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Re: ELisp futures and continuations/coroutines

From: Thien-Thi Nguyen
Subject: Re: ELisp futures and continuations/coroutines
Date: Sun, 22 May 2011 15:17:32 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux)

() Ted Zlatanov <address@hidden>
() Fri, 20 May 2011 10:29:39 -0500

   [knowledge of time is design, not implementation, thus out of scope
    of the proposed "future type"]

Ok, i can respect that.

   Let's get this done, simple though it is, and then see how it will
   integrate with fsm.el and deferred.el.  I really think it will benefit
   everyone to start simple.

   #+begin_src lisp
   (defstruct future callback errorback status value)

   (defun future-done-p (future)
     (future-status future))

   (defun future-errored-p (future)
     (eq (future-status future) 'error))

   (defun future-cancelled-p (future)
     (eq (future-status future) 'cancel))

   (defun future-finish (future &optional status)
     (unless (future-done-p future)
       (setf (future-status future) (or status t))
       (when (future-callback future)
         (funcall (future-callback future) future))))

   (defun future-errored (future error)
     (unless (future-done-p future)
       (setf (future-status future) 'error)
       (when (future-errorback future)
         (funcall (future-errorback future) future error))))

   (defun future-call (future)
     (unless (future-done-p future)
       (let ((ff (future-value future)))
         (when (functionp ff)
           ;; TODO: needs error handling
           (setf (future-value future)
                 (funcall ff))))
       (future-finish future)))

   (defun future-cancel (future)
     (unless (future-done-p future)
       (future-finish future 'cancel)))


The next step (speaking from an armchair designer's pov) would be
to rebase fsm.el and deferred.el onto this data structure.

before:   fsm:                   deferred:
          API                    API
          internals              internals

after:    fsm:                   deferred:
          API                    API
          fsm glue               deferred glue
          struct ‘future’        struct ‘future’

I guess there will be similarities between the fsm and deferred glue that
we'd be wise to "move" into ‘struct future’, but that remains to be seen.

a sig, not big, i fig, you dig?

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