>>>>> "M" == Mauricio =?iso-8859-1?Q?Fern=E1ndez?= <Mauricio> writes:

M> irb(main):005:0> p(*(xs.select { |x| x < 0 })|nil)

 You have written this

                      *(xs.select { |x| x < 0 } | nil)

 #select return an Array and ruby is trying

pigeon% ruby -e '[1,2]|nil'
-e:1:in `|': failed to convert nil into Array (TypeError)
        from -e:1
pigeon% 


Guy Decoux