By definition a Functor is simply a first class method, but these are common in the form of Method and Proc. So for Ruby a Functor is a more specialized as a Higher-order function or Metafunction. Essentally, a Functor can vary its behavior accorrding to the operation applied to it. 

  f = Functor.new { |op, x| x.send(op, x) }
  f + 1  #=> 2
  f + 2  #=> 4
  f + 3  #=> 6
  f * 1  #=> 1
  f * 2  #=> 4
  f * 3  #=> 9
Methods
Public Class methods
new(&function)

[ show source ]

# File lib/core/facets/functor.rb, line 63
  def initialize(&function)
    @function = function
  end
Public Instance methods
method_missing(op, *args, &blk)

Any action against the functor is processesd by the function.

[ show source ]

# File lib/core/facets/functor.rb, line 72
  def method_missing(op, *args, &blk)
    @function.call(op, *args, &blk)
  end
to_proc()

[ show source ]

# File lib/core/facets/functor.rb, line 67
  def to_proc
    @function
  end