Immutable data

What kind of idiot needs to have his data kept constant to keep himself from breaking something? If you can't keep your shit in order without stupid artificial constraints, then you don't know shit about programming.

>>5
Well, my favourite window manager is written in haskell.  I love it very much and I am yet to try a window manager at least half as good.  Also, the nicest (and slowest, sadly) revision control system was also written in haskell.