Parse, Don't Validate (2019)

Validation is checking if something looks like a data structure. Parsing is smashing data into a data structure, and failing out if you can't do it.

At the end of parsing, you have a structure with a type. After validation, you may or may not have a structure with that type, depending on how you chose to validate.

But I think the big win is, parsers are usually much easier to compose (since they themselves are structured functions) and so if you start with the type first, you often get the "validation" behavior aspect of parsing for "free" (usually from a library). Maybe title should have been "Parse, don't manually validate."

But if your type doesn't catch all your invariants, yeah it does feel kinda just like validation.