public static Expr Map(this Expr expr, Func <Expr, Expr> f)
{
Debug.Assert(f != null);
if (expr == null)
{
return(f(null));
}
Expr result = null;
Expr tail = null;
foreach (Expr item in expr.ToEnumerable())
{
Expr mappedItem = f(item);
ExprFactory.AppendItemToList(mappedItem, ref result, ref tail);
}
return(result);
}