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Proposing "alist" macro

From: Adam Porter
Subject: Proposing "alist" macro
Date: Fri, 17 Aug 2018 20:57:07 -0500


I've found the a-list function from the a.el library to be very
helpful for building alists, e.g. instead of:

#+BEGIN_SRC elisp
  (let ((a 1)
        (b 2))
    (list (cons 'one a)
          (cons 'two b)
          (cons 'three 3)))


#+BEGIN_SRC elisp
  (let ((a 1)
        (b 2))
    `((one . ,a)
      (two . ,b)
      (three . 3)))

I can write:

#+BEGIN_SRC elisp
  (let ((a 1)
        (b 2))
    (a-list 'one a
            'two b
            'three 3))

However, a-list runs mapcar and seq-partition at runtime.  Also, few
people have a.el installed, and people seem reluctant to install it.

So I'd like to propose this macro for addition to Emacs:

#+BEGIN_SRC elisp
  (defmacro alist (&rest args)
    "Build an association list from the keys and values in ARGS.
  ARGS is a list of alternating keys and value forms, like a plist.
  For example:

    (alist 'one 1
           \"TWO\" \"2\"
           3 (nth 3 var))

  Expands to:

    (list (cons 'one 1)
          (cons \"TWO\" \"2\")
          (cons 3 (nth 3 var)))"
    `(list ,@(cl-loop for (key value) on args by #'cddr
                      collect `(cons ,key ,value))))

If this is acceptable, I'd be happy to provide a patch with whatever
changes are desired.


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