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On Thu, Oct 30, 2003 at 12:40:17PM -0800, bear wrote: > > > On Thu, 30 Oct 2003 scgmille@xxxxxxxxxxxxxxxxxx wrote: > > >On Thu, Oct 30, 2003 at 11:45:26AM -0800, bear wrote: > > >> On Thu, 30 Oct 2003 scgmille@xxxxxxxxxxxxxxxxxx wrote: > > >> >But they cannot be defined if they don't apply to the general class of > >> >collections. They need to be defined for those concrete classes or a > >> >more specific general one (like ordered tree). > >> > >> Of course they can be defined for generic collections. You can get > >> the last element of a list; it's just the worst possible structure > >> for that operation to be efficient. Similarly, you can get a range > >> of keys from an unordered alist, or any of the other "shortcut" > >> operations. > > > >But what about a dictionary with no ordering at all? > > In that case you just get whichever N elements are most efficient > to get. Or maybe you call the error continuation and make the > user replace them with a call that makes it *explicit* that he's > not interested in orderedness anymore -- but that's self-evident > if he's using an unordered collection type, so it seems needlessly > pedantic to me. Why? You've defined a function called get-n-from-range or what have you, and it does nothing of the sort. Its even worse for other functions where you can't just hand out n values from anywhere. This is the *fundamental* flaw with having a kitchen sink of operators which are efficient for collections you're thinking of. Scott
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