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bug#20784: 25.0.50; pcase documentation on t and nil


From: Michael Heerdegen
Subject: bug#20784: 25.0.50; pcase documentation on t and nil
Date: Fri, 12 Jun 2015 19:31:10 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux)

Stefan Monnier <address@hidden> writes:

> We currently don't have a special "fail" pattern which simply never
> matches.  Of course, you can make one up (e.g. (guard nil)).

(or) would also do it, but raises (error "Please avoid it")  (BTW
(or _) raises that error, too).  Why are those (error "Please avoid it")
calls useful?

> I think making nil such a pattern would probably lead to more
> errors/confusion than anything, since it's extremely rare to need such
> a pattern.

Agreed.

> That's pretty much what SELFQUOTING is.  IF you think renaming it to
> ATOM would help, then we could do that.

I would prefer that over SELFQUOTING because

  SELFQUOTING   is a shorthand for 'SELFQUOTING.

sounds like a tautology.

> As explained the use of `eq' is supposed to be a pure optimization with
> no semantics effect.

I see.  Then I guess it would make sense to merge these two lines in the
` doc?

  STRING                matches if the object is ‘equal’ to STRING.
  ATOM                  matches if the object is ‘eq’ to ATOM.

into

  ATOM                  matches if the object is ‘equal’ to ATOM.


Regards,

Michael.





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