From: Daniel Martin <martin@...>
Date: 2006-08-10T05:05:38+09:00
Subject: Re: Codegolf - Writing a Brainf*ck interpreter

"Simon Strandgaard" <neoneye@gmail.com> writes:

> well here is my 141 bytes long version :-)
>
> eval 'd=[i=0]*8**5'+ARGV[0].gsub(/./){"
> "+%w[i+=1 X+=1 i-=1 X-=1 putc(X) X=STDIN.getc end
> while(X>0)]['>+<-.,]['.index($&)]}.gsub(/X/,'d[i]')

Note that both this and the earlier one you posted don't conform to
the interface of the codegolf challenge: namely, that bf program will
be presented on stdin, and separated from input by a !.

Also, your program fails on this simple bf program:
++++[>++++++++[>++++++++<-]<-]>>[>++++++++++.<-]

A correct bf interpreter using the traditional 8-bit cell should
output nothing.  Yours... doesn't.  True, the codegolf people didn't
say you had to use an 8-bit cell, so maybe this is ok.

However, I hadn't known about putc, and seeing your code gives me some
ideas.

Note that even with your version, you can save two bytes by NOT doing
the .gsub bit, and expanding X into d[a].  Doing that substitution may
save you 15 characters out of the %w block, but
.gsub(/X/,'d[i]')
is seventeen characters long.

Anyway, here's where I'm at, at 168 characters:

j='d="\0"*8**5;a=0'
while i=STDIN.getc
j+='
'+%w{1 a-=1 a+=1 while(d[a]>0)
end putc(d[a]) d[a]=STDIN.getc||exit
d[a]+=1 d[a]-=1}["
<>[].,+-".index(i)||break]
end
eval j