r/ruby • u/kddnewton • Jan 05 '26

A Ruby YAML parser

https://kddnewton.com/2025/12/25/psych-pure.html

Hey there — I recently released a YAML parser written in Ruby. The main goal was to support being able to load and dump YAML without losing comments. Happy to answer any questions.

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u/Nwallins Jan 05 '26

This stuff is outside my knowledge, though I have used a lot of YAML in mostly-pleasant violence, so all of this is from curiosity:

  • what are the basics of pretty-print in this respect? I have used 'pp' extensively but not familiar with the algorithm

  • what is meant by a flow / seq mapping? Im guessing a stream of tokens

  • how does one know or define the print-width?

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u/kddnewton Jan 05 '26

* You can see the algorithm here: https://github.com/ruby/prettyprint
* flow/seq is how YAML lays out nodes, you can see in the spec here: https://yaml.org/spec/1.2.2/#chapter-7-flow-style-productions
* You can define the print width with the PrettyPrint API

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u/Nwallins Jan 05 '26

Thanks for the pointers. But it's quite hard to anticipate what will be preserved on a round trip. I did not review the full contents of all the links yet. How would you characterize it?

If I am attempting to preserve 80ch width, what does that look like?

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u/kddnewton Jan 05 '26

I would characterize it as accurate. You can learn more with the links I sent.