anchor.diff:      declare(undefined).
   
   declare(Type) ->
  -    Id = druuid:v4(),
  -    {ok, Id} = derflow_vnode:declare(Id, Type),
  -    {ok, Id}.
  +    derflow_vnode:declare(druuid:v4(), Type).
   
   bind(Id, Value) ->
       case derflow_vnode:bind(Id, Value) of
  
positive.code:     end.
  
  bind(Id, Module, Function, Args) ->
      Value = Module:Function(Args),
      bind(Id, Value).
  
  read(Id) ->
      {ok, Value, _Next} = derflow_vnode:read(Id),
  
negative.code:     derflow_vnode:bind(Id, Value).
  
  produce(Id, Module, Function, Args) ->
      derflow_vnode:bind(Id, Module:Function(Args)).
  
  consume(Id) ->
      derflow_vnode:read(Id, undefined).
  