instead of hardcoding the mkdir command, which isn't known on all systems, use the $(MKPATH) from ExtUtils::MakeMaker's Makefile, which calls mkpath. As a side benefit, mkpath automatically generates necessary parents as well, so you don't need the --parents argument.

sub MY::postamble {
<<'EOT'
blib/lib/OPTiMaDe/Filter/%.pm: %.yp
        $(MKPATH) (@D)
        yapp -v -m OPTiMaDe::Filter::Parser -o $@ $<
EOT
}
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