The book Advanced R, by Hadley Wickham, shows a very interesting statement:
“To understand R, two slogans are Helpful:
- Everything that exists in an object.
- Everything that happens is a function call.”
– John Chambers
In other words, every action is caused by a function, and functions are things you can change.
+ are all functions. That means you can call these actions as functions.
> a=1:10 > #Two equivalent codes > `[`(a,4)  4 > a  4 > #Other two equivalent codes > `+`(3,7)  10 > 3+7  10
Just a little prank
Imagine you want to do a little prank with your friend who left his R oppened in the office. You could change the
+ function like in the code below and see the magic happens.
> `+`=function(x,y)x-y > 1+1  0
More information on R functions
 Wickham, Hadley. Advanced R. CRC Press, 2014.