validationBuilder.php

<?php
function setupValidation()
{
  $fields = array();
  $fields[] = array(
    "type"  => "presenceOf",
    "field" => "username"
  );
  $fields[] = array(
    "type"  => "presenceOf",
    "field" => "password"
  );
}

function buildValidation(array $fields)
{
  foreach ($fields as $field) {
    switch ($field["type"]) {
      case "presenceOf":
        setupPresenceOf($field);
        break;
      case "date":
        setupDate($field);
        break;
      case "dateTime":
        setupDateTime($field);
        break;
    }
  }
}

function setupPresenceOf(array $field)
{
  // do whatever you wanted
}

function setupDate(array $field)
{
  // do whatever you wanted
}

function setupDateTime(array $field)
{
  // do whatever you wanted
}