Slicer
Write simultaneously the frontend and backend code, in the same language, within the same module. Even better: the Opa Slicer automates the calls between client and server. No more manually written AJAX calls or value serialization! And when auto is not enough, add hints to the code to enforce client or server-side, privacy, synchronous or asynchronous.
JavaScript on the client
Opa generates and is fully compatible with standard JavaScript code. Reuse tons of existing JavaScript libraries and frameworks, such as JQuery which is by default part of the standard library.
JavaScript on the server
Opa generates JavaScript on the server too, using Node.js and MongoDB. Applications built with Opa can be deployed in most cloud straightforwardly and scaled up or down easily.
Database Automation
Database queries are also written directly with Opa.
Opa currently supports the NoSQL databases MongoDB and CouchDB, and more databases (including SQL databases) are planned for future releases.
Opa provides many unique advanced operators and automates the database queries for maximal productivity.
Typechecker
Opa unique feature is its advanced typechecker that automatically verifies your application code, looking for bugs and inconsistencies, and crunching debugging time.
The Opa Type Checker was designed to bring static verifications to dynamic programming experience. Type checking is incredibly fast and features type inference: Application code stays lean and clean.
Truly Non-Blocking
Modern applications use a lot of asynchronous calls. Dealing with callbacks manually can be painful, and failing to do so properly blocks the application runtime.
To make asynchronous programming easy without blocking the application, Opa-generated JavaScript code uses smart continuations.
In the following example the Opa compiler automatically takes care of everything.
MVC Support
Opa support MVC (Model-View-Controller) programming and provides a scaffolding mechanism to get started instantly.
Just minutes away from creating a real application.
HTML5 Native Support
Opa is built for the modern web. HTML5 fragments can be inserted directly. No more messing with single and double quotes! CSS3 elements including selectors are also easier than ever to use.
Powerful syntax
Opa is JavaScript on steroids with many syntax and feature enhancements. Database, types, pointers, autoclose, higher-order functions, etc. The list is way too long to fit here. Find it on the reference card.
Power Rows
The core of Opa uses Power Rows: A powerful, statically-typed, extension of JavaScript objects.
Power Rows is one of the features that makes Opa safe and fun at the same time.
To find more about Opa, visit http://opa.io or http://opalang.org
