Customize printing of one of the mutually recursive types in deriving show

[ChengCat]

For the following program, it seems that I can't have a customized printing function for the type a, while using deriving show to generate the print function for type b.

type a = { x: b; y: int }
and b = A | B a | C a
[@@deriving show]

[michael-schwarz]

I am facing a similar issue, where I have mutable records with circular references:

type compinfo = {
    mutable cfields: fieldinfo list;
    (** Information about the fields. Notice that each fieldinfo has a
      * pointer back to the host compinfo. This means that you should not
      * share fieldinfo's between two compinfo's *)
    mutable cattr:   attributes;
    [...]
}
and fieldinfo = {
    mutable fcomp: compinfo;
     (** The host structure that contains this field. There can be only one
      * [compinfo] that contains the field. *)
    [...]
}
and [...]

Is there a way of defining a custom printer (or to_yojson in my case specifically) for fieldinfo while using the default one for compinfo?