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• Is shipping a Clojure desktop app realistic?

  - by Cedric Martin

  I'm currently shipping a desktop Java application. It is a plain old Java 5 Java / Swing app and so far everything worked nicely. Java 5 was targetted because some users were on OS X version / computers that shall never have Java 6 (we may lift this limitation soon and switch to a newer Java and simply abandoning my users stuck with Java 5). I'm quickly getting up to speed with Clojure but I haven't really done lots of Clojure-to-Java and Java-to-Clojure yet and I was wondering if it was realistic to ship a Clojure desktop application instead of a Java application? The application I'm shipping is currently about 12 MB with all the .jar so adding Clojure doesn't seen to be too much of an issue. My plan would be to have Clojure call Java APIs: my application is already divided in several independent jars. If I understand correctly calling Clojure from Java is harder than calling Java code from Clojure which is why I'd basically rewrite all the UI (part of the UI, mixing Swing components and self-made BufferedImages needs to be rewritten anyway due to the rise of retina display), and do all the 'wiring' from Clojure. So that's the problem I'm facing: is it realistic to ship a Clojure desktop app? (it certainly doesn't seem to be very widespread but then shipping plain Java desktop apps ain't that common either and I'm doing it anyway) Technically, what would need to be done? (compared to shipping a Java app)

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• Setting the Classpath and Accessing code from book: Programming Clojure

  - by user130153

  (I posted this same question on the Clojure list but haven't got an answer yet. Is anyone here ready to help?) I am going through Programming Clojure and I recently downloaded the code from the books official website. For other utils I can do, for example, (require 'clojure.contrib.str-utils) and it works. But how do I load code from the book? (require 'examples.introduction) throws the following exception: java.io.FileNotFoundException: Could not locate examples/ introduction__init.class or examples/introduction.clj on classpath: (NO_SOURCE_FILE:0) [Thrown class clojure.lang.Compiler$CompilerException] Here is the full backtrace: Backtrace: 0: clojure.lang.Compiler.eval(Compiler.java:4543) 1: clojure.core$eval__3990.invoke(core.clj:1728) 2: swank.commands.basic$eval_region__686.invoke(basic.clj:36) 3: swank.commands.basic$listener_eval__695.invoke(basic.clj:50) 4: clojure.lang.Var.invoke(Var.java:346) 5: user$eval__1200.invoke(NO_SOURCE_FILE) 6: clojure.lang.Compiler.eval(Compiler.java:4532) 7: clojure.core$eval__3990.invoke(core.clj:1728) 8: swank.core$eval_in_emacs_package__307.invoke(core.clj:55) 9: swank.core$eval_for_emacs__384.invoke(core.clj:123) 10: clojure.lang.Var.invoke(Var.java:354) 11: clojure.lang.AFn.applyToHelper(AFn.java:179) 12: clojure.lang.Var.applyTo(Var.java:463) 13: clojure.core$apply__3243.doInvoke(core.clj:390) 14: clojure.lang.RestFn.invoke(RestFn.java:428) 15: swank.core$eval_from_control__310.invoke(core.clj:62) 16: swank.core$eval_loop__313.invoke(core.clj:67) 17: swank.core$spawn_repl_thread__445$fn__476$fn__478.invoke(core.clj: 173) 18: clojure.lang.AFn.applyToHelper(AFn.java:171) 19: clojure.lang.AFn.applyTo(AFn.java:164) 20: clojure.core$apply__3243.doInvoke(core.clj:390) 21: clojure.lang.RestFn.invoke(RestFn.java:428) 22: swank.core$spawn_repl_thread__445$fn__476.doInvoke(core.clj:170) 23: clojure.lang.RestFn.invoke(RestFn.java:402) 24: clojure.lang.AFn.run(AFn.java:37) 25: java.lang.Thread.run(Unknown Source) I am trying both Clojure Box and Enclojure in NetBeans on Windows XP. Is it a classpath issue? Where should I place the folder that contains code from the book? Please help me out with my variable enviroment settings as well.

