/r/dailyprogrammer Challenge #202 - Easter Challenge

easter.fs

( easter.fs 2015-02-21T18.23 by fbwright )
( An implementation of the Butcher's algorithm )
: easter { year -- year month day }
  year 19 mod { a } year 100 / { b } year 100 mod { c }
  19 a * b + b 4 / - 15 + b b 8 + 25 / - 1 + 3 / - 30 mod { d }
  32 b 4 mod 2 * + c 4 / 2 * + d - c 4 mod - 7 mod { e }
  d e + 114 + d 11 * a + e 22 * + 451 / 7 * - { f }
  f 31 mod 1+ ( day ) f 31 / ( month ) year ;
: test ( -- ) cr
  2014 easter . . . cr ( Should be 2014 4 20 )
  2015 easter . . . cr ( Should be 2015 4 5 )
  2016 easter . . . cr ( Should be 2016 3 27 )
  2017 easter . . . cr ( Should be 2017 4 16 )
;