dhall-json: Add a defaultConversion for converting maps

[sjakobi]

No description provided.

[sjakobi]

I believe there are more aspects where these defaultOptions diverge from the default behaviour of dhall-yaml[-ng], for example omission. I think it would be nice if these defaultOptions would exactly match the CLI defaults, and were in fact used by the executables.

I wonder whether we should also try to share these Options between dhall-json and dhall-yaml[-ng]…

[Gabriella439]

Yeah, I think this is fine. My understanding is that dhall-yaml already has a dependency on dhall-json anyway

[sjakobi]

Right. dhall-to-json currently has it's own Options record:

dhall-haskell/dhall-json/dhall-to-json/Main.hs

Lines 27 to 37 in 85645a2

	data Options
	= Options
	{ explain :: Bool
	, pretty :: Bool
	, omission :: Value -> Value
	, conversion :: Conversion
	, approximateSpecialDoubles :: Bool
	, file :: Maybe FilePath
	, output :: Maybe FilePath
	}
	| Version

The fields that it shares with dhall-to-yaml[-ng] could in principle live in a common DhallToXOptions record or something like that.