WordPress Theme's functions.php file with useful constants and boilerplate code for registering menus and sidebars.

WP functions.php

<?php

/* DEFINE CONSTANTS
========================================== */

define('THEME_DIR', get_stylesheet_directory_uri() );
define('THEME_IMAGES_DIR', THEME_DIR . '/assets/img' );

/* REGISTER MENUS
========================================== */

function register_my_menus()
{
  register_nav_menus(
    array(
      'primary_menu'  => 'Primary Menu',
    )
  );
}

add_action('init', 'register_my_menus');

/* REGISTER SIDEBARS
========================================= */

if( function_exists('register_sidebar') )
{
  // Primary Sidebar
  register_sidebar(
    array(
      'name'          => 'Primary Sidebar',
      'id'            => 'primary_sidebar',
      'description'   => 'Sidebar description.',
      'before_widget' => '<div class="widget">',
      'after_widget'  => '</div>',
      'before_title'  => '<h4>',
      'after_title'   => '</h4>',
    )
  );
  // Single Page Sidebar
  register_sidebar(
    array(
      'name'          => 'Single Sidebar',
      'id'            => 'single_sidebar',
      'description'   => 'Sidebar description.',
      'before_widget' => '<div class="widget">',
      'after_widget'  => '</div>',
      'before_title'  => '<h4>',
      'after_title'   => '</h4>',
    )
  );
}


/* ADD THEME SUPPORT FOR POST THUMBNAIL, POST FORMATS
======================================================= */

if(function_exists('add_theme_support'))
{
  add_theme_support('post-formats', array('link','quote','gallery'));
  add_theme_support('post-thumbnails', array('post'));
}

/* Callback function called for every comment displayed
====================================================== */
function my_comments_callback($comment, $args, $depth)
{
  $GLOBALS['comment'] = $comment;

  if(get_comment_type() == 'pingback' || get_comment_type() == 'trackback') : ?>

    <li id="comment-<?php comment_ID(); ?>" class="pingback">
      <article <?php comment_class('clearfix'); ?>>
        <header>
          <h5>Pingback</h5>
          <p><?php edit_comment_link(); ?></p>
        </header>

        <p><?php comment_author_link(); ?></p>

      </article>
    </li>

  <?php elseif(get_comments_type() == 'comment') : ?>

    <li id="comment-<?php comment_ID(); ?>">
      <article class="<?php comment_class('clearfix'); ?>">
        <header>
          <h5><?php comment_author_link(); ?></h5>
          <p>
            <span>on <?php comment_date(); ?> at <?php comment_time(); ?> - </span>
            <?php comment_reply_link(array_merge($args, array('depth' => $depty, 'max-depth' => $args['max-depth']))); ?>
          </p>
        </header>

        <figure class="comment-avatar">
          <?php
            $avatar_size = 80;
            if($comment->comment_parent != 0 )
            {
              $avatar_size = 64;
            }
            echo get_avatar($comment, $avatar_size);
          ?>
        </figure>

        <?php if($comment->comment_approved == '0' : ?>

          <p class="waiting-moderation">Comment waiting moderation</p>

        <?php endif; ?>

          <?php comment_text(); ?>
      </article>
    </li>

  <?php endif;
}

// CUSTOM COMMENTS FORM
// ===================================

function my_custom_comment_form($defaults)
{
  // remove the note on the top of the form
  $defaults['comment_notes_before'] = '';
  $defaults['id_form'] = 'comment_form';
  $defaults['comment_field'] =  '<p>' .
                                  '<textarea name="comment" id="comment" cols="30" rows="10"><textarea>' .
                                '</p>';

  return $defaults;
}

function my_custom_default_comment_fields()
{
  $commenter = wp_get_current_commenter();
  $req = get_option('require_name_email');
  $aria_req = $req ? "aria-required=true" : '';

  $fields = array(
    'author'  =>  '<p>' .
                    '<input type="text" id="author" name="author" value="' . esc_attr($commenter['comment_author']) . '" ' . $aria_req . '>' .
                    '<label for="author">Name ' . $req ? '*' : '' . '</label>' .
                  '</p>',
    'email'   =>  '<p>' .
                    '<input type="text" id="email"  name="email"  value="' . esc_attr($commenter['comment_author_email']) . '" ' . $aria_req . '>' .
                    '<label for="email">Email ' . $req ? '*' : '' . '</label>' .
                  '</p>',
    'url'   =>    '<p>' .
                    '<input type="text" id="url"  name="url"  value="' . esc_attr($commenter['comment_author_url']) . '">' .
                    '<label for="url">Website ' . $req ? '*' : '' . '</label>' .
                  '</p>',
  );

  return $fields;
}

add_filter('comment_form_defaults', 'my_custom_comment_form');
add_filter('comment_form_default_fields', 'my_custom_default_comment_fields');

/* LOAD CUSTOM WIDGETS
====================== */
require_once('functions/widget-ad.php');

?>