How does one systematically traverse OCaml representations of Coq ASTs terms?

Question

I want to be able to (tree) traverse Coq terms (e.g. in OCaml or using their s-expression representation in any language).

My main challenge is to figure out how to do this systematically because I noticed two things that make arbitrary tree traversal difficult (or at least none obvious to me):

1. There might be arbitrary OCaml records with any size in the OCaml data type. Thus, I don't know what the "key" names or the length of the record (represented as a list in the s-exp) would be.
2. There are types that could be any type -- due to type variables 'a. Therefore making pattern matching challenging in a programmatically (since I don't know what constructors might appear before hand).

Thus, I am unsure how to traverse "Coq ASTs" programmatically in a systematic way in code that I write (say in OCaml, Coq or even Python).

So: How do I programmatically traverse Coq AST terms from their ocaml representation?

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More details

For example, let me give you a concrete example when interacting with coq-serapi:

Run the proof script first (why not):

(Add () "
Theorem add_easy_0: forall n:nat, 0 + n = n. simpl. reflexivity. Show Proof.")
(Exec 5)

then send the proof term back (a lambda term) to coq-serapi to parse into a "nice" AST for us (argh had to wrap it in a definition of coq returns a syntax error):

(Parse () "Definition id := (fun n : nat => eq_refl).")

then one gets the coq-ast (from the OCaml code I believe):

(Answer 2 Ack)
(Answer 2
 (ObjList
  ((CoqAst
    ((v
      ((control ()) (attrs ())
       (expr
        (VernacDefinition (NoDischarge Definition)
         (((v (Name (Id id)))
           (loc
            (((fname ToplevelInput) (line_nb 1) (bol_pos 0) (line_nb_last 1)
              (bol_pos_last 0) (bp 11) (ep 13)))))
          ())
         (DefineBody () ()
          ((v
            (CLambdaN
             ((CLocalAssum
               (((v (Name (Id n)))
                 (loc
                  (((fname ToplevelInput) (line_nb 1) (bol_pos 0)
                    (line_nb_last 1) (bol_pos_last 0) (bp 22) (ep 23))))))
               (Default Explicit)
               ((v
                 (CRef
                  ((v (Ser_Qualid (DirPath ()) (Id nat)))
                   (loc
                    (((fname ToplevelInput) (line_nb 1) (bol_pos 0)
                      (line_nb_last 1) (bol_pos_last 0) (bp 26) (ep 29)))))
                  ()))
                (loc
                 (((fname ToplevelInput) (line_nb 1) (bol_pos 0)
                   (line_nb_last 1) (bol_pos_last 0) (bp 26) (ep 29)))))))
             ((v
               (CRef
                ((v (Ser_Qualid (DirPath ()) (Id eq_refl)))
                 (loc
                  (((fname ToplevelInput) (line_nb 1) (bol_pos 0)
                    (line_nb_last 1) (bol_pos_last 0) (bp 33) (ep 40)))))
                ()))
              (loc
               (((fname ToplevelInput) (line_nb 1) (bol_pos 0)
                 (line_nb_last 1) (bol_pos_last 0) (bp 33) (ep 40)))))))
           (loc
            (((fname ToplevelInput) (line_nb 1) (bol_pos 0) (line_nb_last 1)
              (bol_pos_last 0) (bp 18) (ep 40)))))
          ())))))
     (loc
      (((fname ToplevelInput) (line_nb 1) (bol_pos 0) (line_nb_last 1)
        (bol_pos_last 0) (bp 0) (ep 42)))))))))
(Answer 2 Completed)

but if you inspect the s-expression more carefully there are potential issues. For example, reading the coq-serapi documentation we know we are getting a coq_object in the reply:

| CoqAst of Vernacexpr.vernac_control   (*
Coq Abstract Syntax tress, as produced by the parser

and thus the first thing is likely a vernac_control (or a CAst.t honestly I'm not sure what the and vernac_control = vernac_control_r CAst.t ocaml syntax means. But there are only two options so it's easy to systematize). The main issue is if we get the type CAst.t. Look at it's def:

type 'a t = private {
v : 'a;
loc : Loc.t option;
}

so basically v can be any type due to the type variable 'a. Which seems like a nightmare since how do I write a pattern match? Or a python if statement to detect what even the constructor options might be? I think this is the most serious issue if I want to even attempt to write a traversal for this. My fear is definitively confirmed since if you look at the s-expression I copy pasted we received plenty of v names in it...which makes we wonder how do I even traverse the coq-ast.

The other issue (which seems a bit more minor) is that we might get a record. Which is shown as a list in an s-expression...and I suppose we could infer what type of ocaml coq record it is from the lenght and the names of the "indices" but if I receive one that I didn't expect my code will crash.

So how does one traverse a s-expression/ocaml ast systematically?

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Appendix 1:

I think this question is extremely related to this other one: What are Generic Arguments in Coq and how are they structured in their OCaml code? . I think so because this one is about coq term traversal but the other one points out the (apparent?) inconsistencies coq-serapi might give. Thus, there can't be a systematic coq traversal if the terms given to the user from the OCaml code is incosnsistent.