Berry's paradox and elegant LISP programs in Common Lisp

defun s-expressin-length (s)
  (length (write-to-string s)))

(defun complexity (s)
  (s-expressin-length (eval s)))

(complexity  '(car '(a b)))  

(defun is-elegant (s)
  (cond ((eq (s-expressin-length s) (complexity s))
         t)
        (t
         nil)))

(defun berry1 (lst)
  (cond ((null lst) nil)
        (t
         (cond ((and (is-elegant lst) 
                     (>= (complexity lst) (s-expressin-length #'berry1)))
                #'berry1)
               (t
                lst)))))

(defun berry (lst)
  (cond ((null lst) nil)
        (t
         (cond ((and (is-elegant (car lst)) 
                     (>= (complexity (car lst)) (s-expressin-length #'berry))))
                #'berry)
               (t
                (berry (cdr lst))))))

Ref: http://www.cs.umaine.edu/~chaitin/lisp.html

Tags: lisp

Links para referências sobre Lisp

Livros

• The Little Lisper, Daniel P. Friedman, Matthias Felleisen
• Common Lisp the Language, 2nd Edition, Guy L. Steele Jr.
• On Lisp, Paul Graham
• Structure and Interpretation of Computer Programs, Abelson, Sussman, Sussman
• LISP 1.5 Programmer's Manual, John McCarthy, Paul W. Abrahams, Daniel J. Edwards, Timothy P. Hart, Michael I. Levin.

Artigos

• Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I, John McCarthy (artigo original)
• The Roots of Lisp, Paul Graham

Tags: Lisp, livros artigos

Breve descrição de utilidades em CL, instalação de packages, asdf, etc

As notas aqui descritas estão pensadas para SBCL - Steel Bank Common Lisp em Debian - GNU/Linux.

1. Pedir a CL para não gritar (inlcuir a instrução no ficheiro ~/.sbclrc):

(setf *print-case* :downcase)

1. A maneira mais simples de instalar e manter os packages em CL é usando o ASDF. Há dois manuais que valem a pena ser lidos:
   • ASDF Manual
   • e o asdf-install: ASDF-Install - Bringing Lisp Libraries to you ou ainda CLiki - ASDF-Install
2. Exemplo de instalação usando o asdf: Para instalar a LTK - The Lisp Toolkit faz-se:

(require 'asdf-install)
(asdf-install:install 'ltk)

O asdf faz o download dos ficheiros e diz

Downloading 240780 bytes from http://www.peter-herth.de/ltk/ltk-0.91.tgz ...

e pergunta:

Install where?
1) System-wide install: 
   System in /usr/lib/sbcl/site-systems/
   Files in /usr/lib/sbcl/site/ 
2) Personal installation: 
   System in /home/tca/.sbcl/systems/
   Files in /home/tca/.sbcl/site/ 

respondo 2.

Tags: Common Lisp, CL, utilitities, asdf, sbcl