Partially applied instance methods in Ruby

example.rb

class User
  def initialize(name)
    @name = name
  end

  def greet(greeting, info)
    "#{greeting}, #{@name}! FYI, #{info}."
  end
end

class PartiallyAppliedMethod
  def initialize(name, arguments)
    @name = name
    @arguments = arguments
  end

  def to_proc
    lambda { |instance| instance.public_send(@name, *@arguments) }
  end

  def call(*arguments)
    to_proc.call(*arguments)
  end

  def |(argument)
    PartiallyAppliedMethod.new(@name, @arguments + [argument])
  end
end

class Symbol
  def |(argument)
    PartiallyAppliedMethod.new(self, [argument])
  end
end

users = [User.new("Dave"), User.new("Sally"), User.new("Dan")]

puts users.map(&:greet | "Hello" | "it's Wednesday")