> I guess you meant $$, Yes, I did. I had that originally, then (wrongly) decided I could do without the (,).
> Roger suggested other idioms for copy-by-value but no promise that they > will work for ever. That's what's worrying me. My code (if successful) will be buried in middleware, and risks breaking in years to come. But I guess that's true of all modern code. There's almost a case here for another foreign, eg. ownmem=: 128!:8 On Sat, May 28, 2011 at 12:00 AM, bill lam <[email protected]> wrote: > I guess you meant $$, > > x rho y in APL is equivalent to x ($,) y in J if I remember correctly. > > Roger suggested other idioms for copy-by-value but no promise that they > will work for ever. > > Птн, 27 Май 2011, Ian Clark писал(а): >> Been experimenting with mapped files... >> Looking for a reliable way to detect if a mapped file has changed >> since I last inspected it. >> >> If pronoun: TITLE is mapped to a file, then >> sav=: TITLE >> will create: sav -as not a copy but an alias of TITLE. (Not >> surprisingly, because they share the same memory.) >> >> Thus reassigning sav will change TITLE too, and vice-versa. Which >> makes: sav=:TITLE no good as a way of snapshotting TITLE to detect >> changes. >> >> 1. Can you think of a low-overhead verb: own -used like so: >> sav=: own TITLE >> -which will force J to allocate sav its own separate space in memory? >> >> I've tried these: >> own=: ] >> own=: [: > [: {: 0 ; < >> own=: $ $ ] >> >> The first 2 don't work: sav keeps in step with TITLE, thanks to J's >> optimisation. >> The third defn works --but for how much longer? At some future date it >> might break, thanks to improved J optimisation. >> >> 2. Is there a more elegant way of checking whether a mapped file has changed? >> >> When I change a mapped noun I cannot see any changes to: >> showmap_jmf_'' --this is on a Mac. >> I can repeatedly read the directory entry using 1!:0 and watch for >> it to change (as its timestamp gets updated). The processing overhead >> is tolerable, but is it the best I can do? >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm > > -- > regards, > ==================================================== > GPG key 1024D/4434BAB3 2008-08-24 > gpg --keyserver subkeys.pgp.net --recv-keys 4434BAB3 > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
