Fold in F# and C#

fold.cs

// FuncList is a functional "cons" list type with Head value and Tail list
public R Fold<T, R>(this FuncList<T> list, Func<R, T, R> func, R init) {
  if (list.IsEmpty) {
    return init;
  }
  else {
    var foldState = func(init, list.Head);
    return list.Tail.Fold(func, foldState);
  }
}

var list = FuncList.Cons(1,
           FuncList.Cons(2,
           FuncList.Cons(3,
           FuncList.Cons(4,
           FuncList.Cons(5,
           FuncList.Empty<int>())))));
list.Fold((x,y) => x * y, 1);

fold.fs

(* Recursive let binding *)
let rec fold f init list =
  match list with
  | [] -> init
  | head::tail ->
    let foldState = f init head
    fold f foldState tail

[ 1 .. 5 ] |> fold (*) 1