@node Streams, Printer, Files, Top @chapter Streams @menu * Stream Concepts:: * Streams Dictionary:: @end menu @node Stream Concepts, Streams Dictionary, Streams, Streams @section Stream Concepts @c including concept-streams @menu * Introduction to Streams:: * Stream Variables:: * Stream Arguments to Standardized Functions:: * Restrictions on Composite Streams:: @end menu @node Introduction to Streams, Stream Variables, Stream Concepts, Stream Concepts @subsection Introduction to Streams A @i{stream} @IGindex{stream} is an @i{object} that can be used with an input or output function to identify an appropriate source or sink of @i{characters} or @i{bytes} for that operation. A @i{character} @IGindex{character} @i{stream} @IGindex{stream} is a source or sink of @i{characters}. A @i{binary} @IGindex{binary} @i{stream} @IGindex{stream} is a source or sink of @i{bytes}. Some operations may be performed on any kind of @i{stream}; Figure 21--1 provides a list of @i{standardized} operations that are potentially useful with any kind of @i{stream}. @group @noindent @w{ close stream-element-type } @w{ input-stream-p streamp } @w{ interactive-stream-p with-open-stream } @w{ output-stream-p } @noindent @w{ Figure 21--1: Some General-Purpose Stream Operations} @end group Other operations are only meaningful on certain @i{stream} @i{types}. For example, @b{read-char} is only defined for @i{character} @i{streams} and @b{read-byte} is only defined for @i{binary} @i{streams}. @menu * Abstract Classifications of Streams (Introduction to Streams):: * Input:: * Open and Closed Streams:: * Interactive Streams:: * Abstract Classifications of Streams:: * File Streams:: * Other Subclasses of Stream:: @end menu @node Abstract Classifications of Streams (Introduction to Streams), Input, Introduction to Streams, Introduction to Streams @subsubsection Abstract Classifications of Streams @node Input, Open and Closed Streams, Abstract Classifications of Streams (Introduction to Streams), Introduction to Streams @subsubsection Input, Output, and Bidirectional Streams A @i{stream}, whether a @i{character} @i{stream} or a @i{binary} @i{stream}, can be an @i{input} @IGindex{input} @i{stream} @IGindex{stream} (source of data), an @i{output} @IGindex{output} @i{stream} @IGindex{stream} (sink for data), both, or (@i{e.g.}, when ``@t{:direction :probe}'' is given to @b{open}) neither. Figure 21--2 shows @i{operators} relating to @i{input} @i{streams}. @group @noindent @w{ clear-input read-byte read-from-string } @w{ listen read-char read-line } @w{ peek-char read-char-no-hang read-preserving-whitespace } @w{ read read-delimited-list unread-char } @noindent @w{ Figure 21--2: Operators relating to Input Streams. } @end group Figure 21--3 shows @i{operators} relating to @i{output} @i{streams}. @group @noindent @w{ clear-output prin1 write } @w{ finish-output prin1-to-string write-byte } @w{ force-output princ write-char } @w{ format princ-to-string write-line } @w{ fresh-line print write-string } @w{ pprint terpri write-to-string } @noindent @w{ Figure 21--3: Operators relating to Output Streams.} @end group A @i{stream} that is both an @i{input} @i{stream} and an @i{output} @i{stream} is called a @i{bidirectional} @IGindex{bidirectional} @i{stream} @IGindex{stream} . See the @i{functions} @b{input-stream-p} and @b{output-stream-p}. Any of the @i{operators} listed in @i{Figure~21--2} or @i{Figure~21--3} can be used with @i{bidirectional} @i{streams}. In addition, Figure 21--4 shows a list of @i{operators} that relate specificaly to @i{bidirectional} @i{streams}. @group @noindent @w{ y-or-n-p yes-or-no-p } @noindent @w{ Figure 21--4: Operators relating to Bidirectional Streams.} @end group @node Open and Closed Streams, Interactive Streams, Input, Introduction to Streams @subsubsection Open and Closed Streams @i{Streams} are either @i{open} @IGindex{open} or @i{closed} @IGindex{closed} . Except as explicitly specified otherwise, operations that create and return @i{streams} return @i{open} @i{streams}. The action of @i{closing} a @i{stream} marks the end of its use as a source or sink of data, permitting the @i{implementation} to reclaim its internal data structures, and to free any external resources which might have been locked by the @i{stream} when it was opened. Except as explicitly specified otherwise, the consequences are undefined when a @i{closed} @i{stream} is used where a @i{stream} is called for. Coercion of @i{streams} to @i{pathnames} is permissible for @i{closed} @i{streams}; in some situations, such as for a @i{truename} computation, the result might be different for an @i{open} @i{stream} and for that same @i{stream} once it has been @i{closed}. @node Interactive Streams, Abstract Classifications of Streams, Open and Closed Streams, Introduction to Streams @subsubsection Interactive Streams An @i{interactive stream} @IGindex{interactive stream} is one on which it makes sense to perform interactive querying. The precise meaning of an @i{interactive stream} is @i{implementation-defined}, and may depend on the underlying operating system. Some examples of the things that an @i{implementation} might choose to use as identifying characteristics of an @i{interactive stream} include: @table @asis @item @t{*} The @i{stream} is connected to a person (or equivalent) in such a way that the program can prompt for information and expect to receive different input depending on the prompt. @item @t{*} The program is expected to prompt for input and support ``normal input editing''. @item @t{*} @b{read-char} might wait for the user to type something before returning instead of immediately returning a character or end-of-file. @end table The general intent of having some @i{streams} be classified as @i{interactive streams} is to allow them to be distinguished from streams containing batch (or background or command-file) input. Output to batch streams is typically discarded or saved for later viewing, so interactive queries to such streams might not have the expected effect. @i{Terminal I/O} might or might not be an @i{interactive stream}. @node Abstract Classifications of Streams, File Streams, Interactive Streams, Introduction to Streams @subsubsection Abstract Classifications of Streams @node File Streams, Other Subclasses of Stream, Abstract Classifications of Streams, Introduction to Streams @subsubsection File Streams Some @i{streams}, called @i{file streams} @IGindex{file stream} , provide access to @i{files}. An @i{object} of @i{class} @b{file-stream} is used to represent a @i{file stream}. The basic operation for opening a @i{file} is @b{open}, which typically returns a @i{file stream} (see its dictionary entry for details). The basic operation for closing a @i{stream} is @b{close}. The macro @b{with-open-file} is useful to express the common idiom of opening a @i{file} for the duration of a given body of @i{code}, and assuring that the resulting @i{stream} is closed upon exit from that body. @node Other Subclasses of Stream, , File Streams, Introduction to Streams @subsubsection Other Subclasses of Stream The @i{class} @b{stream} has a number of @i{subclasses} defined by this specification. Figure 21--5 shows some information about these subclasses. @group @noindent @w{ Class Related Operators } @w{ @b{broadcast-stream} @b{make-broadcast-stream} } @w{ @b{broadcast-stream-streams} } @w{ @b{concatenated-stream} @b{make-concatenated-stream} } @w{ @b{concatenated-stream-streams} } @w{ @b{echo-stream} @b{make-echo-stream} } @w{ @b{echo-stream-input-stream} } @w{ @b{echo-stream-output-stream} } @w{ @b{string-stream} @b{make-string-input-stream} } @w{ @b{with-input-from-string} } @w{ @b{make-string-output-stream} } @w{ @b{with-output-to-string} } @w{ @b{get-output-stream-string} } @w{ @b{synonym-stream} @b{make-synonym-stream} } @w{ @b{synonym-stream-symbol} } @w{ @b{two-way-stream} @b{make-two-way-stream} } @w{ @b{two-way-stream-input-stream} } @w{ @b{two-way-stream-output-stream} } @noindent @w{ Figure 21--5: Defined Names related to Specialized Streams} @end group @node Stream Variables, Stream Arguments to Standardized Functions, Introduction to Streams, Stream Concepts @subsection Stream Variables @i{Variables} whose @i{values} must be @i{streams} are sometimes called @i{stream variables} @IGindex{stream variable} . Certain @i{stream variables} are defined by this specification to be the proper source of input or output in various @i{situations} where no specific @i{stream} has been specified instead. A complete list of such @i{standardized} @i{stream variables} appears in Figure 21--6. The consequences are undefined if at any time the @i{value} of any of these @i{variables} is not an @i{open} @i{stream}. @group @noindent @w{ Glossary Term Variable Name } @w{ @i{debug I/O} @b{*debug-io*} } @w{ @i{error output} @b{*error-output*} } @w{ @i{query I/O} @b{*query-io*} } @w{ @i{standard input} @b{*standard-input*} } @w{ @i{standard output} @b{*standard-output*} } @w{ @i{terminal I/O} @b{*terminal-io*} } @w{ @i{trace output} @b{*trace-output*} } @noindent @w{ Figure 21--6: Standardized Stream Variables} @end group Note that, by convention, @i{standardized} @i{stream variables} have names ending in ``@t{-input*}'' if they must be @i{input} @i{streams}, ending in ``@t{-output*}'' if they must be @i{output} @i{streams}, or ending in ``@t{-io*}'' if they must be @i{bidirectional} @i{streams}. User programs may @i{assign} or @i{bind} any @i{standardized} @i{stream variable} except @b{*terminal-io*}. @node Stream Arguments to Standardized Functions, Restrictions on Composite Streams, Stream Variables, Stream Concepts @subsection Stream Arguments to Standardized Functions The @i{operators} in Figure 21--7 accept @i{stream} @i{arguments} that might be either @i{open} or @i{closed} @i{streams}. @group @noindent @w{ broadcast-stream-streams file-author pathnamep } @w{ close file-namestring probe-file } @w{ compile-file file-write-date rename-file } @w{ compile-file-pathname host-namestring streamp } @w{ concatenated-stream-streams load synonym-stream-symbol } @w{ delete-file logical-pathname translate-logical-pathname } @w{ directory merge-pathnames translate-pathname } @w{ directory-namestring namestring truename } @w{ dribble open two-way-stream-input-stream } @w{ echo-stream-input-stream open-stream-p two-way-stream-output-stream } @w{ echo-stream-ouput-stream parse-namestring wild-pathname-p } @w{ ed pathname with-open-file } @w{ enough-namestring pathname-match-p } @noindent @w{ Figure 21--7: Operators that accept either Open or Closed Streams } @end group The @i{operators} in Figure 21--8 accept @i{stream} @i{arguments} that must be @i{open} @i{streams}. @group @noindent @w{ clear-input output-stream-p read-char-no-hang } @w{ clear-output peek-char read-delimited-list } @w{ file-length pprint read-line } @w{ file-position pprint-fill read-preserving-whitespace } @w{ file-string-length pprint-indent stream-element-type } @w{ finish-output pprint-linear stream-external-format } @w{ force-output pprint-logical-block terpri } @w{ format pprint-newline unread-char } @w{ fresh-line pprint-tab with-open-stream } @w{ get-output-stream-string pprint-tabular write } @w{ input-stream-p prin1 write-byte } @w{ interactive-stream-p princ write-char } @w{ listen print write-line } @w{ make-broadcast-stream print-object write-string } @w{ make-concatenated-stream print-unreadable-object y-or-n-p } @w{ make-echo-stream read yes-or-no-p } @w{ make-synonym-stream read-byte } @w{ make-two-way-stream read-char } @noindent @w{ Figure 21--8: Operators that accept Open Streams only } @end group @node Restrictions on Composite Streams, , Stream Arguments to Standardized Functions, Stream Concepts @subsection Restrictions on Composite Streams The consequences are undefined if any @i{component} of a @i{composite stream} is @i{closed} before the @i{composite stream} is @i{closed}. The consequences are undefined if the @i{synonym stream symbol} is not @i{bound} to an @i{open} @i{stream} from the time of the @i{synonym stream}'s creation until the time it is @i{closed}. @c end of including concept-streams @node Streams Dictionary, , Stream Concepts, Streams @section Streams Dictionary @c including dict-streams @menu * stream:: * broadcast-stream:: * concatenated-stream:: * echo-stream:: * file-stream:: * string-stream:: * synonym-stream:: * two-way-stream:: * input-stream-p:: * interactive-stream-p:: * open-stream-p:: * stream-element-type:: * streamp:: * read-byte:: * write-byte:: * peek-char:: * read-char:: * read-char-no-hang:: * terpri:: * unread-char:: * write-char:: * read-line:: * write-string:: * read-sequence:: * write-sequence:: * file-length:: * file-position:: * file-string-length:: * open:: * stream-external-format:: * with-open-file:: * close:: * with-open-stream:: * listen:: * clear-input:: * finish-output:: * y-or-n-p:: * make-synonym-stream:: * synonym-stream-symbol:: * broadcast-stream-streams:: * make-broadcast-stream:: * make-two-way-stream:: * two-way-stream-input-stream:: * echo-stream-input-stream:: * make-echo-stream:: * concatenated-stream-streams:: * make-concatenated-stream:: * get-output-stream-string:: * make-string-input-stream:: * make-string-output-stream:: * with-input-from-string:: * with-output-to-string:: * *debug-io*:: * *terminal-io*:: * stream-error:: * stream-error-stream:: * end-of-file:: @end menu @node stream, broadcast-stream, Streams Dictionary, Streams Dictionary @subsection stream [System Class] @subsubheading Class Precedence List:: @b{stream}, @b{t} @subsubheading Description:: A @i{stream} is an @i{object} that can be used with an input or output function to identify an appropriate source or sink of @i{characters} or @i{bytes} for that operation. For more complete information, see @ref{Stream Concepts}. @subsubheading See Also:: @ref{Stream Concepts}, @ref{Printing Other Objects}, {@ref{Printer}}, {@ref{Reader}} @node broadcast-stream, concatenated-stream, stream, Streams Dictionary @subsection broadcast-stream [System Class] @subsubheading Class Precedence List:: @b{broadcast-stream}, @b{stream}, @b{t} @subsubheading Description:: A @i{broadcast stream} is an @i{output} @i{stream} which has associated with it a set of zero or more @i{output} @i{streams} such that any output sent to the @i{broadcast stream} gets passed on as output to each of the associated @i{output} @i{streams}. (If a @i{broadcast stream} has no @i{component streams}, then all output to the @i{broadcast stream} is discarded.) The set of operations that may be performed on a @i{broadcast stream} is the intersection of those for its associated @i{output} @i{streams}. Some output operations (@i{e.g.