[QUIZ] SerializableProc (#38)

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I'm a Proc addict. I use them all over the place in my code. Because of that,
whenever I end up needing persistence and I call Marshal.dump() or YAML.dump()
on some object hierarchy, I get to watch everything explode (since Procs cannot
be serialized).

This week's Ruby Quiz is to build a Proc that can be serialized.

I'm not aware of any possible way to add serialization capabilities to Ruby's
core Proc, which rules out a complete solution. However, even if what we build
is a hack, at least one person finds it super useful.

The task then is to build SerializableProc. It should support being serialized
by Marshal, PStore, and YAML and otherwise behave as close to a Proc as
possible. Put another way, make the following code run for your creation:

require "pstore"
require "yaml"

code = # Build your SerializableProc here!

File.open("proc.marshalled", "w") { |file| Marshal.dump(code, file) }
code = File.open("proc.marshalled") { |file| Marshal.load(file) }

code.call

store = PStore.new("proc.pstore")
store.transaction do
store["proc"] = code
end
store.transaction do
code = store["proc"]
end

code.call

File.open("proc.yaml", "w") { |file| YAML.dump(code, file) }
code = File.open("proc.yaml") { |file| YAML.load(file) }

code.call