anchor.diff:  ;; => 4
   ----
   
  -It there also `mapcat` function that allows remove one neesting level of promises,
  +It there also `mapcat` function that allows remove one nesting level of promises,
   and is pretty useful if the function that you want to apply to promise also return a
   promise instance instead of value:
   
  
positive.code: This is a list of possible states of one promise:
  
  - `resolved`: means that the promise contains a value.
  - `rejected`: means thet the promise contains an error.
  - `pending`: means that the promise does not have value.
  
  The promise can be considered *done* when is resolved or rejected.
  
negative.code: plain value or an other promise.
  
  If an exception is raised inside the `do*` block, it will return the rejected
  promise instead of re-raising the exception on the stack.
  
  
  [NOTE]
  ====
  In both platforms the promise factory function is executed synchronously and
  making it blocking or not blocking is user responsibility.
  ====
  
  
  