bf.ps

% A Brainfuck interpreter written in PostScript
% 2023-12-05 Nicolas Seriot https://github.com/nst/bfps
% ps2pdf bf.ps && open bf.pdf

/Courier findfont 12 scalefont setfont
32 740 moveto

/P (+[-[<<[+[--->]-[<<<]]]>>>-]>-.-- -.>..>.<<<<-.<+.>>>>>.>.<<.<-.) def
/p 0 def                                                % program pointer
/C { P p 1 getinterval } def                            % read program char

/M 30000 string def                                     % memory array
/m 0 def                                                % memory pointer
/V { M m get } def                                      % read mem value

{
    p P length ge { exit } if                           % exit if out of prog

    C (+) eq { M m V 1 add 255 and put } if             % increment mem value
    C (-) eq { M m V 1 sub 255 and put } if             % decrement mem value
    C (>) eq { /m m 1 add def } if                      % move p to right
    C (<) eq { /m m 1 sub def } if                      % move p to left

    C ([) eq {
        p                                               % push p on stack
        V 0 eq {                                        % if V == 0
            mark
            {                                           % move after matching ]
                C ([) eq { 0 } if
                C (]) eq { pop } if
                counttomark 0 eq { pop exit } if
                /p p 1 add def
            } loop                                      
        } if
    } if
    
    C (]) eq {
        /x exch def                                     % pop p for matching [
        V 0 ne { /p x def p    } if                     % jump back if V != 0
    } if
    
    C (.) eq { /s 1 string def s 0 V put s show } if    % show mem value
    C (,) eq { /f (%lineedit) (r) file def f read pop M m 3 -1 roll put } if

    /p p 1 add def                                      % move p to right
} loop