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A stream, whether a character stream or a binary stream, can be an input stream (source of data), an output stream (sink for data), both, or (e.g., when “:direction :probe” is given to open) neither.
Figure 21–2 shows operators relating to input streams.
clear-input read-byte read-from-string
listen read-char read-line
peek-char read-char-no-hang read-preserving-whitespace
read read-delimited-list unread-char
Figure 21–2: Operators relating to Input Streams.
Figure 21–3 shows operators relating to output streams.
clear-output prin1 write finish-output prin1-to-string write-byte force-output princ write-char format princ-to-string write-line fresh-line print write-string pprint terpri write-to-string Figure 21–3: Operators relating to Output Streams.
A stream that is both an input stream and an output stream is called a bidirectional stream . See the functions input-stream-p and output-stream-p.
Any of the operators listed in Figure~21–2 or Figure~21–3 can be used with bidirectional streams. In addition, Figure 21–4 shows a list of operators that relate specificaly to bidirectional streams.
y-or-n-p yes-or-no-p Figure 21–4: Operators relating to Bidirectional Streams.