Clear Nexus Chrome extension in PureScript
The Legal implications of SPAM
In 2003 President G. W. Bush signed a new law named “Controlling the Assault of Non-Solicited Pornography And Marketing (CAN-SPAM) Act of 2003” which is an approach to the growing number of complaints over commercial spam-emails. In this context, a commercial email is "any electronic mail message the primary purpose of which is the commercial advertisement or promotion of a commercial product or service.“ Thus, in order to regulate the traffic of commercial email, the US congress determined that all recipients of such a kind of emails must have the right to decline them.
Regarding this, having an automatized system to allow recipients of commercial emails to decide whether or not they want to be sent email from an organization becomes pretty handy, specially for people involved in marketing and sales who are very prone to inadvertently spam their potential clients.
Clear Nexus: a type-safe and functional solution
Clear Nexus is a two-part service consisting of a Chrome extension which communicates to a back-end server process. It allows you to determine if the owner of an email address has unsubscribed from your organization’s commercial emails, which means that sending content to that address would violate the CAN-SPAM law, as well as offering an easy way for recipients to start rejecting emails by letting them join a do-not-contact list maintained by the back-end.
At Stack Builders, we believe that Functional Programming is a great way to write composable and modular applications. That’s why when making the technical decisions about which technologies to use for the implementation of Clear Nexus, we chose two of the heavyweight contenders in this field. First, we chose Haskell (and the Servant library) for the back-end, since, from our experience as software developers, it has been an amazing tool when it comes to building expressive, type-safe applications.
Implementation of a Chrome extension in PureScript
When designing Clear Nexus there were three main concerns:
- How to querying the DOM of the Gmail’s main page in order to get information from the textarea.
- How to handle asynchronous operations with the Chrome-storage API.
- How to handle asynchronous requests to the Clear Nexus back-end.
Basically, Clear Nexus keeps a loop querying the Gmail’s DOM for emails typed in the compose text-area. Once an email is detected, an AJAX request is sent to the back-end and when it answers back, the extension processes the response and determines if the requested email is either subscribed or unsubscribed. After this, the loop starts again and the extension keeps listening to new events in the compose area.
In this fashion, it was possible to approach all of the aforementioned concerns properly:
The FFI was used to wrap some operations of the Chrome-storage API - for example, in order to store the admin-token in the storage, we wrapped a function which used the Chrome.storage.sync.set operation, and gave it a type inside PureScript. On the other hand, as manipulating the Chrome-storage is effectful, a Chrome effect was specifically defined to add better specificity to the functions manipulating it.
The main loop of the application was implemented as a “recursive callback” between two functions which call each other when an asynchronous operation has completed: The first one executes a callback when an email has been detected in the compose text-area. The second operation is the callback itself which performs the request to the back-end and which subsequently performs more asynchronous actions depending on the answer of the back-end. Nonetheless, this callback calls again the first operation to repeat the loop.
At Stack Builders, we are passionate about technologies that promote best practices and design patterns in the software industry. We believe that open source is a great way to disseminate this knowledge throughout the community, so we’re releasing our Chrome extension under the MIT license.
If you’d like to learn more about how to write Chrome extensions in PureScript, take a look at our repo and contribute either by leaving your comments, describing issues or opening pull requests!
Finally, if your team needs help in constructing application front or back-ends using functional languages, reach out to us at Stack Builders and we’d be happy to discuss your project with you.
If you’d like to use Clear Nexus for your own sales and marketing efforts, you can sign up for a free account here.