I’ve seen this topic mentioned a few times on Slack, but though it worth asking here so the answers are better preserved. I want to write a parser with error recovery ( for this ). So as a user is inputing the source code, the parser should run and attempt to parse the input. If it fails to do so, it…

Released what I have done so far. [image] parser-recoverable 1.0.0 On the whole, I’m not completely satisfied with the result, but at least I have a recoverable implementation of sequence which is enough for me to work with for now. The main issue for my dissati…

Elm Markup does parsing with recovery and it sounds like it takes roughly the same approach as @klazuka describes. This module is likely relevant: Tolerant Parser though not well documented because it’s internal :sweat_smile:

Thanks for all of these most helpful replies. [image] evancz: The easiest way is probably to define a simple notion of “chunks” that any file can be broken into. This will work nicely for what I am trying to do. The file is a series of ‘declarations’. I can either chunk on newline followed b…

On the chunking - I looked into doing it with elm/regex which is easy to do: Regex.fromString "\\n(?=\\w)" |> Maybe.withDefault Regex.never |> (\r -> Regex.split r source) But for interactive work, I will also need to know the start and end positions of each chunk. For that reason, I think…

I’ve been trying to collect my thoughts on this, feel free to chip in if anything chimes for you! [image] evancz: Just start by figuring out if it can get the error messages you’d like to see! I think this is good advice, as recovery may need to understand the context of an error in order to…

[image] klazuka: recovery: when committed to a failed rule*, discard tokens until you reach some sentinel token (or arbitrary logic) which indicates a point from which you can recover. I can see recovery is often likely to consist of chomping until one of some list of characters is reached. …

If your project also provides a source editor, then one thing you can do to mitigate the missing, closing token (e.g. ], ), }) would be to always insert a matching, closing token when the user types an opening token. This doesn’t guarantee that you’ll always have a closing token, but it will probabl…

Yes, having the editor insert the closing ], ), } will help. My project does include a source editor, if it did not I would not bother trying to do error recovery on the parsing. Top-level chunking is enough to restart the parser and allows multiple errors to be reported per file. Imagine for ex…

Here’s also some research, if your keen to get into the details https://tree-sitter.github.io/tree-sitter/#underlying-research

That’s some hard-core reading material right there… thanks, I’ll give it a go. I am wondering how much of this stuff is implementable on top of elm/parser. If that does not expose the features needed, I’ll most likely just stick with what I can do with extending elm/parser as I don’t really want to…

So I feel like I am now making some good progress with this. I have taken Matt’s TolerantParser as a starting point, the current WIP is here: https://github.com/the-sett/parser-recoverable Example Don’t get too excited, but I created a little example to start trying it out: cd examples elm-live…

Parsers with Error Recovery

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Parsers with Error Recovery

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