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  • Mutation Problem - Clojure

    - by Silanglaya Valerio
    having trouble changing an element of my function represented as a list. code for random function: (defn makerandomtree-10 [pc maxdepth maxwidth fpx ppx] (if-let [output (if (and (< (rand) fpx) (> maxdepth 0)) (let [head (nth operations (rand-int (count operations))) children (doall (loop[function (list) width maxwidth] (if (pos? width) (recur (concat function (list (makerandomtree-10 pc (dec maxdepth) (+ 2 (rand-int (- maxwidth 1))) fpx ppx))) (dec width)) function)))] (concat (list head) children)) (if (and (< (rand) ppx) (>= pc 0)) (nth parameters (rand-int (count parameters))) (rand-int 100)))] output )) I will provide also a mutation function, which is still not good enough. I need to be able to eval my statement, so the following is still insufficient. (defn mutate-5 "chooses a node changes that" [function pc maxwidth pchange] (if (< (rand) pchange) (let [output (makerandomtree-10 pc 3 maxwidth 0.5 0.6)] (if (seq? output) output (list output))) ;mutate the children of root ;declare an empty accumulator list, with root as its head (let [head (list (first function)) children (loop [acc(list) walker (next function)] (println "----------") (println walker) (println "-----ACC-----") (println acc) (if (not walker) acc (if (or (seq? (first function)) (contains? (set operations) (first function))) (recur (concat acc (mutate-5 walker pc maxwidth pchange)) (next walker)) (if (< (rand) pchange) (if (some (set parameters) walker) (recur (concat acc (list (nth parameters (rand-int (count parameters))))) (if (seq? walker) (next walker) nil)) (recur (concat acc (list (rand-int 100))) (if (seq? walker) (next walker) nil))) (recur acc (if (seq? walker) (next walker) nil)))) ))] (concat head (list children))))) (side note: do you have any links/books for learning clojure?)

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  • Appending and prepending to XML files with Clojure

    - by Isaac Copper
    I have an XML file with format similar to: <root> <baby> <a>stuff</a> <b>stuff</b> <c>stuff</c> </baby> ... <baby> <a>stuff</a> <b>stuff</b> <c>stuff</c> </baby> </root> And a Clojure hash-map similar to: {:a "More stuff" :b "Some other stuff" :c "Yet more of that stuff"} And I'd like to prepend XML (¶) created from this hash-map after the <root> tag and before the first <baby> (¶) The XML to prepend would be like: <baby> <a>More stuff</a> <b>Some other stuff</b> <c>Yet more of that stuff</c> </baby> I'd also like to be able to delete the last one (or n...) <baby>...</baby>s from the file. I'm struggling with coming up with an idiomatic was to prepend and append this data. I can do raw string manipulations, or parse the XML using xml/parse and xml-seq and then roll through the nodes and (somehow?) replace the data there, but that seems messy. Any tips? Ideas? Hints? Pointers? They'd all be much appreciated. Thank you!

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  • Efficient Clojure workflow?

    - by Alex B
    I am developing a pet project with Clojure, but wonder if I can speed up my workflow a bit. My current workflow (with Compojure) is: Start Swank with lein swank. Go to Emacs, connect with M-x slime-connect. Load all existing source files one by one. This also starts a Jetty server and an application. Write some code in REPL. When satisfied with experiments, write a full version of a construct I had in mind. Eval (C-c C-c) it. Switch REPL to namespace where this construct resides and test it. Switch to browser and reload browser tab with the affected page. Tweak the code, eval it, check in the browser. Repeat any of the above. There are a number of annoyances with it: I have to switch between Emacs and the browser (or browsers if I am testing things like templating with multiple browsers) all the time. Is there a common idiom to automate this? I used to have a JavaScript bit that reloads the page continuously, but it's of limited utility, obviously, when I have to interact with the page for more than a few seconds. My JVM instance becomes "dirty" when I experiment and write test functions. Basically namespaces become polluted, especially if I'm refactoring and moving the functions between namespaces. This can lead to symbol collisions and I need to restart Swank. Can I undef a symbol? I load all source files one by one (C-c C-k) upon restarting Swank. I suspect I'm doing it all wrong. Switching between the REPL and the file editor can be a bit irritating, especially when I have a lot of Emacs tabs open, alongside the browser(s). I'm looking for ways to improve the above points and the entire workflow in general, so I'd appreciate if you'd share yours. P. S. I have also used Vimclojure before, so Vimclojure-based workflows are welcome too.

