Dan writes:
"
One frustration I encountered which significantly complicated the solution
was that this:
adverbWhichProducesAnAdverb =: 1 : '/'
anotherAdverb =: ~
totalAdverb =: adverbWhichProducesAnAdverb anotherAdverb
+ totalAdverb
|syntax error: totalAdverb
| +totalAdverb
is a syntax error in J. I haven’t thought through why that is, or should
be, the case (grammatically speaking), but this is not the first time it’s
tripped me up [2].
In the case of the pare.ijs script, it precluded any meaningful amount of
code reuse. If someone has a grammatical explanation for this error, I’d
love to be walked through it.
"
This is my take:
The sentence ( x a0 a1 ) is equivalent to ( (x a0) a1 ); so, when (x a0)
produces an adverb, ( (x a0) a1 ) produces a train of two adverbs. In
contrast, ( x (a0 a1) ) tries to pass the adverb (x a0) as an argument to
the adverb (a1) but this is not permitted and the current official J
complains accordingly; older J interpreters allowed it but this bug (or
facility, depending on your perspective) was removed and I can only blame
myself for that :j [0]. This facility is restored in a Jx permissive
interpreter [1], and it might help to clarify the issue:
JVERSION NB. J...
Installer: j602a_win.exe
Engine: j803/2014-10-19-11:11:11
Library: 6.02.023
(<'/') `:6 <adv
/(("_)(((`'')(&(<@:(,^:(0:``:)&6@:(<@:((0;1;0)&({::))))@:[)))((`_)(`:6))))
((<'/') `:6) <adv
/(("_)(((`'')(&(<@:(,^:(0:``:)&6@:(<@:((0;1;0)&({::))))@:[)))((`_)(`:6))))
(<'/') (`:6 <adv)
|syntax error
| (<'/')(`:6<adv)
|[-5]
In comparison,
JVERSION NB. Jx...
Installer: j602a_win.exe
Engine: j701/2014-10-14/10:02/x/wd
Library: 6.02.023
(<'/') (`:6 <adv) NB. Boxing the / adverb boxed
┌─┐
│/│
└─┘
(<'"') (`:6 <adv) NB. Boxing the " conjunction
┌─┐
│"│
└─┘
I hope it helps.
[0] [Jprogramming] J Myths Puzzles
http://www.jsoftware.com/pipermail/programming/2008-February/009871.html
[1] [Jprogramming] J Extensions
http://www.jsoftware.com/pipermail/programming/2014-March/035925.html
On Tue, Dec 15, 2015 at 6:23 PM, Dan Bron <[email protected]> wrote:
> Raul wrote:
> > Yeah... personally, I consider explicit code to be a subset of tacit
> code.
>
> I think of explicit and tacit as two distinct but related languages. That
> “:” is tacit doesn’t mean the programs written in it are tacit: I could
> (theoretically) write a tacit Lisp interpreter, but that doesn’t mean the
> Lisp programs I pass to it are written in J.
>
> > Still, even if you do not like the appearance of the code I offered,
> > perhaps you could at least tell me if there is something wrong with
> > what it does?
>
> This question somewhat misses the point.
>
> Say this were English class and I asked you to compose a haiku on the
> topic of winter. Say then that you came back with a sublime, stirring
> sonnet on winter that captured the bitter winds; the trees sparking with
> ice crystals as if they were fruiting diamonds; the lamps glowing in
> twilight windows; the yearning for spring. In short, you delivered to me a
> beautiful poem which precisely evoked the subject. A work of art whose like
> hasn’t been seen before in the world.
>
> Except the assignment was a haiku, and you gave me a sonnet.
>
> In other words, the “how” is not a means here, but an end. The requirement
> for tacit is precisely that: a requirement. It is a fundamental part of the
> specification, not a suggestion on coding style. Note that, absent this
> requirement, Am would *not be required at all*, as we could simply write
> the target modifiers explicitly and dispense with the intermediate
> metaprogramming step.
>
> If it helps, your audience is J programmers, not end users. The result to
> keep your eye on is the *actual notation*, not the output of the program.
> The object is not to transform inputs to outputs, but to assist J
> programmers in writing purely (purely!) tacit code. Just as there are
> guides on how to compose haikus, here we are writing a guide on how to
> write J, tacitly.
>
> If you want to talk about *why* that’s a goal, I’d be happy to have that
> conversation (but not today; I’m not feeling very eloquent).
