1.rb

def gen_times(factor)
  return Proc.new { |n| n * factor }
end

times3 = gen_times(3)
times5 = gen_times(5)

times3.call(12)               #=> 36
times5.call(5)                #=> 25
times3.call(times5.call(4))   #=> 60

2.rb

@proc   = Proc.new { |a,b,c| puts [a,b,c].inspect }
@lambda = lambda   { |a,b,c| puts [a,b,c].inspect }

@proc.call 1,2,3
# => [1,2,3]
@lambda.call 1,2,3
# => [1,2,3]

# Proc is chilled out. Proc just ignores any more arguments than it is expecting
@proc.call 1,2,3,4,5,6,7,8
# => [1,2,3]

# Procs also pass in nil in lieu of missing arguments
@proc.call 1,2
# => [1, 2, nil]

# lambda is not so chill
@lambda.call 1,2,3,4,5,6,7,8
# => ArgumentError: wrong number of arguments (8 for 3)
@lambda.call 1,2
# => ArgumentError: wrong number of arguments (2 for 3)

3.rb

module Kernel
  def proc(&block)
    Proc.new &block
  end
end

4.rb

def proc_object
  obj = Proc.new { return 'returning from the proc' }
  obj[]
  return 'returning from the method body'
end

def lambda_object
  obj = lambda { return 'returning from the proc' }
  obj[]
  return 'returning from the method body'
end

proc_object
#=> "returning from the proc"

lambda_object
#=> "returning from the method body"