<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def html_format(value):
 """ Returns the value formatted in HTML, depends on MARKUP_LANGUAGE setting. """

    if not value:
        return ''
    elif MARKUP_LANGUAGE == 'markdown':
        return markdown(value)
    elif MARKUP_LANGUAGE == 'textile':
        return textile(value)
    elif MARKUP_LANGUAGE == 'restructuredtext':
        return restructuredtext(value)
    elif '</p>' not in value:
        return linebreaks(value)
    return value