Next steps for BASIC

[rikardn]

I need some guidance on how to proceed with the MS-BASIC.

Currently there is no more room to add things to the BASIC ROM so we would need to remove parts or all of the current BASIC implementation to make room for the MICROSOFT implementation. Do we want to keep the current implementation or parts of it? Any other ideas?

[FeralChild64]

We'll definitely need to replace some of our implementation with the space-optimized Microsoft. I can immediately think of two areas:

1. Compressed messages - these were developed in part to avoid huge similarity with BASIC and to have a different mechanism.
   It's possible that getting rid of the compression mechanism and storing everything using the Microsoft format might actually save us some ROM bytes (at least for the plain C64 build), because the decompression routines also takes some space (print_packed_freq_string.s alone is 105 bytes; a routine for uncompressed strings would be like 10 times smaller).
   Challenge: the MEGA65 build is smart and puts these strings in one of the extra ROM blocks, that's why even with transcendentals and dos/tape wedges enabled and larger memory model it still has about 1 KB space free in the BASIC_0 block. You would need to adapt this too. But it should be rather easy to use XEMU MEGA65 emulator (https://github.lgb.hu/xemu/) to test this.

2. BASIC strings with back pointer - I have implemented BASIC string support in a way similar to what BASIC 3.5 implements - they use a backpointer to speed up the garbage collection. You could make this mechanism optional to save some space. But the MEGA65 build should definitely use my implementation, as we don't suffer from ROM shortage that much there.
   Challenge: enhanced memory models (over 38K) might need additional adjustments.

[FeralChild64]

(BTW - I have enabled the transcendentals also for MEGA65 build)

[rikardn]

Since the current partial BASIC has a totally different architecture from the Microsoft BASIC it would be really hard to add the Microsoft BASIC incrementally. Also adding different memory models etc to the Microsoft BASIC would be a big undertaking.

A feasible strategy would be to add the Microsoft BASIC as it is and make it possible to select between the two BASICs. When the MS-BASIC is working consolidation of the two could be possible, but I don't see that its going to be easy. Perhaps moving one feature at a time into the MS-BASIC could work. This needs to be optional to keep the original BASIC intact if desired.

[FeralChild64]

That was the initial idea - to only provide several known routines at well-known location, for compatibility purposes, but implement everything differently, as far as only possible, to avoid possible copyright claims.

I'll have a look at your latest PR, but not today. I don't want to promise anything, but I intend to spend some time on this project again. The situation has changed - there seems to be more interest, the MEGA65 bistream became more mature, and now open-sourcing of Microsoft BASIC.