# Pastebin gEtL9QWM
multi sub postcircumfix:<{; }>(\SELF, @indices, :$exists!) {
    sub recurse-at-key(\SELF, \indices, \counter){
        my \idx = indices[counter];
        nqp::if(nqp::islt_i(counter, indices.elems),
            nqp::if(
                nqp::istype(idx, List),
                nqp::stmts(
                    my int $i = 0;
                    nqp::while(
                        nqp::islt_i($i, idx.elems),
                        nqp::if(
                            SELF.EXISTS-KEY(idx[$i++]),
                            recurse-at-key(SELF{idx[$i-1]}, indices, counter + 1)
                        )
                    ).Slip
                ),
                nqp::if(
                    SELF.EXISTS-KEY(idx),
                    recurse-at-key(SELF{idx}, indices, counter + 1),
                    False
                )
            ),
            True
        )
    }

    recurse-at-key(SELF, @indices, 0)
}