The Power of Composition - Scott Wlaschin - NDC Oslo 2020

fizbuzz.fs

open Microsoft.FSharp.Core

type FizzBuzzResult =
    | Unhadnled of int
    | Handled of string

let isDivisiblyBy n divisor =
    n % divisor = 0
    
let handle divisor label n =
    let ok = isDivisiblyBy n divisor
    match ok with
    | true -> Handled label
    | _ -> Unhadnled n

let printFizzBuzz fbr =
    match fbr with
    | Handled h -> printfn "Handled %s" h
    | Unhadnled h -> printfn "Unhandled %i" h

let ifUnhandledDo f prevFizzBuzz =
    match prevFizzBuzz with
    | Handled s -> Handled s
    | Unhadnled i -> f i

let fizBuzz n =
        n
        |> handle 15 "FizzBuzz"
        |> ifUnhandledDo (handle 3 "fizz")
        |> ifUnhandledDo (handle 5 "buzz")
        |> printFizzBuzz

[0..100] |> List.iter fizBuzz