(e: Expression) in-tag: t := (evaluate: e) (as: String) in-tag: t
(s: String) in-tag: t := "<" .. t .. ">" .. s .. "</" .. t words head .. ">"

(s: String) operator? :=
  s head in?: "~!@#$%^&*-_=+./\\|<>?:"

(s: String) type: (c: String) :=
  s in-tag: ("span class=\"" .. c .. "\"")

(s: String) escape :=
  s match: {
    "" -> ""
    $< . ss -> "&lt;" .. ss escape
    $> . ss -> "&gt;" .. ss escape
    $& . ss -> "&amp;" .. ss escape
    s . ss -> s . ss escape
  }

(s: String) keywordfy :=
  if: s operator?
    then: { s }
    else: { s .. ":" }