import re

def simulate_harness_walk(form, whitelist):
    if isinstance(form, str):
        return True
    if isinstance(form, list):
        fn = form[0]
        if fn not in whitelist:
            return False
        return all(simulate_harness_walk(arg, whitelist) for arg in form[1:])
    return True

if __name__ == "__main__":
    whitelist = ["message", "insert", "plist-get", "list", "quote"]
    
    print("--- Test 1: Safe Call ---")
    safe_form = ["message", "Hello World"]
    res1 = simulate_harness_walk(safe_form, whitelist)
    print(f"Result: {res1}")
    
    print("\n--- Test 2: Unsafe Call (Direct) ---")
    unsafe_form = ["shell-command", "rm -rf /"]
    res2 = simulate_harness_walk(unsafe_form, whitelist)
    print(f"Result: {res2}")
    
    print("\n--- Test 3: Nested Malicious Call ---")
    # (message (shell-command "evil"))
    nested_form = ["message", ["shell-command", "evil"]]
    res3 = simulate_harness_walk(nested_form, whitelist)
    print(f"Result: {res3}")
    
    status = "PASS" if res1 and not res2 and not res3 else "FAIL"
    print(f"\nFinal Status: {status}")