[Jprogramming] Recursive algorithm

[Robert O'Boyle]

Hi

When I was first got into J, I found the following statement in Chapter 6 of
J for C at
file:///C:/j602/help/jforc/loopless_code_i_verbs_have_r.htm#_Toc191734341

	Order of Execution in Implied Loops

	Whenever a verb is applied to an operand whose rank is higher than
the 	verb's rank, an implied loop is created, as we have discussed above.
The order in which the verb is applied to the cells is undefined.  The
order used on one machine may not be that used on another one, and the
ordering may not be predictable at all.  If your verb has side 	effects, you
must insure that they do not depend on the order of 	execution.

	Current versions of the interpreter apply the verb to cells in
order, 	but that may change in future releases.

I also read in either J for C or LJ that one should avoid control structures
(for, while, etc) as much as possible due to the performance penalty. This
put me in quite a bind re much of my work which is temporally based. So I
have generally used rank to do much of my looping (thus my recent query) but
always being wary of potential issues in future J versions. It would be good
for J to clarify all this. 

Bob

-----Original Message-----
From: programming-bounces at jsoftware.com
[mailto:programming-bounces at jsoftware.com] On Behalf Of Raul Miller
Sent: March 14, 2011 9:28 AM
To: Programming forum
Cc: Zsbán Ambrus
Subject: Re: [Jprogramming] Recursive algorithm

On Mon, Mar 14, 2011 at 7:15 AM, Zsbán Ambrus <ambrus at math.bme.hu> wrote:
> (For loops could have the advantage that I think jsoftware has made
> some vague statements on the mailing lists that if you use the rank
> operator on verbs with side effects, it might not always call the verb
> as many times or in the right order in some case of optimizations in
> future versions.  This is belivable because (u/\. y) already does such
> an optimization, and in fact I think that's a right idea.)

I do not recall any official statement of that nature, *ever*.

I believe that that is "folk wisdom" based on experience with other
languages.

-- 
Raul
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm