Hello List!
In some of my JSONs I have part "list of any values", for example:
[1, "hi", "false", 2.71]
To parse it I create type like:
data RespItem = forall a. FromJSON a => RespItem {
riItem :: [a] }
,-------------------------------------------------------------------
| btw, I try `(FromJSON a, Show a, Generic a) => ...` also but don't
| see any difference, so I'm not sure what is right constraints list.
`-------------------------------------------------------------------
And GHC does not allow to derive automatically with "deriving" Show
and Generic instances for existential types, as I see. So I write:
instance Generic RespItem
instance Show RespItem
Also this type `RespItem` in part of another one:
data Resp = Resp {
rHeadings :: [T.Text]
, rRow :: [RespItem]
} deriving (Generic, Show)
Interesting is that now auto-`deriving` works! OK, but I need to
to instantiate `FromJSON` for RespItem because next step must be
`FromJSON` for Resp. So I'm trying:
instance FromJSON RespItem where
parseJSON ??? = ???
and here I get different errors, and absolutely don't understand how to
parse it, I get "ambiguous type error..." and so on (which is right,
sure).
===
Best regards, Paul
