Json.Decode dislikes recursion

[surprisetalk]

It seems that Json.Decode can't be used recursively.

Consider the following example:

[
  { "whatever": 1
  , "something": 2
  , "things": 
    [  { "whatever": 3
       , "something": 4
       , "things": []
       }
    ,  { "whatever": 5
       , "something": 6
       , "things": []
       }
    ] 
  }
]

decodeThings : Json.Decoder (List Thing)
decodeThings =
  Json.list decodeThing

decodeThing : Json.Decoder Thing
decodeThing =
  Json.object3 Thing
    ("whatever" := Json.int)
    ("something" := Json.int)
    ("things" := decodeThings)

The web console has the following complaint: TypeError: undefined is not an object (evaluating 'decoder.tag').

The error seems to be occurring in runHelp in https://github.com/elm-lang/core/blob/master/src/Native/Json.js.
If you place a console.log( decoder, value ) before switch( decoder.tag ) in a compiled file, you'll see that the parent function doesn't pass a decoder object to the recursed child.

My current workaround (😅) is something like:

decodeThings1 : Json.Decoder (List Thing)
decodeThings1 =
  Json.list decodeThing1

decodeThing1 : Json.Decoder Thing
decodeThing1 =
  Json.object3 Thing
    ("whatever" := Json.int)
    ("something" := Json.int)
    ("things" := decodeThings2)

decodeThings2 : Json.Decoder (List Thing)
decodeThings2 =
  Json.list decodeThing2

decodeThing2 : Json.Decoder Thing
decodeThing2 =
  Json.object2 Thing
    ("whatever" := Json.int)
    ("something" := Json.int)

I'm willing fix this issue, but I would love some guidance on where to look!

Thank you friends.

ts

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[jvoigtlaender]

This is a known compiler issue. See elm/compiler#873 and the discussion there (explicitly considering JSON decoding in the comments). The current workaround is to make use of lazy from http://package.elm-lang.org/packages/elm-community/json-extra/1.0.0/Json-Decode-Extra#lazy.

[jvoigtlaender]

This is a known compiler issue. See elm/compiler#873 and the discussion there (explicitly considering JSON decoding in the comments). The current workaround is to make use of lazy from http://package.elm-lang.org/packages/elm-community/json-extra/1.0.0/Json-Decode-Extra#lazy.