with-open-stream - ANSI Common Lisp

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with-open-stream (Macro)

Syntax:

— Macro: with-open-stream (var stream) {declaration}* {form}* → {result}*

Arguments and Values:

var—a variable name.

stream—a form; evaluated to produce a stream.

declaration—a declare expression; not evaluated.

forms—an implicit progn.

results—the values returned by the forms.

Description:

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. stream is automatically closed on exit from with-open-stream, no matter whether the exit is normal or abnormal. The stream has dynamic extent; its extent ends when the form is exited.

The consequences are undefined if an attempt is made to assign the the variable var with the forms.

Examples:

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

Side Effects:

The stream is closed (upon exit).