What does at do actually in clojure? I saw this example in internet making a loop for overtone and cant get the meaning of at:
(defn looper [nome sound]
(let [beat (nome)]
(at (nome beat) (sound))
(apply-at (nome (inc beat)) looper nome sound [])))`
The at command is a part of overtone, not Clojure.
The overtone cheatsheet shows that it is a timing function:
https://github.com/overtone/overtone/raw/master/docs/cheatsheet/overtone-cheat-sheet.pdf
Also you can look at both github and the wiki:
https://github.com/overtone/overtone
https://github.com/overtone/overtone/wiki
http://overtone.github.io/
Related
I have a rabbitMQ connection that seems to be started at compile time (when I type lein compile) and then blocks the building of my project. Here are more details on the problem. Let us say this is the clojure file bla_test.clj
(import (com.rabbitmq.client ConnectionFactory Connection Channel QueueingConsumer))
;; And then we have to translate the equivalent java hello world program using
;; Clojure's excellent interop.
;; It feels very strange writing this sort of ceremony-oriented imperative code
;; in Clojure:
;; Make a connection factory on the local host
(def connection-factory
(doto (ConnectionFactory.)
(.setHost "localhost")))
;; and get it to make you a connection
(def connection (.newConnection connection-factory))
;; get that to make you a channel
(def channel (. connection createChannel))
;;HERE I WOULD LIKE TO USE THE SAME CONNECTION AND THE SAME CHANNEL INSTANCE AS OFTEN AS
;; I LIKE
(dotimes [ i 10 ]
(. channel basicPublish "" "hello" nil (. (format "Hello World! (%d)" i) getBytes)))
The clojure file above is part of a bigger clojure program that I build using lein. My problem is that when I compile with "lein compile", a connection is done because of the line (def connection (.newConnection connection-factory)) and then the compilation is stopped! How can I avoid this? Is there a way to compile without building connection? How can I manage to use the same instance of channel over several calls coming from external components?
Any help would be appreciated.
Regards,
Horace
The Clojure compiler must evaluate all top-level forms, because it can be required to run arbitrary code when expanding calls to macros.
The usual solution to issues like the one you describe is to define a top-level Var holding an object of a dereferenceable type, for example an atom or a promise, and have an initialization function provide the value at runtime. (You could also use a delay and specify the value inline; this is less flexible, since it makes it more difficult to use a different value for testing etc.)
Perhaps a possible solution to use (<! c) outside go macro could be done with macro and its macro expansion time :
This is my example:
(ns fourclojure.asynco
(require [clojure.core.async :as async :refer :all]))
(defmacro runtime--fn [the-fn the-value]
`(~the-fn ~the-value)
)
(defmacro call-fn [ the-fn]
`(runtime--fn ~the-fn (<! my-chan))
)
(def my-chan (chan))
(defn read-channel [the-fn]
(go
(loop []
(call-fn the-fn)
(recur)
)
))
(defn paint []
(put! my-chan "paint!")
)
And to test it:
(read-channel print)
(repeatedly 50 paint)
I've tried this solution in a nested go and also works. But I'm not sure if it could be a correct path
The reason about this question is releated to this other question Isn't core.async contrary to Clojure principles?, #aeuhuea comment that "It seems to me that this prevents simplicity and composability. Why is it not a problem?" and #cgrand response "The limitation of the go macro (its locality) is also a feature: it enforces source code locality of stateful operations."
But force to localize your code is not the same as "complect"?
Regarding the title of your question:
>!must be called in a go block because it's designed to. If you are interested in the go-block state-machine mechanics, I can highly recommend Timothy Baldridges Youtube videos on that http://www.youtube.com/channel/UCLxWPHbkxjR-G-y6CVoEHOw
Remember that there is always blocking take and put >!! and <!!. I don't know which part of your code is supposed to provide a "solution" for not being able to use <! and >! outside of a go block, however looping around events dispatched from a single channel is common practice. Here is a modified version of read-channel
(defn do-channel [f ch]
(go-loop []
(when-let [v (<! ch)]
(f v)
(recur))))
put! puts asynchronously, an effect that you usually don't intend. In your example, to put the string "paint" into the channel 50 times, I'd recommend a one-liner like this one:
(do-channel println (to-chan (repeat 50 "print")))
Here is a comment as an answer to your edit:
Channels are not designed to be used as mutable data-structures, period. They have a buffer and that buffer can be thought of as a mutable queue. However we don't use channels to store a value in there, just to take it out a few lines later again.
