This is a simple implementation of Async/Await.
Inspired by the Async/Await implementation of TypeScript.
This implementation uses generator.el included in Emacs 25 and promise.el.
For detailed tutorials on its use, see What about Async/Await? (TypeScript)
You can install from MELPA using package.el.
The package name is async-await.
See async-await-examples.el for details.
(require 'async-await)
(defun wait-async (n)
(promise-new (lambda (resolve _reject)
(run-at-time n
nil
(lambda ()
(funcall resolve n))))))
(async-defun example2 ()
(print (await (wait-async 0.5)))
(message "---")
(print (await (wait-async 1.0)))
(message "---")
(print (await (wait-async 1.5)))
(message "---")
(message "await done"))
(example2) =>
0.5
---
1.0
---
1.5
---
await done
The result of the execution is outputted from the top to the bottom
like the order written in the code. However, asynchronously!An example using `url-retrieve 'as a more complicated example.
(require 'async-await)
(require 'url-http)
(require 'xml)
(require 'dom)
(defun xml-retrieve (url)
"Return `Promise' to resolve with XML object obtained by HTTP request."
(promise-new
(lambda (resolve reject)
(url-retrieve url
(lambda (status)
;; All errors are reliably captured and rejected with appropriate values.
(if (plist-get status :error)
(funcall reject (plist-get status :error))
(condition-case ex
(with-current-buffer (current-buffer)
(if (not (url-http-parse-headers))
(funcall reject (buffer-string))
(search-forward-regexp "\n\\s-*\n" nil t)
(funcall resolve (xml-parse-region))))
(error (funcall reject ex)))))))))
(defun get-text-first-tag (xml tag)
"Returns the first text that matches TAG in XML."
(decode-coding-string (dom-text (cl-first (dom-by-tag xml tag)))
'utf-8))
(defun get-short-text-first-tag (xml tag)
"Truncate the text obtained with `get-text-first-tag'."
(concat (truncate-string-to-width (get-text-first-tag xml tag) 64)
" ..."))
(defun wait-seconds (seconds fn &rest args)
"Return `Promise' to execute the function after the specified time."
(promise-new (lambda (resolve _reject)
(run-at-time seconds
nil
(lambda ()
(funcall resolve (apply fn args)))))))
(async-defun example8 ()
"Example using `xml-retrieve'."
(condition-case reason
(let* ((wikipedia-url (concat "https://en.wikipedia.org/w/api.php"
"?format=xml&action=query&prop=extracts"
"&exintro=&explaintext=&titles="))
(xml-gnu (await (xml-retrieve (concat wikipedia-url "GNU"))))
;; Request after 2 seconds for load reduction.
(xml-emacs (await (wait-seconds 2
#'xml-retrieve
(concat wikipedia-url "Emacs")))))
(print (get-short-text-first-tag xml-gnu 'extract))
(print (get-short-text-first-tag xml-emacs 'extract)))
(error (message "error: %s" reason))))