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Message-ID:  <5933602064531107.WA.kellysmith12.21gmail.com@listserv.uni-heidelberg.de>
Date:         Wed, 19 Feb 2020 14:34:33 +0100
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From:         Kelly Smith <kellysmith12.21@GMAIL.COM>
Subject: Re: Discussion: Specialized Syntax
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Status: R

On Wed, 19 Feb 2020 12:27:31 +0100, Bruno Le Floch <blflatex@GMAIL.COM> wrote:

>On 2/19/20 10:25 AM, Jonathan Spratte wrote:
>> Hi,
>>
>>> - Defining an environment that sets up active characters to emulate
>>>   traditional BNF syntax is very concise, but comes at the cost of
>>>   delimited arguments and catcode madness.
>>
>> You could as well use a letter-by-letter parser that doesn't need altered
>> category codes. Take a look at the pgf module `parser`. That's not `expl3`
>> but could give you an idea on what's possible.
>>
>> Best,
>> Jonathan
>>
>
>I've been *toying* for a long time (haven't gone very far) with the idea
>of writing a parser generator, but I couldn't decide how powerful to
>make it.  One option would be to support "parsing expression grammars"
>(PEGs), which can be parsed in linear time using a packrat parser (but
>use a lot of memory, possibly problematic).  Another option would be to
>stick with more traditional things like LL or LR parser.  To be honest,
>I don't know enough about parsers and what useful languages they cover
>to decide.  Thoughts welcome.
>
>Best,
>Bruno

Given that the machinery already exists in the regex module, I would
suggest making a lexer generator and then complementing it with
a parser generator.

Some quick reading suggests that LALR parsers (e.g. YACC) would be
a good balance of expressiveness and efficiency. Since this would be
used for document syntax, the parsers do not need to be very powerful,
since user-facing syntax should be relatively simple and certainly
should be unambiguous.

Warmly,
Kelly