Hi,

Given any Event constructor, the 'conv' method passes in the field name to 'val' for each field. There is a Z instance for each Event arity. The call "conv E1::E1" works but requires that I explicitly specify the type. Is there any way to avoid that having to do that? 

For some reason 'conv' does not have enough information to know the type. Is there a way to do this with functional dependencies or type classes or something else?

Here is the paste http://lpaste.net/107632 and here is the error:

*Main> conv E1

<interactive>:3:1:

    No instance for (Z e0 (String -> E1)) arising from a use of `conv'

    The type variable `e0' is ambiguous

    Possible fix: add a type signature that fixes these type variable(s)

    Note: there are several potential instances:

      instance (Event e, Field a) => Z e (a -> e)

        -- Defined at testfamily.hs:28:10

      instance Event e => Z e e -- Defined at testfamily.hs:20:10

    Possible fix: add an instance declaration for (Z e0 (String -> E1))

    In the expression: conv E1

    In an equation for `it': it = conv E1

Thanks for any help,

Grant