There are many projects that call out for a custom language parser. If you need something standard, you can probably lift the code from someplace on the Internet. If you need something custom, you might consider reading [Federico Tomassetti’s] tutorial on using ANTLR to build a complete parser-based system. [Frederico] also expanded on this material for his book, but there’s still plenty to pick up from the eight blog posts.
His language, Sandy, is complex enough to be a good example, but not too complex to understand. In addition to the posts, you can find the code on GitHub.
The implementation code is Java, but you can still learn a lot even if you plan to use another language. The posts take you through building a lexer (the part that breaks text into tokens), the parser, handling syntax highlighting and autocompletion, creating an abstract syntax tree, and more.
The example compiler generates Java bytecode, so it can produce output that can run anywhere Java can run.
If you are using C, you might consider looking up lex and yacc or flex and bison to get similar results. You might also be interested in using LLVM as a very specific kind of parser if you are wanting to parse C or C++. Either way, a custom language is just the ticket to give your custom CPU project a boost.