open System

let day number thing=    

    printfn  "on the %s day of christmas my true love gave to me \n%s\n" number thing 

/// One day of Christmas    

type OneDay = { number: string ; thing : string }

​

let first = { number = "first" ; thing = "a partridge in a pear tree"}

let second = { number = "second" ; thing = "two turtle doves"}

let third = { number = "third" ; thing = "three french hens"}

let fourth = { number = "fourth" ; thing = "four calling birds"}

let fifth = { number = "fifth" ; thing = "five gold rings"}

let sixth = { number = "sixth" ; thing = "six geese a laying"}

​

let allDays = [| first ; second ; third ; fourth ; fifth ; sixth ;

                {number = "seventh" ; thing = "seven swans a swimming" } ;

                {number = "eighth" ; thing = "eight maids a milking"} ;

                {number = "ninth" ; thing = "nine ladies dancing"} ;

                {number = "tenth" ; thing = "ten lords a leaping"} ;

                {number = "eleventh" ; thing = "eleven pipers piping"} ;

                {number = "twelth" ; thing = "twelve drummers drumming"} ;

        |]

​

for theDay in 0..allDays.Length-1 do

    let myDay = allDays.[theDay]

    let allThings = String.Join(",",allDays.[..theDay] |> Array.mapi (fun i d -> (if i=0 && theDay<> 0 then "and " else "")+d.thing)|> Array.rev )

    day myDay.number allThings