\define date-str(date)
<$list filter="[[$date$]splitbefore[-]]" variable=x >
<$list filter="[[$date$]removeprefix<x>splitbefore[-]removesuffix[-]]" variable=m>
<$list filter="[[data-months]getindex<m>]" variable="mname">
<$list filter="[[$date$]splitbefore[-]removesuffix[-]]" variable=y>
<$list filter="[[$date$]removeprefix<x>removeprefix<m>removeprefix[-]]" variable=d>
<<mname>> <<d>>, <<y>>
</$list>
</$list>
</$list>
</$list>
</$list>
\end
The date of the event was <$macrocall $name="date-str" date={{!!mydate}}/>.
\define date-str(date)
<$list filter="[[$date$]splitbefore[-]]" variable=x >
<$list filter="[[$date$]removeprefix<x>splitbefore[-]removesuffix[-]]" variable=m>
<$list filter="[[data-months]getindex<m>]" variable="mname">
<$list filter="[[$date$]splitbefore[-]removesuffix[-]]" variable=y>
<$list filter="[[$date$]removeprefix<x>removeprefix<m>removeprefix[-]]" variable=d><<mname>> <<d>>, <<y>></$list></$list></$list></$list></$list>
\end
<$macrocall $name=date-str date={{!!modified}} >> />