Example for Json.Decode.value wrong in documentation

[jvoigtlaender]

The example at http://package.elm-lang.org/packages/elm-lang/core/2.1.0/Json-Decode#value is missing some brackets. Adding them gives:

variadic2 : (a -> b -> List c -> value) -> Decoder a -> Decoder b -> Decoder (List c) -> Decoder value
variadic2 f a b cs =
    customDecoder (list value) (\jsonList ->
        case jsonList of
          one :: two :: rest ->
              Result.map3 f
                (decodeValue a one)
                (decodeValue b two)
                (decodeValue cs rest)

          _ -> Result.Err "expecting at least two elements in the array")

But that's not type-correct according to http://elm-lang.org/try. (It complains about mismatched types Value vs. List Value in the 2nd argument of (decodeValue cs rest).)

[jvoigtlaender]

A possible fix is this:

variadic2 : (a -> b -> List c -> value) -> Decoder a -> Decoder b -> Decoder c -> Decoder value
variadic2 f a b c =
    customDecoder (list value) (\jsonList ->
        case jsonList of
          one :: two :: rest ->
              Result.map3 f
                (decodeValue a one)
                (decodeValue b two)
                (combine (List.map (decodeValue c) rest))

          _ -> Result.Err "expecting at least two elements in the array")

where

combine : List (Result x a) -> Result x (List a)
combine = List.foldr (Result.map2 (::)) (Ok [])

is a function analogous to http://package.elm-lang.org/packages/Apanatshka/elm-signal-extra/5.4.1/Signal-Extra#combine (or to http://hackage.haskell.org/package/base-4.8.1.0/docs/Data-Traversable.html#v:sequenceA).

[jvoigtlaender]

A possible fix is this:

variadic2 : (a -> b -> List c -> value) -> Decoder a -> Decoder b -> Decoder c -> Decoder value
variadic2 f a b c =
    customDecoder (list value) (\jsonList ->
        case jsonList of
          one :: two :: rest ->
              Result.map3 f
                (decodeValue a one)
                (decodeValue b two)
                (combine (List.map (decodeValue c) rest))

          _ -> Result.Err "expecting at least two elements in the array")

where

combine : List (Result x a) -> Result x (List a)
combine = List.foldr (Result.map2 (::)) (Ok [])

is a function analogous to http://package.elm-lang.org/packages/Apanatshka/elm-signal-extra/5.4.1/Signal-Extra#combine (or to http://hackage.haskell.org/package/base-4.8.1.0/docs/Data-Traversable.html#v:sequenceA).

[jvoigtlaender]

Closing via https://github.com/elm-lang/core/pull/365.

[jvoigtlaender]

Closing via https://github.com/elm-lang/core/pull/365.