Add a CFG grammar processor

[gropax]

Add preprocessing in order to:

• [x] Parse meta symbols from original productions (*, +, ?)
• Cleanup grammar by removing:
  • [ ] duplicate rules A -> Ba | Ba
  • [x] epsilon rules A -> ε
  • [ ] unit rules A -> B
  • [x] unreachable symbols S -> a ; A -> b
  • [x] unproductive rules S -> A ; A -> Aa
  • [ ] remove cycles
• Remove left-recursion
• Generate a grammar in Chomsky Normal Form

[gropax]

Create a processor class for each process.

class Processor
  def initialize(grammar)
    @original = grammar
  end

  def process
  end
end

class UnreachableRulesProcessor < Processor
  condition -> { !unreachable_symbols.empty? }
  process :remove_unreachable_symbols

  def remove_unreachable_symbols
     #...
  end
end