DecimalEnv

This library provides two macros to be able to use Decimals with regular Elixir operators i.e.

iex(1)> import DecimalEnv
iex(2)> decimal do
...(2)>   21.0 + "21.0"
...(2)> end
#Decimal<42.0>

It is possible to provide a decimal context as argument for the macro i.e

iex(1)> import DecimalEnv
iex(2)> decimal [precision: 2] do
...(2)>   1 / 3
...(2)> end
#Decimal<0.33>

For more information about context check Decimal.Context struct in Decimal repository.

Not all the Elixir statements are valid. The purpose of these macros is to make it easier to write formulas involving Decimal type, so writing Elixir code inside the decimal block is discouraged i.e.

iex(1)> import DecimalEnv
iex(2)> Enum.reduce([10.99, 10.01, 20.99, 0.01], 0.00,
...(2)>   fn x, acc ->
...(2)>     decimal do: x + acc
...(2)>   end)
#Decimal<42.00>

The previous example calculates the sum of a list of Floats, but returns the result as a Decimal type. The code is more clear than its equivalent without the macro:

iex(1)> Enum.reduce([10.99, 10.01, 20.99, 0.01], Decimal.new(0.00),
...(2)>   fn x, %Decimal{} = acc ->
...(2)>     Decimal.add(Decimal.new(x), acc)
...(2)>   end)
#Decimal<42.00>

The only statement offered is if statement i.e:

iex(1)> import DecimalEnv
iex(1)> a = 42.0
iex(3)> decimal do
...(3)>   if a > 10, do: a, else: 10
...(3)> end
#Decimal<42.0>

The guard in the if statement should be a decimal comparison.

It is posible to assign variables inside the block, but pattern matching is not available i.e:

iex(1)> import DecimalEnv
iex(2)> decimal [precision: 2] do
...(2)>   a = div(42.1, 2.0)
...(2)>   a * 2
...(2)> end
#Decimal<42>

Constant values inside the decimal block are precalculated at compile time.

To avoid calculating the Decimal value every time a variable external to the block is mentioned inside the block, use the :bind option:

iex> import DecimalEnv
iex> a = 3
iex> x = 4
iex> decimal bind: [a: a] do
...>   a * (x + 1 + a * a)
...> end
#Decimal<42>

In the previous example, the variable a is converted to Decimal only one time instead of three times. The variable x only appears one time, so there is no need to add it to the bind Keyword list.

Additionally you can change the name of the external variable by changing the name of the key associated with it i.e:

iex> import DecimalEnv
iex> a = 3
iex> x = 4
iex> decimal bind: [b: a] do
...>   b * (x + 1 + b * b)
...> end
#Decimal<42>

In the previous example, the external variable a is renamed to b inside the decimal block.

Installation

Add it to your mix.exs

def deps do
  [{:decimal_env, "~> 0.2"}]
end

Author

Alexander de Sousa.

License

DecimalEnv is released under the MIT License. See the LICENSE file for further details.