On Aug 30, 7:52 pm, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote:
> In the ant simulation the world function looks like this
>
> (def world
> (apply vector
> (map (fn [_]
> (apply vector (map (fn [_] (ref (struct cell 0 0)))
> (range dim))))
> (range dim))))
>
> I'm not sure why the calls to '(apply vector' are required. I have two
> theories:
>
> * It is to work round the lazy nature of map and force the creation of
> all of the refs. If this is the case, can anyone enlighten me as to
> why this might be necessary?
> * It is a performance optimisation to make lookups of faster later.
>
> A third theory is that neither of the above theories is correct.
>
> Can anyone provide me with some insight?
vector takes individual elements as arguments and map
returns a list. If we simply (vector (map ..)) the entire
list returned by map is seen as a single element. Hence
'apply'.
user=> (vector 1 2 3)
[1 2 3]
user=> (map inc [1 2 3])
(2 3 4)
user=> (vector (map inc [1 2 3]))
[(2 3 4)]
user=> (apply vector (map inc [1 2 3]))
[2 3 4]
user=>
Parth
>
> Thanks,
>
> Rob Lally.
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