Annotations are used to define tasks
crodas/Build do not build things unless they are needed:
- When there is no output file
- When any input file changes

<?php // Tasks.php
/** 
 * @Task(build_site) 
 */
function concat_files($output, Array $input, Array $settings $builder)
{
  /* Do something with the input files */
  $content = "";
  foreach ($input as $f) {
    $content .= file_get_contents($f);
  }
  
  /* Write it in the $output file */
  file_put_contents($output, $content);
}

<?php // build.php

$builder  = new crodas\Build("/tasks.php");
$bundle_js = $build->build_site(['foo.js', 'xxx.js']);