VSI  Pascal  provides  routines  that  give  information   about
  variable-length parameter lists.

1  –  ARGUMENT

  The ARGUMENT function specifies an argument in a variable-length
  parameter list that was created using the LIST attribute.

  Syntax:

     ARGUMENT( parameter-name, n )

  The 'parameter-name' argument specifies the name of a  parameter
  declared  with the LIST attribute.  The 'n' specifies a positive
  integer value that identifies the argument.  The first  argument
  in  a  list  is always 1.  An error occurs if the value supplied
  for 'n' is less than  1,  or  exceeds  the  ARGUMENT_LIST_LENGTH
  parameter (which indicates the total number of arguments).

  If the LIST parameter is a value parameter,  ARGUMENT  indicates
  the  corresponding  value  in  the  argument  list.  If the LIST
  parameter is a VAR parameter, ARGUMENT is  a  reference  to  the
  corresponding variable in the argument list.

2  –  ARGUMENT_LIST_LENGTH

  The  ARGUMENT_LIST_LENGTH  function  returns  an  integer  value
  representing  the  number  of  arguments  in  a  variable-length
  parameter list that was created using the LIST attribute.

  Syntax:

     ARGUMENT_LIST_LENGTH( parameter-name )

  The  'parameter-name'  argument  specifies  the  name   of   the
  parameter declared with the LIST attribute.

  When creating a variable-length parameter list,  you  can  place
  the  LIST attribute on only the last formal parameter.  When you
  call  the  routine,  you  can  specify  any  number  of   actual
  parameters,  or  arguments,  that  correspond to the last formal
  parameter declared with LIST.

3  –  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.