Function builtin_modify_list 

fn builtin_modify_list(
    args: &[RValue],
    _: &[(String, RValue)],
) -> Result<RValue, RError>

Modify a list by replacing/adding/removing elements from another list.

For each named element in val:

• If the value is NULL, remove that name from x
• Otherwise, replace or add the element in x

@param x a list to modify @param val a list of replacements @return modified copy of x @namespace utils