A Look at DSLs

Share this article

If you have never seen or written any XML thus far, consider yourself very lucky.

XML started out as a very friendly and sane way to represent data so that it would be human readable and machine readable at the same time. Of course, this sounded pretty darn great, until people began building incredibly large systems (and, arguably, overengineered systems) based on XML. This site is a welcoming place for programmers of all backgrounds, so we won’t mention any specific technologies … but, you know who you are ;)

XML isn’t all horrible – it makes a lot of sense for some applications. But, you can’t get around the fact that XML is annoying as heck sometimes and some applications really need some more flexibility than XML can provide.

A DSL (domain specific language) is a small, special purpose language that’s meant to do a few things, but do them well. An example would be the Gemfile “DSL” that comes with Rails. In fact, the lack of XML was one of the biggest lures of Rails (for me, and most likely for many others).

The thing is, XML is only data. It isn’t a programming language; so, you can’t really express any computations with it. And, it’s not the most readable in many cases.

Web frameworks aren’t the only place where the type of situation arises that XML (or, any other similar data canning format, for that matter) doesn’t make much sense. Vim and Emacs both have domain specific languages. Financial applications, in general, usually have some kind of DSL attached with them. The thing is, a DSL comes with power that no data representation format can offer.

That’s not to say DSLs can’t be used for data representation! They sure can, and, in fact, if designed properly, they work better than many other traditional systems such as XML or JSON.

Back in the “olden days”, DSLs weren’t so easy to write. You had to define the language using a formal method, generate a lexer and parser, and finally compile or interpret the language. It was really a lot of work, because you had write WRITE A FREAKING COMPILER.

But, with dynamic languages, life is much easier and DSLs are really exploding in popularity. The basic idea is, instead of writing a
compiler, we use the power of Ruby itself to help develop the language. We define a few methods and, using these methods, the user of the DSL can accomplish their goal using Ruby. This kind of programming is often termed “metaprogramming“, since it manipulates other code.

The special idea is, unless you really want to, you’re completely hidden away from Ruby. This doesn’t look much like Ruby:

[gist id=”2949777″]

But, it is a very simple DSL that we can use Ruby to define.

So far, we’ve only just talked about it. Let’s get on with actually creating a DSL with Ruby!

Definition

First of all, we need to understand what exactly we want the language to do and what the DSL should look like.

Let’s imagine a robot; he can only move forward, backward, right and left some number of units. We have to keep track of his coordinates in reference to the point where he started, which we will call the origin. He can also fire and we have to keep track of the coordinates at which the robot fires.

That’s a fairly clear description. It might be something used for a website that hosts competitions for robots like these (upload your code and it pits your robot against others). That would be fun if the DSL had a few more features! But, we’ll go with KISS for now.

Now, we need to have some example code to go with this:

[gist id=”2949812″]

Okay, that’s nice. That clearly shows what we want our language to look like. We’ve just got to implement it.

Implementation

Implementing the DSL is incredibly easy, in fact, so easy that you’ll want to do it all the time!

We load a bit of code from a file, and use a special little method called “instance_eval” to run it as Ruby code, but with some special methods given to it. In our DSL, we’ll want to define the methods “forward”, “backward”, “right”, “left” and “fire”.

To do this, we define a class (you can call it anything you want, I’m going to call it Robot):

[gist id=”2949873″]

Add in the methods:

[gist id=”2949894″]

Now, just as a practical demonstration, we add in code that prints out the name of the method called:

We now use instance_eval. It can be used on any (pretty much) any object, and, it takes a block as an argument. Here it is:

[gist id=”2949938″]

That should print out the order of the methods when run. Why is that awesome? Because that shows us that the sky is the limit!

Since we can define whatever the heck we want in the Robot class, creating a DSL becomes very easy and allows for lots of creativity.

Remember, we want to keep track of the coordinates of the robot and the coordinates at which we fired. Let’s tackle the former first.

