Ports

• (current-input-port [input-port]) gets or sets an input port used by read, read-char, char-ready?, read-line, read-string, and read-string-avail! when a specific input port is not provided.
• (current-output-port [output-port]) gets or sets an output port used by display, write, print, write-char, and printf when a specific output port is not provided.
• (current-error-port [output-port]) gets or sets an output port used by the default error display handler.
• (global-port-print-handler [proc]) gets or sets a procedure that takes an arbitrary value and an output port. This global port print handler is called by the default port print handler (see section 11.1.9) to print values into a port.