"defined %hash" is an error in perl 5.22+
Index: Datum/Parser.y
--- Datum/Parser.y.orig
+++ Datum/Parser.y
@@ -581,7 +581,7 @@ sub yy_keyword {
                 'usr2'         => $USR2,
                 'warning'      => $WARNING,
                 'yes'          => $YES
-               ) unless defined %Keyword;
+               ) unless %Keyword;
     return undef unless /^(\w+)/ && exists $Keyword{$1};
     my $word = $1;
     s/^\w+//;
