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