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  • dealing cards in Clojure

    - by Ralph
    I am trying to write a Spider Solitaire player as an exercise in learning Clojure. I am trying to figure out how to deal the cards. I have created (with the help of stackoverflow), a shuffled sequence of 104 cards from two standard decks. Each card is represented as a (defstruct card :rank :suit :face-up) The tableau for Spider will be represented as follows: (defstruct tableau :stacks :complete) where :stacks is a vector of card vectors, 4 of which contain 5 cards face down and 1 card face up, and 6 of which contain 4 cards face down and 1 card face up, for a total of 54 cards, and :complete is an (initially) empty vector of completed sets of ace-king (represented as, for example, king-hearts, for printing purposes). The remainder of the undealt deck should be saved in a ref (def deck (ref seq)) During the game, a tableau may contain, for example: (struct-map tableau :stacks [[AH 2C KS ...] [6D QH JS ...] ... ] :complete [KC KS]) where "AH" is a card containing {:rank :ace :suit :hearts :face-up false}, etc. How can I write a function to deal the stacks and then save the remainder in the ref?

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  • Improving my first Clojure program

    - by StackedCrooked
    After a few weekends exploring Clojure I came up with this program. It allows you to move a little rectangle in a window. Here's the code: (import java.awt.Color) (import java.awt.Dimension) (import java.awt.event.KeyListener) (import javax.swing.JFrame) (import javax.swing.JPanel) (def x (ref 0)) (def y (ref 0)) (def panel (proxy [JPanel KeyListener] [] (getPreferredSize [] (Dimension. 100 100)) (keyPressed [e] (let [keyCode (.getKeyCode e)] (if (== 37 keyCode) (dosync (alter x dec)) (if (== 38 keyCode) (dosync (alter y dec)) (if (== 39 keyCode) (dosync (alter x inc)) (if (== 40 keyCode) (dosync (alter y inc)) (println keyCode))))))) (keyReleased [e]) (keyTyped [e]))) (doto panel (.setFocusable true) (.addKeyListener panel)) (def frame (JFrame. "Test")) (doto frame (.add panel) (.pack) (.setDefaultCloseOperation JFrame/EXIT_ON_CLOSE) (.setVisible true)) (defn drawRectangle [p] (doto (.getGraphics p) (.setColor (java.awt.Color/WHITE)) (.fillRect 0 0 100 100) (.setColor (java.awt.Color/BLUE)) (.fillRect (* 10 (deref x)) (* 10 (deref y)) 10 10))) (loop [] (drawRectangle panel) (Thread/sleep 10) (recur)) Despite being an experienced C++ programmer I found it very challenging to write even a simple application in a language that uses a radically different style than what I'm used to. On top of that, this code probably sucks. I suspect the globalness of the various values is a bad thing. It's also not clear to me if it's appropriate to use references here for the x and y values. Any hints for improving this code are welcome.

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  • Parsing data with Clojure, interval problem.

    - by Andrea Di Persio
    Hello! I'm writing a little parser in clojure for learning purpose. basically is a TSV file parser that need to be put in a database, but I added a complication. The complication itself is that in the same file there are more intervals. The file look like this: ###andreadipersio 2010-03-19 16:10:00### USER COMM PID PPID %CPU %MEM TIME root launchd 1 0 0.0 0.0 2:46.97 root DirectoryService 11 1 0.0 0.2 0:34.59 root notifyd 12 1 0.0 0.0 0:20.83 root diskarbitrationd 13 1 0.0 0.0 0:02.84` .... ###andreadipersio 2010-03-19 16:20:00### USER COMM PID PPID %CPU %MEM TIME root launchd 1 0 0.0 0.0 2:46.97 root DirectoryService 11 1 0.0 0.2 0:34.59 root notifyd 12 1 0.0 0.0 0:20.83 root diskarbitrationd 13 1 0.0 0.0 0:02.84 I ended up with this code: (defn is-header? "Return true if a line is header" [line] (> (count (re-find #"^\#{3}" line)) 0)) (defn extract-fields "Return regex matches" [line pattern] (rest (re-find pattern line))) (defn process-lines [lines] (map process-line lines)) (defn process-line [line] (if (is-header? line) (extract-fields line header-pattern)) (extract-fields line data-pattern)) My idea is that in 'process-line' interval need to be merged with data so I have something like this: ('andreadipersio', '2010-03-19', '16:10:00', 'root', 'launchd', 1, 0, 0.0, 0.0, '2:46.97') for every row till the next interval, but I can't figure how to make this happen. I tried with something like this: (def process-line [line] (if is-header? line) (def header-data (extract-fields line header-pattern))) (cons header-data (extract-fields line data-pattern))) But this doesn't work as excepted. Any hints? Thanks!

