Generic Function

Summary

A function used by listen that returns t if there is input available.

Package

stream

Signature

stream-listen stream => result

Arguments

stream

A stream.

Values

result

A generalized boolean.

Description

The generic function stream-listen is called to determine if there is data immediately available on the stream stream , without hanging.

result should be true if here is input, and nil otherwise (including at end of file).

This method must be implemented for subclasses of buffered-stream that handle input.

There is a built-in primary method specialized on buffered-stream which returns nil . There is a built-in :around method specialized on buffered-stream which checks for input in the buffer and calls the next method if the buffer is empty. Thus a primary method specialized on a subclass of buffered-stream need only check the underlying data source.

The built-in method on fundamental-input-stream uses stream-read-char-no-hang and stream-unread-char . Most streams should define their own method as this is usually trivial and more efficient than the method provided.

See also

buffered-stream
stream-read-char-no-hang
stream-unread-char