Class: Grammar

Inherits:
Object
  • Object
show all
Defined in:
lib/cofgratx/cfg/grammar.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Grammar

Returns a new instance of Grammar.



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# File 'lib/cofgratx/cfg/grammar.rb', line 4

def initialize
  @rules = { }
end

Instance Attribute Details

#rules ⇒ Object (readonly)

Returns the value of attribute rules.



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# File 'lib/cofgratx/cfg/grammar.rb', line 2

def rules
  @rules
end

Instance Method Details

#add_rules(non_terminal_symbol, *rules) ⇒ Object 



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# File 'lib/cofgratx/cfg/grammar.rb', line 8

def add_rules non_terminal_symbol, *rules
  @rules[non_terminal_symbol.to_sym] ||= NonTerminal.new
  good_rules = []

  rules.each do |rule, translation|
    0.upto(rule.size) do |index|
      if rule[index].class == Symbol
        rule[index] = (@rules[rule[index]] ||= NonTerminal.new)
      end
    end
    new_rule = Rule.new( rule, translation )
    if new_rule.valid_translation?
      good_rules << Rule.new( rule, translation )
    else
      raise GrammarError.new(new_rule.translation_error_message)
    end
  end

  @rules[non_terminal_symbol.to_sym].add_rules *good_rules
end

#clear_rule(non_terminal_symbol) ⇒ Object 



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# File 'lib/cofgratx/cfg/grammar.rb', line 29

def clear_rule non_terminal_symbol
  @rules[non_terminal_symbol.to_sym] = NonTerminal.new
end

#match?(string, starting_non_terminal) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/cofgratx/cfg/grammar.rb', line 33

def match? string, starting_non_terminal
  #the grammar only matches if the string has no remainder
  raise "Unknown initial non terminal: '#{starting_non_terminal}'" unless @rules[starting_non_terminal.to_sym]
  candidate_matches = @rules[starting_non_terminal.to_sym].extract(string)
  candidate_matches.select{|m| m[1] == "" and m[0] != nil}.size > 0
end

#translate(string, starting_non_terminal) ⇒ Object 



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# File 'lib/cofgratx/cfg/grammar.rb', line 40

def translate string, starting_non_terminal
  raise "Unknown initial non terminal: '#{starting_non_terminal}'" unless @rules[starting_non_terminal.to_sym]
  candidate_matches = @rules[starting_non_terminal.to_sym].translate(string)
  candidate_matches.select{|m| m[1] == "" and m[0] != nil}
end