Function interp_op_add 

fn interp_op_add(
    args: &[RValue],
    _named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Addition operator as a function (unary positive or binary addition).

@param e1 first operand (or sole operand for unary +) @param e2 second operand (optional) @return sum of e1 and e2, or e1 unchanged for unary +