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• What's so great about Clojure?

  - by marco-fiset

  I've been taking a look at Clojure lately and I stumbled upon this post on Stackoverflow that indicates some projects following best practices, and overall good Clojure code. I wanted to get my head around the language after reading some basic tutorials so I took a look at some "real-world" projects. After looking at ClojureScript and Compojure (two the the aforementioned "good" projects), I just feel like Clojure is a joke. I don't understand why someone would pick Clojure over say, Ruby or Python, two languages that I love and have such a clean syntax and are very easy to pick up whereas Clojure uses so much parenthesis and symbols everywhere that it ruins the readability for me. I think that Ruby and Python are beautiful, readable and elegant. They are easy to read even for someone who does not know the language inside out. However, Clojure is opaque to me and I feel like I must know every tiny detail about the language implementation in order to be able to understand any code. So please, enlighten me! What is so good about Clojure? What is the absolute minimum that I should know about the language in order to appreciate it?

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• Can I use swank-clojure with the clojure 1.2 master branch?

  - by Rob

  I'm happily using swank-clojure, installed via elpa. But I'd like to do some work with deftype, defprotocol, etc., which aren't aren't available in clojure 1.1. To use my own class paths, I'm using the excellent suggestion by Rick Moynihan in the stackoverflow question about setting custom classpaths, which was to set up a script like: #!/bin/bash java -server -cp "./lib/*":./src clojure.main -e "(do (require 'swank.swank) (swank.swank/start-repl))" And that works swimmingly if the clojure jar file in lib is 1.1, but with 1.2, it blows up: Exception in thread "main" java.lang.NoSuchMethodError: clojure.lang.RestFn.<init>(I)V (macroexpand.clj:1) at clojure.lang.Compiler.eval(Compiler.java:5274) at clojure.lang.Compiler.load(Compiler.java:5663) at clojure.lang.RT.loadResourceScript(RT.java:330) at clojure.lang.RT.loadResourceScript(RT.java:321) at clojure.lang.RT.load(RT.java:399) at clojure.lang.RT.load(RT.java:371) at clojure.core$load__5663$fn__5671.invoke(core.clj:4255) at clojure.core$load__5663.doInvoke(core.clj:4254) at clojure.lang.RestFn.invoke(RestFn.java:409) ...and many, many more So is there some magical incantation to make this work, or is clojure 1.2 compatibility not there yet?

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• Can Clojure's thread-based agents handle c10k performance?

  - by elliot42

  I'm writing a c10k-style service and am trying to evaluate Clojure's performance. Can Clojure agents handle this scale of concurrency with its thread-based agents? Other high performance systems seem to be moving towards async-IO/events/greenlets, albeit at a seemingly higher complexity cost. Suppose there are 10,000 clients connected, sending messages that should be appended to 1,000 local files--the Clojure service is trying to write to as many files in parallel as it can, while not letting any two separate requests mangle the same single file by writing at the same time. Clojure agents are extremely elegant conceptually--they would allow separate files to be written independently and asynchronously, while serializing (in the database sense) multiple requests to write to the same file. My understanding is that agents work by starting a thread for each operation (assume we are IO-bound and using send-off)--so in this case is it correct that it would start 1,000+ threads? Can current-day systems handle this number of threads efficiently? Most of them should be IO-bound and sleeping most of the time, but I presume there would still be a context-switching penalty that is theoretically higher than async-IO/event-based systems (e.g. Erlang, Go, node.js). If the Clojure solution can handle the performance, it seems like the most elegant thing to code. However if it can't handle the performance then something like Erlang or Go's lightweight processes might be preferable, since they are designed to have tens of thousands of them spawned at once, and are only moderately more complex to implement. Has anyone approached this problem in Clojure or compared to these other platforms? (Thanks for your thoughts!)

