On Thu, May 20, 2010 at 2:26 PM, Daniel Werner
<[email protected]> wrote:
> On 20 May 2010 11:42, Anders Rune Jensen <[email protected]> wrote:
>> The algorithm:
>>
>> (defn change-state [cur-state]
>> (when (> (:value cur-state) 10)
>> (assoc cur-state :message "danger, danger")))
>>
>> How I'd have to write it when using an agent:
>>
>> (defn change-state [cur-state]
>> (cond (> (:value cur-state) 10)
>> (assoc cur-state :message "danger, danger")
>> :else cur-state))
>
> In this example, you could also have written your function using 'if',
> which is not much more complex than your original definition using
> 'when':
>
> (defn change-state [cur-state]
> (if (> (:value cur-state) 10)
> (assoc cur-state :message "danger, danger")
> cur-state))
>
> Of course, like you already said, this is a trivial example, but it
> shows an important fact about agent actions: They don't modify state.
I've been contemplating how to answer this for a little while. I think
I'll just show you the code that prompted me to write the macro:
(defn track-removed-on-agent [cur-state index]
(let [pindex (cur-state :playlist-index)]
(cond (= pindex index)
(cond
(= (count @playlist/tracks) 0) (stop-on-agent cur-state)
(>= pindex (count @playlist/tracks))
(let [new-index (dec pindex)]
(cond (= (cur-state :state) player-state/playing)
(play-track-i-on-agent cur-state new-index)
:else
(assoc cur-state :playlist-index new-index)))
:else
(cond (= (cur-state :state) player-state/playing)
(play-track-i-on-agent cur-state pindex)))
(> pindex index)
(assoc cur-state :playlist-index (dec pindex))
:else cur-state)))
Where is the bug in the above code?
Any code that can help me write code with less bugs for *free* is
welcome in my book. I don't know about yours?
--
Anders Rune Jensen
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