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  • Can't import clojure records

    - by Zubair
    I have created a record like this: (defrecord User [user-id email]) :but when I try to access it from another name-space I get the error: (User. "name" "email") java.lang.IllegalArgumentException: Unable to resolve classname: User It works when I do: (oe.model.modelcore.User. "name" "email") : I know I will need to import the Java class, but is there any way for clojure to do this automatically when I do: (use 'oe.model.modelcore :reload)

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  • (partial apply str) and apply-str in clojure's ->

    - by Jason Baker
    If I do the following: user=> (-> ["1" "2"] (partial apply str)) #<core$partial__5034$fn__5040 clojure.core$partial__5034$fn__5040@d4dd758> ...I get a partial function back. However, if I bind it to a variable: user=> (def apply-str (partial apply str)) #'user/apply-str user=> (-> ["1" "2" "3"] apply-str) "123" ...the code works as I intended it. I would assume that they are the same thing, but apparently that isn't the case. Can someone explain why this is to me?

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  • Iterator blocks in Clojure?

    - by Checkers
    I am using clojure.contrib.sql to fetch some records from an SQLite database. (defn read-all-foo [] (with-connection *db* (with-query-results res ["select * from foo"] (into [] res)))) Now, I don't really want to realize the whole sequence before returning from the function (i.e. I want to keep it lazy), but if I return res directly or wrap it some kind of lazy wrapper (for example I want to make a certain map transformation on result sequence), SQL-related bindings will be reset and connection will be closed after I return, so realizing the sequence will throw an exception. How can I enclose the whole function in a closure and return a kind of iterator block (like yield in C# or Python)? Or is there another way to return a lazy sequence from this function?

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  • How to return the output of a recursive function in Clojure

    - by Silanglaya Valerio
    Hi everyone! I'm new to functional languages and clojure, so please bear with me... I'm trying to construct a list of functions, with either random parameters or constants. The function that constructs the list of functions is already working, though it doesn't return the function itself. I verified this using println. Here is the snippet: (def operations (list #(- %1 %2) #(+ %1 %2) #(* %1 %2) #(/ %1 %2))) (def parameters (list \u \v \w \x \y \z)) (def parameterlistcount 6) (def paramcount 2) (def opcount 4) (defn generateFunction "Generates a random function list" ([] (generateFunction 2 4 0.5 0.6 '())) ([pc maxdepth fp pp function] (if (and (> maxdepth 0) (< (rand) fp)) (dotimes [i 2] (println(conj (generateFunction pc (dec maxdepth) fp pp function) {:op (nth operations (rand-int opcount))}))) (if (and (< (rand) pp) (> pc 0)) (do (dec pc) (conj function {:param (nth parameters (rand-int parameterlistcount))})) (conj function {:const (rand-int 100)}))))) Any help will be appreciated, thanks!

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  • Clojure: Equivalent to Common Lisp READ function?

    - by jkndrkn
    Hi there. When I want to read in an S-expression stored in a file into a running Common Lisp program, I do the following: (defun load-file (filename) "Loads data corresponding to a s-expression in file with name FILENAME." (with-open-file (stream filename) (read stream))) If, for example, I have a file named foo.txt that contains the S-expression (1 2 3), the above function will return that S-expression if called as follows: (load-file "foo.txt"). I've been searching and searching and have not found an equally elegant solution in Clojure. Any ideas? Thanks!

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  • Overriding equals, hashCode and toString in a Clojure deftype

    - by mikera
    I'm trying to create a new type in Clojure using deftype to implement a two dimensional (x,y) coordinate, which implements a "Location" protocol. I'd also like to have this implement the standard Java equals, hashCode and toString methods. My initial attempt is: (defprotocol Location (get-x [p]) (get-y [p]) (add [p q])) (deftype Point [#^Integer x #^Integer y] Location (get-x [p] x) (get-y [p] y) (add [p q] (let [x2 (get-x q) y2 (get-y q)] (Point. (+ x x2) (+ y y2)))) Object (toString [self] (str "(" x "," y ")")) (hashCode [self] (unchecked-add x (Integer/rotateRight y 16))) (equals [self b] (and (XXXinstanceofXXX Location b) (= x (get-x b)) (= y (get-y b))))) However the equals method still needs some way of working out if the b parameter implements the Location protocol. What is the right approach? Am I on the right track?

