Wrong example because of old set variable?

[jcrodriguez1989]

In section 7.5 it does (and says):

If we try to get the value it refers to, R displays an error message:

eval(my_expr)

 [,1] [,2] [,3]

[1,] 1 4 7 [2,] 2 5 8 [3,] 3 6 9

We haven’t created a variable called my_expr, so R cannot evaluate an expression that asks for it.

But what if we create such a variable now and then re-evaluate the expression?

I think a was previously set, and the idea is to have:

eval(my_expr) Error in eval(my_expr) : object 'a' not found