The following example implements the user-defined function sleep, which causes the AVM to sleep for a specified number of milliseconds:

FUNCTION sleep RETURNS INTEGER (msecs AS INTEGER):
  DEFINE VARIABLE cFunction AS CHARACTER NO-UNDO INITIAL "sleep".
  DEFINE VARIABLE cLibrary  AS CHARACTER NO-UNDO INITIAL "libc.so.1".
  DEFINE VARIABLE hCall     AS HANDLE    NO-UNDO.
  
  CREATE CALL hCall.
  ASSIGN
    cLibrary             = "kernel32.dll" WHEN OPSYS = "WIN32"
    cFunction            = "Sleep" WHEN OPSYS = "WIN32"
    hCall:CALL-NAME      = cFunction
    hCall:LIBRARY        = cLibrary
    hCall:CALL-TYPE      = DLL-CALL-TYPE
    hCall:NUM-PARAMETERS = 1.
  
  hCall:SET-PARAMETER(1, "LONG", "INPUT", msecs).
  hCall:INVOKE( ).
  
  DELETE OBJECT hCall.
  RETURN msecs.
END FUNCTION.

Note that the code determines on which OS it is running, and invokes the appropriate Windows DLL or UNIX shared library.