/* 

  Leap year (Rosetta code) in Picat.

  http://rosettacode.org/wiki/Leap_year
  """
  Determine whether a given year is a leap year in the Gregorian calendar
  """


  This Picat model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/


% import util.
% import cp.


main => go.


go =>

  println(leap_years=[Y : Y in 1900..2038, leap_year(Y)]),
  
  println(leap_years=[Y : Y in 1900..2038, leap_year2(Y)]),

  println(leap_years=[Y : Y in 1900..2038, leap_year3(Y)]),


  println(leap_years=[Y : Y in 1600..1610, leap_year(Y)]),

  foreach(Y in [1600,1700,1899,1900,2000,2006,2012])
     println(Y=cond(leap_year(Y),leap_year,not_leap_year))
  end,

  nl.


leap_year(Year) => 
  (Year mod 4 == 0, Year mod 100 != 0) 
  ; 
  Year mod 400 == 0. 

% alternative approach
leap_year2(Year), Year mod 4 == 0, Year mod 100 != 0 => true.
leap_year2(Year), Year mod 400 == 0 => true.


% silly approach :-)
leap_year3(Year) => 
  ';'((Year mod 4 == 0 && Year mod 100 != 0), Year mod 400 == 0).