[Haskell-cafe] How to derive instance for type without exported constructor?

[Grigory Sarnitskiy]

> This time I've checked that it really compiles. Pretty much sure it works.

But how?! I'can't compile it:

test.hs:11:2:
    Conflicting definitions for `put''
    Bound at: test.hs:11:2-5
              test.hs:13:2-5
              test.hs:20:2-5
    In the default-methods for class Binary'

test.hs:12:2:
    Conflicting definitions for `get''
    Bound at: test.hs:12:2-5
              test.hs:15:2-5
              test.hs:21:2-5
    In the default-methods for class Binary'