}, @b{fresh-line}) return @i{values} based on the state of the @i{stream} at the time of the operation. Since these @i{values} might differ for each of the @i{component streams}, it is necessary to describe their return value specifically: @table @asis @item @t{*} @b{stream-element-type} returns the value from the last component stream, or @b{t} if there are no component streams. @item @t{*} @b{fresh-line} returns the value from the last component stream, or @b{nil} if there are no component streams. @item @t{*} The functions @b{file-length}, @b{file-position}, @b{file-string-length}, and @b{stream-external-format} return the value from the last component stream; if there are no component streams, @b{file-length} and @b{file-position} return @t{0}, @b{file-string-length} returns @t{1}, and @b{stream-external-format} returns @t{:default}. @item @t{*} The functions @b{streamp} and @b{output-stream-p} always return @i{true} for @i{broadcast streams}. @item @t{*} The functions @b{open-stream-p} tests whether the @i{broadcast stream} is @i{open}_2, not whether its component streams are @i{open}. @item @t{*} The functions @b{input-stream-p} and @i{interactive-stream-p} return an @i{implementation-defined}, @i{generalized boolean} value. @item @t{*} For the input operations @b{clear-input} @b{listen}, @b{peek-char}, @b{read-byte}, @b{read-char-no-hang}, @b{read-char}, @b{read-line}, and @b{unread-char}, the consequences are undefined if the indicated operation is performed. However, an @i{implementation} is permitted to define such a behavior as an @i{implementation-dependent} extension. @end table For any output operations not having their return values explicitly specified above or elsewhere in this document, it is defined that the @i{values} returned by such an operation are the @i{values} resulting from performing the operation on the last of its @i{component streams}; the @i{values} resulting from performing the operation on all preceding @i{streams} are discarded. If there are no @i{component streams}, the value is @i{implementation-dependent}. @subsubheading See Also:: @ref{broadcast-stream-streams} , @ref{make-broadcast-stream} @node concatenated-stream, echo-stream, broadcast-stream, Streams Dictionary @subsection concatenated-stream [System Class] @subsubheading Class Precedence List:: @b{concatenated-stream}, @b{stream}, @b{t} @subsubheading Description:: A @i{concatenated stream} is an @i{input} @i{stream} which is a @i{composite stream} of zero or more other @i{input} @i{streams}, such that the sequence of data which can be read from the @i{concatenated stream} is the same as the concatenation of the sequences of data which could be read from each of the constituent @i{streams}. Input from a @i{concatenated stream} is taken from the first of the associated @i{input streams} until it reaches @i{end of file}_1; then that @i{stream} is discarded, and subsequent input is taken from the next @i{input stream}, and so on. An @i{end of file} on the associated @i{input streams} is always managed invisibly by the @i{concatenated stream}---the only time a client of a @i{concatenated stream} sees an @i{end of file} is when an attempt is made to obtain data from the @i{concatenated stream} but it has no remaining @i{input streams} from which to obtain such data. @subsubheading See Also:: @ref{concatenated-stream-streams} , @ref{make-concatenated-stream} @node echo-stream, file-stream, concatenated-stream, Streams Dictionary @subsection echo-stream [System Class] @subsubheading Class Precedence List:: @b{echo-stream}, @b{stream}, @b{t} @subsubheading Description:: An @i{echo stream} is a @i{bidirectional} @i{stream} that gets its input from an associated @i{input} @i{stream} and sends its output to an associated @i{output} @i{stream}. All input taken from the @i{input} @i{stream} is echoed to the @i{output} @i{stream}. Whether the input is echoed immediately after it is encountered, or after it has been read from the @i{input stream} is @i{implementation-dependent}. @subsubheading See Also:: @ref{echo-stream-input-stream; echo-stream-output-stream} , @b{echo-stream-output-stream}, @ref{make-echo-stream} @node file-stream, string-stream, echo-stream, Streams Dictionary @subsection file-stream [System Class] @subsubheading Class Precedence List:: @b{file-stream}, @b{stream}, @b{t} @subsubheading Description:: An @i{object} of @i{type} @b{file-stream} is a @i{stream} the direct source or sink of which is a @i{file}. Such a @i{stream} is created explicitly by @b{open} and @b{with-open-file}, and implicitly by @i{functions} such as @b{load} that process @i{files}. @subsubheading See Also:: @ref{load} , @ref{open} , @ref{with-open-file} @node string-stream, synonym-stream, file-stream, Streams Dictionary @subsection string-stream [System Class] @subsubheading Class Precedence List:: @b{string-stream}, @b{stream}, @b{t} @subsubheading Description:: A @i{string stream} is a @i{stream} which reads input from or writes output to an associated @i{string}. The @i{stream element type} of a @i{string stream} is always a @i{subtype} of @i{type} @b{character}. @subsubheading See Also:: @ref{make-string-input-stream} , @ref{make-string-output-stream} , @ref{with-input-from-string} , @ref{with-output-to-string} @node synonym-stream, two-way-stream, string-stream, Streams Dictionary @subsection synonym-stream [System Class] @subsubheading Class Precedence List:: @b{synonym-stream}, @b{stream}, @b{t} @subsubheading Description:: A @i{stream} that is an alias for another @i{stream}, which is the @i{value} of a @i{dynamic variable} whose @i{name} is the @i{synonym stream symbol} of the @i{synonym stream}. Any operations on a @i{synonym stream} will be performed on the @i{stream} that is then the @i{value} of the @i{dynamic variable} named by the @i{synonym stream symbol}. If the @i{value} of the @i{variable} should change, or if the @i{variable} should be @i{bound}, then the @i{stream} will operate on the new @i{value} of the @i{variable}. @subsubheading See Also:: @ref{make-synonym-stream} , @ref{synonym-stream-symbol} @node two-way-stream, input-stream-p, synonym-stream, Streams Dictionary @subsection two-way-stream [System Class] @subsubheading Class Precedence List:: @b{two-way-stream}, @b{stream}, @b{t} @subsubheading Description:: A @i{bidirectional} @i{composite stream} that receives its input from an associated @i{input} @i{stream} and sends its output to an associated @i{output} @i{stream}. @subsubheading See Also:: @ref{make-two-way-stream} , @ref{two-way-stream-input-stream; two-way-stream-output-stream} , @b{two-way-stream-output-stream} @node input-stream-p, interactive-stream-p, two-way-stream, Streams Dictionary @subsection input-stream-p, output-stream-p [Function] @code{input-stream-p} @i{stream} @result{} @i{generalized-boolean} @code{output-stream-p} @i{stream} @result{} @i{generalized-boolean} @subsubheading Arguments and Values:: @i{stream}---a @i{stream}. @i{generalized-boolean}---a @i{generalized boolean}. @subsubheading Description:: @b{input-stream-p} returns @i{true} if @i{stream} is an @i{input} @i{stream}; otherwise, returns @i{false}. @b{output-stream-p} returns @i{true} if @i{stream} is an @i{output} @i{stream}; otherwise, returns @i{false}. @subsubheading Examples:: @example (input-stream-p *standard-input*) @result{} @i{true} (input-stream-p *terminal-io*) @result{} @i{true} (input-stream-p (make-string-output-stream)) @result{} @i{false} (output-stream-p *standard-output*) @result{} @i{true} (output-stream-p *terminal-io*) @result{} @i{true} (output-stream-p (make-string-input-stream "jr")) @result{} @i{false} @end example @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{stream} is not a @i{stream}. @node interactive-stream-p, open-stream-p, input-stream-p, Streams Dictionary @subsection interactive-stream-p [Function] @code{interactive-stream-p} @i{stream} @result{} @i{generalized-boolean} @subsubheading Arguments and Values:: @i{stream}---a @i{stream}. @i{generalized-boolean}---a @i{generalized boolean}. @subsubheading Description:: Returns @i{true} if @i{stream} is an @i{interactive stream}; otherwise, returns @i{false}. @subsubheading Examples:: @example (when (> measured limit) (let ((error (round (* (- measured limit) 100) limit))) (unless (if (interactive-stream-p *query-io*) (yes-or-no-p "The frammis is out of tolerance by ~D Is it safe to proceed? " error) (< error 15)) ;15 (error "The frammis is out of tolerance by ~D @end example @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{stream} is not a @i{stream}. @subsubheading See Also:: @ref{Stream Concepts} @node open-stream-p, stream-element-type, interactive-stream-p, Streams Dictionary @subsection open-stream-p [Function] @code{open-stream-p} @i{stream} @result{} @i{generalized-boolean} @subsubheading Arguments and Values:: @i{stream}---a @i{stream}. @i{generalized-boolean}---a @i{generalized boolean}. @subsubheading Description:: Returns @i{true} if @i{stream} is an @i{open} @i{stream}; otherwise, returns @i{false}. @i{Streams} are open until they have been explicitly closed with @b{close}, or until they are implicitly closed due to exit from a @b{with-output-to-string}, @b{with-open-file}, @b{with-input-from-string}, or @b{with-open-stream} @i{form}. @subsubheading Examples:: @example (open-stream-p *standard-input*) @result{} @i{true} @end example @subsubheading Affected By:: @b{close}. @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{stream} is not a @i{stream}. @node stream-element-type, streamp, open-stream-p, Streams Dictionary @subsection stream-element-type [Function] @code{stream-element-type} @i{stream} @result{} @i{typespec} @subsubheading Arguments and Values:: @i{stream}---a @i{stream}. @i{typespec}---a @i{type specifier}. @subsubheading Description:: @b{stream-element-type} returns a @i{type specifier} that indicates the @i{types} of @i{objects} that may be read from or written to @i{stream}. @i{Streams} created by @b{open} have an @i{element type} restricted to @b{integer} or a @i{subtype} of @i{type} @b{character}. @subsubheading Examples:: @example ;; Note that the stream must accomodate at least the specified type, ;; but might accomodate other types. Further note that even if it does ;; accomodate exactly the specified type, the type might be specified in ;; any of several ways. (with-open-file (s "test" :element-type '(integer 0 1) :if-exists :error :direction :output) (stream-element-type s)) @result{} INTEGER @i{OR}@result{} (UNSIGNED-BYTE 16) @i{OR}@result{} (UNSIGNED-BYTE 8) @i{OR}@result{} BIT @i{OR}@result{} (UNSIGNED-BYTE 1) @i{OR}@result{} (INTEGER 0 1) @i{OR}@result{} (INTEGER 0 (2)) @end example @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{stream} is not a @i{stream}. @node streamp, read-byte, stream-element-type, Streams Dictionary @subsection streamp [Function] @code{streamp} @i{object} @result{} @i{generalized-boolean} @subsubheading Arguments and Values:: @i{object}---an @i{object}. @i{generalized-boolean}---a @i{generalized boolean}. @subsubheading Description:: Returns @i{true} if @i{object} is of @i{type} @b{stream}; otherwise, returns @i{false}. @b{streamp} is unaffected by whether @i{object}, if it is a @i{stream}, is @i{open} or