Custom ADTs should come with accompanying JSON parsers.

[ilyasergey]

The rough idea, extracted from a recent discussion. Let us have fixpoint combinator.

let rec fix pf = pf (fun _ -> fix pf)

Then each (possibly recursive) type can be also compiled to a JSON parser of its values in a parser-combinator style. For example:

type Tree = Leaf | Node of Tree * Uint32 * Tree

would be compiled to something like:

let node_parser self = seq parse_string("Node") @@ seq (self ()) @@ seq parse_uint32 (self())
let leaf_parser = parse_string "Leaf"
let tree_parser = fix (fun self -> alt leaf_parser (node_parser self))

Parsers for polymorphic types would need to take lists of parsers for data types, corresponding to their type parameters, which they can use in their implementation.

let pair_parser params = 
  let a_parser = get params 1 in
  let b_parser = get params 2 in
  seq parse_string("Pair") @@ seq a_parser b_parser