open System

​

type WeekDays = | Monday  = 1 | Tuesday = 2 | Wednesday = 3 | Thursday = 4 | Friday = 5

                | Saturday = 6 | Sunday = 7

​

let nextDay =

    function

    | WeekDays.Monday    -> WeekDays.Tuesday

    | WeekDays.Tuesday   -> WeekDays.Wednesday

    | WeekDays.Wednesday -> WeekDays.Thursday

    | WeekDays.Thursday  -> WeekDays.Friday

    | WeekDays.Friday    -> WeekDays.Saturday

    | WeekDays.Saturday  -> WeekDays.Sunday

    | WeekDays.Sunday    -> WeekDays.Monday

    | _ -> failwith "Invalid Week Day"

​

type ChargeCalc = | J5 | J6 | J7

​

let count charge =

    function

    | WeekDays.Monday -> 1 | WeekDays.Tuesday -> 1 | WeekDays.Wednesday -> 1

    | WeekDays.Thursday -> 1 | WeekDays.Friday -> 1

    | WeekDays.Saturday ->

        match charge with

            | J5 -> 0

            | _  -> 1

    | WeekDays.Sunday -> if charge = J7 then 1 else 0

    | _ -> invalidArg "day" "wrong week day"

​

​

let countDays charge limit weekday = Seq.unfold(fun (sum, day) ->

    if  sum  >= limit then None else Some (count charge day, (sum + count charge day, nextDay day))) (0, weekday)

​

[WeekDays.Monday; WeekDays.Tuesday; WeekDays.Wednesday; WeekDays.Thursday; WeekDays.Friday; WeekDays.Saturday; WeekDays.Sunday]

|> List.map (fun d -> d, countDays J6 2 d |> Seq.length)

|> List.map (fun (d, count) -> printfn "%A %d" d count)

|> ignore

​