[brundolf]

If you're referring to the "parse, don't validate" article, it's using the word in a different sense. The idea is that you make a data model that can only represent valid values, and then the code that handles foreign data transforms it into that type for downstream code to handle instead of just returning a boolean that says "yep, this data's fine"

[Karrot_Kream]

Right, but where this gets obnoxious is when you're writing code at the "edge", where customers can send you data, and the formats which you accept and process can change wholly and frequently. I've dealt with this problem before in a Scala setting where we were created sealed traits to have Value classes for each of our input types, but it was obnoxious enough that adding a new form of input was pretty costly from an implementation time perspective, enough that handling a new input format was something we planned explicitly for as a team. Sure, you could circumvent this by using something like Rust serde_json's Json Value type, but then you're basically rolling an unergonomic form of what you could do in a couple lines of Python.

I've mostly come to the conclusion that dynamic languages work well wherever business requirements change frequently and codepaths are wide but shallow (e.g. many different codepaths but none of them are particularly involved). Static languages work better for codepaths that are narrow but deep, where careful parsing at API edges and effective type-level modelling of data can create high-confidence software; in these situations the logic is often complicated enough where requirements just can't change that frequently. I wish we had a "best of both world" style to help where you have wide and deep codepaths, but alas that'll have to wait for more PLT (and probably a time when we aren't forming silly wars over dynamic vs static typing as if one was wholly superior than the other.)