Hi, I see that Pharo 3.0 has a Collection>>flatCollect:. This is great as the method proved to be very valuable in the context of Moose. However, the current Pharo implementation is less ideal: Collection>>flatCollect: aBlock ^ Array streamContents: [:stream | self do: [:ea | stream nextPutAll: (aBlock value: ea)]] The Moose one is: Collection>>flatCollect: aBlock "Evaluate aBlock for each of the receiver's elements and answer the list of all resulting values flatten one level. Assumes that aBlock returns some kind of collection for each element. Equivalent to the lisp's mapcan" "original written by a. Kuhn and released under MIT" | stream | self isEmpty ifTrue: [ ^ self copy ]. stream := (self species new: 0) writeStream. self do: [ :each | stream nextPutAll: (aBlock value: each) ]. ^ stream contents The difference is in the type returned. The Pharo one always returns Array, while the Moose one returns a collection of the same species as the receiver. Does anyone have anything against the Moose implementation? Doru -- www.tudorgirba.com "Every thing has its own flow"