CollectionX
   ->begin (Iterator)

CollectionY
   ->begin (Iterator)

CollectionZ
   ->begin (Iterator)
   ->end (Iterator)

ProgressBar

Flowers

Algorithms
   - showProgress - Bound to ProgressBar
   - growFlowers - Bound to Flowers

code:
   ...
   use CollectionX ;
   use CollectionY ;
   use Algorithms qw( showProgress, growFlowers ) ;
   ...
   my colX = new CollectionX ;
   colX->... ;
   while( showProgress(CollectionX->begin) ) {
   }
   my colY = CollectionY ;
   colY->... ;
   while( showProgress(colY->begin) ) {
   }
   my colY = CollectionY ;
   colY->... ;
   while( growFlowers(colY->begin) ) {
   }