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• Insertions into Zipper trees on XML files in Clojure

  - by ivar

  I'm confused as how to idiomatically change a xml tree accessed through clojure.contrib's zip-filter.xml. Should be trying to do this at all, or is there a better way? Say that I have some dummy xml file "itemdb.xml" like this: <itemlist> <item id="1"> <name>John</name> <desc>Works near here.</desc> </item> <item id="2"> <name>Sally</name> <desc>Owner of pet store.</desc> </item> </itemlist> And I have some code: (require '[clojure.zip :as zip] '[clojure.contrib.duck-streams :as ds] '[clojure.contrib.lazy-xml :as lxml] '[clojure.contrib.zip-filter.xml :as zf]) (def db (ref (zip/xml-zip (lxml/parse-trim (java.io.File. "itemdb.xml"))))) ;; Test that we can traverse and parse. (doall (map #(print (format "%10s: %s\n" (apply str (zf/xml-> % :name zf/text)) (apply str (zf/xml-> % :desc zf/text)))) (zf/xml-> @db :item))) ;; I assume something like this is needed to make the xml tags (defn create-item [name desc] {:tag :item :attrs {:id "3"} :contents (list {:tag :name :attrs {} :contents (list name)} {:tag :desc :attrs {} :contents (list desc)})}) (def fred-item (create-item "Fred" "Green-haired astrophysicist.")) ;; This disturbs the structure somehow (defn append-item [xmldb item] (zip/insert-right (-> xmldb zip/down zip/rightmost) item)) ;; I want to do something more like this (defn append-item2 [xmldb item] (zip/insert-right (zip/rightmost (zf/xml-> xmldb :item)) item)) (dosync (alter db append-item2 fred-item)) ;; Save this simple xml file with some added stuff. (ds/spit "appended-itemdb.xml" (with-out-str (lxml/emit (zip/root @db) :pad true))) I am unclear about how to use the clojure.zip functions appropriately in this case, and how that interacts with zip-filter. If you spot anything particularly weird in this small example, please point it out.

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• How can I define a clojure type that implements the servlet interface?