closed. @subsubheading Examples:: @example (streamp *terminal-io*) @result{} @i{true} (streamp 1) @result{} @i{false} @end example @subsubheading Notes:: @example (streamp @i{object}) @equiv{} (typep @i{object} 'stream) @end example @node read-byte, write-byte, streamp, Streams Dictionary @subsection read-byte [Function] @code{read-byte} @i{stream {&optional} eof-error-p eof-value} @result{} @i{byte} @subsubheading Arguments and Values:: @i{stream}---a @i{binary} @i{input} @i{stream}. @i{eof-error-p}---a @i{generalized boolean}. The default is @i{true}. @i{eof-value}---an @i{object}. The default is @b{nil}. @i{byte}---an @i{integer}, or the @i{eof-value}. @subsubheading Description:: @b{read-byte} reads and returns one byte from @i{stream}. If an @i{end of file}_2 occurs and @i{eof-error-p} is @i{false}, the @i{eof-value} is returned. @subsubheading Examples:: @example (with-open-file (s "temp-bytes" :direction :output :element-type 'unsigned-byte) (write-byte 101 s)) @result{} 101 (with-open-file (s "temp-bytes" :element-type 'unsigned-byte) (format t "~S ~S" (read-byte s) (read-byte s nil 'eof))) @t{ |> } 101 EOF @result{} NIL @end example @subsubheading Side Effects:: Modifies @i{stream}. @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{stream} is not a @i{stream}. Should signal an error of @i{type} @b{error} if @i{stream} is not a @i{binary} @i{input} @i{stream}. If there are no @i{bytes} remaining in the @i{stream} and @i{eof-error-p} is @i{true}, an error of @i{type} @b{end-of-file} is signaled. @subsubheading See Also:: @ref{read-char} , @ref{read-sequence} , @ref{write-byte} @node write-byte, peek-char, read-byte, Streams Dictionary @subsection write-byte [Function] @code{write-byte} @i{byte stream} @result{} @i{byte} @subsubheading Arguments and Values:: @i{byte}---an @i{integer} of the @i{stream element type} of @i{stream}. @i{stream}---a @i{binary} @i{output} @i{stream}. @subsubheading Description:: @b{write-byte} writes one byte, @i{byte}, to @i{stream}. @subsubheading Examples:: @example (with-open-file (s "temp-bytes" :direction :output :element-type 'unsigned-byte) (write-byte 101 s)) @result{} 101 @end example @subsubheading Side Effects:: @i{stream} is modified. @subsubheading Affected By:: The @i{element type} of the @i{stream}. @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{stream} is not a @i{stream}. Should signal an error of @i{type} @b{error} if @i{stream} is not a @i{binary} @i{output} @i{stream}. Might signal an error of @i{type} @b{type-error} if @i{byte} is not an @i{integer} of the @i{stream element type} of @i{stream}. @subsubheading See Also:: @ref{read-byte} , @ref{write-char} , @ref{write-sequence} @node peek-char, read-char, write-byte, Streams Dictionary @subsection peek-char [Function] @code{peek-char} @i{{&optional} peek-type input-stream eof-error-p eof-value recursive-p} @result{} @i{char} @subsubheading Arguments and Values:: @i{peek-type}---a @i{character} or @b{t} or @b{nil}. @i{input-stream}---@i{input} @i{stream designator}. The default is @i{standard input}. @i{eof-error-p}---a @i{generalized boolean}. The default is @i{true}. @i{eof-value}---an @i{object}. The default is @b{nil}. @i{recursive-p}---a @i{generalized boolean}. The default is @i{false}. @i{char}---a @i{character} or the @i{eof-value}. @subsubheading Description:: @b{peek-char} obtains the next character in @i{input-stream} without actually reading it, thus leaving the character to be read at a later time. It can also be used to skip over and discard intervening characters in the @i{input-stream} until a particular character is found. If @i{peek-type} is not supplied or @b{nil}, @b{peek-char} returns the next character to be read from @i{input-stream}, without actually removing it from @i{input-stream}. The next time input is done from @i{input-stream}, the character will still be there. If @i{peek-type} is @b{t}, then @b{peek-char} skips over @i{whitespace}_2 @i{characters}, but not comments, and then performs the peeking operation on the next character. The last character examined, the one that starts an @i{object}, is not removed from @i{input-stream}. If @i{peek-type} is a @i{character}, then @b{peek-char} skips over input characters until a character that is @b{char=} to that @i{character} is found; that character is left in @i{input-stream}. If an @i{end of file}_2 occurs and @i{eof-error-p} is @i{false}, @i{eof-value} is returned. { }{If @i{recursive-p} is @i{true}, this call is expected to be embedded in a higher-level call to @b{read} or a similar @i{function} used by the @i{Lisp reader}.} When @i{input-stream} is an @i{echo stream}, characters that are only peeked at are not echoed. In the case that @i{peek-type} is not @b{nil}, the characters that are passed by @b{peek-char} are treated as if by @b{read-char}, and so are echoed unless they have been marked otherwise by @b{unread-char}. @subsubheading Examples:: @example (with-input-from-string (input-stream " 1 2 3 4 5") (format t "~S ~S ~S" (peek-char t input-stream) (peek-char #\4 input-stream) (peek-char nil input-stream))) @t{ |> } #\1 #\4 #\4 @result{} NIL @end example @subsubheading Affected By:: @b{*readtable*}, @b{*standard-input*}, @b{*terminal-io*}. @subsubheading Exceptional Situations:: If @i{eof-error-p} is @i{true} and an @i{end of file}_2 occurs an error of @i{type} @b{end-of-file} is signaled. If @i{peek-type} is a @i{character}, an @i{end of file}_2 occurs, and @i{eof-error-p} is @i{true}, an error of @i{type} @b{end-of-file} is signaled. If @i{recursive-p} is @i{true} and an @i{end of file}_2 occurs, an error of @i{type} @b{end-of-file} is signaled. @node read-char, read-char-no-hang, peek-char, Streams Dictionary @subsection read-char [Function] @code{read-char} @i{{&optional} input-stream eof-error-p eof-value recursive-p} @result{} @i{char} @subsubheading Arguments and Values:: @i{input-stream}---an @i{input} @i{stream designator}. The default is @i{standard input}. @i{eof-error-p}---a @i{generalized boolean}. The default is @i{true}. @i{eof-value}---an @i{object}. The default is @b{nil}. @i{recursive-p}---a @i{generalized boolean}. The default is @i{false}. @i{char}---a @i{character} or the @i{eof-value}. @subsubheading Description:: @b{read-char} returns the next @i{character} from @i{input-stream}. When @i{input-stream} is an @i{echo stream}, the character is echoed on @i{input-stream} the first time the character is seen. Characters that are not echoed by @b{read-char} are those that were put there by @b{unread-char} and hence are assumed to have been echoed already by a previous call to @b{read-char}. { }{If @i{recursive-p} is @i{true}, this call is expected to be embedded in a higher-level call to @b{read} or a similar @i{function} used by the @i{Lisp reader}.} If an @i{end of file}_2 occurs and @i{eof-error-p} is @i{false}, @i{eof-value} is returned. @subsubheading Examples:: @example (with-input-from-string (is "0123") (do ((c (read-char is) (read-char is nil 'the-end))) ((not (characterp c))) (format t "~S " c))) @t{ |> } #\0 #\1 #\2 #\3 @result{} NIL @end example @subsubheading Affected By:: @b{*standard-input*}, @b{*terminal-io*}. @subsubheading Exceptional Situations:: If an @i{end of file}_2 occurs before a character can be read, and @i{eof-error-p} is @i{true}, an error of @i{type} @b{end-of-file} is signaled. @subsubheading See Also:: @ref{read-byte} , @ref{read-sequence} , @ref{write-char} , @ref{read; read-preserving-whitespace} @subsubheading Notes:: The corresponding output function is @b{write-char}. @node read-char-no-hang, terpri, read-char, Streams Dictionary @subsection read-char-no-hang [Function] @code{read-char-no-hang} @i{{&optional} input-stream eof-error-p eof-value recursive-p} @result{} @i{char} @subsubheading Arguments and Values:: @i{input-stream} -- an @i{input} @i{stream designator}. The default is @i{standard input}. @i{eof-error-p}---a @i{generalized boolean}. The default is @i{true}. @i{eof-value}---an @i{object}. The default is @b{nil}. @i{recursive-p}---a @i{generalized boolean}. The default is @i{false}. @i{char}---a @i{character} or @b{nil} or the @i{eof-value}. @subsubheading Description:: @b{read-char-no-hang} returns a character from @i{input-stream} if such a character is available. If no character is available, @b{read-char-no-hang} returns @b{nil}. { }{If @i{recursive-p} is @i{true}, this call is expected to be embedded in a higher-level call to @b{read} or a similar @i{function} used by the @i{Lisp reader}.} If an @i{end of file}_2 occurs and @i{eof-error-p} is @i{false}, @i{eof-value} is returned. @subsubheading Examples:: @example ;; This code assumes an implementation in which a newline is not ;; required to terminate input from the console. (defun test-it () (unread-char (read-char)) (list (read-char-no-hang) (read-char-no-hang) (read-char-no-hang))) @result{} TEST-IT ;; Implementation A, where a Newline is not required to terminate ;; interactive input on the console. (test-it) @t{ |> } @b{|>>}@t{a}@b{<<|} @result{} (#\a NIL NIL) ;; Implementation B, where a Newline is required to terminate ;; interactive input on the console, and where that Newline remains ;; on the input stream. (test-it) @t{ |> } @b{|>>}@t{a{@i{[<--}~]}}@b{<<|} @result{} (#\a #\Newline NIL) @end example @subsubheading Affected By:: @b{*standard-input*}, @b{*terminal-io*}. @subsubheading Exceptional Situations:: If an @i{end of file}_2 occurs when @i{eof-error-p} is @i{true}, an error of @i{type} @b{end-of-file} is signaled . @subsubheading See Also:: @ref{listen} @subsubheading Notes:: @b{read-char-no-hang} is exactly like @b{read-char}, except that if it would be necessary to wait in order to get a character (as from a keyboard), @b{nil} is immediately returned without waiting. @node terpri, unread-char, read-char-no-hang, Streams Dictionary @subsection terpri, fresh-line [Function] @code{terpri} @i{{&optional} output-stream} @result{} @i{@b{nil}} @code{fresh-line} @i{{&optional} output-stream} @result{} @i{generalized-boolean} @subsubheading Arguments and Values:: @i{output-stream} -- an @i{output} @i{stream designator}. The default is @i{standard output}. @i{generalized-boolean}---a @i{generalized boolean}. @subsubheading Description:: @b{terpri} outputs a @i{newline} to @i{output-stream}. @b{fresh-line} is similar to @b{terpri} but outputs a @i{newline} only if the @i{output-stream} is not already at the start of a line. If for some reason this cannot be determined, then a @i{newline} is output anyway. @b{fresh-line} returns @i{true} if it outputs a @i{newline}; otherwise it returns @i{false}. @subsubheading Examples:: @example (with-output-to-string (s) (write-string "some text" s) (terpri s) (terpri s) (write-string "more text" s)) @result{} "some text more text" (with-output-to-string (s) (write-string "some text" s) (fresh-line s) (fresh-line s) (write-string "more text" s)) @result{} "some text more text" @end example @subsubheading Side Effects:: The @i{output-stream} is modified. @subsubheading Affected By:: @b{*standard-output*}, @b{*terminal-io*}. @subsubheading Exceptional Situations:: None. [Reviewer Note by Barmar: What if stream is closed?] @subsubheading Notes:: @b{terpri} is identical in effect to @example (write-char #\Newline output-stream) @end example @node unread-char, write-char, terpri, Streams Dictionary @subsection unread-char [Function] @code{unread-char} @i{character {&optional} input-stream} @result{} @i{@b{nil}} @subsubheading Arguments and Values:: @i{character}---a @i{character}; must be the last @i{character} that was read from @i{input-stream}. @i{input-stream}---an @i{input} @i{stream designator}. The default is @i{standard input}. @subsubheading Description:: @b{unread-char} places @i{character} back onto the front of @i{input-stream} so that it will again be the next character in @i{input-stream}. When @i{input-stream} is an @i{echo stream}, no attempt is made to undo any echoing of the character that might already have been done on @i{input-stream}. However, characters placed on @i{input-stream} by @b{unread-char} are marked in such a way as to inhibit later re-echo by @b{read-char}. It is an error to invoke @b{unread-char} twice consecutively on the same @i{stream} without an intervening call to @b{read-char} (or some other input operation which implicitly reads characters) on that @i{stream}. Invoking @b{peek-char} or @b{read-char} commits all previous characters. The consequences of invoking @b{unread-char} on any character preceding that which is returned by @b{peek-char} (including those passed over by @b{peek-char} that has a @i{non-nil} @i{peek-type}) are unspecified. In particular, the consequences of invoking @b{unread-char} after @b{peek-char} are unspecified. @subsubheading Examples:: @example (with-input-from-string (is "0123") (dotimes (i 6) (let ((c (read-char is))) (if (evenp i) (format t "~&~S ~S~ @t{ |> } 0 #\0 @t{ |> } 2 #\1 @t{ |> } 4 #\2 @result{} NIL @end example @subsubheading