Newbie questions

[saurabhnanda]

I'm struggling with validating an incoming JSON (newbie alert!).

1. Is there a typo in this example in the docs? Do we really mean to pass "" as the first argument to digestJSON
2. Is it possible to get a slightly longer code snippet where the Form v m a is being constructed using the record constructor and not the tuple constructor?

[ocharles]

1. That indeed looks like a typo
2. Like this?

pokeForm :: Monad m => Form Text m Pokemon
pokeForm = liftA2 (\name number -> Pokemon { pokemonName = name, pokemonNumber = number}) 
                  ("name" .: nonEmptyText)
                  ("number" .: parseInteger)
  where
    nonEmptyText = check "Name cannot be empty" (not . T.null) $ text Nothing

[saurabhnanda]

Something like that. What's an easier way to write it?

do
  pokemonName <- "name" .: nonEmptyText
  pokemonNumber <- "number" .: parseInteger
  return Pokemon{..}

[ocharles]

You can do exactly that if you enable {-# LANGUAGE ApplicativeDo #-} and use the latest version of GHC.

[saurabhnanda]

Does that mean I can't do a monadic operation like uniqueness checks against a DB in this validation layer?

[ocharles]

There is no Monad instance for Form, but you can still lift any m computation into it. Check the docs for digestive-functors. The lack of Monad just means the validation for one field can't depend on the contents of another field

[saurabhnanda]

So, would it be this:

monadic $ do
  pokemonName <- "name" .: nonEmptyText
  pokemonNumber <- "number" .: parseInteger
  return Pokemon{..}

[ocharles]

No, because monadic lifts an m operation, but "name" .: nonEmptyText is a Form operation. Also, I think you might have better luck with questions of what you're actually trying to do, and will probably get more responses on Haskell StackOverflow or the mailing lists.

[saurabhnanda]

I actually want to raise a PR to make the docs better with examples of common use-cases.

[ocharles]

Ok, then it probably wants to be for digestive-functors itself, but I'll happily take docs patches here too!

…

On Wed, 8 Feb 2017, 4:48 pm Saurabh Nanda, ***@***.***> wrote: I actually want to raise a PR to make the docs better with examples of common use-cases. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#10 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AABRjrRdY8eqRW3lvjN5HseYOwTr_e3Nks5rafHvgaJpZM4LZu-X> .