I am following this tutorial: https://practicalli.github.io/blog/posts/web-scraping-with-clojure-hacking-hacker-news/ and I have had a hard time dealing with the :require part of the ns macro. This tutorial shows how to parse HTML and pull out information from it with a library called enlive, and to use it, I first had to put
...
:dependencies [[org.clojure/clojure "1.10.1"]
[enlive "1.1.6"]]
...
in my project.clj, and require the library in core.clj as the following:
(ns myproject.core
(:require [net.cgrand.enlive-html :as html])
(:gen-class))
I spent so much time finding out the name net.cgrand.enlive-html, since it was different from the package's name itself (which is just enlive), and I couldn't find it through any of the lein commands (I eventually found it out by googling).
How can I easily find out what name to require?
Practical approach
If your editor/IDE helps with auto-completion and
docs, that might be a first route.
Other than that, libraries usually have some read-me online, where they show off
what they do (what to require, how to use that).
Strict approach
If you really have nothing about a library, you will find the downloaded
library in you ~/.m2/repository directory. Note that deps without the naming
convention of "group/artifact" will just double on the artifact name, Next is
the version. So you can find your libraries JAR file here:
.m2/repository/enlive/enlive/1.1.6/enlive-1.1.6.jar.
JAR files are just ZIP-Files. Inside the JAR file you will usually find the
source files of the library. The directory structure reflects the package
structure. E.g. one file there is net/cgrand/enlive_html.clj (note the use
of the _ instead of -, this is due to name munging for the JVM). You then
can require the file in your REPL and explore with doc or dir etc. Or you
open this file, to see the docs and source code in one chunk.
Usually I get this from the documentation / tutorial for the library.
https://github.com/cgrand/enlive Check out the Quick Tutorial, which starts with the needed require.
Related
When I look at something like, say, the clojure.data.json source code I can see a namespace looking, for example, like this:
(ns clojure.data.json...)
So when I want to :require that in my .clj Clojure files, I simply do something like this:
(ns so.example
(:require [clojure.data.json :as json])
...
However in the dependencies in my .clj I have:
:dependencies [[org.clojure/data.json "0.2.4"]
So the clojure.data.json "became" org.clojure/data.json.
Now for, say, server.socket I have in my dependencies:
[server-socket "1.0.0"]
So this time no ".org" added, no slash, but the dot became a dash.
What's the relation between :require in Clojure source files and :dependencies in project.clj? Is there any "logic"?
How can I find what's the correct line to put in the dependencies?
The dependency vectors in project.clj are the maven artifact coordinates to resolve the dependency by finding the appropriate jar. Leiningen will attempt to find the apropriate jars and add them to your classpath so that namespace definitions and other resources can be loaded from inside their archive contents at runtime. The require statement in your code specifies a resource to look for in the class path. For example if you require clojure.data.json, Clojure will look for a resource with the path clojure/data/json.clj somewhere in your classpath, and attempt to load the definition for the namespace clojure.data.json from that resource.
There is no relationship. Namespace is something defined in the source code file. A dependency is based on a project name and is decided by the author(s) when they publish it. You'll almost always find the proper dependency information on the project github site or at Clojars, or in some cases, maven.
I'm trying out clojure on my second day and I don't understand almost anything yet. I am working with the Programming Clojure 2nd ed. and I am stuck with libraries.
I have Leiningen and have the REPL running. The book first tells the reader to run a simple
(require 'clojure.java.io)
which works just fine (I get a nil). Then it wants to load a file called introduction.clj by running another simple
(require 'examples.introduction)
where I get an error message
FileNotFoundException Could not locate clojure/java/introduction__init.class
or clojure/java/introduction.clj on classpath: clojure.lang.RT.load (RT.java:432)
I downloaded the introduction.clj file and looked where should I place it. The error and the book says the command will search in my classpath, but I have no idea where or what that is (after 1h of searching and reading I still don't get it, sorry). I ran a few commands and I had many classpaths listed (from which none contain a clojure/java/io.clj).
So I tried another approach - find the io.clj file on my disk and simply copy the file there and run it with a command
(require 'clojure.java.introduction)
This doesn't seem to work either. By the way, the io.clj file I found was in "C:\Program Files\clojure\src\clj\clojure\java". I tried running several other .clj files from the java folder as well from the clojure folder, like javadoc.clj or inspector.clj and all seem to work just fine with the above mentioned command. Only the new file doesn't seem to load this way.
