Brainf*** interpreter in TeX

bf.tex

% Brainf*** interpreter
% Usage:
%
%    tex bf <file>
%
% Be aware that this interpreter is very slow...

\newcount\memptr \newcount\maxptr \newcount\minptr
\newcount\memval \newcount\maxval \newcount\minval

\minptr=0 \maxptr=65535
\minval=0 \maxval=255

\let\inbuf=\empty \let\outbuf=\empty

\catcode`\@=11

% Plain old TeX does not have a good (read: expandable) way
% to convert from an ASCII codepoint to the actual character...
% If using XeTeX/LuaTeX, we could use \Uchar
\newtoks\xchar
\begingroup\catcode`\^^@=12
\gdef\setxchar{\begingroup\afterassignment\setxch@r\lccode`^^@}
\gdef\setxch@r{\lowercase{\global\xchar{^^@}}\endgroup}
\endgroup


% the machine
\newif\ifdirty \newif\ifvalid
\def\getmemloc{%
  \xdef\memloc{\expandafter\noexpand\csname mem\the\memptr\endcsname}%
  \expandafter\ifx\memloc\relax
    \expandafter\global
    \expandafter\chardef\memloc\z@
  \fi}
\def\readmem{\global\memval\memloc\relax \global\validtrue}
\def\maybefetch{\ifvalid\else \getmemloc \readmem \fi}
\def\writemem{%
  \expandafter\global
  \expandafter\chardef\memloc\memval
  \global\dirtyfalse}
\def\moveptr#1{\ifdirty \ifvalid\else \getmemloc\fi \writemem \fi
  \checkadvance \memptr #1\minptr \maxptr
  \global\validfalse}
\def\addval#1{\maybefetch
  \checkadvance \memval #1\minval \maxval
  \global\dirtytrue}
\def\checkadvance#1#2#3#4{% register delta min max
  \global\advance#1#2\relax
  \ifnum#1<#3%
    %\wlog{\string#1 underflow! wrapped to \number#3^^J}%
    \global#1=#4%
  \else\ifnum#1>#4%
    %\wlog{\string#1 overflow! wrapped to \number#2^^J}%
    \global#1=#3%
  \fi\fi}
\def\gettok#1{\expandafter\gettok@\expandafter#1#1\relax}
\def\gettok@#1#2#3\relax{\memval=`#2\relax\xdef#1{#3}}
\def\puttok#1{\setxchar=\memval \xdef#1{#1\the\xchar}}
\def\morein{\maybeflush \global\read\sixt@@n to\inbuf}
\def\flushout{\immediate\write\sixt@@n{\outbuf}%
  \global\let\outbuf\empty}
\def\maybeflush{\relax\ifx\outbuf\empty\else \flushout \fi}


% brainf*** commands
\def\setcatcode{%
  \catcode`[\@ne
  \catcode`]\tw@
  \catcode`<\active
  \catcode`>\active
  \catcode`+\active
  \catcode`-\active
  \catcode`,\active
  \catcode`.\active}

{\setcatcode
\gdef<{\moveptr\m@ne}
\gdef>{\moveptr\@ne}
\gdef+{\addval\@ne}
\gdef-{\addval\m@ne}
\gdef,{\ifx\inbuf\empty \morein \fi
  \gettok\inbuf \global\dirtytrue}
\gdef.{\maybefetch
  \ifnum\memval=`\^^J\flushout \else \puttok\outbuf \fi}
\gdef\setzero{-}
\gdef\bfloop#1{\def\body{#1}%
  \ifx\body\setzero \expandafter\bfclear % [-] optimization
  \else \expandafter\bfiterate \fi \dobf}
\gdef\bfclear{\ifvalid\else \getmemloc\fi
  \global\memval\z@ \writemem}
\gdef\bfiterate{\maybefetch
  \ifnum\memval=\z@ \else {\expandafter\dobf\body}\expandafter\bfiterate \fi}}


% stream scanner
\def\dobf{\futurelet\next\dobf@}
\def\dobf@{%
  \ifcat\noexpand\next\bgroup
    \let\next\bfloop % let TeX scan a group (balanced [...])
  \else\ifcat\noexpand\next\egroup
    \let\next\relax % we're done
  \else
    \let\next\dobf@@
  \fi\fi
  \next}%
\def\dobf@@#1{\ifcat\noexpand#1\noexpand~#1\fi \dobf}


\def\uncatcodespecials{\def\do##1{\catcode`##1=12 }\dospecials\do\^^M}
\def\readbf#1 {\uncatcodespecials \setcatcode
  %\loggingall
  {\expandafter\dobf\input#1 }\maybeflush\end}

\expandafter\readbf

hello.b

++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..
+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.