gistfile1.fs

open System
open System.Collections.Generic

// first arg is always 'this' so assuming that it cannot be null
let rec equals(a : 'T, b : obj) comparisons = 
    if obj.ReferenceEquals(a, b) then true
    else 
        match b with
        | null -> false
        | (:? 'T as b) -> comparisons |> Seq.forall(fun c -> c a b)
        | _ -> false

// get values and compares them using obj.Equals (deals with nulls in both positions then calls <first arg>.Equals(<second arg>))
let Eq f a b = obj.Equals(f a, f b) 
// get values and compares them using IEqualityComparer
let (=>) f (c : IEqualityComparer<_>) a b = c.Equals(f a, f b)

type A(name) =
  member __.Name = name
  override this.Equals(that) = 
    equals (this, that) [
        (fun x -> x.Name) => StringComparer.InvariantCultureIgnoreCase
        ]

type B(parent:A, name) =
  member __.Parent = parent
  member __.Name = name
  override this.Equals(that) = 
    equals(this, that) [
        Eq(fun x -> x.Parent)
        (fun x -> x.Name) => StringComparer.InvariantCultureIgnoreCase
    ]