Affected By:: @b{*standard-input*}, @b{*terminal-io*}. @subsubheading See Also:: @ref{peek-char} , @ref{read-char} , @ref{Stream Concepts} @subsubheading Notes:: @b{unread-char} is intended to be an efficient mechanism for allowing the @i{Lisp reader} and other parsers to perform one-character lookahead in @i{input-stream}. @node write-char, read-line, unread-char, Streams Dictionary @subsection write-char [Function] @code{write-char} @i{character {&optional} output-stream} @result{} @i{character} @subsubheading Arguments and Values:: @i{character}---a @i{character}. @i{output-stream} -- an @i{output} @i{stream designator}. The default is @i{standard output}. @subsubheading Description:: @b{write-char} outputs @i{character} to @i{output-stream}. @subsubheading Examples:: @example (write-char #\a) @t{ |> } a @result{} #\a (with-output-to-string (s) (write-char #\a s) (write-char #\Space s) (write-char #\b s)) @result{} "a b" @end example @subsubheading Side Effects:: The @i{output-stream} is modified. @subsubheading Affected By:: @b{*standard-output*}, @b{*terminal-io*}. @subsubheading See Also:: @ref{read-char} , @ref{write-byte} , @ref{write-sequence} @node read-line, write-string, write-char, Streams Dictionary @subsection read-line [Function] @code{read-line} @i{{&optional} input-stream eof-error-p eof-value recursive-p}@* @result{} @i{line, missing-newline-p} @subsubheading Arguments and Values:: @i{input-stream}---an @i{input} @i{stream designator}. The default is @i{standard input}. @i{eof-error-p}---a @i{generalized boolean}. The default is @i{true}. @i{eof-value}---an @i{object}. The default is @b{nil}. @i{recursive-p}---a @i{generalized boolean}. The default is @i{false}. @i{line}---a @i{string} or the @i{eof-value}. @i{missing-newline-p}---a @i{generalized boolean}. @subsubheading Description:: Reads from @i{input-stream} a line of text that is terminated by a @i{newline} or @i{end of file}. { }{If @i{recursive-p} is @i{true}, this call is expected to be embedded in a higher-level call to @b{read} or a similar @i{function} used by the @i{Lisp reader}.} The @i{primary value}, @i{line}, is the line that is read, represented as a @i{string} (without the trailing @i{newline}, if any). If @i{eof-error-p} is @i{false} and the @i{end of file} for @i{input-stream} is reached before any @i{characters} are read, @i{eof-value} is returned as the @i{line}. The @i{secondary value}, @i{missing-newline-p}, is a @i{generalized boolean} that is @i{false} if the @i{line} was terminated by a @i{newline}, or @i{true} if the @i{line} was terminated by the @i{end of file} for @i{input-stream} (or if the @i{line} is the @i{eof-value}). @subsubheading Examples:: @example (setq a "line 1 line2") @result{} "line 1 line2" (read-line (setq input-stream (make-string-input-stream a))) @result{} "line 1", @i{false} (read-line input-stream) @result{} "line2", @i{true} (read-line input-stream nil nil) @result{} NIL, @i{true} @end example @subsubheading Affected By:: @b{*standard-input*}, @b{*terminal-io*}. @subsubheading Exceptional Situations:: If an @i{end of file}_2 occurs before any characters are read in the line, an error is signaled if @i{eof-error-p} is @i{true}. @subsubheading See Also:: @ref{read; read-preserving-whitespace} @subsubheading Notes:: The corresponding output function is @b{write-line}. @node write-string, read-sequence, read-line, Streams Dictionary @subsection write-string, write-line [Function] @code{write-string} @i{string {&optional} output-stream {&key} start end} @result{} @i{string} @code{write-line} @i{string {&optional} output-stream {&key} start end} @result{} @i{string} @subsubheading Arguments and Values:: @i{string}---a @i{string}. @i{output-stream} -- an @i{output} @i{stream designator}. The default is @i{standard output}. @i{start}, @i{end}---@i{bounding index designators} of @i{string}. The defaults for @i{start} and @i{end} are @t{0} and @b{nil}, respectively. @subsubheading Description:: @b{write-string} writes the @i{characters} of the subsequence of @i{string} @i{bounded} by @i{start} and @i{end} to @i{output-stream}. @b{write-line} does the same thing, but then outputs a newline afterwards. @subsubheading Examples:: @example (prog1 (write-string "books" nil :end 4) (write-string "worms")) @t{ |> } bookworms @result{} "books" (progn (write-char #\*) (write-line "test12" *standard-output* :end 5) (write-line "*test2") (write-char #\*) nil) @t{ |> } *test1 @t{ |> } *test2 @t{ |> } * @result{} NIL @end example @subsubheading Affected By:: @b{*standard-output*}, @b{*terminal-io*}. @subsubheading See Also:: @ref{read-line} , @ref{write-char} @subsubheading Notes:: @b{write-line} and @b{write-string} return @i{string}, not the substring @i{bounded} by @i{start} and @i{end}. @example (write-string string) @equiv{} (dotimes (i (length string) (write-char (char string i))) (write-line string) @equiv{} (prog1 (write-string string) (terpri)) @end example @node read-sequence, write-sequence, write-string, Streams Dictionary @subsection read-sequence [Function] @code{read-sequence} @i{sequence stream {&key} start end} @result{} @i{position} @i{sequence}---a @i{sequence}. @i{stream}---an @i{input} @i{stream}. @i{start}, @i{end}---@i{bounding index designators} of @i{sequence}. The defaults for @i{start} and @i{end} are @t{0} and @b{nil}, respectively. @i{position}---an @i{integer} greater than or equal to zero, and less than or equal to the @i{length} of the @i{sequence}. @subsubheading Description:: Destructively modifies @i{sequence} by replacing the @i{elements} of @i{sequence} @i{bounded} by @i{start} and @i{end} with @i{elements} read from @i{stream}. @i{Sequence} is destructively modified by copying successive @i{elements} into it from @i{stream}. If the @i{end of file} for @i{stream} is reached before copying all @i{elements} of the subsequence, then the extra @i{elements} near the end of @i{sequence} are not updated. @i{Position} is the index of the first @i{element} of @i{sequence} that was not updated, which might be less than @i{end} because the @i{end of file} was reached. @subsubheading Examples:: @example (defvar *data* (make-array 15 :initial-element nil)) (values (read-sequence *data* (make-string-input-stream "test string")) *data*) @result{} 11, #(#\t #\e #\s #\t #\Space #\s #\t #\r #\i #\n #\g NIL NIL NIL NIL) @end example @subsubheading Side Effects:: Modifies @i{stream} and @i{sequence}. @subsubheading Exceptional Situations:: Should be prepared to signal an error of @i{type} @b{type-error} if @i{sequence} is not a @i{proper sequence}. Should signal an error of @i{type} @b{type-error} if @i{start} is not a non-negative @i{integer}. Should signal an error of @i{type} @b{type-error} if @i{end} is not a non-negative @i{integer} or @b{nil}. Might signal an error of @i{type} @b{type-error} if an @i{element} read from the @i{stream} is not a member of the @i{element type} of the @i{sequence}. @subsubheading See Also:: @ref{Compiler Terminology}, @ref{write-sequence} , @ref{read-line} @subsubheading Notes:: @b{read-sequence} is identical in effect to iterating over the indicated subsequence and reading one @i{element} at a time from @i{stream} and storing it into @i{sequence}, but may be more efficient than the equivalent loop. An efficient implementation is more likely to exist for the case where the @i{sequence} is a @i{vector} with the same @i{element type} as the @i{stream}. @node write-sequence, file-length, read-sequence, Streams Dictionary @subsection write-sequence [Function] @code{write-sequence} @i{sequence stream {&key} start end} @result{} @i{sequence} @i{sequence}---a @i{sequence}. @i{stream}---an @i{output} @i{stream}. @i{start}, @i{end}---@i{bounding index designators} of @i{sequence}. The defaults for @i{start} and @i{end} are @t{0} and @b{nil}, respectively. @subsubheading Description:: @b{write-sequence} writes the @i{elements} of the subsequence of @i{sequence} @i{bounded} by @i{start} and @i{end} to @i{stream}. @subsubheading Examples:: @example (write-sequence "bookworms" *standard-output* :end 4) @t{ |> } book @result{} "bookworms" @end example @subsubheading Side Effects:: Modifies @i{stream}. @subsubheading Exceptional Situations:: Should be prepared to signal an error of @i{type} @b{type-error} if @i{sequence} is not a @i{proper sequence}. Should signal an error of @i{type} @b{type-error} if @i{start} is not a non-negative @i{integer}. Should signal an error of @i{type} @b{type-error} if @i{end} is not a non-negative @i{integer} or @b{nil}. Might signal an error of @i{type} @b{type-error} if an @i{element} of the @i{bounded} @i{sequence} is not a member of the @i{stream element type} of the @i{stream}. @subsubheading See Also:: @ref{Compiler Terminology}, @ref{read-sequence} , @ref{write-string; write-line} , @b{write-line} @subsubheading Notes:: @b{write-sequence} is identical in effect to iterating over the indicated subsequence and writing one @i{element} at a time to @i{stream}, but may be more efficient than the equivalent loop. An efficient implementation is more likely to exist for the case where the @i{sequence} is a @i{vector} with the same @i{element type} as the @i{stream}. @node file-length, file-position, write-sequence, Streams Dictionary @subsection file-length [Function] @code{file-length} @i{stream} @result{} @i{length} @subsubheading Arguments and Values:: @i{stream}---a @i{stream associated with a file}. @i{length}---a non-negative @i{integer} or @b{nil}. @subsubheading Description:: @b{file-length} returns the length of @i{stream}, or @b{nil} if the length cannot be determined. For a binary file, the length is measured in units of the @i{element type} of the @i{stream}. @subsubheading Examples:: @example (with-open-file (s "decimal-digits.text" :direction :output :if-exists :error) (princ "0123456789" s) (truename s)) @result{} #P"A:>Joe>decimal-digits.text.1" (with-open-file (s "decimal-digits.text") (file-length s)) @result{} 10 @end example @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{stream} is not a @i{stream associated with a file}. @subsubheading See Also:: @ref{open} @node file-position, file-string-length, file-length, Streams Dictionary @subsection file-position [Function] @code{file-position} @i{stream} @result{} @i{position} @code{file-position} @i{stream position-spec} @result{} @i{success-p} @subsubheading Arguments and Values:: @i{stream}---a @i{stream}. @i{position-spec}---a @i{file position designator}. @i{position}---a @i{file position} or @b{nil}. @i{success-p}---a @i{generalized boolean}. @subsubheading Description:: Returns or changes the current position within a @i{stream}. When @i{position-spec} is not supplied, @b{file-position} returns the current @i{file position} in the @i{stream}, or @b{nil} if this cannot be determined. When @i{position-spec} is supplied, the @i{file position} in @i{stream} is set to that @i{file position} (if possible). @b{file-position} returns @i{true} if the repositioning is performed successfully, or @i{false} if it is not. An @i{integer} returned by @b{file-position} of one argument should be acceptable as @i{position-spec} for use with the same file. For a character file, performing a single @b{read-char} or @b{write-char} operation may cause the file position to be increased by more than 1 because of character-set translations (such as translating between the @r{Common Lisp} @t{#\Newline} character and an external ASCII carriage-return/line-feed sequence) and other aspects of the implementation. For a binary file, every @b{read-byte} or @b{write-byte} operation increases the file position by 1. @subsubheading Examples:: @example (defun tester () (let ((noticed '()) file-written) (flet ((notice (x) (push x noticed) x)) (with-open-file (s "test.bin" :element-type '(unsigned-byte 8) :direction :output :if-exists :error) (notice (file-position s)) ;1 (write-byte 5 s) (write-byte 6 s) (let ((p (file-position s))) (notice p) ;2 (notice (when p (file-position s (1- p))))) ;3 (write-byte 7 s) (notice (file-position s)) ;4 (setq file-written (truename s))) (with-open-file (s file-written :element-type '(unsigned-byte 8) :direction :input) (notice (file-position s)) ;5 (let ((length (file-length s))) (notice length) ;6 (when length (dotimes (i length) (notice (read-byte s)))))) ;7,... (nreverse noticed)))) @result{} tester (tester) @result{} (0 2 T 2 0 2 5 7) @i{OR}@result{} (0 2 NIL 3 0 3 5 6 7) @i{OR}@result{} (NIL NIL NIL NIL NIL NIL) @end example @subsubheading Side Effects:: When the @i{position-spec} argument is supplied, the @i{file position} in the @i{stream} might be moved. @subsubheading Affected By:: The value returned by @b{file-position} increases monotonically as input or output operations are performed. @subsubheading Exceptional Situations:: If @i{position-spec} is supplied, but is too large or otherwise inappropriate, an error is signaled. @subsubheading See Also:: @ref{file-length} , @ref{file-string-length} , @ref{open} @subsubheading