Basically, yes. It's interesting that you refer to them that way; it brings
to mind locales, which are another type of namespace, and suggests the
possibility of unifying lexical environments with locales. I think doing that
would be a bad idea, though, because locales are shared mutable state, and it
would be good to have less of that rather than more. Hence, my proposal
applies only to lexical scopes.
The idea is that, if I have something like:
f=. {{
a=. 5
b=. 6
g=. {{ ... a ... }}
a=. 7
... }}
When g (or, rather, the verb it denotes) is created, it will remember and
carry around the lexical environment in which it was created, which includes
an association between a and 5. (Since g refers to a, we say that it 'closes
over' it. The term 'closure' comes from graph theory.) This association is
frozen at the time g is created; hence, it never sees a=5. The environment is
manifest in the AR as a list of key-value associations; users can twiddle or
create their own environments, but should not generally have much call to.
Obviously, this comprises a break to compatibility, but the fallout seems
fairly minor. Such name punning would be quite confusing.
Since closure only applies to lexical variables, this breaks no use of
globals. EG the following, at global scope:
a=: 5
fn=: {{ ... a ... }}
a=: 7
Will work just the same as it ever did.
A question: should g close over b? It is not referred to directly in g, but
the latter might construct references to b using "., or a user might ask for
it when debugging. I vote no, because of the potential for space leaks. g
can include a dummy reference to b, if it really wants; and perhaps a global
toggle can be added for debugging purposes. (This also relates to my comment
in github issue #153.)
What say?
-E
On Tue, 17 Jan 2023, Henry Rich wrote:
Is it about namespaces then? That is indeed a vexed question. I will
take this under advisement. I will need more help I'm sure.
Henry Rich
On 1/17/2023 10:15 PM, Elijah Stone wrote:
It is the other way around--lack of closures means we must write
_more_ tacit code, not less. E.G.:
{{
a=. something
{{ something referring to a }} A y NB. doesn't work
}}
Whereas:
{{
a=. something
(something referring to a) A y NB. works
}}
I am proposing a mechanism to make the former work (among other things).
On Tue, 17 Jan 2023, Henry Rich wrote:
I don't follow any of this thread, because I don't understand what is
missing from standard J. I find J adequate for everything I want to
do. What am I missing?
I can see that if you want to write all-tacit code you have trouble
if you need to feed a verb result into a modifier.
Suppose though that I am content with writing explicit definitions.
What do I need beyond the standard language, and for what use case?
Henry Rich
On 1/17/2023 9:23 PM, Elijah Stone wrote:
(Curried modifiers, as you say, are a solution, but, again, another
half-solution.)
On Tue, 17 Jan 2023, Raul Miller wrote:
Here, I suspect that you're only getting noun values in your closure
-- you'll have to sprinkle those noun references with something like
`:6 if you want anything else. That's probably not a huge problem.
But, thinking about this, personally I'm not seeing a lot of
motivation for this approach, either. (What problems would this solve?
I'm sure there are some great motivating examples out there. And
closures certainly have a lot of popularity. But... position in a list
can be thought of as being conceptually analogous to a variable, so it
should be apparent that we already have some support for the
algorithmic role of closures.)
(I should perhaps also note, here, that conjunctions and adverbs which
have verb results are self-currying.)
Anyways... I'm not thinking particularly deep thoughts here -- I'm
just reflexively reaching for motivating examples (which might assist
in forming some of those sorts of thoughts).
Thanks,
--
Raul
On Tue, Jan 17, 2023 at 7:01 PM Elijah Stone <elro...@elronnd.net>
wrote:
I suggest:
[x] u &:: (k;v;k;v...) y
Will evaluate u with bindings kvkv... (raveled) active. Should
work for both
explicit and tacit. Implementation is allowed to coalesce; e.g.,
u &:: (k;v)
&:: (k;v) `'' may be rendered u &:: (k;v;k;v), deduplicated, &c.
Substitution also ok; eg (f%#) &:: ('f';+/`'') becomes +/%#.
I would like for verbs defined inside of explicit verbs to be
implicitly
closed; this is obviously a compat break, but.
On Tue, 17 Jan 2023, Elijah Stone wrote:
> I don't love the proposal, as I think a conception of verbs as
first class
> should involve _less_ hackery with representations, not more.
But I don't
> feel that strongly either way.
>
> More fruitful, IMO, would be to work out how to add closures, as
I think
> there
> is a more urgent need for that (u./v. is a band-aid). Perhaps
taking
> inspiration from kernel (but skipping the mutation!).
>
> On Mon, 16 Jan 2023, Henry Rich wrote:
>
>> I have never understood the zeal for having verbs return verbs,
but it
>> must be real if some are willing to use dangerous backdoor
hacks into JE
>> to achieve it. ARs make it possible to pass verbs around, but
executing
>> them requires dropping into explicit code. To remedy this, I
offer a
>> proposal, backward compatible with older J:
>>
>> 1. (". y) and Apply (x 128!:2 y) to be modified so that if the
result of
>> execution is not a noun, it is replaced by its AR (instead of
'' as
>> previously).
>>
>> 2. (". y) and Apply to be modified so that if y (for ".) or x (for
>> Apply) is boxed, the sentence is executed as usual except that
each box
>> is converted using (box 5!:0) before being put onto the
execution stack.
>>
>> The idea is that you can execute (".
>> expr-producing-AR,exp-producing-AR,...) without having to get any
>> modifiers involved.
>>
>> Sentence execution can produce ARs, and can take ARs created by
verbs to
>> represent verbs and modifiers. That sounds pretty classy to
me, but I
>> don't know whether it's first-class.
>>
>> Henry Rich
>>
>>
>>
>>
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