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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
Make a Lisp. The implementation is split in a series of steps that increase in complexity. You have tests for each step. You can chose whatever language you are already comfortable with. Most likely there is already an implementation in that language that you can take a peek at if you get stuck.
Finally, I would suggest you to take a look at the Truffle/GraalVM ecosystem(https://www.graalvm.org/graalvm-as-a-platform/language-implementation-framework/). The documentation is not exactly very elaborate, but a few good resources are Mumbler(http://cesquivias.github.io/blog/2014/10/13/writing-a-language-in-truffle-part-1-a-simple-slow-interpreter/#mumbler-language), SimpleLanguage(https://github.com/graalvm/simplelanguage), and (https://www.endoflineblog.com/graal-truffle-tutorial-part-4-parsing-and-the-trufflelanguage-class).