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  • Clojure and NoSQL databases

    - by Mad Wombat
    I am currently trying to pick between different NoSQL databases for my project. The project is being written in clojure and javascript. I am currently looking at three candidates for storage. What are the relative strengths and weaknesses of MongoDB, FleetDB and CouchDB? Which one is better supported in Clojure? Which one is better supported under Linux? Did I miss a better product (has to be free and OSS)?

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  • Hidden features of Clojure

    - by danlei
    Which lesser-known but useful features of Clojure do you find yourselves using? Feel free to share little tricks and idioms, but try to restrict yourselves to Core and Contrib. I found some really interesting information in answers to these similar questions: Hidden features of Haskell Hidden features of Python Hidden features of Java Hidden features of C There are many more "Hidden feature" questions for other languages, so I thought it would be nice to have one for Clojure, too.

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  • Learning functional/clojure programming - practical excersises?

    - by Konrad Garus
    I'm learning functional programming with Clojure. What practical excersises can you recommend? Online repositories with solutions would be perfect. One idea I can think of is going through all the popular algorithms on sorting, trees, graphs etc. and implementing them in Clojure myself. While it could work, it may be pretty steep and I'm likely to do it inefficiently (compared to someone who knows what she's doing).

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  • Profiling tool for Clojure?

    - by j-g-faustus
    Hi, does anyone know of a good profiling tool or library for Clojure? I would prefer something that could be used from the REPL, along the lines of (with-profiling ...) in Allegro Common Lisp back in the day. Is there anything along those lines? Or do you have any experience with (non-commercial) Java profilers that work well with Clojure?

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  • F# vs. Clojure

    - by nikolai
    What are the most significant differencies between the F# and Clojure ? Which constructs has F# which Clojure does not have and vice versa? Does F# have macros?

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  • "reduce" or "apply" using logical functions in Clojure

    - by Alex B
    I cannot use logical functions on a range of booleans in Clojure (1.2). Neither of the following works due to logical functions being macros: (reduce and [... sequence of bools ...]) (apply or [... sequence of bools ...]) The error saying that I "can't take value of a macro: #'clojure.core/and". How to apply these logical functions (macros) without writing boilerplate code?

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  • Extending a Java Swing class in Clojure

    - by mikera
    I'm trying to extend a Java Swing component in Clojure, i.e. I want to extend a javax.swing.JComponent and add some custom methods implemented in pure Clojure in addition to all the standard inherited methods. I've tried using "proxy" which works great if I just want a single instance (in the same way as an anonymous inner class). However I'd really like a named class so that I can generate an arbitrary number of instances. What's the recommended way of doing this?

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  • How do I set up the Clojure classpath in Emacs after installing with ELPA?

    - by derefed
    I'm trying to add paths to my classpath in the Clojure REPL that I've set up in Emacs using ELPA. Apparently, this isn't the $CLASSPATH environment variable, but rather the swank-clojure-classpath variable that Swank sets up. Because I used ELPA to install Swank, Clojure, etc., there are a ton of .el files that take care of everything instead of my .emacs file. Unfortunately, I can't figure out how to change the classpath now. I've tried using (setq 'swank-clojure-extra-classpaths (list ...)) both before and after the ELPA stuff in my .emacs, and I've tried adding paths directly to swank-clojure-classpath in .emacs, .emacs.d/init.el, and .emacs.d/user/user.el, but nothing works. What I'm ultimately trying to do is to add both the current directory "." and the directory in which I keep my Clojure programs. I'm assuming swank-clojure-classpath is the thing I need to set here. Thanks for your help.

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  • How do I set up the Clojure classpath in Emacs after installing with ELPA?

    - by derefed
    I'm trying to add paths to my classpath in the Clojure REPL that I've set up in Emacs using ELPA. Apparently, this isn't the $CLASSPATH environment variable, but rather the swank-clojure-classpath variable that Swank sets up. Because I used ELPA to install Swank, Clojure, etc., there are a ton of .el files that take care of everything instead of my .emacs file. Unfortunately, I can't figure out how to change the classpath now. I've tried using (setq 'swank-clojure-extra-classpaths (list ...)) both before and after the ELPA stuff in my .emacs, and I've tried adding paths directly to swank-clojure-classpath in .emacs, .emacs.d/init.el, and .emacs.d/user/user.el, but nothing works. What I'm ultimately trying to do is to add both the current directory "." and the directory in which I keep my Clojure programs. I'm assuming swank-clojure-classpath is the thing I need to set here. Thanks for your help.

