Translate chars in string (naive version)

proc translate(c: char): char =
  const
    a = "abcdef"
    b = "123456"

  let o = a.find(c)
  if o >= 0:
    return b[o]
  else:
    return c

proc main() =
  var s = "that is the abc"
  for c in s.mitems():
    c = c.translate

  echo s

main()