This is an implementation of the ideas presented in "Bidirectionalization for Free!" (paper at POPL'09) by Janis Voigtlaender.
It also includes an automatic deriver for the Zippable type class.
Using the cabal flag "binaries" will enable the creation of a web frontend to bff, in the form of a CGI program. Make sure you understand the security implications before allowing untrusted access to the script.
Using the cabal flag "stats" will generate programs that collect performance statistics about bff and print them as a table.
Using the cabal flag "render" will generate a program that renders collected performance statistics as PDF files.
You may also want to check out later work combining the implementation here with other methods: http://hackage.haskell.org/package/bidirectionalization-combined.