F# by Example: Discriminated Unions

A discriminated union is a type that can be one of several named cases Each case can optionally have associated data

 
type Animal =

The Dog has a single string value (name)

 
    | Dog of name: string

The Cat has two values: a string (name) and an int (lives)

 
    | Cat of name: string * lives: int

Pattern matching allows us to enforce handling all possible cases of the union

 
let describe animal =
    match animal with

For each case, we can destructure and use the associated data

 
    | Dog name -> sprintf "%s says Woof!" name
    | Cat(name, _) -> sprintf "%s says Meow!" name
 
let dog = Dog "Buddy"
let cat = Cat("Whiskers", 9)

Process and print information about each animal This demonstrates how we can work with a collection of mixed animal types

 
for animal in [ dog; cat ] do
    printfn "%s" (describe animal)

by Arpx | source | license