Andrew Coppin wrote: > Maybe I'm just being blind here, but I don't see a monad transformer (or > even a monad) in the standard libraries for producing "unique" values. > Have I missed something? http://haskell.org/haskellwiki/New_monads/MonadSupply linked to from: http://www.haskell.org/haskellwiki/Monad#Interesting_monads