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  • Project Euler #14 and memoization in Clojure

    - by dbyrne
    As a neophyte clojurian, it was recommended to me that I go through the Project Euler problems as a way to learn the language. Its definitely a great way to improve your skills and gain confidence. I just finished up my answer to problem #14. It works fine, but to get it running efficiently I had to implement some memoization. I couldn't use the prepackaged memoize function because of the way my code was structured, and I think it was a good experience to roll my own anyways. My question is if there is a good way to encapsulate my cache within the function itself, or if I have to define an external cache like I have done. Also, any tips to make my code more idiomatic would be appreciated. (use 'clojure.test) (def mem (atom {})) (with-test (defn chain-length ([x] (chain-length x x 0)) ([start-val x c] (if-let [e (last(find @mem x))] (let [ret (+ c e)] (swap! mem assoc start-val ret) ret) (if (<= x 1) (let [ret (+ c 1)] (swap! mem assoc start-val ret) ret) (if (even? x) (recur start-val (/ x 2) (+ c 1)) (recur start-val (+ 1 (* x 3)) (+ c 1))))))) (is (= 10 (chain-length 13)))) (with-test (defn longest-chain ([] (longest-chain 2 0 0)) ([c max start-num] (if (>= c 1000000) start-num (let [l (chain-length c)] (if (> l max) (recur (+ 1 c) l c) (recur (+ 1 c) max start-num)))))) (is (= 837799 (longest-chain))))

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  • Fastest reliable way for Clojure (Java) and Ruby apps to communicate

    - by jkndrkn
    Hi There, We have cloud-hosted (RackSpace cloud) Ruby and Java apps that will interact as follows: Ruby app sends a request to Java app. Request consists of map structure containing strings, integers, other maps, and lists (analogous to JSON). Java app analyzes data and sends reply to Ruby App. We are interested in evaluating both messaging formats (JSON, Buffer Protocols, Thrift, etc.) as well as message transmission channels/techniques (sockets, message queues, RPC, REST, SOAP, etc.) Our criteria: Short round-trip time. Low round-trip-time standard deviation. (We understand that garbage collection pauses and network usage spikes can affect this value). High availability. Scalability (we may want to have multiple instances of Ruby and Java app exchanging point-to-point messages in the future). Ease of debugging and profiling. Good documentation and community support. Bonus points for Clojure support. What combination of message format and transmission method would you recommend? Why? I've gathered here some materials we have already collected for review: Comparison of various java serialization options Comparison of Thrift and Protocol Buffers (old) Comparison of various data interchange formats Comparison of Thrift and Protocol Buffers Fallacies of Protocol Buffers RPC features Discussion of RPC in the context of AMQP (Message-Queueing) Comparison of RPC and message-passing in distributed systems (pdf) Criticism of RPC from perspective of message-passing fan Overview of Avro from Ruby programmer perspective

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  • Java style FOR loop in a clojure interpeter ?

