Apple Befunge

Version 1.1, February 2012, Chris Pressey, Cat's Eye Technologies

Apple Befunge is a "retrolanguage" for the Apple ][+. Being written in Applesoft BASIC, it should also work on an Apple //e or similar model of 8-bit Apple computer (or, of course, an emulator thereof.) It is based largely on Befunge-93, with some Befunge-98-isms, and some instructions and behaviour peculiar to the Apple 8-bit architecture.

Differences from Befunge-93

The Apple ][+ has no lowercase characters. In Apple Befunge, G, P and V do what g, p, and v do in Befunge-93.

The Apple ][+ has no ` (backtick) symbol. Instead, the ' (apostrophe) symbol is used (it's undefined in Befunge-93.)

The Apple ][+ has no ~ (tilde) symbol. Instead, the = (equals sign) symbol is used (it's undefined in Befunge-93.)

The Apple ][+ has no | (vertical bar) symbol. Instead, the letter I is used (it's undefined in Befunge-93.)

The Apple ][+'s screen is only 40x24, not 80x25, and until a scrolling version of the Apple Befunge debugger is made, program size is limited to the screen size.

Enhancements

Letters A through F represent values 10 through 15, respectively.

The ; (semicolon) symbol begins and ends "ignoremode".

If the x argument to G is negative, the result is PEEK(y).

If the x argument to P is negative, the result is POKEy,d.

The ] instruction pops an argument a off the stack; the result is CALLa.

These three instructions allow a direct interface to the architecture of the 8-bit Apple system on which Apple Befunge is running.

Implementations

The distribution contains an Apple disk image, formatted with ESDOS ][. It contains:

• a full visual debugger/editor for Apple Befunge called APPLE BEFUNGE EDITOR; and
• a handful of Befunge programs which have been converted to Apple Befunge format.

The distribution also contains the source code, in ASCII text, for APPLE BEFUNGE EDITOR. It is intended to be copied-and-pasted into an Apple ][+ emulator. This process, and the program itself, have been tested on a recent version of AppleWin.

In version 1.0 of the distribution there was also a program called APPLE BEFUNGE RUNNER; its source code was intended to be pasted into the emulator after that of APPLE BEFUNGE EDITOR, acting as a sort of "diff", adding and deleting lines. This proved to be a nuisance for maintaining APPLE BEFUNGE EDITOR. And I think APPLE BEFUNGE EDITOR alone sort of gets the point across. So in version 1.1, APPLE BEFUNGE RUNNER was abandoned.

License

The source code for APPLE BEFUNGE EDITOR is hereby placed, by me, the author, in the public domain.

Known Bugs and Shortcomings

The coordinate (39,23) can only contain blank space; I have not yet put in code to draw instructions in that part of the screen, without scrolling it. Apparently, I once knew how to do this, but I never bothered; I no longer know how, but I could probably look it up.

Subtle bug in either % (modulo) or ' (greater than) or hex.bf -- not entirely sure which.

A good reorganization of APPLE BEFUNGE EDITOR's source is in order. The push and pop subroutines should probably be as near the beginning of the program as possible. More constant values should be held in variables, as well.