#13498: More storable instances? -------------------------------------+------------------------------------- Reporter: wyager | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 8.0.1 Resolution: | Keywords: Storable, | Foreign, Ptr Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by svenpanne): Replying to [comment:2 wyager]:
the encoding would be quite arbitrary
How is this an argument against adding the encodings? If they function correctly, why does it matter that they aren't "fixed" in some sense?
The general rule of thumb is: The Prelude doesn't make arbitrary choices when there is no obviously "right" way of doing things. Well, there are exceptions, but that's the idea. In our case, there ''are'' various arbitrary choices. Remember that the prime motivation for `Storable` is the FFI, and there are numerous ways used in actual C libraries to encode the equivalent of `Maybe` or `Either`, and none of them is "more correct" than the other.
Why are the tags 8 bit wide, and why are the tag values 0 and 1?
Because it makes sense and works.
`CChar` or `CInt` or `Word` make sense, too, and depending on the circumstances, they would be even better. That was just an example for the arbitrary decisions which would have to be made.
[...]
If you need serialization, you can use `Data.Binary`.
Besides `Data.Binary` being vastly slower than `Storable`, the primary use case here is `Data.Vector.Storable` and `Data.Array.Storable`. You can't write an `Unbox` instance for `Maybe a`, but you can (as I've done here) write a `Storable` instance.
If you directly want to use `Maybe` and `Either` with those containers, nothing is going to stop you from rolling your own. A better approach would probably be `newtype` wrappers for `Maybe` and `Either` with the corresponding `Storable` instances, making your arbitrary decisions explicit. Is using `Binary` really that much slower than your own code? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13498#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler