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


⟨ToRoman⇐R⟩ ← {
  ds ← 1↓¨(¯1+`⊏⊸=)⊸⊔" I IV V IX X XL L XC C CD D CM M"
  vs ← 1e3∾˜ ⥊1‿4‿5‿9×⌜˜10⋆↕3
  R ⇐ {
    𝕨𝕊0: "";
    (⊑⟜ds∾·𝕊𝕩-⊑⟜vs) 1-˜⊑vs⍋𝕩
  }
}