# Monok [](https://travis-ci.org/jmargenberg/monok) [](https://coveralls.io/github/jmargenberg/monok?branch=master)
#### _Monad on :ok_
Provides the infix pipe operators `~>`, `~>>`, and `<~>` for writing clean pipelines that treat `{:ok, result}`
and `{:error, reason}` tuples like functors, monads or applicatives.
Also provides the functions `fmap`, `bind` and `lift` as which are functionally identical but are less cryptic and
can be used without overriding any inifix operators which could potentially conflict with other libraries.
## Why would you ever do this?
Whilst writing overriding infix operators is generally considered bad practice I thought I'd try this out
given just how freqently `{:ok, result}` and `{:error, reason}` tuples are encountered in Elixir.
## Functor Pipelines
Allows you to write clean pipelines that transforms values inside of `{:ok, value}` tuples.
```
iex> {:ok, [1, 2, 3]}
...> ~> (&Enum.sum/1)
...> ~> (&div(&1, 2))
{:ok, 3}
```
If the input is an `{:error, reason}` tuple it is carried through the pipeline without applying any
transformations.
```
iex> {:error, :reason}
...> ~> (&Enum.sum/1)
...> ~> (&div(&1, 2))
{:error, :reason}
```
## Monad Pipelines
Allows you to write clean pipelines that transform values in `{:ok, value}` tuples with functions that also
return `{:ok, value}` tuples.
```
iex> decrement = fn
...> x when x > 0 -> {:ok, x - 1}
...> _ -> {:error, :input_too_small}
...> end
iex> {:ok, 3}
...> ~>> decrement
...> ~>> decrement
{:ok, 1}
```
If at any point in the pipeline an `{:error, reason}` tuple is returned it is carried through without
any of the transformation functions being applied.
```
iex> decrement = fn
...> x when x > 0 -> {:ok, x - 1}
...> _ -> {:error, :input_too_small}
...> end
iex>
...> {:ok, 3}
...> ~>> (fn _ -> {:error, :contrived_example} end)
...> ~>> decrement
...> ~>> decrement
{:error, :contrived_example}
```
## Mixed Pipelines
These pipe operators don't have to be used in seperate pipelines but can be used together or even with the `|>`
standard pipe operator.
```
iex> 7
...> |> (&(if &1 > 5, do: {:ok, &1}, else: {:error, :too_low})).()
...> ~> (&Integer.to_string/1)
...> ~>> (&(if &1 |> String.length() > 0, do: {:ok, &1 <> "!"}, else: {:error, :empty_string}))
{:ok, "7!"}
```
## Potential Changes
My initial hope was to implement the pipe operators as macros that would behave more similarily to `|>`.
For example `{:ok, 1} ~> (&Integer.to_string/1)` would be written as `{:ok, 1} ~> Integer.to_string()`.
Unfortunately it looks like this is infeasible using macros in elixir but I might have another try
at some point.