    - by Kevin
    I have a basic interpreter in clojure. Now i need to implement for (initialisation; finish-test; loop-update) { statements } inside my interpreter. I will attach my interpreter code I got so far. Any help is appreciated. Interpreter (declare interpret make-env) ;; (def do-trace false) ;; ;; simple utilities (def third ; return third item in a list (fn [a-list] (second (rest a-list)))) (def fourth ; return fourth item in a list (fn [a-list] (third (rest a-list)))) (def run ; make it easy to test the interpreter (fn [e] (println "Processing: " e) (println "=> " (interpret e (make-env))))) ;; for the environment (def make-env (fn [] '())) (def add-var (fn [env var val] (cons (list var val) env))) (def lookup-var (fn [env var] (cond (empty? env) 'error (= (first (first env)) var) (second (first env)) :else (lookup-var (rest env) var)))) ;; -- define numbers (def is-number? (fn [expn] (number? expn))) (def interpret-number (fn [expn env] expn)) ;; -- define symbols (def is-symbol? (fn [expn] (symbol? expn))) (def interpret-symbol (fn [expn env] (lookup-var env expn))) ;; -- define boolean (def is-boolean? (fn [expn] (or (= expn 'true) (= expn 'false)))) (def interpret-boolean (fn [expn env] expn)) ;; -- define functions (def is-function? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'lambda (first expn))))) (def interpret-function (fn [expn env] expn)) ;; -- define addition (def is-plus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '+ (first expn))))) (def interpret-plus (fn [expn env] (+ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define subtraction (def is-minus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '- (first expn))))) (def interpret-minus (fn [expn env] (- (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define multiplication (def is-times? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '* (first expn))))) (def interpret-times (fn [expn env] (* (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define division (def is-divides? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '/ (first expn))))) (def interpret-divides (fn [expn env] (/ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define equals test (def is-equals? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '= (first expn))))) (def interpret-equals (fn [expn env] (= (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define greater-than test (def is-greater-than? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '> (first expn))))) (def interpret-greater-than (fn [expn env] (> (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define not (def is-not? (fn [expn] (and (list? expn) (= 2 (count expn)) (= 'not (first expn))))) (def interpret-not (fn [expn env] (not (interpret (second expn) env)))) ;; -- define or (def is-or? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'or (first expn))))) (def interpret-or (fn [expn env] (or (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define and (def is-and? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'and (first expn))))) (def interpret-and (fn [expn env] (and (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define with (def is-with? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'with (first expn))))) (def interpret-with (fn [expn env] (interpret (third expn) (add-var env (first (second expn)) (interpret (second (second expn)) env))))) ;; -- define if (def is-if? (fn [expn] (and (list? expn) (= 4 (count expn)) (= 'if (first expn))))) (def interpret-if (fn [expn env] (cond (interpret (second expn) env) (interpret (third expn) env) :else (interpret (fourth expn) env)))) ;; -- define function-application (def is-function-application? (fn [expn env] (and (list? expn) (= 2 (count expn)) (is-function? (interpret (first expn) env))))) (def interpret-function-application (fn [expn env] (let [function (interpret (first expn) env)] (interpret (third function) (add-var env (first (second function)) (interpret (second expn) env)))))) ;; the interpreter itself (def interpret (fn [expn env] (cond do-trace (println "Interpret is processing: " expn)) (cond ; basic values (is-number? expn) (interpret-number expn env) (is-symbol? expn) (interpret-symbol expn env) (is-boolean? expn) (interpret-boolean expn env) (is-function? expn) (interpret-function expn env) ; built-in functions (is-plus? expn) (interpret-plus expn env) (is-minus? expn) (interpret-minus expn env) (is-times? expn) (interpret-times expn env) (is-divides? expn) (interpret-divides expn env) (is-equals? expn) (interpret-equals expn env) (is-greater-than? expn) (interpret-greater-than expn env) (is-not? expn) (interpret-not expn env) (is-or? expn) (interpret-or expn env) (is-and? expn) (interpret-and expn env) ; special syntax (is-with? expn) (interpret-with expn env) (is-if? expn) (interpret-if expn env) ; functions (is-function-application? expn env) (interpret-function-application expn env) :else 'error)))

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  • Custom language - FOR loop in a clojure interpeter?

