# DecimalEnv
[](https://travis-ci.org/gmtprime/decimal_env) [](https://hex.pm/packages/decimal_env) [](https://hex.pm/packages/decimal_env) [](https://beta.hexfaktor.org/github/gmtprime/decimal_env) [](http://inch-ci.org/github/gmtprime/decimal_env)
This library provides two macros to be able to use `Decimal`s with regular
Elixir operators i.e.
```elixir
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
```elixir
iex(1)> import DecimalEnv
iex(2)> decimal context: [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.
```elixir
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 `Float`s, but returns
the result as a `Decimal` type. The code is more clear than its equivalent
without the macro:
```elixir
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:
```elixir
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:
```elixir
iex(1)> import DecimalEnv
iex(2)> decimal 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:
```elixir
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:
```elixir
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`
```elixir
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.