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  • Concurrent cartesian product algorithm in Clojure

    - by jqno
    Is there a good algorithm to calculate the cartesian product of three seqs concurrently in Clojure? I'm working on a small hobby project in Clojure, mainly as a means to learn the language, and its concurrency features. In my project, I need to calculate the cartesian product of three seqs (and do something with the results). I found the cartesian-product function in clojure.contrib.combinatorics, which works pretty well. However, the calculation of the cartesian product turns out to be the bottleneck of the program. Therefore, I'd like to perform the calculation concurrently. Now, for the map function, there's a convenient pmap alternative that magically makes the thing concurrent. Which is cool :). Unfortunately, such a thing doesn't exist for cartesian-product. I've looked at the source code, but I can't find an easy way to make it concurrent myself. Also, I've tried to implement an algorithm myself using map, but I guess my algorithmic skills aren't what they used to be. I managed to come up with something ugly for two seqs, but three was definitely a bridge too far. So, does anyone know of an algorithm that's already concurrent, or one that I can parallelize myself?

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  • Parallel doseq for Clojure

    - by andrew cooke
    I haven't used multithreading in Clojure at all so am unsure where to start. I have a doseq whose body can run in parallel. What I'd like is for there always to be 3 threads running (leaving 1 core free) that evaluate the body in parallel until the range is exhausted. There's no shared state, nothing complicated - the equivalent of Python's multiprocessing would be just fine. So something like: (dopar 3 [i (range 100)] ; repeated 100 times in 3 parallel threads... ...) Where should I start looking? Is there a command for this? A standard package? A good reference? So far I have found pmap, and could use that (how do I restrict to 3 at a time? looks like it uses 32 at a time - no, source says 2 + number of processors), but it seems like this is a basic primitive that should already exist somewhere. clarification: I really would like to control the number of threads. I have processes that are long-running and use a fair amount of memory, so creating a large number and hoping things work out OK isn't a good approach (example which uses a significant chunk available mem). update: Starting to write a macro that does this, and I need a semaphore (or a mutex, or an atom i can wait on). Do semaphores exist in Clojure? Or should I use a ThreadPoolExecutor? It seems odd to have to pull so much in from Java - I thought parallel programming in Clojure was supposed to be easy... Maybe I am thinking about this completely the wrong way? Hmmm. Agents?

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  • how does one _model_ data from relational databases in clojure ?

    - by sandeep
    I have asked this question on twitter as well the #clojure IRC channel, yet got no responses. There have been several articles about Clojure-for-Ruby-programmers, Clojure-for-lisp-programmers.. but what is the missing part is Clojure for ActiveRecord programmers . There have been articles about interacting with MongoDB, Redis, etc. - but these are key value stores at the end of the day. However, coming from a Rails background, we are used to thinking about databases in terms of inheritance - has_many, polymorphic, belongs_to, etc. The few articles about Clojure/Compojure + MySQL (ffclassic) - delve right into sql. Of course, it might be that an ORM induces impedence mismatch, but the fact remains that after thinking like ActiveRecord, it is very difficult to think any other way. I believe that relational DBs, lend themselves very well to the object-oriented paradigm because of them being , essentially, Sets. Stuff like activerecord is very well suited for modelling this data. For e.g. a blog - simply put class Post < ActiveRecord::Base has_many :comments end class Comment < ActiveRecord::Base belongs_to :post end How does one model this in Clojure - which is so strictly anti-OO ? Perhaps the question would have been better if it referred to all functional programming languages, but I am more interested from a Clojure standpoint (and Clojure examples)

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  • Embedding swank-clojure in java program

    - by user237417
    Based on the Embedding section of http://github.com/technomancy/swank-clojure, I'm using the following to test it out. Is there a better way to do this that doesn't use Compiler? Is there a way to programmatically stop swank? It seems start-repl takes control of the thread. What would be a good way to spawn off another thread for it and be able to kill that thread programatically. import clojure.lang.Compiler; import java.io.StringReader; public class Embed { public static void main(String[] args) throws Exception { final String startSwankScript = "(ns my-app\n" + " (:use [swank.swank :as swank]))\n" + "(swank/start-repl) "; Compiler.load(new StringReader(startSwankScript)); } } Any help much appreciated, hhh

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  • Porting a piece of Lisp code to Clojure (PAIP)

    - by Robert Brown
    I'm reading Paradigms of Artificial Intelligence Programming (PAIP) by Peter Norvig and I'm trying to write all the code in Clojure rather than common Lisp. However I'm stuck on this piece of code on page 39: (defparameter *simple-grammar* '((sentence -> (noun-phrase verb-phrase)) (noun-phrase -> (Article Noun)) (verb-phrase -> (Verb noun-phrase)) (Article -> the a) (Noun -> man ball woman table) (Verb -> hit took saw liked)) "A grammar for a trivial subset of English.") (defvar *grammar* *simple-grammar*) How can I translate this into Clojure? Thanks.

