From: Alex Chaffee <alex@...>
Date: 2013-04-13T08:42:00+09:00
Subject: Re: Trying to understand blocks

http://codelikethis.com/lessons/ruby_blocks/blocks has slides and a
video lecture that might help you out.

Basically, yield is calling an anonymous, invisible function pointer.
It's sort of like

def foo(p)
  p.call("Jim")
end

def bar
   baz = lambda { |n| n.upcase }
   foo(baz)
end

The & turns a proc into a block and back again.

It's one of the oddest parts of Ruby and it's almost (but not
entirely) syntactic sugar so you can use "do" blocks to make your code
look cool. (Not a dis: I think it's great, but it is confusing.)

 - A