Sorry, I guess that wasn't very clear. Let's put a really simple
example with just the pattern-matching subset:
strucjure.regression.sandbox=> (def p (pattern [1 ^x _ 3]))
#'strucjure.regression.sandbox/p
strucjure.regression.sandbox=> p
[1 #strucjure.pattern.Bind{:symbol x, :pattern #strucjure.pattern.Any{}} 3]
strucjure.regression.sandbox=> (def o (output ~p (fnk [x] x)))
#'strucjure.regression.sandbox/o
strucjure.regression.sandbox=> o
#strucjure.pattern.Output{:pattern [1 #strucjure.pattern.Bind{:symbol
x, :pattern #strucjure.pattern.Any{}} 3], :fnk #<
clojure.lang.AFunction$1@18ab1e1c>}
strucjure.regression.sandbox=> ((view ~p) [1 2 3])
[[1 2 3] nil]
strucjure.regression.sandbox=> ((view ~o) [1 2 3])
[2 nil]
strucjure.regression.sandbox=> (pprint (macroexpand-1 '(view ~o)))
(fn
[input3910]
(clojure.core/when
(clojure.core/vector? input3910)
(clojure.core/when
(clojure.core/>= (clojure.core/count input3910) 3)
(clojure.core/let
[input-sym3911 (clojure.core/nth input3910 0)]
(clojure.core/when
(clojure.core/= input-sym3911 '1)
(clojure.core/let
[input-sym3912 (clojure.core/nth input3910 1)]
(clojure.core/let
[x input-sym3912]
(clojure.core/let
[input-sym3913 (clojure.core/nth input3910 2)]
(clojure.core/when
(clojure.core/= input-sym3913 '3)
[(#<sandbox$fn__3090$pos_fn__1649__auto____3091
strucjure.regression.sandbox$fn__3090$pos_fn__1649__auto____3091@62b1f96f>
x)
(clojure.core/seq (clojure.core/subvec input3910 3))])))))))))
You can see towards the end of the generated code where it calls the
fnk directly as #<sandbox$fn__3090...>
The motivation here is that you can define the grammar for a language
once and then make different transformations by attaching output fnks.
It would be very useful if those output fnks could be closures.
It's not obvious in this small example but the compiler produces some
important optimisations, otherwise I could just interpret the grammar
and there would be no problem.
In general, for staged programming it's useful to be able to pass
arbitrary data between stages eg metaocaml
(http://okmij.org/ftp/ML/MetaOCaml.html) often passes refs between
stages. I think some of the terra (http://terralang.org/) examples
pass closures too.
On 28 August 2013 20:54, Aaron Cohen <aa...@assonance.org> wrote:
> This is a little hard for me to follow because I'm not sure what graph or
> output-in are doing.
>
> If the letfn is being generated by your compilation step, why can't that go
> inside of your generated fn rather than outside it?
>
> (clojure.core/fn
> [input__2288__auto__]
> (clojure.core/letfn
> [(num ...)
> (succ ...)
> (zero ...)]
> (num input__2288__auto__)))
>
>
> 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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