[Haskell-cafe] RebindableSyntax Strangeness

[Henry Laxen]

Hi Cafe,

I have encountered the following puzzling behaviour from a very simple
program:

Consider

-- {-# LANGUAGE RebindableSyntax   #-}
module A where
import Data.Time

running this with ghci gives:

A> :i UTCTime
type UTCTime :: *
data UTCTime = UTCTime {utctDay :: Day, utctDayTime :: DiffTime}
  	-- Defined in ‘time-1.9.3:Data.Time.Clock.Internal.UTCTime’
instance [safe] Eq UTCTime
  -- Defined in ‘time-1.9.3:Data.Time.Clock.Internal.UTCTime’
instance [safe] Ord UTCTime
  -- Defined in ‘time-1.9.3:Data.Time.Clock.Internal.UTCTime’
instance [safe] Show UTCTime
  -- Defined in ‘time-1.9.3:Data.Time.LocalTime.Internal.ZonedTime’
instance [safe] FormatTime UTCTime
  -- Defined in ‘time-1.9.3:Data.Time.Format.Format.Instances’
instance [safe] Read UTCTime
  -- Defined in ‘time-1.9.3:Data.Time.Format.Parse’
instance [safe] ParseTime UTCTime
  -- Defined in ‘time-1.9.3:Data.Time.Format.Parse.Instances’

Now uncomment the first line (RebindableSyntax) and rerun it:

A> :i UTCTime
type UTCTime :: *
data UTCTime = UTCTime {utctDay :: Day, utctDayTime :: DiffTime}
  	-- Defined in ‘time-1.9.3:Data.Time.Clock.Internal.UTCTime’
instance [safe] FormatTime UTCTime
  -- Defined in ‘time-1.9.3:Data.Time.Format.Format.Instances’
instance [safe] ParseTime UTCTime
  -- Defined in ‘time-1.9.3:Data.Time.Format.Parse.Instances’

And all of the nice instances for UTCTime have disappeared.  Why?

Best wishes,
Henry Laxen