From: Stefan Monnier <monnier@iro.umontreal.ca>
To: emacs-devel@gnu.org
Subject: Re: Lambda in macrolet becomes a closure? (another breaking change in emacs:))
Date: Mon, 19 Sep 2016 14:12:17 -0400 [thread overview]
Message-ID: <jwvk2e7ix31.fsf-monnier+gmane.emacs.devel@gnu.org> (raw)
In-Reply-To: CAFkz2yq3qxGmY1op5CtoUj7WVGQedm3mnjeL79VYB6F9X_AWDA@mail.gmail.com
> in emacs version "25.1.50.2", this:
> (macrolet ((tm () (let ((fu #'(lambda () t)))
> `(list ,fu))))
> (tm))
Here, `fu' is a function *value*, rather than a function *expression*
(where I take those words to mean that an /expression/ is what you pass
to `eval` and that returns ` /value/).
In `(list ,fu) you take that value and plug it into the source code,
which in general might not work correctly (although you may often get
lucky since in Elisp, many values are "self-quoting" meaning that they
are also valid expressions which evaluate to themselves).
> gives an errror: Symbol’s function definition is void: closure
Indeed, in a lexical-binding context, a function value will sometimes
look like (closure ...) which is not a valid expression (there is no
function nor macro named `closure').
> (macrolet ((tm () (let ((fu #'(lambda () t)))
> `(list (function ,fu)))))
> (tm))
> returns ((closure (t) nil t))
This will sometimes work as well. Probably more often than the previous
example. Yet it's still not correct. To quote a value, you want to use
`quote` rather than `function`. `function` can only be used reliably to
quote a "function expression" rather than a function value. A function
expression is basically either a symbol (the name of a function), or
a sexp of the form (lambda <args> <body>).
> in emacs "24.3.1", both variants returns ((lambda nil t))
Yes, sometimes.
Stefan
next prev parent reply other threads:[~2016-09-19 18:12 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-19 16:43 Lambda in macrolet becomes a closure? (another breaking change in emacs:)) Constantin Kulikov
2016-09-19 18:12 ` Stefan Monnier [this message]
2016-09-23 16:01 ` Michael Heerdegen
2016-09-23 16:13 ` Stefan Monnier
2016-09-23 17:19 ` Constantin Kulikov
2016-09-23 19:03 ` Stefan Monnier
2016-09-25 11:06 ` Constantin Kulikov
2016-09-25 14:15 ` Stefan Monnier
2016-09-25 18:01 ` Michael Heerdegen
2016-09-25 18:53 ` Stefan Monnier
2016-09-27 9:13 ` Constantin Kulikov
2016-09-27 9:19 ` Constantin Kulikov
2016-09-27 11:53 ` Constantin Kulikov
2016-09-27 14:57 ` Michael Heerdegen
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