def visit_EnvNode(node)
      debug_visit(node)
      node.env.each_pair do |key, arg_node|
        world.env[key] = process_EnvArgumentNode(arg_node)
      end
      Yap::Shell::Execution::Result.new(status_code:0, directory:Dir.pwd, n:1, of:1)
    end
def visit_EnvNode(node)
      debug_visit(node)
      node.env.each_pair do |key, arg_node|
        world.env[key] = process_EnvArgumentNode(arg_node)
      end
      Yap::Shell::Execution::Result.new(status_code:0, directory:Dir.pwd, n:1, of:1)
    end
Represents a statement that contains nothing but environment
 variables being set, e.g.:

    yap> A=5
    yap> A=5 B=6
    yap> A=3 && B=6

 The environment variables persist from statement to statement until
 they cleared or overridden.