Steve, thank you very much for your detailed and clear explanation. Yes, I see many refs when I google-search for it and clues in them for the answer. I should have done it before asking. Lazy-seqs bite lazy bones like me.
Thanks, again. --Kei On Jan 24, 10:34 pm, "Stephen C. Gilardi" <squee...@mac.com> wrote: > The map function returns a lazy sequence. Unless something forces the > members of the sequence to be evaluated, they won't be. > > In Form1, you explicitly call an anonymous function that throws. > > In Form2, the sequence returned by map is the last value in the "do" > form, so it is the value of the "do" form. You've asked the repl > (implicitly) to print the value returned by "do". It wants to print > the sequence's members so it requests the value of the first one. To > determine the first value, the anonymous mapped function is called and > throws. > > In Form3, map returns a value and that value is immediately thrown > away. Since nobody asked for the value of its "first", the value of > its "first" was never calculated. Form3 returns :ok because that's the > last value in the "do" and the repl prints :ok. > > A Google search for: > > clojure lazy > > will bring up more references. > > --Steve > > On Jan 25, 2009, at 1:05 AM, Kei Suzuki wrote: > > > > > Form3 makes me puzzled. Form1 and Form2 throw exception as expected. > > Why doesn't Form3? > > > Form1: (do ((fn [] (throw (Exception. "oops")))) :ok) > > Form2: (do ((fn [] (map #(when % (throw (Exception. "oops"))) > > [true])))) > > Form3: (do ((fn [] (map #(when % (throw (Exception. "oops"))) > > [true]))) :ok) > > > Thanks. > > > --Kei > > > > > > smime.p7s > 3KViewDownload --~--~---------~--~----~------------~-------~--~----~ 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 clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
