Class: Aurum::Builder::AugmentedGrammar

Inherits:
Object
  • Object
show all
Defined in:
lib/aurum/grammar/builder/augmented_grammar.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(syntax_rules, start_symbol) ⇒ AugmentedGrammar

Returns a new instance of AugmentedGrammar.



11
12
13
14
15
16
17
18
19
 
# File 'lib/aurum/grammar/builder/augmented_grammar.rb', line 11

def initialize syntax_rules, start_symbol
  @syntax_rules, @start_symbol = syntax_rules, start_symbol
  @start_production = Aurum::Grammar.production(StartSymbol, [start_symbol])
  @all_productions = [@start_production]
  @nonterminals = [StartSymbol, @start_symbol].to_set
  @nullables = {StartSymbol => false, @start_symbol => false}
  @first_sets = {StartSymbol => [].to_set, @start_symbol => [].to_set}
  initialize_for_used_symbols
end

Instance Attribute Details

#all_productions ⇒ Object (readonly)

Returns the value of attribute all_productions.



10
11
12
 
# File 'lib/aurum/grammar/builder/augmented_grammar.rb', line 10

def all_productions
  @all_productions
end

#start_production ⇒ Object (readonly)

Returns the value of attribute start_production.



10
11
12
 
# File 'lib/aurum/grammar/builder/augmented_grammar.rb', line 10

def start_production
  @start_production
end

Instance Method Details

#compute_first_sets ⇒ Object 



41
42
43
44
45
46
47
48
49
50
51
 
# File 'lib/aurum/grammar/builder/augmented_grammar.rb', line 41

def compute_first_sets
  fixed_point do |nonterminal|
    for production in productions(nonterminal)
      for symbol in production.symbols
        is_updated = @first_sets[symbol].inject(false) {|r, s| r |= @first_sets[nonterminal].add?(s) }
        break unless nullable?(symbol) and !is_updated
      end
    end
    is_updated
  end
end

#compute_nullables ⇒ Object 



34
35
36
37
38
39
 
# File 'lib/aurum/grammar/builder/augmented_grammar.rb', line 34

def compute_nullables
  fixed_point do |nonterminal|
    break true if nullable? nonterminal
    @nullables[nonterminal] = productions(nonterminal).any? {|prod| production_nullable?(prod)}
  end
end

#first_set(symbol) ⇒ Object 



25
26
27
 
# File 'lib/aurum/grammar/builder/augmented_grammar.rb', line 25

def first_set symbol
  @first_sets[symbol]
end

#nullable?(symbol) ⇒ Boolean

Returns:

  • (Boolean) 


21
22
23
 
# File 'lib/aurum/grammar/builder/augmented_grammar.rb', line 21

def nullable? symbol
  @nullables[symbol]
end

#productions(nonterminal = nil) ⇒ Object 



29
30
31
32
 
# File 'lib/aurum/grammar/builder/augmented_grammar.rb', line 29

def productions(nonterminal = nil)
  return [@start_production] if nonterminal == StartSymbol
  @syntax_rules.productions(nonterminal)
end