  - by Rob Lachlan

  I'm attempting to use deftype (from the bleeding-edge clojure 1.2 branch) to create a java class that implements the java Servlet interface. I would expect the code below to compile (even though it's not very useful). (ns foo [:import [javax.servlet Servlet ServletRequest ServletResponse]]) (deftype servlet [] javax.servlet.Servlet (service [this #^javax.servlet.ServletRequest request #^javax.servlet.ServletResponse response] nil)) But it doesn't compile. The compiler produces the message: Mismatched return type: service, expected: void, had: java.lang.Object [Thrown class java.lang.IllegalArgumentException] Which doesn't make sense to me, because I'm returning nil. So the fact that the return type of the method is void shouldn't be a problem. For instance, for the java.util.Set interface: (deftype bar [#^Number n] java.util.Set (clear [this] nil)) compiles without issue. So what am I doing wrong with the Servlet interface? To be clear: I know that the typical case is to subclass one of the servlet abstract classes rather than implement this interface directly, but it should still be possible to do this. Stack Trace: The stack trace for the (deftype servlet... is: Mismatched return type: service, expected: void, had: java.lang.Object [Thrown class java.lang.IllegalArgumentException] Restarts: 0: [ABORT] Return to SLIME's top level. Backtrace: 0: clojure.lang.Compiler$NewInstanceMethod.parse(Compiler.java:6461) 1: clojure.lang.Compiler$NewInstanceExpr.build(Compiler.java:6119) 2: clojure.lang.Compiler$NewInstanceExpr$DeftypeParser.parse(Compiler.java:6003) 3: clojure.lang.Compiler.analyzeSeq(Compiler.java:5289) 4: clojure.lang.Compiler.analyze(Compiler.java:5110) 5: clojure.lang.Compiler.analyze(Compiler.java:5071) 6: clojure.lang.Compiler.eval(Compiler.java:5347) 7: clojure.lang.Compiler.eval(Compiler.java:5334) 8: clojure.lang.Compiler.eval(Compiler.java:5311) 9: clojure.core$eval__4350.invoke(core.clj:2364) 10: swank.commands.basic$eval_region__673.invoke(basic.clj:40) 11: swank.commands.basic$eval_region__673.invoke(basic.clj:31) 12: swank.commands.basic$eval__686$listener_eval__687.invoke(basic.clj:54) 13: clojure.lang.Var.invoke(Var.java:365) 14: foo$eval__2285.invoke(NO_SOURCE_FILE) 15: clojure.lang.Compiler.eval(Compiler.java:5343) 16: clojure.lang.Compiler.eval(Compiler.java:5311) 17: clojure.core$eval__4350.invoke(core.clj:2364) 18: swank.core$eval_in_emacs_package__320.invoke(core.clj:59) 19: swank.core$eval_for_emacs__383.invoke(core.clj:128) 20: clojure.lang.Var.invoke(Var.java:373) 21: clojure.lang.AFn.applyToHelper(AFn.java:169) 22: clojure.lang.Var.applyTo(Var.java:482) 23: clojure.core$apply__3776.invoke(core.clj:535) 24: swank.core$eval_from_control__322.invoke(core.clj:66) 25: swank.core$eval_loop__324.invoke(core.clj:71) 26: swank.core$spawn_repl_thread__434$fn__464$fn__465.invoke(core.clj:183) 27: clojure.lang.AFn.applyToHelper(AFn.java:159) 28: clojure.lang.AFn.applyTo(AFn.java:151) 29: clojure.core$apply__3776.invoke(core.clj:535) 30: swank.core$spawn_repl_thread__434$fn__464.doInvoke(core.clj:180) 31: clojure.lang.RestFn.invoke(RestFn.java:398) 32: clojure.lang.AFn.run(AFn.java:24) 33: java.lang.Thread.run(Thread.java:637)

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• Why does Clojure neglect the uniform access principle?

  - by Alexey

  My background is Ruby, C#, JavaScript and Java. And now I'm learning Clojure. What makes me feel uncomfortable about the later is that idiomatic Clojure seems to neglect the Uniform access principle (wiki, c2) and thus to a certain degree encapsulation as well by suggesting to use maps instead of some sort of "structures" or "classes". It feels like step back. So a couple of questions, if anyone informed: Which other design decisions/concerns it conflicted with and why it was considered less important? Did you have the same concern as well and how it end up when you switched from a language supporting UAP by default (Ruby, Eiffel, Python, C#) to Clojure?

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• Is Clojure, Scala and other restrained by the JVM vs CLR

  - by jia93

  The Java implementors seem slow to adopt language improvements, for example compare C# with full closures, expression trees, LINQ etc.. to Java, and even the push back of some stuff to Java 8 will still leave it behind the current implementation of C#. However since I dont intend to use either Java or C# that particular language war isnt of interest too much, im more concerned with the JVM vs CLR. Is this lagging-behind also applicable to the JVM? Will Scala, Clojure etc.. will they be able to continue to innovate or score optimal performance in the face of slowly progressing underlying VM such as JVM? Is Clojure/Scala restrained at present by JVM limitations?

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• Approaching SICP in Clojure instead of Scheme

  - by ironicaldiction

  I am a third year bachelor student in a software engineering program, and I brought up the idea of reading SICP to an adviser to gain a deeper and more fundamental understanding of the principles behind all this software we engineer. He suggested not to learn Scheme to complete the book (because it's not as common as modern dialects of Lisp) but to do the exercises in Clojure instead. It's an already difficult book, if I do attempt the book's exercises in the more modern Clojure, how would that work? For example, I can't find any real solutions, the syntax they teach for Scheme is different, etc.

