// we rebuild the sensor list with every invocation, because things change
function buildSensorList {
  local sList is Lexicon().
  list SENSORS in SensorList.
  for s in SensorList {
    if not sList:HasKey(s:type) {
      sList:add(s:type, s).
    }
  }
  return sList.
}

function HasSensor {
  parameter s.
  local sList is buildSensorList().
  return sList:HasKey(s).
}

function ReadSensor {
  parameter s.

  local sList is buildSensorList().
  if not sList:HasKey(s) {
    return -1. // TODO: is -1 an impossible result for all sensors? I suspect not...
  }
  return s:DISPLAY:TOSCALAR.
}