TikZ calendar: Berechnetes Datum als if-Bedingung (Ostern)

\documentclass[margin=5mm, varwidth]{standalone}
\usepackage{tikz}
 \usetikzlibrary{calendar}

\pgfmathtruncatemacro{\year}{2018}
\begin{document}

% Ostersonntag 
% https://www.tondering.dk/claus/cal/easter.php
\newcommand*{\Easter}[1][\year]{%        \Easter[year]
\pgfmathtruncatemacro{\G}{mod(#1,19)}%
\pgfmathtruncatemacro{\C}{floor(#1/100)}%
\pgfmathtruncatemacro{\H}{mod(\C-floor(\C/4)-floor((8*\C+13)/25)+19*\G+15,30)}%
\pgfmathtruncatemacro{\I}{\H-floor(\H/28)*(1-floor(29/(\H+1))*floor((21-\G)/11))}%
\pgfmathtruncatemacro{\J}{mod(#1+floor(#1/4)+\I+2-\C+floor(\C/4),7)}
\pgfmathtruncatemacro{\L}{\I-\J}%
\pgfmathtruncatemacro{\eastermonth}{3+floor((\L+40)/44)}%
\pgfmathsetmacro{\EasterMonth}{"0\eastermonth"}%   
\pgfmathtruncatemacro{\easterday}{\L+28-31*floor(\eastermonth/4)}%
\pgfmathsetmacro{\EasterDay}{\easterday < 10 ? "0\easterday" : "\easterday"}%
%
#1-\EasterMonth-\EasterDay%
}
Easterdate: \Easter, 
\year-\EasterMonth-\EasterDay

\edef\myEaster{\year-\EasterMonth-\EasterDay}

\pgfkeys{/pgf/calendar/Easter/.default = 0}
\pgfkeys{/pgf/calendar/Easter/.code ={     ? ? ? 
}}

\begin{tikzpicture}
\calendar[dates=\year-04-01 to \year-05-last, week list, 
month label above centered, month text=\%mt \%y-
]
if ( 
%    Easter=-3, % Maundy Thursday
%        Easter=-2, % Good Friday
%        Easter,    % Easter Sunday
%        Easter=1,  % Easter Monday
%        Easter=39, % Feast of the Ascension
%        Easter=49, % Pentecost
%        Easter=50 % Whit Monday
)[red]
%if (equals=2018-4-1) [red]; % geht
%if (equals=\year-\EasterMonth-\EasterDay) [red] % geht
if (equals=\myEaster) [red]  % geht nicht.
;
\end{tikzpicture}

\end{document}