Clojure has a number of tools to work with agents. One of them is validators. When an agent's message function returns a value, any validator functions assigned to that agent receive the agent's data before it does. If the validators return true, all is well. The agent is updated and processing continues. However, if any validator returns false or raises an error, an error is raised on the agent.

This can be a handy tool to make sure that the data assigned to your agent conforms to your expectations, and it can be an important check on the consistency and validity of your data.

For this recipe, we'll read data from a CSV file and convert the values in some of the columns to integers. We'll use a validator to ensure that this actually happens.