Procs vs Lambdas

gistfile1.rb

# You can return from a lambda, and it will behave as expected.

write_two_words = lambda { |x, y| return "#{x} #{y}" }
puts write_two_words.call("hi", "there")        # => hi there

def foo
  # If you *explicitly* return from a Proc, you will actually return from the caller. 
  # Note that if you omit the "return" keyword, it behaves just like a lambda.
  write_two_words = Proc.new { |x, y| return "#{x} #{y}" }
  puts write_two_words.call("hi", "there")
  puts "This never gets written, the Proc made foo return"
end
foo

# A lambda checks the number of arguments
write_two_words = lambda { |x, y| "#{x} #{y}" }
write_two_words.call("hello")  # ArgumentError: wrong number of arguments (1 for 2)

# A proc does not check the number of arguments
write_two_words = Proc.new { |x, y| "#{x} #{y}" }
write_two_words.call("hello")  # => "hello "