This example demonstrates an interesting technique for injecting dependencies
using procs or otherwise performing side effects using procs. In the present
case we implement a very simple side-effects system that takes effect
handlers as procs. The log module exports a proc as a default value.
The proc, when run, returns the module, allowing access to its methods and
constants. In essence, importing the log module returns a closure that returns
the module.
For more information on using side-effects or algebraic effects in Ruby, see the Affect gem.