instance Random DiffTime

[Domen Kožar]

instance Random DiffTime where
  random :: (RandomGen g) => g -> (DiffTime, g)
  random g =
    let (i, g') = random g
     in (picosecondsToDiffTime $ fromIntegral (i :: Integer), g')

  randomR :: RandomGen g => (DiffTime, DiffTime) -> g -> (DiffTime, g)
  randomR (a, b) g =
    let (i, g') = randomR (diffTimeToPicoseconds a, diffTimeToPicoseconds b) g
     in (picosecondsToDiffTime i, g')

[Ashley Yakeley]

Hello, what's the issue here?

[Domen Kožar]

I'm in a need of such instance, so I figured I'd open an issue.

[Ashley Yakeley]

That this should be added to the time library, is that correct?

This means taking a package dependency on random -- this might be OK but I need to check.

[Ashley Yakeley]

Currently random depends on splitmix which depends on time, so the code can't go here. You'll have to put in the random package instead.

[Daniel Casanueva]

Currently random depends on splitmix which depends on time, so the code can't go here. You'll have to put in the random package instead.

I believe this is only the case for non-ghc compilers. I think they are trying to avoid depending on time there.

[Domen Kožar]

haskell/random#156

[Daniel Casanueva]

For reference:

https://github.com/haskellari/splitmix/blob/799700374ec214bf9a87ede1758ec73be676ed22/splitmix.cabal#L89-L108

[ˌbodʲɪˈɡrʲim]

time is a GHC boot package and should not depend on non-boot packages (such as random).