# Leap

Given a year, report if it is a leap year.

The tricky thing here is that a leap year in the Gregorian calendar occurs:

```plain
on every year that is evenly divisible by 4
  except every year that is evenly divisible by 100
    unless the year is also evenly divisible by 400
```

For example, 1997 is not a leap year, but 1996 is.  1900 is not a leap
year, but 2000 is.

If your language provides a method in the standard library that does
this look-up, pretend it doesn't exist and implement it yourself.

## Notes

Though our exercise adopts some very simple rules, there is more to
learn!

For a delightful, four minute explanation of the whole leap year
phenomenon, go watch [this youtube video][video].

[video]: http://www.youtube.com/watch?v=xX96xng7sAE

## Running tests

In order to run the tests, issue the following command from the exercise
directory:

For running the tests provided, `rebar3` is used as it is the official build and
dependency management tool for erlang now. Please refer to [the tracks installation
instructions](http://exercism.io/languages/erlang/installation) on how to do that.

In order to run the tests, you can issue the following command from the exercise
directory.

```bash
$ rebar3 eunit
```

### Test versioning

Each problem defines a macro `TEST_VERSION` in the test file and
verifies that the solution defines and exports a function `test_version`
returning that same value.

To make tests pass, add the following to your solution:

```erlang
-export([test_version/0]).

test_version() ->
  1.
```

The benefit of this is that reviewers can see against which test version
an iteration was written if, for example, a previously posted solution
does not solve the current problem or passes current tests.

## Questions?

For detailed information about the Erlang track, please refer to the
[help page](http://exercism.io/languages/erlang) on the Exercism site.
This covers the basic information on setting up the development
environment expected by the exercises.

## Source

JavaRanch Cattle Drive, exercise 3 [http://www.javaranch.com/leap.jsp](http://www.javaranch.com/leap.jsp)

## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.