Lua 5.x parser, Looking beyond luaX_lookahead()

[Alexander Walz]

 

Hello,

 

is there a save way to check for tokens beyond that luaX_lookahead() will offer ?

 

Especially, I would like to implement Maple-style `(...) -> expr` anonymous/lambda functions in Lua.

 

After dozens and dozens of hours, I am too dumb obviously to succeed, unfortunately.

 

Thank you. Alex
agena.sourceforge.net

 



[Sainan]

It is relatively easy to modify the lexer to parse all tokens up-front and then have the parser be able to look anywhere. You can take a look at Pluto[1] which makes such a modification.

And yet, Pluto's lambda syntax is `|...| -> expr`, partially because it predates the "look anywhere" patch iirc, but also less ambiguity is always nice. :^)

[1] https://github.com/PlutoLang/Pluto/

-- Sainan

[Luiz Henrique de Figueiredo]

You may use my Lua token processor for experimenting by writing Lua code:

https://web.tecgraf.puc-rio.br/~lhf/ftp/lua/#ltokenp

[Alexander Walz]

With all due respect: "It is relatively easy to modify the lexer to parse " Nope. It is not "easy" if you check all this with Valgrind. And yep, Pluto's x < y < z chaining is marvelloeus. It may work in 5.x, but in 5.1 it ... it will do, with some changes. Long live Lua.


-----Original-Nachricht-----
Betreff: Re: Lua 5.x parser, Looking beyond luaX_lookahead()
Datum: 2025-10-13T20:57:23+0200
Von: "'Sainan' via lua-l" <lu...@googlegroups.com>
An: "lu...@googlegroups.com" <lu...@googlegroups.com>

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[Sainan]

I'm not sure what you mean. I think this was one of the easier patches; I assumed it would need a lot of messing with the internals, but it basically just worked. And Pluto's entire test suite (which includes most of Lua's) goes through Valgrind without a hitch.

Also, Lua 5.1 is not something I would recommend, e.g. see the recent Redis 10.0 CVE which was entirely avoidable by just not using unmaintained versions of Lua that are older than Lua was when it was released.

-- Sainan