`MonadEx` introduces monads into Elixir. Monads encapsulate state and control the flow of code. A monad's bind operation is similar, but more powerful, than Elixir's built-in pipelines.
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### Included Monads
- A simple container representing either something or nothing.
- A container representing success or failure.
- Lists are naturally monads, and conform to the necessary protocols.
- Keeps a log in addition to tracking a value. The log may be a string, array, or any other 'Monoid'.
- Holds a shared, environment state.
- Also holds a shared environment state in addition to tracking a value.
### Extending Monads
Monads may easily be extending by one of two ways:
1. Use the provided `Monad.Behaviour`.
1. Call `use Monad.Behaviour` first in your monad.
2. Implement `return/1`.
3. Implement `bind/2`.
2. Conform to the `Monad` protocol. Additionally, you should conform to the `Functor` and `Applicative` protocols.
### Composing Monads
Monads may be combined to make even more useful constructs. For example, you may want to use a state monad in combination with a result monad. The state monad can track a shared environment and the result monad can keep track of the success or failure state.
### Other Useful Monads
`MonadEx` does not contain the following monads, but they may be useful in some situations. These monads and others may be added later.
3. Random number generation
## Resources for Understanding Monads
* [Functors, Applicatives, and Monads in Pictures](http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html)
* [Three Useful Monads](http://adit.io/posts/2013-06-10-three-useful-monads.html)
* [Functors, Applicative Functors, and Monoids](http://learnyouahaskell.com/functors-applicative-functors-and-monoids)
* [A Fistful of Monads](http://learnyouahaskell.com/a-fistful-of-monads)
* [A Few Monads More](http://learnyouahaskell.com/for-a-few-monads-more)
* [Category Theory for Beginners](http://www.slideshare.net/kenbot/category-theory-for-beginners)
* [Functional Programming Patterns](http://www.slideshare.net/ScottWlaschin/fp-patterns-buildstufflt)
* [Haskell Docs](https://wiki.haskell.org/Monad)
Many of the problems that arise with monads is first not understanding functors,
applicatives, and monads. See the listed resources for learning more about
Another gotcha to watch out for is omitting parentheses. Omitting unnecessary
parentheses is a great feature; however, just like Elixir's built-in pipelines,
forgetting parentheses can create ambiguity and unexpected results. For example,
the following (contrived) code is ambiguous:
~>> transform flag
~>> process :all
It should instead be replaced with:
<!-- TODO: Include info about `(& &1)` -->
Code contributions are welcomed. In order to maintain the integrity of the
project, all pull requests must contain documentation and unit tests. See the
existing tests and documentation for examples. Some easy ideas to contribute is
to add more types of monads.
`MonadEx` is licensed under the MIT license, which is reproduced in its entirety here:
>Copyright (c) 2015 Robert Brown
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