The TRUNCATE procedure indicates that the current file component
  and all components following it are to be deleted.  TRUNCATE can
  only be used on a file that has sequential organization.

  Syntax:

     TRUNCATE( file_variable [[, ERROR := error-recovery]] );

  The 'file_variable' is the name of the file variable  associated
  with the file to be truncated.

  The 'error-recovery' specifies the action  to  be  taken  if  an
  error occurs during execution of the routine.  By default, after
  the first error, the error message is printed and  execution  is
  stopped.

  The file must be in inspection mode before TRUNCATE  is  called.
  After  the  procedure  has  been  executed,  the  mode is set to
  generation so that you can write to the file.

  After the appropriate components have  been  deleted,  the  file
  remains  positioned  at the new end-of-file, but the file buffer
  itself is undefined.  Thus, EOF and UFB are both set to TRUE.

  See the "HP Pascal Language Reference  Manual"  for  a  complete
  description of the TRUNCATE procedure.