"Jim - FooBar();" <jimpil1...@gmail.com> writes:
>> What's update-position? Shouldn't that be (updatePosition p coords),
>> as you say IPieces have an updatePosition method? And since you use
>> that for side effects (you don't use the return value), are your
>> IPiece implementors actually deftypes with :volatile-mutable or
>> :unsynchronized-mutable fields?
>
> No, my IPiece implementors are records that hold a java.awt.Point
> object. This is indeed the only piece of mutable state in the whole
> namespace. (updatePosition p coords) will simply call 'setLocation()'
> on the Point of p. Are you saying that my defrecords should be
> deftypes?
No no, I assumed you were in plain-clojure land, and then
(do (updatePosition p ...)
...)
suggests that p is mutable. defrecords aren't mutable, but deftypes can
be made mutable. But of course, if your defrecords have mutable java
objects as fields, your code makes sense again.
But probably that's not a good approach. When mutating the positions in
a move, there's no way back. If everything was immutable, i.e.,
updatePosition would return a new piece with different coords (as vector
or map), then your game engine could try abritrary many moves (creating
new worlds/game boards) ahead of time to judge what moves lead to
success, and then perform the best (or a good) one, i.e., alter the ref
representing the current board with the board where one piece has moved.
Now, you can't plan because when trying out a move, you've already
changed the world.
I think the book Land of Lisp by Conrad Barski has an entertaining
chapter where he implements some game engine that plans moves ahead and
judges their benefit. It's in Common Lisp, but he does it functionally
without mutation.
Bye,
Tassilo
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