Macro decl_fake_generic 

macro_rules! decl_fake_generic {
    ($name:ident, $i:expr) => { ... };
}

Creates a fake generic. This is a necessary hack, at the moment, to declare types (with the decl_type macro) that have generic parameters. Now also implements ocaml::ToValue and ocaml::FromValue so it can be used in generic structs.