Sometimes, in order to stay flexible and fit, you need to do some (type) gymnastics 🤸

Slowly getting the hang of #chumsky #parser combinator #crate 🤓

One concept (among others!) I haven't learned yet, but _will_ run into, is #recursion in chumsky. I know, there are good docs on it - it's just something I haven't gotten to yet.

All in all, I'm very happy with chumsky so far. Kudos to its maintainers! 🙂 🎩

#Rust #RustLang

@janriemer Recursion couldn't be easier!

let a = recursive(|a| /* definition of a */);

Make sure you don't end up with accidental left recursion though. Check out the docs for the new pratt parser combinator if you want a really neat way to do complex expression parsing.

@jsbarretto This looks very easy indeed - thank you!  

Yes, thank you for the hint regarding left recursion (see little anecdote in second toot). 👍

If I understand correctly, `memoized` should be used for left recursive grammars in general, no!?

I always thought pratt parsing was only for parsing expressions (like 1+2*5 etc.), but not general left recursive parsing, but this is more an intuition, so I might be wrong.😇

https://docs.rs/chumsky/1.0.0-alpha.6/chumsky/trait.Parser.html#method.memoized

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@janriemer So... Yes, `memoized` does exist, and does allow the parsing of left-recursive grammars. However, it does come with some overhead: if you can rewrite your grammar to be right-recursive, you'll almost certainly be happier in the long run (this goes for pretty much any top-down approach to parsing out there FWIW).

I'd be interested to know what the right-recursive section of your grammar looks like: the pratt parser can almost certainly handle it, whatever it is.

@jsbarretto Thank you for all the tips, Joshua! 🤗

So two places in the grammar might be interesting:

1. Conditional Expressions:
Think of something like this:
foo && (bar || baz)

So this might not be very different from math expressions and so pratt parsing should be possible, right!?🤔

Here is a direct link to the parsing code and line (⚠️ nom macros ahead!)
https://gitlab.com/seloxidate/selector/-/blob/e6a7aa290c6027c9fd595ed89bebc4d3c1de4773/src/parsers/conditional_expression.rs#L43

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@jsbarretto

2. Eval Name:
Basically method calls - think of something like this to parse:
myClass.myMethod(foo.bar())

I can imagine that this might not be suitable for pratt parsing (it's not a classical math expression), but I haven't really put much thought into it yet, so maybe it's perfecty fine to apply pratt parsing!?

Here is a direct link to the parsing code and line (⚠️ nom macros ahead!)
https://gitlab.com/seloxidate/selector/-/blob/e6a7aa290c6027c9fd595ed89bebc4d3c1de4773/src/parsers/eval_name.rs#L16

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