[R] abbreviate function using 'with'

[e-letter]

Readers,

A csv file was created:

column1,column2,column3,column4
1,10,3,2
2,20,6,4
3,30,12,16
4,40,24,256

The csv was imported:

testcsv<-read.csv('/path/to/test.csv')
testsum<-testcsv[2,2]+testcsv[2,3]+testcsv[2,4]

What is the correct syntax to abbreviate the following command using
the function 'with', to avoid repetitive use of the declaration
'testcsv'? Tried the following, but received the error shown:

with(testcsv,testsum<-[2,2]+[2,3]+[2,4])
Error: unexpected '[' in "with(testcsv,testsum<-["

and:

with(testcsv,{testsum<-[2,2]+[2,3]+[2,4]})
Error: unexpected '[' in "with(testcsv,{testsum<-["