How do I increment a character and compare two characters in EK9?

  letter <- 'a'

  letter++        moves from 'a' to 'b'
  letter++        moves from 'b' to 'c'
  letter++        moves from 'c' to 'd'

  if letter == 'd'          exact match
  if letter > 'a'           ordering (alphabetical)
  ordering <- 'a' <=> 'z'  spaceship comparison

  str <- $letter            character to string

defines module qa.operators.characterops

  defines function

    <?- Compare two characters and return spaceship ordering. -?>
    compareChars() as pure
      ->
        left as Character
        right as Character
      <- rtn as Integer: left <=> right

    <?- Check if two characters are equal. -?>
    charsEqual() as pure
      ->
        left as Character
        right as Character
      <- rtn as Boolean: left == right

  defines program

    CharacterOpsDemo()
      stdout <- Stdout()

      // === CHARACTER LITERAL ===

      letter <- 'a'
      stdout.println(`Starting letter: ${letter}`)

      // === INCREMENT ===

      letter++
      stdout.println(`After first ++: ${letter}`)

      letter++
      stdout.println(`After second ++: ${letter}`)

      letter++
      stdout.println(`After third ++: ${letter}`)

      // === COMPARISON VIA FUNCTION ===

      targetLetter <- 'd'
      matched <- charsEqual(letter, targetLetter)
      stdout.println(`Letter equals target: ${matched}`)

      // === SPACESHIP ORDERING VIA FUNCTION ===

      ordering <- compareChars(letter, targetLetter)
      stdout.println(`letter <=> target: ${ordering}`)

      alphaOrder <- compareChars('a', 'z')
      stdout.println(`'a' <=> 'z': ${alphaOrder}`)

      // === DECREMENT ===

      letter--
      stdout.println(`After --: ${letter}`)

      // === STRING CONVERSION ===

      charStr <- $letter
      stdout.println(`Character as string: ${charStr}`)

      // === ISSET ===

      require letter?
      unsetChar <- Character()
      require ~unsetChar?

      // === SORTED CHARACTER LIST ===

      chars <- List() of Character
      chars += 'z'
      chars += 'a'
      chars += 'm'

      sorted <- cat chars | sort | collect as List of Character
      stdout.println(`Sorted chars: ${sorted}`)

letter = letter + 1

letter++