clisp 2.47

Version of implementation CLISP of programming language Lisp

A version of clisp compiler and interpreter.

Examples:

Factorial - Lisp (22):

This example uses recursive factorial definition (which is natural for Lisp). Features:

math operators: (- n 1) is prefix notation equivalent to n-1 in infix notation;
comparison operators: (= n 0) evaluates to T if n is zero, and to nil (used as false) otherwise;
conditional operator if: Lisp expressions are evaluated using brackets, so they can be written in several lines;
function definition using defun;
Common Lisp macro loop;
format specifiers in format: ~D corresponds to printing an integer, and ~% is end-of-line.

(defun factorial (n)
  (if (= n 0)
      1
      (* n (factorial (- n 1))) ) )

(loop for i from 0 to 16
   do (format t "~D! = ~D~%" i (factorial i)) )

Factorial - Lisp (121):

In this example the inner loop with collect clause produces a list of numbers from 1 to n. After this operation * is applied to this list, and the product of the numbers is printed.

(loop for n from 0 to 16
   do (format t "~D! = ~D~%" n 
        (apply '* (loop for i from 1 to n 
                        collect i)) ) )

Hello, World! - Lisp (21):

When executed in interactive mode, program output looks as follows:

Hello, World!
NIL

First line contains standard output, second — the result of expression evaluation (in this case there is none).

(format t "Hello, World!~%")

Fibonacci numbers - Lisp (24):

This example uses iterative definition of Fibonacci numbers, though expressed through recursive calls of fib-iter.

(defun fibonacci (n)
  (defun fib-iter (a b count)
    (if (zerop count)
	b
	(fib-iter (+ a b) a (- count 1)) ) )
  (fib-iter 1 0 n) )

(loop for i from 1 to 16
   do (format t "~D, " (fibonacci i))
   finally (format t "...~%") )

Quadratic equation - Lisp (172):

Common Lisp provides complex numbers as datatype, printed as #C(real imag). write-to-string converts a number into a string.

Note that for interactive evaluation it’s enough to add (quadratic-roots-2 1 0 1) to see the result of calculation, while for compiled execution you’ll have to wrap call of this function in printing command, like (format t (quadratic-roots-2 1 0 1)).

(defun quadratic-roots-2 (A B C)
  (cond ((= A 0) (string "Not a quadratic equation."))
    (t
    (let ((D (- (* B B) (* 4 A C))))
      (cond ((= D 0) (concatenate 'string "x = " (write-to-string (/ (+ (- B) (sqrt D)) (* 2 A)))))
        (t
        (values (concatenate 'string "x1 = " (write-to-string (/ (+ (- B) (sqrt D)) (* 2 A))))
                (concatenate 'string "x2 = " (write-to-string (/ (- (- B) (sqrt D)) (* 2 A)))))))))))

Fibonacci numbers - Lisp (23):

This example uses recursive definition of Fibonacci numbers and expands use of loop macro to finally clause (expression evaluated after the loop is done).

(defun fibonacci (n)
  (if (< n 3)
      1
      (+ (fibonacci (- n 1)) (fibonacci (- n 2))) ) )

(loop for i from 1 to 16
   do (format t "~D, " (fibonacci i))
   finally (format t "...~%") )

CamelCase - Lisp (277):

(defun camel-case (s)
  (remove #\Space 
          (string-capitalize
           (substitute #\Space nil s :key #'alpha-char-p))))

(princ (camel-case (read-line)))