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: ([EMAIL PROTECTED]@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) |/\| [EMAIL PROTECTED] | |\ | | 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" <[EMAIL PROTECTED]> To: "Programming forum" <[email protected]> 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 <[EMAIL PROTECTED]> > 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 <[EMAIL PROTECTED]> 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 > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
