I created a new datatype to solve this problem:
http://gist.github.com/958001
c-fn creates a comparable function;
(let [fnmaker4 (fn [coll] (c-fn [n] (nth coll n)))
ints (range)]
(= (fnmaker4 ints) (fnmaker4 ints)))
=> true
On Thu, May 5, 2011 at 10:41 PM, Alan <a...@malloys.org> wrote:
> On May 5, 1:28 pm, Ken Wesson <kwess...@gmail.com> wrote:
> > On Thu, May 5, 2011 at 4:16 PM, Alan <a...@malloys.org> wrote:
> > > (let [fnmaker4 (fn [coll] (fn [n] (nth coll n)))
> > > ints (range)]
> > > (= (fnmaker4 ints) (fnmaker4 ints)))
> >
> > > You want to make it impossible to compare functions that close over
> > > infinite sequences? What is the point of being able to compare
> > > functions if there are cases in which using the functions will
> > > succeed, and the existing comparison strategy would not cause errors,
> > > but your new proposal does?
> >
> > Hm, that is a problem. You'd need to compare not the sequences, but
> > their generator functions. :)
> >
> > > Similarly, if you try to eval such a function, your proposed function-
> > > eval semantics would, as I understand it, store its closed-over values
> > > in a class constant somewhere. Then there's some secret place holding
> > > onto the head of my lazy sequences for me? No thanks.
> >
> > Your fnmaker4 already holds onto the head of ints, above, so that this:
> >
> > user=> (def q (fnmaker4 (iterate inc 0)))
> > #'user/q
> > user=> (q 119)
> > 119
> > user=> (q 0)
> > 0
> >
> > can work properly.
>
> Right. But if I drop all references to the returned function after I'm
> done with it, it gets GCed. If there's some class holding a reference
> to it forever, it will never get cleaned up. For example, ((fnmaker4
> (range)) 1e6) will (I think?) currently result in a million ints being
> held in memory at once, as things are now. Those things will get
> thrown away shortly thereafter, though. I'm not sure I fully
> understand your proposal, but it seems to me like you might be making
> these stick around permanently if I include the right mixture of eval,
> quoting, and unquoting in that expression.
>
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