Re: [Haskell-cafe] Writing a Storable instance for a C union

On 12/14/2013 12:24 AM, Nikita Karetnikov wrote:

instance Storable MyStruct where peek p = do v0 <- peekByteOff p 0 v1 <- peekByteOff p 4 return $ MyStruct v0 v1

But that would require to define a Storable instance for the Union type, which is exactly the point of the thread. How can I do so? (Note that Foo, Word64, and (Ptr a) are instances of Storable themselves.)

It's as simple as : peek p = do v0 <- peekByteOff p 0 case v0 of 1 -> MyStruct <$> peekByteOff p 4 2 -> FooStruct <$> peek... But this function can only have a single type, hence my suggestion that you should create a union type to represent the C union : type SomeUnion = MyStruct Byte | FooStruct Integer | ...