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bug#27584: 26.0.50; alist-get: Add optional arg TESTFN

From: Tino Calancha
Subject: bug#27584: 26.0.50; alist-get: Add optional arg TESTFN
Date: Mon, 10 Jul 2017 22:02:34 +0900 (JST)
User-agent: Alpine 2.20 (DEB 67 2015-01-07)

On Mon, 10 Jul 2017, Michael Heerdegen wrote:

Tino Calancha <address@hidden> writes:

I rewrote it as follows:

  (declare (compiler-macro
            (lambda (form)
              (pcase pred
                (''eq `(assq ,key ,alist))
                ((or ''equal 'nil) `(assoc ,key ,alist))
                ((and (guard (macroexp-const-p key)) ''eql)
                 (if (floatp key)
                     `(assoc ,key ,alist) `(assq ,key ,alist)))
                (t form)))))

Is this a good idea in general?  PRED could also be function-quoted, or
a variable bound to `eq'.  And KEY could be an expression that evaluates
to a float.  That would fail the `floatp' test.
Well, this code is now in the 'Limbo', because we are thinking
to use the Nico solution (`assoc' having an optional arg PRED).
That said, its fun to discuss about it.
You know, this compiler macro is inspired in the one used by `cl-assoc' i.e., `cl--compiler-macro-assoc'. If you find a problem
on it, then the same problem might arise in `cl-assoc' :-S

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