    - by Mark
    I have a basic interpreter in clojure. Now i need to implement for (initialisation; finish-test; loop-update) { statements } Implement a similar for-loop for the interpreted language. The pattern will be: (for variable-declarations end-test loop-update do statement) The variable-declarations will set up initial values for variables.The end-test returns a boolean, and the loop will end if end-test returns false. The statement is interpreted followed by the loop-update for each pass of the loop. Examples of use are: (run ’(for ((i 0)) (< i 10) (set i (+ 1 i)) do (println i))) (run ’(for ((i 0) (j 0)) (< i 10) (seq (set i (+ 1 i)) (set j (+ j (* 2 i)))) do (println j))) inside my interpreter. I will attach my interpreter code I got so far. Any help is appreciated. Interpreter (declare interpret make-env) ;; needed as language terms call out to 'interpret' (def do-trace false) ;; change to 'true' to show calls to 'interpret' ;; simple utilities (def third ; return third item in a list (fn [a-list] (second (rest a-list)))) (def fourth ; return fourth item in a list (fn [a-list] (third (rest a-list)))) (def run ; make it easy to test the interpreter (fn [e] (println "Processing: " e) (println "=> " (interpret e (make-env))))) ;; for the environment (def make-env (fn [] '())) (def add-var (fn [env var val] (cons (list var val) env))) (def lookup-var (fn [env var] (cond (empty? env) 'error (= (first (first env)) var) (second (first env)) :else (lookup-var (rest env) var)))) ;; for terms in language ;; -- define numbers (def is-number? (fn [expn] (number? expn))) (def interpret-number (fn [expn env] expn)) ;; -- define symbols (def is-symbol? (fn [expn] (symbol? expn))) (def interpret-symbol (fn [expn env] (lookup-var env expn))) ;; -- define boolean (def is-boolean? (fn [expn] (or (= expn 'true) (= expn 'false)))) (def interpret-boolean (fn [expn env] expn)) ;; -- define functions (def is-function? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'lambda (first expn))))) (def interpret-function ; keep function definitions as they are written (fn [expn env] expn)) ;; -- define addition (def is-plus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '+ (first expn))))) (def interpret-plus (fn [expn env] (+ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define subtraction (def is-minus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '- (first expn))))) (def interpret-minus (fn [expn env] (- (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define multiplication (def is-times? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '* (first expn))))) (def interpret-times (fn [expn env] (* (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define division (def is-divides? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '/ (first expn))))) (def interpret-divides (fn [expn env] (/ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define equals test (def is-equals? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '= (first expn))))) (def interpret-equals (fn [expn env] (= (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define greater-than test (def is-greater-than? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '> (first expn))))) (def interpret-greater-than (fn [expn env] (> (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define not (def is-not? (fn [expn] (and (list? expn) (= 2 (count expn)) (= 'not (first expn))))) (def interpret-not (fn [expn env] (not (interpret (second expn) env)))) ;; -- define or (def is-or? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'or (first expn))))) (def interpret-or (fn [expn env] (or (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define and (def is-and? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'and (first expn))))) (def interpret-and (fn [expn env] (and (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define print (def is-print? (fn [expn] (and (list? expn) (= 2 (count expn)) (= 'println (first expn))))) (def interpret-print (fn [expn env] (println (interpret (second expn) env)))) ;; -- define with (def is-with? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'with (first expn))))) (def interpret-with (fn [expn env] (interpret (third expn) (add-var env (first (second expn)) (interpret (second (second expn)) env))))) ;; -- define if (def is-if? (fn [expn] (and (list? expn) (= 4 (count expn)) (= 'if (first expn))))) (def interpret-if (fn [expn env] (cond (interpret (second expn) env) (interpret (third expn) env) :else (interpret (fourth expn) env)))) ;; -- define function-application (def is-function-application? (fn [expn env] (and (list? expn) (= 2 (count expn)) (is-function? (interpret (first expn) env))))) (def interpret-function-application (fn [expn env] (let [function (interpret (first expn) env)] (interpret (third function) (add-var env (first (second function)) (interpret (second expn) env)))))) ;; the interpreter itself (def interpret (fn [expn env] (cond do-trace (println "Interpret is processing: " expn)) (cond ; basic values (is-number? expn) (interpret-number expn env) (is-symbol? expn) (interpret-symbol expn env) (is-boolean? expn) (interpret-boolean expn env) (is-function? expn) (interpret-function expn env) ; built-in functions (is-plus? expn) (interpret-plus expn env) (is-minus? expn) (interpret-minus expn env) (is-times? expn) (interpret-times expn env) (is-divides? expn) (interpret-divides expn env) (is-equals? expn) (interpret-equals expn env) (is-greater-than? expn) (interpret-greater-than expn env) (is-not? expn) (interpret-not expn env) (is-or? expn) (interpret-or expn env) (is-and? expn) (interpret-and expn env) (is-print? expn) (interpret-print expn env) ; special syntax (is-with? expn) (interpret-with expn env) (is-if? expn) (interpret-if expn env) ; functions (is-function-application? expn env) (interpret-function-application expn env) :else 'error))) ;; tests of using environment (println "Environment tests:") (println (add-var (make-env) 'x 1)) (println (add-var (add-var (add-var (make-env) 'x 1) 'y 2) 'x 3)) (println (lookup-var '() 'x)) (println (lookup-var '((x 1)) 'x)) (println (lookup-var '((x 1) (y 2)) 'x)) (println (lookup-var '((x 1) (y 2)) 'y)) (println (lookup-var '((x 3) (y 2) (x 1)) 'x)) ;; examples of using interpreter (println "Interpreter examples:") (run '1) (run '2) (run '(+ 1 2)) (run '(/ (* (+ 4 5) (- 2 4)) 2)) (run '(with (x 1) x)) (run '(with (x 1) (with (y 2) (+ x y)))) (run '(with (x (+ 2 4)) x)) (run 'false) (run '(not false)) (run '(with (x true) (with (y false) (or x y)))) (run '(or (= 3 4) (> 4 3))) (run '(with (x 1) (if (= x 1) 2 3))) (run '(with (x 2) (if (= x 1) 2 3))) (run '((lambda (n) (* 2 n)) 4)) (run '(with (double (lambda (n) (* 2 n))) (double 4))) (run '(with (sum-to (lambda (n) (if (= n 0) 0 (+ n (sum-to (- n 1)))))) (sum-to 100))) (run '(with (x 1) (with (f (lambda (n) (+ n x))) (with (x 2) (println (f 3))))))

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  • How do I pull `static final` constants from a Java class into a Clojure namespace?