Notes:: Implementations that have character files represented as a sequence of records of bounded size might choose to encode the file position as, for example, <<@i{record-number}>>*<<@i{max-record-size}>>+<<@i{character-within-record}>>. This is a valid encoding because it increases monotonically as each character is read or written, though not necessarily by 1 at each step. An @i{integer} might then be considered ``inappropriate'' as @i{position-spec} to @b{file-position} if, when decoded into record number and character number, it turned out that the supplied record was too short for the specified character number. @node file-string-length, open, file-position, Streams Dictionary @subsection file-string-length [Function] @code{file-string-length} @i{stream object} @result{} @i{length} @subsubheading Arguments and Values:: @i{stream}---an @i{output} @i{character} @i{file stream}. @i{object}---a @i{string} or a @i{character}. @i{length}---a non-negative @i{integer}, or @b{nil}. @subsubheading Description:: @b{file-string-length} returns the difference between what @t{(file-position @i{stream})} would be after writing @i{object} and its current value, or @b{nil} if this cannot be determined. The returned value corresponds to the current state of @i{stream} at the time of the call and might not be the same if it is called again when the state of the @i{stream} has changed. @node open, stream-external-format, file-string-length, Streams Dictionary @subsection open [Function] @code{open} @i{filespec {&key} direction element-type if-exists if-does-not-exist external-format}@* @result{} @i{stream} @subsubheading Arguments and Values:: @i{filespec}---a @i{pathname designator}. @i{direction}---one of @t{:input}, @t{:output}, @t{:io}, or @t{:probe}. The default is @t{:input}. @i{element-type}---a @i{type specifier} for @i{recognizable subtype} of @b{character}; or a @i{type specifier} for a @i{finite} @i{recognizable subtype} of @i{integer}; or one of the @i{symbols} @b{signed-byte}, @b{unsigned-byte}, or @t{:default}. The default is @b{character}. @i{if-exists}---one of @t{:error}, @t{:new-version}, @t{:rename}, @t{:rename-and-delete}, @t{:overwrite}, @t{:append}, @t{:supersede}, or @b{nil}. The default is @t{:new-version} if the version component of @i{filespec} is @t{:newest}, or @t{:error} otherwise. @i{if-does-not-exist}---one of @t{:error}, @t{:create}, or @b{nil}. The default is @t{:error} if @i{direction} is @t{:input} or @i{if-exists} is @t{:overwrite} or @t{:append}; @t{:create} if @i{direction} is @t{:output} or @t{:io}, and @i{if-exists} is neither @t{:overwrite} nor @t{:append}; or @b{nil} when @i{direction} is @t{:probe}. @i{external-format}---an @i{external file format designator}. The default is @t{:default}. @i{stream}---a @i{file stream} or @b{nil}. @subsubheading Description:: @b{open} creates, opens, and returns a @i{file stream} that is connected to the file specified by @i{filespec}. @i{Filespec} is the name of the file to be opened. If the @i{filespec} @i{designator} is a @i{stream}, that @i{stream} is not closed first or otherwise affected. The keyword arguments to @b{open} specify the characteristics of the @i{file stream} that is returned, and how to handle errors. If @i{direction} is @t{:input} or @t{:probe}, or if @i{if-exists} is not @t{:new-version} and the version component of the @i{filespec} is @t{:newest}, then the file opened is that file already existing in the file system that has a version greater than that of any other file in the file system whose other pathname components are the same as those of @i{filespec}. An implementation is required to recognize all of the @b{open} keyword options and to do something reasonable in the context of the host operating system. For example, if a file system does not support distinct file versions and does not distinguish the notions of deletion and expunging, @t{:new-version} might be treated the same as @t{:rename} or @t{:supersede}, and @t{:rename-and-delete} might be treated the same as @t{:supersede}. @table @asis @item @t{:direction} These are the possible values for @i{direction}, and how they affect the nature of the @i{stream} that is created: @table @asis @item @t{:input} Causes the creation of an @i{input} @i{file stream}. @item @t{:output} Causes the creation of an @i{output} @i{file stream}. @item @t{:io} Causes the creation of a @i{bidirectional} @i{file stream}. @item @t{:probe} Causes the creation of a ``no-directional'' @i{file stream}; in effect, the @i{file stream} is created and then closed prior to being returned by @b{open}. @end table @item @t{:element-type} The @i{element-type} specifies the unit of transaction for the @i{file stream}. If it is @t{:default}, the unit is determined by @i{file system}, possibly based on the @i{file}. @item @t{:if-exists} @i{if-exists} specifies the action to be taken if @i{direction} is @t{:output} or @t{:io} and a file of the name @i{filespec} already exists. If @i{direction} is @t{:input}, not supplied, or @t{:probe}, @i{if-exists} is ignored. These are the results of @b{open} as modified by @i{if-exists}: @table @asis @item @t{:error} An error of @i{type} @b{file-error} is signaled. @item @t{:new-version} A new file is created with a larger version number. @item @t{:rename} The existing file is renamed to some other name and then a new file is created. @item @t{:rename-and-delete} The existing file is renamed to some other name, then it is deleted but not expunged, and then a new file is created. @item @t{:overwrite} Output operations on the @i{stream} destructively modify the existing file. If @i{direction} is @t{:io} the file is opened in a bidirectional mode that allows both reading and writing. The file pointer is initially positioned at the beginning of the file; however, the file is not truncated back to length zero when it is opened. @item @t{:append} Output operations on the @i{stream} destructively modify the existing file. The file pointer is initially positioned at the end of the file. If @i{direction} is @t{:io}, the file is opened in a bidirectional mode that allows both reading and writing. @item @t{:supersede} The existing file is superseded; that is, a new file with the same name as the old one is created. If possible, the implementation should not destroy the old file until the new @i{stream} is closed. @item @b{nil} No file or @i{stream} is created; instead, @b{nil} is returned to indicate failure. @end table @item @t{:if-does-not-exist} @i{if-does-not-exist} specifies the action to be taken if a file of name @i{filespec} does not already exist. These are the results of @b{open} as modified by @i{if-does-not-exist}: @table @asis @item @t{:error} An error of @i{type} @b{file-error} is signaled. @item @t{:create} An empty file is created. Processing continues as if the file had already existed but no processing as directed by @i{if-exists} is performed. @item @b{nil} No file or @i{stream} is created; instead, @b{nil} is returned to indicate failure. @end table @item @t{:external-format} This option selects an @i{external file format} for the @i{file}: The only @i{standardized} value for this option is @t{:default}, although @i{implementations} are permitted to define additional @i{external file formats} and @i{implementation-dependent} values returned by @b{stream-external-format} can also be used by @i{conforming programs}. The @i{external-format} is meaningful for any kind of @i{file stream} whose @i{element type} is a @i{subtype} of @i{character}. This option is ignored for @i{streams} for which it is not meaningful; however, @i{implementations} may define other @i{element types} for which it is meaningful. The consequences are unspecified if a @i{character} is written that cannot be represented by the given @i{external file format}. @end table When a file is opened, a @i{file stream} is constructed to serve as the file system's ambassador to the @r{Lisp} environment; operations on the @i{file stream} are reflected by operations on the file in the file system. A file can be deleted, renamed, or destructively modified by @b{open}. For information about opening relative pathnames, see @ref{Merging Pathnames}. @subsubheading Examples:: @example (open @i{filespec} :direction :probe) @result{} # (setq q (merge-pathnames (user-homedir-pathname) "test")) @result{} # (open @i{filespec} :if-does-not-exist :create) @result{} # (setq s (open @i{filespec} :direction :probe)) @result{} # (truename s) @result{} # (open s :direction :output :if-exists nil) @result{} NIL @end example @subsubheading Affected By:: The nature and state of the host computer's @i{file system}. @subsubheading Exceptional Situations:: If @i{if-exists} is @t{:error}, (subject to the constraints on the meaning of @i{if-exists} listed above), an error of @i{type} @b{file-error} is signaled. If @i{if-does-not-exist} is @t{:error} (subject to the constraints on the meaning of @i{if-does-not-exist} listed above), an error of @i{type} @b{file-error} is signaled. If it is impossible for an implementation to handle some option in a manner close to what is specified here, an error of @i{type} @b{error} might be signaled. An error of @i{type} @b{file-error} is signaled if @t{(wild-pathname-p @i{filespec})} returns true. An error of @i{type} @b{error} is signaled if the @i{external-format} is not understood by the @i{implementation}. The various @i{file systems} in existence today have widely differing capabilities, and some aspects of the @i{file system} are beyond the scope of this specification to define. A given @i{implementation} might not be able to support all of these options in exactly the manner stated. An @i{implementation} is required to recognize all of these option keywords and to try to do something ``reasonable'' in the context of the host @i{file system}. Where necessary to accomodate the @i{file system}, an @i{implementation} deviate slightly from the semantics specified here without being disqualified for consideration as a @i{conforming implementation}. If it is utterly impossible for an @i{implementation} to handle some option in a manner similar to what is specified here, it may simply signal an error. With regard to the @t{:element-type} option, if a @i{type} is requested that is not supported by the @i{file system}, a substitution of types such as that which goes on in @i{upgrading} is permissible. As a minimum requirement, it should be the case that opening an @i{output} @i{stream} to a @i{file} in a given @i{element type} and later opening an @i{input} @i{stream} to the same @i{file} in the same @i{element type} should work compatibly. @subsubheading See Also:: @ref{with-open-file} , @ref{close} , @b{pathname}, @b{logical-pathname}, @ref{Merging Pathnames}, @ref{Pathnames as Filenames} @subsubheading Notes:: @b{open} does not automatically close the file when an abnormal exit occurs. When @i{element-type} is a @i{subtype} of @b{character}, @b{read-char} and/or @b{write-char} can be used on the resulting @i{file stream}. When @i{element-type} is a @i{subtype} of @i{integer}, @b{read-byte} and/or @b{write-byte} can be used on the resulting @i{file stream}. When @i{element-type} is @t{:default}, the @i{type} can be determined by using @b{stream-element-type}. @node stream-external-format, with-open-file, open, Streams Dictionary @subsection stream-external-format [Function] @code{stream-external-format} @i{stream} @result{} @i{format} @subsubheading Arguments and Values:: @i{stream}---a @i{file stream}. @i{format}---an @i{external file format}. @subsubheading Description:: Returns an @i{external file format designator} for the @i{stream}. @subsubheading Examples:: @example (with-open-file (stream "test" :direction :output) (stream-external-format stream)) @result{} :DEFAULT @i{OR}@result{} :ISO8859/1-1987 @i{OR}@result{} (:ASCII :SAIL) @i{OR}@result{} ACME::PROPRIETARY-FILE-FORMAT-17 @i{OR}@result{} # @end example @subsubheading See Also:: the @t{:external-format} @i{argument} to the @i{function} @ref{open} and the @ref{with-open-file} @i{macro}. @subsubheading Notes:: The @i{format} returned is not necessarily meaningful to other @i{implementations}. @node with-open-file, close, stream-external-format, Streams Dictionary @subsection with-open-file [macro] @subsubheading Syntax:: @code{with-open-file} @i{@r{(}stream filespec @{@i{options}@}{*}@r{)} @{@i{declaration}@}{*} @{@i{form}@}{*}}@* @result{} @i{results} @subsubheading Arguments and Values:: @i{stream} -- a variable. @i{filespec}---a @i{pathname designator}. @i{options} -- @i{forms}; evaluated. @i{declaration}---a @b{declare} @i{expression}; not evaluated. @i{forms}---an @i{implicit progn}. @i{results}---the @i{values} returned by the @i{forms}. @subsubheading Description:: @b{with-open-file} uses @b{open} to create a @i{file stream} to @i{file} named by @i{filespec}. @i{Filespec} is the name of the file to be opened. @i{Options} are used as keyword arguments to @b{open}. The @i{stream} @i{object} to which the @i{stream} @i{variable} is @i{bound} has @i{dynamic extent}; its @i{extent} ends when the @i{form} is exited. @b{with-open-file} evaluates the @i{forms} as an @i{implicit progn} with @i{stream} bound to the value returned by @b{open}. When control leaves the body, either normally or abnormally (such as by use of @b{throw}), the file is automatically closed. If a new output file is being written, and control leaves abnormally, the file is aborted and the file system is left, so far as possible, as if the file had never been opened. It is possible by the use of @t{:if-exists nil} or @t{:if-does-not-exist nil} for @i{stream} to be bound to @b{nil}. Users of @t{:if-does-not-exist nil} should check for a valid @i{stream}. The consequences are undefined if an attempt is made to @i{assign} the @i{stream} @i{variable}. The compiler may choose to issue a warning if such an attempt is detected. @subsubheading Examples:: @example (setq p (merge-pathnames "test")) @result{} # (with-open-file (s p :direction :output :if-exists :supersede) (format s "Here are a couple~ (with-open-file (s p) (do ((l (read-line s) (read-line s nil 'eof))) ((eq l 'eof) "Reached end of file.") (format t "~&*** ~A~ @t{ |> } *** Here are a couple @t{ |> } *** of test data lines @result{} "Reached end of file." @end example @example ;; Normally one would not do this intentionally because it is ;; not perspicuous, but beware when using :IF-DOES-NOT-EXIST NIL ;; that this doesn't happen to you accidentally... (with-open-file (foo "no-such-file" :if-does-not-exist nil) (read foo)) @t{ |> } @b{|>>}@t{hello?