Hmm, I didn't read the definition of `board-map' carefully. It seems the second form
(dosync (board-map deref board)) is the best among the three, as it views `board' as a whole. The other two might have the potential problem of printing incoordinated values of entries in `board', i.e. the entries of `board' might change during the iteration in the `map' form. Am I right? Thanks, Guanpeng Xu On Tue, Jan 31, 2012 at 11:46 AM, Guanpeng Xu <herberteu...@gmail.com>wrote: > Hi all, > > In section 11.2.1 of the book /The Joy of Clojure/, the author shows > the effect of > `dosync' by starting 100 threads and then watching the value of a Ref: > > (go make-move 100 100) > (board-map #(dosync (deref %)) board) > > Here, the first `go' form starts 100 threads, their effect is > modifying `board' using > `dosync' and `alter'. `board-map' is defined as > > (defn board-map [f bd] > (vec (map #(vec (for [s %] (f s))) bd))) > > I don't quite understand the use of `dosync' in the second `board-map' > form. In > my testing, the following three seems identical: > > (board-map #(dosync (deref %) board) > (dosync (board-map deref board)) ;; Should be the same as above > (board-map deref board) ;; Without `dosync' at all > > The docstring of `deref' says "Within a transaction, returns the in- > transaction-value > of ref, else returns the most-recently-committed value of ref." So > the above three > forms are all the same, right? Or is there any difference between > them? > > Thanks in advance, > Guanpeng Xu -- 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