We begin by adding in the constructor (and getting rid of the “puts” in the methods, which were only there as an example):

[gist id=”2949987″]

We’ve added in the requisite data structures as object variables in order to keep track of information about our beloved robot.

Now, we fill in the movement methods so that they actually modify the information we’re keeping track of:

[gist id=”2950009″]

We add in the “fire” method and the logic needed to store the fired_at locations:

[gist id=”2950025″]

Before testing, we should add in some “puts” so that we can actually see what’s going on:

[gist id=”2950041″]

Finally, we add the instance_eval back in, with a little bit of test code to see if what we’ve developed is on the right track:

[gist id=”2950088″]

With that, you should get an output of the coordinates and fired_at’s of the robot.

That’s how easy it is develop a DSL! As a recap, this is all we did:

  • Made a class
  • Added methods (optional, although without them a DSL isn’t really anything)
  • Added constructor (optional)
  • Used instance_eval

That’s all there is to it! No wonder DSLs are so popular – they give us a lot of power for very little code.

Remember that you still have Ruby by your side. Consider this bit of code:

[gist id=”2950128″]

If you run it, you should see that the robot ends on (0, 6). We’ve used Ruby to create some abstraction for the robot, so that we can build bigger programs!

Tips

There a few things to remember while designing DSLs:

  • Keep a very simple API – short names, straightforward ideas
  • Remember that Ruby’s on your side – use it to its full advantage alongside your DSL
  • DSL stands for Domain Specific Language – you’re not trying to invent another Ruby here, so, keep it small
  • If the DSL is going to be user inputted onto a server – never trust your users

The last point deserves a bit more explanation. If you’re using the Robot DSL to pit user built robots against one another, in a setting where someone uploads their code onto your server and then your server runs the code, be extremely wary of what your users can do!

DSLs do NOT shield you from what Ruby can do – all of the code should be sandboxed and (basically) all syscall access turned off. Letting external code run wild on your servers will get you hacked before you can say “domain specific language”!

Conclusion

I hope you’ve enjoyed the ride; we’ve developed a domain specific language in about 50 lines of code. That’s pretty awesome!

The sky really is the limit with DSLs! It’s so easy to build them, and even easier to make them better! Just add on or change the methods in the class on which instance_eval is called.

Thanks for reading, and I hope that knowledge will come in handy.

Dhaivat PandyaDhaivat Pandya
View Author

I'm a developer, math enthusiast and student.

