Thanks! Interesting use of the dual/under operator &. Although I had studied the form, this usage didnot occur to me!
As an extension question: p1 =: i. &. (p:^:_1) NB. primes strictly less than number so, p1 37 2 3 5 7 11 13 17 19 23 29 31 In the generated list, I want the number included if it is prime. What would that extension be using &. ? Or, does that need compelete verb definition? Regards, Yuva On 9/21/06, Henry Rich <[EMAIL PROTECTED]> wrote:
The easiest way to explain the results is that you have to put parentheses around the value when you substitute for a name. This is like mathematics, where if y is 2+x y*2 is (2+x)*2 not 2+x*2 So, if pl =. p: i. (p:^:_1) then p1 n is like (p: i. (p:^:_1)) n which is not what you want. (It is a hook, which you can read about in the references. It is equivalent to (p: n) i. (p:^:_1 n) ). To get what you want, you can write p1 =: verb : 'p: i. (p:^:_1) y' or p1 =: p: @: i. @: (p:^:_1) (read about @: to understand this) or p1 =: i.&.(p:^:_1) (read about &.) You should know that names ARE NOT replaced by their parenthesized values when a sentence is executed. That's just a convenient fiction. The actual details are in the references. Henry Rich > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > Yuvaraj Athur Raghuvir > Sent: Wednesday, September 20, 2006 7:52 PM > To: Programming forum > Subject: [Jprogramming] Explicit to Tacit - newbie question > > Hello, > > J is fascinating. Am learning slowly.... > > In the following why does pl not work? > > n =. 30 > p:^:_1 n > 10 > p: i. p:^:_1 n NB. list of primes less than n > 2 3 5 7 11 13 17 19 23 29 > pl =. p: i. p: ^: _1 > pl n NB. Does not work! > 1 > p: i. (p: ^: _1) 30 > 2 3 5 7 11 13 17 19 23 29 > pl =. p: i. (p:^:_1) NB. Is it a paranthesis problem? > 5!:5 < 'pl' NB. J removes the paranthesis > anyways... > p: i. p:^:_1 > > > Regards, > Yuva > ---------------------------------------------------------------------- > For information about J forums see > http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
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