Yeah, as far as I can tell eval can't emit pointers so we can't pass
closures or references at all except by indirection through an
existing singleton (like a named var).
On 28 August 2013 19:34, Aaron Cohen <aa...@assonance.org> wrote:
> Sorry, that one doesn't work. It worked in my repl, but I must have been
> using old code.
>
>
> On Wed, Aug 28, 2013 at 2:27 PM, Aaron Cohen <aa...@assonance.org> wrote:
>>
>> How about this alternative?
>>
>> (deftype Wrapper [f]
>> clojure.lang.IFn
>> (invoke [this] (f))
>> (invoke [this a] (f a))
>> ; repeat until you get bored
>> )
>>
>> (defn e [f]
>> (let [wr (Wrapper. f)]
>> (eval `(~wr 1))))
>>
>> (e inc)
>>
>> (e (with-meta (fn [x] (+ 4 x)) {}))
>>
>>
>>
>> On Wed, Aug 28, 2013 at 1:59 PM, Jamie Brandon
>> <ja...@scattered-thoughts.net> wrote:
>>>
>>> That sort of works for my use case.
>>>
>>> What I want to do is define a grammar...
>>>
>>> (def num-graph
>>> (graph
>>> num ~(or ~succ ~zero)
>>> succ (succ ^x ~num)
>>> zero zero))
>>>
>>> ... attach actions ....
>>>
>>> (def num-out
>>> (output-in num-graph
>>> 'zero (fnk [] 0)
>>> 'succ (fnk [x] (inc x))))
>>>
>>> ... and compile the result ...
>>>
>>> strucjure.regression.tests> (graph->view 'num num-out)
>>> (clojure.core/letfn
>>> [(num ...)
>>> (succ ...)
>>> (zero ...)]
>>> (clojure.core/fn
>>> [input__2288__auto__]
>>> (num input__2288__auto__)))
>>>
>>> This works fine as long as the fnks dont close over anything, but
>>> that's very limiting.
>>>
>>> If I eval that code and *then* wrap it in (binding ...) I can have
>>> closures but that now means that I can't do call-site compilation.
>>> I'll have to poke around a bit more...
>>>
>>> On 28 August 2013 18:32, Aaron Cohen <aa...@assonance.org> wrote:
>>> > I'm not sure if you'll consider this hacky or not.
>>> >
>>> > (def ^:dynamic *fn-helper*)
>>> >
>>> > (defn eval-at-one [f] (binding [*fn-helper* f] (eval '(*fn-helper*
>>> > 1))))
>>> >
>>> >
>>> > On Wed, Aug 28, 2013 at 1:28 PM, Jamie Brandon
>>> > <ja...@scattered-thoughts.net> wrote:
>>> >>
>>> >> 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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