How to get a partial AST for a partial input?

[jadetang]

Hello, we are using this tool, it works well for our project. Now I want to implement the autocomplete in the LSP where most of the time the input is incomplete. Is it possible to get a partial AST? I read the error label and recovery document and examples, but I am not sure that can work for me, because I don't need to continue parsing in case something goes wrong. Any suggestion is appreciated.

[breml]

Hi @jadetang Me personally, I have never tried to build a parser with pigeon, that works on partial AST. That being said, two ideas come to mind:

• As you have already mentioned, the error label and recovery are the features, that might be helpful for this scenario.
• Alternatively, you might want to create a grammar, that supports something like <the_thing> / <maybe_the_thing>, where <maybe_the_thing> is defined such, that it matches something, that could become <the_thing>, but is not yet complete (basically matching the prefix).
• Do some research, if there are papers about using PEG for partial AST, maybe you are lucky.

But since I have never done such a thing, I might not be of a lot of help.

[jadetang]

@breml thanks, I think the second approach sounds promising. I will try that.