Source code in the quackery programming language

  [ over 3 < if [ 1 - ]
    dup 4 / over +
    over 100 / -
    swap 400 / +
    swap 1 - 
    [ table 
      0 3 2 5 0 3
      5 1 4 6 2 4 ]
    + + 7 mod ]                     is dayofweek  ( day month year --> weekday )

  [ dup 400 mod 0 = iff
      [ drop true ]  done
    dup 100 mod 0 = iff
      [ drop false ] done
    4 mod 0 = ]                     is leap       (           year --> b       )

  [ swap 1 -
    [ table
      31 [ dup leap 28 + ]
      31 30 31 30 31 31 30
      31 30 31 ]
    do nip ]                        is monthdays  (     month year --> n       )

  [ number$
    2 times
      [ char - join
        over 10 < if 
          [ char 0 join ]
        swap number$ join ] 
      echo$ ]                       is echoymd    ( day month year -->         )

  [ dip
      [ 2dup monthdays
        dup temp put
        unrot dayofweek ]
    - dup 0 < if [ 7 + ]
    temp take swap - ]              is lastwkday  ( month year wkd --> n       )

  [ temp put 
    12 times
      [ i^ 1+ over
        2dup temp share lastwkday 
        unrot echoymd cr ] 
    drop temp release ]            is lastwkdays  (       year wkd -->        )

  [ 0 lastwkdays ]                 is lastsundays (           year -->        )

  2013 lastsundays