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Re: The poor state of documentation of pcase like things.


From: Michael Heerdegen
Subject: Re: The poor state of documentation of pcase like things.
Date: Sat, 19 Dec 2015 16:14:15 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux)

address@hidden (Phillip Lord) writes:

> (pcase '(3 1 2)
>    (`(_ 1 2)
>    (message "Matched a list of anything followed by (2 3)")))
>
> prints nothing.
>
> while this...
>
> (pcase '(3 1 2)
>    (`(,_ 1 2)
>    (message "Matched a list of anything followed by (2 3)")))
>
> prints the message (which should be "followed by (2 3)").
>
> I am a bit surprised to find that _ needs , in these examples, and I
> think that it's a bug.

I think it's intentional, and it fits the documentation.

We think of elements in a backquoted list to be all quoted unless
explicitly unquoted.  It makes no sense that '_ matches any expression.
It matches only the symbol _, and that can be useful, too.


Michael.




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