Uri Guttman wrote: >>>>>> "p" == pugs-commits <pugs-comm...@feather.perl6.nl> writes: > > p> This document attempts to document the list of builtin functions in > Perl 6. > p> It assumes familiarity with Perl 5 and prior synopses. > p> @@ -870,6 +870,10 @@ > p> comparisons. C<@by> differs from C<$by> in that each criterion is > p> applied, in order, until a non-zero (tie) result is achieved. > > p> +If C<$by> is a code object of arity zero or one, it is applied on each > item > p> +of C<@values>, and C<@values> is sorted by comparing the result values > with > p> +C<< &infix:<cmp> >> (Schwartzian Transform). > p> + > > the ST is a specific implementation of this optimization. the concept is > caching key extractions and expressions so they become O(N) and not O(N > log N) which saves tons of cpu in larger complex sorts. but how the > caching is done is really independent of the sort API/signature. as > perl6 synopses aren't supposed to discuss implementation (they are > language specs) calling it the schwartzian transform is somewhat out of > place.
I agree. As I wrote in the commit message, "feel free to improve the wording" - the specs are open for hacking, especially S29, which is in "draft" status. > and some other questions: > > and how does that style handle multiple keys? What do you mean? The comparison is carried out on the return values of the closure. > how is sort ordering > specified? Currently it is not specified, it defaults to infix:<cmp>. If you can suggest a non-confusing way to specify both a transformation closure and a comparison method, please go ahead. > how does it know to do string vs numeric sorting? infix:<cmp> does numeric comparison if both operands are numbers, and string comparison otherwise. > damian's > Perl6::Sort and my Sort::Maker address those issues but this SIG short cut > doesn't (yet). > > also Sort::Maker generates sorts in 4 styles which may be of use to any > implementors of perl6's sort. and it has an old (prize winner at TPC4) > article on this topic that may be of some interest. and it only won a > technical award because damian withdrew as he was the winner the > previous two years in a row! :) I'll take a look. Cheers, Moritz
