Function Recursion

Function can call themselves recursively. Each time execution passes into the function the local variables are (re)created. There is a special keyword: $self, which can be used to force a function to refer to itself. This is only necessary if you plan to rename the function after it has been created. 
fac = function ( a ) 
{
  if(a <= 1) 
  {
      return 1;
  else
      return a*fac (a-1);   // return a*$self (a-1);
  }
};
In the previous example a factorial computation is performed using recursion[*]. In the second return statement, the function calls itself until a≤1. In the event that the function is later copied to another variable, and the original destroyed, the function will no longer work. To avoid this, use the special keyword $self in place of the function self-reference.