On Sun, Jan 16, 2011 at 6:22 AM, Jürgen Hötzel <juer...@hoetzel.info> wrote: > Hi, > I came across this issue while implementing a lazy, efficient flatten that > also uses the whole sequence abstraction (flatten java arrays....). > The problem with (seq x) is, that it will throw an Exception if called on > something, that cannot be coerced to sequence, so I just used sequencial? > like the current implementation of flatten: > (defn my-flatten [coll] > (mapcat (fn [p] (if (sequential? (first p)) (mapcat my-flatten p) p)) > (partition-by sequential? coll))) > But this will obviously fail to flatten anything that doesn't > implement clojure.lang.Sequential (like java.arrays).
Unfortunately, right now that's a big gap in the clojure.core functionality. It's quick to fix, though the fix is a bit of a hack as it uses the exception-throwing behavior of (seq x). On the plus side this guarantees that it meets its contract. (defn seqable? [x] (try (seq x) (catch Exception _))) (def m-seq seqable?) (defn seqable-ns? [x] (if-not (instance? java.lang.String x) (seqable? x))) (def m-seq-ns seqable-ns?) Anything seqable is returned unchanged by seqable? and m-seq, which return nil rather than throw if the thing is not seqable. The two names for the same function are just to improve code readability: seqable? for use as a predicate and m-seq for uses like (if-let [x (m-seq foo)] (do-something-with x)) The -ns versions differ only in that they pretend Strings aren't seqable, for those fairly common cases where you want to treat strings as atomic rather than as character sequences; for instance if you're probing a data structure made of nested colls and wish to regard whole strings as leaf nodes in the traversal instead of their individual characters. -- 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 Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
