nanopre

nanopre is a zero-dependency, no-unsafe implementation of an extremely minimal C-style text preprocessor. At present, nanopre is in a minimum viable product state, which is to say that while it is functional and free of bugs to the best of my knowledge, it is not battle-tested, stable, or feature-complete.

Features

• Context::define allows specifying 'macros,' strings of the form [a-zA-z_][a-zA-Z0-9_]* which should be replaced by an arbitrary string everywhere they appear in the input (when surrounded by word boundaries). Macros cannot currently accept arguments or expand to other macros or preprocessor directives.
• The directives #if, #elseif, #else, and #endif allow the conditional inclusion of code based on the evaluation of simple boolean expressions. The literals are 0 and 1, the supported operators are &&, ||, and !, and parentheses may be used for grouping. Evaluation is left-associative. While no other tokens are permitted in these expressions, they are evaluated after macro substitution, so you may use macros which evaluate to 1 or 0 as a substitute for variables.
• Optionally, #include can be supported by defining a struct which implements Includes and passing it to Context::with_includes. The struct is responsible for mapping include paths to their contents.

Planned Features

• #define for defining macros within the input.
• A way to optionally trap unknown preprocessor directives. Currently, these are left as is.
• More descriptive error handling, depending on how complex this is to implement.

Credits

nanopre is in part inspired by Diggsey's minipre, which I used before building this project.