This is a port of a classic text-based "lunar lander" game to Prolog.
The first time I saw a computer was when my father took me to an open-house at the IBM headquarters in Atlanta in the late 1970's, when I was around ten years old. I wasn't impressed with the big sterile glass rooms filled with big orange computers, but there was a room in the basement where a couple of bearded guys asked me to sit down at a terminal and play a game.
It was this lunar landing game. For each ten seconds of game time, it asks how much thrust you want to use, and then it tells you your new altitude, velocity, and remaining fuel. I crashed, and then I had to get up to let the next kid take a turn.
It was simple, primitive even, but I was immediately fascinated with computers. I saw that a computer would let me create little simulated universes that followed whatever rules I could imagine.
So after that I kept bugging my dad to buy me books about programming. A couple of years later, my parents bought me a computer. Thanks Mom and Dad!
I did some research, and I found the original Lunar Lander program by Jim Storer, written in the FOCAL programming language in 1969. I've rewritten it in Prolog so that it can be run on modern systems with Prolog installed. The program here is pretty close to what I remember. One difference is that, on crashing into the moon surface, that program announced "IT'S ALL OVER BUT THE SHOUTING", which confused me as a ten-year-old. I thought the shouting was for joy.
This code is based upon these sources:
- Jim Storer's original lunar landing simulation code in FOCAL
- FOCAL Programming Manual
- David Ahl's port to BASIC in BASIC Computer Games (1978)
If you have SWI-Prolog installed, you can run the game by executing this command:
swipl lunar.pl
Alternatively, you can start SWI-Prolog and then load the file:
swipl
?- [lunar].
If you have GNU Prolog installed, you can run the game by executing this command:
gprolog --consult-file lunar.pl
Alternatively, you can start GNU Prolog and then load the file:
gprolog
?- [lunar].
You can compile lunar.pl into a standalone executable using gplc:
gplc lunar.pl
This will create an executable named lunar in the current directory, which you can then run directly:
./lunar
If you have Ciao Prolog installed, you can run the game by executing this command:
ciao run lunar.pl
Or, you can start the Ciao shell and then load the file:
ciao
?- [lunar].
You can compile lunar.pl into a standalone executable using ciaoc:
ciaoc -o lunar lunar.pl
This will create an executable named lunar in the current directory, which you can then run directly:
./lunar
Here is an example play session:
CONTROL CALLING LUNAR MODULE. MANUAL CONTROL IS NECESSARY
YOU MAY RESET FUEL RATE K EACH 10 SECS TO 0 OR ANY VALUE
BETWEEN 8 & 200 LBS/SEC. YOU'VE 16000 LBS FUEL. ESTIMATED
FREE FALL IMPACT TIME-120 SECS. CAPSULE WEIGHT-32500 LBS
FIRST RADAR CHECK COMING UP
COMMENCE LANDING PROCEDURE
TIME,SECS ALTITUDE,MILES+FEET VELOCITY,MPH FUEL,LBS FUEL RATE
0 120 0 3600.00 16000.0 K=:0
10 109 5016 3636.00 16000.0 K=:0
20 99 4224 3672.00 16000.0 K=:0
30 89 2904 3708.00 16000.0 K=:0
40 79 1056 3744.00 16000.0 K=:0
50 68 3960 3780.00 16000.0 K=:0
60 58 1056 3816.00 16000.0 K=:0
70 47 2904 3852.00 16000.0 K=:170
80 37 1474 3539.86 14300.0 K=:200
90 27 5247 3140.80 12300.0 K=:200
100 19 4537 2710.41 10300.0 K=:200
110 12 5118 2243.83 8300.0 K=:200
120 7 2285 1734.97 6300.0 K=:200
130 3 1990 1176.06 4300.0 K=:200
140 0 5040 556.96 2300.0 K=:170
150 0 1040 -21.20 600.0 K=:0
160 0 1087 14.80 600.0 K=:0
170 0 606 50.80 600.0 K=:30
180 0 436 -27.90 300.0 K=:0
190 0 581 8.10 300.0 K=:8
200 0 425 13.17 220.0 K=:10
210 0 253 10.30 120.0 K=:9
220 0 95 11.11 30.0 K=:100
FUEL OUT AT 220.30 SECS
ON THE MOON AT 226.11 SECS
IMPACT VELOCITY OF 21.35 M.P.H.
FUEL LEFT: 0.00 LBS
CONGRATULATIONS ON A POOR LANDING
TRY AGAIN?
(ANS. YES OR NO):NO
CONTROL OUT