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  • Clojure lots of threads

    - by Timothy Baldridge
    I just got done watching Rick Hickey's "Clojure Concurrency" talk, and I have a few questions about threads. Let's say I have a situation with lots of Agents, let's say 10,000 of them running one machine. I'd rather not have 10,000 CPU threads running at once, but I don't want threads to be blocked by the actions of other threads. In this example I won't really be waiting for replies, instead each Agent will be sending a message or two, and then waiting until it gets a message. How would I structure a program like this without getting 10k OS threads which would probably end up slowing the system down.

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  • Clojure - tail recursive sieve of Eratosthenes

    - by Konrad Garus
    I have this implementation of the sieve of Eratosthenes in Clojure: (defn sieve [n] (loop [last-tried 2 sift (range 2 (inc n))] (if (or (nil? last-tried) (> last-tried n)) sift (let [filtered (filter #(or (= % last-tried) (< 0 (rem % last-tried))) sift)] (let [next-to-try (first (filter #(> % last-tried) filtered))] (recur next-to-try filtered)))))) For larger n (like 20000) it ends with stack overflow. Why doesn't tail call elimination work here? How to fix it?

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  • Chain call in clojure?

    - by Konrad Garus
    I'm trying to implement sieve of Eratosthenes in Clojure. One approach I would like to test is this: Get range (2 3 4 5 6 ... N) For 2 <= i <= N Pass my range through filter that removes multiplies of i For i+1th iteration, use result of the previous filtering I know I could do it with loop/recur, but this is causing stack overflow errors (for some reason tail call optimization is not applied). How can I do it iteratively? I mean invoking N calls to the same routine, passing result of ith iteration to i+1th.

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  • Clojure / HBase: How to Import HBaseTestingUtility in v0.94.6.1

    - by David Williams
    In Clojure, if I want to start a test cluster using the hbase testing utility, I have to annotate my dependencies with: [org.apache.hbase/hbase "0.92.2" :classifier "tests" :scope "test"] First of all, I have no idea what this means. According to leiningens sample project.clj ;; Dependencies are listed as [group-id/name version]; in addition ;; to keywords supported by Pomegranate, you can use :native-prefix ;; to specify a prefix. This prefix is used to extract natives in ;; jars that don't adhere to the default "<os>/<arch>/" layout that ;; Leiningen expects. Question 1: What does that mean? Question 2: If I upgrade the version: [org.apache.hbase/hbase "0.94.6.1" :classifier "tests" :scope "test"] Then I receive a ClassNotFoundException Exception in thread "main" java.lang.ClassNotFoundException: org.apache.hadoop.hbase.HBaseConfiguration Whats going on here and how do I fix it?

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  • Dynamic scoping in Clojure?

