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Various programming stuff

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Using clojure from Windows

In this small article I’m going to post a guide on how to install and use clojure from Windows using good old’ cmd.exe.

Unfortunately, most guides on the official clojure site have instructions on using Clojure from Windows through Powershell or WSL. For my own reasons I hate both these approaches and only use the cmd.exe to interact with the Windows command line.

There are more or less two approaches to using clojure. Using leiningen or using the clj tools. The clojure official guide seems to be biased towards clj tools. However I think that leiningen may be easier for new users. I’ll cover both approaches here.

Warning Before doing anything else please make sure to install Java. You need a version of java that is at least 1.8. Try running java -version in cmd.exe to make sure you have java and it is the correct version.

Leiningen

To install leiningen you just download the lein.bat file from their page and put it in a folder in your PATH. You’ll then run lein and it will download all dependencies and install itself!

To start a clojure repl to be able to play with clojure you write lein repl. If everything went smooth you should see a prompt and if you write (+ 1 2) you should get 3. To exit press ctrl+d or write exit.

To start a new project you’ll use lein new [template name] [project name]. For example, to create a new app you’ll write: lein new app leinapp. You’ll get a new directory called leinapp. The important stuff in this directory are:

  • project.clj: The basic descriptor of your project; here you can set various attrs of your project and also add dependencies
  • src\leinapp: The source directory of your project. This is where you’ll put your code.
  • test\leinapp: Add tests here

There should be a core.clj file inside your src\leinapp folder. The main function is the entry point of the app. Try running lein run from the project folder and you should get the output of the main function.

Add this to the end of the core.clj to define a foo function:

(defn foo []
  "bar")

And run lein repl. You should get a repl command prompt for your application in the leinapp.core namespace (if you named your app leinapp). Type (foo) and you should see "bar".

To create a stand alone jar with your code (called uberjar) you can use lein uberjar. This will create a file named target\uberjar\leinapp-0.1.0-SNAPSHOT-standalone.jar. Then try java -jar target\uberjar\leinapp-0.1.0-SNAPSHOT-standalone.jar (notice I’m still on the leinapp project folder) and you’ll see the output of main!

clj

Using the clj is a more modern approach to clojure development. As I said before the official clojure page seems to be biased towards using this approach. The problem is that it seems to require Powershell to run as you can see on the clj on Windows page.

Thankfully, the good people at the clojurians slack pointed me to deps.clj project. This is an implementation of clj in clojure and can be installed natively on Windows by downloading the .zip from the releases page. This zip should contain a deps.exe file. Put that executable it in your path. You can also rename it to clj.exe if you want. Also if you have the powershell installed you can run this command from cmd.exe PowerShell -Command "iwr -useb https://raw.githubusercontent.com/borkdude/deps.clj/master/install.ps1 | iex" to install it automatically.

You can now run deps and you should get a clojure repl similar to lein repl.

To create a new project skeleton you can use the use the deps-new project. To install it run the following command from cmd.exe: deps -Ttools install io.github.seancorfield/deps-new "{:git/tag """v0.4.9"""}" :as new (please notice that there are various problems with the quoting on windows but this command should work fine).

To create a new app run: deps -Tnew app :name organization/depsapp and you’ll get your app in the depsapp folder. If you want a similar form as with lein, try deps -Tnew app :name depsapp/core :target-dir depsapp. Now the depsapp folder will contain:

  • deps.edn: The basic descriptor of your project; here you can set various attrs of your project and also add dependencies. This more or less changes the project.clj we got from leiningen.
  • src\depsapp: The source directory of your project. This is where you’ll put your code.
  • test\depsapp: Add tests here

To run the project, try: deps -M -m depsapp.core or deps  -M:run-m or deps  -X:run-x to directly run the greet function (run-m and run-x are aliases defined in deps.edn take a peek).

To start a REPL, run deps. Notice this will start on the user namespace, so you’ll need to do something like:

user=> (require 'depsapp.core)
nil
user=> (depsapp.core/foo)
"bar"

to run a (foo) function that you’ve added in the core.clj file.

To run the tests use: deps -T:build test.

To create the uberjar you’ll run: deps -T:build ci (tests must pass). Then execute it directly using java -jar target\core-0.1.0-SNAPSHOT.jar.

Also, notice that it’s really simple to create a new project with deps without the deps-new. For example, create a folder named manualapp and in this folder create a deps.edn file containing just the string {}. Then add another folder named src with a hello.clj file containing something like:

(ns hello)

(defn foo []
  "bar")

(defn run [opts]
  (println "Hello world"))

You can then open a REPL on the project using deps or run the run function using deps -X hello/run.

VSCode integration

Both leining and clj projects can easily be used with VSCode. First of all, install the calva package in your VSCode. Then, open your clojure project in VScode and press ctrl+shift+p to bring up the command pallete. Here write “Jack” (from jack-in) and select it (also this has the shortctut ctrl+alt+c ctrl+alt+j). Select the correct project type (leiningen or deps.edn). A repl will be opened to the side; you can then go to your core.clj file and run ctrl+alt+c enter to load the current file.

Then you can move to the repl on the side and run the function with (foo) or run (-main). Also you can write (foo) in your source file and press ctrl+enter to execute it and see the result; the ctrl+enter will execute the form where your cursor is. See this for more.

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