PRESENT

 The PRESENT function returns  a  Boolean  value  that  indicates
 whether  the  actual  argument  list  of  a  routine contains an
 argument that corresponds to a formal parameter.   (The  PRESENT
 function  is usually used to supply a default value or to take a
 default action when the argument for a parameter is omitted.)


 Syntax:

    PRESENT (parameter-name)


 The 'parameter-name' parameter is the name of a formal parameter
 with  the  TRUNCATE attribute.  The 'parameter-name' must be the
 name of a formal parameter of the function from which PRESENT is
 called,  or  from  a  subroutine of that function.  The function
 result indicates whether the argument  list  of  the  containing
 routine   specifies  an  actual  argument  corresponding  to  an
 optional parameter.

 Parameters that do not have the TRUNCATE attribute and  also  do
 not follow a parameter with the TRUNCATE attribute in the formal
 parameter list, are allowed; in their case, the PRESENT function
 always returns TRUE.

 Default parameters are considered to be present in the  argument
 list, and the PRESENT function returns TRUE when passed the name
 of a parameter with a default value.