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4d47's solution

to Leap in the Perl 6 Track

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.

Resources

Remember to check out the Perl 6 documentation and resources pages for information, tips, and examples if you get stuck.

Running the tests

There is a test suite and module included with the exercise. The test suite (a file with the extension .t) will attempt to run routines from the module (a file with the extension .pm6). Add/modify routines in the module so that the tests will pass! You can view the test data by executing the command perl6 --doc *.t (* being the name of the test suite), and run the test suite for the exercise by executing the command prove . --exec=perl6 in the exercise directory. You can also add the -v flag e.g. prove . --exec=perl6 -v to display all tests, including any optional tests marked as 'TODO'.

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.

leap.t

#!/usr/bin/env perl6
use v6;
use Test;
use JSON::Fast;
use lib $?FILE.IO.dirname;
use Leap;
plan 4;

my Version:D $version = v4;

if Leap.^ver !~~ $version {
  warn "\nExercise version mismatch. Further tests may fail!"
    ~ "\nLeap is {Leap.^ver.gist}. "
    ~ "Test is {$version.gist}.\n";
}

my $c-data = from-json $=pod.pop.contents;
for $c-data<cases>.values {
  given is-leap-year .<input><year> -> $result {
    subtest .<description>, {
      plan 2;
      isa-ok $result, Bool;
      is-deeply $result, .<expected>, 'Result matches expected';
    }
  }
}

=head2 Canonical Data
=begin code
{
  "exercise": "leap",
  "version": "1.3.0",
  "cases": [
    {
      "description": "year not divisible by 4: common year",
      "property": "leapYear",
      "input": {
        "year": 2015
      },
      "expected": false
    },
    {
      "description": "year divisible by 4, not divisible by 100: leap year",
      "property": "leapYear",
      "input": {
        "year": 1996
      },
      "expected": true
    },
    {
      "description": "year divisible by 100, not divisible by 400: common year",
      "property": "leapYear",
      "input": {
        "year": 2100
      },
      "expected": false
    },
    {
      "description": "year divisible by 400: leap year",
      "property": "leapYear",
      "input": {
        "year": 2000
      },
      "expected": true
    }
  ]
}
=end code
unit class Leap;

method is_leap(Int(Cool) $year --> Bool) {
    $year %% 4 && ($year !%% 100 || $year %% 400)
}

What can you learn from this solution?

A huge amount can be learnt 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 I could read more about to develop my understanding?

Community comments

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over 2 years ago
4d47 says

Coercive type declarations