Comment by solatic | Hacker News Reader

Comment by solatic | Hacker News Reader

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> This happened to me literally just an hour ago when I wanted to put a DSL in a field in a config file. json-schema (the "config" schema) doesn't let me write code to validate this and reject it.

You can embed DSLs in CUE. It's a bit unwieldy because you have to essentially reproduce the DSL grammar in CUE, and it may not be performant, but yeah, it's doable. Can you provide more details?

> You might argue that "these rules bolted on top aren't part of the schema" or "this is validation that you can do after the json schema validates" but there is benefit to combining them - namely, code coherence and validation error consistency.

I would argue that it's a slippery slope. Consider v1 where an enum is statically defined as Employee or Manager. Then in v2 we add VP and CEO. Then in v3 actually the list of permitted titles needs to be fetched from a database populated by HR. Is it still correct to put this in configuration validation? What if the person writing the configuration doesn't have permissions to read from HR's database? So nothing should work?

>You can embed DSLs in CUE

CUE lets you embed functions too it looks like it's almost a programming language itself.

The closer a configuration language gets to a programming language the less of a reason I see for it to exist.

>I would argue that it's a slippery slope. Consider v1 where an enum is statically defined as Employee or Manager. Then in v2 we add VP and CEO. Then in v3 actually the list of permitted titles needs to be fetched from a database populated by HR. Is it still correct to put this in configuration validation?

No, coupling to a database would be bad design IMO, but grabbing those enums from other config files in the same folder that are parsed earlier I have done a lot.

I've also used libraries that provide lists of timezones and country codes as enums and plugged them in to the parser so you couldnt invent your own country code.

And Ive written validators that reference other bits of the config (e.g. the list of permitted titles is in another part of the config).

All of these things I would argue are good and useful and not worth sacrificing in exchange for preventing possible misuse (like coupling parsers to a DB).

I actually wrote this parser in the first place because I wanted to create a good metalanguage for tersely defining strongly typed executable specifications in YAML (i.e. Gherkin done right). Tons of stuff I wanted to strictly validate wouldnt have been possible with config-based schema validation and with YAML's weak, implicit typing it was a fucking mess.

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