I recently saw the following message from June Kim in the Chat Forum [0].
http://procyonic.org/blog/?p=171
I miss closure in J.
which seems to imply the closures are missing in J.
Perhaps I am misunderstanding the concept but, as far as I can see,
closures or similar alternatives are available in J, at least within the
(wicked) tacit dialect which is my focus of interest.
One indication that closures (or similar alternatives) are available in J
is the solution [1] to the Rosetta Code J task Closures/Value capture,
which presumably involves closures. The following is another example: the
function derivative (verb) described in the Wikipedia entry [2] can be
implemented easily with wicked spells. ;) I am not showing at the details
because this can be an interesting future Jym exercise but the outline of
the implementation in the form of an edited session follows.
First some good news, at least from my perspective, the functionality of a
new updated version of the old Wicked Tacit Toolkit (WTT) [3] survives all
the improvements up to version Beta-9.
JVERSION
Engine: j805/j64/windows
Beta-9: commercial/2016-07-05T15:45:22
Library: 8.04.15
Qt IDE: 1.4.10/5.4.2
Platform: Win 64
Installer: J804 install
InstallPath: j:/program files/j
Contact: www.jsoftware.com
Running the (new) WTT,
(0!:1) < '/ ... /Wicked Tacit Toolkit.ijs'
NB.
NB.
----------------------------------------------------------------------------
NB. Wicked Tacit Toolkit...
NB.
----------------------------------------------------------------------------
.
.
.
Defining the producing adverb,
NB. Derivative (secant)...
Der=. ... NB. A one-liner, in terms of the utilities, is not shown to
avoid a spoiler
The defined word Der is a wicked fixed adverb; actually, it is a recurrent
adverb (aka, multiple adverb (a double adverb in this instance)). I guess
I am not spoiling much by showing its linear representation which is faulty
(unfortunately, linear representations often are faulty for complex fixed
tacit adverbs, not to mention wicked tacit adverbs).
type'Der'
┌──────┐
│adverb│
└──────┘
66 Wrap'Der' NB. It is fixed...
((("_)(((`'')(&(,^:(0:``:)&6 :.(<@:((,'0') ,&:< ]))@:(<@:((,'0') ,
&:< ])@:((<,^:(0:``:)&6 :.(<@:((,'0') ,&:< ]))@:(,^:(0:``:)&6 :.(<
@:((,'0') ,&:< ]))@:(([ ,^:(0:`@:) ,^:(0:``:)&6 :.(<@:((,'0') ,&:<
]))@:(<@:((,'0') ,&:< ])@:] ; >@:((<+)"_) ; >@:((<])"_))) ; >@:((
<-)"_) ; [) ; >@:((<%)"_) ; ] ,^:(0:`") _:)) ,~ <) ; >@:((<,~)"_)
; >@:((<<)"_))@:(,^:(0:``:)&6 :.(<@:((,'0') ,&:< ]))@:(<@:((0;1;0)
&({::))))@:[)))((`_)(`:6))))(,^:(0:``:)&6 :.(<@:((,'0') ,&:< ]))@:
((<@:((,'0') ,&:< ])@:(,^:(0:`/))@:(,^:(0:`&)) >@:((<>)"_))@:>@:{:
, <@:((,'0') ,&:< ])@:}:)@:))(((`'')(&(,^:(0:``:)&6 :.(<@:((,'0')
,&:< ]))@:((<(,'0');"_) ; ] ; (<(,'0');(@:(,^:(0:``:)&6 :.(<@:((,
'0') ,&:< ]))@:(<@:((0;1;0)&({::)))))((((`''`)(`(((@:[)(&`))(`:6))
))(`((`_)(`:6))))(`:6)))"_)@:[)))((`_)(`:6)))
( double=. *: 0.000001 Der ) NB. Is the verb double a closure (*: and
0.000001 persist)?
(*:@:(9.9999999999999995e_7 + ]) - *:) % 9.9999999999999995e_7"_
*: double 0 1 2 3 4
1e_12 4 16 36 64
Since the produced verb double is fixed it becomes independent of the
producing adverb Der. Likewise, an intermediate adverb can be defined as,
der=. 0.000001 Der NB. Is the adverb der is also a closure (0.000001
persists)?
type'der'
┌──────┐
│adverb│
└──────┘
66 Wrap'der' NB. It is fixed
("_)(((`'')(&(,^:(0:``:)&6 :.(<@:((,'0') ,&:< ]))@:((<@:((,'0') ,&
:< ])@:(,^:(0:`/))@:(,^:(0:`&)) >@:((<>)"_))@:>@:{: , <@:((,'0') ,
&:< ])@:}:)@:((9.9999999999999995e_7;,^:(0:``:)&6 :.(<@:((,'0') ,&
:< ]))@:(,^:(0:``:)&6 :.(<@:((,'0') ,&:< ]))@:(([ ,^:(0:`@:) ,^:(0
:``:)&6 :.(<@:((,'0') ,&:< ]))@:(<@:((,'0') ,&:< ])@:] ; >@:((<+)"
_) ; >@:((<])"_))) ; >@:((<-)"_) ; [) ; >@:((<%)"_) ; ] ,^:(0:`")
_:)) ,~ <)@:(,^:(0:``:)&6 :.(<@:((,'0') ,&:< ]))@:(<@:((0;1;0)&({:
:))))@:[)))((`_)(`:6)))
Again, once der is produced it becomes independent of Der because it is
fixed.
*: der
(*:@:(9.9999999999999995e_7 + ]) - *:) % 9.9999999999999995e_7"_
*: der 0 1 2 3 4
1e_6 2 4 6 8
These examples show that nouns and verbs in an "environment" can be
embedded in verbs and adverbs. Adverbs can be embedded in adverbs and
verbs, as well (and verbs, adverbs and conjunctions can be taken indirectly
as arguments by verbs and adverbs; for instance, by wrapping them in
gerunds or boxed arrays). Alas, user defined tacit conjunctions apparently
are not possible employing current official interpreters; one would have to
revert to official Golden Age interpreters or use alternative Unbox/Jx
interpreters.
I cannot pretend that I am very familiar with the concept of closures; yet,
it seems to me that, the conventional way for producing closures in J would
be via explicit adverbs or conjunctions with nested (local) explicit verbs,
adverbs or conjunctions which could be deliver as products (of course,
these constructions are not supported, not yet anyway). The methods I have
partially shown for producing fixed tacit verbs and adverbs are
unconventional (then again, J, tacit writing and wicked spells are
unconventional) but the effects seem to be the same or at least very
similar.
Any enlightenment would be appreciated.
References
[0] [Jchat] Interesting Critique of J
http://www.jsoftware.com/pipermail/chat/2016-July/007002.html
[1] Tacit (unorthodox) version in task Closures/Value capture
http://rosettacode.org/wiki/Closures/Value_capture#Tacit_.28unorthodox.29_version
[2] First-class functions in Applications of Closure (computer programming)
https://en.wikipedia.org/wiki/Closure_(computer_programming)#First-class_functions
[3] [Jprogramming] Tacit Toolkit (was dyadic J)
http://www.jsoftware.com/pipermail/programming/2015-December/043757.html
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