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Re: Three questions about pcase for Stefan

From: Stefan Monnier
Subject: Re: Three questions about pcase for Stefan
Date: Sat, 23 Jan 2016 10:36:33 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1.50 (gnu/linux)

> i.e., floats do not count as "atom".  This is consistent, also explained
> correctly in the doc, but may nonetheless be confusing.  What led you to
> this decision?

Testing equality of floating point numbers is very rarely correct.

> 2.  Do you think we can already bury the old deprecated special behavior
> of the atoms nil and t as patterns?

Far from that.  IIUC, it's even still used in a GNU ELPA package.
We'll have to live with it for a reasonably long time.
And to tell you the truth, I don't think it's a great idea to make nil
and t match themselves.  We can plan on making them signal errors, OTOH
(for Emacs-26.1 or Emacs-27.1).

> 3.  Is it correct to say that not only the functions used in a pred
> pattern, but any ordinary Lisp code part of any pattern (guard, app,
> let, etc.) should be pure in the same sense?



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