    - by j-g-faustus
    Hi, I'm looking for an idiomatic way to get dynamically scoped variables in Clojure (or a similar effect) for use in templates and such. Here is an example problem using a lookup table to translate tag attributes from some non-HTML format to HTML, where the table needs access to a set of variables supplied from elsewhere: (def *attr-table* ; Key: [attr-key tag-name] or [boolean-function] ; Value: [attr-key attr-value] (empty array to ignore) ; Context: Variables "tagname", "akey", "aval" '( ; translate :LINK attribute in <a> to :href [:LINK "a"] [:href aval] ; translate :LINK attribute in <img> to :src [:LINK "img"] [:src aval] ; throw exception if :LINK attribute in any other tag [:LINK] (throw (RuntimeException. (str "No match for " tagname))) ; ... more rules ; ignore string keys, used for internal bookkeeping [(string? akey)] [] )) ; ignore I want to be able to evaluate the rules (left hand side) as well as the result (right hand side), and need some way to put the variables in scope at the location where the table is evaluated. I also want to keep the lookup and evaluation logic independent of any particular table or set of variables. I suppose there are similar issues involved in templates (for example for dynamic HTML), where you don't want to rewrite the template processing logic every time someone puts a new variable in a template. Here is one approach using global variables and bindings. I have included some logic for the table lookup: ;; Generic code, works with any table on the same format. (defn rule-match? [rule-val test-val] "true if a single rule matches a single argument value" (cond (not (coll? rule-val)) (= rule-val test-val) ; plain value (list? rule-val) (eval rule-val) ; function call :else false )) (defn rule-lookup [test-val rule-table] "looks up rule match for test-val. Returns result or nil." (loop [rules (partition 2 rule-table)] (when-not (empty? rules) (let [[select result] (first rules)] (if (every? #(boolean %) (map rule-match? select test-val)) (eval result) ; evaluate and return result (recur (rest rules)) ))))) ;; Code specific to *attr-table* (def tagname) ; need these globals for the binding in html-attr (def akey) (def aval) (defn html-attr [tagname h-attr] "converts to html attributes" (apply hash-map (flatten (map (fn [[k v :as kv]] (binding [tagname tagname akey k aval v] (or (rule-lookup [k tagname] *attr-table*) kv))) h-attr )))) (defn test-attr [] "test conversion" (prn "a" (html-attr "a" {:LINK "www.google.com" "internal" 42 :title "A link" })) (prn "img" (html-attr "img" {:LINK "logo.png" }))) user=> (test-attr) "a" {:href "www.google.com", :title "A link"} "img" {:src "logo.png"} This is nice in that the lookup logic is independent of the table, so it can be reused with other tables and different variables. (Plus of course that the general table approach is about a quarter of the size of the code I had when I did the translations "by hand" in a giant cond.) It is not so nice in that I need to declare every variable as a global for the binding to work. Here is another approach using a "semi-macro", a function with a syntax-quoted return value, that doesn't need globals: (defn attr-table [tagname akey aval] `( [:LINK "a"] [:href ~aval] [:LINK "img"] [:src ~aval] [:LINK] (throw (RuntimeException. (str "No match for " tagname))) ; ... more rules [(string? ~akey)] [] ))) Only a couple of changes are needed to the rest of the code: In rule-match?, when syntax-quoted the function call is no longer a list: - (list? rule-val) (eval rule-val) + (seq? rule-val) (eval rule-val) In html-attr: - (binding [tagname tagname akey k aval v] - (or (rule-lookup [k tagname] *attr-table*) kv))) + (or (rule-lookup [k tagname] (attr-table tagname k v)) kv))) And we get the same result without globals. (And without dynamic scoping.) Are there other alternatives to pass along sets of variable bindings declared elsewhere, without the globals required by Clojure's binding? Is there an idiomatic way of doing it, like Ruby's binding or Javascript's function.apply(context)?

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  • Clojure: Testing every value from map operation for truth

    - by Ralph
    How can I test that every value in the collection returned by map is true? I am using the following: (defn test [f coll] (every? #(identity %) (map f coll))) with the anonymous function #(identity %), but I was wondering if there is a better way. I cannot use (apply and ...) because and is a macro. UPDATE: BTW, I am making my way through The Haskell Road to Logic, Maths, and Programming, by Kees Doets and Jan can Eijck, but doing the exercises in Clojure. It's a very interesting book.

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  • Extract page from PDF using iText and clojure

    - by KobbyPemson
    I am trying to extract a single page from a pdf with clojure by translating the splitPDF method I found here http://viralpatel.net/blogs/itext-tutorial-merge-split-pdf-files-using-itext-jar/ I keep getting this error IOException Stream Closed java.io.FileOutputStream.writeBytes (:-2) This prevents me from opening the document while the repl is still open. Once I close the repl I'm able to access the document. Why do I get the error? How do I fix it ? How can I make it more clojurey? (import '(com.itextpdf.text Document) '(com.itextpdf.text.pdf PdfReader PdfWriter PdfContentByte PdfImportedPage BaseFont) '(java.io File FileInputStream FileOutputStream InputStream OutputStream)) (defn extract-page [src dest pagenum] (with-open [ d (Document.) os (FileOutputStream. dest)] (let [ srcpdf (->> src FileInputStream. PdfReader.) destpdf (PdfWriter/getInstance d os)] (doto d (.open ) (.newPage )) (.addTemplate (.getDirectContent destpdf) (.getImportedPage destpdf srcpdf pagenum) 0 0))))

