diff --git a/bok-macro/src/repos.rs b/bok-macro/src/repos.rs
index df1afef..d3e5ec0 100644
--- a/bok-macro/src/repos.rs
+++ b/bok-macro/src/repos.rs
@@ -278,7 +278,72 @@ pub(crate) fn derive_repository(input: TokenStream) -> TokenStream {
 
     let name = input.ident.clone();
 
-    let expanded = quote! {
+    let ::syn::Data::Struct(items) = &input.data else {
+        use ::syn::spanned::Spanned;
+        return ::syn::Error::new(
+            input.span(),
+            "#[derive(::bok::Repository)]: not called on a struct",
+        )
+        .to_compile_error()
+        .into();
+    };
+
+    if items
+        .fields
+        .iter()
+        .find(|&f| {
+            f.ident
+                .as_ref()
+                .is_some_and(|id| id.to_string() == "_bok_repo")
+        })
+        .is_none()
+    {
+        use ::syn::spanned::Spanned;
+        return ::syn::Error::new(
+            input.span(),
+            "#[derive(::bok::Repository)]: struct is not a bok repo. use \
+             `#[::bok::repository(..)]` first",
+        )
+        .to_compile_error()
+        .into();
+    }
+    // holds the list of all package names, snake case
+    let mut all_pkgs =
+        Vec::<(String, ::syn::Path)>::with_capacity(items.fields.len());
+
+    for it in items.fields.iter() {
+        let Some(id) = &it.ident else { continue };
+        let id_str = id.to_string();
+        if id_str.starts_with("_p_") {
+            let path = {
+                let ::syn::Type::Path(phantom_path) = &it.ty else {
+                    continue;
+                };
+                let segment = phantom_path.path.segments.last().unwrap();
+                let ::syn::PathArguments::AngleBracketed(bracketed) =
+                    &segment.arguments
+                else {
+                    panic!("derive: phantom without anglebracket?");
+                };
+                let ::syn::GenericArgument::Type(::syn::Type::Path(t)) =
+                    bracketed.args.first().expect("phantom bracketed, no args")
+                else {
+                    panic!(
+                        "derive: phantom bracketed, generic not a type path"
+                    );
+                };
+                t.path.clone()
+            };
+            let name = id_str.strip_prefix("_p_").unwrap().to_owned();
+            all_pkgs.push((name, path));
+        }
+    }
+    all_pkgs.sort_by(|a, b| a.0.cmp(&b.0));
+    let pkgs_num: usize = all_pkgs.len();
+    let (pkg_names, pkg_types): (Vec<String>, Vec<::syn::Path>) =
+        all_pkgs.into_iter().map(|(a, b)| (a, b)).unzip();
+
+    quote! {
         impl ::bok::Repository for #name {
             fn name(&self) -> ::bok::RepoName {
                 (module_path!().to_owned() + "::" + ::std::stringify!(#name)).as_str().into()
@@ -286,10 +351,22 @@ pub(crate) fn derive_repository(input: TokenStream) -> TokenStream {
             fn path(&self) -> ::bok::Path<::bok::RepoName> {
                 (module_path!().to_owned() + "::" + ::std::stringify!(#name)).as_str().into()
             }
+            fn pkg_list(&self) -> &[&'static str] {
+                const PKGS : [&'static str; #pkgs_num] = [
+                    #(#pkg_names),
+                    *
+                ];
+                &PKGS
+            }
+            fn get(&self, pkg_name: &str) -> Option<::std::boxed::Box<dyn ::bok::Pkg>> {
+                match pkg_name {
+                #(#pkg_names => Some(::std::boxed::Box::new(#pkg_types::default())),)
+                *
+                _ => None,
+                }
+            }
         }
-    };
-
-    TokenStream::from(expanded)
+    }.into()
 }
 struct PathList(Vec<::syn::Path>);
 
diff --git a/bok/src/lib.rs b/bok/src/lib.rs
index dfc2a96..e6c3366 100644
--- a/bok/src/lib.rs
+++ b/bok/src/lib.rs
@@ -50,6 +50,8 @@ macro_rules! moduse {
 pub trait Repository: ::core::fmt::Debug {
     fn name(&self) -> RepoName;
     fn path(&self) -> Path<RepoName>;
+    fn pkg_list(&self) -> &[&'static str];
+    fn get(&self, pkg_name: &str) -> Option<::std::boxed::Box<dyn Pkg>>;
 }
 
 /// This is an empty Package List.
@@ -66,6 +68,13 @@ impl Repository for RepositoryEmpty {
     fn path(&self) -> Path<RepoName> {
         "::bok::RepositoryEmpty".into()
     }
+    fn pkg_list(&self) -> &[&'static str] {
+        const PKGS: [&'static str; 0] = [];
+        &PKGS
+    }
+    fn get(&self, _pkg_name: &str) -> Option<::std::boxed::Box<dyn Pkg>> {
+        None
+    }
 }
 
 /// Print the code of the package