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make-echo-stream

make-echo-stream Function

Syntax:

make-echo-stream input-stream output-stream → echo-stream

Arguments and Values:

input-stream—an input stream.

output-stream—an output stream.

echo-stream—an echo stream.

Description:

Creates and returns an echo stream that takes input from input-stream and sends output to output-stream.

Examples:

(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))) 
→ "this-is-read-and-echoed \* this-is-direct-output"

See Also:

echo-stream-input-stream, echo-stream-output-stream, make-two-way-stream concatenated-stream-streams Function

Syntax:

concatenated-stream-streams concatenated-stream → streams

Arguments and Values:

concatenated-stream – a concatenated stream.

streams—a list of input streams.

Description:

Returns a list of input streams that constitute the ordered set of streams the concatenated-stream still has to read from, starting with the current one it is reading from. The list may be empty if no more streams remain to be read.

The consequences are undefined if the list structure of the streams is ever modified.

Expanded Reference: make-echo-stream​

Basic Usage​

make-echo-stream creates a bidirectional stream where all input read from the input stream is echoed (written) to the output stream.

(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)))
=> "this-is-read-and-echoed * this-is-direct-output"

Echoed Characters Appear in Output​

Characters read from the input side are automatically copied to the output side.

(let ((out (make-string-output-stream)))
  (let ((echo (make-echo-stream
                (make-string-input-stream "abc")
                out)))
    (read-char echo)
    (read-char echo)
    (read-char echo)
    (get-output-stream-string out)))
=> "abc"

Direct Output Mixed with Echoed Input​

You can also write directly to an echo stream, which goes to the output stream.

(let ((out (make-string-output-stream)))
  (let ((echo (make-echo-stream
                (make-string-input-stream "in")
                out)))
    (write-string "pre-" echo)
    (read-char echo)
    (read-char echo)
    (write-string "-post" echo)
    (get-output-stream-string out)))
=> "pre-in-post"