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by crdoconnor
3573 days ago
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>What other ways do you have in mind that would be a viable replacement? Where there is not very much repetition required, simply use repetition instead (e.g. in the above example I would just copy & paste use-db to the relevant locations). The increased readability makes it worth the repetition where there's not a lot of it. Where there is a lot of repetition I'd consider that a bug or feature required in the schema and would refactor the YAML schema and the parsing code so that less repetition is necessary for most configs. I don't consider the above CI config particularly easy to understand and even with the node anchors and references there's a bunch of repetition (e.g spinach 1, spinach 2, spinach 3, etc.). That's partly because of the node anchors and references. It would look better if they refactored the schema. |
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Without a looping or sequence construct, this will be hard to avoid, and once you go that route, you might as well adopt a Lisp as your config syntax.
Before there was XML, there was SGML, and SGML has DSSSL, which was a Scheme dialect, and that was a brilliant idea which has been ditched for XML and its surrounding specs. S-Expressions are natural for the task. There are still prominent uses of S-Expressions, even in the OCaml world, where Jane Street uses it for configuration and serialization.
The full power of a Lisp may be too much and risky, but you can restrict the spec and allow only certain constructs, so that you can ensure it will evaluate to a result in a quick and deterministic way.
The little "templating" feature used in gitlab-ci.yml is a huge benefit, and as long as parsers limit the feature, it's a good compromise between complexity and comfort.
There is a lot of experience with using Lisp for configuration, and that experience can be leveraged to come up with a good S-Expressions based config format that's flexible, deterministic, and known to terminate in constant time. If you're careful with the spec, you could even validate the config fully.