Portability | portable |
---|---|
Stability | stable |
Maintainer | wren@community.haskell.org |
This module presents a type class for numbers which have
representations for transfinite values. The idea originated from
the IEEE-754 floating-point special values, used by
Data.Number.LogFloat. However not all Fractional
types
necessarily support transfinite values. In particular, Ratio
types including Rational
do not have portable representations.
For the Glasgow compiler (GHC 6.8.2), GHC.Real defines 1%0
and 0%0
as representations for infinity
and notANumber
,
but most operations on them will raise exceptions. If toRational
is used on an infinite floating value, the result is a rational
with a numerator sufficiently large that it will overflow when
converted back to a Double
. If used on NaN, the result would
convert back as negativeInfinity
.
Hugs (September 2006) stays closer to the haskell98 spec and offers no way of constructing those values, raising arithmetic overflow errors if attempted.
- class (Num a, Ord a) => Transfinite a where
- infinity :: a
- negativeInfinity :: a
- notANumber :: a
- isInfinite :: a -> Bool
- isNaN :: a -> Bool
Documentation
class (Num a, Ord a) => Transfinite a whereSource
Many numbers are not Bounded
yet, even though they can
represent arbitrarily large values, they are not necessarily
able to represent transfinite values such as infinity itself.
This class is for types which are capable of representing such
values. Notably, this class does not require the type to be
Fractional
nor Floating
since integral types could also have
representations for transfinite values.
In particular, this class extends the Ord
projection to have
a maximum value infinity
and a minimum value negativeInfinity
,
as well as an exceptional value notANumber
. All the natural
laws regarding infinity
and negativeInfinity
should pertain.
Additionally, infinity - infinity
should return notANumber
(as should 0/0
and infinity/infinity
if the type is
Fractional
). Any operations on notANumber
will also return
notANumber
, and any equality or ordering comparison on
notANumber
must return False
.
Minimum complete definition is infinity
, isInfinite
, and
isNaN
.
A transfinite value which is greater than all finite values.
Adding or subtracting any finite value is a no-op. As is
multiplying by any non-zero positive value (including
infinity
), and dividing by any positive finite value. Also
obeys the law negate infinity = negativeInfinity
with all
appropriate ramifications.
A transfinite value which is less than all finite values.
Obeys all the same laws as infinity
with the appropriate
changes for the sign difference.
notANumber :: aSource
An exceptional transfinite value for dealing with undefined
results when manipulating infinite values. Since NaN shall
return false for all ordering and equality operations, there
may be more than one machine representation of this value
.
isInfinite :: a -> BoolSource
Return true for both infinity
and negativeInfinity
,
false for all other values.
Return true only for notANumber
.