    - by Joe Holloway
    I am trying to wrap a Java library with a Clojure binding. One particular class in the Java library defines a bunch of static final constants, for example: class Foo { public static final int BAR = 0; public static final int SOME_CONSTANT = 1; ... } I had a thought that I might be able to inspect the class and pull these constants into my Clojure namespace without explicitly def-ing each one. For example, instead of explicitly wiring it up like this: (def *foo-bar* Foo/BAR) (def *foo-some-constant* Foo/SOME_CONSTANT) I'd be able to inspect the Foo class and dynamically wire up *foo-bar* and *foo-some-constant* in my Clojure namespace when the module is loaded. I see two reasons for doing this: A) Automatically pull in new constants as they are added to the Foo class. In other words, I wouldn't have to modify my Clojure wrapper in the case that the Java interface added a new constant. B) I can guarantee the constants follow a more Clojure-esque naming convention I'm not really sold on doing this, but it seems like a good question to ask to expand my knowledge of Clojure/Java interop. Thanks

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  • Clojure agents consuming from a queue

    - by erikcw
    I'm trying to figure out the best way to use agents to consume items from a Message Queue (Amazon SQS). Right now I have a function (process-queue-item) that grabs an items from the queue, and processes it. I want to process these items concurrently, but I can't wrap my head around how to control the agents. Basically I want to keep all of the agents busy as much as possible without pulling to many items from the Queue and developing a backlog (I'll have this running on a couple of machines, so items need to be left in the queue until they are really needed). Can anyone give me some pointers on improving my implementation? (def active-agents (ref 0)) (defn process-queue-item [_] (dosync (alter active-agents inc)) ;retrieve item from Message Queue (Amazon SQS) and process (dosync (alter active-agents dec))) (defn -main [] (def agents (for [x (range 20)] (agent x))) (loop [loop-count 0] (if (< @active-agents 20) (doseq [agent agents] (if (agent-errors agent) (clear-agent-errors agent)) ;should skip this agent until later if it is still busy processing (not sure how) (send-off agent process-queue-item))) ;(apply await-for (* 10 1000) agents) (Thread/sleep 10000) (logging/info (str "ACTIVE AGENTS " @active-agents)) (if (> 10 loop-count) (do (logging/info (str "done, let's cleanup " count)) (doseq [agent agents] (if (agent-errors agent) (clear-agent-errors agent))) (apply await agents) (shutdown-agents)) (recur (inc count)))))

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  • In Clojure - How do I access keys in a vector of structs

    - by Nick
    I have the following vector of structs: (defstruct #^{:doc "Basic structure for book information."} book :title :authors :price) (def #^{:doc "The top ten Amazon best sellers on 16 Mar 2010."} best-sellers [(struct book "The Big Short" ["Michael Lewis"] 15.09) (struct book "The Help" ["Kathryn Stockett"] 9.50) (struct book "Change Your Prain, Change Your Body" ["Daniel G. Amen M.D."] 14.29) (struct book "Food Rules" ["Michael Pollan"] 5.00) (struct book "Courage and Consequence" ["Karl Rove"] 16.50) (struct book "A Patriot's History of the United States" ["Larry Schweikart","Michael Allen"] 12.00) (struct book "The 48 Laws of Power" ["Robert Greene"] 11.00) (struct book "The Five Thousand Year Leap" ["W. Cleon Skousen","James Michael Pratt","Carlos L Packard","Evan Frederickson"] 10.97) (struct book "Chelsea Chelsea Bang Bang" ["Chelsea Handler"] 14.03) (struct book "The Kind Diet" ["Alicia Silverstone","Neal D. Barnard M.D."] 16.00)]) I would like to sum the prices of all the books in the vector. What I have is the following: (defn get-price "Same as print-book but handling multiple authors on a single book" [ {:keys [title authors price]} ] price) Then I: (reduce + (map get-price best-sellers)) Is there a way of doing this without mapping the "get-price" function over the vector? Or is there an idiomatic way of approaching this problem?

