Example of using nom parsers from a proc macro

This project is organised as 3 crates:

• nom_macro is the main project, exposing the proc macro and the generated types
• parser holds the nom parsers
• macro_parser provides the macro to parse at compile time

We need to separate them because a proc macro project can only export proc macros functions, no other types. If we want the main project to expose the parsers or the generated types along with the macro, we need to have them available in their own crate. So the parser crate is imported by macro_parser, and the parsers are reexported by nom_macro. If we do not need to make them available outside of the proc_macro, they can stay inside the proc macro crate.

The macro_parser crate provides a function-like macro that expects a string literal. If anything other than a string literal is provided (number, variable, etc), the macro will fail. The string literal then goes through a nom parser, that extracts a part of it. The quote crate is then used to generate a structure that contains the parsed value, and that structure is compiled in place of the macro.