In this chapter, we'll setup our system to run Clojure. We'll install all the required dependencies and run the "Hello World" program.

Clojure Tutorial - Installing and Testing Required Dependencies

We need help from our editors to tame the LISPy syntax. This chapter walks through the tools we will need and why.

Editor Tools

How to Set up Visual Studio Code for Clojure Development

Setup IntellJ IDE for Clojure development.

Clojure IDE Setup - Using the Cursive Plugin With IntelliJ

How to Use Emacs with Clojure - 6 Packages You'll Need

Getting Started

Clojure is neither compiled nor has its own VM. Instead, it runs on VMs of other languages. In this lesson, we'll learn about official and unofficial ports and support status.

Understanding the Benefits of Clojure's Hosted Nature

Let's get our hands dirty with native data types and common operations.

Clojure Basics - Syntax and Native Data Types

C-style languages invisibly impose a syntax, whereas Lisps do not. This makes Lisps more expressive and easier to grasp.

What is Syntaxlessness? How to Write More Expressive Code

Since Clojure is hosted, it can tap into ecosystems of other languages. This has led to multiple build tools for different ecosystems. Choosing the right build tool might get tough for a beginner as the pros and cons might not be known. In this module, we'll learn about the general state of build tools in Clojure and choose the right tool for our project.

Clojure Build Tools - Leiningen, Boot, Shadow CLJS & Figwheel

Enough talking, let's create a new repository and set up a project from scratch, using Shadow CLJS.

How to Set Up a Shadow CLJS Project From Scratch

Our first project is now in place. In this chapter, we'll learn how to build and run it. We'll also explore some other build targets and explore Shadow with Reagent, a ClojureScript wrapper to React.

Getting Familiar With The Shadow CLJS API

The REPL is an essential element of a Lisper's toolkit. In this chapter, we'll solidify our grasp of the REPL and editor integration. We'll also learn about some problems that come with the REPL.

An Introduction to Clojure REPL and Evaluating Code Inline

Paredit is a tool to help with structural editing. It helps you write and modify S-Expressions with so much ease that the brackets will almost disappear! In this chapter, we'll learn fundamental Paredit commands.

A Clojure Beginner's Guide to Structural Editing with Paredit

Language Semantics

Clojure offers many control flow conditionals, like if-else blocks. In this chapter, we'll study the API of a few such methods.

Clojure Conditionals - Understanding Flow Control Operators

Atoms are thread-safe containers for handling mutable state. In this chapter, we'll learn how to create and manipulate atoms. We'll also learn how to hook into an atom's lifecycle and execute side-effects.

Atoms in Clojure - How to Create and Manipulate Them

There are many ways to define a function and parse arguments. In this chapter, we'll learn more about function definition, destructuring and some helpful higher-order functions.

Clojure Functions - Definitions, Distinctions, and Examples

Clojure sequences are abstract. In this chapter, we'll make sense of what exactly we mean by that, and learn about common operations.

Sequence Operations

Nested calls can become hard to manage. Threading macros help us take control. In this chapter, we'll learn about the concept of threading macros and study three commonly-used versions.

Threading Macros in Clojure - Thread-Last vs Thread-First vs As

Clojure lets you write code close to the metal ie the host language. In this chapter, we'll learn about constructs and techniques to interact with JavaScript within Clojure.

Clojure Constructs and Techniques to Interact with JavaScript

Standard Library

Walkthrough the components and concepts we will implement, with a video demo of the final app.

Overview

In this chapter, we will bootstrap a project using create-cljs-app and understand the code generated. We'll also study Hiccup, a CLJS alternative for JSX, and various ways to require namespaces.

Clojure Project Setup with create-cljs-app

Reagent is a minimalist Clojure wrapper for React. It exposes all React APIs including hooks and is one of the most popular Clojure projects. This chapter is a theoretical introduction to Reagent. We'll learn about components, third-party integrations and local state.

What is Reagent? The Minimalist Clojurescript React Wrapper

We have already learned how third-party components fit with Reagent. In this chapter, we'll implement React Router in the Tinycanva app.

How to Install React Router from NPM and Set Up Routes

In this chapter, we'll set up our UI library and CSS build process using PostCSS.