dsl
Share this article
Read Next
Leveraging Progressive Web Apps (PWAs) for Enhanced Mobile User Engagement
Leveraging Progressive Web Apps (PWAs) for Enhanced Mobile User Engagement
SitePoint Sponsors
10 Artificial Intelligence APIs for Developers
10 Artificial Intelligence APIs for Developers
SitePoint Sponsors
The Ultimate Guide to Navigating SQL Server With SQLCMD
The Ultimate Guide to Navigating SQL Server With SQLCMD
Nisarg Upadhyay
Retrieval-augmented Generation: Revolution or Overpromise?
Retrieval-augmented Generation: Revolution or Overpromise?
Kateryna ReshetiloOlexandr Moklyak
How to Deploy Apache Airflow on Vultr Using Anaconda
How to Deploy Apache Airflow on Vultr Using Anaconda
Vultr
Cloud Native: How Ampere Is Improving Nightly Arm64 Builds
Cloud Native: How Ampere Is Improving Nightly Arm64 Builds
Dave NearyAaron Williams
How to Create Content in WordPress with AI
How to Create Content in WordPress with AI
Çağdaş Dağ
A Beginner’s Guide to Setting Up a Project in Laravel
A Beginner’s Guide to Setting Up a Project in Laravel
Claudio Ribeiro
Enhancing DevSecOps Workflows with Generative AI: A Comprehensive Guide
Enhancing DevSecOps Workflows with Generative AI: A Comprehensive Guide
Gitlab
Creating Fluid Typography with the CSS clamp() Function
Creating Fluid Typography with the CSS clamp() Function
Daine Mawer
Comparing Full Stack and Headless CMS Platforms
Comparing Full Stack and Headless CMS Platforms
Vultr
7 Easy Ways to Make a Magento 2 Website Faster
7 Easy Ways to Make a Magento 2 Website Faster
Konstantin Gerasimov
Powerful React Form Builders to Consider in 2024
Powerful React Form Builders to Consider in 2024
Femi Akinyemi
Quick Tip: How to Animate Text Gradients and Patterns in CSS
Quick Tip: How to Animate Text Gradients and Patterns in CSS
Ralph Mason
Sending Email Using Node.js
Sending Email Using Node.js
Craig Buckler
Creating a Navbar in React
Creating a Navbar in React
Vidura Senevirathne
A Complete Guide to CSS Logical Properties, with Cheat Sheet
A Complete Guide to CSS Logical Properties, with Cheat Sheet
Ralph Mason
Using JSON Web Tokens with Node.js
Using JSON Web Tokens with Node.js
Lakindu Hewawasam
How to Build a Simple Web Server with Node.js
How to Build a Simple Web Server with Node.js
Chameera Dulanga
Building a Digital Fortress: How to Strengthen DNS Against DDoS Attacks?
Building a Digital Fortress: How to Strengthen DNS Against DDoS Attacks?
Beloslava Petrova
Crafting Interactive Scatter Plots with Plotly
Crafting Interactive Scatter Plots with Plotly
Binara Prabhanga
GenAI: How to Reduce Cost with Prompt Compression Techniques
GenAI: How to Reduce Cost with Prompt Compression Techniques
Suvoraj Biswas
How to Use jQuery’s ajax() Function for Asynchronous HTTP Requests
How to Use jQuery’s ajax() Function for Asynchronous HTTP Requests
Aurelio De RosaMaria Antonietta Perna
Quick Tip: How to Align Column Rows with CSS Subgrid
Quick Tip: How to Align Column Rows with CSS Subgrid
Ralph Mason
15 Top Web Design Tools & Resources To Try in 2024
15 Top Web Design Tools & Resources To Try in 2024
SitePoint Sponsors
7 Simple Rules for Better Data Visualization
7 Simple Rules for Better Data Visualization
Mariia Merkulova
Cloudways Autonomous: Fully-Managed Scalable WordPress Hosting
Cloudways Autonomous: Fully-Managed Scalable WordPress Hosting
SitePoint Team
Best Programming Language for AI
Best Programming Language for AI
Lucero del Alba
Quick Tip: How to Add Gradient Effects and Patterns to Text
Quick Tip: How to Add Gradient Effects and Patterns to Text
Ralph Mason
Logging Made Easy: A Beginner’s Guide to Winston in Node.js
Logging Made Easy: A Beginner’s Guide to Winston in Node.js
Vultr
How to Optimize Website Content for Featured Snippets
How to Optimize Website Content for Featured Snippets
Dipen Visavadiya
Psychology and UX: Decoding the Science Behind User Clicks
Psychology and UX: Decoding the Science Behind User Clicks
