Data.Scientific
provides a space efficient and arbitrary precision
scientific number type.
Scientific
numbers are represented using
scientific notation. It uses
a coefficient c :: Integer
and a base10 exponent e :: Int
(do note that
since we're using an Int
to represent the exponent these numbers aren't truly
arbitrary precision. I intend to change this to Integer in the future!). A
scientific number corresponds to the Fractional
number:
fromInteger c * 10 ^^ e
.
The main application of Scientific
is to be used as the target of parsing
arbitrary precision numbers coming from an untrusted source. The advantages over
using Rational
for this are that:

A
Scientific
is more efficient to construct. Rational numbers need to be constructed using%
which has to compute thegcd
of thenumerator
anddenominator
. 
Scientific
is safe against numbers with huge exponents. For example:1e1000000000 :: Rational
will fill up all space and crash your program. Scientific works as expected:
> read "1e1000000000" :: Scientific
1.0e1000000000
 Also, the space usage of converting scientific numbers with huge exponents to
Integral's (like:
Int
) or RealFloats (like:Double
orFloat
) will always be bounded by the target type.