Discussion about libraries for Haskell

Ganesh Sittampalam | 12 Sep 2012 08:04

getModificationTime and directory-1.2

Hi,

directory 1.2 switches to being based on 'time' rather than 'old-time'.
Because time values are exposed in its external API, this is causing
some disruption. In particular something like this pattern seems
relatively common:

getModTime :: FilePath -> IO EpochTime
getModTime path = do
  (TOD s _) <- getModificationTime path
  return $! fromIntegral s

i.e. get the modification time of a file in seconds since the UNIX epoch.

The replacement is something like:

  t <- getModificationTime path
  return $! fromInteger $ floor
         $ t `diffUTCTime` UTCTime (fromGregorian 1970 1 1) 0

But if you want to be backwards compatible then cabal flags and CPP are
needed, so it's all a bit verbose.

Amongst the dependencies of darcs, I've found myself making a similar
change to three packages now (unix-compat, tar, zip-archive), so I
wonder if it's worth putting this function somewhere central?

One problem is that it's too late to put it in directory, because
1.2.0.0 was shipped with ghc 7.6.1 and so packages need to work against
that version.

(Continue reading)

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Simon Hengel | 12 Sep 2012 08:28

Re: getModificationTime and directory-1.2

On Wed, Sep 12, 2012 at 07:04:18AM +0100, Ganesh Sittampalam wrote:
> The replacement is something like:
> 
>   t <- getModificationTime path
>   return $! fromInteger $ floor
>          $ t `diffUTCTime` UTCTime (fromGregorian 1970 1 1) 0

Not sure if it makes any difference, but I use:

    floor . utcTimeToPOSIXSeconds <$> getModificationTime path

Cheers,
Simon

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Ganesh Sittampalam | 13 Sep 2012 07:53

Re: getModificationTime and directory-1.2

On 12/09/2012 07:28, Simon Hengel wrote:
> On Wed, Sep 12, 2012 at 07:04:18AM +0100, Ganesh Sittampalam wrote:
>> The replacement is something like:
>>
>>   t <- getModificationTime path
>>   return $! fromInteger $ floor
>>          $ t `diffUTCTime` UTCTime (fromGregorian 1970 1 1) 0
> 
> Not sure if it makes any difference, but I use:
> 
>     floor . utcTimeToPOSIXSeconds <$> getModificationTime path

Thanks, that's much nicer. I missed utcTimeToPOSIXSeconds.

Since there hasn't been any support for the idea of the separate
package, I think I'll default to submitting patches for conditional
compilation to each affected project, and only make the separate
packages if the maintainers are keen.

Ganesh