I wonder why MADescription isn't a "valuable" object. It is... it doesn't understand the #value: message selector. #value: could map to the accessor #read: and #value:value: to the the accessor #write:to: Is there a reason why it isn't this way. It would make it very useful from a polymorphic point of view. E.g. #size value: #(1 2 7). [ :value | value size ] value: #(1 2 7). (MANumberDescription new accessor: #size) value: #(1 2 7). Regards, Esteban A. Maringolo