8.2 Default Ports
For most simple I/O functions, the target port is an optional
argument, and the default is the current input port or
current output port. Furthermore, error messages are written
to the current error port, which is an output port. The
current-input-port, current-output-port, and
current-error-port functions return the corresponding current
ports.
Examples:
If you start the racket program in a terminal, then the
current input, output, and error ports are all connected to the
terminal. More generally, they are connected to the OS-level stdin,
stdout, and stderr. In this guide, the examples show output written to
stdout in purple, and output written to stderr in red italics.
Examples:
The current-port functions are actually parameters, which means
that their values can be set with parameterize.
See Dynamic Binding: parameterize for an introduction to parameters.
Example: