Hi Steve, Thanks! I like quicksort-4. It all fixes a problem that bugged me in all the other examples, which is that "bigger" is a lie. The real semantic is "not smaller", which quicksort-4 captures perfectly.
I will have to get used to thinking of "remove" as the opposite of "filter." The English connotations of the former are too imperative for me, but I don't know a better word for it. Stuart > On Oct 20, 2008, at 11:16 AM, Stuart Halloway wrote: > >> Hi all, >> >> I seem to recall Rich saying "I like the destructuring part of >> pattern >> matching." In my efforts to appreciate that statement, I am playing >> around with porting simple Haskell examples to Clojure, trying to use >> destructuring (and multimethods) where the Haskell does pattern >> matches. >> >> For example: >> >> -- Haskell >> qsort [] = [] >> qsort (x:xs) = qsort smaller ++ [x] ++ qsort bigger >> where smaller = filter (<x) xs >> bigger = filter (>=x) xs >> >> [...] > >> I am confident that the Clojure could be prettier, but not sure how. >> Suggestions? > > Here are a couple of ideas: > > The first is a more literal translation of the Haskell code with > 'when providing the nil case: > > (defn quicksort-3 [[x & xs]] > (when x > (let [smaller (filter #(< % x) xs) > bigger (filter #(>= % x) xs)] > (lazy-cat (quicksort-3 smaller) > [x] > (quicksort-3 bigger))))) > > The second uses the filter/remove complementary pair so there's only > one predicate: > > (defn quicksort-4 [[x & xs]] > (when x > (let [smaller #(< % x)] > (lazy-cat (quicksort-4 (filter smaller xs)) > [x] > (quicksort-4 (remove smaller xs)))))) > > --Steve > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
