Hi all, I just uploaded mmap to hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mmap The package provides memory mapping abstractions for both POSIX and Windows systems like Vista, Linux and Mac OSX. This library provides a wrapper to mmap(2) or MapViewOfFile, allowing files or devices to be lazily loaded into memory as strict or lazy ByteStrings, ForeignPtrs or even plain Ptrs, using the virtual memory subsystem to do on-demand loading. Modifications are also supported. Package includes a cp-like copy utility that uses different mechanisms to copy contents of file. Here come some statistics from using it on 90MB file: Windows: Prelude copy: 10.453 sec ByteString copy: 0.625 sec ByteString.Lazy copy: 0.516 sec MMap copy: 0.281 sec MMap copy lazy: 0.250 sec Linux: Prelude copy: 3.332 sec ByteString copy: 0.280 sec ByteString.Lazy copy: 0.292 sec MMap copy: 0.264 sec MMap copy lazy: 0.200 sec Mac OSX ppc Tiger 10.4 Prelude copy: 5.719 sec ByteString copy: 0.701 sec ByteString.Lazy copy: 0.864 sec MMap copy: 1.073 sec MMap copy lazy: 1.414 sec Hardware is different on those systems, so only relative comparison makes sense. Memory mapping provides significant advantages on Windows and Linux, not so on Mac OSX. Seems like mmap on Mac is not very well implemented. Any feedback is welcome! -- Gracjan