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to Leap in the PureScript Track

Published at Oct 07 2019 · 0 comments
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.

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.

Source

JavaRanch Cattle Drive, exercise 3 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.

Main.purs

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 Data.Boolean
import Data.Eq((==))
import Data.EuclideanRing(mod)

isLeapYear :: Int -> Boolean
isLeapYear year
    | year `dividesBy` 400 = true
    | year `dividesBy` 100 = false
    | year `dividesBy` 4 = true
    | otherwise = false

dividesBy :: Int -> Int -> Boolean
dividesBy m n = (m `mod` n == 0)

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