Henning Thielemann wrote:
I have seen several libraries where all functions of a monad have the monadic result (), e.g. Binary.Put and other writing functions. This is a clear indicator, that the Monad instance is artificial and was only chosen because of the 'do' notation.
I completely disagree with that example. The Put monad is, mainly, a specialized State monad. The internal state being the current fixed-size bytestring memory buffer that has been allocated and is being filled. The monad make the execution sequential so that there is only one memory buffer being filled at a time. In Put, when one memory buffer has been filled it allocates the next one to create a Lazy Bytestring. This is not to say that all M () are really monads, but just that Put () is. -- Chris