ssages used by callback</font><hr>
<tr valign=bottom>
	<th align=left>Symbol
	<td>&nbsp;&nbsp;
	<th align=left>
	<td>&nbsp;&nbsp;
	<th align=left>Use
<tr>	<td colspan=5><hr>
<tr valign=top>	<td><b><tt>GSDLL_STDIN</tt></b>
	<td>&nbsp;
	<td>1
	<td>&nbsp;
	<td>get <b><tt>count</tt></b> characters to <b><tt>str</tt></b> from stdin, return number of characters read
<tr valign=top>	<td><b><tt>GSDLL_STDOUT</tt></b>
	<td>&nbsp;
	<td>2
	<td>&nbsp;
	<td>put <b><tt>count</tt></b> characters from <b><tt>str</tt></b>
		