12 days

(reduce #(let[[d g]%2 p(cons g %)](doseq[l(cons d p)](println l))(newline)p)nil (map vector(map #(format"On the %s day of Christmas my true love gave to me"%)'(first second third fourth fifth sixth seventh eighth ninth tenth eleventh twelfth))["a partridge in a pear tree" "two turtle doves" "three french hens" "four calling birds" "five golden rings" "six geese a-laying" "seven swans a-swimming" "eight maids a-milking" "nine ladies dancing" "ten lords a-leaping" "eleven pipers piping" "twelve drummers drumming"]))