It's interesting but not very practical. It's an "algebra of types" with only constants, no variables, since C does not have type variables. Thus it misses much of the point of algebraic data types in a language like Haskell (deep composability and generics with very little code to write).

Take one of the most basic sum types in Haskell's base library, Maybe:

    data Maybe a = Nothing | Just a

This simple construction gives you the ability to write functions over optional values and avoid the issues with null pointers. This would be an amazing feature to have in C but it can't be achieved due to C's very limited type system.