/*
 * call-seq: scan(pattern)
 *
 * Tries to match with +pattern+ at the current position. If there's a match,
 * the scanner advances the "scan pointer" and returns the matched string.
 * Otherwise, the scanner returns +nil+.
 *
 *   s = StringScanner.new('test string')
 *   p s.scan(/\w+/)   # -> "test"
 *   p s.scan(/\w+/)   # -> nil
 *   p s.scan(/\s+/)   # -> " "
 *   p s.scan(/\w+/)   # -> "string"
 *   p s.scan(/./)     # -> nil
 *
 */
static VALUE
strscan_scan(self, re)
    VALUE self, re;
{
    return strscan_do_scan(self, re, 1, 1, 1);
}