17.21 emacs-deferred

“Simple asynchronous functions for emacs lisp”

• GitHub Source

Basic Deferred Chain

(deferred:$
  (deferred:next
    (lambda () (message "deferred start")))
  (deferred:nextc it
    (lambda ()
      (message "chain 1")
      1))
  (deferred:nextc it
    (lambda (x)
      (message "chain 2 : %s" x)))
  (deferred:nextc it
    (lambda ()
      (read-minibuffer "Input a number: ")))
  (deferred:nextc it
    (lambda (x)
      (message "Got the number : %i" x)))
  (deferred:error it
    (lambda (err)
      (message "Wrong input : %s" err))))

• This s-exp returns immediately.
• Asynchronous tasks start subsequently.
• The macro deferred:$ chains deferred objects.
• The anaphoric variable it holds a deferred object in the previous line.
• The next deferred task receives the value that is returned by the previous deferred one.
• Inputting a wrong value, such as alphabets, this s-exp raises an error. The error is caught by the errorback function defined by deferred:error.