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• How to run Clojure tests on Windows?

  - by anta40

  I put Clojure in C:\clojure-1.1.0, and start the REPL by: java -cp clojure.jar clojure.main In \test\clojure\test_clojure, there are a bunch of test files. How to run these? For example, I tried: java -cp ......\clojure.jar clojure.main data_structures.clj And it didn't work.

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• Understanding clojure keywords

  - by tjb1982

  I'm taking my first steps with Clojure. Otherwise, I'm somewhat competent with JavaScript, Python, Java, and a little C. I was reading this artical that describes destructuring vectors and maps. E.g. => (def point [0 0]) => (let [[x y] point] => (println "the coordinates are:" x y)) the coordinates are: 0 0 but I'm having a difficult time understanding keywords. At first glance, they seem really simple, as they just evaluate to themselves: => :test :test But they seem to be used is so many different ways and I don't understand how to think about them. E.g., you can also do stuff like this: => (defn full-name [& {first :first last :last}] => (println first last)) => (full-name :first "Tom" :last "Brennan") Tom Brennan nil This doesn't seem intuitive to me. I would have guessed the arguments should have been something more like: (full-name {:first "Tom" :last "Brennan"}) because it looks like in the function definition that you're saying "no required arguments, but a variable number of arguments comes in the form of a single map". But it seems more like you're saying "no required arguments, but a variable number of arguments comes which should be a list of alternating keywords and values... ?" I'm not really sure how to wrap my brain around this. Also, things like this confuse me too: => (def population {:humans 5 :zombies 1000}) => (:zombies population) 1000 => (population :zombies) 1000 How do maps and keywords suddenly become functions? If I could get some clarification on the use of keywords in these two examples, that would be really helpful. Update I've also seen http://stackoverflow.com/questions/3337888/clojure-named-arguments and while the accepted answer is a great demonstration of how to use keywords with destructuring and named arguments, I'm really looking more for understanding how to think about them--why the language is designed this way and how I can best internalize their use.

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• Using clojure.contrib functions in slime REPL

  - by Tyler

  I want to use the functions in the clojure.contrib.trace namespace in slime at the REPL. How can I get slime to load them automatically? A related question, how can I add a specific namespace into a running repl? On the clojure.contrib API it describes usage like this: (ns my-namespace (:require clojure.contrib.trace)) But adding this to my code results in the file being unable to load with an "Unable to resolve symbol" error for any function from the trace package. I use leiningen 'lein swank' to start the ServerSocket and the project.clj file looks like this (defproject test-project "0.1.0" :description "Connect 4 Agent written in Clojure" :dependencies [[org.clojure/clojure "1.2.0-master-SNAPSHOT"] [org.clojure/clojure-contrib "1.2.0-SNAPSHOT"]] :dev-dependencies [[leiningen/lein-swank "1.2.0-SNAPSHOT"] [swank-clojure "1.2.0"]]) Everything seems up to date, i.e. 'lein deps' doesn't produce any changes. So what's up?

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• StackOverflow in compojure web project

