encode does not resolve ambiguity between string and numeric values

[nikita-volkov]

This one is related to #20.

{-# LANGUAGE OverloadedStrings, DeriveGeneric #-}
import Data.Yaml
import GHC.Generics (Generic)

data A = A { phone :: String }
  deriving (Generic, Show)

instance ToJSON A
instance FromJSON A

main = do
  print $ encode $ A "+72304234342"
  print $ (decode $ encode $ A "+72304234342" :: Maybe A)

outputs:

"phone: +72304234342\n"
Nothing

As you can see the decode parser fails on the result of encode.

There are two ways of solving this:

1. Resolve the Parsing result type is not dictated by the output type #20
2. Put the ambiguous string values in quotes

I again vote for the first way.

[snoyberg]

#20 would require a complete overhaul of the encoding/decoding situation. It's not really a solution, it's creating a new system. For my own uses (and I think many others), the convenience of ToJSON/FromJSON isn't something we're going to give up on. But there's nothing stopping you from having your own ToYAML/FromYAML typeclasses.

Meanwhile, I think it's worth looking at option (2).

[nikita-volkov]

Okay, I understand you

[ellis]

Here's my vote to do something about this. The issue makes the yaml library unusable for me, because files which are written cannot be read back if they contain strings properties which happen to be even somewhat numeric. UTCTime is another type which can't be read back once written.
The same data can be written and read back when using Aeson.encode, but not with the yaml library.

[snoyberg]

Handled by Data.Yaml.Parser module.