/*
 * call-seq: exist?(pattern)
 *
 * Looks _ahead_ to see if the +pattern+ exists _anywhere_ in the string,
 * without advancing the scan pointer.  This predicates whether a #scan_until
 * will return a value.
 *
 *   s = StringScanner.new('test string')
 *   s.exist? /s/            # -> 3
 *   s.scan /test/           # -> "test"
 *   s.exist? /s/            # -> 6
 *   s.exist? /e/            # -> nil
 */
static VALUE
strscan_exist_p(self, re)
    VALUE self, re;
{
    return strscan_do_scan(self, re, 0, 0, 0);
}