  - by Anders Rune Jensen

  Hi I've been playing around with clojure and have been using it to build a simple little audio player. The strange thing is that sometimes, maybe one out of twenty, when contact the server I will get the following error: 2010-04-20 15:33:20.963::WARN: Error for /control java.lang.StackOverflowError at clojure.lang.RT.seq(RT.java:440) at clojure.core$seq__4245.invoke(core.clj:105) at clojure.core$filter__5084$fn__5086.invoke(core.clj:1794) at clojure.lang.LazySeq.sval(LazySeq.java:42) at clojure.lang.LazySeq.seq(LazySeq.java:56) at clojure.lang.RT.seq(RT.java:440) at clojure.core$seq__4245.invoke(core.clj:105) at clojure.core$filter__5084$fn__5086.invoke(core.clj:1794) at clojure.lang.LazySeq.sval(LazySeq.java:42) at clojure.lang.LazySeq.seq(LazySeq.java:56) at clojure.lang.RT.seq(RT.java:440) at clojure.core$seq__4245.invoke(core.clj:105) at clojure.core$filter__5084$fn__5086.invoke(core.clj:1794) at clojure.lang.LazySeq.sval(LazySeq.java:42) at clojure.lang.LazySeq.seq(LazySeq.java:56) at clojure.lang.RT.seq(RT.java:440) at clojure.core$seq__4245.invoke(core.clj:105) at clojure.core$filter__5084$fn__5086.invoke(core.clj:1794) at clojure.lang.LazySeq.sval(LazySeq.java:42) at clojure.lang.LazySeq.seq(LazySeq.java:56) at clojure.lang.RT.seq(RT.java:440) ... If I do it right after again it always works. So it appears to be related to timing or something. The code in question is: (defn add-track [t] (common/ref-add tracks t)) (defn add-collection [coll] (doseq [track coll] (add-track track))) and (defn ref-add [ref value] (dosync (ref-set ref (conj @ref value)))) where coll is extracted from this function: (defn tracks-by-album [album] (sort sort-tracks (filter #(= (:album %) album) @tracks))) so it does appear to be the tracks-by-album function from the stack trace. I just don't see why it sometimes works and sometimes doesn't.

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• Wrong number of args passed to: repl$repl

  - by grm

  Hi, I have a trouble with a compojure "Getting started" example that I do not seem to understand. When I run the example from http://weavejester.github.com/compojure/docs/getting-started.html ...I get the following error at the lein repl step: ~/hello-www> lein repl src/hello_www/core.clj Exception in thread "main" java.lang.IllegalArgumentException: Wrong number of args passed to: repl$repl (NO_SOURCE_FILE:0) at clojure.lang.Compiler.eval(Compiler.java:5359) at clojure.lang.Compiler.eval(Compiler.java:5311) at clojure.core$eval__4350.invoke(core.clj:2364) at clojure.main$eval_opt__6502.invoke(main.clj:228) at clojure.main$initialize__6506.invoke(main.clj:247) at clojure.main$script_opt__6526.invoke(main.clj:263) at clojure.main$main__6544.doInvoke(main.clj:347) at clojure.lang.RestFn.invoke(RestFn.java:483) at clojure.lang.Var.invoke(Var.java:381) at clojure.lang.AFn.applyToHelper(AFn.java:180) at clojure.lang.Var.applyTo(Var.java:482) at clojure.main.main(main.java:37) Caused by: java.lang.IllegalArgumentException: Wrong number of args passed to: repl$repl at clojure.lang.AFn.throwArity(AFn.java:439) at clojure.lang.AFn.invoke(AFn.java:43) at clojure.lang.Var.invoke(Var.java:369) at clojure.lang.AFn.applyToHelper(AFn.java:165) at clojure.lang.Var.applyTo(Var.java:482) at clojure.core$apply__3776.invoke(core.clj:535) at leiningen.core$_main__59$fn__61.invoke(core.clj:94) at leiningen.core$_main__59.doInvoke(core.clj:91) at clojure.lang.RestFn.applyTo(RestFn.java:138) at clojure.core$apply__3776.invoke(core.clj:535) at leiningen.core$_main__59.invoke(core.clj:97) at user$eval__67.invoke(NO_SOURCE_FILE:1) at clojure.lang.Compiler.eval(Compiler.java:5343) ... 11 more I have tried both the stable and the developer version of lein without any success. Any ideas on what I could look for next? I get the same result both on linux and cygwin. When I run it manually, it seems to work fine on linux: java -cp "lib/*" clojure.main src/hello_www/core.clj 2010-05-17 19:34:17.280::INFO: Logging to STDERR via org.mortbay.log.StdErrLog 2010-05-17 19:34:17.281::INFO: jetty-6.1.14 2010-05-17 19:34:17.382::INFO: Started [email protected]:8080

