Matching an expression and pushing a different one

[jhoobergs]

I am writing a parser for a subset of yaml (https://github.com/m8rex/yaml-subset) and I need to be able to match for a - but push a a space ( ) to the stack.

The reason for this is that if you place a hash in a list in yaml, you get something like this:

---
field:
  - type: item
    other: value

To match the indentation of the inner hash, I would need to push a space onto the stack, when matching the - of the list.

I would like something like PUSH_OTHER("-", " ").

I looked into the code quickly, but it seems that the pushes happen with span's into the source text, which does not make it easy to push something else. Any thoughts?

[tomtau]

A side note: I saw there was this yaml grammar: https://github.com/aofdev/yaml-peg/blob/main/src/parser/grammar/yaml.pest but not sure whether it's complete / correct

[jhoobergs]

The main difference is that I want to preserve the comments, which is rater hard in yaml, but needed for formatting purposes. I also don't think that it is complete.

[yshavit]

Would there be any appetite for doing this, if I were to look into creating a PR? Or is it something this project actively wants to avoid?

Another example of when it would be useful: a rule that starts with either [ or (, and then ends with ] or ) respectively.

[yshavit]

This has been completed as of #1092. The syntax is:

PUSH_LITERAL( <literal string> )

This is slightly different from the proposed PUSH_OTHER, in that it only takes one argument, and always matches. You can get the equivalent of PUSH_OTHER by combining this with a sequence match:

"-" ~ PUSH_LITERAL(" ")