X11-Basic game ports

I long wanted to code on a mobile device, or at least fiddle with code, which is more plausible. Most apps made for that are huge and involved, but there are exceptions.

Enter X11-Basic. It's a 4.6MB app available in F-Droid, runs on very old Android devices, and comes with a ton of examples. Also a 700-page reference manual, which is daunting at first sight. I tried and failed twice to learn the dialect. But third time was the charm; see below for a survival guide. It applies to version 1.27, latest as of mid-April 2022.

For development I installed the Linux version from source, which is quick but tricky. Tip: use make static as explained in the documentation, and manually copy the resulting executables to /usr/local/bin or so.

Game ports

Only two because trying to port more advanced games simply didn't work:

Land/Lord

Port of the shell script edition by No Time To Play. You might want to replace QUIT with END (two places in the main program), to play inside the IDE. Also, depending on your screen size, you might have to trim the text a lot. Look up the classic game Hamurabi if you're not familiar with the rules.

Tip: on Android, change the screen focus to "cursor" in the settings.

Switch|Off

Another clone, of an even simpler game usually known as Lights Out, though the game is a lot older than the one bearing that name. Because I couldn't figure out how to solve the puzzle, I changed it to a more intuitive variation.

On small screens, change the screen focus to "top" in the settings.

Remember that a big part of the fun with Basic games is tweaking them. For example I changed Land/Lord on the tablet to say "disaster!" out loud when the plague strikes, while on the phone I trimmed down the text to fit a very small screen. Figure out your own variations!

Survival guide

Don't panic! While the reference manual is over 700 pages long, most of that is a list of all statements and functions. You only need to read — or at least skim — the first few chapters. Mainly, an X11-Basic program looks like this:

' main program first

@hello

quit

procedure hello()
	print @hello$()
return

function hello$()
	return "Hello, world!"
endfunc

You can expand @ to GOSUB for procedures, but not functions. Other notes:

• The COLOR() modifier for PRINT is explained on page 492 of the manual...
• ...and you can't reset colors to the terminal defaults, only attributes.
• DIV and MOD operators have low precedence; use them with parentheses.
• You can't DIM a scalar variable, so just initialize it.
• Can't use a colon to place multiple statements on the same line, either.
• The THEN keyword isn't supported; there's no single-line IF.
• Repeating the FOR loop variable in NEXT is mandatory.
• Line numbers in error messages are off by one.
• CONTINUE only works in SELECT; use GOTO in loops.
• Array indices start from zero.

Speaking of which, there are nice touches like array literals (only for numeric arrays):

chances() = [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]

Also the EXIT IF statement can make for nice compact code in some cases. On the minus side, the parser is kind of fragile. Error messages can be confusing, or worse, absent. To wit:

> print "Hello, ": print "world!" 
Hello, ": PRINT "world!

Or for an even more baffling example:

> let a = 1: let b = 2 
> print a 
0
> print b 
0

Not to mention (a real error I made):

> dim a(10) 
> let a[0] = 1 
> print a(0) 
0
> print a[0] 
1  

But keep it simple and things should work. Well enough. Usually.