sub itter_maker {  # return a function that passes back data allowed by the given predicate subroutine
  my $predicate = shift; #CODE ref
  my $done = 0;
  my $fh = IO::File->new($datafile) or die "can't open $datafile: $!\n";
  return(
    sub {
      return if $done;
      my (@data,$row,$key);
      my $found = 0;
      while(  ! $found  &&  ! $done  &&  defined( $row= <$fh> )  ) {
        chomp($row);
        ($found, $done) = $predicate->($row, \$key, \@data);
      }
      return ($key,\@data) if $found;
      return;
    });
}