anchor.diff:  
   -behavior('clojerl.IHash').
   -behavior('clojerl.IEquiv').
  +-behavior('clojerl.IStringable').
   
  --export([ ?CONSTRUCTOR/1
  +-export([ ?CONSTRUCTOR/0
  +        , ?CONSTRUCTOR/1
           , year/1
           , month/1
           , day/1
  
positive.code: -type type() :: #{ ?TYPE => ?M
                   , date  => calendar:datetime()
                   }.
  
  -spec ?CONSTRUCTOR(calendar:datetime()) -> type().
  ?CONSTRUCTOR(Timestamp) when is_integer(Timestamp), -?EPOCH =< Timestamp ->
  
negative.code: 
  -export([hash/1]).
  -export([equiv/2]).
  -export([str/1]).
  
  %% EPOCH = calendar:datetime_to_gregorian_seconds({{1970, 1, 1}, {0, 0, 0}}).
  -define(EPOCH, 62167219200).
  