| 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