R0b

alias calc {
  var %num $1-
  var %math $2
  var %pos $pos(%num,$(%math,2))

  var %side.1 = $remove($left(%num,%pos),$(%math,2))
  var %side.2 = $right(%num,$+(-,%pos))

  var %x 2
  while (%x) {
    set $+(%,len.,%x) $calc($count($($+(%,side.,%x),2),$chr(58)) + 1)
    dec %x
  }

  if (%len.1 == %len.2) {
    :loop
    var %x %len.1
    var %s 1
    if (%cs1.1) { inc %s 1 }
    while (%x) {
      set $+(%,cs,%s,.,%x) $gettok($($+(%,side.,%s),2),$(%x,2),58)
      dec %x 1
    }
    if (!%cs2.1) { goto loop }
    var %x %len.1 
    while (%x) {
      var %c = $calc($($+(%,cs1.,%x),2) %math $($+(%,cs2.,%x),2))
      set %ans $+($chr(58),%c,%ans)
      dec %x 1
    }
  }

  echo -a Num: %num Ans: $right(%ans,-1)

  unset %len.*
  unset %calc.*
  unset %cs*
  unset %ans
}