Elixir provides MapSet module to handle sets—lists of unique elements (shall I say “arrays” instead of lists here?). They are very handy under many circumstances. During my work on the minor update in Exvalibur, I changed the list I mistakenly used before to be MapSet. And there was a pitfall. Everywhere is the code I used different function clauses for empty list. But MapSet is a module. That said, this code
