gistfile1.rb

require 'pattern-match'
require 'set'

module PatternMatch
  class PatternSetDeconstructor < PatternDeconstructor
    def initialize(klass, *subpatterns)
      super(*subpatterns)
      @klass = klass
    end

    def match(vals)
      super do |val|
        next false unless val.kind_of?(@klass)
        members = val.to_a
        next false unless @subpatterns.length <= members.length
        members.permutation(@subpatterns.length).find do |perm|
          perm.zip(@subpatterns).all? {|i, pat| pat.match([i]) }
        end
      end
    end
  end
end

def Set.pattern_matcher(*subpatterns)
  PatternMatch::PatternSetDeconstructor.new(self, *subpatterns)
end

match(Set[3, 1, 4, 6]) do
  with(Set.(a, b), guard { a + 5 == b }) do
    p [a, b]
  end
end