}@b{<<|} @result{} HELLO? ;This value was read from the terminal, not a file! ;; Here's another bug to avoid... (with-open-file (foo "no-such-file" :direction :output :if-does-not-exist nil) (format foo "Hello")) @result{} "Hello" ;FORMAT got an argument of NIL! @end example @subsubheading Side Effects:: Creates a @i{stream} to the @i{file} named by @i{filename} (upon entry), and closes the @i{stream} (upon exit). In some @i{implementations}, the @i{file} might be locked in some way while it is open. If the @i{stream} is an @i{output} @i{stream}, a @i{file} might be created. @subsubheading Affected By:: The host computer's file system. @subsubheading Exceptional Situations:: See the @i{function} @b{open}. @subsubheading See Also:: @ref{open} , @ref{close} , @b{pathname}, @b{logical-pathname}, @ref{Pathnames as Filenames} @node close, with-open-stream, with-open-file, Streams Dictionary @subsection close [Function] @code{close} @i{stream {&key} abort} @result{} @i{result} @subsubheading Arguments and Values:: @i{stream}---a @i{stream} (either @i{open} or @i{closed}). @i{abort}---a @i{generalized boolean}. The default is @i{false}. @i{result}---@b{t} if the @i{stream} was @i{open} at the time it was received as an @i{argument}, or @i{implementation-dependent} otherwise. @subsubheading Description:: @b{close} closes @i{stream}. Closing a @i{stream} means that it may no longer be used in input or output operations. The act of @i{closing} a @i{file stream} ends the association between the @i{stream} and its associated @i{file}; the transaction with the @i{file system} is terminated, and input/output may no longer be performed on the @i{stream}. If @i{abort} is @i{true}, an attempt is made to clean up any side effects of having created @i{stream}. If @i{stream} performs output to a file that was created when the @i{stream} was created, the file is deleted and any previously existing file is not superseded. It is permissible to close an already closed @i{stream}, but in that case the @i{result} is @i{implementation-dependent}. After @i{stream} is closed, it is still possible to perform the following query operations upon it: @b{streamp}, @b{pathname}, @b{truename}, @b{merge-pathnames}, @b{pathname-host}, @b{pathname-device}, @b{pathname-directory},@b{pathname-name}, @b{pathname-type}, @b{pathname-version}, @b{namestring}, @b{file-namestring}, @b{directory-namestring}, @b{host-namestring}, @b{enough-namestring}, @b{open}, @b{probe-file}, and @b{directory}. The effect of @b{close} on a @i{constructed stream} is to close the argument @i{stream} only. There is no effect on the @i{constituents} of @i{composite streams}. For a @i{stream} created with @b{make-string-output-stream}, the result of @b{get-output-stream-string} is unspecified after @b{close}. @subsubheading Examples:: @example (setq s (make-broadcast-stream)) @result{} # (close s) @result{} T (output-stream-p s) @result{} @i{true} @end example @subsubheading Side Effects:: The @i{stream} is @i{closed} (if necessary). If @i{abort} is @i{true} and the @i{stream} is an @i{output} @i{file stream}, its associated @i{file} might be deleted. @subsubheading See Also:: @ref{open} @node with-open-stream, listen, close, Streams Dictionary @subsection with-open-stream [Macro] @code{with-open-stream} @i{@r{(}var stream@r{)} @{@i{declaration}@}{*} @{@i{form}@}{*}}@* @result{} @i{@{@i{result}@}{*}} @subsubheading Arguments and Values:: @i{var}---a @i{variable} @i{name}. @i{stream}---a @i{form}; evaluated to produce a @i{stream}. @i{declaration}---a @b{declare} @i{expression}; not evaluated. @i{forms}---an @i{implicit progn}. @i{results}---the @i{values} returned by the @i{forms}. @subsubheading Description:: @b{with-open-stream} performs a series of operations on @i{stream}, returns a value, and then closes the @i{stream}. @i{Var} is bound to the value of @i{stream}, and then @i{forms} are executed as an @i{implicit progn}. @i{stream} is automatically closed on exit from @b{with-open-stream}, no matter whether the exit is normal or abnormal. The @i{stream} has @i{dynamic extent}; its @i{extent} ends when the @i{form} is exited. The consequences are undefined if an attempt is made to @i{assign} the the @i{variable} @i{var} with the @i{forms}. @subsubheading Examples:: @example (with-open-stream (s (make-string-input-stream "1 2 3 4")) (+ (read s) (read s) (read s))) @result{} 6 @end example @subsubheading Side Effects:: The @i{stream} is closed (upon exit). @subsubheading See Also:: @ref{close} @node listen, clear-input, with-open-stream, Streams Dictionary @subsection listen [Function] @code{listen} @i{{&optional} input-stream} @result{} @i{generalized-boolean} @subsubheading Arguments and Values:: @i{input-stream}---an @i{input} @i{stream designator}. The default is @i{standard input}. @i{generalized-boolean}---a @i{generalized boolean}. @subsubheading Description:: Returns @i{true} if there is a character immediately available from @i{input-stream}; otherwise, returns @i{false}. On a non-interactive @i{input-stream}, @b{listen} returns @i{true} except when at @i{end of file}_1. If an @i{end of file} is encountered, @b{listen} returns @i{false}. @b{listen} is intended to be used when @i{input-stream} obtains characters from an interactive device such as a keyboard. @subsubheading Examples:: @example (progn (unread-char (read-char)) (list (listen) (read-char))) @t{ |> } @b{|>>}@t{1}@b{<<|} @result{} (T #\1) (progn (clear-input) (listen)) @result{} NIL ;Unless you're a very fast typist! @end example @subsubheading Affected By:: @b{*standard-input*} @subsubheading See Also:: @ref{interactive-stream-p} , @ref{read-char-no-hang} @node clear-input, finish-output, listen, Streams Dictionary @subsection clear-input [Function] @code{clear-input} @i{{&optional} input-stream} @result{} @i{@b{nil}} @subsubheading Arguments and Values:: @i{input-stream}---an @i{input} @i{stream designator}. The default is @i{standard input}. @subsubheading Description:: Clears any available input from @i{input-stream}. If @b{clear-input} does not make sense for @i{input-stream}, then @b{clear-input} does nothing. @subsubheading Examples:: @example ;; The exact I/O behavior of this example might vary from implementation ;; to implementation depending on the kind of interactive buffering that ;; occurs. (The call to SLEEP here is intended to help even out the ;; differences in implementations which do not do line-at-a-time buffering.) (defun read-sleepily (&optional (clear-p nil) (zzz 0)) (list (progn (print '>) (read)) ;; Note that input typed within the first ZZZ seconds ;; will be discarded. (progn (print '>) (if zzz (sleep zzz)) (print '>>) (if clear-p (clear-input)) (read)))) (read-sleepily) @t{ |> } > @b{|>>}@t{10}@b{<<|} @t{ |> } > @t{ |> } >> @b{|>>}@t{20}@b{<<|} @result{} (10 20) (read-sleepily t) @t{ |> } > @b{|>>}@t{10}@b{<<|} @t{ |> } > @t{ |> } >> @b{|>>}@t{20}@b{<<|} @result{} (10 20) (read-sleepily t 10) @t{ |> } > @b{|>>}@t{10}@b{<<|} @t{ |> } > @b{|>>}@t{20}@b{<<|} ; Some implementations won't echo typeahead here. @t{ |> } >> @b{|>>}@t{30}@b{<<|} @result{} (10 30) @end example @subsubheading Side Effects:: The @i{input-stream} is modified. @subsubheading Affected By:: @b{*standard-input*} @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{input-stream} is not a @i{stream designator}. @subsubheading See Also:: @b{clear-output} @node finish-output, y-or-n-p, clear-input, Streams Dictionary @subsection finish-output, force-output, clear-output [Function] @code{finish-output} @i{{&optional} output-stream} @result{} @i{@b{nil}} @code{force-output} @i{{&optional} output-stream} @result{} @i{@b{nil}} @code{clear-output} @i{{&optional} output-stream} @result{} @i{@b{nil}} @subsubheading Arguments and Values:: @i{output-stream}---an @i{output} @i{stream designator}. The default is @i{standard output}. @subsubheading Description:: @b{finish-output}, @b{force-output}, and @b{clear-output} exercise control over the internal handling of buffered stream output. @b{finish-output} attempts to ensure that any buffered output sent to @i{output-stream} has reached its destination, and then returns. @b{force-output} initiates the emptying of any internal buffers but does not wait for completion or acknowledgment to return. @b{clear-output} attempts to abort any outstanding output operation in progress in order to allow as little output as possible to continue to the destination. If any of these operations does not make sense for @i{output-stream}, then it does nothing. The precise actions of these @i{functions} are @i{implementation-dependent}. @subsubheading Examples:: @example ;; Implementation A (progn (princ "am i seen?") (clear-output)) @result{} NIL ;; Implementation B (progn (princ "am i seen?") (clear-output)) @t{ |> } am i seen? @result{} NIL @end example @subsubheading Affected By:: @b{*standard-output*} @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{output-stream} is not a @i{stream designator}. @subsubheading See Also:: @ref{clear-input} @node y-or-n-p, make-synonym-stream, finish-output, Streams Dictionary @subsection y-or-n-p, yes-or-no-p [Function] @code{y-or-n-p} @i{{&optional} control {&rest} arguments} @result{} @i{generalized-boolean} @code{yes-or-no-p} @i{{&optional} control {&rest} arguments} @result{} @i{generalized-boolean} @subsubheading Arguments and Values:: @i{control}---a @i{format control}. @i{arguments}---@i{format arguments} for @i{control}. @i{generalized-boolean}---a @i{generalized boolean}. @subsubheading Description:: These functions ask a question and parse a response from the user. They return @i{true} if the answer is affirmative, or @i{false} if the answer is negative. @b{y-or-n-p} is for asking the user a question whose answer is either ``yes'' or ``no.'' It is intended that the reply require the user to answer a yes-or-no question with a single character. @b{yes-or-no-p} is also for asking the user a question whose answer is either ``Yes'' or ``No.'' It is intended that the reply require the user to take more action than just a single keystroke, such as typing the full word @t{yes} or @t{no} followed by a newline. @b{y-or-n-p} types out a message (if supplied), reads an answer in some @i{implementation-dependent} manner (intended to be short and simple, such as reading a single character such as @t{Y} or @t{N}). @b{yes-or-no-p} types out a message (if supplied), attracts the user's attention (for example, by ringing the terminal's bell), and reads an answer in some @i{implementation-dependent} manner (intended to be multiple characters, such as @t{YES} or @t{NO}). If @i{format-control} is supplied and not @b{nil}, then a @b{fresh-line} operation is performed; then a message is printed as if @i{format-control} and @i{arguments} were given to @b{format}. In any case, @b{yes-or-no-p} and @b{y-or-n-p} will provide a prompt such as ``@t{(Y or N)}'' or ``@t{(Yes or No)}'' if appropriate. All input and output are performed using @i{query I/O}. @subsubheading Examples:: @example (y-or-n-p "(t or nil) given by") @t{ |> } (t or nil) given by (Y or N) @b{|>>}@t{Y}@b{<<|} @result{} @i{true} (yes-or-no-p "a ~S message" 'frightening) @t{ |> } a FRIGHTENING message (Yes or No) @b{|>>}@t{no}@b{<<|} @result{} @i{false} (y-or-n-p "Produce listing file?") @t{ |> } Produce listing file? @t{ |> } Please respond