function createRangeNode (start, end, step) {
    if (step === undefined) {
      return new RangeNode(new ConstantNode(start), new ConstantNode(end))
    } else {
      return new RangeNode(new ConstantNode(start), new ConstantNode(end), new ConstantNode(step))
    }
  }
Helper function to create a RangeNode
@param {number} start
@param {number} end
@param {number} [step]
@return {RangeNode}