pipes.txt

                       | Upstream output | Upstream input | Downstream input | Downstream output | Base monad | Return value
  Proxy a' a b' b m r  | a'              | a              | b'               | b                 | m          | r       
  Effect m r           | Void            | ()             | ()               | Void              | m          | r
  Pipe a b m r         | ()              | a              | ()               | b                 | m          | r
  Producer b m r       | Void            | ()             | ()               | b                 | m          | r
  Consumer a m r       | ()              | a              | ()               | Void              | m          | r
  Client a' a m r      | a'              | a              | ()               | Void              | m          | r
  Server b' b m r      | Void            | ()             | b'               | b                 | m          | r