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F# Hello World! 

F# Hello World! 



Click on RUN button to see the output

F sharp Online Compiler

Write, Run & Share F# code online using OneCompiler's F# online compiler for free. It's one of the robust, feature-rich online compilers for F# language, running on the latest version 4.0. Getting started with the OneCompiler's F# compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as F#. OneCompiler also has reference programs, where you can look for the sample programs and start learning. Happy learning!!

Read inputs from stdin

OneCompiler's F# online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample F# program which takes name as input and prints hello message with your name.

open System
let name = Console.ReadLine()
Console.Write("Hello 0.\n", name)         

About F#

F#(F sharp) is a functional programming language which was developed by Microsoft in the year 2005. F# is .net implementation of OCaml. It can be used in variety of applications like graphic designing, Telecommunications, AI, CPU design, compiler programming, web applications, games etc.,

Syntax help

Data Types

Integer Data types

Data typeDescriptionSizeRange
sbyte8-bit signed integer1 byte-128 to 127
byte8-bit unsigned integer1 byte0 to 255
int1616-bit signed integer2 bytes-32768 to 32767
unit1616-bit unsigned integer2 bytes0 to 65,535
int/int3232-bit signed integer4 bytes-2,147,483,648 to 2,147,483,647
uint3232-bit unsigned integer4 bytes0 to 4,294,967,295
int6464-bit signed integer8 bytes-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
uint6464-bit unsigned integer8 bytes0 to 18,446,744,073,709,551,615
bigintarbitrary precision integerAt least 4 bytesIntegers

Float Data types

Data typeDescriptionSizeRange
float3232-bit signed floating point number4 bytes±1.5e-45 to ±3.4e38
float64-bit signed floating point number8 bytes±5.0e-324 to ±1.7e308
decimal128-bit signed floating point number16 bytes±1.0e-28 to ±7.9e28

Text and Boolean Data types

Data typeDescriptionSizeRange
charsingle character2 bytesU+0000 to U+ffff
stringText20 + (2 * length of the string) bytes0 to up to 2 billion characters
boolStores either true or false1 byteTrue or false


Variable is a name given to the storage area in order to manipulate them in our programs.

let variable_name:data-type = value

Mutable variable declaration

let mutable variable_name:data-type = value


1. If-Else:

When ever you want to perform a set of operations based on a condition or set of conditions then If or IF-ELSE or Nested If-Elif-Else are used.


if conditional-expression then
   // code


if conditional-expression then
   // code
   // code

Nested If-Elif-Else

if conditional-expression then
  // code
elif conditional-expression then
   // code
elif conditional-expression then
   // code
   // code

2. For:

For loop is used to iterate a set of statements based on a condition.


Iteration occurs in ascending order

for var = start-expression to end-expression do
  // code  


Iteration occurs in descending order.

for var = start-expression downto end-expression do
  // code  


This loops is used when iteration occurs over enumerable collection like arrays, lists, sequences, range expression etc.

for pattern in enumerable-collection-expr do
   // code


let listItems = [1,2,3,4,5]
for x in listItems do
   printfn "%d" x

3. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations is not known in advance.

while condition-expr do   
 // code 


In F#, You can declare and use functions similar to Variables. In simpler words, you can understand them as user-defined variables.

How to define a function

let [inline] function-name parameter-list [ : return-type ]
   = function-body

How to call a function

let Var = function-name parameter-list

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