Adding optional support for lambda-style functions

[bavalpey]

I am the author of the TTSLua addon, and am wondering the best way to go about adding a configuration option that will support lambda-style functions.
Since my issue (#2515) on the matter received little to no attention, I thought I would take it upon myself to implement this and submit a PR.

A lambda-style function, supported for instance by moonsharp, is an expression that has the form |paramList| Expr where paramList can be empty.
It's essentially just adding a new rule to the grammar for exp, like so: exp ::= ... | ‘|’ [parlist] ‘|’ exp

That means that, |x, y| x+y would be equivalent to function(x, y) return x + y end

Hooking into the parser inside an addon to support this does not seem to be the right approach. It seems shaky to call into the parser methods defined within parser within the add on logic.

I believe I have a handle on how to implement it - adding a rule within the parseExpUnit method of compile.lua. However, I am more interested in how users would enable support for the syntax via configuration.
Since it isn't really a "symbol", it does not make sense for it to be a nonStandardSymbol like the others. It also isn't a replacement of an existing keyword, so special seems unfit as well.
Is there precedent to add a specific configuration option to support this?

[CppCXY]

The best solution is to rewrite the parser for your language after you have forked it. I know that MoonSharp is a Lua runtime implemented in C#, so I suggest that you could consider implementing these features on my language server.

[bavalpey]

This really doesn't seem like the best solution. Why would I splinter off into yet another language server or yet another parser? The tokenizer for this one is already written, and the syntax for moonsharp is literally exactly lua 5.2 with the lambda expressions added in.

I don't want to sound combative but I think it's a disservice to the community to write yet another language server or another parser when this one works just fine.

And the lambda expressions are just syntactic sugar for function(paramList) return expr end and can be used wherever an expression is expected.

I need to add support for one additional expression, and this repo already has a fully fledged parser.
In fact I've already hooked into it properly and have it able to parse properly. Now I just need to figure out how to hook into the diagnostics.

That's not the point of this post. The point of this post is to ask the maintainers how best to allow users to opt in to such functionality.

[CppCXY]

Since luals does not provide configuration support for third-party dialects, you can only add it to nonStandardSymbol.
Also, if you want your code to be formatted, you need to modify https://github.com/CppCXY/EmmyLuaCodeStyle.