>
> So: yes, absolutely, your code produces the correct output for a given set
> of inputs. But while that’s necessary, it’s not sufficient.
>
> It may help clarify my aims if I provide an example of what I’m looking
> for. So I went ahead and implemented the idea I referenced earlier:
>
> > Exercise for the very ambitious reader: define a tacit adverb opTheat
> > (operating theatre), which, given a verb (the surgeon), derives another
> > tacit adverb, such that
> >
> > surgeon opTheat
> > ((<":0)`) (surgeon`) (@.(0; 1 2))
> >
> > The objective is to be able to provide an convenient utility / interface
> for
> > adverbial programmers, so that their responsibility is only to write the
> > core a.r.-transforming function (i.e. perform the surgery), and not
> always
> > have to prepare the patient and the operating theatre themselves.
>
>
> You can see the implementation at [1], but the short story is you can now
> create perfectly tacit adverbs simply by creating a (tacit) verb which
> expects an atomic representation as input, and produces another atomic
> representation as output.
>
> This permits us to produce arbitrary J structures, of any part of speech,
> tacitly. Here’s the example we’ve been working with from Pepe:
>
> NB. Given the fork (v0 v1 v2), bends the outer tines
> NB. such that it produces (v0@[ v1 v2@])
> NB. For rationale, see the thread:
> NB.
> http://www.jsoftware.com/pipermail/programming/2015-December/043657.html
> xform =. (left center right)`'' ('[' atop~ ])`(']' atop~
> ])`]@.((;:'left right') i. [)"0 L:1 ]
> atop =. '@' <@; <@:,&boxopen
>
> Notice this is simply a tacit verb which both operates on and produces the
> atomic representation of a simple 3-verb train. Now, we only need to pass
> this verb to our magical new adverb, and:
>
> (+: + -:) xform Pare
> +:@[ + -:@]
>
> Thus:
>
> 3 4 (+: + -:) xform Pare 2 4
> 7 10
>
> Or, as a simpler example, the identity adverb:
>
> + ]Pare
> +
> +/ ]Pare
> +/
> 3 ]Pare
> 3
> a: ]Pare
> ++
> ||
> ++
>
> Note that this actually executed the resulting a.r. to produce a (derived)
> entity. Returning to the original goal of Am, which was simply to produce
> the a.r. directly and defer execution to the caller, then:
>
> Ar =: ] Par NB. Note “Par”, not “Pare” (no “e, no Execution)
>
> +/ Ar
> +-------+
> |+-+---+|
> ||/|+-+||
> || ||+|||
> || |+-+||
> |+-+---+|
> +-------+
>
> (+/ % #) Ar
> +-----------------+
> |+-+-------------+|
> ||3|+-------+-+-+||
> || ||+-+---+|%|#|||
> || |||/|+-+|| | |||
> || ||| ||+||| | |||
> || ||| |+-+|| | |||
> || ||+-+---+| | |||
> || |+-------+-+-+||
> |+-+-------------+|
> +-----------------+
>
> Now, the implementation is rough and I’m sure there’s room for
> improvement, but note to Pepe: no wickedness was employed :)
>
> One frustration I encountered which significantly complicated the solution
> was that this:
>
> adverbWhichProducesAnAdverb =: 1 : '/'
> anotherAdverb =: ~
>
> totalAdverb =: adverbWhichProducesAnAdverb anotherAdverb
>
> + totalAdverb
> |syntax error: totalAdverb
> | +totalAdverb
>
> is a syntax error in J. I haven’t thought through why that is, or should
> be, the case (grammatically speaking), but this is not the first time it’s
> tripped me up [2].
>
> In the case of the pare.ijs script, it precluded any meaningful amount of
> code reuse. If someone has a grammatical explanation for this error, I’d
> love to be walked through it.
>
> -Dan
>
> [1] Pare script: Process Atomic Representations and Execute:
> http://www.jsoftware.com/svn/DanBron/trunk/environment/pare.ijs <
> http://www.jsoftware.com/svn/DanBron/trunk/environment/pare.ijs>
>
> [2] Verb pipeline utility foundering on the inability to create adverb
> trains via derived adverbs:
> http://www.jsoftware.com/pipermail/programming/2010-June/019755.html <
> http://www.jsoftware.com/pipermail/programming/2010-June/019755.html>
>
>
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
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