Even safer parseJson

[Avaq]

parseJson(Array, '{}') -> Nothing()

I'm very fond of the get and gets style of type validation, because it forces you to do it. It would've already saved me on multiple occasions if parseJson (or any x -> Any function for that matter) had this built-in, because after doing a "safe" JSON parse, it doesn't always occur to me the return value may still be of an unwanted type.

An alternative is to extract this behaviour out to its own function, which is used solely for type validation:

validate :: TypeRep -> a -> Maybe a

const parseJsonArray = compose(chain(validate(Array)), parseJson);

I think this second solution is more elegant in terms of modularity but it lacks the safety that comes from forcing you to do the type validation.

Side note: TypeRep may be changed to a predicate, but the idea remains the same.

[Avaq]

ℹ️ I've started work on this.

[davidchambers]

I love the idea of being able to do this:

> S.parseJson($.Array($.Number).test, 'XXX')
Nothing()

> S.parseJson($.Array($.Number).test, '["foo","bar","baz"]')
Nothing()

> S.parseJson($.Array($.Number).test, '[1,2,3]')
Just([1, 2, 3])

If we're to do this, we should address #149 as well. :)

[Avaq]

If we're to do this, we should address #149 as well

It's my intent. But since the two issues have been collecting dust I figured I'd get at the low hanging fruit first. I'll implement it using TypeRep, once merged it would clear the way for the type validation overhaul, which would then also affect parseJson.