This is a proposal for the WG2 "port operations" work item. It provides useful iterators over generic ports, and ways to combine and alias ports. It is mostly based on Chicken's ports unit and CL's streams facilities.
(port-for-each iterator reader port)
Applies iterator to the successive results of calling reader on port until it returns an EOF object (not including the EOF object), discarding the results. Returns undefined values.
(port-map iterator reader port)
Applies iterator to the successive results of calling reader on port until it returns an EOF object (not including the EOF object), returning a list of the collected results.
(port-fold iterator reader port seed ...)
Applies iterator to the successive results of calling reader on port, passing the seed values as additional arguments to iterator. The results returned by iterator become the new seed values. When reader returns an EOF object, the last results of iterator are returned.
(copy-port source sink reader writer)
Reads all remaining data from source using the procedure reader and writes it to sink using the procedure writer. Reader defaults to read-char and writer to write-char. This procedure does not check that source and sink are actually ports, so reader and writer may perform arbitrary operations as long as they can be invoked as (reader source) and (writer value sink), respectively. Returns undefined values.
(make-broadcast-port port ...)
Returns a custom output port that emits everything written into it to the ports. An operation can only be performed on a broadcast port if it can be performed on all the ports. Closing the broadcast port does not close any of the ports. If no ports are specified, the result serves as a sink that discards all its output.
(broadcast-port? obj)
Returns #t if obj is a broadcast port, and #f otherwise.
(make-concatenated-port port ...)
Returns a custom input port that reads its input from each port until it returns an EOF object, then returns just one EOF object itself. An operation can only be performed on a concatenated port if it can be performed on all the ports. Closing the concatenated port does not close any of the ports. If no ports are specified, the result serves as an empty source.
(concatenated-port? obj)
Returns #t if obj is a concatenated port, and #f otherwise.
(make-alias-port parameter)
Returns a port which passes any port operations invoked on it to the current value of the dynamic variable parameter.
(alias-port? obj)
Returns #t if obj is an alias port, and #f otherwise.