Formatted Output to Character Streams in LISP

Last Updated : 26 Jul, 2022

Lisp is a programming language that has an overall style that is organized around expressions and functions. Every Lisp procedure is a function, and when called, it returns a data object as its value. It is also commonly referred to as “functions” even though they may have side effects.

Formatted Output to Character Streams:

The function format is used to produce nice formatted text, good-looking messages, and so on. the format can generate a string or output to a stream.

Syntax:

format destination control-string &rest arguments

where,

destination -> standard output
control-string -> hold the characters that to output and printing directive.

A format directive consists of a tilde (~), optional prefix parameters separated by commas, an optional colon (:) and at-sign (@) modifiers, and a single character indicating the type of directive.

The prefix parameters are generally integers, notated as optionally signed decimal numbers. The following commonly used directives used for output streams are:

S.No.	Directives	Description
1	~B	For binary arguments.
2	~D	For decimal arguments.
3	~S	Is followed by S-expressions.
4	~A	Is followed by ASCII arguments.
5	~O	For octal arguments.
6	~$	Dollar and floating point arguments.
7	~E	Exponential floating-point arguments.
8	~F	For Fixed-format floating-point arguments.
9	~C	For character arguments.
10	~X	For hexadecimal arguments.
11	~*	The next argument is ignored.
12	~?	Indirection. The next argument must be a string, and the one after it a list.
13	~%	A new line is printed.
14	~^	Up and out. This is an escape construct.
15	~>	Terminates a ~<. It is an error elsewhere.
16	~}	This terminates a ~{. It is an error elsewhere.
17	~;	This separates clauses in ~[ and ~< constructions. It is an error elsewhere.
18	~(str~)	Case conversion.
19	~[str0~;str1~;…~;strn~]	Conditional expression. This is a set of control strings, called clauses.
20	~W	Write. In an argument, a Lisp object is printed obeying every printer control variable.

Example 1:

Lisp

; Formatted Output to Character Streams in LISP 
(format t "Hello, World!") 
(format nil "foo") 
(setq x 10) 
(format nil "The answer is ~D." x) 
(format nil "The answer is ~3D." x) 
(format nil "The answer is ~3,'0D." x) 
(format nil "The answer is ~:D." (expt 47 x)) 
(setq y "cat")  
(format nil "Look at the ~A!" y) 
(setq n 3) 
(format nil "~D item~:P found." n) 
(format nil "~R dog~:[s are~; is~] here." n (= n 1)) 
(format nil "~R dog~:*~[s are~; is~:;s are~] here." n) 
(format nil "Here ~[are~;is~:;are~] ~:*~R pupp~:@P." n)

Output:

Example 2:

Lisp

;Formatted Output to Character Streams in LISP 
(defun perimeterofsquare() 
   (terpri) 
   (princ "Enter side length: ") 
   (setq length (read)) 
   (setq peri (* 4 length)) 
   (format t "Length: = ~F~% Perimeter = ~F" length peri) 
) 
(perimeterofsquare)