Tanya Kumari
Build a Full-stack App with Node.js and htmx
Build a Full-stack App with Node.js and htmx
James Hibbard
Digital Transformation with AI: The Benefits and Challenges
Digital Transformation with AI: The Benefits and Challenges
Priyanka Prajapat
Quick Tip: Creating a Date Picker in React
Quick Tip: Creating a Date Picker in React
Dianne Pena
How to Create Interactive Animations Using React Spring
How to Create Interactive Animations Using React Spring
Yemi Ojedapo
10 Reasons to Love Google Docs
10 Reasons to Love Google Docs
Joshua KrausZain Zaidi
How to Use Magento 2 for International Ecommerce Success
How to Use Magento 2 for International Ecommerce Success
Mitul Patel
5 Exciting New JavaScript Features in 2024
5 Exciting New JavaScript Features in 2024
Olivia GibsonDarren Jones
Tools and Strategies for Efficient Web Project Management
Tools and Strategies for Efficient Web Project Management
Juliet Ofoegbu
Choosing the Best WordPress CRM Plugin for Your Business
Choosing the Best WordPress CRM Plugin for Your Business
Neve Wilkinson
ChatGPT Plugins for Marketing Success
ChatGPT Plugins for Marketing Success
Neil Jordan
Managing Static Files in Django: A Comprehensive Guide
Managing Static Files in Django: A Comprehensive Guide
Kabaki Antony
The Ultimate Guide to Choosing the Best React Website Builder
The Ultimate Guide to Choosing the Best React Website Builder
Dianne Pena
Exploring the Creative Power of CSS Filters and Blending
Exploring the Creative Power of CSS Filters and Blending
Joan Ayebola
How to Use WebSockets in Node.js to Create Real-time Apps
How to Use WebSockets in Node.js to Create Real-time Apps
Craig Buckler
Best Node.js Framework Choices for Modern App Development
Best Node.js Framework Choices for Modern App Development
Dianne Pena
SaaS Boilerplates: What They Are, And 10 of the Best
SaaS Boilerplates: What They Are, And 10 of the Best
Zain Zaidi
Understanding Cookies and Sessions in React
Understanding Cookies and Sessions in React
Blessing Ene Anyebe
Enhanced Internationalization (i18n) in Next.js 14
Enhanced Internationalization (i18n) in Next.js 14
Emmanuel Onyeyaforo
Essential React Native Performance Tips and Tricks
Essential React Native Performance Tips and Tricks
Shaik Mukthahar
How to Use Server-sent Events in Node.js
How to Use Server-sent Events in Node.js
Craig Buckler
Five Simple Ways to Boost a WooCommerce Site’s Performance
Five Simple Ways to Boost a WooCommerce Site’s Performance
Palash Ghosh
Elevate Your Online Store with Top WooCommerce Plugins
Elevate Your Online Store with Top WooCommerce Plugins
Dianne Pena
Unleash Your Website’s Potential: Top 5 SEO Tools of 2024
Unleash Your Website’s Potential: Top 5 SEO Tools of 2024
Dianne Pena
How to Build a Chat Interface using Gradio & Vultr Cloud GPU
How to Build a Chat Interface using Gradio & Vultr Cloud GPU
Vultr
Enhance Your React Apps with ShadCn Utilities and Components
Enhance Your React Apps with ShadCn Utilities and Components
David Jaja
10 Best Create React App Alternatives for Different Use Cases
10 Best Create React App Alternatives for Different Use Cases
Zain Zaidi
Control Lazy Load, Infinite Scroll and Animations in React
Control Lazy Load, Infinite Scroll and Animations in React
Blessing Ene Anyebe
Building a Research Assistant Tool with AI and JavaScript
Building a Research Assistant Tool with AI and JavaScript
Mahmud Adeleye
Understanding React useEffect
Understanding React useEffect
Dianne Pena
Web Design Trends to Watch in 2024
Web Design Trends to Watch in 2024
Juliet Ofoegbu
Building a 3D Card Flip Animation with CSS Houdini
Building a 3D Card Flip Animation with CSS Houdini
Fred Zugs
How to Use ChatGPT in an Unavailable Country
How to Use ChatGPT in an Unavailable Country
Dianne Pena
An Introduction to Node.js Multithreading
An Introduction to Node.js Multithreading
Craig Buckler
How to Boost WordPress Security and Protect Your SEO Ranking
