How To Make A Directory In Clojure

Each language has its own set of tools to learn, and ClojureScript is no different. In this book, we will focus on two very important tools - clj for general-purpose build tasks, and Figwheel for live reloading of code. We'll begin by looking at our new friend clj, the built-in command-line tool for managing dependencies and building code. Like JavaScript's npm, clj is a configuration-based dependency manger as well as a simple build tool. The reader who has some familiarity with building software projects should feel at home rather quickly, but do not worry if this is your first exposure to using a build process.

We will walk through the essentials in enough detail to get comfortable building ClojureScript applications. As it happens with most programming languages, you can use many techniques in order to copy a file. This example uses the simplest method for copying a file with a single function call. For reasons of simplicity, the input and output filenames are hard-coded in the project files and are assigned to two variables named input and output, respectively. After that, a call to clojure.java.io/copy creates a copy of the input file.

Profiles allows you to customize your project.clj setup for development, production, or the REPL. Profiles allow you to customize any aspect of your project.clj. You can bring in specific dependencies, include additional directories, and change compilation options, among other things. Our project.clj has only one profile, uberjar, which is used for compiling our production application. There is not a great comparison for "profiles" in Node.js. The fastest way to create a new project is to use lein new command, that accepts one required argument — name of the project.

A deps.edn file lets us specify script aliases that allow us to declare a shorthand for a number of commands or even run a Clojure file. You should be able to descend into the newly create directory clojure-examples. This would normally be used as an outline of a Clojure project. For the purposes of demonstrating Clojure source code in org-mode, this project is only used to allow Leiningen to deal with Java class paths and resolve dependencies.

In this case, it will download the Clojure core into your machine. If other dependencies are required, they should be added to the project.clj file. For the purposes of this demonstration, simply creating the project is sufficient to proceed.

Clojure's philosophy is based on Lisp, which means that Clojure code contains lots of parentheses. Additionally, Clojure is a functional and dynamically typed programming language that has support for concurrent programming, which means Clojure's functions have no side effects. As the implementation of Clojure is based on the Java Virtual Machine, Clojure data types are Java data types, which means that all Clojure values are in reality references to Java classes. Moreover, most Clojure data types are immutable, which means they can't be changed after they've been created. Finally, Clojure has an unusual way of checking for equality.

In order to find out whether two lists are the same, Clojure checks the actual values of the two lists. Most programming languages don't do that because it might be a slow process, especially when dealing with large lists. Nevertheless, Clojure avoids that risk by keeping a hash for each one of its objects and by comparing the hashes of two objects instead of actually visiting all their values.

This works as long as the objects are immutable, because if objects are mutable and one of the objects changes, its hash table won't be updated to reflect that change. The philosophy behind tools.build is that your project build is inherently a program - a series of instructions to create one or more project artifacts from your project source files. One detail that sometimes trips up newcomers to ClojureScript is the fact that we name directories in the project with underscores but we name namespaces with hyphens.

This is a convention borrowed from Clojure, which compiles namespaces into Java classes, naming the classes according to their file path. Since hyphens are not allowed in Java class names, they are not allowed in the file paths either. ClojureScript follows Clojure's lead and requires that hyphens in a namespace be converted to underscores in the filesystem path. It is a quirk, but it is one that is easy to live with once we are aware of it. When you launch Figwheel it not only starts a live building/reloading process but it also optionally launches a CLJS REPL into your running application. This REPL shares compilation information with the ClojureScript compiler, allowing the REPL to be aware of the code changes as well.

The REPL also has some special built-in control functions that allow you to control the auto-building process and execute various build tasks without having to stop and rerun figwheel.main. At this point, you should have all the tools you need to start organizing your projects. You now know that namespaces organize maps between symbols and vars, and that vars are references to Clojure objects . Def stores an object and updates the current namespace with a map between a symbol and a var that points to the object. When we invoke clj -m cljs.main ..., several things happen. First, any dependencies specified in deps.edn will be downloaded.

This download will only happen on the initial run, and the packages will be cached locally for subsequent runs. Second, the Java Virtual Machine will be started and the Clojure compiler loaded. Next, Clojure will load the code specified by the -m flag.

In our case, we specify cljs.main, which is the entrypoint for the ClojureScript compiler. This code is available to us because we added the package for the ClojureScript compiler (org.clojure/clojurescript) to deps.edn. The Clojure language comes with a command-line tool that can be used for compiling both Clojure and ClojureScript. While other build tools exist, the clj tool is the defacto option. It is a simple tool, but it is powerful enough to use even on a large project.

We will use it for managing dependencies, compiling, and testing our projects. Using a single tool for all of these concerns should come as a welcome change from the proliferation of tools in the JavaScript landscape. Before proceeding any farther, we should install Java and Clojure. Since instructions change slightly with each release, readers are encouraged to follow the most recent instructions at the official Clojure Getting Started Guide. One interesting feature of ClojureScript is that we do not need to install it manually - we only need to specify it as a dependency of our project.

Once Clojure is installed, we can create a new project. Once your directory structure is created, copy paste the code shown below to my-first-clojure-app/src/my_first_clojure_app/core.clj . This is the core file where the main code for running the Clojure app should be present. Clojure community encourages a high amount of abstraction, so you should be creating a lot of such libraries with a small amount of code in the core.clj file. Leiningen is extensible — if necessary, you can add your own commands.

