[WP] Query posts and list them using a template

functions.php

<?php
/*
Plugin Name: The Loop
Plugin URI: https://gist.github.com/3180818
Description: Query posts and display them.
Version: 0.2
Author: Ivaylo Draganov
Author URI: http://druuf.com/
*/

/**
 * Query posts and display them using template parts.
 *
 * @author   Ivaylo Draganov <iv.draganov@druuf.com>
 * @param    (array) $query_args - WP_Query arguments
 * @param    (array|string) $template_names - template path(s) and file name(s) relative to the theme dir
 * @param	 (boolean) $echo
 * @uses     query_posts
 * @uses     locate_template
**/
function custom_loop( $query_args = array(), $template_names = '', $echo = true) {

	// default args
	$defaults = array();

	// Parse incomming $args into an array and merge it with $defaults
	$query_args = wp_parse_args( $query_args, $defaults );

	// Get posts from certain user
	if ( isset( $query_args['author'] ) ) {
		if( 'current' == $query_args['author'] ) {
			global $user_ID;
			$query_args['author'] = $user_ID;
		} else if ( is_numeric( $query_args['author'] ) ) {
			$query_args['author'] = intval( $query_args['author'] );
		} else {
			unset($query_args['author']);
		}
	}

	// Get children of current post
	if ( isset( $query_args['post_parent'] ) ) {
		if( 'current' == $query_args['post_parent'] ) {
			global $post;
			$query_args['post_parent'] = $post->ID;
		} else if ( is_numeric( $query_args['post_parent'] ) ) {
			$query_args['post_parent'] = intval( $query_args['post_parent'] );
		} else {
			unset($query_args['post_parent']);
		}
	}

	// The Template
	$template_names = (array) $template_names;
	$template_names[] = 'content.php';

	// The Query
	query_posts( $query_args );

	// buffer output
	ob_start();

	// The Loop
	while ( have_posts() ) : the_post();

		// Locate and load the template
		locate_template( $template_names, true, false );

	endwhile;

	// get output buffer
	$output = ob_get_clean();

	// Reset Query
	wp_reset_query();

	// Give it to the world
	if ( $echo ) {
		echo $output;
	} else {
		return $output;
	}
}

/**
 * A shortcode using the above function
 *
 * @note output buffer used to capture and return the results of the WP loop
 */
add_shortcode( 'theloop', 'custom_loop_shortcode' );

function custom_loop_shortcode( $atts ) {

	// EXAMPLE USAGE:
	// [theloop query="showposts=100&post_type=page&post_parent=453" template="content-custom.php"]

	// Defaults
	$atts = shortcode_atts( array(
			'query' => '',
			'template' => ''
		), $atts );

	// de-funkify query
	$atts['query'] = html_entity_decode( $atts['query'] );

	// call our neat function
	$out = custom_loop( $atts['query'], $atts['template'], false );

	// return it, phew...
	return $out;

}