[cl-json-devel] Guidance requested: how to dispatch members to external decoders?

[Hraban Luyat]

Hello,

As far as I understand the decoder API it is mostly geared towards
defining the decoder for an entire snippet in one place. I would like
to know what the recommended way is to separate the definition of the
decoder over separate modules.

The semantics of my incoming messages are thus:

object:
  - "type": string denoting the type
  - "payload": type-specific payload

I want to create a decoder that only extracts the type and uses that
to determine which decoder to send the payload to. Then it continues
with whatever lisp object the decoder returned.

What I thought would be appropriate is to create a generic function;

(defgeneric json->data (type payload))

and then simply register decoders as follows:

(defmethod json->data ((type (eq :foo)) payload)
  "Decode message of type foo."
  ...)

(defmethod json->data ((type (eq :bar)) payload)
  "Decode message of type bar."
  ...)

But now I am not really sure how to glue this together. What would you
recommend? Is this the right frame of mind at all or should I take a
totally different approach?

Thanks!

Hraban