Class: Sequitur::SequiturGrammar

Inherits:
DynamicGrammar show all
Defined in:
lib/sequitur/sequitur_grammar.rb

Instance Attribute Summary collapse

Attributes inherited from DynamicGrammar

#productions, #root, #trace

Instance Method Summary collapse

Methods inherited from DynamicGrammar

#to_string

Constructor Details

#initialize(anEnum) ⇒ SequiturGrammar

Constructor. Build the grammar from an enumerator of tokens



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# File 'lib/sequitur/sequitur_grammar.rb', line 13

def initialize(anEnum)
  super()
  # Make start production compliant with utility rule

  2.times { root.incr_refcount }

  @digrams = {}
  @parsed = []
  anEnum.each { |a_token| add_token(a_token) }
end

Instance Attribute Details

#digrams ⇒ Object (readonly)

A hash with pairs of the form: digram key => digram



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# File 'lib/sequitur/sequitur_grammar.rb', line 7

def digrams
  @digrams
end

#parsed ⇒ Object (readonly)

The input



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# File 'lib/sequitur/sequitur_grammar.rb', line 10

def parsed
  @parsed
end

Instance Method Details

#add_token(aToken) ⇒ Object

Add the given token to the grammar.



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# File 'lib/sequitur/sequitur_grammar.rb', line 26

def add_token(aToken)
  parsed << aToken
  super
end

#check_unicity ⇒ Object

Check the invariant: Every digram appearing in a rhs must occur at most once in the grammar.



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# File 'lib/sequitur/sequitur_grammar.rb', line 33

def check_unicity()
  all_digrams = {}
  productions.each do |a_prod|
    prod_digrams = a_prod.digrams
    prod_digrams.each_with_index do |a_digram, index|
      next if index && a_digram == a_prod.digrams[index - 1]
      if all_digrams.include? a_digram.key
        msg = "Digram #{a_digram.symbols} occurs twice!"
        colliding = all_digrams[a_digram.key]
        msg << "\nOnce in production #{colliding.production.object_id}"
        msg << "\nSecond in production #{a_prod.object_id}"
        msg << "\n#{to_string}"
        fail StandardError, msg unless colliding == a_prod
      else
        all_digrams[a_digram.key] = a_digram
      end
    end
  end
end