Get current input field data in callback function

[eluser]JavaJunky[/eluser]
Is there a way inside a validation callback function to get the data related to the field currently being validated?

I'm trying to write one function that I can use to validate multiple fields, but I want to be able to know which field I'm validating in the callback function.

I want to do something like this:

Code:

function my_value_check($str) {
   $this_field = ??? // THE CURRENT FIELD BEING VALIDATED (can be field label)
   switch($this_field) {
      case "first_name":
         // checks $str against data for "first_name"
      ...
   }
   // return true or false
}