Utility.fs

Utility.fs

namespace global  // note use of GLOBAL namespace

type NonEmptyList<'a> = {
    First:'a
    Rest: 'a list
    }

module NonEmptyList =
    // aList:'a list -> NonEmptyList<'a> option
    let ofList aList =
        match aList with
        | [] -> None
        | head::tail -> Some {First=head; Rest=tail}

    // aNonEmptyList:NonEmptyList<'a> -> 'a list
    let toList aNonEmptyList =
        aNonEmptyList.First :: aNonEmptyList.Rest

    let length aNonEmptyList =
        aNonEmptyList.Rest.Length + 1

    let map f aNonEmptyList = {
        First = f aNonEmptyList.First
        Rest = List.map f aNonEmptyList.Rest
        }