[colorforth] Extending the character set - Take II

[Bill Parker <hodjiii@xxxxxxxxx>]

I'm still on my personal crusade to kick the
ColorForth 'space' character out of it's premium 4-bit
spot.  I have looked at quite a bit of ColorForth code
samples (from the net) and have yet to find an
instance where space-terminated compression results in
a smaller compressed data stream than simply appending
a 'last character' bit.

Here is the latest idea that I am playing around with
for an alternate use of the 0 000 encoding slot:

Use the 0 000 as a 'shift' character which changes the
interpretation of the character which follows.  a-z
become A-Z and the other encodings fall out as
follows:

1101 000 K  [was k]   1110 000 <  [was 8]
1101 001 Z  [was z]   1110 001 (  [was 9]
1101 010 J  [was j]   1110 010 '  [was 1]
1101 011 #  [was 3]   1110 011 _  [was -]
1101 100 $  [was 4]   1110 100 )  [was 0]
1101 101 %  [was 5]   1110 101 >  [was .]
1101 110 ~  [was 6]   1110 110 "  [was 2]
1101 111 &  [was 7]   1110 111 |  [was /]

The entire bank of 1111 encodings is open so they are
available for the user to define their own
application-specific symbols.

Note that the 'shift' character may not be the last
character within a 32-bit word (since it is then
indistinguishable from the normal zeroes which pad out
the end of word).  In comments, this means that the
shift character must 'travel' to the next 32-bit word
when it is discovered that the character it applies to
will not fit within the current 32-bit word.

The addition of edit-time complexity (and perhaps a
little at load/display time as well) doubles the
available character set size.  Entering the 'shift'
character becomes a mode that modifies subsequent
menus the user is presented so this fits nicely into
the existing 24-key user interface.  (In fact, the
mismatch with the user interface is why I ultimately
abandoned my earlier attempts at extending the
character set.)

And, perhaps the nicest feature of all.  An extended
character set ColorForth is completely compatible with
existing ColorForth source blocks.  None of the
existing encodings are alterred so you can freely
import standard ColorForth source blocks.  You may
also freely export source blocks which do not contain
any 'shift' characters to a standard ColorForth system.

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