[Haskell] Should inet_ntoa Be Pure?

[Dominic Steinitz]

>  Axel Simon wrote:
>
>  > > > Does anyone know why these are in the IO monad? Aren't they
>  > pure functions
 > > > > converting between dotted-decimal strings and a 32-bit network 
byte ordered
 > > > > binary value?
 > >
 > > I guess the answer is no for both: The first one can fail
 >
>  That doesn't mean that it should be in the IO monad; using Maybe
>  would suffice.

Agreed. Perhaps I wasn't clear enough in my original question. There 
appears to be no intrinsic reason why they should be in the IO monad.

 > >
 > > Hence ntoa needs to be an IO action so that the value is read
 > > immediately before the next ntoa call is executed.
 >
 > That shouldn't be an issue so long as the buffer contents are
 > converted to a Haskell String before the function is called again
 > within the same thread.
 >
 > However, I wouldn't rely upon all implementations of inet_ntoa() being
 > thread-safe.

>  > What you could do is to apply unsafePerformIO to
 >
 > [snip]
 >
 > Or you could just re-implement the functions in Haskell.
 >
 > Apart from the re-entrancy issues with inet_ntoa(), many
 > implementations of inet_addr() have misfeatures, e.g. allowing octets
 > to be expressed in octal or hex, or allowing numbers outside of the
 > 0-255 range (in which case, the top bits overflow into the next
 > octet).

Perhaps better would be:

inet_addr' :: (Octet,Octet,Octet,Octet) -> HostAddress
inet_ntoa' :: HostAddress -> (Octet,Octet,Octet,Octet)

I see Peter Simons has already written something:

http://cryp.to/hsdns/docs/Network.IP.Address.html#v%3Aha2tpl

Dominic.