Function resolve 

pub fn resolve(name: &str) -> Option<&'static str>

Map a std.* module name to its bundled Bop source.

Returns None for any path outside the stdlib — chain this with your own crate::BopHost::resolve_module so user modules still resolve:

use bop::{BopError, BopHost};

impl BopHost for MyHost {
    fn resolve_module(&mut self, name: &str) -> Option<Result<String, BopError>> {
        if let Some(src) = bop::stdlib::resolve(name) {
            return Some(Ok(src.to_string()));
        }
        // fall back to your own resolver (filesystem,
        // embedded modules, etc.)
        self.my_own_resolver(name)
    }
}