let dateRange (startDate : System.DateTime) (endDate : System.DateTime) =

    let start = startDate.Date

    let finish = endDate.Date

    if start = finish then Seq.singleton start

    else

        let shouldContinue =

            if start < finish then fun d -> d <= finish

            else fun d -> d >= finish

        let moveNext =

            if start < finish then fun (d : System.DateTime) -> d.AddDays(1.0)

            else fun (d : System.DateTime) -> d.AddDays(-1.0)

        let rec getNext (nextDate : System.DateTime) =

            seq {

                if shouldContinue nextDate then

                    yield nextDate

                    yield! getNext (nextDate |> moveNext)

            }

        getNext start

​

dateRange (System.DateTime.Parse("08/01/2023 12:00:00 AM")) (System.DateTime.Parse("08/20/2023 12:00:00 AM"))

  |> Seq.map (sprintf """{ "date": "%A" }""")

  |> String.concat ","

  |> printfn "%s"