{ @empty-string describe-error := "string is empty"

  (s: String) indent: (n: Integer) :=
    s lines (map: { l | $  (repeat: n) .. l }) (join: "\n")

  (s: String) word-wrap: (length: Integer) :=
    s lines
      (map: { l |
        if: (l all?: @space?)
          then: { l }
          else: { (l take-while: @space?) .. (wrap-line: l to: length acc: "") }
      })
      unlines

  wrap-line: "" to: _ acc: acc := acc
  wrap-line: l to: length acc: acc :=
    { words = l words

      condition: {
        acc empty? ->
          wrap-line: words tail unwords to: length acc: words head

        acc length > length ->
          acc .. "\n" .. (wrap-line: l to: length acc: "")

        acc length + 1 + words head length > length ->
          acc .. "\n" .. (wrap-line: words tail unwords to: length acc: words head)

        otherwise ->
          wrap-line: words tail unwords to: length acc: (acc .. " " .. words head)
      }
    } call
} call

(s: String) plural :=
  s case-of: {
    r"o$"i ->
      s .. "es"
    r"[aeiou]$"i ->
      s .. "s"
    r"(?<root>.+[aeiou])y$"i ->
      s .. "s"
    r"(lay-by|stand-by)$"i ->
      s .. "s"
    r"(?<root>.+)y$"i ->
      \root .. "ies"
    r"(?<root>.+)us$"i ->
      \root .. "i"
    r"(?<root>.+)sis$"i ->
      \root .. "es"
    r"(?<root>.+)(ex|ix)$"i ->
      \root .. "ices"
    r"(?<root>.+)(ss|sh|ch|dge)$"i ->
      s .. "es"
    _ ->
      s .. "s"
  }