Any help appreciated :)
Clojure runs on the Java Virtual Machine, so you will need to learn a bit about PATH and CLASSPATH concepts:
See: http://docs.oracle.com/javase/tutorial/essential/environment/paths.html
Regarding the error message, the Clojure runtime is expecting to find introduction.clj in the directory clojure\java\example\introduction.clj (not where it really should be - see below).
The convention for Clojure namespaces is that the last component is the file name, while any previous components are parent directories. So
clojure.java.introduction
would have to be in the directory (relative to your source "root" or classpath)
clojure\java\introduction.clj
(The lein REPL automatically adds your source root to the classpath).
Another concept you need to understand is where the "root" of your source code is located. For Leiningen (the build tool you are using) the default is either "src" or "src/main/clojure" - as documented in the Leiningen sample project file on GitHub).
Finally, if you get really stuck, it seems the complete project for the book is available on GitHub.
Looking at the project, I see that you should actually be placing the file under src\examples\introduction.clj
Are you reading the book "Programming Clojure"?
I have encountered the same problem. It ban be sovled as follows:
If you start clojure by java:
I work in windows, the clojure.jar is placed in D:\backup\clojure-1.5.1, and the source code of the book "Programming Clojure" is placed in D:\study\clojure\shcloj-code\code. You should first delete the user.clj file in folder D:\study\clojure\shcloj-code\code.
java -cp d:\backup\clojure-1.5.1\clojure-1.5.1.jar;d:\study\clojure\shcloj-code\code clojure.main -r
If you work in linux, replace the ";" with ":"
If you start clojure by lein
You should first cd to the D:\study\clojure\shcloj-code\code folder, and then
lein repl
You should also delete the user.clj file in folder D:\study\clojure\shcloj-code\code.
I am using a method from the contrib.string libraries but lein is having trouble finding the library.
In my project.clj I have :dependencies [[org.clojure/clojure "1.4.0"]] inside of defproject and then (use '[clojure.string :only (join)]) (use '[clojure.contrib.string :only (as-str)]) inside of src/file.clj
Do I need to add another dependency to include contrib? I have found examples of 1.2, but there seems to have been a shift and the documentation is, well, lacking.
Monolithic contrib is long gone, it had been split into several modules when clojure 1.3.0 was released. Now clojure.string belongs to standard clojure library. There are no as-str function in that namespace, but given its name I assume that you need str function.
UPD: I searched for as-str function and found that it works in the same way as str do, but takes only name of keywords and symbols, ignoring namespace and ':' keyword prefix. I think now you can do it only by writing the same functionality by yourself (I also had to do the same in my recent code).
the contrib.string is merged into clojure.string in clojure-1.4.0.
I'm new to Clojure and Leiningen, and I've determined that some of what I'll want to use is located in clojure.contrib.generic.math-functions. I found API information for that at http://richhickey.github.com/clojure-contrib/branch-1.1.x/math-api.html, but I can't find anything that helps me figure out what I should put into my project.clj file for that dependency.
I have tried [clojure.contrib.generic.math-functions "1.1"], [clojure.contrib.generic.math-functions "1.1.x"], and [clojure.contrib.generic.math-functions "1.1.0"]. For each of those, I get something like...
...
Caused by: org.apache.maven.artifact.resolver.MultipleArtifactsNotFoundException: Missing:
----------
1) clojure.contrib.generic.math-functions:clojure.contrib.generic.math-functions:jar:1.1
All clojure-contrib namespaces are shipped within a single jar file, for which the dependency has to be listed like:
[org.clojure/clojure-contrib "1.2.0"]
Please note that there are different versions available of that artifact. The 1.2.0 is the current stable release.
In order to use functions coming from the math-functions namespace in your clojure code, you need to either require or use such namespace, usually done within the ns form at the beginning of your source file:
(ns my.namespace
(:use [clojure.contrib.generic.math-functions]))
Have a look here to see the differences between use and require.
The next version of Leiningen will have a search task for precisely this purpose. It will search Clojars, Maven Central, and any other repositories your project has listed, provided they offer up downloadable indices. It's already implemented, so if you run Leiningen from git you can use it.
