my $done = 0;
# ...
  sub {
      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  $allow;
      return;