Manual page for eof-object?(3scm)

eof-object? - test if an object is the end-of-file object

LIBRARY

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

SYNOPSIS

(eof-object? obj)

DESCRIPTION

Returns #t if obj is an end-of-file object, otherwise returns #f.

The end-of-file object is returned by various I/O procedures when they reach end of file.

RETURN VALUES

Returns a single boolean object.

EXAMPLES

(eof-object? (eof-object))
          => #t

(eof-object? #\space)
          => #f

APPLICATION USAGE

This procedure is used on the result of I/O read operations, such as read(3scm), to see if the port has an end-of-file condition. It also appears in the context of generators (e.g. SRFI 158).

COMPATIBILITY

There is a slight difference between R6RS and the other reports.

R4RS, IEEE Scheme, R5RS, R7RS: The precise set of end-of-file objects will vary among implementations, but in any case no end-of-file object will ever be an object that can be read in using read.
: No object which satisfies this predicate satisfies any of these predicates: boolean?, bytevector?, char?, null?, number?, pair?, port?, procedure?, string?, symbol?, vector?, or any record type predicate.
R6RS: There is a unique end-of-file object. (This also satisfies the R7RS requirements).

ERRORS

This procedure can raise exceptions with the following condition types:

&assertion (R6RS): The wrong number of arguments was passed.
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.

STANDARDS

R4RS, IEEE Scheme, R5RS, R6RS, R7RS

HISTORY

This procedure was unchanged in Scheme from R2RS (AI Memo No.~848, 1985) until R6RS, which is when the end-of-file object become a unique object for the first item. R7RS branched off from R5RS and did not adopt the R6RS semantics for this object.

LISP 1.5 had an end-of-file character that printed as $EOF$ and an end-of-record character that printed as $EOR$. PDP-10 MacLISP had an optional other argument to read that let the program specify its own end-of-file object. Scheme before R2RS would have used this implementation of read.

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.