How to Set Up a UI Library & CSS Build Process Using PostCSS

Reframe is a flux-like library for uni-directional data flow. In this chapter we'll study the six-step Reframe loop.

Introduction to React State Management

Let's implement the concepts learned in the chapter on Reagent and React Router to build a login page..... plus the magic of REPL!

App Structure and Authentication UI

Set up Firebase project and configure authentication.

Setting Up Firebase Projects and Authentication for Clojure Apps

In this chapter, we'll initiate the Reframe loop for our login form, dispatch form submit events and handle them, ie implement steps 1 and 2.

Auth Event Handlers

We dispatched an event and wrote a handler. The handler returned an effects map, with a custom effect `:firebase/email-auth`. In this chapter, we'll create the custom effect handler and initialize the Firebase app.

Auth Effects and Firebase Initialization

In this chapter,  we'll connect the UI to the Reframe loop and create loading indicators and subscriptions to check if the user logged in successfully.

How to Create Firebase Data Subscriptions in Reframe

We have authenticated our users, but now they're stuck on the login screen. This chapter is about building re-usable containers to redirect users to authorized pages.

How to Build Reusable Containers for Clojure Apps with Reagent

In this chapter, we will integrate Reframe and Firebase to save the graphic "entity". This is analogous to a POST request with a traditional REST API.

How to Store Reframe Data in Firebase Without a REST API

Create Reframe handlers to read and delete graphics. Analogous to GET and DELETE in a REST API.

Read and Delete Graphics

Integrate Reagent and Reframe to create UI for listing and deleting graphics.

How to Integrate Reagent and Reframe With Clojure to Create a UI

Making graphic list items clickable; and the editor(detail) route. In the process, we'll learn how to use React's Higher Order Components with Reagent.

Using React Higher Order Components to Frame a Canvas Editor

In this chapter, we will integrate FabricJS with our app and create an HTML canvas-based editor.

How to Create an HTML Canvas Editor with Clojure and FabricJS

We have an editor in place, but it doesn't save data to Firebase. It is also not equipped to load data from Firebase. In this chapter, we'll create Reframe components to store data. We'll then update the editor to load data from Firebase. We will also extend the editor functionality.

Saving graphics

Tinycanva

Packaging an app consists of multiple steps, like configuration, minification etc. In this chapter, we'll package our app with production configuration and create an optimized JS bundle, that can be deployed on any CDN.

Production packaging

Large apps degrade user experience and one way to control that is to split our code into chunks. This chapter will walk through tools afforded by Shadow to split our app code. We'll also implement the splits and analyze performance gains.

Code splitting

Shadow comes bundled with a test runner. Clojure comes bundled with a unit testing library. In this chapter, we'll implement the two and learn about testing techniques for Reframe handlers.

Unit Testing with Clojure - Techniques for Reframe handlers

Going forward - information about online Clojure communities, server-side Clojure concepts, companies and job boards.

Conclusion

Advance Concepts

Clojure is a functional hosted LISP known for its expressiveness, which has excellent interop with Javascript, Java, and Microsoft's Common Language Runtime (CLR). 

Many developers praise the elegance and productivity Clojure allows, but for many it seems like an esoteric language with an "ugly" syntax that is impossible to get started with. This course will change that view and show you how to be productive with this marvelous language.

In this course, we'll build a web-based graphics editor similar to Canva. We'll explore Clojure from the perspective of a JavaScript developer. Along the way, we'll also explore state management, authentication, API integration with Google Firebase and interop with NPM.

This course takes you from zero to an understanding of Clojure semantics, LISP tools, and building a production-ready React application in just a few hours. 

We'll start with the basics and build up to writing a fullstack app with both frontend and backend in Clojure. 

The frontend, built using ClojureScript (Clojure that runs on JavaScript) will be a single page React application with routing, key-based authentication and API integration, which will save, list, edit and delete graphics.
 

The backend is hosted on Google Firebase. 

Throughout the course, we'll learn about tools like REPL that aid development. Towards the end, we'll learn about advanced concepts like code splitting and end-to-end testing.

