Add `@\f1` through `@\f8` to capture function keys in `(get key $)`

[susan-davis]

The Z-machine allows input up to F12; my Mac keyboard has up to F19. With the caveat that supporting any function key beyond F12 won't work on the Z-machine, having a syntax for capturing function keys would be very nice to have.

[susan-davis]

(This might need a smidgeon of 6502 work for the Å-machine 6502 terp.)

[dstelzer]

Is the intent that they'd work as terminating characters on Z-machine (so you could use them during line input, not just key input)?

[susan-davis]

That's against the Z-machine standard, if I'm understanding it correctly. Only ZSCII characters defined for both input and output can be in the buffer from read, whereas characters defined for input only can be read from read_char.

[susan-davis]

The 6502 terp probably doesn't need to support F9 and higher, since the C64 and C128 both have only F1 to F8.

[dstelzer]

It's weird, but from a different part of the spec:

In Versions 5 and later, the game may provide a “terminating characters table” by giving its byte address in the word at $2e in the header. This table is a zero-terminated list of input character codes which cause aread to finish the command (in addition to new-line). Only function key codes are permitted: these are defined as those between 129 and 154 inclusive, together with 252, 253 and 254. The special value 255 means “any function key code is terminating”.

I think the intent is that the function keys can interrupt a line of input, and @read will report what terminating character was used, so the game can look at that and swap the input for something else. It was probably used in Zork Zero or one of those?

[susan-davis]

That would be useful, actually. I'm imagining a case where you use the function keys to switch to a different screen where a different character is doing something else, or perhaps to pull up a screen representing some text on a display near the PC, or an image. On a modern interpreter, or on the web, that's less of a big deal, but screen real estate is at a premium if you're in 40 x 25.

Hmm. My current WIP riffs off Suspended. If this will actually work, I'll use it.

[dstelzer]

It's possible on Z-machine, but the Å-machine doesn't currently support interrupting line input, so we'd have to think about the implications there as well. And the Å-machine only has 31 control characters available; each non-printable key uses one of these, so I'm hesitant to commit 12 of them at once, especially when the C64 only has eight.

A similar mechanism could potentially be used for timers interrupting input, which is similarly supported by the Z-machine but not made available in Dialog.

[susan-davis]

@\f1 through @\f8 is a reasonable set.