To do this you need to create a project, in which exists leiningen.command_name namespace, containing implementation of your command as a function with name command_name. This function receives project's object as an argument. More detailed information on writing plugins you can find in following blog post. One of example of plugins for Leiningen is thelein-swank plugin, that implements support for Swank server — you can find it in Leiningen's repository with source code.

Let's build the "learn a language" program with Leiningen. We have a very basic project at make-a-clojure-baby/leiningen/lein-build. Under that the directory, the file src/learn_a_language/important_phrases.clj is the same as the one listed above. The index.html was created with a single div that we can load our application into, and it includes the JavaScript file that will load our application with its dependencies. Normally, you'd simply create the .dir-locals.el manually and edit it like any other Emacs Lisp code. If you, however, feel overwhelmed by its syntax you can simply do M-x add-dir-local-variable and you'll be able to select the major-mode, the variable and its value interactively.

One small problem with this approach is that the resulting.dir-local.el will be created in the current directory, which may be a problem depending on what you're trying to do. Users ofProjectile may leverage the project-aware projectile-edit-dir-locals command instead. Clojure-lsp will look for project specific settings in a file called .lsp/config.edn. It will search from your project root folder up the directory structure so you can have multiple projects share the same settings.

Till now you have been using lein repl to explore the intricacies of the Clojure code you have seen so far. In the real world, you make actual applications and then ship/release those applications. More often than not those applications will sit alongside some legacy Java applications that have already been built and are running on the JVM in production. So, in this section, you will learn how to create effective production code and ship it. This tutorial assumes that you have leiningen installed and running. Target-path is the directory where compiled files will be placed when you run lein uberjar to build your production application.

If you have used webpack before, this is similar to the output key instructing webpack where it should output your bundles. It first checks the clojure.lang.Compiler/LOADER dynamic var. From scouring the code it seems this is used to set the loader internally during a specific scope, but what this ultimately is used for I have no idea. It does give you a way to override the classloader that Clojure uses, by giving that var a root binding.

A key concept when working with Clojure is "the classpath", a concept which we inherit from Clojure's host language Java. It's a sequence of paths that Clojure checks when looking for a Clojure source file (.clj), a Java Class file (.class), or other resources. So it's a lookup path, conceptually similar to the PATH in your shell, or the "library path" in other dynamic languages.

Project's source code should be stored in src directory, tests — in test directory, and additional resources, used by project — in resources directory. The lib directory is used to store libraries, used by project — they are copied there with the lein depscommand. List of libraries is calculated using information about dependencies, declared in project. If you want to use library, that isn't stored in one of the Maven's repositories, then you can just copy this library into lib directory, and it will available to your project.

The Clojure namespace clojure.java.io contains useful functions to work with files. We can pass a java.io.File instance as arguments or use the same arguments that can be passed to the file function that is also in this namespace. The function will create all parent directories for the file. The return result is true if the directories are created (they didn't exist before) and false when the directories didn't have to be created . The entire Metabase application is compiled and assembled into a single .jar file which can run on any modern JVM. There is a script which will execute all steps in the process and output the final artifact for you.

You can pass the environment variable MB_EDITION before running the build script to choose the version that you want to build. If you don't provide a value, the default is oss which will build the Community Edition. You're missing nothing, you are correct in that the test function will be pure. What I was looking for is for an approach that would leave me with two functions in the "production code", one pure and another one isolating the side-effects.

I would only need to test the second one without the need for additional mocks. Your Procfile should declare what process types make your app run. It also uses profiles that are intended for development, which can let test libraries and test configuration sneak into production. It needs to be in src/pinheiro/main.clj from the project root. Once you declared in deps.edn that src is where your classpathstarts, we say that it's pinheiro/main.clj in your classpath. As for symbols, you've been using them this entire time without even realizing it.

For example, when you write (map inc ), both map and inc are symbols. Symbols are data types within Clojure, and I'll explain them thoroughly in the next chapter. If you want to just use the symbol itself, and not the thing it refers to, you have to quote it. Quoting any Clojure form tells Clojure not to evaluate it but to treat it as data. The next few examples show what happens when you quote a form.

--main invokes aClojure function, in this case cljs.main. The cljs.main function supports a variety of command line arguments to specify common tasks. We're using--compile to specify that we want to compile the hello-world.corenamespace. This is followed by --repl to say that we want a REPL to launch immediately when compilation completes. Directory and load them from there, to do so is really to make them part of your application's source code, which rather defeats the purpose. You may wish to load that kind of frequently changing resource in a known filesystem location and load from there instead, rather than using the classpath.

Since our application is called guestbook, this is the root namespace for the project. Let's take a look at all the namespaces that have been created for us. The first time you execute lein run, lein might automatically download some files that are required for building the project. Additionally, keep in mind that lein can do many more things than what I describe here.

The next most important lein commands arelein clean, which cleans up a Clojure project, and lein repl, which starts the Clojure console. But sometimes you need to call Clojure functions from Java. People usually use Clojure because they have huge applications written in Java. They probably want to extend that application and create the new feature in Clojure.

Clojure's many advantages of speed and crispness of code make it an ideal candidate to be integrated into your code base. I am assuming you will encounter the same situation making you want to create the new feature as a Clojure function and call the function in Java. Clojure provides the required classes to call the Clojure code in your Java app and then run it.

The Clojure code will run through an interpreter as a side effect in Java and then the results can be imported and analyzed. The app-routes function will take in a redis-component as an argument which it will then pass to its route handlers. Make a new file handlers.clj in your src/clojure_for_js_devs directory, and add the following code.