Clojure is unlike other languages as it is hosted on, and can leverage, existing VMs. This means that you can learn Clojure once and write it on the backend with JVM or CLR, and the frontend with JavaScript. If a new technology like Rust takes over the world tomorrow, you will probably be able to continue to write Clojure because a Rust port is already in the making.

By the end of this course, you'll have a superpower: the ability to write fullstack Clojure applications.

Build a Fullstack Web Graphics Editor in Clojure and React

This is a course on Clojure for React developers in which we'll build a web-based graphics editor similar to Canva.

Tinycanva: Clojure for React Developers

The concept of tree-based codes aka LISPs

Editor integrations that make writing LISPs easy

Mental models for Clojure's rich standard library

Understanding of tools like NREPL to aid fast feedback

Hosted nature of Clojure and its ability to tap into JVM, JavaScript, CLR and other language ecosystems

Syntaxlessness and expressiveness of the language

How to create React applications with Clojure

Integration with APIs using Google Firebase

Key-based authentication and access control

Integration with React Router and Fabric JS

Map of communities and resources that can help when you get stuck

Clojure lets you write concise code. A major factor that supports this is its rich standard library.
So far we have studied syntax, build tools, and nREPL. In this module, we'll build on top of that knowledge to understand the most commonly used functions.

We highly recommend that you follow along and try the examples yourself using inline eval. This is also a good time to practice some Paredit commands. We'll reuse the setup for 

 and create a new namespace for each chapter. So start your 

, start the Node runtime, and connect your editor to the REPL. It's time to code.

 command and the REPL, check the chapters on Shadow CLJS API and NREPL under the 

In this chapter, we'll learn about various conditional functions. The code examples are present in the 

 namespace. By now, you should be comfortable figuring out the disk path of the file that holds this namespace.

Q: What is the correct disk path for this namespace?

touch src/first_project/conditionals.cljs

If you guessed it right, great. If you got it wrong, you might want to review the chapter on 

 function already. It takes three arguments:

(if true
  "Var is true"
  "Var is false") ; => "Var is true"

 denotes the result of inline evaluation with nREPL.

Empty data structures (lists, vectors, maps, and sets) are truthy. 

(if []
  "Truthy"
  "Falsy") ; => "Truthy"

You might find yourself in a position where you need to execute more than one S-Expression in the 

 block. For example, instead of just returning a string, you may want to print and return it, like this :

(comment
  (if nil
    (print "Truthy")
    "Truthy"
    "Falsy"))

---
title: Clojure Conditionals - Understanding Flow Control Operators
slug: stdlib-conditionals
description: Clojure offers many control flow conditionals, like if-else blocks. In this chapter, we'll study the API of a few such methods.
privateVideoUrl: https://fullstack.wistia.com/medias/sgi92h7rqo
code: https://gitlab.com/fullstackio/books/newline-course-apps/shivek-khurana-tinycanva-clojure-for-react-developers-app/-/tree/main/code/module_03/lesson_03.00/App/source_code/first-project?ref_type=heads
---

# Conditionals

## Introduction

Clojure lets you write concise code. A major factor that supports this is its rich standard library.
So far we have studied syntax, build tools, and nREPL. In this module, we'll build on top of that knowledge to understand the most commonly used functions.

We highly recommend that you follow along and try the examples yourself using inline eval. This is also a good time to practice some Paredit commands. We'll reuse the setup for `first-project` and create a new namespace for each chapter. So start your `watch`, start the Node runtime, and connect your editor to the REPL. It's time to code.

If you need a reminder on the `watch` command and the REPL, check the chapters on Shadow CLJS API and NREPL under the _Language Semantics_ section.

In this chapter, we'll learn about various conditional functions. The code examples are present in the `first-project.conditionals` namespace. By now, you should be comfortable figuring out the disk path of the file that holds this namespace.

## Create `first-project.conditionals` namespace

Q: What is the correct disk path for this namespace?

A:

```bash
touch src/first_project/conditionals.cljs
```

If you guessed it right, great. If you got it wrong, you might want to review the chapter on `Project Structure` again.

