Bug with zero or more rule

[heckad]

Gram file

start: stmts

stmts: stmt*

stmt: block

block: "{" stmts "}"

Input

{ {} }

Result

  File "<unknown>", line 1
    { {} }
       ^
SyntaxError: input.txt

The problem in the generated parse rule for the block stmt Code

    @memoize
    def block(self) -> Optional[Any]:
        # block: "{" stmts "}"
        mark = self._mark()
        if (
            (literal := self.expect("{"))
            and
            (stmts := self.stmts())
            and
            (literal_1 := self.expect("}"))
        ):
            return [literal, stmts, literal_1];
        self._reset(mark)
        return None;

(stmts := self.stmts()) shoud be (stmts := self.stmts()) is not None because an empty array is interpreted as false.

[0dminnimda]

stmt* have a value of None if no stmt was found. I haven't checked i, but it think that stmts returns None and block doesn't handle it

An easy, but possible problematic way to solve this is recursively checking expressions until we find single Repeat A possibly more compilated way to solve this is to properly handle this is stmts

I will look into that

[0dminnimda]

Unfortunately here we need a more general indicator of a failure The problem with using None is that if user wants to return it:

start: stmts

stmts: r=stmt* { None if not r else r }

stmt: block

block: "{" stmts "}"

[heckad]

I haven't checked i, but it think that stmts returns None and block doesn't handle it

stmts returns an empty array not None. And that is interpreted as False. None is a good marker.

[0dminnimda]

stmts returns an empty array not None

Yes, initially i was wrong about it

[heckad]

My attempt to solve the problem