How to Boost WordPress Security and Protect Your SEO Ranking
Jaya Iyer
Understanding How ChatGPT Maintains Context
Understanding How ChatGPT Maintains Context
Dianne Pena
Building Interactive Data Visualizations with D3.js and React
Building Interactive Data Visualizations with D3.js and React
Oluwabusayo Jacobs
JavaScript vs Python: Which One Should You Learn First?
JavaScript vs Python: Which One Should You Learn First?
Olivia GibsonDarren Jones
13 Best Books, Courses and Communities for Learning React
13 Best Books, Courses and Communities for Learning React
Zain Zaidi
5 jQuery.each() Function Examples
5 jQuery.each() Function Examples
Florian RapplJames Hibbard
Implementing User Authentication in React Apps with Appwrite
Implementing User Authentication in React Apps with Appwrite
Yemi Ojedapo
AI-Powered Search Engine With Milvus Vector Database on Vultr
AI-Powered Search Engine With Milvus Vector Database on Vultr
Vultr
Understanding Signals in Django
Understanding Signals in Django
Kabaki Antony
Why React Icons May Be the Only Icon Library You Need
Why React Icons May Be the Only Icon Library You Need
Zain Zaidi
View Transitions in Astro
View Transitions in Astro
Tamas Piros
Getting Started with Content Collections in Astro
Getting Started with Content Collections in Astro
Tamas Piros
What Does the Java Virtual Machine Do All Day?
What Does the Java Virtual Machine Do All Day?
Peter Kessler
Become a Freelance Web Developer on Fiverr: Ultimate Guide
Become a Freelance Web Developer on Fiverr: Ultimate Guide
Mayank Singh
Layouts in Astro
Layouts in Astro
Tamas Piros
.NET 8: Blazor Render Modes Explained
.NET 8: Blazor Render Modes Explained
Peter De Tender
Mastering Node CSV
Mastering Node CSV
Dianne Pena
A Beginner’s Guide to SvelteKit
A Beginner’s Guide to SvelteKit
Erik KückelheimSimon Holthausen
Brighten Up Your Astro Site with KwesForms and Rive
Brighten Up Your Astro Site with KwesForms and Rive
Paul Scanlon
Which Programming Language Should I Learn First in 2024?
Which Programming Language Should I Learn First in 2024?
Joel Falconer
Managing PHP Versions with Laravel Herd
Managing PHP Versions with Laravel Herd
Dianne Pena
Accelerating the Cloud: The Final Steps
Accelerating the Cloud: The Final Steps
Dave Neary
An Alphebetized List of MIME Types
An Alphebetized List of MIME Types
Dianne Pena
The Best PHP Frameworks for 2024
The Best PHP Frameworks for 2024
Claudio Ribeiro
11 Best WordPress Themes for Developers & Designers in 2024
11 Best WordPress Themes for Developers & Designers in 2024
SitePoint Sponsors
Top 10 Best WordPress AI Plugins of 2024
Top 10 Best WordPress AI Plugins of 2024
Dianne Pena
20+ Tools for Node.js Development in 2024
20+ Tools for Node.js Development in 2024
Dianne Pena
The Best Figma Plugins to Enhance Your Design Workflow in 2024
The Best Figma Plugins to Enhance Your Design Workflow in 2024
Dianne Pena
Harnessing the Power of Zenserp for Advanced Search Engine Parsing
Harnessing the Power of Zenserp for Advanced Search Engine Parsing
Christopher Collins
Build Your Own AI Tools in Python Using the OpenAI API
Build Your Own AI Tools in Python Using the OpenAI API
Zain Zaidi
The Best React Chart Libraries for Data Visualization in 2024
The Best React Chart Libraries for Data Visualization in 2024
Dianne Pena
7 Free AI Logo Generators to Get Started
7 Free AI Logo Generators to Get Started
Zain Zaidi
Turn Your Vue App into an Offline-ready Progressive Web App
Turn Your Vue App into an Offline-ready Progressive Web App
Imran Alam
Clean Architecture: Theming with Tailwind and CSS Variables
Clean Architecture: Theming with Tailwind and CSS Variables
Emmanuel Onyeyaforo
How to Analyze Large Text Datasets with LangChain and Python
How to Analyze Large Text Datasets with LangChain and Python
Matt Nikonorov
Get the freshest news and resources for developers, designers and digital creators in your inbox each week
Loading form