Class: RLTK::Parser::State

Inherits:
Object
  • Object
show all
Defined in:
lib/rltk/parser.rb

Overview

The State class is used to represent sets of items and actions to be used during parsing.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(tokens, items = []) ⇒ State

Instantiate a new State object.

Parameters:

  • tokens (Array<Symbol>) —

    Tokens that represent this state

  • items (Array<CFG::Item>) (defaults to: []) —

    Items that make up this state



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# File 'lib/rltk/parser.rb', line 1444

def initialize(tokens, items = [])
	@id      = nil
	@items   = items
	@actions = tokens.inject(Hash.new) { |h, t| h[t] = Array.new; h }
end

Instance Attribute Details

#actions ⇒ Hash{Symbol => Array<Action>} (readonly)

Returns Maps lookahead symbols to actions.

Returns:

  • (Hash{Symbol => Array<Action>}) —

    Maps lookahead symbols to actions



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# File 'lib/rltk/parser.rb', line 1438

def actions
  @actions
end

#id ⇒ Integer

Returns State’s ID.

Returns:

  • (Integer) —

    State’s ID.



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# File 'lib/rltk/parser.rb', line 1432

def id
  @id
end

#items ⇒ Array<CFG::Item> (readonly)

Returns Item objects that comprise this state.

Returns:

  • (Array<CFG::Item>) —

    Item objects that comprise this state



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# File 'lib/rltk/parser.rb', line 1435

def items
  @items
end

Instance Method Details

#==(other) ⇒ Boolean

Compare one State to another. Two States are equal if they have the same items or, if the items have been cleaned, if the States have the same ID.

Parameters:

  • other (State) —

    Another State to compare to

Returns:

  • (Boolean) 


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# File 'lib/rltk/parser.rb', line 1457

def ==(other)
	if self.items and other.items then self.items == other.items else self.id == other.id end
end

#add_reduction(production) ⇒ void

This method returns an undefined value.

Add a Reduce action to the state.

Parameters:

  • production (Production) —

    Production used to perform the reduction



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# File 'lib/rltk/parser.rb', line 1466

def add_reduction(production)
	action = Reduce.new(production)
	
	# Reduce actions are not allowed for the ERROR terminal.
	@actions.each { |k, v| if CFG::is_terminal?(k) and k != :ERROR then v << action end }
end

#append(item) ⇒ Object Also known as: <<

Parameters:

  • item (CFG::Item) —

    Item to add to this state.



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# File 'lib/rltk/parser.rb', line 1474

def append(item)
	if item.is_a?(CFG::Item) and not @items.include?(item) then @items << item end
end

#clean ⇒ void

This method returns an undefined value.

Clean this State by removing the list of CFG::Item objects.



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# File 'lib/rltk/parser.rb', line 1482

def clean
	@items = nil
end

#close(productions) ⇒ vod

Close this state using productions.

Parameters:

  • productions (Array<CFG::Production>) —

    Productions used to close this state.

Returns:

  • (vod) 


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# File 'lib/rltk/parser.rb', line 1491

def close(productions)
	self.each do |item|
		if (next_symbol = item.next_symbol) and CFG::is_nonterminal?(next_symbol)
			productions[next_symbol].each { |p| self << p.to_item }
		end
	end
end

#conflict_on?(sym) ⇒ :SR, ...

Checks to see if there is a conflict in this state, given a input of sym. Returns :SR if a shift/reduce conflict is detected and :RR if a reduce/reduce conflict is detected. If no conflict is detected nil is returned.

Parameters:

  • sym (Symbol) —

    Symbol to check for conflicts on.

Returns:

  • (:SR, :RR, nil) 


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# File 'lib/rltk/parser.rb', line 1507

def conflict_on?(sym)
	
	reductions	= 0
	shifts		= 0
	
	@actions[sym].each do |action|
		if action.is_a?(Reduce)
			reductions += 1
			
		elsif action.is_a?(Shift)
			shifts += 1
			
		end
	end
	
	if shifts == 1 and reductions > 0
		:SR
	elsif reductions > 1
		:RR
	else
		nil
	end
end

#each ⇒ void

This method returns an undefined value.

Iterate over the state’s items.



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# File 'lib/rltk/parser.rb', line 1534

def each
	current_item = 0
	while current_item < @items.count
		yield @items.at(current_item)
		current_item += 1
	end
end

#on(symbol, action) ⇒ void

This method returns an undefined value.

Specify an Action to perform when the input token is symbol.

Parameters:

  • symbol (Symbol) —

    Symbol to add action for.

  • action (Action) —

    Action for symbol.



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# File 'lib/rltk/parser.rb', line 1548

def on(symbol, action)
	if @actions.key?(symbol)
		@actions[symbol] << action
	else
		raise ParserConstructionException, "Attempting to set action for token (#{symbol}) not seen in grammar definition."
	end
end

#on?(symbol) ⇒ Array<Action>

Returns that actions that should be taken when the input token is symbol.

Parameters:

  • symbol (Symbol) —

    Symbol we want the actions for.

Returns:

  • (Array<Action>) —

    Actions that should be taken.



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# File 'lib/rltk/parser.rb', line 1562

def on?(symbol)
	@actions[symbol].clone
end