[Haskell-cafe] another FFI question

Hello, I am reading the FFI spec. The following is unclear to me. Say I have data Bonzo = A | B |C and I want to "poke" Bonzo to an Int A -> 0 B -> 1 C -> 4 I have made Bonzo an instance of Storable. How do I write the poke functions and call them? Thanks, Vasili