module Ast
    
  class OperatorExpression < Expression
    attr_reader  :operator, :left, :right

    def initialize operator, left, right
      @operator, @left, @right = operator, left, right
    end
    def attributes
      [:operator, :left, :right]
    end
    def inspect
      self.class.name + ".new(" + operator.inspect + ", " +  left.inspect + "," + right.inspect + ")"  
    end
    def to_s
      "#{left} #{operator} #{right}"
    end
    def compile context , into
      puts "compile operator #{to_s}"
      r_val = right.compile(context , into)
      if operator == "="    # assignment, value based
        raise "Can only assign variables, not #{left}" unless left.is_a?(NameExpression) 
        l_val = context.locals[left.name]
        if( l_val ) #variable existed, move data there
          l_val = l_val.move( into , r_val)
        else
          if r_val.is_a? Vm::IntegerConstant
            next_register = context.function.next_register
            l_val = Vm::Integer.new(next_register).load( into , r_val )
          else
            l_val = r_val
          end
        end
        context.locals[left.name] = l_val
        return l_val
      end

      l_val = left.compile(context , into)

      case operator
      when ">"
        code = l_val.less_or_equal into , r_val
      when "+"
        code = l_val.plus into , r_val
      when "-"
        code = l_val.minus into , r_val
      else
        raise "unimplemented operator #{operator} #{self}"
      end
    end
  end
end