[Jprogramming] Truncating

[ramacd]

Folks;

The benefit I saw was that of the verb being separable from the noun.

If I have:

   i.&.(p:^:_1) x

or, in a more general case:

   f g h x   NB. f,g,h verbs; x noun

which is different from

(f g h) x

just like

   (p: i. p^:_1) x

is different. However, adding the ()'s in

   (i.&.(p:^:_1) x

preserves meaning.

To have a separable expression, you have to do something like:

  (f at g@h) x  NB. eeew!

To me, the point isn't the "pattern" evoked by the &. conjunction, it's the
whole concept of verb expressions and the expansion of possibilities, which
APL only skimmed with f/ and f.g

The thing that does tug at me, it is getting my head around how a dyadic
verb has an inverse. I think the same thing happens with #^:_1but I haven't
yet seen nor thought up a good explanation for how those inverse cases were
derived.

------------------------------------------------------------------------
|\/| Randy A MacDonald   | APL: If you can say it, it's done.. (ram)
|/\| ramacd at nbnet.nb.ca  |
|\ |                     | The only real problem with APL is that
BSc(Math) UNBF'83        | it is "still ahead of its time."
Sapere Aude              |     - Morten Kromberg
Natural Born APL'er      | Demo website: http://156.34.84.219/
-----------------------------------------------------(INTP)----{ gnat }-

----- Original Message ----- 
From: "Roger Hui" <rhui000 at shaw.ca>
To: "Programming forum" <programming at jsoftware.com>
Sent: Monday, March 05, 2007 11:51 AM
Subject: Re: [Jprogramming] Truncating


> The point is not the number of characters but a
> pattern that is useful in other areas.  In this case
> the pattern is duality.  For other examples of
> duality, please see:
> http://www.jsoftware.com/jwiki/Essays/Under
>
>
>
> ----- Original Message -----
> From: Geoff Canyon <geoffc at inspiredlogic.com>
> Date: Sunday, March 4, 2007 10:04 pm
> Subject: Re: [Jprogramming] Truncating
>
> > Wow -- that's great stuff. I tried it, and it worked a treat. If I
> >
> > understand correctly, the &. command joins the i. and the
> > (p:^:_1),
> > which is the inverse of p:. So this command says: apply the
> > inverse
> > of the prime function to 10000 to find what the order of that
> > prime
> > is, then iterate up to that number, then get the primes up to that
> >
> > index. I'm curious -- how is the use of &. better than just
> > writing
> > out what is needed. As far as I can see these are equivalent:
> >
> > i.&.(p:^:_1)10000
> > p:i.(p:^:_1)10000
> >
> > They take the same number of characters to type, so why is the
> > former
> > preferred to the latter?
> >
> > regards,
> >
> > Geoff
> >
> > On Mar 4, 2007, at 12:42 AM, Raul Miller wrote:
> >
> > > On 3/4/07, Geoff Canyon <geoffc at inspiredlogic.com> wrote:
> > >> based on a calculation? For example, suppose I want to generate all
> > >> the primes < 10,000.
> > >
> > >   i.&.(p:^:_1)10000
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>