Task

Create a function taking a positive integer as its parameter and returning a string containing the Roman numeral representation of that integer. Modern Roman numerals are written by expressing each digit separately, starting with the left most digit and skipping any digit with a value of zero.



In Roman numerals:

 1990 is rendered: 1000=M, 900=CM, 90=XC; resulting in MCMXC
 2008 is written as 2000=MM, 8=VIII; or MMVIII
 1666 uses each Roman symbol in descending order: MDCLXVI


R1000=. ;L:1 ,{ <@(<;._1);._2]0 :0
  C CC CCC CD D DC DCC DCCC CM
  X XX XXX XL L LX LXX LXXX XC
  I II III IV V VI VII VIII IX
)
 
rfd=: ('M' $~ <.@%&1000) , R1000 {::~ 1000&|