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---------- Forwarded message ----------
From: Sebastiaan Visser <[email protected]>
Date: 2011/11/18
Subject: Minor bug in system-uuid
To: [email protected]

There seems to be a minor bug in system-uuid package, the Read
instance fails when reading UUIDs inside some other datatype,
for example Either. Probably due to some issues with read
precedence.

Here is a simple example that shows the problem:

> import Data.UUID
> import System.UUID.V4
> import System.Random
>
> type T = Either UUID Char
>
> main :: IO ()
> main =
>   do u <- uuid
>
>      -- Showing and reading UUIDs works fine.
>      print (read (show u) :: UUID)
>
>      -- Just showing UUIDs inside an Either works as expected.
>      let l = Left u    :: T
>          r = Right 'a' :: T
>      print l
>      print r
>
>      -- Showing UUIDs inside an Either and reading it back fails.
>      let l' = read (show l) :: T
>          r' = read (show r) :: T
>      print l'
>      print r'

The problem doesn't seem to appear in your old 'uuid' package.