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  • Clojure: seq (cons) vs. list (conj)

    - by dbyrne
    I know that cons returns a seq and conj returns a collection. I also know that conj "adds" the item to the optimal end of the collection, and cons always "adds" the item to the front. This example illustrates both of these points: user=> (conj [1 2 3] 4) //returns a collection [1 2 3 4] user=> (cons 4 [1 2 3]) //returns a seq (4 1 2 3) For vectors, maps, and sets these differences make sense to me. However, for lists they seem identical. user=> (conj '(3 2 1) 4) (4 3 2 1) user=> (cons 4 '(3 2 1)) (4 3 2 1) Are there any examples using lists where conj vs. cons exhibit different behaviors, or are they truly interchangeable? Phrased differently, is there an example where a list and a seq cannot be used equivalently?

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  • stop and split generated sequence at repeats - clojure

    - by fitzsnaggle
    I am trying to make a sequence that will only generate values until it finds the following conditions and return the listed results: case head = 0 - return {:origin [all generated except 0] :pattern 0} 1 - return {:origin nil :pattern [all-generated-values] } repeated-value - {:origin [values-before-repeat] :pattern [values-after-repeat] { ; n = int ; x = int ; hist - all generated values ; Keeps the head below x (defn trim-head [head x] (loop [head head] (if (> head x) (recur (- head x)) head))) ; Generates the next head (defn next-head [head x n] (trim-head (* head n) x)) (defn row [x n] (iterate #(next-head % x n) n)) ; Generates a whole row - ; Rows are a max of x - 1. (take (- x 1) (row 11 3)) Examples of cases to stop before reaching end of row: [9 8 4 5 6 7 4] - '4' is repeated so STOP. Return preceding as origin and rest as pattern. {:origin [9 8] :pattern [4 5 6 7]} [4 5 6 1] - found a '1' so STOP, so return everything as pattern {:origin nil :pattern [4 5 6 1]} [3 0] - found a '0' so STOP {:origin [3] :pattern [0]} :else if the sequences reaches a length of x - 1: {:origin [all values generated] :pattern nil} The Problem I have used partition-by with some success to split the groups at the point where a repeated value is found, but would like to do this lazily. Is there some way I can use take-while, or condp, or the :while clause of the for loop to make a condition that partitions when it finds repeats? Some Attempts (take 2 (partition-by #(= 1 %) (row 11 4))) (for [p (partition-by #(stop-match? %) head) (iterate #(next-head % x n) n) :while (or (not= (last p) (or 1 0 n) (nil? (rest p))] {:origin (first p) :pattern (concat (second p) (last p))})) # Updates What I really want to be able to do is find out if a value has repeated and partition the seq without using the index. Is that possible? Something like this - { (defn row [x n] (loop [hist [n] head (gen-next-head (first hist) x n) steps 1] (if (>= (- x 1) steps) (case head 0 {:origin [hist] :pattern [0]} 1 {:origin nil :pattern (conj hist head)} ; Speculative from here on out (let [p (partition-by #(apply distinct? %) (conj hist head))] (if-not (nil? (next p)) ; One partition if no repeats. {:origin (first p) :pattern (concat (second p) (nth 3 p))} (recur (conj hist head) (gen-next-head head x n) (inc steps))))) {:origin hist :pattern nil}))) }

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  • Executing a dynamically bound function in Clojure

    - by Carl Smotricz
    I'd like to pre-store a bunch of function calls in a data structure and later evaluate/execute them from within another function. This works as planned for functions defined at namespace level with defn (even though the function definition comes after my creation of the data structure) but will not work with functions defined by let [name (fn or letfn inside the function. Here's my small self-contained example: (def todoA '(funcA)) (def todoB '(funcB)) (def todoC '(funcC)) (def todoD '(funcD)) ; unused (defn funcA [] (println "hello funcA!")) (declare funcB funcC) (defn runit [] (let [funcB (fn [] (println "hello funcB"))] (letfn [(funcC [] (println "hello funcC!"))] (funcA) (eval todoA) ; OK (funcB) ; OK (eval todoB) ; "Unable to resolve symbol: funcB in this context" at line 2 (funcC) ; OK (eval todoC) ; "Unable to resolve symbol: funcC in this context" at line 3 ))) Is there a simple fix I could undertake to get eval'd quoted calls to functions to work for functions defined inside another function?

