Some thoughts on really stupid things that have tripped me up: - How do I exit Clojure - srsly C-c
- Whatsa JVM - does this mean Clojure is really just Java with parens? - Whatsa Classpath? this answer presents the *ALL* important opportunity to mention that *nix uses `:' to separate paths whereas windz uses `;' - How do I access Clojure documentation - e.g. where is `man Clojure' - Is a Clojure docstring the same as Javadoc? - Is Clojure stable? - Where's the Clojure manual? - What happened to setf? - Why are Clojure's docstring placements different than other lisps - Where do I make donations? - Why are Clojure's defun params passed in a [] vector? - Does Clojure do TCO? - Whatsa TCO? - How do I compile Clojure? OR Where's the Clojure Compiler? - How does Clojure's nil differ from other Lisps? - Clojure has a `cons' function and a `conj' function - whats the difference? - At what point do calls out to external Java interfaces limit/alter Clojures' internal handling of sequences ---- How do I avoid interopearating with Java - e.g. when is Clojure all I need for task X ---- When should I make use of external Java libraries - Whatsa Clojure Sequence - how does it corellate to language X - Whatsa Collection - how does it corellate to language X - Whatsa Map - how does it corellate to language X On Dec 19, 12:41 am, "Adrian Cuthbertson" <adrian.cuthbert...@gmail.com> wrote: > > Suggestions for entries welcome here. > > > > Rich > > Here's another that was a "gotcha" for me for an hour or two... > > Why after using map/reduce/for to change a java object does the object > remain unchanged? > > (defn initv1 [myseq] (let [v (java.util.Vector.)] (for [x myseq] > (.addElement v x)) v)) > (initv1 [1 2 3]) > ; => (java.util.Vector. []) > > ; or... > > (defn initv2 [myseq] (let [v (java.util.Vector.)] (map (fn [x] (.addElement > v x)) myseq) v)) > (initv2 [1 2 3]) > ; => (java.util.Vector. []) > > As map/reduce/for are lazy, the "let" construct does not actually "take" any > elements from the map/reduce/for. In this case, use doseq... > > (defn initv3 [myseq] (let [v (java.util.Vector.)] (doseq [x myseq] > (.addElement v x)) v)) > (initv3 [1 2 3]) > ; => (java.util.Vector. [1 2 3]) > > (Actually this happened in a more complex function, but the essence was that > a new java object was instantiated in a let and I'd used a map to call a > method on that object with all the items from a sequence. I could not > understand why the object remained unchanged afterwards until I simplified > it down to the above example). > > Regards, Adrian --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
