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6.3.5 Stream Functions

Some operations may be performed on any kind of stream; the following is a list of standardized operations that are potentially useful with any kind of stream.

Some General-Purpose Stream Operations

• close
• input-stream-p
• output-stream-p
• interactive-stream-p
• stream-element-type
• streamp
• with-open-stream

Function: close stream &key abort => result ¶

close closes stream. Closing a stream means that it may no longer be used in input or output operations. The act of closing a file stream ends the association between the stream and its associated file; the transaction with the file system is terminated, and input/output may no longer be performed on the stream.

STREAM

a stream (either open or closed).

ABORT

a boolean with a ‘false’ default value. If abort is ‘true’, an attempt is made to clean up any side effects of having created stream. If stream performs output to a file that was created when the stream was created, the file is deleted and any previously existing file is not superseded.

Function: input-stream-p stream => boolean ¶

Function: output-stream-p stream => boolean ¶

input-stream-p returns ‘true’ if stream is an input stream; otherwise, returns ‘false’.

output-stream-p returns ‘true’ if stream is an output stream; otherwise, returns ‘false’.

Function: interactive-stream-p stream => boolean ¶

Returns ‘true’ if stream is an interactive stream¹³; otherwise, returns ‘false’.

Function: stream-element-type stream => typespec ¶

stream-element-type returns a type specifier that indicates the types of objects that may be read from or written to stream. Streams created by open have an element type restricted to integer or a subtype of type character.

Function: streamp object => boolean ¶

Returns ‘true’ if object is of type stream; otherwise, returns ‘false’.

Function: with-open-stream (var stream) declaration* form* => results ¶

with-open-stream performs a series of operations on stream, returns a value, and then closes the stream. Var is bound to the value of stream, and then forms are executed as an implicit progn.

VAR

a variable name; bound to stream.

STREAM

a form; evaluated to produce a stream. The stream has dynamic extent; its extent ends when the form is exited.

DECLARATION

a declare expression; not evaluated.

FORM

an implicit progn.

RESULTS

the values returned by the forms.

(with-open-stream (s (make-string-input-stream "1 2 3 4"))
    (+ (read s) (read s) (read s))) =>  6

Listing 6.1: Example of with-open-stream