An empty tank zero array would be inconsistent. The number of elements in an array is the product of its dimensions, and the multiplicative identity is 1, not 0.
Thanks, -- Raul On Tuesday, December 19, 2017, Jimmy Gauvin <[email protected]> wrote: > Hi, > > Thinking about nothing, specifically about the empty scalar or empty > 0-cell. > > Erling H. - " I experience an inconsistency in this model in the sense > that an array of rank greater than zero can be empty, a 0-cell can not." > > The internal structure of a J array could support a rank 0 empty object. > However, short of poking into memory, there does not seem to be a way of > generating an empty scalar. > > ┌───────┬─┬───────┬─┬─┬─────┬───┐ > │data │ │type │n│r│shape│val│ > ├───────┼─┼───────┼─┼─┼─────┼───┤ > │8 │ │integer│1│0│ │8 │ > ├───────┼─┼───────┼─┼─┼─────┼───┤ > │8 9 │ │integer│2│1│2 │8 9│ > ├───────┼─┼───────┼─┼─┼─────┼───┤ > │'' │ │literal│0│1│0 │ │ > ├───────┼─┼───────┼─┼─┼─────┼───┤ > │0$0 │ │boolean│0│1│0 │ │ > ├───────┼─┼───────┼─┼─┼─────┼───┤ > │0$8 │ │integer│0│1│0 │ │ > ├───────┼─┼───────┼─┼─┼─────┼───┤ > │0 0 0$8│ │integer│0│3│0 0 0│ │ > ├───────┼─┼───────┼─┼─┼─────┼───┤ > │(0$0)$8│ │integer│1│0│ │8 │ > └───────┴─┴───────┴─┴─┴─────┴───┘ > n = number of values > r = rank > > NB. Trying to get n=0 and r=0 > > (0$0) $ (0$0) > |length error > | (0$0) $(0$0) > (0$0) $ '' > |length error > | (0$0) $'' > > > > > > On Tue, Dec 19, 2017 at 4:28 AM, Erling Hellenäs <[email protected] > > > wrote: > > > Hi all ! > > > > In APL we had the same array model as in Fortran. An array was an array > > and you indexed it like in most other languages, except that you could > use > > an array as index and therefore could get very varying results. The only > > problems I personally experienced with this model was that you could not > > put all the indexes in one variable. I also wanted to have the index to > the > > left. To keep the right-to-left normal flow of the language. I wrote > > special indexing functions to handle this, but never used them in > > production. > > > > In J we have the n-cell array model. A difference is that a scalar is > just > > another array, it just is imagined as having zero dimensions. I APL there > > were scalars and there were arrays, basically two different data > > structures. I experience an inconsistency in this model in the sense that > > an array of rank greater than zero can be empty, a 0-cell can not. At > least > > in the interpreter I wrote, there is a lot of special handling of 0-cells > > because they actually have content, although there are no array > dimensions > > which could reasonably contain any such content. > > > > In the dyadic rank operator a k-cell without any zero dimension can be > > empty because a containing array is. This causes the very particular > > special handling I mentioned in the thread "[Jprogramming] i. (2 2 $ 1 2 > 3 > > 4)" > > > > Simplicity is important for performance, it is important for our ability > > to predict the behaviour of the code without testing it in the terminal > and > > to limit the number of test cases needed to verify the functonality of a > > program. > > > > Is there any documentation of the design decision to select the n-cell > > array model? > > > > Are there any threads in the forum where this array model is discussed? > > > > Maybe someone also wants to share their knowledge from internal > > discussions about this design decision. > > > > Cheers, > > > > Erling Hellenäs > > > > ---------------------------------------------------------------------- > > 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
