What "bailout" functionality is available in pest to parse non-context-free syntax?

[ahelwer]

For example, tree-sitter has an external scanner written in C to parse the non-context-free part of a language while using the grammar for everything else. Is something similar available for pest?

[tomtau]

There's no general escape hatch, but there are language constructs where it can parse expressions that go beyond CFG: see https://pest.rs/book/grammars/syntax.html#the-stack-wip

[ahelwer]

Thanks. Unfortunately I don't think stacks will fully work to parse TLA+, because the vertically-aligned blocks often aren't preceded by whitespace on the line. For example, this nested conjunction list:

op ==
  /\ x
  /\ /\ y
     /\ y
  /\ x

Is there a way to access the column position (in codepoints) inside the PEG and push that to the stack somehow then match on it?

@beggers as FYI

[tomtau]

not sure if this works: https://pest.rs/book/grammars/syntax.html#indentation-sensitive-languages ?

[ahelwer]

It does not, since the preceding space in the line is not whitespace.