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
