On: A reasonable configuration language

[skybrian]

Sure, it doesn't allow side effects, but what can it depend on? If a file defines a language that downloads a dependency from a URL, does that count? How about if it's automatically cached?

Once you start getting dependencies from others, it seems like a configuration language could drift into package management.

[ianburrell → skybrian]

Downloading anything has side effects and can't be allowed by side effect free language. It is pretty rare that config language allow downloads.

Downloading dependencies isn't usually done by config languages. Config languages generate a config, JSON or YAML, from source. The config file can be used by engine that applies the config including downloading dependencies.

[anileated → ianburrell]

Thinking inside the program, downloading dependencies certainly doesn’t need to have side effects. It may add new failure modes, that’s all.

If you step outside then sure, it has side effects, but so does simply running the program (any program), in 100% of the cases.

[skybrian → ianburrell]

XML isn't rare and it has URL's baked in. But yes, it's a bad idea.