FizzBuzz decision tree

gistfile1.fs

type Result = 
  | Text of string
  | Number of int
  override self.ToString() = 
    match self with
    | Text s -> s
    | Number i -> i.ToString()
    
type Tree =
  | Branch of (int -> Result) * Tree
  | Leaf of Result

let rule f s = 
  function 
  | i when f i -> Text s
  | i -> Number i

let fizz = rule (fun i -> i % 3 = 0) "fizz"
let buzz = rule (fun i -> i % 5 = 0) "buzz"
let fizzbuzz = rule (fun i -> i % 3 = 0 && i % 5 = 0) "fizzbuzz"
let lucky = rule (fun i -> i.ToString().Contains "3") "lucky"
let noMatch = string >> Text

let tree =
  [ fizz; buzz; fizzbuzz; lucky; noMatch ]
  |> List.rev 
  |> Seq.fold (fun c n -> Branch(n, c)) (Branch (string >> Text, Text "" |> Leaf))

let rec calculate i tree = 
  match tree with
  | Branch(check, next) -> 
    match check i with
    | Number i -> calculate i next
    | r -> r
  | Leaf r -> r

{ 1..20 } |> Seq.iter (fun i -> calculate i tree |> printfn "%+A")