Decimal alternatives and similar packages
Based on the "Math" category.
Alternatively, view Decimal alternatives based on common mentions on social networks and blogs.

vector
An efficient implementation of Intindexed arrays (both mutable and immutable), with a powerful loop optimisation framework . 
hgeometry
HGeometry is a library for computing with geometric objects in Haskell. It defines basic geometric types and primitives, and it implements some geometric data structures and algorithms. The main two focusses are: (1) Strong type safety, and (2) implementations of geometric algorithms and data structures that have good asymptotic running time guarantees. 
dimensional
Dimensional library variant built on Data Kinds, Closed Type Families, TypeNats (GHC 7.8+). 
numhask
A haskell numeric prelude, providing a clean structure for numbers and operations that combine them. 
poly
Fast polynomial arithmetic in Haskell (dense and sparse, univariate and multivariate, usual and Laurent) 
eigen
Haskel binding for Eigen library. Eigen is a C++ template library for linear algebra: matrices, vectors, numerical solvers, and related algorithms.
InfluxDB  Power RealTime Data Analytics at Scale
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README
HaskellDecimal
Fixedprecision decimal numbers, where the precision is carried with the numbers at runtime.
The Decimal
type is mainly intended for doing financial arithmetic
where the number of decimal places may not be known at compile time
(e.g. for a program that handles both Yen and Dollars) and the
application must not drop pennies on the floor. For instance if you
have to divide $10 between three people then one of them has to get
$3.34.
The number of decimal places in a value is represented as a Word8, allowing for up to 255 decimal places. Functions preserve precision. Addition and subtraction operators return a result with the precision of the most precise argument, so 2.3 + 5.678 = 7.978. Multiplication and division use whatever precision is necessary up to 255 decimal places.
QuickCheck Specification
Data.Decimal includes a set of QuickCheck properties which act as both tests and a formal specification. To run the tests do:
cabal configure enabletests cabal build cabal test
or
stack test