Open and Closed Streams (ANSI and GNU Common Lisp Document)

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#### 21.1.1.3 Open and Closed Streams

Streams are either open or closed .

Except as explicitly specified otherwise, operations that create and return streams return open streams.

The action of closing a stream marks the end of its use as a source or sink of data, permitting the implementation to reclaim its internal data structures, and to free any external resources which might have been locked by the stream when it was opened.

Except as explicitly specified otherwise, the consequences are undefined when a closed stream is used where a stream is called for.

Coercion of streams to pathnames is permissible for closed streams; in some situations, such as for a truename computation, the result might be different for an open stream and for that same stream once it has been closed.