CLISP

Implementation of programming language Lisp

CLISP is ANSI Common Lisp implementation. It implements ANSI standard of the dialect with a lot of extensions.

CLISP includes interpreter, compiler, debugger and multiple extensions like long arithmetics, arbitrary precision floating numbers, regular expressions etc. It is written in C and Common Lisp. Currently CLISP is part of GNU Project and is available under GNU GPL.

Links:

Examples:

Factorial:

Example for versions Corman Common Lisp 3.0, SBCL 1.0.1, SBCL 1.0.29, clisp 2.47, gcl 2.6.6

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:

Example for versions Corman Common Lisp 3.0, SBCL 1.0.1, SBCL 1.0.29, clisp 2.47, gcl 2.6.6

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!:

Example for versions Corman Common Lisp 3.0, SBCL 1.0.1, SBCL 1.0.29, clisp 2.47, gcl 2.6.6

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:

Example for versions Corman Common Lisp 3.0, clisp 2.47, gcl 2.6.6

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:

Example for versions Corman Common Lisp 3.0, SBCL 1.0.1, SBCL 1.0.29, clisp 2.47, gcl 2.6.6

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:

Example for versions Corman Common Lisp 3.0, SBCL 1.0.1, SBCL 1.0.29, clisp 2.47, gcl 2.6.6

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:

Example for versions Corman Common Lisp 3.0, SBCL 1.0.1, SBCL 1.0.29, clisp 2.47 
(defun camel-case (s)
  (remove #\Space 
          (string-capitalize
           (substitute #\Space nil s :key #'alpha-char-p))))

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