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  • Huge file in Clojure and Java heap space error

    - by trzewiczek
    I posted before on a huge XML file - it's a 287GB XML with Wikipedia dump I want ot put into CSV file (revisions authors and timestamps). I managed to do that till some point. Before I got the StackOverflow Error, but now after solving the first problem I get: java.lang.OutOfMemoryError: Java heap space error. My code (partly taken from Justin Kramer answer) looks like that: (defn process-pages [page] (let [title (article-title page) revisions (filter #(= :revision (:tag %)) (:content page))] (for [revision revisions] (let [user (revision-user revision) time (revision-timestamp revision)] (spit "files/data.csv" (str "\"" time "\";\"" user "\";\"" title "\"\n" ) :append true))))) (defn open-file [file-name] (let [rdr (BufferedReader. (FileReader. file-name))] (->> (:content (data.xml/parse rdr :coalescing false)) (filter #(= :page (:tag %))) (map process-pages)))) I don't show article-title, revision-user and revision-title functions, because they just simply take data from a specific place in the page or revision hash. Anyone could help me with this - I'm really new in Clojure and don't get the problem.

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  • Clojure: Avoiding stack overflow in Sieve of Erathosthene?

    - by nixx
    Here's my implementation of Sieve of Erathosthene in Clojure (based on SICP lesson on streams): (defn nats-from [n] (iterate inc n)) (defn divide? [p q] (zero? (rem q p))) (defn sieve [stream] (lazy-seq (cons (first stream) (sieve (remove #(divide? (first stream) %) (rest stream)))))) (def primes (sieve (nats-from 2))) Now, it's all OK when i take first 100 primes: (take 100 primes) But, if i try to take first 1000 primes, program breaks because of stack overflow. I'm wondering if is it possible to change somehow function sieve to become tail-recursive and, still, to preserve "streamnes" of algorithm? Any help???

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  • Good workflow with emacs+swank+slime+clojure?

    - by grm
    I just wanted opinion on good workflow using the emacs environment with clojure+swank+slime. I often find myself doing very repetitive keycommands and wonder if there is an obvious better way. I include swank with lein and start my project using lein swank from shell. Then I connect with emacs and do the correct use commands so that I can start to use (run-tests ). Then I do some coding and then want to test. To run the test I need to change buffer in emacs to the swank-repl C-x o, then I need to go to the prompt M-, then repeat the command M-p, then enter, maybe with an exception, then back to the code buffer and continue all over again with all the emacs commands. I find it a bit repetitive. I guess the solution would be to start hack on emacs and maybe add a shortcut for doing this repetitive task, but I would love to hear some suggestions because I can't be the only one who find this tedious?

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  • Anonymous iterators blocks in Clojure?

    - by Checkers
    I am using clojure.contrib.sql to fetch some records from an SQLite database. (defn read-all-foo [] (let [sql "select * from foo"] (with-connection *db* (with-query-results res [sql] (into [] res))))) Now, I don't really want to realize the whole sequence before returning from the function (i.e. I want to keep it lazy), but if I return res directly or wrap it some kind of lazy wrapper (for example I want to make a certain map transformation on result sequence), SQL bindings will be gone after I return, so realizing the sequence will throw an error. How can I enclose the whole function in a closure and return a kind of anonymous iterator block (like yield in C# or Python)? Or is there another way to return a lazy sequence from this function?

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  • Clojure for a lisp illiterate

    - by dbyrne
    I am a lifelong object-oriented programmer. My job is primarily java development, but I have experience in a number of languages. Ruby gave me my first real taste of functional programming. I loved the features Ruby borrowed from the functional paradigm such as closures and continuations. Eventually, I graduated to Scala. This has been a great way to gradually learn to approach non-trivial problems in a functional manner. Now I am interested in Clojure. I know all the sexy features that make it enticing (software transactional memory, macros, etc.), but I just can't get used to "thinking in lisp". I've seen Rich Hickey's screencasts aimed at java programmers, but they are geared towards explaining language features and not approaching real world problems. I am looking for any advice or resources which have made this transition easier for others.

