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.