Check for parameters in function module calls

IS REQUESTED: 
Consider the following function module call in a program. 
          CALL FUNCTION 'ZSURESH_TEST1' 

EXPORTING 

   CARRID         = 'AA' 

 IMPORTING 

   CONNID         = connid 

*   FLDATE        = 

* CARRNAME  =  . 

Here the FLDATE and CARRNAME parameters are not required. 
So there is no need in retrieving the same in the function module.

In these cases, we can use IS REQUESTED as follows:

  
   If CARRNAME is requested. 
     Select single CARRNAME from SCARR Where carrid eq I_carrid. 
     Endif.   

Since in the above function call, CARRNAME is not requested,
the above SELECT statement is not executed. 
So unnecessary database calls can be restricted.

IS REQUESTED is allowed only in a function module and not 
even in a subroutine called by the function module.  
  
IS SUPPLIED: 

This checks whether the parameter = < p= >  was passed during 
runtime (IMPORTING). For this the parameter = < p= >  should 
be optional, else the system raises an error. This statement can be 
used in function modules and methods.