Pattern Matching with Option

Pattern matching is a fundamental technique in F# to handle Option values. It allows us to determine whether a value is present or absent and to destructure the value when it is present. Pattern matching helps us handle both Some and None cases effectively.

Let’s take an example:

let divide a b =
    if b = 0 then None
    else Some (a / b)

This will work as:

let result1 = divide 5 6 // => int option = Some 0
let result2 = divide 5 0 // => int option = None

This is an example of how it can be convenient to handle errors. Usually 5 / 0 would return a System.DivideByZeroException but with Option we can handle it without an exception.

Then, for we extract the value from the result we can also use Pattern Matching:

match result1 with
| None -> printfn "Division failed"
| Some x -> printfn "Result = %d" x

// prints: "Result = 0"

This is how we usually handle to extract values from Some to work with them in our code.

We can use it to generalize it in a function:

let printResult option =
    match option with
    | None -> printfn "Division failed"
    | Some x -> printfn "Result = %d" x

And use it to work with both variables:

printResult result1 // prints: Result = 0
printResult result2 // prints: "Division failed"