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  • Unresponsive Clojure REPL after exception

    - by Hendekagon
    If I start a REPL and then do something that throws an exception like (use 'non-existent-thing) ** then after that the REPL ceases to evaluate anything I enter. Is there a special key I can press to make it turn round, face me, uncross its arms and listen once more ? Or must I ctrl-d, restart, type everything up to where I was and get it right this time ? ** which results in: Exception in thread "Thread-1" java.lang.RuntimeException: java.io.FileNotFoundException: Could not locate non_existent_thing__init.class or non_existent_thing.clj on classpath: (NO_SOURCE_FILE:0)

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  • Factor Clojure code setting many different fields in a Java object

    - by chris
    How do I factor code setting many different fields in a Java object? I would like to factor (set! (. employee name) "Chris") (set! (. employee age) 100) (set! (. employee salary) 5000) to (doseq [field '((name "Chris") (age 100) (salary 5000))] (set! (. employee (first field)) (second field))) However this won't work because the period is a macro, and tries to evaluate (first field) literally. By the way, I understand that setting fields is not good practice. I need to inter-operate with legacy code.

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  • How to do animation using swing and clojure ?

    - by Humberto Pinheiro
    I'm trying to animate a chess piece in a board. First I created a java.util.Timer object that "scheduleAtFixedRate" a TimerTask implemented as a proxy function. So I kept a record of the piece to move (piece-moving-record) and when it's apropriate (when the user move the piece using the mouse) the TimerTask proxy function should be test if the record is not nil and execute the piece-moving function. The piece-moving function just updates the x and y coordinates of the piece, according to a vector pre-calculated. I put a add-watch on the piece-moving-record so when it changes it should repaint the board (canvas). The paint method tests if this piece-moving-record is not nil to paint it. The problem is that the animation doesn't appear. The piece just jump to the destiny, without the movement between. There is some problem with the animation scheme ou there is a better way to do it?

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  • Coverting a vector of maps to map of maps in clojure

    - by Osman
    Hi, I've a vector of maps like this: [ {:categoryid 1, :categoryname "foo" } {:categoryid 2, :categoryname "bar" } {:categoryid 3, :categoryname "baz" } ] and would like to generate a map of maps like this for searching by categoryname { "foo" {:categoryid 1, :categoryname "foo" }, "bar" {:categoryid 2, :categoryname "bar" }, "baz" {:categoryid 3, :categoryname "baz" } } How can i achieve?

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  • Performance Problem with Clojure Array

    - by dbyrne
    This piece of code is very slow. Execution from the slime-repl on my netbook takes a couple minutes. Am I doing something wrong? (def test-array (make-array Integer/TYPE 400 400 3)) (doseq [x (range 400), y (range 400), z (range 3)] (aset test-array x y z 0))

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  • How to benchmark functions in clojure

    - by Peter Tillemans
    I know I can get the time take to evaluate a function can be printed out on the screen/stdout using the time function/macro. The time macro returns the value of the evaluated function, which makes it great to use it inline. However I want to automatically measure the runtime under specific circumstances. is there a function which returns the elapsed time in some library to hep with this benchmarking?

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  • Accessing vars from another clojure namespace?

    - by erikcw
    In my main namespace, I have a top level var named "settings" which is initialized as an empty {}. My -main fn sets the contents of settings using def and conj based on some command line args (different database hosts for production/development, etc). I'm trying to access the contents of this map from another namespace to pull out some of the settings. When I try to compile with lein into an uberjar, I get a traceback saying "No such var: lb/settings". What am I missing? Is there a more idiomatic way to handle app wide settings such as these? Is it safe to use "def" inside of -main like I am, or should I be use an atom or ref to make this threadsafe? Thanks! (ns main (:use ...) (:gen-class)) (def settings {}) (defn -main [& args] (with-command-line-args... ;set devel? based on args (if (true? devel?) (def settings (conj settings {:mongodb {:host "127.0.0.1"} :memcached {:host "127.0.0.1"}})) (def settings (conj settings {:mongodb {:host "PRODUCTION_IP"} :memcached {:host "PRODUCTION_IP"}}))) ;file2.clj (ns some-other-namespace (:require [main :as lb] ...) ;configure MongoDB (congo/mongo! :db "dbname" :host (:host (mongodb lb/settings)))) ...

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  • Clojure multimethod dispatching on functions and values

    - by Josh Glover
    I have a function that returns the indexes in seq s at which value v exists: (defn indexes-of [v s] (map first (filter #(= v (last %)) (zipmap (range) s)))) What I'd like to do is extend this to apply any arbitrary function for the existence test. My idea is to use a multimethod, but I'm not sure exactly how to detect a function. I want to do this: (defmulti indexes-of ???) (defmethod indexes-of ??? [v s] ;; v is a function (map first (filter v (zipmap (range) s)))) (defmethod indexes-of ??? [v s] ;; v is not a function (indexes-of #(= v %) s)) Is a multimethod the way to go here? If so, how can I accomplish what I'm trying to do?

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