/// Creates a function from a sequence that, when called, returns the items in the sequence
let enumerate (xs: seq<_>)  = 
    use en = xs.GetEnumerator()
    fun () ->
        en.MoveNext() |> ignore
        en.Current

let f = [1;2;3;4;5] |> enumerate

f() |> printf "val = %i"
f() |> printf "val = %i"
f() |> printf "val = %i"
f() |> printf "val = %i"
f() |> printf "val = %i"
f() |> printf "val = %i" // This line will throw