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Re: [ELPA] New package: xr

From: Stefan Monnier
Subject: Re: [ELPA] New package: xr
Date: Fri, 01 Mar 2019 08:51:39 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

>> I'm definitely in favor of using the standard * + and ?
> They are suggestive but I find `?' a bit on the hacky side. For instance,
> you can't break the line after the operator, since it requires
> a space following.

Oh, indeed, that's a problem.

> Interestingly, (not (any ...)) and (not (in ...)) are valid, but (not (char
> ...)) isn't (although there is `not-char').

I guess this means we should go with `in`.
Tho it should be easy to add (not (char ...)) if needed.

BTE, I don't like (not (any ...)) and (not (in ...)) in any case:
the negation should be within the `char`, `in`, or `any` not around it.
This is because the negation of a regexp RE could be defined as a regexp
which matches all strings not matched by RE (and hence when RE is (any
...), it will also match all strings of length != 1).

This form of negation is supported in lex.el, for example.

> Another implementation leak: since `any' is also an alias for `not-newline',
> `char' and `in' are as well:
> (rx any char in) => "..."

But XR doesn't have to abuse this, luckily.


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