current-input-port, current-output-port, current-error-port - get the current (default) ports

LIBRARY

(import (rnrs))                     ;R6RS
(import (rnrs io ports))            ;R6RS
(import (rnrs io simple))           ;R6RS
(import (scheme r5rs))              ;R7RS
(import (scheme base))              ;R7RS

SYNOPSIS

(current-input-port)
(current-output-port)
(current-error-port)

DESCRIPTION

These return default textual ports for regular input, output and error output. Normally, these default ports are associated with standard input, standard output, and standard error, respectively.

The return value of current-input-port and current-output-port can be dynamically re-assigned using with-input-from-file(3scm) and with-output-to-file(3scm) respectively.

A port returned by one of these procedures may or may not have an associated transcoder; if it does, the transcoder is implementation-dependent.

R7RS
These procedures are parameter objects, which can be overridden with parameterize(7scm).

IMPLEMENTATION NOTES

Standard input, output and error ports are concepts in general purpose operating systems. The implementation should hook these ports up to whatever standard I/O mechanism is provided by the operating system, if any.

The error port should usually be unbuffered so that no output is lost if the program exits unexpectedly.

RETURN VALUES

These procedures return a single value; a port.

EXAMPLES

(display "There was an error.0 (current-error-port))

COMPATIBILITY

R7RS defines these procedures as parameters. They are likely to internally be some form of parameters in all implementations, however, because of how with-input-from-file(3scm), etc, works. But one cannot expect to portably use them as parameters outside of R7RS.

ERRORS

This procedure can raise exceptions with the following condition types:
&assertion (R6RS)
The wrong number of arguments was passed or an argument was outside its domain.
R7RS
The assertions described above are errors. Implementations may signal an error, extend the procedure's domain of definition to include such arguments, or fail catastrophically.

SEE ALSO

standard-input-port(3scm), parameterize(7scm), with-input-from-file(3scm)

STANDARDS

R4RS, IEEE Scheme, R5RS, R6RS, R7RS

HISTORY

The current-error-port procedure first appeared in R6RS. The other procedures are standard since R2RS.

AUTHORS

This page is part of the scheme-manpages project. It includes materials from the RnRS documents. More information can be found at https://github.com/schemedoc/manpages/.

Markup created by unroff 1.0sc,    March 04, 2023.