Jetbrains has open sourced a low-level language toolkit called Nitra which comprises a language for describing grammars and a build tool to compile them.
In a blog post introducing Nitra back in November 2013 Hadi Hariri explained that is isn't just another parser generator and gave this example of its ability to extend C# with a new .? operator:
At that time Nitra had already been under development for over a year. Now its team, led by Vlad Chistyakov, has decided that, while it is "still work in progress", it provides a "minimum viable feature set, as well as a good architectural base for future development" and its source has been made available on GitHub, released under the Simplified BSD license.
Its description on GitHub tells us:
Nitra is a language workbench. You can use Nitra for the creation or extend a general-purpose programming language or a domain-specific language (DSL). At present Nitra allows you to create dynamically expanding parsers. In the future, Nitra will allow to create full support for programming languages: compilers, IDE support.
In his blog post announcing its open-sourcing Matt Ellis gives a fuller definition:
Nitra is a language for describing grammars, and the abstract syntax trees to represent them and also a build tool to compile the grammars into parsers, and generate the classes required to represent and navigate the AST. And it’s also a set of language services that use the grammar to provide automatic syntax highlighting, outlining and brace matching.
Creating parsers and ASTs (abstract syntax trees) is something JetBrains is already very good at but, as Ellis explains by taking away some of the gruntwork Nitra will allow the company to
"support more languages, quicker, and to focus on the higher levels in the stack of language tooling, such as analyses and quick fixes".
He also warns that if you want to use Nitra "expect to get your hands dirty" and lists the following as what it currently supports:
Grammars to define lexer-less parsers and ASTs that can be extended at compile time or runtime, supporting composition of languages, or languages with extensible syntax, such as Nemerle
A Visual Studio language service that uses Nitra to parse files and provide automatic syntax highlighting, outlining and brace matching. Current work is to increase the automatic support here to include go to declarations, find usages and rename refactorings