You will also run into problems if your functions close over any data:
user> (let [f (fn [] 1)] (eval `(~f)))
1
nil
user> (let [x 1 f (fn [] x)] (eval `(~f)))
IllegalArgumentException No matching ctor found for class
user$eval38616$f__38617 clojure.lang.Reflector.invokeConstructor
(Reflector.java:163)
I'm struggling with this as well, I'm definitely interested in finding
a non-hacky way to pass closures through eval without leaking memory.
Perhaps something like:
(let [x 1
f (fn [] x)
f-sym (gensym)]
(intern *ns* gensym (weak-ref f))
(with-meta (eval `(fn [] (do-stuff-with @~f))) {::strong-ref f}))
So that way f will be freed up when the resulting fn is gced.
On 28 August 2013 17:59, Ben Wolfson <wolf...@gmail.com> wrote:
> On Wed, Aug 28, 2013 at 9:27 AM, Jamie Brandon
> <ja...@scattered-thoughts.net> wrote:
>>
>>
>> If you aren't worried about leaking memory, a possible workaround is
>> to intern the fn in some namespace and then put the symbol in the
>> macro output.
>
>
> Hrm, I hope it doesn't come to that---as long as I'm creating the functions
> with their metadata, I can make things work, because I can add extra
> information to the with-meta call or do extra things when making the call.
> What I'd like, though, is for it to be possible to copy the metadata over to
> a new function by client code, just using the regular (with-meta (fn [blah]
> blah) (meta old-fn)) mechanism. But then the sneaky symbol, or whatever
> extra thing, in the metadata, that's used in the form to be eval-ed is
> pointing to the original function, not the one passed in. Maybe just
> providing a utility for fixing up the metadata is the right move, though
> it's kidn of dissatisfying.
>
>
> --
> Ben Wolfson
> "Human kind has used its intelligence to vary the flavour of drinks, which
> may be sweet, aromatic, fermented or spirit-based. ... Family and social
> life also offer numerous other occasions to consume drinks for pleasure."
> [Larousse, "Drink" entry]
>
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