Ports

• current-input-port: parameter for an input port used by read, read-char, char-ready?, read-line, read-string, and read-string! when a specific input port is not provided.
• current-output-port: parameter for an output port used by display, write, print, write-char, and printf when a specific output port is not provided.
• current-error-port: parameter for an output port used by the default error display handler.
• global-port-print-handler: parameter for 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.