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.
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.
For library documentation, follow Useful OCaml resources.
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JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp
(* leap - 1.5.1 *)
open OUnit2
open Leap
let ae exp got _test_ctxt = assert_equal exp got ~printer:string_of_bool
let tests = [
"year not divisible by 4 in common year" >::
ae false (leap_year 2015);
"year divisible by 2, not divisible by 4 in common year" >::
ae false (leap_year 1970);
"year divisible by 4, not divisible by 100 in leap year" >::
ae true (leap_year 1996);
"year divisible by 100, not divisible by 400 in common year" >::
ae false (leap_year 2100);
"year divisible by 400 in leap year" >::
ae true (leap_year 2000);
"year divisible by 200, not divisible by 400 in common year" >::
ae false (leap_year 1800);
]
let () =
run_test_tt_main ("leap tests" >::: tests)
let leap_year year =
let divisible_by_4 = year mod 4 == 0
and divisible_by_100 = year mod 100 == 0
and divisible_by_400 = year mod 400 == 0 in
match divisible_by_4 with
| false -> false
| true ->
match divisible_by_100 with
| false -> true
| true -> divisible_by_400
This is my incredibly verbose interpretation of the leap year method, using match fallthroughs. All of my let's more than likely get optimized away and the branch path is the same as less descriptive implementation.
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