Help fill in the missing two missing functions TODO! https://www.partiallyapplied.com/blog/church/

church.rb

module Church
  module_function

  def encode number
    -> function do
      -> value do
        number.times.reduce value do |accumulator|
          function.call accumulator
        end
      end
    end
  end

  def decode function
    function.(-> n { n + 1 }).(0)
  end
end

include Church

decode encode 0
#=> 0

decode encode 42
#=> 42

incrementer = -> n { n + 1 }
encode(3).(incrementer).(1)
#=> 4

increment = -> function { -> value { "???" } } # TODO
decode increment.(encode(3))
#=> 4

oneself = -> function { -> value { function.(value) } }
decode oneself.(encode(3))
#=> 3

square = -> function { -> value { function.(function.(value)) } }
decode square.(encode(3))
#=> 9

first = -> x { x[0] }
encode(1).(first).(%i[foo bar])
#=> :foo

encode(2).(first).(%i[foo bar])
#=> "f"

multiply = -> f1, f2 { -> value { f1.(f2.(value)) } }
decode multiply.(encode(3), encode(4))
#=> 12

add = -> f1, f2 { -> value { "???" } } # TODO
decode add.(encode(3), encode(4))
#=> 7