Published at Sep 19 2019
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Instructions

Test suite

Solution

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

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

```
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.

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.

JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp

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

```
module Test.Main where
import Prelude
import Effect (Effect)
import Test.Unit (TestSuite, suite, test)
import Test.Unit.Main (runTest)
import Test.Unit.Assert as Assert
import Leap as Leap
main :: Effect Unit
main = runTest suites
suites :: TestSuite
suites = do
suite "Leap.isLeapYear" do
test "leap year" do
Assert.equal true $ Leap.isLeapYear 1996
test "non-leap year" do
Assert.equal false $ Leap.isLeapYear 1997
test "non-leap even year" do
Assert.equal false $ Leap.isLeapYear 1998
test "century" do
Assert.equal false $ Leap.isLeapYear 1900
test "second century" do
Assert.equal false $ Leap.isLeapYear 1800
test "fourth century" do
Assert.equal true $ Leap.isLeapYear 2400
test "y2k" do
Assert.equal true $ Leap.isLeapYear 2000
```

```
module Leap where
import Prelude
isLeapYear :: Int -> Boolean
isLeapYear n = fourHundred || (four && (not hundred))
where
fourHundred = n `mod` 400 == 0
hundred = n `mod` 100 == 0
four = n `mod` 4 == 0
```

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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