Let square x = x * x

Let add xy = x y Functions, functions as parameters expected ( see higher-order function ):

Let do_twice f x = f ( f x) The statement

Printfn "% A" ( do_twice square 5) are 625 (the square of the square of 5 ) from. The do_twice function and using the composition operator and after eta - reduction as

Do_twice let f = f >> f be written.

In the example above for the square type int - determined > int, that is, square is a function that expects a parameter of type int and returns a value of type int. For do_twice gives the type ( 'a - >' a) -> 'a - >' a This means do_twice is a function as its first parameter a value of type ( 'a - >' a) gets (a function with a parameter of type ' a and a return value of type ' a). As second parameter it is given a value of type 'a and returns a value of type ' a back. 'a has the role of a type variable ( roughly comparable to generic or template parameters in Java / C , see Polymorphism (programming) ) here.

In F #, parameters without parentheses, etc., separated by spaces, to pass to the function. Only when a different function is required as a parameter of the return value, staples must be placed to define the evaluation of the expressions. In printfn " % A" (add 5 8) are the values ​​5 and 8 to the add function; its return value is a parameter for the function printfn.

F # allows Closures and Currying used:

Let add xy = x y      let inc = add 1 In the definition of inc the first parameter of the function is bound to add the value 1. The result of this partial function application is a new function with only one parameter. The evaluation of the expression

Inc 5 supplies as a result 6

F # supports tuple:

Let u = (3, 6)      Let V = (2, -3)      Let add ( a, b) (C, D ) = (A C, B D)      let x, y = add u v F # provides discriminated unions and pattern matching:

/ / An element of type tree is either a " road " and contains two elements of type "tree",      / / Or it is a "leaf" and contains an integer      type tree =      | Branch of tree * tree      | Leaf of int        let rec x = total tree          match x with          | Branch (l, r) - > tree sum l r sum tree          | Leaf (x ) -> x In F # and object- oriented programming is possible. Example of a class declaration:

Type Person =          val name: string          val mutable age: int          new ( n, a) = { name = n; age = a}          member x.Name = x.name          member x.Age              with get () = x.age              and set ( v) = x.age <- v          member x.Print () = printfn "% s is% i years old. " x.name x.age F # is compliant with the Common Language Infrastructure. Thus it can be accessed in F # to types that are written in other. NET languages ​​, and vice versa. Null pointers are only required for the interaction with classes from the. NET Framework.

Syntax

In F # code two syntax forms are possible: simple syntax and detailed syntax. The simple syntax is used by default, but with this form, the indents are very important. They play at the detailed syntax of a smaller role, because there determine more keywords like begin, end and in the beginning and end of code blocks.

Example of the simple and detailed syntax:

Let mutable x = 1   while x <3 do      x <- x 1 / / let mutable x = 1   while x <3 do      x <- x 1 done type Person =      val name: string      val mutable age: int / / / / type Person = class      val name: string      val mutable age: int end In the simple syntax, the indenting is mandatory, at the detailed you could omit it as well.

Development environment and compiler

F # code is compiled, this creates intermediate code in the Common Intermediate Language (CIL ), just as with programs written in C # or VB.NET.

F # is not in the free Visual Studio Express Editions included, but one can be installed by a free toolkit. F # is included editions directly from the paid Visual Studio.

There is also an interactive environment or F # interpreter, F # Interactive or shortly FSI. Now we can write the code directly into the console. Entries in the interpreter are with; ; complete, which also multiline entries are possible. After compiling F # Interactive executes the code and writes the signature of all types and values ​​compiled in the console window. Error messages are output.

Example

The following examples give "Hello World" from.

Let main = System.Console.WriteLine (" Hello World") or

Printfn "Hello World" The following function implements the recursive Ackermann function:

Let rec ack m, n =        if m = 0 then n 1        else if n = 0 then ack (m - 1 ) 1        else ACK ( m - 1 ) (ACK m (n - 1)) Web Links

• Microsoft F # Developer Center on MSDN (English)
• F # from Microsoft Research Homepage (English)
• The F # Survival Guide (English)