We use channels as helping construct that may be used to bring execution of two or more different pieces of source-code in two or more different places in line. E.g. a go-block here does not continue to execute until it has received a value produced by another go-block. >! and >!! help us to distinguish whether they are used in a thread-blocking context or in a go-block (blocking a spawned process).
Also, please refer to this answer: Clojure - Why does execution hang when doing blocking insert into channel? (core.async)
You should not use >!! or <!! inside of a go-block, neither transparently or nested in a function call. Rich Hickey himself has commented on that in a recent bug report (http://dev.clojure.org/jira/browse/ASYNC-29?focusedCommentId=32414&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-32414).
Looking at the source-code of >! you will see that it only throws an exception. As a matter of fact, go will replace >! with different source-code. go spawns a state-machine controlled process. Depending on the context you may want to make this explicitly known or nest the go block inside of a macro or function (like in the code examples that you have provided).
Regarding David Nolens (swannodettes) helpers: They have been implemented by Rich Hickey and Nolen himself into the core.async library. Nolen said himself that they are superseded in this presentation (http://www.youtube.com/watch?v=AhxcGGeh5ho). Notice that go-loop has been implemented since after Nolens commit.
I'm using Lamina to implement Functional reactive programming (FRP).
As a starter, I try to code a very simple clock in order to understand the library basics.
According to the Lamina 0.5.0-rc4 API documentation, there is lamina.time API:
http://ideolalia.com/lamina/lamina.time.html#var-now
I want to implement a very simple clock where:
Interval of every second as Observable time Streaming Collection/List/Seq (I don't quite understand the difference yet) （EDIT: now I understood it's called Channels on Lamina)
Now as Observable Streaming data
Println Now on every second (subscribe or for-each Observable time Collection)
Any feedback is welcome. Thanks.
EDIT: I quit.
After some research, I conclude the best way to code FRP is ClojureScript with RxJs(ReactiveExtention from MS).
See the example Code for ClojureScript + RxJs + node.js in my related Qestion Here:
ClojureScript on node.js, code
You could try Bacon.js, a successor to Rx.js created after its author complained about its obscure API. Bacon.js is very clean and can integrate with jQuery, Backbone.js, AngularJS, and even Node.js. Basically you can wrap any kind of events into a Bacon's event stream and start do wonderful things with them.
Bonus : you could even try yolk, described as "A thin Clojurescript wrapper around bacon.js".
-- edit : quick typo fixes
I found a good article:
http://adambard.com/blog/why-clojure-part-2-async-magic/
-LAMINA: ADVANCED ASYNCHRONOUS PROCESSING
(ns example.helloperiodically
(:require [lamina.core :as lamina]))
(def ch (lamina/periodically 1000 (fn [] "Hello World!")))
(def loop-forever (comp doall repeatedly))
(defn consumer []
(loop-forever
(fn [] (println #(lamina/read-channel ch)))))
(defn main []
(-> (Thread. consumer) .start))
Why not try ProAct.js - it implements both the functional and object-oriented approaches. It has a package for node.js (proact.js) - it stable and well tested.
I used to like to include all of clojure.contrib, and require all the libraries. This makes find-doc useful as a discovery tool.
Nowadays (clojure 1.4) clojure.contrib is split into many sub-libraries. And that rather spoils my scheme, and it also means that I am constantly having to restart the JVM every time I need a new library.
So I'm busy constructing a project.clj file with many lines:
[org.clojure/algo.generic "0.0.6"]
....
[org.clojure/data.xml "0.0.4"]
....
So that I can get leiningen to put every clojure contrib library on the classpath, whether I need them or not.
And I reckon that this is going to be a spectacular pain in the neck, what with the version numbers, and all.
And I wonder if anyone has a better way to do the same thing?
EDIT: Thinking about it, if there's a web page somewhere that has a list of library names and current versions, I can turn that into a project file fairly easily.
You could use pomegranate if you just want to run it in the REPL (which seems like it would be the only appropriate use case, right?). You can have it look up the latest versions using the Maven Central API. I think this is better than maintaining some sort of dependencies project, generated or otherwise.