## if

We have seen the `if` function already. It takes three arguments:

-   a variable to check
-   an S-Expression to execute if the variable is truthy
-   an S-Expression to execute if the variable is falsy

```clojure { actualFilename=./protected/source_code/first-project/src/first_project/conditionals.cljs endLine=5 startLine=3 statedFilename=first-project/src/first_project/condtionals.cljs url=https&#x3A;//gitlab.com/fullstackio/books/Build-Canva-with-Clojurescript/module_03/lesson_03.00/protected/source_code/first-project/src/first_project/conditionals.cljs#L3 }
(if true
  "Var is true"
  "Var is false") ; => "Var is true"
```

The inline comment starting with `=>` denotes the result of inline evaluation with nREPL.

Empty data structures (lists, vectors, maps, and sets) are truthy. `nil` is falsy.

```clojure { actualFilename=./protected/source_code/first-project/src/first_project/conditionals.cljs endLine=10 startLine=8 statedFilename=first-project/src/first_project/condtionals.cljs url=https&#x3A;//gitlab.com/fullstackio/books/Build-Canva-with-Clojurescript/module_03/lesson_03.00/protected/source_code/first-project/src/first_project/conditionals.cljs#L8 }
(if []
  "Truthy"
  "Falsy") ; => "Truthy"
```

You might find yourself in a position where you need to execute more than one S-Expression in the `if` or `else` block. For example, instead of just returning a string, you may want to print and return it, like this :

```clojure { actualFilename=./protected/source_code/first-project/src/first_project/conditionals.cljs endLine=17 startLine=13 statedFilename=first-project/src/first_project/condtionals.cljs url=https&#x3A;//gitlab.com/fullstackio/books/Build-Canva-with-Clojurescript/module_03/lesson_03.00/protected/source_code/first-project/src/first_project/conditionals.cljs#L13 }
(comment
  (if nil
    (print "Truthy")
    "Truthy"
    "Falsy"))
```

Shivek Khurana

Closure lets you write concise code. A major factor that supports this fact is

standard library. So far we have studied syntax, build tools and N-repell. In

we will build on top of that knowledge and understand the most commonly used

We highly recommend that you follow along and try the examples yourself using

This is also a good time to practice some paraded commands. We will reuse the

first project and create a new namespace for each chapter. So start your watch

start the node runtime and connect your editor to the repel. In this chapter,

we will learn about various conditional functions. The code examples are

dot conditionals namespace. What is the "Connect this path for this namespace?"

If you guessed it right, great. If you got it wrong, you might want to review

project structure again. We have seen a function already. It takes three

check, an s-expression to execute if the variable is truthy and one if the

Empty data structures like lists, vectors and maps are truthy, whereas nil is

You might find yourself in a position where you need to execute more than one s

in the if or else block. For example, instead of just returning the string,

what if you wanted to print and return like so. This s-expression is invalid

command so it doesn't interfere with other examples. In cases like these, you

Do takes an arbitrary number of s expressions and executes them in order.

If not, it is similar to if except it executes the first block if the variable

The function is same as wrapping if with a not function, not inverses the

variable. Some if statements might not care about the else clause. For example,

render a component only when a variable is truthy. The when function can be

It takes n arguments. The first argument is the Boolean expression to evaluate

rest of the arguments are the expressions to execute. When also has a when not

which is similar to when, except it executes the block only if the test

In cases where when or when not do not execute, nil is returned.

Quant or short for condition is similar to switch case. Quant takes even number

the arguments in even positions are the expressions to test and the arguments

are the output of those expressions. It also takes an else block which acts as

If the else is not specified and no case matches, nil is returned by the fault.

If you write this function in your editor and try to execute test X 91,

you might see an error saying that test X is not defined. This happens if you

of the definition of test X function. Your options here are to save so that the

watch rebuilds the process or to inline evaluate the definition of the function

Quant P is a modified version of Quant that takes a predicate function, a value

For each case, the predicate function is called on the value and test value.

The conversion of test Y function would look as follows. Case is similar to

In Quant P and case, the else blocks are not explicit, but the last element is

default. In this module, we learned about various conditionals and also groomed

N repellent paraded. Just like the chapter on paraded, think of this chapter as

It will not be fair to assume that you will memorize the entire API in one

Try it once and refer to it as many times as you wanted. If you ever get stuck

examples, you might find closure docs.org website to be helpful.