enclosing with() in a function

Hi All,

I want to enclose with() in a function mean_on_element. Obviously, it
is not working. The problem is how to specify the element name with a
function body. Does anybody have any suggestion? Thanks!

data=list(x=1:10)
with(data, mean(x))

[1] 5.5

mean_on_element=function(data, elem_name) {

+   with(data, mean(elem_name))
+ }

mean_on_element(data, 'x')

[1] NA
Warning message:
In mean.default(elem_name) :
  argument is not numeric or logical: returning NA

Tom