even / odd classifier using proc

classifier.rb

f = proc do |p|
  Hash.new.merge(
   ->{ p.odd? }.call => 'odd',
   ->{ p.even? }.call => 'even'
  ).fetch(true)
end
=> #<Proc:0x00007ff91188af38@(irb):1>

> f[1]
=> "odd"
> f[2]
=> "even"