On 10/03/13 12:32, Gary Verhaegen wrote:
Not all of your application can be purely functional, because it
inevitably needs to interact with the outside world at some point.
yes that is true...however, I often find that my first impression of
what the functional boundaries are, is not necessarily the correct
one...for example, when I started writing my board-game engine, I was
pretty sure that when the time comes to code chess I'd need side-effects
to achieve castling and en-passant moves (because they depend on other
pieces and their state). At the time I was pretty happy introducing
limited side effects.
Having finished my engine ,and after having coded fully functional
implementations of chess, checkers and tic-tac-toe I can confirm that I
did not need side effects anywhere other than showing stuff on screen
and talking to the disk (for saving-loading games). Absolutely nothing!
Both castling and en-passant can be coded with the help of meta-data and
a specialised mover (a higher order fn) for such occasions...nothing
more - nothing less! it wasn't immediately apparent how - but it was
indeed possible and in fact very elegant!
of course, now you will ask : 'how is performance in such a purely
functional and cpu-intensive game?'
Well, I don't have a good answer for that until I manage to add pruning
to my parallel minimax. at the moment and after numerous optimizations,
I can do an exhaustive search down to level 4 usually in less than 8sec
with an average branching factor of 26. In the best case, pruning can
cut this down in half which sounds pretty impressive if I ever manage it!
Jim
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