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I am using LALR(1) parsing from lark-parser library. I have written a grammar to parse an ORM like language. An example of my language is pasted below:

Table1 .join(table=Table2, left_on=[column1], right_on=[column_2]) .group_by(col=[column1], agg=[sum]) .join(table=Table3, left_on=[column1], right_on=[column_3]) .some_column

My grammar is:

start: [CNAME (object)*] object: "." (CNAME|operation) operation: [(join|group) (object)*] join: "join" "(" [(join_args ",")* join_args] ")" join_args: "table" "=" CNAME | "left_on" "=" list | "right_on" "=" list group: "group_by" "(" [(group_args ",")* group_args] ")" group_args: "col" "=" list | "agg" "=" list list: "[" [CNAME ("," CNAME)*] "]" %import common.CNAME //# Variable name declaration %import common.WS //# White space declaration %ignore WS

When I parse the language, it gets parsed correctly but I get shift-reduce conflict warning. I believe that this is due to collision at object: "." (CNAME|operation), but I may be wrong. Is there any other way to write this grammar ?

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I think you should replace

operation: [(join|group) (object)*]

With just

operation: join | group

You've already allowed repetition of object in

start: [CNAME (object)*]

So also allowing object* at the end of operation is ambiguous, leading to the conflict.

Personally, I would have gone for something like:

start : [ CNAME ("." qualifier)* ] qualifier: CNAME | join | group

Because I don't see the point of object. But that's just a minor style difference.

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