Output Functions

The output functions are split into two categories: those that work with character streams and those that work with binary streams. Due to its extreme complexity, the function format—which operates on streams of characters—is discussed in a section separate from that of the other character-output functions.

Output to Character Streams:

Each of these routines accepts an optional argument called output-stream that specifies where the output should be sent. Output-stream defaults to the value of the variable “standard-output” if unspecified or nil. The value of the variable “terminal-io” is used if the value is t.

write object &key :stream :escape :radix :base :circle :pretty :level :length :case :gensym :array

write object &key :stream :escape :radix :base :circle :pretty :level :length :case :gensym :array :readably :right-margin :miser-width :lines :pprint-dispatch

• The output stream designated by: stream, which by default has the value of “standard-output,” receives the printed version of the object.

prin1 object &optional output-stream
print object &optional output-stream
pprint object &optional output-stream
princ object &optional output-stream

• prin1 sends an object’s printed representation to the output stream. When necessary, escape characters are utilized.
• Print is identical to prin1, with the exception that a newline and a space is used to separate the printed representation of an item. print outputs the object.
• In order to provide “beautiful” output, the object is printed with the “print-pretty” flag set to non-nil when using pprint rather than print. pprint gives no results.
• Except for the absence of escape characters in the output, princ is identical to prin1. It gives the object back as the value.

write-to-string object &key :escape :radix :base :circle :pretty :level :length :case :gensym :array
prin1-to-string object
princ-to-string object

• The object is effectively printed, and a string is created from the output characters and returned.

write-char character &optional output-stream

• write-char writes the character to output-stream and returns the character.

write-string string & optional output-stream & key :start :end

• The write-string command output streams the characters of the supplied string substring. A substring of a string is delimited by the: start and: end parameters in a typical way.

terpri &optional output-stream
fresh-line &optional output-stream

• A newline is output to the output stream by the function terpri. However, terpri always returns nil, unlike (write-char #Newline output-stream), which is equivalent in effect.
• Similar to terpri, fresh-line only outputs a newline if the stream is not already at the beginning of a line.

finish-output &optional output-stream
force-output &optional output-stream
clear-output &optional output-stream

• The function finish-output tries to ensure that all output sent to the output-stream has reached its destination, and only then returns nil.
• The function force-output initiates the clearing of any internal buffers but returns nil without waiting for completion or acknowledgment.
• The function clear-output tries to abort any outstanding output operation in progress in order to allow as small output as possible to continue to the destination.

Example :

Output :

Output to Binary Streams:

write-byte integer binary-output-stream

• write-byte outputs an integer value of one byte. If the integer does not fit the description provided as the ‘element-type’ argument to open when the stream was established, it is an error. The result is an integer value.

Formatted Output:

The function format is highly helpful for creating well-formatted text, attractive messages, and other things. A stream or a string can be produced by format.

Syntax:

format destination control-string &rest arguments

The standard output is the syntax’s destination, while the control-string variable holds the characters that will be output along with the printing instruction.

With the exception of the tilde (~), which begins a directive, the format outputs the characters of the control string. It is specified by the character following the tilde, which may be followed by prefix parameters and modifiers. A tilde (~), optional prefix parameters separated by commas, an optional colon (:) and at-sign (@) modifiers, and a single character designating the type of directive this is make up a format directive.

Typically, the prefix parameters are integers with optionally signed decimal notation.

The following table tabulates some of the commonly used directives with their descriptions:

Example :

Output :

Pre-requisites: Introduction to LISP

Lisp provides a huge set of facilities for performing input/output. All the input/output operations are performed on streams of several kinds. While reading and writing binary data is possible, the majority of Common Lisp input/output methods read or write characters. For reading and writing individual characters or lines of data, there are straightforward primitives. However, reading and writing written representations of any arbitrary Lisp objects is the most helpful input/output operation.

Lisp Objects:

Lisp objects are typically intricate data structures rather than text strings. They differ from text strings in terms of attributes because of how they are internally represented. However, Lisp offers a representation of the majority of objects in the form of written text, known as the printed representation, which is used for I/O facilities. This makes it possible to access and discuss Lisp objects.

The characters of a Lisp object’s printed representation are transmitted to a stream via functions like print. The (Lisp) printer is a group of functions that accomplishes this. The (Lisp) reader is a group of routines that performs the read function, which accepts characters from a stream, interprets them as a printed representation of a Lisp object, creates that object, and returns it.