[vcf-midatlantic] 2:00am BASIC epiphany

[Evan Koblentz]

I had a spontaneous idea tonight for removing two lines of my Lego robot 
code.

As usual, this epiphany on my part is probably TOTALLY FRIGGIN' OBVIOUS 
to most of you, but I'm proud that I figured it out on my own. :)

Before, on the forklift robot, this was my code for checking the 
upper/lower touch sensors (limit switches) and moving the forklift motor 
appropriately. I had it at 9 lines (not counting REMarks) which was 
greatly reduced from Dan R.'s original 16 lines.

3010 IF PEEK (49249) > 127 AND PEEK(L) = 64 THEN RETURN
3020 IF PEEK (49249) > 127 THEN POKE L,16
3030 IF PEEK(L) = 80 THEN RETURN
3040 IF PEEK(49249) > 127 THEN GOTO 3020
3050 IF PEEK(49250) > 127 AND PEEK(L) = 128 THEN RETURN
3060 IF PEEK(49250) > 127 THEN POKE L,32
3070 IF PEEK(L) = 160 THEN RETURN
3080 IF PEEK(49250) > 127 THEN GOTO 3060
3090 RETURN

Background: In that code, PEEK(49249) in Applesoft checks joystick 
button 0 and PEEK(49250) checks button 1. If their value is greater than 
127 then you know they're currently being pressed. PEEK(L) checks the 
value at the address of the interface card. 64/128 are the sensors 
attached to ports (bits) 6 and 7, respectively. POKE L,16/32 turns on 
the motor (in opposite directions) that's attached via a connector 
spanned to ports 4/5. Lines 3030 and 3070 stop the motors if the sensors 
become active ** while ** the motor is moving, because then the total 
value being read from the interface box is sensor + the motor.

The idea that popped into my head tonight: you can combine lines 
3010/3020 into one, and also lines 3050/3060 into one, thereby reducing 
the routine by two lines and having the same effect.

3010 IF PEEK (49249) > 127 AND PEEK(L) <> 64 THEN POKE L,16
3020 IF PEEK(L) = 80 THEN RETURN
3030 IF PEEK(49249) > 127 THEN GOTO 3010
3040 IF PEEK(49250) > 127 AND PEEK(L) <> 128 POKE L,32
3050 IF PEEK(L) = 160 THEN RETURN
3060 IF PEEK(49250) > 127 THEN GOTO 3040
3070 RETURN

So instead of saying, "Exit the routine if the lower/upper touch sensors 
are active, which we know is true if the value at address L is 64 or 
128," instead I'm saying, "Turn on the motor ** ONLY IF ** the 
lower/upper touch sensors aren't active."

I can't test it until this weekend at the soonest, but I am ** pretty 
sure ** it'll work -- or at least I don't see any obvious reason why it 
would ** not ** work. After all, the forklift motor can't turn on when 
either sensor is active, because I'm not programmatically allowing it -- 
right?

If it works, then I'll convert it to IBM BASIC too. The button PEEKs 
become STRIG (stick trigger) values, and the POKEs become OUT.

Saving two lines of interpreted / non-compiled BASIC isn't going to have 
any significant impact on program execution speed or disk space, but it 
makes the code that much easier for non-programmers to understand, and 
it gives me that much more confidence of about being than just another 
English major. :)