Finding out if a function is inside another function R

I have a main function e.g. "a" that is called inside 4 different functions, e.g. "a1", "a2", "a3", "a4". I want to have an if statement checking when function "a" is called inside either "a1", "a2", "a3", "a4".

funct1 <- function(a){
  if(functionNameThatItIsInside == "a2"){
     var1 <- 24243
   }

if(functionNameThatItIsInside == "a1"){
     var1 <- 22525
   }

if(functionNameThatItIsInside == "a1"){
     var1 <- 2525
   }

if(functionNameThatItIsInside == "a1"){
     var1 <- 636364
   }
}

or something like this.

Thanks