How to write code in F# for what functors do in OCaml?

Question

I have many programs written in OCaml, some of them use functors. Now, I am considering of writing and re-writing a part of code in F# (to benefit some advantages that OCaml doe

Answer 1

Here is a bit different approach that achieves same outcome using a generic class and one object per type.

type Comparison = Less | Equal | Greater

type Set<'a>(compare : 'a -> 'a -> Comparison) =

    member this.Empty : 'a list = []

    member this.Add x s = 
         match s with
         | [] -> [x]
         | hd::tl ->
             match compare x hd with
             | Equal   -> s         (* x is already in s *)
             | Less    -> x :: s    (* x is smaller than all elements of s *)
             | Greater -> hd :: this.Add x tl


let compare x y = if x = y then Equal else if x < y then Less else Greater

let compareFloats (x : float) (y : float) = if x = y then Equal else if x < y then Less else Greater

// Note that same generic compare function can be used for stringSet and intSet
// as long as the type parameter is explicitly given
let stringSet = Set(compare)
let intSet = Set(compare)

// Type parameter not needed, because compareFloats is not generic
let floatSet = Set(compareFloats)

let try1 () = stringSet.Add "foo" stringSet.Empty   // -> ["foo"]
let try2 () = intSet.Add 2 intSet.Empty             // -> [2]
let try3 () = floatSet.Add 3.0 floatSet.Empty       // -> [3.0]