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to Leap in the PureScript Track

Published at May 20 2020 · 0 comments
Test suite

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

Submitting Incomplete Solutions

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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

import Effect (Effect)
import Effect.Console (logShow)

type Year = Int

-- | Checks divisible by 4 but not by 100 condition 
isLeapYear :: Year -> Boolean
isLeapYear year = 
  mod year 4 == 0 && mod year 100 /= 0 || mod year 4 == 0 && isException year
        -- | Checks if year is an exception to first rule
        isException :: Year -> Boolean
        isException x = eq (mod x 100) (mod x 400)

main :: Effect Unit
main = do
  logShow $ isLeapYear(1996)
  logShow $ isLeapYear(2000)
  logShow $ isLeapYear(2100)
  logShow $ isLeapYear(1997)

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