I uploaded a package implementing persistent vectors using array mapped tries (based on the implementation in clojure). Version 0.1.0.0 was broken, so I am starting off with 0.1.0.1. http://hackage.haskell.org/package/persistent-vector Persistent vectors are a sequence container offering efficient and purely functional append (snoc), indexing, and updates. This is similar to Data.Sequence from containers. The array mapped trie is closely related to the data structure used in the unordered-containers package. Comparison to Sequence: * Faster indexing and append * Slightly slower updates to existing elements * O(1) slicing * Sequence offers efficient prepend and concatenate (persistent-vector does not implement prepend, while concatenate is O(n)). I tried to model the API after Sequence as much as was reasonable, but a few functions are still missing. Some are reasonable to implement and some would be difficult to make efficient. The results from criterion (mostly comparing against Sequence and IntMap) are posted here: http://pages.cs.wisc.edu/~travitch/pvec.html The *Vec* runs are the vectors from this package and IM and Seq are IntMap and Sequence from containers. Hopefully someone will find this useful. Comments and suggestions are definitely welcome for anything: API, implementation, test suite, or benchmarks.