Comment by nickdrozd

The "states" (A, B, C) correspond to goto targets. The "colors" (0, 1, 2, 3) are runtime data. At each state, the current color is read, and an instruction is executed (print some color, move left or right, goto some state) based on which color is there. Transliterated into C it looks like this:

  #include "machine.h"
  
  int main(void)
  {
   A:
    switch (SCAN) {
      case 0:
        WRITE(1); RIGHT; goto B;
  
      case 1:
        WRITE(3); LEFT; goto B;
  
      case 2:
        WRITE(1); RIGHT; goto H;
  
      case 3:
        WRITE(2); RIGHT; goto A;
    }
  
   B:
    switch (SCAN) {
      case 0:
        WRITE(2); LEFT; goto C;
  
      case 1:
        WRITE(3); RIGHT; goto B;
  
      case 2:
        WRITE(1); LEFT; goto C;
  
      case 3:
        WRITE(2); RIGHT; goto A;
    }
  
   C:
    switch (SCAN) {
      case 0:
        WRITE(3); RIGHT; goto B;
  
      case 1:
        WRITE(1); LEFT; goto B;
  
      case 2:
        WRITE(3); LEFT; goto C;
  
      case 3:
        WRITE(2); RIGHT; goto C;
    }
  
   H:
    HALT;
  }

Question: are there any opportunities to rewrite this logic in a more "structured" style, or to make any other optimizations?