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• Setting up Clojure Project And Sub Projects

  - by octopusgrabbus

  This is primarily a lein question about setting up a major project and its sub-projects, and is not intended to be a discussion question. Instead, I am interested in either a pointer to documentation or to a Clojure/lein best practices link. I have a municipal property assessments application that splits two master flies into different subset files, depending on whether a billing transfer is taking place or we want to batch update new accounts, rather than making our assessment department enter new accounts once in their system and then again in the tax collection system. My application is going to be large enough, that I can see a common library lein project with support functions, like splitting apart the files, and then individual lein projects that use the common library. Should the lein projects be set up at the same level and support included through the project.clj/core.clj files? Is there an advantage to creating lein new projects underneath a major project? Is there a problem with combing all functions in one project? I can probably make my one core.clj contain all flavors of the program, but coming from a C/C++ and Python background, I would prefer to have a lot of little projects.

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• Does approaching SICP in clojure have a high chance of success? [on hold]

  - by ironicaldiction

  I am a third year bachelor student in a software engineering program, and I brought up the idea of reading SICP to an adviser to gain a deeper and more fundamental understanding of the principles behind all this software we engineer. He suggested not to learn scheme to complete the book (because it's not as common as modern dialects of lisp) but to do the exercises in clojure instead. My worry is that completing exercises in clojure instead of scheme will make an already difficult book tortuous. If I do attempt the book's exercises in the more modern clojure, will it be difficult to succeed (for example, because I can't find any real solutions, the syntax they teach for scheme is different, etc.), or do you think approaching the book in clojure could be just as successful as approaching it in scheme? I'm really not knowledgeable enough about either clojure or scheme to make an argument about this, so I wanted to know if I should bring it up or not.

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• Mutating XML in Clojure

  - by mac

  Clojures clojure.xml/parse, clojure.zip/xml-zip and clojure.contrib.zip-filter.xml/xml- are excellent tools for pulling values out of xml, but what if I want to change the xml (the result of clojure.zip/xml-zip) based on what I learn from xml- "queries" and write the result back out as xml? I would have expected that (clojure.contrib.prxml/prxml (clojure.xml/parse xml-content)) spit back xml, but that is not the case.

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• Comparing Clojure books

  - by Michiel Borkent

  Currently there is (afaik) one completed Clojure book available: Programming Clojure by Stuart Halloway. Two are being written and partially available at Manning: The Joy of Clojure by Fogus and Houser Clojure in Action by Amit Rathore Another one is about to be published in May: Practical Clojure (The Definitive Guide) by Luke Van der Hart Are these books more or less the same and meant as a general introduction to Clojure? Does it make sense to buy them all, or is there a risk of having three very similar books? Will there be books that go into more specialized areas of Clojure and targetted for 'intermediate' or 'advanced' Clojure programmers?

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• Clojure load files

  - by Nate

  I'm trying to set up a simple clojure project, and I'm not sure how to load files between the project. I'm sure that the answer is in the documentation, but I can't find a simple answer any where and I'm not sure where to look. Essentially, my directory looks like this: Clojure/ clojure/ clojure.jar other clojure files clojure-contrib/ clojure-contrib.jar other contrib files project/ main.clj utils.clj And I want main.clj to be something like this: (ns project.main (:require project.utils)) (greet) and utils.clj to be something like this: (ns project.utils) (defn greet [] (println "Hello, World!")) But that fails with: Exception in thread "main" java.io.FileNotFoundException: Could not locate project/utils__init.class or project/utils.clj on classpath: (main.clj:1) When I attempt to run it. How do you set up a simple clojure project?

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• Using Clojure instead of Python for scalability (multi core) reasons, good idea?

