1.16.4.5 Port generators

Generator Syntax: :port vars port

Generator Syntax: :port vars port read-proc

Read from the port until the eof–object is read. If a port reader procedure read-proc is supplied: The generator first evaluates port and read-proc, which must result in an input port p and a procedure r. Then the variable is run through the sequence obtained by (r p) while the result does not satisfy eof-object?.