I think I got it :)
The two (swap! a inc) forms are added to the map at read-time - which
is before they are evaluated. However, since we are associating the
(swap! a inc) key with a value twice, only the last one counts. So the
atom is inc'ed to 1 once (because keys can only be in the map once),
and assoc'ed with the value 2 (because that's the second assoc we're
doing to the (swap! a inc) form).
The PersistantArrayMap, on the other hand, is more gullible and
trusting towards the parsed array of forms that the reader presents
it, and therefor accepts the (swap! a inc) key twice, which in turn
causes it to evaluate twice; into two different keys with two
different associations.
On Tue, Feb 17, 2009 at 8:28 PM, Christian Vest Hansen
<karmazi...@gmail.com> wrote:
> That's odd.
>
> Might you have uncovered a bug regarding:
>
> user=> (class {1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9})
> clojure.lang.PersistentHashMap
> user=> (class {1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8})
> clojure.lang.PersistentArrayMap
>
> While with the atom code we have:
>
> user=> (class (let [a (atom 0)] {(swap! a inc) 1 (swap! a inc) 2 3 3 4
> 4 5 5 6 6 7 7 8 8 9 9}))
> clojure.lang.PersistentArrayMap
> user=> (class (let [a (atom 0)] {(swap! a inc) 1 (swap! a inc) 2 3 3 4
> 4 5 5 6 6 7 7 8 8}))
> clojure.lang.PersistentArrayMap
>
>
>
> On Tue, Feb 17, 2009 at 8:03 PM, Christophe Grand <christo...@cgrand.net>
> wrote:
>>
>> While kicking the tires, I encountered this "behavior":
>>
>> user=> (let [a (atom 0)] {(swap! a inc) 1 (swap! a inc) 2 3 3 4 4 5 5 6
>> 6 7 7 8 8 9 9})
>> {3 3, 4 4, 5 5, 6 6, 7 7, 8 8, 9 9, 1 2}
>> user=> (let [a (atom 0)] {(swap! a inc) 1 (swap! a inc) 2 3 3 4 4 5 5 6
>> 6 7 7 8 8})
>> {1 1, 2 2, 3 3, 4 4, 5 5, 6 6, 7 7, 8 8}
>>
>> Granted, it's not casual Clojure code but it's surprising.
>>
>> Christophe
>>
>> --
>> Professional: http://cgrand.net/ (fr)
>> On Clojure: http://clj-me.blogspot.com/ (en)
>>
>>
>>
>> >>
>>
>
>
>
> --
> Venlig hilsen / Kind regards,
> Christian Vest Hansen.
>
--
Venlig hilsen / Kind regards,
Christian Vest Hansen.
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