Decker uses a novel scripting language called Lil. This morning I cobbled together a simple alternative frontend for the interpreter that might be handy for some styles of learning and experimentation: the Lil Playground.
To support this new environment, I also now offer a Lil syntax highlighting module for CodeMirror, a popular browser-based code editor component.
as a guy who wrote a Lezer/Codemirror parser for his domain-specific language, I love to see someone else doing that particular thing. I really need to get into Decker.