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Re: How can I write this function better?

From: John Mastro
Subject: Re: How can I write this function better?
Date: Tue, 14 Mar 2017 10:48:27 -0700

user <> wrote:
> Hello help-gnu-emacs, I'm looking for pointers with my luser-0x0
> function. I'm sure there are better ways I could write this. I'm not
> asking to have you rewrite it for me, that'd be rude of me, but rather
> what I should to look at, such as documentation or learning new
> constructs etc. I'm _very_ new to programming and Lisp (learning Lisp
> and Forth as my first languages; quite fun). An explanation, which I
> first wrote for myself, is below the code.

Here was my first thought on how I would personally write it. I wouldn't
say it's better (they achieve the same thing) but perhaps it will give
you an idea or two.

The things I changed were:
  - Make the region beginning and end positions arguments to the function
    (which default to the region-or-buffer) when called interactively
  - Only call `file-name-extension' when the buffer is visiting a file,
    otherwise just use ".txt"
  - Call `write-region' directly (rather than via `apply')
  - Use `call-process' with a destination buffer rather than
    `start-process' with a sentinel
  - Delete the temporary file at the end unless an optional argument
    says not to

Regarding the last point, `start-process' does have an advantage, which
is that the process is asynchronous. However, that may not matter for
this, if the upload will proceed quickly and/or you would wait for it to
finish before moving on anyway. For instance, if the upload takes a
while, then it might be odd to have its output added to your kill-ring
at some point later anyway.

Here's the code (lightly tested):

    (defun luser-0x0 (beg end &optional keep-file)
      "Upload region from BEG to END
    When called interactively, BEG and END default to the bounds of
    the region if active, or the buffer otherwise. If KEEP-FILE is
    non-nil, do not delete the temporary file that was uploaded."
       (if (use-region-p)
           (list (region-beginning) (region-end))
         (list (point-min) (point-max))))
      (let ((file (make-temp-file "0x0" nil
                                  (if (buffer-file-name)
                                      (file-name-extension (buffer-file-name) t)
        (write-region beg end file)
          (call-process "curl" nil (current-buffer) nil
                        "-F" (concat "file=@" file) "";)
          (kill-new (message "%s" (buffer-string))))
        (if keep-file
          (delete-file file t)

Hope that helps


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