On Oct 27, 4:36 pm, Chris Maier <[email protected]> wrote:
> On Wed, Oct 27, 2010 at 10:18 AM, rb <[email protected]> wrote:
> > P.s. I still don't understand though why the 'calls' argument to the
> > store-calls function is not a held reference to the head of the lazy
> > seq...
>
> I think (and someone please correct me if I'm wrong) that the head of
> 'calls' isn't being retained because you recur on (rest calls),
> replacing your hold on the head with the next item downstream. Now
> nobody's holding on to the head, so it gets GC'd. Keep recurring, and
> you just move down the sequence, always dropping what you were holding
> onto, thus allowing it all to be GC'd.
>
> Chris
Yes, this is quite clear in the case of the loop construct:
(loop [calls calls
conn nil
stmt nil
year nil
month nil]
(if-let [c (first calls)]
...
(recur (rest calls) conn stmt year month))))
The 'calls' variable bound in the loop is clearly not retained.
What bothers me is the function argument:
(defn store-calls
[source calls]
...
Here the lazy seq coming in as the second arg is bound to a local
variable named 'calls'. I would think this counts as retainment of the
head of the lazy seq (for the lifetime of the function), but it
apparently doesn't.
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