(require '[cemerick.pomegranate :refer [add-dependencies]])
(add-dependencies
:coordinates '[[clj-http "0.5.8"]]
:repositories {"clojars" "http://clojars.org/repo"})
(require '[clj-http.client :as client])
;; contrib project names from https://github.com/clojure
(def contrib ["tools.nrepl" "tools.trace" "tools.namespace" "tools.macro"
"test.generative" "math.numeric-tower" "core.match" "core.logic"
"data.priority-map" "core.contracts" "tools.cli" "java.jmx"
"java.jdbc" "java.classpath" "data.xml" "data.json" "core.unify"
"core.incubator" "core.cache" "algo.monads" "data.generators"
"core.memoize" "math.combinatorics" "java.data" "tools.logging"
"data.zip" "data.csv" "algo.generic" "data.codec"
"data.finger-tree"])
(defn add-contrib-dependencies
"look up the latest version of every contrib project in maven central,
and add them as dependencies using pomegranate."
[project-names]
(add-dependencies
:coordinates
(map (juxt
(comp symbol (partial format "org.clojure/%s"))
(fn [proj]
(Thread/sleep 100)
(-> "http://search.maven.org/solrsearch/select?q=%s&rows=1&wt=json"
(format proj)
(client/get {:as :json})
:body :response :docs first :latestVersion)))
project-names)))
Now you can just invoke this function on the list of project names:
user=> (add-contrib-dependencies contrib)
{[org.clojure/data.zip "0.1.1"] nil,
[org.clojure/java.classpath "0.2.0"] nil,
[org.clojure/core.cache "0.6.2"] nil, ...}
UPDATE: as suggested earlier, I had made this answer into a library. It can be used either as nREPL middleware or invoked manually from a running REPL session. The code can be found at https://github.com/rplevy/contrib-repl, where usage instructions can also be found.
I feel your pain. It should be helpful http://dev.clojure.org/display/community/Where+Did+Clojure.Contrib+Go
I have a Clojure program that I build as a JAR file using Maven. Embedded in the JAR Manifest is a build-version number, including the build timestamp.
I can easily read this at runtime from the JAR Manifest using the following code:
(defn set-version
"Set the version variable to the build number."
[]
(def version
(-> (str "jar:" (-> my.ns.name (.getProtectionDomain)
(.getCodeSource)
(.getLocation))
"!/META-INF/MANIFEST.MF")
(URL.)
(.openStream)
(Manifest.)
(.. getMainAttributes)
(.getValue "Build-number"))))
but I've been told that it is bad karma to use def inside defn.
What is the Clojure-idiomatic way to set a constant at runtime? I obviously do not have the build-version information to embed in my code as a def, but I would like it set once (and for all) from the main function when the program starts. It should then be available as a def to the rest of the running code.
UPDATE: BTW, Clojure has to be one of the coolest languages I have come across in quite a while. Kudos to Rich Hickey!
I still think the cleanest way is to use alter-var-root in the main method of your application.
(declare version)
(defn -main
[& args]
(alter-var-root #'version (constantly (-> ...)))
(do-stuff))
It declares the Var at compile time, sets its root value at runtime once, doesn't require deref and is not bound to the main thread. You didn't respond to this suggestion in your previous question. Did you try this approach?
You could use dynamic binding.
(declare *version*)
(defn start-my-program []
(binding [*version* (read-version-from-file)]
(main))
Now main and every function it calls will see the value of *version*.
While kotarak's solution works very well, here is an alternative approach: turn your code into a memoized function that returns the version. Like so:
(def get-version
(memoize
(fn []
(-> (str "jar:" (-> my.ns.name (.getProtectionDomain)
(.getCodeSource)
(.getLocation))
"!/META-INF/MANIFEST.MF")
(URL.)
(.openStream)
(Manifest.)
(.. getMainAttributes)
(.getValue "Build-number")))))
I hope i dont miss something this time.
If version is a constant, it's going to be defined one time and is not going to be changed you can simple remove the defn and keep the (def version ... ) alone. I suppose you dont want this for some reason.
If you want to change global variables in a fn i think the more idiomatic way is to use some of concurrency constructions to store the data and access and change it in a secure way
For example:
(def *version* (atom ""))
(defn set-version! [] (swap! *version* ...))