(blog ‘lucindo)

A submissão campeã do prêmio Best of show do IOCCC de 1989 foi o seguinte interpretador Lisp (aqui modificado para compilar no gcc de hoje):

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define p char*
#define P ,(p)
#define T(E) !strcmp(E,“()”)
#define U return
#define W while
#define X sbrk(199)
#define z atof
#define e isspace
#define D A(_)
#define E S(C(_))
#define B(y) p y(_)p _;{
#define G(y,V) B(y)p i;U sprintf(i=X,“%lf”,z(E)V z(S(C(D)))),i;}

        p sbrk(),*S(),*j(),*O,*H;K,Y,M=14;double
      z();Q(_)p _;{int V=0;W(e(*_))_++;H=_;W(V|!(e
    (*H)|*H==‘)’||(*H==‘(’&&H-_)))V+=(*H==‘(’)-(*H==
      ‘)’),H++;U H-_;}B(C)U _++,Y=Q(_),_=strncpy(X,_,Y),_[
    Y]=0,_;}B(A)_++,_+=Q(_);W(e(*_))_++;U O=X,*O=‘(’,strcpy(
  O+1,_),O;}B(Z)U _;}B(c)U C(E);}B(q)U A(E);}B(t)p i=E;U H=S(C
(D)),sprintf(O=X,T(H                 )?“(%s)”:“(%s %s”,i,H+1)

         ,O;}B(F)U S(C(A(T(E)?D:_)));}L(i,s)p

i,*s;{U isdigit(*i)     ?         z(i)!=z(s):strcmp(i,s);}
  B(b)U L(E,S(C(D)))?“()”:“t”;}B(R)U E;}B(o)U z(E)<z(S(C(D)))?
    “t”:“()”;}G(f,+)G(g,-)G(h,*)p r[4][2]={“function”   P R,
      “quote”P C,“lambda”P Z,“defun”P j};B(j)U r[M][1]=D,*
    r[M++]=C(_);}p not[99][2]={“if”P F,“equal”P b,“<”
      P o,“+”P f,“-”P g,“*”P h,“car”P c,“cdr”P q,
        “cons”P t,“t”,“t”};B(S)int Li,s;p u;if(
          isdigit(*_)|T(_))U _;for(Y=M;Y–;)
        if(!strcmp(_,*r[Y]))U r[Y][1]
          ;u=E,_=D;if(*u-‘(’)U(*((p(*)())u)
        )(_);s=Li=M;W(!T(_))r[M][1]=E,*r[M++]
    =“”,_=D;O=C(u);W(!T(O))*r[Li++]=C(O),O=A(O);U O=S
    (C(A(u))),M=s,O;}main(){H=O=X,Y=0;W(Y|!e(K=getchar()))K==
    EOF?exit(0):0,Y+=(K==‘(’)-(K==‘)’),*H++=K;*H=0,puts(S(O))
                ,
        main();{printf(“XLISP 4.0n”);}}

Essa implementação foi feita por Jari Arkko, Ora Lassila e Esko Nuutila da Universidade Tecnológica de Helsinki. Ele implementa as operações:

+	-	*	<	()
car	cdr	cons	defun	equal
function if	lambda	quote	t

Os autores propõe o seguinte teste:

(+ 2.5 3.1)
(defun fib (n)
  (if (< n 2)
      1
      (+ (fib (- n 2)) (fib (- n 1)))))
(fib 10)
(defun ! (x) (if (equal x 0) 1 (* x (! (- x 1)))))
(! 7)
(defun fn1 (fn) (+ (fn 1 2) (fn 3 4)))
(defun fn2 (a b) (+ a b))
(fn1 (function +))
(fn1 (function fn2))
(fn1 (function (lambda (z1 z2) (+ z1 z2))))
(quote a)
(cons (quote (a b)) (quote (c d e)))
(cons (quote (f)) ())
(car (quote (a b c)))
(cdr (cdr (quote (g h i))))

Mais informações aqui.

Download: jar.2.c (versão alterada para gcc 4.x)

Everyone always wants new things. Everybody likes new inventions, new technology. People will never be replaced by machines. In the end, life and business are about human connections, and computers are about trying to murder you in a lake. And to me, the choice is easy.

Michael Scott