How do I work with strings in EK9?

  greeting <- "Hello World"
  stdout.println(`Welcome to ${lang} version ${ver}`)

  .upperCase(), .lowerCase(), .trim(), .length(), .count(char)
  .rightPadded(n), .leftPadded(n)

  brownFox <- cat sentence | skip 10 | head 9 | collect as String

defines module qa.strings

  defines function

    charToLowerCaseString()
      -> ch as Character
      <- result as String: ch? <- $ch.lowerCase() else String()

    stringComparator()
      ->
        s1 as String
        s2 as String
      <-
        comparison as Integer: s1 <=> s2

    justStringValue()
      -> s1 as String
      <- rtn as String: s1

    isO()
      -> ch as Character
      <- found as Integer: ch == 'o' or ch == 'O' <- 1 else Integer()

  defines program
    StringDemo()
      stdout <- Stdout()

      // === STRING LITERALS ===

      // Double-quoted strings
      greeting <- "Hello World"
      stdout.println(greeting)

      // String interpolation with backticks
      languageName <- "EK9"
      versionNumber <- 1
      stdout.println(`Welcome to ${languageName} version ${versionNumber}`)

      // Escape sequences: \t tab, \n newline, \\ backslash, \" quote
      withTab <- "Column1\tColumn2"
      stdout.println(withTab)

      withNewline <- "Line1\nLine2"
      stdout.println(withNewline)

      // Unicode escapes for non-ASCII characters
      danish <- "\u00C6\u00D8\u00C5"
      stdout.println(`Danish letters: ${danish}`)

      // Unset string
      unsetString <- String()
      require ~unsetString?

      // === STRING METHODS ===

      sentence <- "The Quick Brown Fox"

      // Case conversion
      stdout.println(`Upper: ${sentence.upperCase()}`)
      stdout.println(`Lower: ${sentence.lowerCase()}`)

      // Padding
      stdout.println(`Right padded: [${sentence.rightPadded(30)}]`)
      stdout.println(`Left padded: [${sentence.leftPadded(30)}]`)

      // Trimming
      paddedSentence <- sentence.rightPadded(30)
      stdout.println(`Trimmed: [${paddedSentence.trim()}]`)

      // Length — two equivalent syntaxes
      stdout.println(`Length (method): ${sentence.length()}`)
      stdout.println(`Length (operator): ${length sentence}`)

      // Count character occurrences
      stdout.println(`Count of 'o': ${sentence.count('o')}`)

      // === CONCATENATION ===

      part1 <- "The Quick Brown Fox"
      part2 <- "Jumps Over The Lazy Dog"
      fullSentence <- `${part1} ${part2}`
      stdout.println(fullSentence)

      // === HASHCODE ===

      hashValue <- #? sentence
      stdout.println(`Hashcode: ${hashValue}`)

      // === STRINGS ARE STREAMABLE ===

      // Strings stream as character sequences
      // Extract a substring using skip and head
      brownFox <- cat fullSentence | skip 10 | head 9 | collect as String
      stdout.println(`Extracted: [${brownFox}]`)

      // Going beyond string length is safe — returns what is available
      endPart <- cat fullSentence | skip 35 | head 20 | collect as String
      stdout.println(`End part: [${endPart}]`)

      // Join a list of strings via stream collect
      spacer <- " "
      wordParts <- [part1, spacer, part2]
      rejoined <- cat wordParts | collect as String
      stdout.println(`Rejoined: ${rejoined}`)

      // Count occurrences of o/O using stream map
      oCount <- cat fullSentence | map with isO | collect as Integer
      stdout.println(`Count of o/O: ${oCount}`)

      // Find unique characters used (sorted, lowercase)
      charsUsed <- cat fullSentence | map with charToLowerCaseString | sort with stringComparator | uniq by justStringValue | collect as String
      stdout.println(`Unique chars: [${charsUsed}]`)

      // === COMPARISON ===

      alpha <- "abc"
      beta <- "def"
      require alpha < beta
      require beta > alpha
      require alpha <> beta
      require alpha == "abc"
      require alpha <= "abc"
      require alpha >= "abc"

      // Min operator
      fruit1 <- "apple"
      fruit2 <- "banana"
      lesser <- fruit1 <? fruit2
      require lesser == "apple"
      stdout.println(`Min: ${lesser}`)

greeting <- "Hello World" + 42

greeting <- "Hello World"