# OK

**Elegant error handling in elixir pipelines. See [Handling Errors in Elixir](http://insights.workshop14.io/2015/10/18/handling-errors-in-elixir-no-one-say-monad.html) for a more detailed explanation**

[Documentation for OK is available on hexdoc](https://hexdocs.pm/ok)

## Installation

[Available in Hex](https://hex.pm/packages/ok), the package can be installed as:

  1. Add ok to your list of dependencies in `mix.exs`:

        def deps do
          [{:ok, "~> 1.0.0"}]
        end

## Usage

The erlang convention for functions that can fail is to return a result tuple.
A result tuple is a two-tuple tagged either as a success(`:ok`) or a failure(`:error`).

The OK module works with result tuples by treating them as a result monad.

```elixir
{:ok, value} | {:error, reason}
```

### '~>>' Macro

This macro allows pipelining result tuples through a pipeline of functions.
The `~>>` macro is the is equivalent to bind/flat_map in other languages.

```elixir
import OK, only: :macros

def get_employee_data(file, name) do
  {:ok, file}
  ~>> File.read
  ~>> Poison.decode
  ~>> Dict.fetch(name)
end

def handle_user_data({:ok, data}), do: IO.puts("Contact at #{data["email"]}")
def handle_user_data({:error, :enoent}), do: IO.puts("File not found")
def handle_user_data({:error, {:invalid, _}}), do: IO.puts("Invalid JSON")
def handle_user_data({:error, :key_not_found}), do: IO.puts("Could not find employee")

get_employee_data("my_company/employees.json")
|> handle_user_data
```

### Railway programming

`OK` can be used for railway programming.
An explanation of this is available in this [blog](http://www.zohaib.me/railway-programming-pattern-in-elixir/)