\Subleq program interpreter

    \Executes the program specified in scode, stops when the instruction
    \ pointer becomes negative.
    procedure RunSubleq ( SCode, CodeLength);
    integer   SCode, CodeLength;
    define  MaxMemory = 3 * 1024;
    integer Memory ( MaxMemory );
    integer IP, A, B, C, I;
    begin
        begin
            for I := 0 to MaxMemory - 1 do Memory( I ) := 0;
            \Load the program into Memory
            for I := 0 to CodeLength do Memory( I ) := SCode( I );
            \Start at instruction 0
            IP := 0;
            \Execute the instructions to IP is < 0
            while IP >= 0 do begin
                \Get three words at IP and advance IP past them
                A  := Memory( IP     );
                B  := Memory( IP + 1 );
                C  := Memory( IP + 2 );
                IP := IP + 3;
                \Execute according to A, B and C
                if  A = -1 then begin
                    \Input a character to B
                    Memory( B ) := ChIn(1)
                    end
                else if B = -1 then begin
                    \Output character from A
                    ChOut(0, Memory ( A ) )
                    end
                else begin
                    \Subtract and branch if <= 0
                    Memory( B ) := Memory( B ) - Memory( A );
                    if Memory( B ) <= 0 then IP := C
                end
            end \while-do
        end
    end \RunSubleq \;

    \Test the interpreter with the hello-world program specified in the task
    integer Code;
    begin
        Code := [ 15,  17,  -1,  17,  -1,  -1
               ,  16,   1,  -1,  16,   3,  -1
               ,  15,  15,   0,   0,  -1,  72
               , 101, 108, 108, 111,  44,  32
               , 119, 111, 114, 108, 100,  33
               ,  10,   0 ];
        RunSubleq( Code, 31 )
    end