with Y or N. @b{|>>}@t{n}@b{<<|} @result{} @i{false} @end example @subsubheading Side Effects:: Output to and input from @i{query I/O} will occur. @subsubheading Affected By:: @b{*query-io*}. @subsubheading See Also:: @ref{format} @subsubheading Notes:: @b{yes-or-no-p} and @b{yes-or-no-p} do not add question marks to the end of the prompt string, so any desired question mark or other punctuation should be explicitly included in the text query. @node make-synonym-stream, synonym-stream-symbol, y-or-n-p, Streams Dictionary @subsection make-synonym-stream [Function] @code{make-synonym-stream} @i{symbol} @result{} @i{synonym-stream} @subsubheading Arguments and Values:: @i{symbol}---a @i{symbol} that names a @i{dynamic variable}. @i{synonym-stream}---a @i{synonym stream}. @subsubheading Description:: Returns a @i{synonym stream} whose @i{synonym stream symbol} is @i{symbol}. @subsubheading Examples:: @example (setq a-stream (make-string-input-stream "a-stream") b-stream (make-string-input-stream "b-stream")) @result{} # (setq s-stream (make-synonym-stream 'c-stream)) @result{} # (setq c-stream a-stream) @result{} # (read s-stream) @result{} A-STREAM (setq c-stream b-stream) @result{} # (read s-stream) @result{} B-STREAM @end example @subsubheading Exceptional Situations:: Should signal @b{type-error} if its argument is not a @i{symbol}. @subsubheading See Also:: @ref{Stream Concepts} @node synonym-stream-symbol, broadcast-stream-streams, make-synonym-stream, Streams Dictionary @subsection synonym-stream-symbol [Function] @code{synonym-stream-symbol} @i{synonym-stream} @result{} @i{symbol} @subsubheading Arguments and Values:: @i{synonym-stream}---a @i{synonym stream}. @i{symbol}---a @i{symbol}. @subsubheading Description:: Returns the @i{symbol} whose @b{symbol-value} the @i{synonym-stream} is using. @subsubheading See Also:: @ref{make-synonym-stream} @node broadcast-stream-streams, make-broadcast-stream, synonym-stream-symbol, Streams Dictionary @subsection broadcast-stream-streams [Function] @code{broadcast-stream-streams} @i{broadcast-stream} @result{} @i{streams} @subsubheading Arguments and Values:: @i{broadcast-stream}---a @i{broadcast stream}. @i{streams}---a @i{list} of @i{streams}. @subsubheading Description:: Returns a @i{list} of output @i{streams} that constitute all the @i{streams} to which the @i{broadcast-stream} is broadcasting. @node make-broadcast-stream, make-two-way-stream, broadcast-stream-streams, Streams Dictionary @subsection make-broadcast-stream [Function] @code{make-broadcast-stream} @i{{&rest} streams} @result{} @i{broadcast-stream} @subsubheading Arguments and Values:: @i{stream}---an @i{output} @i{stream}. @i{broadcast-stream}---a @i{broadcast stream}. @subsubheading Description:: Returns a @i{broadcast stream}. @subsubheading Examples:: @example (setq a-stream (make-string-output-stream) b-stream (make-string-output-stream)) @result{} # (format (make-broadcast-stream a-stream b-stream) "this will go to both streams") @result{} NIL (get-output-stream-string a-stream) @result{} "this will go to both streams" (get-output-stream-string b-stream) @result{} "this will go to both streams" @end example @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if any @i{stream} is not an @i{output} @i{stream}. @subsubheading See Also:: @ref{broadcast-stream-streams} @node make-two-way-stream, two-way-stream-input-stream, make-broadcast-stream, Streams Dictionary @subsection make-two-way-stream [Function] @code{make-two-way-stream} @i{input-stream output-stream} @result{} @i{two-way-stream} @subsubheading Arguments and Values:: @i{input-stream}---a @i{stream}. @i{output-stream}---a @i{stream}. @i{two-way-stream}---a @i{two-way stream}. @subsubheading Description:: Returns a @i{two-way stream} that gets its input from @i{input-stream} and sends its output to @i{output-stream}. @subsubheading Examples:: @example (with-output-to-string (out) (with-input-from-string (in "input...") (let ((two (make-two-way-stream in out))) (format two "output...") (setq what-is-read (read two))))) @result{} "output..." what-is-read @result{} INPUT... @end example @subsubheading Exceptional Situations:: Should signal an error of @i{type} @b{type-error} if @i{input-stream} is not an @i{input} @i{stream}. Should signal an error of @i{type} @b{type-error} if @i{output-stream} is not an @i{output} @i{stream}. @node two-way-stream-input-stream, echo-stream-input-stream, make-two-way-stream, Streams Dictionary @subsection two-way-stream-input-stream, two-way-stream-output-stream @flushright @i{[Function]} @end flushright @code{two-way-stream-input-stream} @i{two-way-stream} @result{} @i{input-stream} @code{two-way-stream-output-stream} @i{two-way-stream} @result{} @i{output-stream} @subsubheading Arguments and Values:: @i{two-way-stream}---a @i{two-way stream}. @i{input-stream}---an @i{input} @i{stream}. @i{output-stream}---an @i{output} @i{stream}. @subsubheading Description:: @b{two-way-stream-input-stream} returns the @i{stream} from which @i{two-way-stream} receives input. @b{two-way-stream-output-stream} returns the @i{stream} to which @i{two-way-stream} sends output. @node echo-stream-input-stream, make-echo-stream, two-way-stream-input-stream, Streams Dictionary @subsection echo-stream-input-stream, echo-stream-output-stream [Function] @code{echo-stream-input-stream} @i{echo-stream} @result{} @i{input-stream} @code{echo-stream-output-stream} @i{echo-stream} @result{} @i{output-stream} @subsubheading Arguments and Values:: @i{echo-stream}---an @i{echo stream}. @i{input-stream}---an @i{input} @i{stream}. @b{output-stream}---an @i{output} @i{stream}. @subsubheading Description:: @b{echo-stream-input-stream} returns the @i{input} @i{stream} from which @i{echo-stream} receives input. @b{echo-stream-output-stream} returns the @i{output} @i{stream} to which @i{echo-stream} sends output. @node make-echo-stream, concatenated-stream-streams, echo-stream-input-stream, Streams Dictionary @subsection make-echo-stream [Function] @code{make-echo-stream} @i{input-stream output-stream} @result{} @i{echo-stream} @subsubheading Arguments and Values:: @i{input-stream}---an @i{input} @i{stream}. @i{output-stream}---an @i{output} @i{stream}. @i{echo-stream}---an @i{echo stream}. @subsubheading Description:: Creates and returns an @i{echo stream} that takes input from @i{input-stream} and sends output to @i{output-stream}. @subsubheading Examples:: @example (let ((out (make-string-output-stream))) (with-open-stream (s (make-echo-stream (make-string-input-stream "this-is-read-and-echoed") out)) (read s) (format s " * this-is-direct-output") (get-output-stream-string out))) @result{} "this-is-read-and-echoed * this-is-direct-output" @end example @subsubheading See Also:: @ref{echo-stream-input-stream; echo-stream-output-stream} , @b{echo-stream-output-stream}, @ref{make-two-way-stream} @node concatenated-stream-streams, make-concatenated-stream, make-echo-stream, Streams Dictionary @subsection concatenated-stream-streams [Function] @code{concatenated-stream-streams} @i{concatenated-stream} @result{} @i{streams} @subsubheading Arguments and Values:: @i{concatenated-stream} -- a @i{concatenated stream}. @i{streams}---a @i{list} of @i{input} @i{streams}. @subsubheading Description:: Returns a @i{list} of @i{input} @i{streams} that constitute the ordered set of @i{streams} the @i{concatenated-stream} still has to read from, starting with the current one it is reading from. The list may be @i{empty} if no more @i{streams} remain to be read. The consequences are undefined if the @i{list structure} of the @i{streams} is ever modified. @node make-concatenated-stream, get-output-stream-string, concatenated-stream-streams, Streams Dictionary @subsection make-concatenated-stream [Function] @code{make-concatenated-stream} @i{{&rest} input-streams} @result{} @i{concatenated-stream} @subsubheading Arguments and Values:: @i{input-stream}---an @i{input} @i{stream}. @i{concatenated-stream}---a @i{concatenated stream}. @subsubheading Description:: Returns a @i{concatenated stream} that has the indicated @i{input-streams} initially associated with it. @subsubheading Examples:: @example (read (make-concatenated-stream (make-string-input-stream "1") (make-string-input-stream "2"))) @result{} 12 @end example @subsubheading Exceptional Situations:: Should signal @b{type-error} if any argument is not an @i{input} @i{stream}. @subsubheading See Also:: @ref{concatenated-stream-streams} @node get-output-stream-string, make-string-input-stream, make-concatenated-stream, Streams Dictionary @subsection get-output-stream-string [Function] @code{get-output-stream-string} @i{string-output-stream} @result{} @i{string} @subsubheading Arguments and Values:: @i{string-output-stream}---a @i{stream}. @i{string}---a @i{string}. @subsubheading Description:: Returns a @i{string} containing, in order, all the @i{characters} that have been output to @i{string-output-stream}. This operation clears any @i{characters} on @i{string-output-stream}, so the @i{string} contains only those @i{characters} which have been output since the last call to @b{get-output-stream-string} or since the creation of the @i{string-output-stream}, whichever occurred most recently. @subsubheading Examples:: @example (setq a-stream (make-string-output-stream) a-string "abcdefghijklm") @result{} "abcdefghijklm" (write-string a-string a-stream) @result{} "abcdefghijklm" (get-output-stream-string a-stream) @result{} "abcdefghijklm" (get-output-stream-string a-stream) @result{} "" @end example @subsubheading Side Effects:: The @i{string-output-stream} is cleared. @subsubheading Exceptional Situations:: The consequences are undefined if @i{stream-output-string} is @i{closed}. The consequences are undefined if @i{string-output-stream} is a @i{stream} that was not produced by @b{make-string-output-stream}. The consequences are undefined if @i{string-output-stream} was created implicitly by @b{with-output-to-string} or @b{format}. @subsubheading See Also:: @ref{make-string-output-stream} @node make-string-input-stream, make-string-output-stream, get-output-stream-string, Streams Dictionary @subsection make-string-input-stream [Function] @code{make-string-input-stream} @i{string {&optional} start end} @result{} @i{string-stream} @subsubheading Arguments and Values:: @i{string}---a @i{string}. @i{start}, @i{end}---@i{bounding index designators} of @i{string}. The defaults for @i{start} and @i{end} are @t{0} and @b{nil}, respectively. @i{string-stream}---an @i{input} @i{string stream}. @subsubheading Description:: Returns an @i{input} @i{string stream}. This @i{stream} will supply, in order, the @i{characters} in the substring of @i{string} @i{bounded} by @i{start} and @i{end}. After the last @i{character} has been supplied, the @i{string stream} will then be at @i{end of file}. @subsubheading Examples:: @example (let ((string-stream (make-string-input-stream "1 one "))) (list (read string-stream nil nil) (read string-stream nil nil) (read string-stream nil nil))) @result{} (1 ONE NIL) (read (make-string-input-stream "prefixtargetsuffix" 6 12)) @result{} TARGET @end example @subsubheading See Also:: @ref{with-input-from-string} @node make-string-output-stream, with-input-from-string, make-string-input-stream, Streams Dictionary @subsection make-string-output-stream [Function] @code{make-string-output-stream} @i{{&key} element-type} @result{} @i{string-stream} @subsubheading Arguments and Values:: @i{element-type}---a @i{type specifier}. The default is @b{character}. @i{string-stream}---an @i{output} @i{string stream}. @subsubheading Description:: Returns an @i{output} @i{string stream} that accepts @i{characters} and makes available (via @b{get-output-stream-string}) a @i{string} that contains the @i{characters} that were actually output. The @i{element-type} names the @i{type} of the @i{elements} of the @i{string}; a @i{string} is constructed of the most specialized @i{type} that can accommodate @i{elements} of that @i{element-type}. @subsubheading Examples:: @example (let ((s (make-string-output-stream))) (write-string "testing... " s) (prin1 1234 s) (get-output-stream-string s)) @result{} "testing... 