[R] Making R lazy

[Lorenzo Isella]

Dear All,
I hope this is not too off-topic.
I am wondering if there is any possibility to make an R code lazy i.e. 
to prevent it from calculating quantities which are not used in the code.
As an example: you are in a rush to modify your code and at the end it 
ends up with "dead branches", let's say a sequence which is calculated 
but not used in any following calculations, not printed on screen, not 
stored in a file etc...
It would be nice to teach R to automagically skip its calculation when I 
run the script (at least in a non-interactive way).
I know that such a situation is probably the result of bad programming 
habits, but it may arise all the same.
If I understand correctly, what I am asking for is something different 
from any kind of garbage collection which would take place, if ever, 
only after the array has been calculated.
Any suggestions (or clarifications if I am on the wrong track) are 
appreciated.
Cheers

Lorenzo