Contents

# File: digram.rb

module Sequitur # Module for classes implementing the Sequitur algorithm

# In linguistics, a digram is a sequence of two letters.
# In Sequitur, a digram is a sequence of two consecutive symbols that
# appear in a production rule. Each symbol in a digram 
# can be a terminal or not.
class Digram
  # The sequence of two consecutive grammar symbols.
  #   The two symbols should respond to the :hash message.
  attr_reader(:symbols)
  
  # An unique hash key of the digram
  attr_reader(:key)
  
  # The production in which the digram occurs
  attr_reader(:production)
  
  # Constructor.
  # A digram represents a sequence of two symbols 
  # (that appears in a rhs of a production).
  # Terminal symbols must respond to the :hash message.
  # @param symbol1 [StringOrSymbol] First element of the digram
  # @param symbol2 [StringOrSymbol] Second element of the digram
  # @param aProduction [Production] Production in which the RHS 
  #   the sequence symbol1 symbol2 appears.
  def initialize(symbol1, symbol2, aProduction)
    @symbols = [symbol1, symbol2]
    @key = "#{symbol1.hash.to_s(16)}:#{symbol2.hash.to_s(16)}" 
    @production = aProduction
  end
  
  # Equality testing.
  #   true iff keys of both digrams are equal, false otherwise
  # @param other [Digram] another to compare with
  # @return [true/false]
  def ==(other)
    return key == other.key
  end
  
  # Does the digram consists of twice the same symbols?
  # @return [true/false] true when symbols.first == symbols.last
  def repeating?()
    return symbols[0] == symbols[1]
  end
  
end # class

end # module

# End of file

Version data entries

3 entries across 3 versions & 1 rubygems

Version	Path
sequitur-0.1.09	lib/sequitur/digram.rb
sequitur-0.1.07	lib/sequitur/digram.rb
sequitur-0.1.05	lib/sequitur/digram.rb