How to generate a sequence of rules that produced the AST?

[brando90]

Hi,

I was wondering, during the parsing of the string one creates an AST. I was wondering if there was an easy way to extract the rules that generated a specific AST from a specific order traversal ? (note: non-terminals be expanded in different orders e.g. BFS or DFS so the sequence would correspond to such an ordering)?

[MegaIng]

There is the Transformer, Visitor and Interpreter classes that visit the nodes of the tree.

If that does not do what you want, you will need to provide an example of what you want. Potentially the internal tree_matcher does what you want.

Note that if you want to match how it is parsed in reverse, that doesn't really make sense since we are implementing different algorithms that don't directly walk the grammar in a tangible way.

[MegaIng]

@brando90 Ok, I just pushed the rules_generator. You can see how to use it from test.py. It is not perfect, and will as example introduce unnecessary parentheses. (But that is also partly because of a bug I found in tree_matcher I think).

[brando90]

@MegaIng awesome! Will go through it now. The attempt I described worked for simple grammars (bnf) but it does work at all with the ebnf one that Lark supports. If I see but fixes I will let you know.

[brando90]

@MegaIng Hi Megalng, I was going through the code and was finding that it is trickier to understand that I expected (probably my own inexperience with Lark than anything else + not knowing even conceptually what the algorithm should be for ebnfs) but was wondering if you'd mind explaining the main idea(s) in English? I was hoping that would help me understand what I am reading (since right now I am not even sure what the intended algorithm is and trying to infer that only from source code is sort of tricky - perhaps due to implementation details).

Thanks again for getting that together for me! And your time is very much appreciated.

[MegaIng]

@brando90 I will go through it and create comments. For further questions you can just open an issue over there. Or maybe even better, write me on gitter.

[MegaIng]

@brando90 I pushed a bit of documentation in rules_generator. For further questions, I would suggest opening an issue over at the repo or sending me a PM on gitter.