Game variations

[Yann Dirson]

Here are a couple of thoughts about how we could allow game variations
to be used, for greater user convenience. Do any of you have other
ideas about using variations, that would need enhancements in tagua ?

Listing all of them early would make it easier to get a good design
early on, if things have to be changed.

- [practicing against an AI player] when the player realizes one of
his moves was really bad, he could just select the move to be changed,
and request tagua to "rewind to here", while moving those moves to a
variation, and continue playing the main game. Currently, we can
either use undo (and lose knowledge about one's own weaknesses, from
which there may be things to learn), or continue playing in a
variation, which is not really what variations are usually used for.

- when preparing a move (against AI or network player), it would be
nice to allow the player to simulate some moves (as one could do with
a real board besides the computer ;) before choosing one's move.
Obviously the game's mainline is not a good place for such moves, so
using a variation for this would be nice.

Both of these seem to require allowing a variation with an empty
mainline, which is not possible to represent in tagua currently (as I
gathered from some comments in the code), and which is not possible to
represnt in a standard PGN file either. However, I have seen
described a PGN non-standard extension which can represent this:
whereas the "<move> ( ... )" syntax is a "variation branch rooted
before <move>", the "(* ... )" syntax is a "variation branch rooted
here". See "Continuations" in
http://www.enpassant.dk/chess/palview/manual/pgn.htm#pgntagsnewp4

Best regards,
--
Yann

[Paolo Capriotti]

I like both proposals, and think that using that nonstandard PGN
extension is a good idea.
Here is a ticket for this issue: http://trac.tagua-project.org/ticket/72

Another possible enhancement could be a "detach" feature where you
select a move, click "detach", and have the whole variation leading to
that move (plus all the variations after it) appear in another tab (or
another window, but that's a different story). That could also be used
to study variations while playing against an AI or on the internet.


Paolo