Shortcode to show group field

curiculum-shortcode.php

<?php

add_shortcode('eduinaf-loop', 'eduinaf_loop');

function eduinaf_loop( $attr = array() ) {
  $post = get_post();
  $curriculum = get_post_meta( $post->ID, '_eduinaf_curriculum_scolastico', true );
  $output = '';
  
  if ( empty( $curriculum ) ) {
    return $output;
  }
  
  $output .= '<ul>';
  
  foreach ( $curriculum as $entry ) {
    $output .= '<li>';
		$output .= 'Livello scolastico: ' . esc_attr( $entry['_livello_scolastico'] ) . '</br>';
		$output .= 'Materia: ' . esc_attr( $entry['_materia'] ) . '<br/>';
		$output .= 'Argomento: ' . esc_attr( $entry['_argomento'] );
		$output .= '</li>';
  }
  
  $output .= '</ul>';
  
  return $output;
}