Also, the Leiningen tutorial covers this. Type "lein help tutorial".
You can generally find what you need at clojars.org - it's the default repository for leiningen. The current stable release of Clojure is 1.2.0, so you'd have this in your leiningen project.clj:
[org.clojure/clojure "1.2.0"]
[org.clojure/clojure-contrib "1.2.0"]
To use the generic math functions in your clojure, require or use it in your namespace declaration at the top of your source file:
(ns your-namespace
(:use [clojure.contrib.generic.math-functions :as mathf]))
This allows you to refer to the functions in that namespace like this:
(mathf/abs -10) ;; => 10
:use-ing namespaces with :as is the preferred way to use functions from other namespaces in your code. require is ok, but you'd have to prefix your functions with the entire namespace (e.g. clojure.contrib.generic.math-functions/abs) so that's not practical. Using a namespace without :as allows you to use these functions without any prefix at all (e.g. abs), but you're more likely to get namespace clashes and it might be difficult to see where functions come from, especially if you :use many libraries.
You can browse all libraries available from the default leiningen repository by checking out http://clojars.org/repo/. The structure of clojure-contrib will change when 1.3.0 is out, so you'll have to include the specific contrib library if you're using version 1.3.0-alpha-xx:
[org.clojure.contrib/generic "1.3.0-alpha4"]
Now that the clojure.contrib has been broken up, the math functions are in something called math.numeric-tower. The lein dependency is specified like this:
[org.clojure/math.numeric-tower "0.0.1"]
You can use or require as seems appropriate, for example
(use '[clojure.math.numeric-tower])
I'm trying to set up a simple clojure project, and I'm not sure how to load files between the project. I'm sure that the answer is in the documentation, but I can't find a simple answer any where and I'm not sure where to look.
Essentially, my directory looks like this:
Clojure/
clojure/
clojure.jar
other clojure files
clojure-contrib/
clojure-contrib.jar
other contrib files
project/
main.clj
utils.clj
And I want main.clj to be something like this:
(ns project.main
(:require project.utils))
(greet)
and utils.clj to be something like this:
(ns project.utils)
(defn greet [] (println "Hello, World!"))
But that fails with:
Exception in thread "main" java.io.FileNotFoundException: Could not locate project/utils__init.class or project/utils.clj on classpath: (main.clj:1)
When I attempt to run it. My classpath includes the top Clojure/ directory and both jars. I also tried putting the project/ directory in the classpath as well, with no luck.
How do you set up a simple clojure project?
You don't mention what your environment is (i.e. Emacs/SLIME/Swank, vim/Vimclojure), so I'm going to assume you are trying to invoke it from the command line.
You need to have your Clojure/ project directory in the classpath:
java -cp path/to/clojure.jar:path/to/clojure-contrib.jar:path/to/Clojure ...
Make sure to check that paths are correct relative to current working directory. It needs to point to the root of your namespace (i.e. if running in Clojure/, the path is .).
In fact, your project layout Works On My Machine(tm), with the exception that I have use instead of require (but you should've got a different error anyway if you got to the point when Clojure could find all your files).
This answer I posted to another question should hopefully give you an idea of how your filenames should relate to namespace names for things to work. However, since your question is "how to set up a simple Clojure project", the following is a better start:
Go to GitHub and grab Leiningen.
Follow the instructions in the README. You'll end up doing something like
$ lein new my-project
$ cd my-project
# ... edit project.clj ...
$ lein deps
Hack away! You'll need to put your files in the correct places. That will mean putting your source files in the directory tree rooted at my-project/src, with your core namespace most likely residing at my-project/src/my_project/core.clj. But really, I've explained all the details in the answer linked to above, so please read it (and do leave a comment if I missed something). :-)
Leiningen will take care of the basic project layout and setting up the classpath for a REPL / swank / nailgun for you (if you haven't yet come across the latter two, you will soon -- but that's a separate topic, the swank part of which I have covered to a certain degree e.g. in this SO answer), so hopefully you'll never need to deal with the java -cp ... nonsense by hand. (The swank-related answer I linked to in the last parenthetical remark has details on how to set up swank with the correct classpath from within Emacs.)