[Jprogramming] Nested structures. Idioms? Combinators?

[Henry Rich]

Look also at 128!:2, which takes a verb as a string argument and applies 
that verb to y.

Henry Rich


On 2/9/2016 9:10 PM, Matthew Baulch wrote:
> Thanks. I think this is what I was looking for.
>
> I was aware of 'noun define' but didn't know it could be used in this way.
> Good point about c0.
>
> Documentation, I agree, is particularly important with this style of code.
> My view is certainly not that definitions spanning multiple lines should be
> commonplace. It is nice to know, however, that it is possible.
>
> Cheers.
> 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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