Bertram Felgenhauer wrote:
(This mail is related to http://permalink.gmane.org/gmane.comp.lang.haskell.libraries/3788 )
What I'm proposing is to make SocketOption a proper ADT and change get- and setSocketOption to functions that take type constructors instead of tags as arguments, i.e.
getSocketOption :: Socket -> (a -> SocketOption) -> IO a setSocketOption :: Socket -> (a -> SocketOption) -> a -> IO ()
To make that work, the two functions are implemented in a type class.
I think this is a reasonable design, despite the slight misuse of algebraic data types. I thought about using a type class with a functional dependency to express the relationship between the option tag and the option type, but that ends up being more elaborate for not much gain. Simon PJ pointed out to me an alternative design using GADTs: data SocketOption a where ReuseAddr :: SocketOption Int ... getSocketOption :: Socket -> SocketOption a -> IO a setSocketOption :: Socket -> SocketOption a -> a -> IO () This seems to me the best design, but requiring GADTs isn't really practical for this widely-used API. So I'm in favour of Bertram's proposal above... any other comments? Cheers, Simon