Customizing Display, Write, and Print

Each output port has its own port display handler, port write handler, and port print handler. These handlers are invoked to output S-expressions to the port when the standard display, write or print procedure is applied to the port. A port display/write/print handler takes a two arguments: the value to be printed and the destination port. The handler's return value is ignored.

• (port-display-handler output-port) returns the current port display handler for output-port.
• (port-display-handler output-port proc) sets the display handler for output-port to proc.
• (port-write-handler output-port) returns the current port write handler for output-port.
• (port-write-handler output-port proc) sets the write handler for output-port to proc.
• (port-print-handler output-port) returns the current port print handler for output-port.
• (port-print-handler output-port proc) sets the print handler for output-port to proc.

The default port display and write handlers print Scheme expressions with MzScheme's built-in printer (see section 14.4). The default print handler calls the global port print handler (the value of the global-port-print-handler parameter; see section 9.4.1.2); the default global port print handler is the same as the default write handler.