/// <summary>
/// Validate a parenthesized expression.
/// </summary>
/// <param name="e">
/// is the expression. </param>
/// <returns> null. </returns>
public virtual object visit(ParExpr e)
{
visitExprs(e.GetEnumerator());
return(null);
}
/// <param name="e">
/// is the par expression. </param>
/// <returns> e </returns>
public virtual object visit(ParExpr e)
{
printExprs(e.GetEnumerator());
return(e);
}