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json-builder is a data structure agnostic json serialization library. Most existing serializers operate on a specific data structure that corresponds to a json value. Other pieces of data must then marshaled into that data structure before they can be serialized to json.

json-builder avoids this marshaling, and thus is potentially more efficient when you want to serialize arbitrary data structures. Moreover, I've found that writing a serializer using this API to be somewhat simpler than writing a marshaller into the data structures used by the json or aeson packages.

Unfortunately, json-builder cannot yet read or process json data. Moreover, it's not clear to me how to pull a similar kind of trick above, and avoid unnecessary data structures.

This library revolves around a single typeclass Value that represents pieces of data that can be serialized to the Json format. It's member is toJson, which returns a newtyped Builder that represents the concrete syntax of that value.

class Value a where
  toJson :: a -> Json

Arrays are represented by an abstract type with a singleton constructor element and a monoid instance. Thus arbitrary sequences can be serialized using mempty and mappend.

element :: Value a => a -> Array
instance Monoid Array

Objects are similar. There is a typeclass JsString that distinguishes strings from other Json values, a singleton constructor, and a monoid instance. Note that rows with duplicate keys will appear in the output; it is up to the user of this interface to ensure that keys are unique.

class Value a => JsString a

row :: (JsString a, Value b) => a -> b -> Object
instance Monoid Object