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Re: Make peg.el a built-in library?

From: Helmut Eller
Subject: Re: Make peg.el a built-in library?
Date: Sat, 09 Oct 2021 10:12:03 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux)

On Sat, Oct 09 2021, Michael Heerdegen wrote:

>> "how do you jump over arbitrary text preceding a match?" (the answer
>> seems to be: "use `or' and recursion", at least this is what I found
>> out by myself after a while).
> No - using recursive rules of the kind
>  (rule   [maches what I want])
>  (search (or rule (and (any) search)))
> to advance over preceding text is not a good method in Emacs, this hits
> Emacs' maximum recursion level after a bunch of lines if we advance one
> character each time (which can't be avoided when searching text).  Is
> there a better solution for this kind of problem?

Self-recursion can sometimes be rewritten using *.  In peg.el, * is "inlined"
and so doesn't run out of stack:

 (rule   [maches what I want])
 (search (and (* (not rule) (any)) rule))

It's kinda like rewriting a self tail call to a while loop.

For the general case, peg.el would need some form of proper tail calls.


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