Automatically generating a JSON parser from types is such a killer feature I don’t even think that much about until I have to interact with a third-party HTTP API and suddenly have to write reams and reams of code to very carefully ensure the data is the right shape.
- Automatically generating a JSON parser from types is such a killer feature I don’t even think that much about until I have to interact with a third-party HTTP API and suddenly have to write reams and reams of code to very carefully ensure the data is the right shape.
A lot of people seem to like how most dynamic languages just map JSON to plain object/dict/hash values, but I feel like in practice that just leads to tons of error messages along the lines of “no such key "foo" in dict” because people just use the half-parsed things directly.(This gets at the heart of type-driven design. If you write stuff like parse :: Dict -> MyType then you isolate the “key does not exist” errors to one spot. But if you write validate :: Dict -> ExceptT Err () then you don’t… and now it’s easy to forget to call validate.)(To put it another way, the `parse` version checks that the input is valid, then *preserves* that information in the type system, strengthening the type. The `validate` version does all the same checks… but then it just throws all the information gained in that process away!)IME, people in dynamic languages almost never program this way, though—they prefer to use validation and some form of shotgun parsing. My guess as to why? Writing that kind of code in dynamically-typed languages is often a lot more boilerplate than it is in statically-typed ones!