F# Basic Tutorial
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F# - Variables
F# - Variables
A variable is a name given to a storage area that our programs can manipulate. Each variable has a specific type, which determines the size and layout of the variable s memory; the range of values that can be stored within that memory; and the set of operations that can be appped to the variable.
Variable Declaration in F#
The let keyword is used for variable declaration −
For example,
let x = 10
It declares a variable x and assigns the value 10 to it.
You can also assign an expression to a variable −
let x = 10 let y = 20 let z = x + y
The following example illustrates the concept −
Example
let x = 10 let y = 20 let z = x + y printfn "x: %i" x printfn "y: %i" y printfn "z: %i" z
When you compile and execute the program, it yields the following output −
x: 10 y: 20 z: 30
Variables in F# are immutable, which means once a variable is bound to a value, it can’t be changed. They are actually compiled as static read-only properties.
The following example demonstrates this.
Example
let x = 10 let y = 20 let z = x + y printfn "x: %i" x printfn "y: %i" y printfn "z: %i" z let x = 15 let y = 20 let z = x + y printfn "x: %i" x printfn "y: %i" y printfn "z: %i" z
When you compile and execute the program, it shows the following error message −
Duppcate definition of value x Duppcate definition of value Y Duppcate definition of value Z
Variable Definition With Type Declaration
A variable definition tells the compiler where and how much storage for the variable should be created. A variable definition may specify a data type and contains a pst of one or more variables of that type as shown in the following example.
Example
let x:int32 = 10 let y:int32 = 20 let z:int32 = x + y printfn "x: %d" x printfn "y: %d" y printfn "z: %d" z let p:float = 15.99 let q:float = 20.78 let r:float = p + q printfn "p: %g" p printfn "q: %g" q printfn "r: %g" r
When you compile and execute the program, it shows the following error message −
x: 10 y: 20 z: 30 p: 15.99 q: 20.78 r: 36.77
Mutable Variables
At times you need to change the values stored in a variable. To specify that there could be a change in the value of a declared and assigned variable, in later part of a program, F# provides the mutable keyword. You can declare and assign mutable variables using this keyword, whose values you will change.
The mutable keyword allows you to declare and assign values in a mutable variable.
You can assign some initial value to a mutable variable using the let keyword. However, to assign new subsequent value to it, you need to use the ← operator.
For example,
let mutable x = 10 x ← 15
The following example will clear the concept −
Example
let mutable x = 10 let y = 20 let mutable z = x + y printfn "Original Values:" printfn "x: %i" x printfn "y: %i" y printfn "z: %i" z printfn "Let us change the value of x" printfn "Value of z will change too." x <- 15 z <- x + y printfn "New Values:" printfn "x: %i" x printfn "y: %i" y printfn "z: %i" z
When you compile and execute the program, it yields the following output −
Original Values: x: 10 y: 20 z: 30 Let us change the value of x Value of z will change too. New Values: x: 15 y: 20 z: 35Advertisements