[skybrian]

This is a good design pattern, but be wary of doing validation too early. The design pattern allows you to do it as early or late as you like, but doesn't tell you when to do it. Often it's best to do it as part of parsing/validating some larger object.

See Steven Witten's "I is for Intent" [1] for some ideas about the use of unvalidated data in a UI context.

[1] https://acko.net/blog/i-is-for-intent/

[lolinder]

I read through that piece and strongly disagree with the premise that their insight is somehow at odds with leaning into the type system for correctness.

The legitimate insight that they have is that anchoring the state as close as possible to the user input is valuable—I think that that is a great insight with a lot of good applications.

However, there's nothing that says you can't take that user-centric state and put it in a strongly typed data structure as soon as possible, with a set of clearly defined and well-typed transitions mapping the user-centric state to the derived states.

Edit: looks like there was discussion on this the other day, with a number of people making similar observations—https://news.ycombinator.com/item?id=39269886

[skybrian]

A text file and an abstract syntax tree can both be rigorously represented using types, but one is before parsing and other is after parsing. The question is which one is more suitable for editing?

Text has more possible states than the equivalent AST, many of which are useful when you haven't typed in all the code yet. Incomplete code usually doesn't parse.

This suggests that drafts should be represented as text, not an AST.

And maybe similarly for drafts of other things? Drafts will have some representation that follows some rules, but maybe they shouldn't have to follow all the rules. You may still want to save drafts and collaborate on them even though they break some rules.

In a system that's not an editor, though, maybe it makes sense to validate early. For a command-line utility, the editor is external, provided by the environment (a shell or the editor for a shell script) so you don't need to be concerned with that.