1234" @end example None.. @subsubheading See Also:: @ref{get-output-stream-string} , @ref{with-output-to-string} @node with-input-from-string, with-output-to-string, make-string-output-stream, Streams Dictionary @subsection with-input-from-string [Macro] @code{with-input-from-string} @i{@r{(}var string {&key} index start end@r{)} @{@i{declaration}@}{*} @{@i{form}@}{*}}@* @result{} @i{@{@i{result}@}{*}} @subsubheading Arguments and Values:: @i{var}---a @i{variable} @i{name}. @i{string}---a @i{form}; evaluated to produce a @i{string}. @i{index}---a @i{place}. @i{start}, @i{end}---@i{bounding index designators} of @i{string}. The defaults for @i{start} and @i{end} are @t{0} and @b{nil}, respectively. @i{declaration}---a @b{declare} @i{expression}; not evaluated. @i{forms}---an @i{implicit progn}. @i{result}---the @i{values} returned by the @i{forms}. @subsubheading Description:: Creates an @i{input} @i{string stream}, provides an opportunity to perform operations on the @i{stream} (returning zero or more @i{values}), and then closes the @i{string stream}. @i{String} is evaluated first, and @i{var} is bound to a character @i{input} @i{string stream} that supplies @i{characters} from the subsequence of the resulting @i{string} @i{bounded} by @i{start} and @i{end}. The body is executed as an @i{implicit progn}. The @i{input} @i{string stream} is automatically closed on exit from @b{with-input-from-string}, no matter whether the exit is normal or abnormal. The @i{input} @i{string stream} to which the @i{variable} @i{var} is @i{bound} has @i{dynamic extent}; its @i{extent} ends when the @i{form} is exited. The @i{index} is a pointer within the @i{string} to be advanced. If @b{with-input-from-string} is exited normally, then @i{index} will have as its @i{value} the index into the @i{string} indicating the first character not read which is @t{(length @i{string})} if all characters were used. The place specified by @i{index} is not updated as reading progresses, but only at the end of the operation. @i{start} and @i{index} may both specify the same variable, which is a pointer within the @i{string} to be advanced, perhaps repeatedly by some containing loop. The consequences are undefined if an attempt is made to @i{assign} the @i{variable} @i{var}. @subsubheading Examples:: @example (with-input-from-string (s "XXX1 2 3 4xxx" :index ind :start 3 :end 10) (+ (read s) (read s) (read s))) @result{} 6 ind @result{} 9 (with-input-from-string (s "Animal Crackers" :index j :start 6) (read s)) @result{} CRACKERS @end example The variable @t{j} is set to @t{15}. @subsubheading Side Effects:: The @i{value} of the @i{place} named by @i{index}, if any, is modified. @subsubheading See Also:: @ref{make-string-input-stream} , @ref{Traversal Rules and Side Effects} @node with-output-to-string, *debug-io*, with-input-from-string, Streams Dictionary @subsection with-output-to-string [Macro] @code{with-output-to-string} @i{@r{(}var {&optional} string-form {&key} element-type@r{)} @{@i{declaration}@}{*} @{@i{form}@}{*}}@* @result{} @i{@{@i{result}@}{*}} @subsubheading Arguments and Values:: @i{var}---a @i{variable} @i{name}. @i{string-form}---a @i{form} or @b{nil}; if @i{non-nil}, evaluated to produce @i{string}. @i{string}---a @i{string} that has a @i{fill pointer}. @i{element-type}---a @i{type specifier}; evaluated. The default is @b{character}. @i{declaration}---a @b{declare} @i{expression}; not evaluated. @i{forms}---an @i{implicit progn}. @i{results}---If a @i{string-form} is not supplied or @b{nil}, a @i{string}; otherwise, the @i{values} returned by the @i{forms}. @subsubheading Description:: @b{with-output-to-string} creates a character @i{output} @i{stream}, performs a series of operations that may send results to this @i{stream}, and then closes the @i{stream}. The @i{element-type} names the @i{type} of the elements of the @i{stream}; a @i{stream} is constructed of the most specialized @i{type} that can accommodate elements of the given @i{type}. The body is executed as an @i{implicit progn} with @i{var} bound to an @i{output} @i{string stream}. All output to that @i{string stream} is saved in a @i{string}. If @i{string} is supplied, @i{element-type} is ignored, and the output is incrementally appended to @i{string} as if by use of @b{vector-push-extend}. The @i{output} @i{stream} is automatically closed on exit from @b{with-output-from-string}, no matter whether the exit is normal or abnormal. The @i{output} @i{string stream} to which the @i{variable} @i{var} is @i{bound} has @i{dynamic extent}; its @i{extent} ends when the @i{form} is exited. If no @i{string} is provided, then @b{with-output-from-string} produces a @i{stream} that accepts characters and returns a @i{string} of the indicated @i{element-type}. If @i{string} is provided, @b{with-output-to-string} returns the results of evaluating the last @i{form}. The consequences are undefined if an attempt is made to @i{assign} the @i{variable} @i{var}. @subsubheading Examples:: @example (setq fstr (make-array '(0) :element-type 'base-char :fill-pointer 0 :adjustable t)) @result{} "" (with-output-to-string (s fstr) (format s "here's some output") (input-stream-p s)) @result{} @i{false} fstr @result{} "here's some output" @end example @subsubheading Side Effects:: The @i{string} is modified. @subsubheading Exceptional Situations:: The consequences are undefined if destructive modifications are performed directly on the @i{string} during the @i{dynamic extent} of the call. @subsubheading See Also:: @ref{make-string-output-stream} , @b{vector-push-extend}, @ref{Traversal Rules and Side Effects} @node *debug-io*, *terminal-io*, with-output-to-string, Streams Dictionary @subsection *debug-io*, *error-output*, *query-io*, @subheading *standard-input*, *standard-output*, @subheading *trace-output* @flushright @i{[Variable]} @end flushright @subsubheading Value Type:: For @b{*standard-input*}: an @i{input} @i{stream} For @b{*error-output*}, @b{*standard-output*}, and @b{*trace-output*}: an @i{output} @i{stream}. For @b{*debug-io*}, @b{*query-io*}: a @i{bidirectional} @i{stream}. @subsubheading Initial Value:: @i{implementation-dependent}, but it must be an @i{open} @i{stream} that is not a @i{generalized synonym stream} to an @i{I/O customization variables} but that might be a @i{generalized synonym stream} to the value of some @i{I/O customization variable}. The initial value might also be a @i{generalized synonym stream} to either the @i{symbol} @b{*terminal-io*} or to the @i{stream} that is its @i{value}. @subsubheading Description:: These @i{variables} are collectively called the @i{standardized} @i{I/O customization variables}. They can be @i{bound} or @i{assigned} in order to change the default destinations for input and/or output used by various @i{standardized} @i{operators} and facilities. The @i{value} of @b{*debug-io*}, called @i{debug I/O}, is a @i{stream} to be used for interactive debugging purposes. The @i{value} of @b{*error-output*}, called @i{error output}, is a @i{stream} to which warnings and non-interactive error messages should be sent. The @i{value} of @b{*query-io*}, called @i{query I/O}, is a @i{bidirectional} @i{stream} to be used when asking questions of the user. The question should be output to this @i{stream}, and the answer read from it. The @i{value} of @b{*standard-input*}, called @i{standard input}, is a @i{stream} that is used by many @i{operators} as a default source of input when no specific @i{input} @i{stream} is explicitly supplied. The @i{value} of @b{*standard-output*}, called @i{standard output}, is a @i{stream} that is used by many @i{operators} as a default destination for output when no specific @i{output} @i{stream} is explicitly supplied. The @i{value} of @b{*trace-output*}, called @i{trace output}, is the @i{stream} on which traced functions (see @b{trace}) and the @b{time} @i{macro} print their output. @subsubheading Examples:: @example (with-output-to-string (*error-output*) (warn "this string is sent to *error-output*")) @result{} "Warning: this string is sent to *error-output* " ;The exact format of this string is @i{implementation-dependent}. (with-input-from-string (*standard-input* "1001") (+ 990 (read))) @result{} 1991 (progn (setq out (with-output-to-string (*standard-output*) (print "print and format t send things to") (format t "*standard-output* now going to a string"))) :done) @result{} :DONE out @result{} " \"print and format t send things to\" *standard-output* now going to a string" (defun fact (n) (if (< n 2) 1 (* n (fact (- n 1))))) @result{} FACT (trace fact) @result{} (FACT) ;; Of course, the format of traced output is implementation-dependent. (with-output-to-string (*trace-output*) (fact 3)) @result{} " 1 Enter FACT 3 | 2 Enter FACT 2 | 3 Enter FACT 1 | 3 Exit FACT 1 | 2 Exit FACT 2 1 Exit FACT 6" @end example @subsubheading See Also:: @b{*terminal-io*}, @b{synonym-stream}, @ref{Time} , @ref{trace; untrace} , {@ref{Conditions}}, {@ref{Reader}}, {@ref{Printer}} @subsubheading Notes:: The intent of the constraints on the initial @i{value} of the @i{I/O customization variables} is to ensure that it is always safe to @i{bind} or @i{assign} such a @i{variable} to the @i{value} of another @i{I/O customization variable}, without unduly restricting @i{implementation} flexibility. It is common for an @i{implementation} to make the initial @i{values} of @b{*debug-io*} and @b{*query-io*} be the @i{same} @i{stream}, and to make the initial @i{values} of @b{*error-output*} and @b{*standard-output*} be the @i{same} @i{stream}. The functions @b{y-or-n-p} and @b{yes-or-no-p} use @i{query I/O} for their input and output. In the normal @i{Lisp read-eval-print loop}, input is read from @i{standard input}. Many input functions, including @b{read} and @b{read-char}, take a @i{stream} argument that defaults to @i{standard input}. In the normal @i{Lisp read-eval-print loop}, output is sent to @i{standard output}. Many output functions, including @b{print} and @b{write-char}, take a @i{stream} argument that defaults to @i{standard output}. A program that wants, for example, to divert output to a file should do so by @i{binding} @b{*standard-output*}; that way error messages sent to @b{*error-output*} can still get to the user by going through @b{*terminal-io*} (if @b{*error-output*} is bound to @b{*terminal-io*}), which is usually what is desired. @node *terminal-io*, stream-error, *debug-io*, Streams Dictionary @subsection *terminal-io* [Variable] @subsubheading Value Type:: a @i{bidirectional} @i{stream}. @subsubheading Initial Value:: @i{implementation-dependent}, but it must be an @i{open} @i{stream} that is not a @i{generalized synonym stream} to an @i{I/O customization variables} but that might be a @i{generalized synonym stream} to the @i{value} of some @i{I/O customization variable}. @subsubheading Description:: The @i{value} of @b{*terminal-io*}, called @i{terminal I/O}, is ordinarily a @i{bidirectional} @i{stream} that connects to the user's console. Typically, writing to this @i{stream} would cause the output to appear on a display screen, for example, and reading from the @i{stream} would accept input from a keyboard. It is intended that standard input functions such as @b{read} and @b{read-char}, when used with this @i{stream}, cause echoing of the input into the output side of the @i{stream}. The means by which this is accomplished are @i{implementation-dependent}. The effect of changing the @i{value} of @b{*terminal-io*}, either by @i{binding} or @i{assignment}, is @i{implementation-defined}. @subsubheading Examples:: @example (progn (prin1 'foo) (prin1 'bar *terminal-io*)) @t{ |> } FOOBAR @result{} BAR (with-output-to-string (*standard-output*) (prin1 'foo) (prin1 'bar *terminal-io*)) @t{ |> } BAR @result{} "FOO" @end example @subsubheading See Also:: @b{*debug-io*}, @b{*error-output*}, @b{*query-io*}, @b{*standard-input*}, @b{*standard-output*}, @b{*trace-output*} @node stream-error, stream-error-stream, *terminal-io*, Streams Dictionary @subsection stream-error [Condition Type] @subsubheading Class Precedence List:: @b{stream-error}, @b{error}, @b{serious-condition}, @b{condition}, @b{t} @subsubheading Description:: The @i{type} @b{stream-error} consists of error conditions that are related to receiving input from or sending output to a @i{stream}. The ``offending stream'' is initialized by the @t{:stream} initialization argument to @b{make-condition}, and is @i{accessed} by the @i{function} @b{stream-error-stream}. @subsubheading See Also:: @ref{stream-error-stream} @node stream-error-stream, end-of-file, stream-error, Streams Dictionary @subsection stream-error-stream [Function] @code{stream-error-stream} @i{condition} @result{} @i{stream} @subsubheading Arguments and Values:: @i{condition}---a @i{condition} of @i{type} @b{stream-error}. @i{stream}---a @i{stream}. @subsubheading Description:: Returns the offending @i{stream} of a @i{condition} of @i{type} @b{stream-error}. @subsubheading Examples:: @example (with-input-from-string (s "(FOO") (handler-case (read s) (end-of-file (c) (format nil "~&End of file on ~S." (stream-error-stream c))))) "End of file on #." @end example @subsubheading See Also:: @b{stream-error}, @ref{Conditions} @node end-of-file, , stream-error-stream, Streams Dictionary @subsection end-of-file [Condition Type] @subsubheading Class Precedence List:: @b{end-of-file}, @b{stream-error}, @b{error}, @b{serious-condition}, @b{condition}, @b{t} @subsubheading Description:: The @i{type} @b{end-of-file} consists of error conditions related to read operations that are done on @i{streams} that have no more data. @subsubheading See Also:: @ref{stream-error-stream} @c end of including dict-streams @c %**end of chapter