Thorsten I am starting to look at a review of Double Ended. I have succeeded to build the devector example using Clang 3.6 and 4.0 with their corresponding libc++. When I run the example I get only one line of output: Reversed lines: This does not tell me much at all and I have not found out what it is expected to do. It seems to read a file, which is not supplied or described. I have not found anything in the documentation. On another topic, I have not seen in the documentation any discussion of models for what is going on. I am aware of Chris Okasaki's book "Purely Function Data Structures" (1998) and a lot of subsequent literature. Does this work relate at all to previous work? Answers will help me to put together a review. Best wishes John Fletcher