name: string
validator: {$ref: "http://firebase.com/schema/types/string#"}
compile:
  console.log("compile string");
  api.addConstraint("!next.exists() || next.isString()")


  if (api.getField("enum") != null){
    var enum_constraint = "!next.exists()";
    for (var idx in api.getField("enum")){
      var enum_option = api.getField("enum")[idx];
      enum_constraint = enum_constraint + "||next === '" + enum_option + "'";
    }
    api.addConstraint(enum_constraint);
  }