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

[Eric Abrahamsen]

Eric Abrahamsen <eric@ericabrahamsen.net> writes:

> <tomas@tuxteam.de> writes:
>
>> On Tue, Nov 08, 2022 at 08:18:15AM -0800, Eric Abrahamsen wrote:
>>> Ihor Radchenko <yantar92@posteo.net> writes:
>>> 
>>> > Eric Abrahamsen <eric@ericabrahamsen.net> writes:
>>> >
>>> >>> Is there any progress merging peg.el to Emacs?
>>> >>> I do not see any obvious blockers in the discussion, but the merge never
>>> >>> happened?
>>
>> [...]
>>
>>> > As the comment in peg.el states, the definitions are adapted from the
>>> > original PEG paper [...]
>>
>>> This is what I was saying in my original message, though: if peg.el is
>>> going to go into core, it probably needs more/better docs than code
>>> comments and "read this paper". Its likely users will be Elisp library
>>> authors like me, who are just trying to free themselves from regexp hell
>>> and want a relatively straightforward alternative.
>>
>> Yes. Coming from regexp they are deceivingly similar but frustratingly
>> different.
>>
>> The best way I found to wrap my head around them is that they are a
>> fancy notation for a recursive descent parser. Thus slightly more
>> powerful than regexps, but slightly less than a full YACC (i.e. LALR
>> or thereabouts).
>>
>> What is attractive about them is that one can do "full" parsers
>> (as long as your grammar is roughly LL(k)) without having to build
>> two storey buildings. I guess it takes some practice, though (I
>> haven't).
>>
>> I think comparing them to treesitter is a category error.
>
> Okay, this is all sounding good. I'm going to read the paper, try to get
> my head around all this, and write some docs for peg.el.

Okay, here's a first stab. I read the paper, and understood about half
of it, which seemed like enough. It was interesting to see that the
paper explicitly calls out the exact greedy-matching behavior I'd
encountered.

I'm sure I've got some of the conventions wrong, here, and it's
unfortunate that there's already a manual node called "Expression
Parsing", but I don't know what to call this except "Expression Parsing
Grammars"...

Eric

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