From: 7stud -- <bbxx789_05ss@...>
Date: 2011-05-12T04:28:52+09:00
Subject: Re: Scope problem (?) in implementing Design Patterns in Ruby

RichardOnRails wrote in post #998059:
>

1) Your case statement syntax doesn't work in ruby 1.9.2:

prog.rb:4: syntax error, unexpected ':', expecting keyword_then or ',' 
or ';' or '\n'

You have to use 'then' in place of a colon.

2) Next, I get this error:

prog.rb:67:in `evaluate': uninitialized constant Not::All (NameError)
  from prog.rb:74:in `<main>'

which relates to this code:

class Not < Expression
  def initialize(expression)
    @expression = expression
  end

  def evaluate(dir)
    all = All.new.evaluate(dir)
    other = @expression.evaluate(dir)
    all - other
  end
end

In ruby, constants are looked up like directories and files.  When you 
are inside the Not class (which is a module), the 'directory' you are in 
for constant lookups is the 'Not' directory.  When you write All.new, 
because the name All is not preceded by a directory name, ruby looks in 
the current 'directory' for the constant All.  The current directory is 
Not, so ruby is looking for Not::All, i.e. the 'file' All in the 
'directory' Not.  However, All is not defined inside Not, so you get an 
error.  In fact, there is not constant named All defined anywhere in 
your program.

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