select lens

gistfile1.txt

attribute :subject,  [Lenses.get_predicate(RDF::DC11.subject), Lenses.literals_to_strings, Lenses.select(only_foos)]
attribute :subject2, [Lenses.get_predicate(RDF::DC11.subject), Lenses.literals_to_strings, Lenses.select(only_bars)]

def select(test)
  Lens[
    get: lambda do |source_values|
      raise unless source_values.is_a?(Set)
      source_values.select{|v| test(v)}
    end,
    put: lambda do |source_values, new_values|
      raise unless source_values.is_a?(Set)
      source_values.reject{|v| test(v)} + new_values
    end
  ]
end