A8.9 Project: the robot's safety logic

The starter gives GO_ROWS, the truth table rows (numbered 8C + 4K + 2L + D) where G = 1, and draft(c, k, l, d), which takes four bits and returns 1 on those rows and 0 otherwise. 1. Write go(c, k, l, d), taking four bits, as a single return line using at most six of and, or and not in total. It may not use GO_ROWS or call draft. Any true result means drive. 2. Check go against draft on all sixteen combinations, treating a true result as 1 and a false one as 0, and print matches: True if they agree on every one, or matches: False if not. 3. Drive the robot. Set docking = 0. In a loop, read close (1 if distance() is under 20, else 0), hit (1 if bumped(), else 0) and low (1 if battery() is under 20, else 0), and call go(close, hit, low, docking). While it is true, drive forward. When it is false, stop, print one line in exactly the form stopped: C=1 K=0 L=0 D=0 using the values that stopped it, and end the loop. The robot must finish in the band before the wall without touching it.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

GO_ROWS = [0, 1, 3, 9, 11]

def draft(c, k, l, d):
    return 1 if 8 * c + 4 * k + 2 * l + d in GO_ROWS else 0

def go(c, k, l, d):
    return 0

The hint students can ask for: Put the five rows on a four-variable Karnaugh map in Gray code order and find the fewest, largest groups; then see whether factoring out a shared literal, or De Morgan, saves operators. Prove go against draft on all sixteen rows before you let it drive. In the loop, read the four inputs as 0 or 1 every time round.

A solution

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

GO_ROWS = [0, 1, 3, 9, 11]

def draft(c, k, l, d):
    return 1 if 8 * c + 4 * k + 2 * l + d in GO_ROWS else 0

def go(c, k, l, d):
    return (not k) and (d or not (c or l))

ok = True
for n in range(16):
    c, k, l, d = n >> 3 & 1, n >> 2 & 1, n >> 1 & 1, n & 1
    if (1 if go(c, k, l, d) else 0) != draft(c, k, l, d):
        ok = False
print(f"matches: {ok}")

docking = 0
while True:
    close = 1 if distance() < 20 else 0
    hit = 1 if bumped() else 0
    low = 1 if battery() < 20 else 0
    if go(close, hit, low, docking):
        forward(50)
        wait(0.1)
    else:
        stop()
        print(f"stopped: C={close} K={hit} L={low} D={docking}")
        break

Any program that meets the task's checks is marked correct in the simulator; this is one way, not the only way.