Robbert van Dalen has ported Enchilada to Factor. Enchilada is a purely-functional concatenative language. In addition to the language implementation itself, his work has also yielded a library for immutable sequences. These immutable sequences are similar to finger trees; random access is O(log n), and concatenation of similar-sized sequences is very efficient. He implemented the full range of operations such as union, intersection, sorting, and so on. Yet another data structure Factor programmers can use is a good thing, since each data structure has its own advantages and disadvantages.
His code can be found in the repository, extra/enchilada and extra/isequences.