[fluoridation]

The logic can be implemented entirely in a parser written in a high level language. For example,

    //const int ZERO = '0';
    const int ZERO = 0x30;

    int convert(const char *s){
        int ret = 0;
        for (; *s; s++){
            ret *= 10;
            ret += *s - ZERO;
        }
        return ret;
    }

After that you just dump the value to the output verbatim. Any high level language can handle this, it's just a change of representation like any other. There's no need to do any further delegation.

[fluoridation]

Replying to myself because I can't edit the comment anymore. I think I see what you mean now. The parser for the language that compiles your parser also needs to know that "10" means 10, and that "0x30" means 48. I guess that also is knowledge that is passed down through compiler generations. I wonder if you could write a simple parser that doesn't contain a single numerical constant.