[Haskell-cafe] pure programs

Informally, a "pure program" an executable such that the stream of bytes entering it totally determines the stream of bytes leaving it. Many useful programs that I would like to write in Haskell don't fall into this category -- for example, network servers -- but a lot of their components do. Can these components can be Haskell functions without IO in their signatures? Though that seems reasonable, it is not, in general, true. For example, System.Info.os is generally treated as pure, though it is not. It's not clear to me how to disambiguate these "born again" values from really pure values. -- _jsn