Re: [Jprogramming] Flavor of J

[Roger Hui]

See also the lab "An Idiosyncratic Introduction to J".
I used that in the Jsoftware booth at math meetings.
Took 5 to 10 minutes, much more if the visitor asked
substantial questions.  To paraphrase a saying 
from another context, I wanted a pool in which 
a child can wade and an elephant can, if not drown, 
be challenged.

Ken took that and expanded it into the lab 
"A J Introduction".



----- Original Message -----
From: Kip Murray <k...@math.uh.edu>
Date: Saturday, September 12, 2009 19:10
Subject: [Jprogramming] Flavor of J
To: Programming forum <programming@jsoftware.com>

> For me the flavor of J is functions (verbs), operators (adverbs 
> and 
> conjunctions), and arrays: the J programmer thinks at this level 
> of abstraction 
> to solve his problems, and the extended example below intends to 
> give visitors a 
> taste of this flavor.
> 
> However, this omits the use of J for windows programming.  
> How would you 
> describe the J flavor of that, and what taste would you give visitors?
> 
> Here is my extended taste of "functions, operators, arrays" for 
> a visitor.
> 
>     ]L =: i. 4   NB. assign (=:) and 
> display (]) a "line" (vector) of 4 integers
> 0 1 2 3
> 
>     ]P =: i. 2 4   NB. a two-line 
> "page" (matrix)
> 0 1 2 3
> 4 5 6 7
> 
>     ]B =: i. 3 2 4   NB. a three page 
> "book" (array)
>   0  1  2  3
>   4  5  6  7
> 
>   8  9 10 11
> 12 13 14 15
> 
> 16 17 18 19
> 20 21 22 23
> 
>     L      NB. show L
> 0 1 2 3
> 
>     +/ L   NB. operator / inserts 
> function + between items, we see sum
> 6
> 
>     P
> 0 1 2 3
> 4 5 6 7
> 
>     +/ P   NB. items of a page are its 
> lines, we see the sum of two lines
> 4 6 8 10
> 
>     B
>   0  1  2  3
>   4  5  6  7
> 
>   8  9 10 11
> 12 13 14 15
> 
> 16 17 18 19
> 20 21 22 23
> 
>     +/ B   NB. items of a book are its 
> pages, we see sum of three pages
> 24 27 30 33
> 36 39 42 45
> 
>     L      NB. show L
> 0 1 2 3
> 
>     +/\ L  NB. operator \ applies +/ to 
> "prefixes", gives cumulative sums
> 0 1 3 6
> 
>     P
> 0 1 2 3
> 4 5 6 7
> 
>     +/\ P
> 0 1 2  3
> 4 6 8 10
> 
>     B
>   0  1  2  3
>   4  5  6  7
> 
>   8  9 10 11
> 12 13 14 15
> 
> 16 17 18 19
> 20 21 22 23
> 
>     +/\ B
>   0  1  2  3
>   4  5  6  7
> 
>   8 10 12 14
> 16 18 20 22
> 
> 24 27 30 33
> 36 39 42 45
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