Bounded and floating types

[Conal Elliott]

Thanks.  That's exactly what I've done:

-- | Wrap a type into one having new least and greatest elements,
-- preserving the existing ordering.
data AddBounds a = MinBound | NoBound a | MaxBound
  deriving (Eq, Ord, Read, Show)

instance Bounded (AddBounds a) where
  minBound = MinBound
  maxBound = MaxBound

Looks like a generally useful tool.   Is there any interest in seeing it
added to a standard lib?

- Conal


On Dec 4, 2007 4:46 AM, Henning Thielemann <lemming at henning-thielemann.de>
wrote:

>
> On Mon, 3 Dec 2007, Conal Elliott wrote:
>
> > I'm using the bounds for event occurrence times.  Or, from another
> angle,
> > for times associated with when values can become known.  Pure values
> have
> > time minBound, while eternally unknowable values (non-occurring events)
> have
> > time maxBound.  Hm.  Now that I put it that way, I realize that I don't
> want
> > to use existing minBound and maxBound if they're finite.  (My event
> types
> > are temporally polymorphic.)  I'm mainly interested in Float/Double
> times,
> > which have infinities in practice but apparently not guaranteed by the
> > language standard.  I guess I'll either (a) bake in Double (temporally
> > monomorphic) and rely on infinities not guaranteed by the standard, or
> (b)
> > keep temporal polymorphism and add infinities to time parameter.  For
> now,
> > (b).
>
> Since you cannot rely on the existence of an infinity value for a floating
> point type with a particular behaviour - you can simply define you own
> type:
>
> data InfinityClosure a  =  NegativeInfinity | Finite a | PositiveInfinity
>
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