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  • Defining a SPI in Clojure

    - by Joe Holloway
    I'm looking for an idiomatic way(s) to define an interface in Clojure that can be implemented by an external "service provider". My application would locate and instantiate the service provider module at runtime and delegate certain responsibilities to it. Let's say, for example, that I'm implementing a RPC mechanism and I want to allow a custom middleware to be injected at configuration time. This middleware could pre-process the message, discard messages, wrap the message handler with logging, etc. I know several ways to do this if I fall back to Java reflection, but feel that implementing it in Clojure would help my understanding. (Note, I'm using SPI in a general sense here, not specifically referring to the way it's defined in the JAR file specification) Thanks

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  • Daemon with Clojure/JVM

    - by Isaac Copper
    I'd like to have a small (not doing too damn much) daemon running on a little server, watching a directory for new files being added to it (and any directories in the main one), and calling another Clojure program to deal with that new file. Ideally, each file would be added to a queue (a list represented by a ref in Clojure?) and the main process would take care of those files in the queue on a FIFO basis. My question is: is having a JVM up running this little program all the time too much a resource hog? And do you have any suggestions as to how go about doing this? Thank you very much!

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  • Why is there a limit of max 20 parameters to a clojure function

    - by GuyC
    Hi, there seems to be a limit to the number of parameters a clojure function can take. When defining a function with more than 20 parameters I receive the following: Obviously this can be avoided, but I was hitting this limit porting the execution model of an existing DSL to clojure, and I have constructs in my DSL like the following, which by macro expansion can be mapped to functions quite easily except for this limit: (defAlias nn1 ((element ?e1) (element ?e2)) number "@doc features of the elements are calculated for entry into the first neural network, the result is the score computed by the latter" (nn1-recall (nn1-feature00 ?e1 ?e2) (nn1-feature01 ?e1 ?e2) ... (nn1-feature89 ?e1 ?e2))) which is a DSL statement to call a neural network with 90 input nodes. Can work around it of course, but was wondering where the limit comes from. Thanks.

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  • Using type hints in Clojure for Java return values

    - by mikera
    I'm working on some Java / Clojure interoperability and came across a reflection warning for the following code: (defn load-image [resource-name] (javax.imageio.ImageIO/read (.getResource (class javax.imageio.ImageIO) resource-name))) => Reflection warning, clojure/repl.clj:37 - reference to field read can't be resolved. I'm surprised at this because getResource always returns a URL and I would therefore expect the compiler to use the appropriate static method in javax.imageio.ImageIO/read. The code works fine BTW so it is clearly finding the right method at run time. So two questions: Why is this returning a reflection warning? What type hint do I need to fix this?

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  • Idiomatic approach for structuring Clojure source code

    - by mikera
    I'm interested in how people structure their Clojure source code. Being used to Java, I'm pretty familiar with the paradigm of one class per source code file, bundling all the data and method definitions with appropriate comments and annotations etc. However Clojure offers a lot more flexibility, and I'm not sure how I should structure my project (likely to end up as a medium sized app, maybe 5,000 lines with three or four distinct subsystems) In particular I'm wrestling with: What guidelines should I use to determine whether code should be in a single namespace vs. separated out into different namespaces? Should each protocol/datatype have it's own namespace + source file with associated set of functions? When should I require vs. use other namespaces?

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  • Controlling symbol generation in Clojure macros

    - by mikera
    I'm trying (as a self-learning exercise) to create a Clojure macro that will generate code to apply a function to a sequence of integers and sum the result, e.g. f(0) + f(1) + f(2) + f(3) This is my attempt: (defmacro testsum [func n] `(fn [x#] (+ ~@( map (fn [i] `(~func x#)) (range n))))) However something seems to go wrong with the x# gensym and I end up with two different versions of x and hence the function doesn't work: (macroexpand '(testsum inc 3)) gives: (fn* ([x__809__auto__] (clojure.core/+ (inc x__808__auto__) (inc x__808__auto__) (inc x__808__auto__)))) This is pretty much exactly what I want apart from the different 809 and 808 versions of x..... What am I doing wrong? I thought that the auto gensym was meant to create a single unique symbol for exactly this kind of purpose? Is there a better way of doing this?

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  • Dynamically generating high performance functions in clojure

    - by mikera
    I'm trying to use Clojure to dynamically generate functions that can be applied to large volumes of data - i.e. a requirement is that the functions be compiled to bytecode in order to execute fast, but their specification is not known until run time. e.g. suppose I specify functions with a simple DSL like: (def my-spec [:add [:multiply 2 :param0] 3]) I would like to create a function compile-spec such that: (compile-spec my-spec) Would return a compiled function of one parameter x that returns 2x+3. What is the best way to do this in Clojure?

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