openTempFile only defined on GHC

[Simon Marlow]

Neil Mitchell wrote:
> Hi
> 
>> Perhaps as a first step, rather than just omitting them from the 
>> export list
>> where they aren't supported, they should be replaced by dummy 
>> definitions that
>> emit a helpful error message?
> 
> Like canonicalizeFilePath, which has a dummy implementation
> everywhere? It's frustrating to have a standard base library which
> isn't standard and portable. I realise that the reason that this was
> added was for race-free temporary file creation, but until they are
> available on Hugs, my code will use a race-full implementation
> everywhere, including GHC.
> 
> Could we perhaps have an implementation of this function for all other
> compilers:
> 
> -- Note: openTempFile is not available on Hugs, which sucks
> openTempFileLocal :: FilePath -> String -> IO (FilePath, Handle)
> openTempFileLocal dir template = do
>    i <- randomRIO (1000::Int,9999)
>    let (file,ext) = splitExtension template
>        s = dir </> (file ++ show i) <.> ext
>    b <- doesFileExist s
>    if b then openTempFileLocal dir template else do
>        h <- openFile s ReadWriteMode
>        return (s, h)
> 
> That's what I use everywhere.

What does the "local" in openTempFileLocal mean?  I'd be perfectly happy to have 
non-race-free implementations of openTempFile for certain compilers/platforms as 
long as we document it (not that we document openTempFile properly at all at the 
moment, which is a bug).

Also note that you can't use </> or <.> here, because filepath is not in base :-)

>> I suspect there are many such examples in the base package, FWIW.  
>> nch98 doesn't
>> implement various bits of System.IO.Error, for example.  Hugs has a very
>> different version of Control.Concurrent.
> 
> I think these should be made very explicit in the documentation.
> Control.Concurrent is understandable, things like file creation
> methods aren't - a user will be annoyed (and I was) to find that their
> program written according to the documentation doesn't work.

I quite agree.  Care to send a patch, or open a ticket?

Cheers,
	Simon