  - by Vandell

  After reading http://clojure.org/rationale and other performance comparisons between Clojure and many languages, I started to think that apart from ease of use, I shouldn't be coding in Python anymore, but in Clojure instead. Actually, I began to fill irresponsisble for not learning clojure seeing it's benefits. Does it make sense? Can't I make really efficient use of all cores using a more imperative language like Python, than a lisp dialect or other functional language? It seems that all the benefits of it come from using immutable data, can't I do just that in Python and have all the benefits? I once started to learn some Common Lisp, read and done almost all exercices from a book I borrowod from my university library (I found it to be pretty good, despite it's low popularity on Amazon). But, after a while, I got myself struggling to much to do some simple things. I think there's somethings that are more imperative in their nature, that makes it difficult to model those thins in a functional way, I guess. The thing is, is Python as powerful as Clojure for building applications that takes advantages of this new multi core future? Note that I don't think that using semaphores, lock mechanisms or other similar concurrency mechanism are good alternatives to Clojure 'automatic' parallelization.

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• How to cast a character to int in Clojure?

  - by Learning Clojure

  How to cast a character to int in Clojure? I am trying to write a rot 13 in clojure, so I need to have something to cast my char to int. I found something called (int), so I put: (int a) Get: CompilerException java.lang.RuntimeException: Unable to resolve symbol: a in this context, compiling:(NO_SOURCE_PATH:13:1) Then I put: (int 'a) Get: ClassCastException clojure.lang.Symbol cannot be cast to java.lang.Character clojure.lang.RT.intCast (RT.java:1087) Then: (rot13 ''a') Get: ClassCastException clojure.lang.PersistentList cannot be cast to java.lang.Character clojure.lang.RT.intCast (RT.java:1087) And: (rot13 "a") Get: ClassCastException java.lang.String cannot be cast to java.lang.Character clojure.lang.RT.intCast (RT.java:1087) So what is the right way to do it? btw, I always get confused with all these clojure syntax. But I can never find any source only help me with my problem. Any suggestions? Thank you!!

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• Clojure editor/IDE recommendations on OS X

  - by Julien Chastang

  I am starting to learn the Clojure programming language. Are there any recommendations for Clojure editors/IDEs on OS X? Update 2009-9-23: The clojure space has changed tremendously since I originally posted this question. Many of the links below, especially those that refer to clojure-mode with emacs, are out-of-date. The best clojure IDE I found was the enclojure Netbeans plugin which was recently released (2009-08-25). Update 2010-4-30: Here is another very good link on this subject by Lau B. Jensen. Also, for my own clojure development, I have actually moved to emacs / swank-clojure.

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• Can the Clojure set and maps syntax be added to other Lisp dialects?

  - by Cedric Martin

  In addition to create list using parentheses, Clojure allows to create vectors using [ ], maps using { } and sets using #{ }. Lisp is always said to be a very extensible language in which you can easily create DSLs etc. But is Lisp so extensible that you can take any Lisp dialect and relatively easily add support for Clojure's vectors, maps and sets (which are all functions in Clojure)? I'm not necessarily asking about cons or similar actually working on these functions: what I'd like to know is if the other could be modified so that the source code would look like Clojure's source code (that is: using matching [ ], { } and #{ } in addition to ( )). Note that if it cannot be done this is not a criticism of Lisp: what I'd like to know is, technically, what should be done or what cannot be done if one were to add such a thing.

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• Clojure Box: Problem with classpath (noob question)

  - by Rainer

  Hello, I'm stuck with "Programming Clojure" on page 37 on a Windows 7 machine. After downloading the "examples" dir into "C:/clojure", I typed: user (require 'examples.introduction) and I got ; Evaluation aborted. java.io.FileNotFoundException: Could not locate examples/ introduction__init.class or examples/introduction.clj on classpath: (NO_SOURCE_FILE:0) My .emacs file looks like this: (setq swank-clojure-extra-classpaths (list "C:/Clojure")) The files in C:/Clojure are there (I triplechecked) Any help will be appreciated.

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