Time library underspecified

[Tom Pledger]

John Meacham writes:
 :
 | another useful thing would be  
 | endOfTime and beginningOfTime constants, representing the minimum and
 | maximum values representable by ClockTime.
 :
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If you plan to use endOfTime and beginningOfTime mainly as sentinels,
and are happy to treat them as +infinity and -infinity for arithmetic,
a separate wrapper type may help.

I've found the following (abridged) useful for 'closing off' data
types which were otherwise open-ended:

> data Close a
>     = Lo
>     | Mid a
>     | Hi
>     deriving (Eq, Ord, Show)
> 
> instance Bounded (Close a) where
>     minBound = Lo
>     maxBound = Hi
> 
> instance Num a => Num (Close a) where ...
> instance Real a => Real (Close a) where ...
> instance Enum a => Enum (Close a) where ...
> instance Integral a => Integral (Close a) where ...

Regards,
Tom