From: Leo Liu <sdl.web@gmail.com>
To: 20268@debbugs.gnu.org
Subject: bug#20268: 25.0.50; pcase-lambda broken
Date: Wed, 08 Apr 2015 09:01:13 +0800 [thread overview]
Message-ID: <m1twwrcu1y.fsf@zeuss-MBP.lan> (raw)
In-Reply-To: <m2zj6k5qqf.fsf@gmail.com> (Leo Liu's message of "Tue, 07 Apr 2015 15:42:32 +0800")
Forgive me to rely here. None of our messages shown up in bug#19670.
> After recent rewrite of pcase-lambda I am seeing:
> (cl-some (pcase-lambda (`[fullsweep_after ,v]) v)
> '([min_bin_vheap_size 46422]
> [min_heap_size 233]
> [fullsweep_after 65535]
>
> [minor_gcs 10]))
>
> Indeed, that's the semantics I chose.
> The previous semantics was for the function to do nothing and return nil
> if the arg doesn't match. The new semantics is the same as the one used
> by pcase-let. It's not without its fault of course, but at least it does
> correspond to the usual idea of "destructuring" and generates more
> efficient code.
I don't mind new semantics but I want to make sense of it so as to use
it with confidence. What I am seeing is:
(funcall (pcase-lambda (`[fullsweep_after ,v]) v) [min_bin_vheap_size 46422])
=> 46422
That doesn't make sense to me. Could you explain why this is the right
thing?
> I think if you prefer to return nil, then the macro should look like
> (pcase-lambda ((`[fullsweep_after ,v]) v))
> which would then naturally let you add additional cases like
> (pcase-lambda ((`[fullsweep_after ,v]) v)
> ((`[min_heap_size ,v]) (/ v 2)))
I didn't choose the multiple-clause version because it is a cheap
shortcut for (lambda (...) (pcase ... ...)).
The single-clause pcase-lambda makes a lot of higher-order functions fun
to use and that is where I am reaping the benefits.
> Admittedly, for the current pcase-lambda (and pcase-let) macro, the
> pcase.el code should be refined so as to emit a warning when it ends up
> ignoring a constant like `fullsweep_after' above.
Yes, I am having a lot of trouble understanding and using pcase-let*
except for trivial cases. I don't want the same thing to happen to
pcase-lambda.
> Stefan
Thanks,
Leo
next prev parent reply other threads:[~2015-04-08 1:01 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-07 7:42 bug#20268: 25.0.50; pcase-lambda broken Leo Liu
2015-04-08 1:01 ` Leo Liu [this message]
2015-04-08 14:35 ` Stefan Monnier
2015-04-08 2:14 ` Stefan Monnier
2015-04-08 13:22 ` Andy Moreton
2015-04-08 15:08 ` Philipp Stephani
2015-04-08 19:25 ` Stefan Monnier
2015-04-08 20:31 ` Drew Adams
2015-04-08 21:29 ` Stefan Monnier
2015-04-08 22:21 ` Drew Adams
2022-02-08 7:52 ` Lars Ingebrigtsen
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