We generally consider passing dictionaries as an implementation detail that users shouldn't rely on for their FFI as specialization optimizations would break FFI code written like that.

The guide in here https://github.com/purescript/documentation/blob/2ecc0e6bea10ecd0304252363b574af309ca59d4/guides/FFI.md#handling-constrained-types talks about how to do that though, so we should probably get rid of that section, or talk about how to explicitly pass the functions you need from the dictionary into the FFI similar to how we do it for data constructors.