New Day Of Year Based On A 10 Month Calendar

MakeDecemberTenAgain

open System

let getNewDate dayOfYear =
    ["Jan";"Feb";"Mar";"Apr";"May";"Jun";"Sep";"Oct";"Nov";"Dec"]
        |> Seq.mapi(fun i m -> if i%2=0 then m, [1..36] else m, [1..37])
        |> Seq.map(fun (m,ad) -> ad |> Seq.map(fun d -> m,d))
        |> Seq.collect(fun a -> a)
        |> Seq.mapi(fun i d -> i, d )
        |> Seq.tryFind(fun (i,d) -> i = dayOfYear)

let dateOfInterest = new DateTime(2017,7,4)
let newDate = getNewDate dateOfInterest.DayOfYear