Ceci n'est pas une pipe
Machines are demand driven input sources like pipes or conduits, but can support multiple inputs.
You design a Machine by writing a Plan. You then construct the machine.
Simple machines that take one input are called a Process and processes form a Category. More generally you can attach a
Process to the output of any type of Machine, yielding a new Machine.
More complicated machines provide other ways of connecting to them.
Typically the use of machines proceeds by using simple plans into machine Tees and Wyes, capping many of the inputs to
those with possibly monadic sources, feeding the rest input (possibly repeatedly) and calling run or runT to get the
answers out.
There is a lot of flexibility when building a machine in choosing between empowering the machine to run its own monadic effects or delegating that responsibility to a custom driver.
A port of this design to scala is available from runarorama/scala-machines
Runar's slides are also available from http://web.archive.org/web/20161029161813/https://dl.dropboxusercontent.com/u/4588997/Machines.pdf
Some worked examples are here https://github.com/alanz/machines-play
Contributions and bug reports are welcome!
Please feel free to contact me through github or on the #haskell IRC channel on irc.freenode.net.
-Edward Kmett