say (('red','blue') X ('small','medium','large') X (1,2,3,4)).tree.map: *.join('-');

##</code><code>##

red-small-1 red-small-2 red-small-3 red-small-4 red-medium-1 red-medium-2 red-medium-3 red-medium-4 red-large-1 red-large-2 red-large-3 red-large-4 blue-small-1 blue-small-2 blue-small-3 blue-small-4 blue-medium-1 blue-medium-2 blue-medium-3 blue-medium-4 blue-large-1 blue-large-2 blue-large-3 blue-large-4