turing-machine-int.fchart

read     (Q, Right);
init:    Qtail := Q;
         Left := list();
         goto loop;
loop:    if eq(Qtail, list()) goto stop else cont;
cont:    Instruction := head(Qtail);
         Qtail := tail(Qtail);
         Operator := head(Instruction);

         if eq(Operator, "right") goto doRight else cont1;
cont1:   if eq(Operator, "left")  goto doLeft  else cont2;
cont2:   if eq(Operator, "write") goto doWrite else cont3;
cont3:   if eq(Operator, "goto")  goto doGoto  else cont4;
cont4:   if eq(Operator, "if")    goto doIf    else error;

doRight: Left := cons(firstsym(Right), Left);
         Right := tail(Right);
         goto loop;
doLeft:  Right := cons(firstsym(Left), Right);
         Left := tail(Left);
         goto loop;
doWrite: Symbol := head(tail(Instruction));
         Right := cons(Symbol, tail(Right));
         goto loop;
doGoto:  Nextlabel := head(tail(Instruction));
         Qtail := newtail(Nextlabel, Q);
         goto loop;
doIf:    Symbol := head(tail(Instruction));
         Nextlabel := head(tail(tail(tail(Instruction))));
         if eq(Symbol, firstsym(Right)) goto jump else loop;

jump:    Qtail := newtail(Nextlabel, Q);
         goto loop;

error:   return "Syntax error: Instruction";

stop:    return Right;