Empty frame, or more accurately zero frames, if it is said to be for anything, is to allow edge cases, the case where the frame contains a 0, to work without a lot of exceptions, without the programmer having to write extra code. An example hopefully illustrates this point.
x ,"1 y=: i.3 4 10 20 30 0 1 2 3 10 20 30 4 5 6 7 10 20 30 8 9 10 11 In this case the left frame is '' and the right frame is }:$y, (,3) in this case. x ,"1 y=: i.2 4 10 20 30 0 1 2 3 10 20 30 4 5 6 7 x ,"1 y=: i.1 4 10 20 30 0 1 2 3 x ,"1 y=: i.0 4 The right frames in the successive examples are (,2), (,1), and (,0). The last is an example of a zero frame, and the example worked with no fuss. The following sequence makes more salient the consistent treatment of frames, including zero frames. $ x,"1 y=: i.3 4 3 7 $ x,"1 y=: i.2 4 2 7 $ x,"1 y=: i.1 4 1 7 $ x,"1 y=: i.0 4 0 7 The reason why zero frames requires extra discussion is because ordinarily you have argument cell(s) for the verb to apply to, and the result cells and hence the result is not in question. With zero frames, there are no argument cells, so the system needs to do something extra (so that you don't have to). (x,"1 y appends vectors to vectors, but when y is i.0 4 it does not have any vectors.) On Thu, Jan 14, 2016 at 10:35 PM, Matthew Baulch <[email protected]> wrote: > And the dictionary defines frame.... such that it may be empty? I'm most > interested in whether, supposing this is the case, allowing empty frames > serve (an)other purpose(s) in the structure of the language. > > Apologies if my original phrasing was unclear. > > Every decision in the design of J seems very deliberate—which I really > appreciate. It just seems that empty frames must serve a purpose. Trying to > work it out. > On 15 Jan 2016 4:21 pm, "bill lam" <[email protected]> wrote: > > > The J dictionary is always correct. > > > > Пт, 15 янв 2016, Matthew Baulch написал(а): > > > Fair enough, though I can't work out whether the dictionary agrees with > > > NuVoc here or not. Either way, which definition of frame is correct? > > > On 15 Jan 2016 3:48 pm, "bill lam" <[email protected]> wrote: > > > > > > > For J implemention, the only authority is the J dictionary since > > > > it defines the J language. You need not worry anything else. > > > > > > > > http://www.jsoftware.com/help/dictionary/dictb.htm > > > > > > > > Пт, 15 янв 2016, Matthew Baulch написал(а): > > > > > I assume the intended definition of 'frame', in relation to verb > > > > arguments, > > > > > is that given on > > > > > > > > > > http://code.jsoftware.com/wiki/Vocabulary/FramingFill > > > > > > > > > > I'm just trying to understand verb/argument combinations with empty > > > > > frame--the most common case, I suppose. > > > > > > > > > > From the wording "each argument is ... an array of [r-cells]. The > > frame > > > > ... > > > > > is the shape of this array of [r-cells]", it seems that a frame > > should > > > > > never be empty, but in fact have a minimum shape of '1'. Of course, > > this > > > > > ties into the wording of many other statements. In the case of > dyadic > > > > > verbs, for instance, > > > > > > > > > > "frames must agree ... they must be identical or one must be a > > prefix of > > > > > the other" (stated in link above) > > > > > > > > > > as opposed to > > > > > > > > > > "frames must agree ... one must have shape 1 or be a prefix of the > > other" > > > > > (the way I see it, assuming equality implies prefix-of) > > > > > > > > > > Can anyone shed some light on this? Is there an important reason > for > > this > > > > > convention that I'm missing, or is it of little consequence? > > > > > > > > > > I'm implementing (or trying to...) a subset of J for the JVM, and > > this is > > > > > one little detail that's bothering me. > > > > > > > > > > Thanks. > > > > > > > > > > Matt Baulch > > > > > > > ---------------------------------------------------------------------- > > > > > 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 > > > > gpg --keyserver subkeys.pgp.net --armor --export 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 > > > > -- > > regards, > > ==================================================== > > GPG key 1024D/4434BAB3 2008-08-24 > > gpg --keyserver subkeys.pgp.net --recv-keys 4434BAB3 > > gpg --keyserver subkeys.pgp.net --armor --export 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 ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