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  • Anonymous iterator blocks in Clojure?

    - by Checkers
    I am using clojure.contrib.sql to fetch some records from an SQLite database. (defn read-all-foo [] (with-connection *db* (with-query-results res ["select * from foo"] (into [] res)))) Now, I don't really want to realize the whole sequence before returning from the function (i.e. I want to keep it lazy), but if I return res directly or wrap it some kind of lazy wrapper (for example I want to make a certain map transformation on result sequence), SQL-related bindings will be reset and connection will be closed after I return, so realizing the sequence will throw an exception. How can I enclose the whole function in a closure and return a kind of anonymous iterator block (like yield in C# or Python)? Or is there another way to return a lazy sequence from this function?

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  • Confused by "let" in Clojure

    - by Tom Dalling
    I just started playing with Clojure, and I wrote a small script to help me understand some of the functions. It begins like this: (def *exprs-to-test* [ "(filter #(< % 3) '(1 2 3 4 3 2 1))" "(remove #(< % 3) '(1 2 3 4 3 2 1))" "(distinct '(1 2 3 4 3 2 1))" ]) Then it goes through *exprs-to-test*, evaluates them all, and prints the output like this: (doseq [exstr *exprs-to-test*] (do (println "===" (first (read-string exstr)) "=========================") (println "Code: " exstr) (println "Eval: " (eval (read-string exstr))) ) ) The above code is all working fine. However, (read-string exstr) is repeated so I tried to use let to eliminate the repetition like so: (doseq [exstr *exprs-to-test*] (let [ex (read-string exstr)] ( (do (println "===" (first ex) "=========================") (println "Code: " exstr) (println "Eval: " (eval ex)) ) )) ) But this works once for the first item in *exprs-to-test*, then crashes with a NullPointerException. Why is the addition of let causing the crash?

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  • Clojure warn-on-reflection and type hints

    - by Ralph
    In the following code, I am getting a warning on reflection: (ns com.example (:import [org.apache.commons.cli CommandLine Option Options PosixParser])) (def *help-option* "help") (def *host-option* "db-host") (def *options* (doto (Options.) (.addOption "?" *help-option* false "Show this usage information") (.addOption "h" *host-option* true "Name of the database host"))) (let [^CommandLine command-line (.. (PosixParser.) (parse *options* (into-array String args))) db-host (.getOptionValue command-line "h")] ; WARNING HERE ON .getOptionValue ; Do stuff with db-host ) I have a type hint on command-line. Why the warning? I am using Clojure 1.2 on OS X 10.6.6 (Apple VM). I assume that I do not get a warning on (.addOption ...) because the compiler knows that (Options.) is a org.apache.commons.cli.Options).

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  • Delayed evaluation in Clojure

    - by StackedCrooked
    I'm having some trouble understanding how the delay macro works in Clojure. It doesn't seem to do what expect it to do (that is: delaying evaluation). As you can see in this code sample: ; returns the current time (defn get-timestamp [] (.getTime (java.util.Date.))) ; var should contain the current timestamp after calling "force" (def current-time (delay (get-timestamp))) However, calling current-time in the REPL appears to immediately evaluate the expression, even without having used the force macro: user=> current-time #<Delay@19b5217: 1276376485859> user=> (force current-time) 1276376485859 Why was the evaluation of get-timestamp not delayed until the first force call?

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  • Getting all matches for a regexp on clojure

    - by Deleteman
    I'm trying to parse an HTML file and get all href's inside it. So far, the code I'm using is: (map #(println (str "Match: " %)) (re-find #"(?sm)href=\"([a-zA-Z.:/]+)\"" str_response)) str_response being the string with the HTML code inside it. According to my basic understanding of Clojure, that code should print a list of matches, but so far, no luck. It doens't crash, but it doens't match anything either. I've tried using re-seq instead of re-find, but with no luck. Any help? Thanks!

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