Class: Aurum::Parser

Inherits:
Object
  • Object
show all
Defined in:
lib/aurum/engine.rb

Defined Under Namespace

Classes: SemanticActionContext, SemanticAttributes

Instance Method Summary collapse

Constructor Details

#initialize(productions, parsing_table) ⇒ Parser

Returns a new instance of Parser.



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# File 'lib/aurum/engine.rb', line 99

def initialize productions, parsing_table
	@productions, @parsing_table = productions, parsing_table
end

Instance Method Details

#parse(lexer) ⇒ Object 



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# File 'lib/aurum/engine.rb', line 103

def parse lexer
	lookahead, state_stack, symbol_stack, value_stack = lexer.next_symbol, [0], [], []
	lookahead_shift = 0
	while (true)
		state = @parsing_table[state_stack.last]
		action = state[lookahead]
		if action.kind_of? ShiftAction
			state_stack.push action.state
			symbol_stack.push lookahead unless action.is_lookahead_shift
			action.is_lookahead_shift ? lookahead_shift += 1 : lookahead = lexer.next_symbol  
		elsif action.kind_of? ReduceAction
			handle = @productions[action.handle]
			lookahead_shift.times { state_stack.pop }					
			lookahead_shift = 0
			if action.is_read_reduce
				state_stack.push state
				symbol_stack.push lookahead
				lookahead = lexer.next_symbol
			end
			state_stack.slice! -handle.symbols.length..-1
			symbols = symbol_stack.slice! -handle.symbols.length..-1					
			handle.nonterminal == Aurum::START and return value_stack.pop
			if handle.action
				context = {handle.nonterminal.name => [SemanticAttributes.new]}
				handle.symbols.reverse.each_with_index do |symbol, index|
					context[symbol.name] = [] unless context.has_key? symbol.name
					context[symbol.name] << (symbol.is_terminal ? symbols[-index-1] : value_stack.pop)
				end
				SemanticActionContext.new(context).instance_eval &handle.action
				value_stack.push context[handle.nonterminal.name][0] if context[handle.nonterminal.name]
			end
			goto = @parsing_table[state_stack.last][handle.nonterminal]
			if goto.kind_of? ShiftAction
				state_stack.push goto.state
				symbol_stack.push nil
			else
				lexer.pushback lookahead
				lookahead = handle.nonterminal
			end
		else
			error_recover
		end
	end
end