[Jprogramming] Nested structures. Idioms? Combinators?

Fri Feb 12 03:11:27 UTC 2016

 > Forgive me if I'm wrong, but I don't see a discussion of 'expressions 
to the
 > right of zero' (such as '-.LF' in '0 : 0 -. LF')
 > in either of your links.

No.  But that isn't surprising when you understand what's going on.

0 : 0 creates a noun.

Because conjunctions are executed before verbs,

0 : 0 -. LF

is the same as

(0 : 0) -. LF

(0 : 0) creates a noun that can be used just as any other noun is used.  
You can add to it, subtract from it, execute it...  The (-. LF) has 
nothing to do with the execution of (:).  What I'm saying is, if you are 
OK with something like

".;._2 (0 : 0)

[which feeds the result of (0 : 0) into a verb], you should ipso facto 
be OK with

(0 : 0) -. LF

which also feeds that result into a verb, just from the left this time.

The (:) in (0 : 0) is executed WHEN (:) IS EXECUTED, i. e. at the 
appropriate time during the parse [see NuVoc for explanations]. After 
(:) has read its fill, execution of the sentence continues. So, you can have

    (0 : 0) ,&(".;._2) (0 : 0)

1 2 3

)

10 20 30

40 50 60

70 80 90

)

10 20 30

40 50 60

70 80 90

1 2 3

Two (0 : 0) in one sentence [the parentheses are not required]! and 
executed right-to-left.

(".) has unlimited potential, but often is put to mundane use. When I 
was starting with J I felt a frisson of daring when I used it, but now 
it's just another verb to me.

Henry Rich

>
> I'd welcome any correction.
>
> Cheers.
> It's pretty well explained at
>
> http://code.jsoftware.com/wiki/Vocabulary/NounExplicitDefinition
>
> The question is, How would you know to read that?  Suggestions welcomed.
>
> When you say "expression following the 0", I'm not sure which 0 you mean.
>
> : is the all-purpose entity creator; the left 0 says 'create a noun', and
> the right
> 0 says 'make that noun from the upcoming lines of input'.
>
> Full details are spelled out in several pages starting at
> http://code.jsoftware.com/wiki/Vocabulary/cor
>
> Henry Rich
>
>
> On 2/11/2016 12:55 AM, Matthew Baulch wrote:
>
>> Thanks everyone. This (let's say) creative use of 0 : 0 makes sense to me
>> now. I wonder if it's an accidental consequence of the implementation that
>> allows an expression following the 0, or whether it's a deliberate design
>> decision. Either way, it makes sense to have it documented. Can't see it in
>> NuVoc or the Dictionary. Of course, I may have overlooked it.
>>
>> Honestly, to obtain something simple like multi-line noun definitions, ".
>> does seem like quite a heavy-handed tool. It does work however, so I
>> probably shouldn't grumble.
>>
>> Cheers.
>>
>> On Wed, Feb 10, 2016 at 10:29 PM, Matthew Baulch <baulch.matt at gmail.com>
>> wrote:
>>
>> Looking at this more closely now. I'm a bit puzzled about the use of -.
>>> here. Obviously this is used here in dyadic form. In x -. LF the LF
>>> characters are, of course, removed from x. What is the x here? I have seen
>>> that it works--not doubting that. Just trying to work out how. Sorry.
>>> There's probably something obvious I've missed.
>>>
>>> On Wed, Feb 10, 2016 at 12:52 AM, Raul Miller <rauldmiller at gmail.com>
>>> wrote:
>>>
>>> If you do not have good names for partial calculations, that might be
>>>> a sign that you need to think a bit more about the abstractions you
>>>> are using. It can be difficult for other people to read if you don't
>>>> make sufficient effort to label your abstractions.
>>>>
>>>> Also, I would note that your 'c0' is not a combinator, as you are not
>>>> using its dyadic definition. So you might want to use a different name
>>>> for that one. Perhaps:
>>>>
>>>> v0=:c0
>>>>
>>>> That said, if you really want to execute really long lines, you can do
>>>> that using ". 0 :0-.LF and indented text. (You need the indentation
>>>> because line feeds will not separate words here.)
>>>>
>>>> For example:
>>>>
>>>> myStruct=: ". 0 :0-.LF
>>>>     v0 p0 c1 p1 c2 p2 c3 p3 c4 p4 c5 p5 c6 p6 c7 p7 c8 p8 c9 p9
>>>>     c10 p10 c11 p11 c12 p12 c13 p13 c14 p14 c15 p15 c16 p16 c17
>>>>     p17 c18 p18 c19 p19 c20 p20 c21 p21 c22 p22 c23 p23 c24 p24
>>>>     c25 p25 c26 p26 c27 p27 c28 p28 c29 p29 c30 p30
>>>> )
>>>>
>>>> I hope this helps,
>>>>
>>>> --
>>>> Raul
>>>>
>>>> On Tue, Feb 9, 2016 at 4:59 AM, Matthew Baulch <baulch.matt at gmail.com>
>>>> wrote:
>>>>
>>>>> Suppose I wish to construct a complex, non-regular deeply nested
>>>>>
>>>> structure:
>>>>
>>>>> to model some inherently non-linear system. A natural approach (for me,
>>>>> anyhow) is to construct a library of combinators, or a domain specific
>>>>> language, with which to specify the (boxed) structure.
>>>>>
>>>>> J rises easily to the task, and before long I'm looking at long function
>>>>> trains of the form
>>>>>
>>>>> myStruct =: c0 p0 c1 p1 c2 p2 ... cN pN
>>>>>
>>>>> where the ci are (combinator) verbs, and the pj are (parameter) nouns.
>>>>> Nice. Easy.
>>>>>
>>>>> Only trouble is, N may be large and J prefers such statements to sit on
>>>>>
>>>> a
>>>>
>>>>> single line. Correct? I can split my definition:
>>>>>
>>>>> msPartA =. .....
>>>>> msPartB =. .....
>>>>> .....
>>>>> msPartX =. .....
>>>>> myStruct =: msPartA msPartB .... msPartX
>>>>>
>>>>> though this feels awkward. The most obvious issue is that the PartA,
>>>>>
>>>> ...,
>>>>
>>>>> PartX are distracting; unless of course I can find a natural way of
>>>>> splitting and naming them. Ideally, the parts should be as close to a
>>>>> comfortable line width as possible. Again, awkward. If myStruct1 and
>>>>> myStruct2 have the same partitioning scheme but myStruct2 (for
>>>>>
>>>> instance) is
>>>>
>>>>> much larger than myStruct1, there will be many sparsely, or many
>>>>> overpopulated lines. Awkward too.
>>>>>
>>>>> I love J. It handles complex regular data so elegantly. How can I bring
>>>>> similar elegance to irregular data? Can my combinators be rescued, or
>>>>> should I use another approach?
>>>>> ----------------------------------------------------------------------
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>>>>>
>>>> ----------------------------------------------------------------------
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>>>>
>>>>
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>>
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