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Bradd W. Szonye wrote: >> Furthermore, I think it's a mistake to give the number of ranks >> instead of the dimension bounds. As I explained in a reply to Bear, >> you can't infer array shape from a list decomposition if the array >> has any 0-bounded dimensions. Per Bothner wrote: > Wild idea (where 'type' is optional): > #[bound ...]type(elements ...) > > This would be the API "rho" operation, if I remember correctly. > Elements would be the "unravelled" values in row-major-order. > E.g. #[2 3]int32(11 12 13 21 22 23) Not bad, but I like your later suggestion for #MxN(...) even better: >> Instead, the external representation for arrays should list the >> dimensions (e.g., #A2x3(...) or #A:2:3(...)). This permits unambiguous >> reading and writing of "empty" multi-dimension arrays, it permits the >> PLT shorthand notation for large, repetitive arrays, and it avoids >> confusion with the #n(...) syntax for vectors. > My main objection [to #A2x3(...)] that it looks too close to the > Common Lisp syntax. E.g. #A2((1 2) (3 4)) could easily be a typo for > #2A((1 2) (3 4)) which means something very different. Good point! > Hence, I'd leave out the A, and make the syntax compatible with > mzscheme: #2x3(...) I thought of that too (after I'd already sent my comment above). I like the idea even better now that I've seen it in type. I especially like how a one-dimensional array in this syntax looks exactly like the PLT vector shorthand (e.g., #5(1 2 3 4 5)). It should be a painless upgrade for MzScheme users. > There is a question of whether the elements should be shown flattened > or nested: #2x3(11 12 13 21 22 23) or #2x3((11 12 13) (21 22 23)) I prefer the nested syntax; it seems like it would support the repeat-last-element shorthand more usefully. (Even if SRFI 58 doesn't specify the repeat-last feature, I'm sure some implementors would do it that way.) > There is also a problem in that the syntax fails in the case of rank-0 > arrays. That is an argument for leaving in the 'A'. I have a better solution: If the "array" has rank 0, also omit the "#"! After all, that's what the Scheme writer will do when printing a scalar. This solution is more obvious if you use "#" instead of "x" for the bound separators, e.g.: Two dimensions #2#3((11 12 13) (21 22 23)) One dimension #3(1 2 3) No dimensions 1 Personally, I like the #2x3(...) syntax better; these examples are just to show how the general pattern applies to the degenerate case. >> I don't think the Scheme reader should support this "array notation" >> for scalars. > I didn't mean to suggest that. I just mentioned it as a "by the way". > However, a Scheme that support general arrays should still support > 0-rank arrays, and so we need to consider the degenerate case. I don't think the reader/writer/programmer interface needs to support an array syntax for 0-rank "arrays," however. Indeed, I suspect that it shouldn't, because it just introduces a "noise" token that can obfuscate data but provide no real information. -- Bradd W. Szonye http://www.szonye.com/bradd