anchor.diff:  plain value or an other promise.
   
   If an exception is raised inside the `do*` block, it will return the rejected
  -promise instead of reraising the exception on the stack.
  +promise instead of re-raising the exception on the stack.
   
   
   [NOTE]
   ====
  -In both platforms the promise factory function is executed synchrously and
  -making it blocking or not blocking is user responsability.
  +In both platforms the promise factory function is executed synchronously and
  +making it blocking or not blocking is user responsibility.
   ====
   
   
  
positive.code: 
  The `alet` macro behaves identical to the `let` with the exception that it always
  return a promise and allows mark async operations with `await` placeholder making it
  looks like synchronous opetation.
  
  If an error occurs at any step the entire composition will be short-circuited,
  returning exceptionally resolved promise.
  
negative.code: ;; => 4
  ----
  
  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:
  
  