I stumbled upon the horrible implementation of SequenceableCollection >> #copyReplaceAll:with: Not only was it horribly documented (only for strings) but also horribly inefficient nicely following the painters algorithm :). On to replacing this craftwork with a stream based solution I figured out that it breaks quite a few tests: Namely the #testCopyReplaceAllWith1Occurence test doesn't work with the following classes anymore: - LinkedList - Interval - SortedCollection - Symbol Now I think this test does't make much sense for SortedCollection/Intervals. SortedCollection enforces a certain order on the objects, meaning that replacing a slice of elements with something else yields a completely new intermediate collection. So unless the collection is first converted to an OrderedCollection I don't see much sense in supporting this method on SortedCollection. For Intervals there's a similar issue. Replacing elements in an Interval doesn't work (yetâ¦) so again, only an indirect OrderedCollection helps there⦠On Symbol there's the problem of #streamContents which should use #species and an intermediate String to build up the Symbol. cami