WP filter to turn email-style quotes into blockquotes

gistfile1.php

<?php

/**
 * Turn email-style quotes into blockquotes
 *
 * For example:
 *
 *   My friend said:
 *
 *   > You are handsome and also
 *   > you are very great
 *
 *   Then she said:
 *
 *   > You are my hero
 *
 * becomes
 *
 *   My friend said:
 *
 *   <blockquote>You are handsome and also you are very great</blockquote>
 *
 *   Then she said:
 *
 *   <blockquote>You are my hero</blockquote>
 *
 * This method is neither elegant nor efficient, but it works.
 */
function teleogistic_process_quotes( $content ) {
	// Find blank lines
	$content = preg_replace( '/\n\s*\n/m', '<BBG_EMPTY_LINE>', $content );

	// Explode on the blank lines
	$content = explode( '<BBG_EMPTY_LINE>', $content );

	foreach ( $content as &$c ) {
		$c = trim( $c );

		// Reduce multiple-line quotes to a single line
		// This works because the first > in a block will not have a
		// line break before it
		$c = preg_replace( '/\n(>|&gt;)(.*)/m', '$2', $c );

		// Blockquote 'em
		$c = preg_replace( '/^(>|&gt;) (.*)/m', '<blockquote>$2</blockquote>', $c );
	}

	// Put everything back as we found it
	$content = implode( "\n\n", $content );

	return $content;
}
add_filter( 'the_content', 'teleogistic_process_quotes', 5 );
add_filter( 'get_comment_text', 'teleogistic_process_quotes', 5 );