I love these puzzles. GNU C supports a label as value for computed goto. This is useful for direct threaded dispatch. You trade off a branch instruction for

I love these puzzles. GNU C supports a label as value for computed goto. This is useful for direct threaded dispatch. You trade off a branch instruction for an address lookup, but it makes the code more structured. int main(void) { void* A[] = {&&A0, &&A1, &&A2, &&A3}; void* B[] = {&&B0, &&B1, &&B2, &&B3}; void* C[] = {&&C0, &&C1, &&C2, &&C3}; goto *A[SCAN]; A0: WRITE(1); RIGHT; goto *B[SCAN]; A1: WRITE(3); LEFT ; goto *B[SCAN]; A2: WRITE(1); RIGHT; HALT; return 0; A3: WRITE(2); RIGHT; goto *A[SCAN]; B0: WRITE(2); LEFT ; goto *C[SCAN]; B1: WRITE(3); RIGHT; goto *B[SCAN]; B2: WRITE(1); LEFT ; goto *C[SCAN]; B3: WRITE(2); RIGHT; goto *A[SCAN]; C0: WRITE(3); RIGHT; goto *B[SCAN]; C1: WRITE(1); LEFT ; goto *B[SCAN]; C2: WRITE(3); LEFT ; goto *C[SCAN]; C3: WRITE(2); RIGHT; goto *C[SCAN]; }