Shared via Pony Playground (https://playground.ponylang.io/?gist=d2c4ae32b9f211747d57b5b80079eedf)

main.pony

Error:
/home/pd/Develop/Secretary/src/ag-movies/movie.pony:21:30: type argument is outside its constraint
class ref Movie is Comparable[Movie ref]
                             ^
    Info:
    /home/pd/Develop/Secretary/src/ag-movies/movie.pony:21:31: argument: Movie ref
    class ref Movie is Comparable[Movie ref]
                                  ^
    /usr/lib/pony/0.25.0/packages/builtin/compare.pony:22:22: constraint: Comparable[Movie ref] #read
    interface Comparable[A: Comparable[A] #read] is Equatable[A]
                         ^
    /home/pd/Develop/Secretary/src/ag-movies/movie.pony:65:3: val method is not a subtype of box method
      fun val lt( other: Movie ): Bool =>
      ^
    /home/pd/Develop/Secretary/src/ag-movies/movie.pony:65:3: Movie ref is not a subtype of Comparable[Movie ref] #read: method 'lt' has an incompatible signature
      fun val lt( other: Movie ): Bool =>
      ^
    /home/pd/Develop/Secretary/src/ag-movies/movie.pony:77:3: val method is not a subtype of box method
      fun val eq( other: Movie ): Bool =>
      ^
    /home/pd/Develop/Secretary/src/ag-movies/movie.pony:77:3: Movie ref is not a subtype of Comparable[Movie ref] #read: method 'eq' has an incompatible signature
      fun val eq( other: Movie ): Bool =>
      ^